Session NP11: Poster Session V: Turbulence & Transport; DIII-D II; Compact Torus; HEDP I; Low Temperature Plasmas; Mini-Conference on Bridging the Divide Between Space and Astrophysical Plasmas

Tornado-like transport in a magnetized plasma

Recent heat transport experiments conducted in the LAPD device at UCLA in which avalanche events have been previously documented [1] have also lead to the identification of a new tornado-like transport phenomenon. These tornados occur much earlier than the avalanches events, essentially in the interval following the application of the bias voltage that causes the injection of an electron beam from a ring-shaped LaB6 cathode into the afterglow of a cold, magnetized plasma. The tornados exhibit a low-frequency (~ 4 kHz) (much lower than drift-waves), spiraling, global eigenmode whose transient behavior is responsible for significant radial transport well outside the heated region. Detailed experimental observations are compared with a Braginskii transport code that includes the effects of ExB convection induced by the spiraling global eigenmode. New insights are gained into the necessary modifications of classical transport to accurately simulate the spiraling effects and the possible interaction with avalanches. [1] B. Van Compernolle et al. Phys Rev. E 91, 031102 (2015) Sponsored by DOE/NSF at BaPSF and NSF 1619505.   

Fluctuation-Induced Bistability: A Model of Heat Flux Hysteresis and Avalanching in Confined Plasmas

We propose a theory-based model which explains the observation of heat flux hysteresis in the absence of a transport barrier. This study also strikes at the fundamental question of ‘what is an avalanche?’. We show that multiscale coupling between mesoscopic and microscopic fluctuations can induced bistability of the local turbulence intensity and system state bifurcation. For the subcritical scenario, i.e., the temperature gradient below its linear threshold, if the intensity of the mesoscale temperature gradient exceeds a certain threshold, the system transitions from a metastable ‘laminar’ state to an absolutely stable excited state. Correspondingly, the effective thermal conductivity jumps from a value close to the neoclassical value to an anomalous value. By reducing the external drive, the excited state returns to the laminar one. Therefore, it is the bistability of the turbulence intensity that induces the heat flux hysteresis. The scaling of the hysteresis strength is obtained. Incorporating turbulent viscosity effect, a stable front of turbulence intensity is formed. This front connects the excited– and laminar states, and propagates as an avalanche. Hysteresis and turbulence intensity avalanche speed are estimated in a unified theoretical framework.   

Impurity transport driven by parallel velocity shear instabilities.

The instability driven by large parallel velocity shear (PVS) is by D'Angelo and P. J. Catto. CT-6B tokamak also reported the existence of PVS driven turbulence in the edge plasma. There are also extensive theoretical investigations, especially, the momentum-energy transport [1], thermal transport [2] as well as inward particular transport [3] are studied, but impurity (non-hydrogenic ions) transport in plasmas with large PVS is never addressed. Impurity accumulation in internal transport barrier (ITB) discharges is reported in JET, JT-60U and DIII-D, especially for the heavier or metal impurities. What's more, the PVS instability has also been discussed in ITB plasmas [4-6]. Therefore, the PVS turbulence could be a mechanism for mitigating the degree of impurity accumulation in ITB plasmas. The present paper thus studied the impurity effects on PVS instability and the associated impurity transport. References: [1] Dong J Q et al 1994 Phys. Plasmas 1 3250. [2] Dimits A et al 2001 Nucl. Fusion 41 1725. [3] Kosuga Y et al 2015 Plasma and Fusion Research 10 3401024. [4] Garbet X et al 2002 Phys. Plasmas 9 3893. [5] Kim S S et al 2011 Nucl. Fusion 51 073021. [6] Dong J Q et al 1998 Phys. Plasmas 5 4328.   

Catastrophic global-avalanche of a hollow pressure filament

New results are presented of a basic heat transport experiment performed in the Large Plasma Device at UCLA. A ring-shaped electron beam source injects low energy electrons along a strong magnetic field into a preexisting, large and cold plasma. The injected electrons are thermalized by Coulomb collisions within a short distance and provide an off-axis heat source that results in a long, hollow, cylindrical region of elevated plasma pressure. The off-axis source is active for a period long compared to the density decay time, i.e., as time progresses the power per particle increases. Two distinct regimes are observed to take place, an early regime dominated by multiple avalanches [1], identified as a sudden intermittent rearrangement of the pressure profile that repeats under sustained heating, and a second regime dominated by broadband drift-Alfv\'en fluctuations. The transition between the two regimes is sudden and global, both radially and axially. The initial regime is characterized by peaked density and temperature profiles, while only the peaked temperature profile survives in the second regime. Recent measurements at multiple axial locations provide new insight into the axial dynamics of the global avalanche. [1] B. Van Compernolle et al., Phys. Rev. E 91, 031102 (2015)   

Current driven by electromagnetic ETG turbulence

Recently, there has been intensive investigation of turbulence induced spontaneous rotation in tokamak. Naturally, current driven by turbulence has also been considered such as the electron temperature gradient (ETG) instability with a fluid mode [1]. The electrostatic gyrokinetic simulation [2] shows that the ETG turbulence driven current density corresponds to 20{\%} of the local bootstrap current density. In this paper, the quasilinear version of the current evolution equation in the presence of electromagnetic (EM) ETG turbulence is presented using EM gyrokinetic equation. There are two types of current driving mechanisms. The first type is the divergence of stress, while the second type is called turbulent acceleration source. Finally, we compare the turbulent driven current to the background bootstrap current. The results demonstrate that the EM effect is important for the turbulent driven current. And the source term contributes a little to the total current. The modification of the current due to EM ETG turbulence is not dramatic in today's tokamak. However, it may play a significant role in future device. \\ \\$[1]$ Tiwari S. et al., IAEA (2014) \newline [2] Yi S. et al., Phys. Plasmas, 23, 102514 (2016)   

Transport increase and confinement degradation caused by MARFE

Recently, the MARFE phenomenon associated with high density plasmas has been observed on J-TEXT Ohmically heated discharges. The MARFE on J-TEXT is charactered by the poloidally local region at high field side (HFS) edge with high density and strong radiation. At the almost same time of MARFE appearance, the density peaking factor and sawtooth oscillation reach maximum and decrease with density increasing, infers that the plasma confinement is saturated. By analyzing the far-forward scattering signals from polarimeter-interferometer, it is found that the local radial density turbulence at high field edge increases significantly after MARFE onset. It is inferred that the local particle transport at MARFE affected region (HFS edge) is enhanced. The enhancement of radial transport at MARFE affected region is considered as the possible reason for confinement saturation on J-TEXT. Furthermore, the trapped electron mode (TEM) with quasi-coherent characteristics is measured by far-forward scattering. The TEMs are always observed in plasmas with low density, and disappear after the plasma density exceeds a threshold. The density threshold of TEM disappearance is consistent with the density threshold of MARFE onset. The evolution of turbulences affirms that the MARFE may be the cause of energy confinement transition from LOC to SOC.   

Competition of Perpendicular and Parallel Flows in a Straight Magnetic Field

In tokamaks, intrinsic rotations in both toroidal and poloidal directions are important for the stability and confinement. Since they compete for energy from background turbulence, the coupling of them is the key to understanding the physics of turbulent state and transport bifurcations, e.g. L-H transition. $V_\perp$ can affect the parallel Reynolds stress via cross phase and energetics, and thus regulates the parallel flow generation. In return, the turbulence driven $V_\parallel$ plays a role in the mean vorticity flux, influencing the generation of $V_\perp$. Also, competition of intrinsic azimuthal and axial flows is observed in CSDX-a linear plasma device with straight magnetic fields. CSDX is a well diagnosed venue to study the basic physics of turbulence-flow interactions in straight magnetic fields. Here, we study the turbulent energy branching between the turbulence driven parallel flow and perpendicular flow. Specifically, the ratio between parallel and perpendicular Reynolds power decreases when the mean perpendicular flow increases. As the mean parallel flow increases, this ratio first increases and then decreases before the parallel flow shear hits the parallel shear flow instability threshold. We seek to understand the flow states and compare with CSDX experiments.   

Theoretical explanations of impurity removal in I-mode and poloidal pedestal asymmetries

We have developed the first self-consistent theoretical model retaining the impurity diamagnetic flow and the 2D features it implies due to its associated non-negligible radial flow. It successfully explains the experimental impurity density and temperature, and radial electric field, in-out asymmetries neoclassically. Moreover, it provides a means of calculating the neoclassical impurity radial flux from currently available measurements, providing insight on optimal tokamak operation to prevent impurity accumulation. In particular, it predicts outward neoclassical impurity flux, and therefore inward fueling, occurs for I-mode operation in C-Mod.   

Influence of zonal vorticity on the cross phase

The study of the evolution of the cross phase $\delta$ between the electron pressure and the potential in the resistive-drift-Afv\'{e}n turbulence under the sheared magnetic field lines are reported. The linear cross phase is established by both the drift-wave dynamics and the Ohm's law and it is vanishingly small in the modes with low $k_\parallel$. The nonlinearly saturated cross phase is correspondingly different from the linear $\delta$ mainly due to the $E\times B$ flux. Numerical computations are performed in order to investigate the roles of $E\times B$ nonlinearity when the self-consistent zonal flow exists on $\delta$ by using BOUT++ platform. In this work, the influence of the non-uniformity of the zonal flow, the gradient and the curvature, on $\delta$ and transport is presented and the departure of $\delta$ from the linear state is particularly highlighted.   

Relationship of the cross phase and the zonal flow in electrostatic ion-temperature-gradient turbulence

The cross phase $\delta $, that is the phase difference between the electric potential and the ion pressure, is examined in the electrostatic ion-temperature-gradient fluid turbulence. It is important to study the cross phase because the thermal transport $\Gamma $ is roughly proportional to sin$\delta $. Three-dimensional numerical simulations are performed in the BOUT$++$ platform with the shifted metric coordinate system. The cross phase seems to show an interesting feature such that it is almost constant when the zonal flow $V$is in the direction of the electron diamagnetic drift and the time evolution of the cross phase oscillates near zero at low poloidal wave number and $\Gamma $ is small. These phenomena are closely correlated with the fluctuation level and depend closely on the curvature $V''$ of the zonal flow.   

Dynamics of Staircase Formation and Evolution in a Reduced Model of Beta Plane Turbulence

Staircase dynamics relevant to both beta-plane geostrophic and drift-wave plasma turbulence is studied numerically and analytically. It evolves an averaged potential vorticity (PV) whose flux is both driven by and regulates enstrophy field. The model's closure uses a mixing length concept. Its link with bistability, vital to staircase generation, is analyzed and verified by integrating the equations numerically. The staircase evolves through meta-stable quasi-periodic configurations, lasting for hundreds of time units, yet interspersed with abrupt mergers of adjacent steps in the staircase. The mergers occur at the staircase lattice defects where it is not completely relaxed to a strictly periodic solution that can be obtained analytically. The other types of stationary solutions are the solitons and kinks in the PV gradient and enstrophy - profiles. The waiting time between mergers increases with decreasing number of steps in the staircase, because of the exponential decrease in their coupling strength with growing spacing. The long-time staircase dynamics is numerically shown to be local to the adjacent steps. The merger reveals itself through the explosive growth of the turbulent PV-flux which, however, abruptly drops to its global constant value when the merger is completed.   

Evidence for Particle Inward Transport, Theoretical prediction and Importance for Reacting Plasmas

The fact that particle transport cannot be described by a diffusion equation but by one [1,2] that would include an inflow term, involving transport in the direction of the density gradient, was evidenced by experiments on magnetically confined plasmas in which the central plasma density was observed to increase as a result of gas injection at the edge of the plasma column. The validity of the proposed equation has been repeatedly confirmed over the years and limitations for the occurrence of particle inflow in a variety of experimental conditions have been uncovered. The direct experimental observation of the inward propagating particle cloud leading to a profile peaking [3] is described and the effects of different degrees of density peaking in fusion burning plasmas are analyzed.\\ 1. B. Coppi and C. Spight, Phys. Rev. Lett., 41, 551 (1978).\\ 2. N. Sharky and B. Coppi, Nucl. Fus. 21, 1363 (1981).\\ 3. C. Mazzotta et al., Proceedings of the 44th EPS Conference on Plasma Physics, Paper P2.179 (2017).   

Simulation of ITG instabilities with fully kinetic ions and drift-kinetic electrons in tokamaks

A turbulence simulation model with fully kinetic ions and drift-kinetic electrons is being developed in the toroidal electromagnetic turbulence code GEM. This is motivated by the observation that gyrokinetic ions are not well justified in simulating turbulence in tokamak edges with steep density profile, where $\rho_i/L$ is not small enough to be used a small parameter needed by the gyrokinetic ordering (here $\rho_i$ is the gyro-radius of ions and $L$ is the scale length of density profile). In this case, the fully kinetic ion model may be useful. Our model uses an implicit scheme to suppress high-frequency compressional Alfven waves and waves associated with the gyro-motion of ions. The ion orbits are advanced by using the well-known Boris scheme, which reproduces correct drift-motion even with large time-step comparable to the ion gyro-period. The field equation in this model is Ampere's law with the magnetic field eliminated by using an implicit scheme of Faraday's law. The current contributed by ions are computed by using an implicit $\delta f$ method. A flux tube approximation is adopted, which makes the field equation much easier to solve. Numerical results of electromagnetic ITG obtained from this model will be presented and compared with the gyrokinetic results.   

Modelling Axial Flow Generation and Profile Evolution in CSDX Linear Device

We report on developments in reduced modelling of profile evolution in CSDX. The model includes effects of turbulence driven axial flows important for enhanced confinement in ITER. Recent studies revealed existence of such flows in CSDX, historically associated with non-vanishing parallel residual stress in the momentum flux. Studies also showed transition to enhanced confinement and amplification of mean axial flow shear as B increases. The model addresses the relation between perpendicular transport and axial flow dynamics and tracks time-space evolution of four fields: density $n$, axial and azimuthal flow profiles $v_z$ and $v_y$ and energy $\varepsilon=\langle \tilde n ^2+\tilde v_z^2+(\nabla_\perp\tilde\phi)^2\rangle/2$. With total energy conserved, parallel compressibility couples parallel and perpendicular directions allowing for the system to access the $\nabla n$ free energy, thus amplifying the parallel flow shear and depleting turbulent fluctuations. In this model, the particle flux is purely diffusive, while residual components are added to the Reynolds stresses. The model addresses: i) $\nabla n$ steepening with $B$, ii) the relation between $v_y'$ and $v_z'$, iii) the surge in parallel Reynolds work indicating coupling of fluctuating energy and parallel flow   

Intermittency in the Helimak, a simple magnetic torus

Irregularly-spaced, large-amplitude bursts are observed in the Helimak plasma turbulence with sufficient definition to investigate their physical basis and possibly improve understanding of the induced particle transport. The Helimak is an experimental realization of a sheared cylindrical slab that generates and heats a plasma with microwaves and confines it in a helical magnetic field. Although it is MHD stable, the plasma is always in a nonlinearly saturated state of microturbulence. The intermittency in this turbulence manifests itself in highly skewed PDFs of the normalized electron density. Cross-conditional averaging exposes large amplitude structures propagating down the density gradient at a few hundred meters per second. Introduction of a radial electric field via bias plates appears to suppress these intermittent transport events (ITEs) for Er pointing down the density gradient. In addition, the cross-conditionally averaged waveforms are relatively unchanged as connection length is varied. Within certain regimes, our measurements are consistent with the predictions of a stochastic model that represents the plasma fluctuations as a random sequence of burst events. Furthermore, we attempt to gain insight into the physical origin of these ITEs by searching for similar statistical behavior in fluid and gyrokinetic simulations.   

Two species continuum kinetic simulation of plasma turbulence

We numerically investigate a problem of plasma turbulence decay in the solar wind using the continuum kinetic Vlasov-Maxwell system. While a previous investigation [Franci et al. ApJ 812 (2015)] has used an electron fluid model with highly resolved PIC ions, recent results in collisionless problems with kinetically resolved electrons indicate that plasma dynamics result in non-Maxwellian electron distributions. In this approach both ion and electron species are resolved kinetically. Following Franci, a uniform two-dimensional geometry with an out-of-plane magnetic field is considered, where an equipartitioned spectrum of magnetic and kinetic energy fluctuations is initialized on a scale well above an ion scale length $r_i = v_A/\Omega_i$. Evolution of the kinetic and magnetic energies to other scales is then observed. A newly implemented kinetic modeling capability in University of Washington’s WARPXM code is used, via a RKDG finite element method with an unstructured physical space and a cartesian velocity space.   

A unified theory of the magnetized collision term for plasmas

Recently, the general form of the magnetized Fokker-Planck equation and coefficients have been derived for plasmas. To calculate the magnetized Fokker-Planck coefficients accurately, a unified theory is developed here. The basic idea is to divide the collision area into two regions: (i) 0 \textless b \textless b$_{\mathrm{c}}$; (ii) b \textgreater b$_{\mathrm{c}}$. Here b is the impact parameter and b$_{\mathrm{c}}$ is chosen to be much larger than the Landau length and much smaller than the inter-particle distance and particles' thermal gyro-radii. For region (i), the collective effects are unimportant and the magnetic field does not affect the collision process, so the usual binary collision theory without magnetic field is employed to calculate the Fokker-Planck coefficients. For region (ii), the wave theory taking account of the magnetic field effects is employed to calculate the magnetized Fokker-Planck coefficients. Synthesize of the results of the two regions will give the exact magnetized Fokker-Planck coefficients and thus the exact magnetized collision term which includes, in a rather complete manner, the collective effects, the magnetic field effects, and the contribution from close collisions.   

Edge transport bifurcation in plasma resistive interchange turbulence

Transport bifurcation and mean E×B shear flow generation in resistive interchange turbulence are explored with self-consistent fluid simulations in a flux-driven system with both closed and open field line regions. The nonlinear evolution of resistive interchange modes shows the presence of two confinement regimes characterized by low and high mean E×B shear flows. By increasing the heat flux above a threshold, large-amplitude fluctuations are induced in the plasma edge region and a transition to the state of reduced turbulent transport occurs as the Reynolds power exceeds the fluctuation energy input rate for a sufficient time period. The flux-gradient relationship shows a sharp bifurcation in the plasma edge transport. [B.Li et al., Phys.Plasmas 24,055905(2017)]   

Dynamics of edge transport bifurcation induced by external biasing

Transport bifurcation and flow generation induced by external biasing at the plasma edge are explored with self-consistent turbulence simulations in a flux-driven system with both closed and open magnetic field lines. With no biasing, the nonlinear evolution of pressure-gradient-driven interchange instabilities produces large-scale turbulent eddies, leading to high levels of convective transport in the edge region. By applying a sufficient biasing at the plasma edge, the turbulent flux abruptly decreases to a much lower level, indicating a strong bifurcation in transport.   

Multi-scale interaction between magnetic island, plasma flow and turbulence in HL-2A ohmic plasmas

Improved understanding of multi-scale physics such as interaction between tearing modes with plasma flows and turbulence can lead to improved control of plasma performance, and thus, have important implication for ITER. The radial profiles of perpendicular flows and density fluctuations in the presence of the m/n$=$2/1 magnetic island were firstly measured in the HL-2A ohmic plasmas by hopping the work frequency of the Doppler backward scattering (DBS) reflectometer system along with a two-dimensional electron cyclotron emission imaging (ECEI) diagnostic identifying the island locations. It has been observed that across the O-point cut the perpendicular flow is quite small at the center of the island and strongly enhanced around the boundary of the island, resulting in a large increase of the flow shear at the island boundary, while across the X-point cut the flow is almost flat in the whole island region. Meanwhile it was found that the density fluctuations are generally weakened inside the island. The results indicate that the perpendicular flow, flow fluctuation and the density fluctuation level were all modulated by the naturally rotating tearing mode across the whole island region.   

Turbulence experiments on the PKU Plasma Test (PPT) device

The PKU Plasma Test (PPT) device is a linear plasma device in Peking University, China. It has a vacuum chamber with 1000mm length and 500mm diameter. A pair of Helmholtz coils can generate toroidal magnetic field up to 2000 Gauss, and plasma was generated by a helicon source. Probes and fast camera were used to diagnose the parameters and got the turbulence spectrums, coherent structure, etc. The dynamics of turbulence, coherent structure and parameter profiles have been analyzed, and it has been found that the turbulence states are related to the equilibrium profiles; Some coherent structures exist and show strongly interactions with the background turbulences; The spatial and temporal evolutions of these coherent structures are related to the amplitude of the density gradient and electric field. These results will help on further studies of plasma transport.   

Towards Multiscale Interactions Between Tearing Modes and Microturbulence

Work on the Madison Symmetric Torus Reversed-Field Pinch (RFP) has shown that large-scale tearing modes present in standard operation are highly detrimental to confinement. These tearing modes, even when reduced in improved confinement regimes of operation, significantly affect zonal flow activity and play a large role in setting microturbulent-induced transport levels. Previous gyrokinetic work has shown that a small but finite tearing fluctuation amplitude is necessary to produce transport values in agreement with experimental observation. This has previously been implemented via an ad-hoc, constant-in-time $A_\parallel$ perturbation. This work details self-consistent modeling of tearing fluctuations in the RFP using the \textsc{Gene} code via the inclusion of a current gradient drive incorporated into the background distribution function. Tearing mode growth rates calculated from gyrokinetic simulations are benchmarked with results from fluid theory. Additionally, first results from multiscale \textsc{Gene} simulations describing tearing mode interactions with RFP microturbulence are presented. This work is supported by the U.S. Department of Energy, Grant No.~DE-FG02-85ER-53121.   

Shear-Flow Instability Saturation by Stable Modes: Hydrodynamics and Gyrokinetics

We present simulations of shear-driven instabilities, focusing on the impact of nonlinearly excited, large-scale, linearly stable modes on the nonlinear cascade, momentum transport, and secondary instabilities. Stable modes, which have previously been shown to significantly affect instability saturation [Fraser \textit{et al.}~PoP 2017], are investigated in a collisionless, gyrokinetic, periodic zonal flow using the \textsc{Gene} code by projecting the results of nonlinear simulations onto a basis of linear eigenmodes that includes both stable and unstable modes. Benchmarking growth rates against previous gyrokinetic studies and an equivalent fluid system demonstrates comparable linear dynamics in the fluid and gyrokinetic systems. Cases of driven and decaying shear-flow turbulence are compared in \textsc{Gene} by using a Krook operator as an effective forcing. For comparison with existing hydrodynamic and MHD shear-flow instability studies, we present results for the shear layer obtained by similar means with the code Dedalus.   

Bicoherence Analysis of Electrostatic Interchange Mode Coupling in a Turbulent Laboratory Magnetosphere

Plasmas confined by a strong dipole field exhibit interchange and entropy mode turbulence, which previous experiments have shown respond locally to active feedback [1]. On the Collisionless Terrella Experiment (CTX), this turbulence is characterized by low frequency, low order, quasi-coherent modes with complex spectral dynamics. We apply bicoherence analysis [2] to study nonlinear phase coupling in a variety of scenarios. First, we study the self-interaction of the naturally occurring interchange turbulence; this analysis is then expanded to include the effects of driven modes in the frequency range of the background turbulent oscillations. Initial measurements of coupling coefficients are presented in both cases. Driven low frequency interchange modes are observed to generate multiple harmonics which persist throughout the plasma, becoming weaker as they propagate away from the actuator in the direction of the electron magnetic drift. Future work is also discussed, including application of wavelet bicoherence analysis, excitation of interchange modes at multiple frequencies, and applications to planetary magnetospheres. \break [1] Roberts, Mauel, and Worstell, Phys Plasmas (2015). \break [2] Grierson, Worstell, and Mauel, Phys Plasmas (2009).   

Experiment-Model Comparisons of Turbulence, Transport, and Flows in a Magnetized Linear Plasma Using a Global Two-Fluid Braginskii Solver

Ongoing experiments and numerical modeling of the dynamics of electrostatic turbulence and transport in the presence of flow shear are being conducted in helicon plasmas in the linear HelCat (Helicon-Cathode) device. Modeling is being done using GBS, a 3D, global two-fluid Braginskii code that solves self-consistently for plasma equilibrium as well as fluctuations. Past experimental measurements of flows have been difficult to reconcile with simple expectations, such as azimuthal flows being dominated by Er x Bz rotation. Therefore, recent measurements have focused on understanding plasma flows, and the role of neutral dynamics. In the model, a set of two-fluid drift-reduced Braginskii equations are evolved using the Global Braginskii Solver Code (GBS). For low-field helicon-sourced Ar plasmas a non-negligible cross-field thermal collisional term must be added to shift the electric potential in the ion momentum and vorticity equations as the ions are unmagnetized. Significant radially and axially dependent neutral profiles are also included in the simulations to try and match those observed in HelCat. Ongoing simulations show a~mode dependence on the axial magnetic field along with strong~axial variations that suggest drift waves may be important in the low-field case.   

Thermal Resonator Experiments Using A Magnetized Electron Temperature Filament

We present results from basic heat transport experiments of a magnetized electron temperature filament that behaves as a thermal resonator. Experiments are performed in the Large Plasma Device at UCLA. A CeB$_{\text{{6}}$ cathode injects low energy electrons along a magnetic field into the center of a pre-existing plasma forming a hot electron filament embedded in a colder plasma. Previous work reported that the filament exhibits spontaneous excitation of thermal waves [Pace et al., Phys. Rev. Lett. 101, 035003 (2008)] and temperature gradient driven drift-Alfv\'{e}n waves that enhance cross-field transport [Burke et al., Phys. Plasmas 7, 1397 (2000)]. We have added to the cathode bias a series of low amplitude pulse trains tuned to the thermal resonance of the filament that externally excite thermal waves. Langmuir probe measurements allow for the determination of the phase velocity and radial decay length of the thermal mode. These results are used to compute the axial and transverse thermal conductivities of the magnetized plasma and compare with those given by classical theory. Agreement of the axial conductivity provides a measurement of electron temperature; deviation of the transverse conductivity suggests anomalous transport or non-uniform excitation.   

Differential Impurity Transport in the Presence of an External Potential

We discuss a generalization of the classical impurity pinch to include the effects of external potentials. This allows us to describe a smooth transition between the behavior of different particle species in thermodynamic equilibrium and the pinch that we encounter in a magnetically confined system. It also allows us to predict the behavior of a variety of systems that are in steady state but not in thermodynamic equilibrium; external potentials can either increase or mitigate the pinch, depending on the context. These effects could have practical implications for a variety of different plasma devices. We are particularly interested in the effects of rotation and of electrostatic potentials.   

Dynamical transitions associated with turbulence in a helicon plasma

Diagnostic capabilities are often cited as a limiting factor in our understanding of transport in fusion devices. Increasingly advanced multichannel diagnostics are being applied to classify transport regimes and to search for ``trigger'' features that signal an oncoming dynamical event, such as an ELM or an L-H transition. In this work, we explore a technique that yields information about global properties of plasma dynamics from a single time series of a relevant plasma quantity. Electrostatic probe data from the Controlled Shear Decorrelation eXperiment (CSDX) is analyzed using recurrence quantification analysis (RQA) in the context of previous work on the transition to weak drift-wave turbulence. The recurrence characteristics of a phase space trajectory provide a quantitative means to classify dynamics and identify transitions in a complex system. We present and quantify dynamical variations in the plasma variables as a function of the background magnetic field strength. A dynamical transition corresponding to the emergence of broadband fluctuations is identified using RQA measures.   

Transport of particles in chaotic, time dependent, magnetic fields

Magnetic fields in regions of low plasma pressure and large currents, such as in interstellar space and gaseous nebulae, are force-free as the Lorentz force vanishes. The three-dimensional Arnold-Beltrami-Childress (ABC) field is an example of three-dimensional, force-free, helical, chaotic magnetic field [1]. However, the ABC field is chaotic only if all three coefficients describing the field are non-zero. Otherwise, the field lines are regular and well behaved. The ABC fields correspond to Beltrami flows. The characteristic motion of particles in the chaotic ABC field is superdiffusive in space [1]. We consider the dynamics of particles when the ABC field is superimposed onto a larger amplitude uniform magnetic field. We further assume the ABC field to have sinusoidal time dependence, with a prescribed frequency. In this case the particles not only undergo cross-field diffusion but also gain energy. We present results on the cross-field diffusion of particles and on their energization and compare to the case when the ABC field is not chaotic. [1] A.K. Ram \textit{et al.}, \textit{Phys. Plasmas} \textbf{21}, 072309 (2014).   

Axial plasma detachment in helicon plasmas during a global transition due to spontaneous self organization: instabilities, bifurcation and the helicon core formation.

We observe axial plasma detachment in a helicon plasma device that occurs simultaneously along with a spontaneous, self-organized global transition in the plasma dynamics via a transport bifurcation with strong hysteresis, at a certain B\textunderscore crit [1]. For B \textless B\textunderscore crit, the plasma is dominated by density gradient driven resistive drift waves. For B \textgreater B\textunderscore crit, the plasma exhibits steepened density and ion temperature gradients, strong shearing in the azimuthal and parallel velocities, and multiple, simultaneously present, radially separated plasma instabilities. The axial detachment also follows the same hysteresis curves associated with the transport bifurcation that led to the transition. The value of B\textunderscore crit depends on the source parameters (pressure, gas flow rate, rf power etc.). This study allows access to new regimes to study plasma turbulence and transport as well as plasma detachment and helicon core formation. We find that the plasma can exist in more than one type of helicon modes. [1] L. Cui \textit{et. al.}, \textit{PoP }\textbf{23} 055704 (2016).   

Magnetic reconnection as a trigger for sub-proton-scale cascade in magnetized plasma turbulence

We provide the first numerical evidences that the development of power-law energy spectra below the so-called ion break can be related to the occurrence of magnetic reconnection, regardless of the actual state of the turbulent cascade at MHD scales. This mechanism is investigated via high-resolution two-dimensional hybrid-kinetic simulations employing complementary approaches (Lagrangian vs Eulerian) and with completely different mechanisms to feed the turbulent dynamics (freely-decaying Alfv\'enic fluctuations vs continuously-driven compressible fluctuations). In both cases, the reconnection-mediated kinetic spectrum of parallel magnetic fluctuations develops a spectral slope of $-2.8$ whether or not an MHD cascade has already developed, without changes even after a successive formation of a power law at larger scales. Once a quasi-steady turbulent state is reached, the total magnetic spectrum exhibits a slope of $-5/3$ in the MHD range and of $-3$ below the ion scales. Based on this and on the analysis of the turbulent and reconnection characteristic time scales, we therefore suggest a scenario where magnetic reconnection may represent a relevant non-local transfer mechanism simultaneously at play in addition to the classical local turbulent energy transfer.   

High Energy Particle Populations and Momentum Transport Associated with Collisionless Reconnection Processes

In the two-fluid description [1] of reconnection processes a new type of ``magneto-thermal'' mode producing reconnection is found [2,3] when the longitudinal electron thermal conductivity is relatively large. The mode is associated with the electron temperature gradient and can have a phase velocity in either directions of the electron or the ion diamagnetic velocity. High-energy particle populations are proposed to be produced as a result of reconnection events through mode-particle resonances that transfer the energy of the reconnecting mode to super-thermal particle populations. The spatial near-singularity of the perturbed electron temperature, that can enhance the thermal energy of particles in one region while depleting that of particles in the adjacent region, may be an additional contributing factor in this context. The modes can extract momentum from the plasma body and in an axisymmetric toroidal confinement configuration could sustain a ``spontaneous rotation'' [4] of the plasma column by carrying away angular momentum of the opposite sign. [1] B. Coppi, Phys. Fluids 8, 2273, 1965. [2] B. Coppi, Plasma Physics Reports (Fizika Plazmy) 42, 5, 383, 2016. [3] B. Coppi, B. Basu and A. Fletcher, Nucl. Fus., to appear, 2017. [4] B. Coppi, Nucl. Fus. 42, 1, 2002.   

Spectroscopic diagnostics of NIF ICF implosions using line ratios of Kr dopant in the ignition capsule

X ray spectroscopy is used on the NIF to diagnose the plasma conditions in the ignition target in indirect drive ICF implosions [1]. A platform is being developed at NIF where small traces of krypton are used as a dopant to the fuel gas for spectroscopic diagnostics using krypton line emissions. The fraction of krypton dopant was varied in the experiments and was selected so as not to perturb the implosion. Our goal is to use X-ray spectroscopy of dopant line ratios produced by the hot core that can provide a precise measurement of electron temperature. Simulations of the krypton spectra using a 1 in 10$^{\mathrm{4\thinspace }}$atomic fraction of krypton in direct-drive exploding pusher with a range of electron temperatures and densities show discrepancies when different atomic models are used. We use our non-LTE atomic model with a detailed fine-structure level atomic structure and collisional-radiative rates to investigate the krypton spectra at the same conditions. Synthetic spectra are generated with a detailed multi-frequency radiation transport scheme from the emission regions of interest to analyze the experimental data with 0.02{\%} Kr concentration and compare and contrast with the existing simulations at LLNL. [1] T. Ma, et al., RSI \textbf{87} (2016).   

Calibration of a High Resolution X-ray Spectrometer for High-Energy-Density Plasmas on NIF

A high-resolution, DIM-based (Diagnostic Instrument Manipulator) x-ray crystal spectrometer has been calibrated for and deployed at the National Ignition Facility (NIF) to diagnose plasma conditions and mix in ignition capsules near stagnation times. Two conical crystals in the Hall geometry focus rays from the Kr He-$\alpha$, Ly-$\alpha$, and He-$\beta$ complexes onto a streak camera for time-resolved spectra, in order to measure electron density and temperature by observing Stark broadening and relative intensities of dielectronic satellites. Signals from these two crystals are correlated with a third crystal that time-integrates the intervening energy range. The spectrometer has been absolutely calibrated using a microfocus x-ray source, an array of CCD and single-photon-counting detectors, and K- and L-absorption edge filters. Measurements of the integrated reflectivity, energy range, and energy resolution for each crystal will be presented. The implications of the calibration on signal levels from NIF implosions and x-ray filter choices will be discussed.   

Calibration of a Multipurpose Bragg-Crystal Spectrometer.

X-ray spectroscopy is an important diagnostic tool in understanding key parameters in high energy density science. The radiative properties of material in ICF implosions carries important information about the temperature and density of the generated plasma. To obtain absolute measurements of x-ray flux, a measurement of the energy-dependent response of the diagnostic is necessary. The calibration of a multipurpose Bragg-crystal spectrometer (MSPEC) is presented. This spectrometer was designed at Lawrence Livermore National Lab and utilizes a variety of elliptical geometries to record x-ray spectra in the 1.0 - 9.0 keV range. A laboratory x-ray source is measured at two symmetric locations: the MSPEC and a Si detector. The resolved spectrum from the MSPEC is recorded onto a CCD and compared to the signal recorded with the Si detector to give the energy dependent response of the MSPEC. The response of different crystals (PET, KAP, CsAP) and different elliptical geometries is measured and discussed.   

Absolute calibration of a compact gamma-ray spectrometer for high intensity laser plasma experiments

Copious amounts of gamma rays are generated in high intensity laser matter experiments, either by bremsstrahlung or by inverse Compton scattering. Measurements of multi-MeV gamma rays in such experiments provide direct indication of hot electrons generated during the interaction. A spectrometer based on forward Compton scattering was recently tested by Espy et al. [1]. We report on an improved design of a similar spectrometer which is significantly more compact (70 cm x 25 cm x 25 cm) and thus extremely convenient to use in laser plasma experiments. In this presentation, we describe the design considerations and recent results of an absolute calibration of the gamma-ray spectrometer. The calibration was performed using a bremsstrahlung source at different electron energies, i.e. 11, 13, 15 and 18 MeV [2]. Experimental spectra show a systematic increase of the maximum cut-off energy, temperature and flux. The results indicate that the spectrometer is effective for an energy range of 4$-$20 MeV with 5-10{\%} energy resolution. References [1] M. A. Espy, A. Gehring, A. Belian et al., Proc. Of SPIE Vol. 9783 97834V-1. [2] R. Schwengner et al., Nucl. Instrum. Meth. A: Accelerators, 555.12 (2005), pp. 211-219.   

Proton deflectometry of laser-driven relativistic electron jet from thin foil target

Near critical density relativistic electron jets from laser solid interaction carry currents approaching the Alfvén-limit and tens of kilo-Tesla magnetic fields. Such jets are often found in kinetic simulations with low areal density targets, but have not been confirmed experimentally. They may be used for X/gamma-ray generation and is also important for the understanding of post-transparency plasma dynamics. With a short-pulse probe beam at the Trident laser facility, we employed proton deflectometry to infer the jet’s properties, structure and the long-time dynamics. We develop corresponding GEANT4 simulation model of the proton deflectometry, with input from the kinetic PIC simulations in 2D and quasi-3D geometry, to compare with the experimental radiography images. Detail comparison of the experimental and simulation features in the deflectometry will be discussed.   

Measuring the temperature history of isochorically heated warm dense metals

A pump-probe platform has been designed for soft X-ray absorption spectroscopy near edge structure measurements in isochorically heated Al or Cu samples with temperature of 10s to 100s of eV. The method is compatible with dual picosecond-class laser systems and may be used to measure the temperature of the sample heated directly by the pump laser or by a laser-driven proton beam Knowledge of the temperature history of warm dense samples will aid equation of state measurements. First, various low- to mid-Z targets were evaluated for their suitability as continuum X-ray backlighters over the range 200-1800 eV using a 10 J picosecond-class laser with relativistic peak intensity Alloys were found to be more suitable than single-element backlighters. Second, the heated sample package was designed with consideration of target thickness and tamp layers using atomic physics codes. The results of the first demonstration attempts will be presented. This work was supported by the U.S. DOE under Contract No. DE-SC0014600   

High-resolution imaging of a shock front in plastic by phase contrast imaging at LCLS

Understanding the propagation of shock waves is important for many areas of high energy density physics, including inertial confinement fusion (ICF) and shock compression science. In order to probe the shock front structures in detail, a diagnostic capable of detecting both the small spatial and temporal changes in the material is required. Here we show the experiment using hard X-ray phase contrast imaging (PCI)$^{\mathrm{1}}$ to probe the shock wave propagation in polyimide with submicron spatial resolution. The experiment was performed at the Matter in Extreme Conditions (MEC) endstation of the Linac Coherent Lightsource (LCLS). PCI together with the femtosecond time scales of x-ray free electron lasers enables the imaging of optically opaque materials that undergo rapid temporal and spatial changes. The result reveals the evolution of the density profile with time. 1. M. A. Beckwith, S. Jiang, A. Schropp et al, Rev. Sci. Instrum. 88, 053501 (2017)   

Additions and improvements to the high energy density physics capabilities in the FLASH code

FLASH is an open-source, finite-volume Eulerian, spatially-adaptive radiation magnetohydrodynamics code that has the capabilities to treat a broad range of physical processes. FLASH performs well on a wide range of computer architectures, and has a broad user base. Extensive high energy density physics (HEDP) capabilities exist in FLASH, which make it a powerful open toolset for the academic HEDP community. We summarize these capabilities, emphasizing recent additions and improvements. We describe several non-ideal MHD capabilities that are being added to FLASH, including the Hall and Nernst effects, implicit resistivity, and a circuit model, which will allow modeling of Z-pinch experiments. We showcase the ability of FLASH to simulate Thomson scattering polarimetry, which measures Faraday due to the presence of magnetic fields, as well as proton radiography, proton self-emission, and Thomson scattering diagnostics. Finally, we describe several collaborations with the academic HEDP community in which FLASH simulations were used to design and interpret HEDP experiments.   

Modeling experimental plasma diagnostics in the FLASH code: proton radiography

Proton radiography is an important diagnostic tool for laser plasma experiments and for studying magnetized plasmas. We describe a new synthetic proton radiography diagnostic recently implemented into the FLASH code. FLASH is an open source, finite-volume Eulerian, spatially adaptive radiation hydrodynamics and magneto-hydrodynamics code that incorporates capabilities for a broad range of physical processes. Proton radiography is modeled through the use of the (relativistic) Lorentz force equation governing the motion of protons through 3D domains. Both instantaneous (one time step) and time-resolved (over many time steps) proton radiography can be simulated. The code module is also equipped with several different setup options (beam structure and detector screen placements) to reproduce a large variety of experimental proton radiography designs. FLASH’s proton radiography diagnostic unit can be used either during runtime or in post-processing of simulation results. FLASH is publicly available at flash.uchicago.edu.   

Modeling experimental plasma diagnostics in the FLASH code: Thomson scattering

Spectral analysis of the Thomson scattering of laser light sent into a plasma provides an experimental method to quantify plasma properties in laser-driven plasma experiments. We have implemented such a synthetic Thomson scattering diagnostic unit in the FLASH code, to emulate the probe-laser propagation, scattering and spectral detection. User-defined laser rays propagate into the FLASH simulation region and experience scattering (change in direction and frequency) based on plasma parameters. After scattering, the rays propagate out of the interaction region and are spectrally characterized. The diagnostic unit can be used either during a physics simulation or in post-processing of simulation results. FLASH is publicly available at flash.uchicago.edu.   

Recent Developments in the VISRAD 3-D Target Design and Radiation Simulation Code

The 3-D view factor code VISRAD is widely used in designing HEDP experiments at major laser and pulsed-power facilities, including NIF, OMEGA, OMEGA-EP, ORION, Z, and LMJ. It simulates target designs by generating a 3-D grid of surface elements, utilizing a variety of 3-D primitives and surface removal algorithms, and can be used to compute the radiation flux throughout the surface element grid by computing element-to-element view factors and solving power balance equations. Target set-up and beam pointing are facilitated by allowing users to specify positions and angular orientations using a variety of coordinates systems ($e.g.$, that of any laser beam, target component, or diagnostic port). Analytic modeling for laser beam spatial profiles for OMEGA DPPs and NIF CPPs is used to compute laser intensity profiles throughout the grid of surface elements. VISRAD includes a variety of user-friendly graphics for setting up targets and displaying results, can readily display views from any point in space, and can be used to generate image sequences for animations. We will discuss recent improvements to conveniently assess beam capture on target and beam clearance of diagnostic components, as well as plans for future developments.   

New Set of Prism Atomic Data, EOS and Opacity tables

We present a new set of atomic data tables generated with the updated data from the latest release of NIST atomic database. The new set also includes corrections for known inconsistencies in atomic structure calculations. Prism's ATBASE suite of atomic physics codes was used to generate high-quality atomic data for simulating the spectral properties and ionization dynamics of plasmas over a wide range of conditions. Atomic energy levels and oscillator strengths are computed using Hartree-Fock and configuration interaction models. Photoionization cross-sections from Hartree-Fock calculations are utilized for both valence-shell and inner-shell transitions. Radiative recombination rate coefficients are calculated from the photoionization cross-sections. Distorted-wave calculations are performed to generate electron collisional excitation and ionization cross-sections and rate coefficients. Autoionization rates include configuration interaction models. For dielectronic recombination related to K-shell spectra (Li-like ions and higher), electron capture rates are computed using autoionization rates and the detailed balance relationship. For lower ionization stages, total dielectronic recombination rate coefficients are based on semi-empirical models. A new set of EOS and opacity tables is generated with PROPACEOS code based on the new atomic data. We will discuss details of the calculations and demonstrate application of the new data to the analysis of several sets of experimental data.   

SpectraPLOT, Visualization Package with a User-Friendly Graphical Interface

SPECT3D is a collisional-radiative spectral analysis package designed to compute detailed emission, absorption, or x-ray scattering spectra, filtered images, XRD signals, and other synthetic diagnostics. The spectra and images are computed for virtual detectors by post-processing the results of hydrodynamics simulations in 1D, 2D, and 3D geometries. SPECT3D can account for a variety of instrumental response effects so that direct comparisons between simulations and experimental measurements can be made. SpectraPLOT is a user-friendly graphical interface for viewing a wide variety of results from SPECT3D simulations, and applying various instrumental effects to the simulated images and spectra. We will present SpectraPLOT's ability to display a variety of data, including spectra, images, light curves, streaked spectra, space-resolved spectra, and drilldown plasma property plots, for an argon-doped capsule implosion experiment example. Future SpectraPLOT features and enhancements will also be discussed.   

Non-LTE modeling with non-thermal electrons

We present a computational tool to simulate self-consistently the time evolution of the non-LTE kinetics and the electron energy distribution function (EEDF). The standard collisional-radiative rate equations for the atomic states\footnote{H.A. Scott, \textit{JQSRT} 71, pp. 689-701, 2001} are solved together with a Boltzmann-Fokker-Planck (BFP) equation for the EEDF. Both elastic and inelastic processes as well as radiative transitions are included. The EEDF is discretized on a non-uniform grid in energy space, and the numerical solution of the BFP equation is based on a set of recently developed algorithms\footnote{H.P. Le \& J.-L. Cambier, \textit{preprint}, 2017}. Several numerical examples are presented to demonstrate the capability of the code.   

Super Configuration Accounting Equation of State for WDM and HED plasma

Rad-Hydro numerical codes require Equation of State (EOS) and opacities. We describe a procedure to obtain an EOS compatible with our STA opacity model. We use our relativistic super-configuration code - STA-2.5 [1] to compute the average \textless Z\textgreater and excitation-ionization internal energy U and chemical potential \textunderscore . These and other data will serve as basic inputs into a Yukawa Monte-Carlo [2] improved version of quotidian EOS [3], known as YMCQ. The screening in the Yukawa potential describing the ion-ion interaction is modified by the data from STA. This integrated procedure yields the excess internal energy due to the non-ideal behavior of the EOS concordant with our opacity model and allows us to have an EOS model applicable from solid matter to very tenuous plasmas as found in laser fusion, astrophysics, or tokamaks. We shall present its application to Carbon, Aluminum and Iron. [1] M. Busquet, M. Klapisch, Bull. American Phys. Soc. 55, 225 (2010) [2] D. Gilles, F. Lambert, J. Cl\'{e}rouin, G. Salin, HEDP 3, 95 (2007); J. M. Caillol, D. Gilles, J. Stat. Phys. 100, 933 (2000) [3] D. M. More, K. H. Warren, D. A. Young, and G. B. Zimmerman, Phys. Fluids 31, 3059 (1998)   

Efficacy of Computational Models of Dense Plasmas

Computational models must balance physics fidelity with computational cost. Because many important applications cannot be modeled with the highest-fidelity models, it is important to assess boundaries in parameter space for which lower-fidelity models still provide useful information other-wise unobtainable. Here, we perform a metastudy in which data from a wide range of computational models used in the high energy-density physics community is examined to reveal physics regimes in which they confer little advantage over simpler models. Model fidelity is measured by comparing high-fidelity predictions with new predictions from two very simple pair potential models. Error metrics are defined, and patterns in the data are sought. This data-driven approach reveals the surprising result that simpler models become applicable not because of higher temperature and/or lower density, but rather based on relative ionization level $\langle Z\rangle/Z$. Moreover, we find that the simpler models tend to fail abruptly as the role of atomic and molecular physics plays an increasing role, suggesting a fairly narrow “transition” between residual chemistry and disordered plasma behavior.   

Higher-Order Advection-Based Remap of Magnetic Fields in an Arbitrary Lagrangian-Eulerian Code

We will present methods formulated for the Eulerian advection stage of an arbitrary Lagrangian-Eulerian code for the new addition of magnetohydrodynamic (MHD) effects. The various physical fields are advanced in time using a Lagrangian formulation of the system. When this Lagrangian motion produces substantial distortion of the mesh, it can be difficult or impossible to progress the simulation forward. This is overcome by relaxation of the mesh while the physical fields are frozen. The code has already successfully been extended to include evolution of magnetic field diffusion during the Lagrangian motion stage. This magnetic field is discretized using an H(div) compatible finite element basis. The advantage of this basis is that the divergence-free constraint of magnetic fields is maintained exactly during the Lagrangian motion evolution. Our goal is to preserve this property during Eulerian advection as well. We will demonstrate this property and the importance of MHD effects in several numerical experiments. In pulsed-power experiments magnetic fields may be imposed or spontaneously generated. When these magnetic fields are present, the evolution of the experiment may differ from a comparable configuration without magnetic fields.   

Multi-species ion transport in ICF relevant conditions

Classical transport theory based on Chapman-Enskog methods provides self consistent approximations for kinetic fluxes of mass, heat and momentum for each ion species in a multi-ion plasma characterized with a small Knudsen number. A numerical method for solving the classic forms of multi-ion transport, self-consistently including heat and species mass fluxes relative to the center of mass, is given in [Kagan-Baalrud, arXiv '16] and similar transport coefficients result from recent derivations [Simakov-Molvig, PoP, '16]. We have implemented a combination of these methods in a standalone test code and in xRage, an adaptive-mesh radiation hydrodynamics code, at LANL. Transport mixing is examined between a DT fuel and a CH capsule shell in ICF conditions. The four ion species develop individual self-similar density profiles under the assumption of P-T equilibrium in 1D and show interesting early time transient pressure and center of mass velocity behavior when P-T equilibrium is not enforced. Some 2D results are explored to better understand the transport mix in combination with convective flow driven by macroscopic fluid instabilities at the fuel-capsule interface. Early transient and some 2D behaviors from the fluid transport are compared to kinetic code results.   

Plasma kinetic effects on atomistic mix in one dimension and at structured interfaces (I)

Kinetic effects on interfacial mix are examined using VPIC simulations. In 1D, comparisons are made to the results of analytic theory in the small Knudsen number limit. While the bulk mixing properties of interfaces are in general agreement, differences arise near the low-concentration fronts during the early evolution of a sharp interface when the species' perpendicular scattering rate dominates over the slowing down rate. In kinetic simulations, the diffusion velocities can be larger or comparable to the ion thermal speeds, and the Knudsen number can be large. Super-diffusive growth in mix widths ($\Delta $x \textasciitilde t$^{\mathrm{a}}$ where a $\ge $1/2) is seen before transition to the slow diffusive process predicted from theory (a $=$1/2). Mixing at interfaces leads to persistent, bulk, hydrodynamic features in the center of mass flow profiles as a result of diffusion and momentum conservation. These conclusions are drawn from VPIC results together with simulations from the RAGE hydrodynamics code with an implementation of diffusion and viscosity from theory and an implicit Vlasov-Fokker-Planck code iFP. In perturbed 2D and 3D interfaces, it is found that 1D ambipolarity is still valid and that initial perturbations flatten out on a-few-ps time scale, implying that finite diffusivity and viscosity can slow instability growth in ICF and HED settings.   

Plasma kinetic effects on atomistic mix in one dimension and at structured interfaces (II)

The Marble campaign seeks to develop a platform for studying mix evolution in turbulent, inhomogeneous, high-energy-density plasmas at the NIF. Marble capsules contain engineered CD foams, the pores of which are filled with hydrogen and tritium. During implosion, hydrodynamic stirring and plasma diffusivity mix tritium fuel into the surrounding CD plasma, leading to both DD and DT fusion neutron production. In this presentation, building upon prior work [Yin et al., Phys. Plasmas 23, 112392 (2016)], kinetic particle-in-cell simulations using the VPIC code are used to examine kinetic effects on thermonuclear burn in Marble-like settings. Departures from Maxwellian distributions are observed near the interface and TN burn rates and inferred temperatures from synthetic neutron time of flight diagnostics are compared with those from treating the background species as Maxwellian.   

Plasma Ion Stratification by Weak Planar Shocks

We derive fluid equations for describing steady-state planar shocks of a moderate strength (0\textless M-1\textless 1 with M the shock Mach number) propagating through an unmagnetized quasineutral collisional plasma comprising two separate ion species. In addition to the standard fluid quantities, such as the total mass density, mass-flow velocity, and electron and average ion temperatures, the equations describe shock stratification in terms of variations in the relative concentrations and temperatures of the two ion species along the shock propagation direction. We have solved these equations analytically for weak shocks (0\textless M-1\textless \textless 1), with the results depending on M, ratios of the ion masses and charges, and the upstream mass fraction of one of the ion species. These analytical results are instrumental for gaining understanding in the behavior of weak shocks, and they have been used to verify kinetic simulations of shocks in multi-ion plasmas.   

Resolving Controversies Concerning the Kinetic Structure of Multi-Ion Plasma Shocks

Strong collisional shocks in multi-ion plasmas are featured in several high-energy-density environments, including Inertial Confinement Fusion (ICF) implosions. Yet, basic structural features of these shocks remain poorly understood (e.g., the shock width's dependence on the Mach number and the plasma ion composition, and temperature decoupling between ion species), causing controversies in the literature; even for stationary shocks in planar geometry [cf., Ref.\footnote{M. S. Greywall, Phys.\ Fluids {\bf 18}, 1439 (1975).}\ and Ref.\footnote{C.\ Bellei {\it et al.}, Phys.\ Plasmas {\bf 21}, 056310 (2014).}]. Using a LANL-developed, high-fidelity, 1D-2V Vlasov-Fokker-Planck code (iFP)\footnote{W. T. Taitano {\it et al.}, J.\ Comp.\ Phys.\ {\bf 297}, 357 (2015); ibid.\ {\bf 318}, 391 (2016); ibid.\ {\bf 339}, 453 (2017).}, as well as direct comparisons to multi-ion hydrodynamic simulations and semi-analytic predictions, we critically examine steady-state, planar shocks in two-ion species plasmas and put forward resolutions to these controversies.   

Study of self-generated electric field at shock front by broadband proton probing and soft X-ray emission

Self-generated electric fields arise from gradients in the electron pressure at shock fronts. We report observations of such E-fields from experiments conducted on OMEGA EP. In the experiments, strong shock waves were generated in low density gas under a quasi-planar geometry and diagnosed by broadband proton radiography. The broad proton spectrum allows energy-dependent measurements of deflection from which one can quantitatively constrain the electrical potential and field thickness. Three UV beams delivering up to 6.4 kJ energy in 2ns were used for shock generation and a short laser pulse of energy up to 850 J, 10 ps duration, was used to accelerate the broadband proton beam for point-projection radiography. Observations show the existence of electric fields with potential \textasciitilde 300 V at the front of a Mach 9 shock in helium gas. A Mach 16 shock is also studied, from which both the field thickness and electric potential are reproduced. Simultaneous spatially resolved soft-x-ray spectroscopy provided additional measurements of shock velocity, particle velocity and thermal emission.   

New generalized Noh solutions for HEDP hydrocode verification

The classic Noh solution describing stagnation of a cold ideal gas in a strong accretion shock wave has been the workhorse of compressible hydrocode verification for over three decades. We describe a number of its generalizations available for HEDP code verification. First, for an ideal gas, we have obtained self-similar solutions that describe adiabatic convergence either of a finite-pressure gas into an empty cavity or of a finite-amplitude sound wave into a uniform resting gas surrounding the center or axis of symmetry. At the moment of collapse such a flow produces a uniform gas whose velocity at each point is constant and directed towards the axis or the center, i. e. the initial condition similar to the classic solution but with a finite pressure of the converging gas. After that, a constant-velocity accretion shock propagates into the incident gas whose pressure and velocity profiles are not flat, in contrast with the classic solution. Second, for an arbitrary equation of state, we demonstrate the existence of self-similar solutions of the Noh problem in cylindrical and spherical geometry. Examples of such solutions with a three-term equation of state that includes cold, thermal ion/lattice, and thermal electron contributions are presented for aluminum and copper. These analytic solutions are compared to our numerical simulation results as an example of their use for code verification.   

Analytic Analysis of Convergent Shocks to Multi-Gigabar Conditions

The gigabar experimental platform at the National Ignition Facility is designed to increase understanding of the physical states and processes that dominate in the hydrogen at pressures from several hundreds of Mbar to tens of Gbar. Recent experiments using a solid CD$_{\mathrm{2}}$ ball reached temperatures and densities of order $10^{7}^{\mathrm{\thinspace }}$K and several tens of $\mbox{g/cm}^{3},$ respectively. These conditions lead to the production of D--D fusion neutrons and x-ray bremsstrahlung photons, which allow us to place constraints on the thermodynamic states at peak compression. We use an analytic model to connect the neutron and x-ray emission with the state variables at peak compression. This analytic model is based on the self-similar Guderley solution of an imploding shock wave and the self-similar solution of the point explosion with heat conduction from Reinicke. Work is also being done to create a fully self-similar solution of an imploding shock wave coupled with heat conduction and radiation transport using a general equation of state. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.   

A Platform for X-Ray Thomson Scattering Measurements of Radiation Hydrodynamics Experiments on the NIF

A recent experiment on the National Ignition Facility(NIF) radiographed the evolution of the Rayleigh-Taylor(RT) instability under high and low drive cases. This experiment showed that under a high drive the growth rate of the RT instability is reduced relative to the low drive case. The high drive launches a radiative shock, increases the temperature of the post-shock region, and ablates the spikes, which reduces the RT growth rate. The plasma parameters must be measured to validate this claim. We present a target design for making X-Ray Thomson Scattering(XRTS) measurements on radiation hydrodynamics experiments on NIF to measure the electron temperature of the shocked region in the above cases. Specifically, we show that a previously fielded NIF radiation hydrodynamics platform can be modified to allow sufficient signal and temperature resolution for XRTS measurements. This work is funded by the~NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, grant number~DE-NA0002956 and the National Science Foundation through the Basic Plasma Science and Engineering program.   

Modeling and design of radiative hydrodynamic experiments with X-ray Thomson Scattering measurements on NIF

Recent experiments at the National Ignition Facility studied the effect of radiation on shock-driven hydrodynamic instability growth. X-ray radiography images from these experiments indicate that perturbation growth is lower in highly radiative shocks compared to shocks with negligible radiation flux. The reduction in instability growth is attributed to ablation from higher temperatures in the foam for highly radiative shocks. The proposed design implements the X-ray Thomson Scattering (XRTS) technique in the radiative shock tube platform to measure electron temperatures and densities in the shocked foam. We model these experiments with CRASH, an Eulerian radiation hydrodynamics code with block-adaptive mesh refinement, multi-group radiation transport and electron heat conduction. Simulations are presented with SiO$_2$ and carbon foams for both the high temperature, radiative shock and the low-temperature, hydrodynamic shock cases. Calculations from CRASH give estimations for shock speed, electron temperature, effective ionization, and other quantities necessary for designing the XRTS diagnostic measurement.   

Computational Analysis of Late-Time, Low Atwood Rayleigh-Taylor Experiments at OMEGA

Numerical simulations have shown a reacceleration phase of the Rayleigh-Taylor instability (RTI) at low Atwood numbers, during which the bubble and spike Froude numbers deviate from their expected asymptotic values [1]. Currently, there is no experimental validation of those results. In this work, we present the design and computational analysis of a laser-driven RTI experiment on OMEGA 60. The design considered enables us to experimentally probe both high Atwood numbers (for validation against previous experiments), and low Atwood numbers, which may allow us to validate theoretical results [1]. Our analyses focus on the behavior of the full target system, as well as simplified models for studying the impact of large-scale expansion effects due to the post-shock pressure profile. [1] P. Ramaprabhu et al., Phys. Fluids 24, 074107 (2012)   

Expansion of Non-Quasi-Neutral Limited Plasmas Driven by Two-Temperature Electron Clouds

Fast heating of an isolated solid mass, under irradiation of ultra-intense ultra-short laser pulse, to averaged temperatures of order of keV is theoretically studied. Achievable maximum ion temperatures are determined as a consequence of the interplay of the electron-to-ion energy deposition and nonrelativistic plasma expansion, where fast ion emission plays an important role in the energy balance. To describe the plasma expansion, we develop a self-similar solution, in which the plasma is composed of three fluids, i.e., ions and two-temperature electrons. Under the condition of isothermal electron expansion in cylindrical geometry, such a fluid system, self-consistently incorporated with the Poisson equation, is fully solved. The charge separation and resultant accelerated ion population due to the induced electrostatic field are quantitatively presented. The analytical model is compared with two-dimensional hydrodynamic simulations to provide practical working windows for the target and laser parameters for the fast heating.    

Detachment experiments in new DIII-D upper divertor

Installation of the Small Angle Slot (SAS) in the upper divertor of DIII-D enables new studies of the effect of target and baffle geometry on divertor detachment. This structure provides a more-closed upper divertor as well as the SAS divertor itself. Initial SAS experiment results indicate that divertor detachment occurs at a lower line-averaged density than in the more-open, lower single null divertor configurations on DIII-D. In contrast, the increased divertor closure of the new installation did not reduce the upstream density required for detachment beyond that achieved with the previous upper divertor structure. Particle pumping in the upper divertor structure is found to produce a $\approx10\%$ reduction in the pedestal density required for detachment compared to the case with no pumping. Comparisons focus on both the onset of detachment (measured by in-target Langmuir probes) as a function of upstream density, as well as the effect of the new divertor configurations on pedestal density profiles.   

Simulation of DIII-D experiments on detachment and divertor closure

While divertor detachment is necessary to control the heat flux to divertor targets in ITER and future tokamak fusion devices, detachment is often associated with high pedestal density, which can be problematic for core plasma performance. Divertor closure experiments on DIII-D have shown that the pedestal electron density at detachment is reduced by \textasciitilde 35{\%} for a configuration with a high degree of outer divertor closure, compared to an open outer divertor configuration. In this work, SOLPS-ITER modeling, with full drift physics engaged, is used to evaluate the experimental open and closed configurations. Realistic power and particle fluxes are assumed at the core boundary. Predicted 2D ionization profiles will be presented, and sensitivity of detachment behavior to particle and thermal diffusivities, cryopump efficiency, and wall pumping assumptions will be addressed. Initial simulations show a 20{\%} decrease in pedestal density at detachment for the closed configuration, and a similar reduction in the pedestal ionization source.   

Effects of Magnetic Coil Misalignments on the SAS Divertor

A new Small Angle Slot (SAS) divertor has recently been installed and tested in DIII-D, promising easier plasma detachment and lower target temperatures. Previous SAS analyses focused on the accuracy of the 2D reconstructed strike geometry and 3D ``vacuum'' analyses of RMPs on the lobes and on the strike point modulation. The present work introduces a kinetic EFIT 2D equilibrium reconstructed from a recent 2017 SAS experiment. The kinetic EFIT and its ``vacuum'' topology due to 3D error and perturbation fields are compared to the previous analyses based on a synthetic equilibrium, showing similar results. The magnetic lobes remain confined within the SAS and the toroidal modulation of the strike point position is only slightly affected. Further simulations of a possible shift of the toroidal field coil are carried out through 3D field-line tracing. The effects of such misalignments including plasma response on the SAS are discussed, together with the corresponding implications for the design of the next envisaged SAS upgrade.   

Numerical exploration of non-axisymmetric divertor closure in the small angle slot (SAS) divertor at DIII-D

In the Small Angle Slot (SAS) divertor in DIII-D, the combination of misaligned slot structure and non-axisymmetric perturbations to the magnetic field causes the strike point to vary radially along the divertor slot and even leave it at some toroidal locations. This effect essentially introduces an opening in the divertor slot from where recycling neutrals can easily escape, and thereby degrade performance of the slot divertor. This effect has been approximated by a finite gap in the divertor baffle. Simulations with EMC3-EIRENE show that a toroidally localized loss of divertor closure can result in non-axisymmetric divertor densities and temperatures. This introduces a density window of 10-15 \% on top of the nominal threshold separatrix density during which a non-axisymmetric onset of local detachment occurs, initially leaving the gap and up to 60 deg beyond that still attached. Conversely, the impact of such toroidally localized divertor perturbations on the toroidal symmetry of midplane separatrix conditions is small.   

Maximizing Heat Dissipation via Target Optimization of the Small-Angle Slot Divertor

The planned SAS 2 divertor uses a combination of grazing target angles and closure to direct recycling neutrals near the strike point, thus facilitating detachment onset. SAS 2 should also provide adequate pumping efficiency to be consistent with high-power steady-state scenarios on DIII-D. Initial SOLPS results indicate significantly higher neutral densities and lower electron temperatures in the SAS 2 slot, compared to a closed reference divertor model with baseline plasma profiles appropriate for high power. A systematic optimization of the parameterized SAS 2 target shape is performed in SOLPS to further reduce target heat fluxes and temperatures at lowest upstream density. To speed up the target optimization process, target neutral densities calculated by Eirene act as a performance metric by proxy for detachment facilitation. The efficacy of this proxy metric is discussed. Results are also presented from SAS 2 neutral pumping simulations in Eirene with a stationary background plasma. The feasibility of mutually satisfactory particle control and detachment control is discussed.   

Impact of Cross-field Drifts on Detachment in DIII-D

Simulations of DIII-D plasmas have revealed the strong role of \textbf{E}$\times$\textbf{B}-drifts in the low field side (LFS) detachment structure. High confinement modes (H-mode) with the $\nabla$B-drift towards the X-point (fwd B$_T$) enter detachment at 20\% higher upstream density, n$_{e,sep}$, than plasmas with the $\nabla$B-drift away from the X-point (rev B$_T$). In contrast, low confinement modes (L-mode) enter detachment at 10\% lower n$_{e,sep}$ in fwd B$_T$. Despite this, both L- and H-modes detached plasmas show strong target flux, J$_{SAT}$, reduction with increasing n$_{e,sep}$ in fwd B$_T$, while only a modest reduction occurs in rev B$_T$. In fwd B$_T$ H-mode, a step-wise transition from attached to strongly detached conditions is observed with increasing ne,sep. UEDGE simulations indicate that the strong poloidal \textbf{E}$\times$\textbf{B}-drift in the private flux region in H-mode drives the difference for the detachment onset relative to L-mode. In fwd B$_T$, the dependence of this poloidal \textbf{E}$\times$\textbf{B}-drift on the divertor conditions can reinforce the plasma into either attached or strongly detached state. In rev B$_T$, radial \textbf{E}$\times$\textbf{B}-drift depletes strike-line n$_e$, limiting the degree of detachment.   

Parallel Energy Transport in Detached DIII-D Divertor Plasmas

A comparison of experiment and modeling of detached divertor plasmas is examined in the context of parallel energy transport. Experimental estimates of power carried by electron thermal conduction versus plasma convection are experimentally inferred from power balance measurements of radiated power and target plate heat flux combined with Thomson scattering measurements of the T$_{e}$ profile along the divertor leg. Experimental profiles of T$_{e}$ exhibit relatively low gradients with T$_{e}$ $<$ 15 eV from the X-point to the target implying transport dominated by convection. In contrast, fluid modeling with SOLPS produces sharp T$_{e}$ gradients for T$_{e}$ $>$ 3 eV, characteristic of transport dominated by electron conduction through the bulk of the divertor. This discrepancy with experimental transport dominated by convection and modeling by conduction has significant implications for the radiative capacity of divertor plasmas and may explain at least part of the difficulty for fluid modeling to obtain the experimentally observed radiative losses. Comparisons are also made for helium plasmas where the match between experiment and modeling is much better. *Work supported by the US DOE under DE-FC02-04ER54698.   

2-D Laser-Calibrated Doppler Images of HeII and CIII Emission on DIII-D

Recent improvements to the DIII-D CIS system have reduced the error bars of the inferred Doppler velocity by over an order of magnitude, i.e. to \textasciitilde 0.1 km/s. Coherence imaging of plasma emission superimposes an interferogram on the plasma image, and the interferometer phase is a sensitive measure of the central wavelength of the emission. A tuneable diode laser calibration image at \textasciitilde 465~nm is automatically acquired between plasma shots and provides the rest wavelength in the lab frame; the wavelength is measured with a wavemeter to 0.01 pm. The interferometer is stabilized mechanically and thermally with a unique system so that the interferometer drift between calibrations is small. These improvements have enabled tomographically inverted images of main ion He II parallel flow in the divertor during He plasma operation. The parallel flow, as expected, is observed to depend on the direction of the $B\times \nabla B$drift, which is reversed by changing the direction of the toroidal field. For many conditions, the C III Doppler velocity is also in the same direction as the main ion. *Work supported by the US DOE under DE-FC02-04ER54698 and DE-AC52-07NA27344. LLNL-ABS-88688.   

Divertor extreme ultraviolet (EUV) survey spectroscopy in DIII-D

An extreme ultraviolet spectrograph measuring resonant emissions of D and C in the lower divertor has been added to DIII-D to help resolve an \textasciitilde 2X discrepancy between bolometrically measured radiated power and that predicted by boundary codes for DIII-D, JET and ASDEX-U. With 290 and 450 gr/mm gratings, the DivSPRED spectrometer, an 0.3 m flat-field McPherson model 251, measures ground state transitions for D (the Lyman series) and C (e.g., C IV, 155 nm) which account for \textgreater 75{\%} of radiated power in the divertor. Combined with Thomson scattering and imaging in the DIII-D divertor, measurements of position, temperature and fractional power emission from plasma components are made and compared to UEDGE/SOLPS-ITER. Mechanical, optical, electrical, vacuum, and shielding aspects of DivSPRED are presented.   

Development of an EMC3-EIRENE Synthetic Imaging Diagnostic

2D and 3D flow measurements are critical for validating numerical codes such as EMC3-EIRENE. Toroidal symmetry assumptions preclude tomographic reconstruction of 3D flows from single camera views. In addition, the resolution of the grids utilized in numerical code models can easily surpass the resolution of physical camera diagnostic geometries. For these reasons we have developed a Synthetic Imaging Diagnostic capability for forward projection comparisons of EMC3-EIRENE model solutions with the line integrated images from the Doppler Coherence Imaging diagnostic on DIII-D. The forward projection matrix is 2.8 Mpixel by 6.4 Mcells for the non-axisymmetric case we present. For flow comparisons, both simple line integral, and field aligned component matrices must be calculated. The calculation of these matrices is a massive embarrassingly parallel problem and performed with a custom dispatcher that allows processing platforms to join mid-problem as they become available, or drop out if resources are needed for higher priority tasks. The matrices are handled using standard sparse matrix techniques.   

Examining Diagnostic Capability for Determining Divertor Neutral Sourcing to the Pedestal on DIII-D*

Neutral fueling from the divertor plays a key role in setting the density pedestal, but can not yet be predicted via numerical models and thus remains a crucial variable in predictive core-edge coupling. New neutral diagnostics are planned to address this issue by constraining predictions of neutral density from the divertor through the SOL into the pedestal: (a) Lyman-alpha imaging and (b) extended poloidal coverage of neutral pressure gauges. Forward modeling diagnostic responses across expected pedestal neutral fueling rates is used to estimate the diagnostic sensitivity and range of applicability. Modeled neutral source rates are obtained through interpretive modeling with the OEDGE code of experiments performed across the range of DIII-D divertor baffling configurations and gas puffing rates that result in a range of density profiles Additional forward modeling with the core/edge coupling code CESOL will be used and compared against interpretive analysis. *Work supported by US DOE under DE-AC05-00OR22725, DE-FC02-04ER54698.   

Understanding tungsten divertor sourcing and SOL transport using multiple poloidally-localized sources in DIII-D ELM-y H-mode discharges

Experiments using metal inserts with novel isotopically-enriched tungsten coatings at the outer divertor strike point (OSP) have provided unique insight into the ELM-induced sourcing, main-SOL transport, and core accumulation control mechanisms of W for a range of operating conditions. This experimental approach has used a multi-head, dual-facing collector probe (CP) at the outboard midplane, as well as W-I and core W spectroscopy. Using the CP system, the total amount of W deposited relative to source measurements shows a clear dependence on ELM size, ELM frequency, and strike point location, with large ELMs depositing significantly more W on the CP from the far-SOL source. Additionally, high spatial (\textasciitilde 1mm) and ELM resolved spectroscopic measurements of W sourcing indicate shifts in the peak erosion rate. Furthermore, high performance discharges with rapid ELMs show core W concentrations of \textasciitilde few 10$^{\mathrm{-5}}$, and the CP deposition profile indicates W is predominantly transported to the midplane from the OSP rather than from the far-SOL region. The low central W concentration is shown to be due to flattening of the main plasma density profile, presumably by on-axis electron cyclotron heating.   

Measurements and modeling of intra-ELM tungsten sourcing and transport in DIII-D

Intra-ELM tungsten erosion profiles in the DIII-D divertor, acquired via W I spectroscopy with high temporal and spatial resolution, are consistent with SDTrim.SP sputtering modeling using measured ion saturation currents and impact energies during ELMs as input and an ad-hoc 2{\%} C$^{\mathrm{2+}}$ impurity flux. The W sputtering profile peaks close to the OSP both during and between ELMs in the favorable B$_{\mathrm{T}}$ direction. In reverse B$_{\mathrm{T}}$ the W source peaks close to the OSP between ELMs but strongly broadens and shifts outboard during ELMs, heuristically consistent with radially outward ion transport via ExB drifts. Ion impact energies during ELMs (inferred taking the ratio of divertor heat flux to the ion saturation current) are found to be approximately equal to T$_{\mathrm{e,ped}}$, lower than the 4*T$_{\mathrm{e,ped}}$ value predicted by the Fundamenski/Moulton free streaming model. These impact energies imply both D main ions and C impurities contribute strongly to W sputtering during ELMs on DIII-D. This work represents progress towards a predictive model to link upstream conditions (i.e., pedestal height) and SOL impurity levels to the ELM-induced W impurity source at both the strike-point and far-target regions in the ITER divertor. Correlations between ELM size/frequency and SOL W fluxes measured via a midplane deposition probe will also be presented.   

Modifications of W and Mo leading edges under plasma loads in DIII-D divertor.

Cracking and melting of W and Mo leading edges were observed in the lower divertor of DIII-D during experiments with intentionally misaligned W monoblocks (MBs) and in the course of the Metal Rings Campaign involving W-coated Mo tile inserts (TIs). MBs were exposed near the attached outer strike point during deuterium and helium L- and H-mode discharges using DiMES. Two of the MBs were misaligned by 0.3 mm and 1 mm, forming leading edges. Particulate ejection from a 1 mm leading edge was observed during the exposure, and evidence of melting and cracking was found post mortem. Two toroidal rings of TIs were installed in the lower outer divertor, the inner one at the floor and the outer one at the shelf. The floor TIs bowed during plasma exposure forming leading edges up to 1.2 mm high; about 40{\%} of these edges experienced melting. Re-solidified melt layers up to 1 mm thick were observed, their shape being consistent with motion in the $j$x$B$ direction with $j$ driven by electron emission.   

Measurements of W Erosion using UV Emission from DIII-D and CTH

of Plasma Facing Components (PFCs) will play a critical role in establishing the performance of reactor-relevant fusion devices, particularly for tungsten (W) divertor targets. Erosion can be diagnosed from spectral line emission together with atomic coefficients representing the 'ionizations per photon' (S/XB). Emission from W I is most intense in the UV region. Thus, UV survey spectrometers (200-400 nm) are used to diagnose W PFCs erosion in the DIII-D divertor and from a W tipped probe in the CTH experiment. Nineteen W emission lines in the UV region are identified between the two experiments, allowing for multiple S/XB erosion measurements. Initial W erosion measurements are compared to erosion using the 400.9 nm W I line. Complete UV spectra will be presented and compared to synthetic spectra for varying plasma conditions. Analysis of the metastable states impact on the S/XB will be presented as well as possible electron temperature and density diagnosis from W I line ratios. supported by USDOE grants DE-SC0015877 {\&} DE-FC02-04ER54698.   

The role of neutral W metastable states in tungsten spectral line emission and erosion diagnostics.

W I spectral emission has been widely used to measure influx rates from W PFCs via S/XB coefficients. These coefficients depend upon calculated W I photon emissivities and effective ionization rate coefficients, each of which can be influenced by long lived metastable states. A review of progress in new atomic calculations for W excitation and ionization is given, along with a description of the remaining challenges. The new data is used to investigate the sensitivity of W I emission and ionization to metastable populations. The metastable-resolved data is generated using a collisional-radiative model. A comparison with W I measured spectra from DIII-D and Auburn CTH plasmas are given. Each spectral line can be associated with a single driving metastable population, simplifying the modeling considerably and giving a potential metastable diagnostic. New atomic coefficients are also generated for use in ERO modeling and compared with previously used data.   

Application of Laser Ablation Inductively Coupled Plasma Mass Spectrometry and Enriched Tungsten Isotopes to Nuclear Fusion Impurity Transport Research

During the DIII-D Metal Rings Campaign of 2016, one divertor tile-array was coated in natural tungsten (W) (26.5\% W-182) and the other array was coated with 93.5\% isotopically enriched W-182. The unique “isotopic fingerprint” of the enriched W-182 coating enabled the eroded W to act as tracer particles. Graphite collector probes (CPs) were inserted into the plasma scrape-off-layer (SOL) at the outboard midplane during operations to sample W escaping the divertor region. The use of W tracer particles and isotopic analysis of the CPs provides unique information on how various plasma operating configurations affect impurity production from the divertor and transport within the SOL. Laser Ablation Mass Spectrometry (LA-MS) is used in order to measure isotopic ratios of the W deposited on the CPs. Initial tests have revealed enrichment on the probes up to nearly 93\% which corresponds with sourcing of impurities from the enriched W-182 tile-array. Additional empirical evidence is provided for understanding divertor high-Z sourcing and transport through trace plasma material interaction studies with low-Z walls. With the Stable Isotopic Mixing Model, relative contribution from each W source is also provided.\par   

Deposition Profile Analysis from DIII-D Metal Rings Campaign Outer-Midplane Collector Probe Diagnostic and Utilization of Enriched Isotopic Tungsten Tracer Particles

The DIII-D Metal Rings Campaign used isotopically-enriched, W-coated divertor tiles coupled with dual-facing midplane collector probes (CPs) in the far Scrape-off Layer (SOL). Inductively Coupled Plasma Mass Spectroscopy (ICP-MS) results are presented characterizing the isotopic ratios of deposited W on the CPs and which give quantitative information on the transport of W from specific poloidal locations within the lower outer divertor region having different isotopically-marked tiles. Rutherford Backscattering Spectrometry (RBS) of these CPs has provided areal densities of elemental W content. These resultant W deposition profiles were compared with DIVIMP modelling of the far-SOL to better understand impurity transport in the edge plasma. CPs were exposed for 37 distinct operating configurations (L-mode/H-mode, forward/reverse Bt, strikepoint position). Radial decay lengths (RDL) between 5 and 50 mm were observed with consistently narrower RDL and higher peak W content on the side of the probes connected along field lines to the inner divertor, indicating a concentration of W in the upstream plasma. Correlations are discussed between peak W content, RDL, and isotopic profiles on the CPs over a wide range of conditions.   

OEDGE Modeling of Collector Probe measurements in L-mode from the DIII-D tungsten ring campaign

During the tungsten ring campaign on DIII-D, a collector probe system with multiple diameter, dual-facing collector rods was inserted into the far scrape off layer (SOL) near the outer midplane to measure the plasma tungsten content. For most probes more tungsten was observed on the side connected along field lines to the inner divertor, with the larger probes showing largest divertor-facing asymmetries The OEDGE code is used to model the tungsten erosion, transport and deposition. It has been enhanced with (i) a peripheral particle transport and deposition model to record the impurity content in the peripheral region outside the regular mesh, and (ii) a collector probe model. The OEDGE results approximately reproduce both the divertor-facing asymmetries and the radial decay of each collector probe profile. The effect of changing impurity transport assumptions and wall location are examined. The measured divertor-facing asymmetries imply a higher tungsten density in the plasma upstream of the probe; this was expected theoretically from the effect of the parallel ion temperature gradient force driving upstream transport of tungsten from the outer divertor and was also found in the code analysis.   

Development of Surface Eroding Thermocouples in DIII-D

The Surface Eroding Thermocouple (SETC) is a specialized diagnostic for characterizing the surface temperature evolution with a high temporal resolution (\textasciitilde 1ms) which is especially useful in areas unobservable by line-of-sight diagnostics (e.g. IR cameras). Recently, SETCs were tested in DiMES and successfully acquired temperature signals during strike point sweeps on the lower divertor shelf. We observed that the SETCs have a sub-10 ms time response and is sufficient to resolve ELM heat pulses. Preliminary analysis shows heat fluxes measured by SETCs and IR camera agree within 20{\%}. Comparison of SETCs, calorimeters and Langmuir probe also show good agreement. We plan to implement an array of SETCs embedded in the tiles forming the new DIII-D small angle slot (SAS) divertor. Strategies to improve the SNR of these SETCs through testing in DiMES before the final installation will be discussed. This work was supported by the US Department of Energy under DE-SC0016318 (UTK), DE-AC05-00OR22725 (ORNL), DE-FG02-07ER54917 (UCSD), DE-FC02-04ER54698 (GA), DE-AC04-94AL85000 (SNL).   

High Performance Double-null Plasma Operation Under Radiating Divertor Conditions

We report on heat flux reduction experiments in which deuterium/neon- or deuterium/argon-based radiating mantle/divertor approaches were applied to high performance double-null (DN) plasmas (H98$\approx$1.4-1.7,$\beta_N\approx4,q95\approx$6) with a combined neutral beam and ECH power input P$_{IN}\approx15$ MW. When the radial location of the ECH deposition is close to the magnetic axis (e.g.,$\hspace{1.5 mm}$$\rho$$\leq$0.20), the radial profiles of both injected and intrinsic impurities are flat to somewhat hollow. For deposition farther out (e.g.,$\hspace{1.5 mm}$$\rho$=0.45), the impurity profiles are highly peaked on axis, which would make high performance DN operation with impurity injection more problematical. Comparison of neon with argon “seeding” with respect to core dilution, energy confinement, and heat flux reduction under these conditions favors argon. Conditions that lead to an improved $\tau_E$ as predicted previously from ELITE code analysis, i.e., very high P$_{IN}$, proximity to magnetic balance, and higher q95, are largely consistent with this data.   

Nonlinear MHD study on the influence of E\texttimes B flow in QH-mode plasma of DIII-D

In~QH-mode experiments with zero-net NBI torque show that there remains~a finite~E\texttimes B rotation in the pedestal region implying that a minimum~E\texttimes B flow or flow shear is required for the plasma to develop the Edge Harmonic Oscillation (EHO), which is a saturated KPM (kink-peeling mode)~characteristic of the QH-mode. To understand the roles of E\texttimes B flow and its shear in the saturation of KPMs,~non-linear MHD simulations~of DIII-D QH-mode plasmas including toroidal mode numbers n $=$ 0 to 10 with different E\texttimes B rotation speed have been performed. These simulation show that ExB~rotation strongly stabilizes high-n modes but destabilizes low-n modes (particularly the~n$=$2 mode) in the linear growth phase, which is consistent~experimental observations and previous linear MHD modelling.   

Investigating electromagnetic effects on transport and turbulence in DIII-D QH-modes

Previous experiments and gyrokinetic simulations in the core ($\rho =$0.3) of QH-modes have found that the coupling of electrostatic turbulence to magnetic fluctuations ($\delta $B) at finite beta is very stabilizing to ITG/TEM turbulence [Guttenfelder, APS-DPP (2015); Ernst, Phys. Plasmas (2016)]. As expected from theory, the electromagnetic (EM) effects are significant as the profile is locally within \textasciitilde 90{\%} of the kinetic ballooning mode (KBM) threshold. Additional gyrokinetic and TGLF simulations have been run in advance of a planned QH-mode experiment aiming to directly measure core $\delta $B using cross polarization scattering (CPS). These ``predict first'' simulations will be shown to highlight the expected strength of EM effects, the scaling of the predicted amplitude of $\delta $B, and the proximity of profiles to the KBM threshold.   

Recent Progress in BOUT$++$ boundary plasma turbulence simulations

BOUT$++$ has been developed and applied for a range of problems that impact on boundary plasma turbulence and transport. A summary of simulation progress and results will be presented including, but not limited to: (1) Modeling tokamak boundary plasma turbulence and understanding its role in setting divertor heat flux widths; (2) Self-consistent calculation of the radial electric field with ion orbit loss mechanism; (3) Simulating the DIII-D and EAST grassy ELM regime; (4) Simulation comparison of EHO state and broadband MHD phase in near-zero torque QH-mode on DIII-D; (5) Simulation of the ELMs triggering by lithium pellet on EAST tokamak; (6) Ideal MHD Stability and Characteristics of Edge Localized Modes on CFETR Our latest transport module solves a set of transport equations with quasi-neutral constraint using vorticity formulation under the BOUT$++$ framework. This new capability enables BOUT$++$ team to simulate boundary plasma transport across the separatrix with self-consistent electric and magnetic drifts, ion orbit loss, and sheath boundary conditions in the scrape-off-layer. Preliminary results \quad of the coupled \quad turbulence and transport simulations will also presented.   

Observations of ELM stabilization during neutral beam injection in DIII-D

Edge localized modes (ELMs) are generally interpreted as peeling-ballooning instabilities, driven by the pedestal current and pressure gradient, with other subdominant effects possibly relevant close to marginal stability. We report observations of transient stabilization of type-I ELMs during neutral beam injection (NBI), emerging from a combined dataset of DIII-D ELMy H-mode plasmas with moderate heating obtained through pulsed NBI waveforms. Statistical analysis of ELM onset times indicates that, in the selected dataset, the likelihood of onset of an ELM lowers significantly during NBI modulation pulses, with the stronger correlation found with counter-current NBI. The effect is also found in rf-heated H-modes, where ELMs appear inhibited when isolated diagnostic beam pulses are applied. Coherent average analysis is used to determine how plasma density, temperature, rotation as well as beam ion quantities evolve during a NB modulation cycle, finding relatively small changes (\textasciitilde 3{\%}) of pedestal Te and ne and toroidal and poloidal rotation variations up to 5 km/s. The effect of these changes on pedestal stability will be discussed.   

Modeling ELM Pellet Pacing with M3D-C$^{1}$

M3D-C$^{1}$, a code for solving the linear or non-linear extended-MHD equations in toroidal geometry, is currently being used for modeling pellet ELM triggering in DIII-D ITER-like plasmas. Initial M3D-C$^{1}$ results run in linear mode show that the localized perturbation due to the pellet destabilizes peeling-ballooning modes. For these simulations the pellet was modeled as a 2D density ring perturbation and the total pressure was kept constant. Calculations of linear peeling-ballooning stability as a function of pellet size and deposition have shown for an initial number of particles = 4e17, only n$_{tor}$ = 20 is unstable. Increasing the number of particles to 1e19 leads to unstable edge modes at the pellet ablation location, suggesting that the 2-D pellet density ring underestimates the effects of the pellet. Linear simulations also suggest that the destabilization seems to be a resistive effect. Placing the density perturbation further inside the pedestal destabilizes n$_{tor}$ $>$ 10. Recent M3D-C$^{1}$ modeling efforts have focused on 3D, 2-fluid nonlinear simulations for ELM pellet pacing.   

ELM behavior and pedestal structure in high-betap plasmas on DIII-D

The pedestal height and width in the DIII-D high-betap EAST-demonstration plasmas are compared with the EPED1 model. It shows that the pedestal height and width agree with the EPED1 prediction for cases with no/weak ITB, while the pedestal height is much lower than the EPED1 prediction when there is strong ITB. For a couple of similar discharges, when the operation conditions are varied slightly, the ELM frequency change is large. The high frequency ELM cases have low pedestal height and strong ITB, while the low frequency cases have high pressure pedestal height and no ITB appears. The time evolution of the kinetic profiles shows that the pedestal structure correlates with the ITB strength at large radius. As the ITB emerges and builds up, the pedestal height decreases.   

Interactions of Fast Ion Losses and MHD During an ELM Cycle

This work focuses on empirically determining correlations between different types of MHD activity in the pedestal region in DIII-D H-modes and fast ion losses to guide future work on discovering the interaction mechanisms between these two phenomena. Using conditional averaging, data of the energetic ion energy-pitch angle distribution, pedestal measurements, and ELM crashes was analyzed to track fast ion and MHD development over the ELM cycle. Prior research has focused on understanding MHD precursors to ELMs and how these magnetic precursors, and separately energetic ion losses, grow before an ELM crash. Later, we observe that during the ELM crash, energetic ion losses occur at uncommon energy - pitch angle phase space. The fast ion losses that occur during the ELM crash have very high pitch angles and relatively low energy, implying a loss of confined ions that could not yet deposit their energy. After the ELM crash, when there is little MHD activity, there is also a lack of consistent fast ion losses, indicating that MHD activity at the plasma edge may enhance fast ion losses.   

ECE Imaging upgrade for ELM imaging measurement on DIII-D

DIII-D ECEI uses liquid crystal polymer (LCP) substrates to combine System-on-Chip receivers with on-board LO multiplication and amplification inside a fully shielded, modular package. It improves x30 sensitivity compared to existing one, while significantly reducing EM interference, environmental noise, and radiation bursts, thereby improving ELM studies in the most ITER relevant, low-collisional regimes on DIII-D. Noise bursts that have been troublesome for ECEI of ELMs have been classified into different types: some indicate important processes involving reconnection and the acceleration of non-thermal electrons, while out-of-band interference had been removed. The upgrade facilitates studies on disruption avoidance during RF heating by static and not rotating MHD. The upgraded system can be used to infer RF heating deposition profiles with absolutely calibrated Te measurements.   

SOLPS modeling of inter/intra-ELM W transport DIII-D

SOLPS will be used for interpretive modeling of SOL tungsten transport in DIII-D to determine the roles of the friction force and the ion temperature gradient force on impurity transport. Modeling will be performed comparing discharges with the outer strike point on each tungsten divertor ring. A gas source with the measured tungsten source rate is placed at the location of each ring in the model to simulate sputtering, allowing for individual rings to source for comparison to tracer isotope studies. Anomalous thermal and particle transport coefficients are adjusted to match the upstream deuterium profiles while impurities use the same transport coefficients. An outer midplane deposition probe provides additional data on the SOL tungsten density. ELM averaged pedestal profiles covering the last 20{\%} of the ELM cycle are used to determine the inter-ELM transport, while individual pedestal profiles measured during the ELM cycle are used to examine intra-ELM tungsten transport. ELM resolved source flux measurements are used to model the intra-ELM transport.   

Prediction of Pressure and Temperature Gradients in the Tokamak Plasma Edge.

An extended plasma fluid theory [1,2] that takes into account kinetic ion orbit loss and electromagnetic forces in the continuity, momentum and energy balances, as well as atomic physics and radiation, has been used to reveal the explicit dependence of the temperature and pressure gradients in the tokamak edge plasma on these various factors. Combining the ion radial momentum balance and the Ohm's Law expression for $E_{r} $ reveals the dependence of the radial ion pressure gradient on VxB forces driven by radial particle fluxes, which depend on ion orbit loss, and other factors. The strong temperature gradients measured in the H-mode edge pedestal could certainly be associated with radiative and atomic physics edge cooling effects and the strong reduction in ion and energy fluxes due to ion orbit loss, as well as to the possible reductions in thermal diffusivities that is usually assumed to be the cause. \quad 1) W. M. Stacey, Nucl. Fusion 57(2017) 066034; 2) Contrib. Plasma Phys.56m 495 (2016).   

GTEDGE-2 A new predictive and interpretive edge-boundary transport capability.

A new code is being assembled for the tokamak plasma and neutral particle transport in the plasma edge, Scrape-Off Layer (SOL) and divertor. The new code will differ from existing codes by including ion orbit loss of thermalized ions and retaining electromagnetic ``pinch'' forces in the momentum balance, thus conserving particles, momentum and energy. Edge plasma transport is based on a 1D Flux-Surface Averaged (FSA) transport solution of the extended fluid theory incorporating ion orbit loss and electromagnetic particle pinch [1], with flux surface compression-expansion effects of gradients and Shafranov shift accounted for using the Miller model [2]. SOL-divertor plasma transport is initially based on a 1-D solution of the particle, momentum and energy equations in the core and edge plasma [3]. Neutral particle transport is based on the GTNEUT interface current balance code [4]. Theoretical models for the Code structure, integration and iteration issues are discussed. 1) Nucl. Fusion 57 (2017) 066034; 2) Phys. Plasmas 15 (2008) 122505; 3) Fusion Plasma Physics, Wiley-VCH (2012) sect 14.10; 4) Phys. Plasmas 13 (2006) 062509.   

Edge Mechanisms for Power Excursion Control in Burning Plasmas.

ITER must have active and preferably also passive control mechanisms that will limit inadvertent plasma power excursions which could trigger runaway fusion heating. We are identifying and investigating the potential of ion-orbit loss, impurity seeding, and various divertor ``choking'' phenomena to control or limit sudden increases in plasma density or temperature by reducing energy confinement, increasing radiation loss, etc., with the idea that such mechanisms could be tested on DIII-D and other existing tokamaks. We are assembling an edge-divertor code (GTEDGE-2) with a neutral transport model and a burn dynamics code, for this purpose. One potential control mechanism is the enhanced ion orbit loss from the thermalized ion distribution that would result from heating of the thermalized plasma ion distribution. Another possibility is impurity seeding with ions whose emissivity would increase sharply if the edge temperature increased. Enhanced radiative losses should also reduce the thermal energy flux across the separatrix, perhaps dropping the plasma into the poorer L-mode confinement regime. We will present some initial calculations to quantify these ideas.   

Calculation of rotation and poloidal asymmetries in DIII-D

The Braginski rate-of-strain tensor model of viscosity, extended to toroidal geometry [1] and arbitrary collisionality [2], predicted central toroidal rotation within an order of magnitude of experiment [3,4] using a circular flux surface model to calculate poloidal asymmetries that determine the magnitude of the Braginski toroidal gyroviscosity. Refinement of the poloidal asymmetry calculation using a Miller model flux surface led to an order of magnitude improvement in agreement with experimental toroidal velocity in the central region of DIII-D [5]. An orthogonalized flux-surface aligned localized coordinate frame [6] has been developed to improve calculations of poloidal asymmetries. We extend this system to calculate poloidal asymmetries and velocities to evaluate how well an accurate calculation of the extended Braginski gyroviscosity can describe the toroidal momentum damping in the central regions of DIII-D. 1) Phys. Fluids 28 (1985) 2800. 2) Nucl. Fusion 25 (1985) 463. 3) Phys. Fluids B 5 (1993) 1828.4 Phys. Plasmas 13 (2006) 062508. 5) Nucl. Fusion 53 (2013) 043011. 6) Phys. Plasma 23 (2016) 052505.   

Changes in Ion Orbit Loss, Intrinsic Rotation and Particle Pinch across the L-H Transition in DIII-D Plasmas

Two interesting new L-H phenomena have been observed in a series of DIII-D discharges. 1) The measured C co-Ip toroidal rotation inside of $\rho$$≤$0.94 was observed to increase at the L-H transition, but actually decreased for $\rho$$>$0.94. A particle-momentum-energy balance shows that the preferential ion orbit loss of ctr-Ip ions causes a co-Ip intrinsic rotation for $\rho$$>$0.94 which is greater in L-mode than in H-mode, thus causing the drop in total measured rotation for $\rho$$>$0.94 at the L-H transition. 2) In two of the three shots the electromagnetic pinch velocity went from weakly inward in L-mode to strongly inward in H-mode for $\rho$$>$0.96, consistent with improved particle confinement in H-mode associated with inward electromagnetic forces on the ions. The calculated edge neutral density, which is proportional to the radial particle flux, drag frequency, and therefore pinch velocity, is greater in H-mode than in L-mode for the two shots with a strongly inward pinch in H-mode of $\rho$$>$0.96, but not for the third shot in which the inward pinch in H-mode was weaker than in L-mode.   

Interpretation of thermal conduction and toroidal momentum transport in DIII-D, taking into account IOL and pinch velocity.

The capability of the Georgia Tech GTEDGE edge transport interpretation code has been upgraded to include improved ion-orbit-loss models for neutral beam and thermalized ions in the edge plasma. We are undertaking a new comparison of various theoretical thermal diffusivity models with the improved interpretation of experimental edge transport now possible.~The experimental values are being compared with various theoretical models, including paleoclassical, neoclassical, ITG, drift ballooning mode, TEM, and ETG. An improved interpretation of viscous drag considering ion orbit loss is considered and compared to that without ion-orbit-loss effects. This effort is examining two H-mode DIII-D shots, {\#}144977 and {\#}123302. The improved interpretation leads to quite different experimental thermal diffusivity profiles in the edge than previously reported when ion-orbit-loss effects are included (as much as 50{\%} lower at the separatrix for shot {\#}123302)..   

Installation and initial operation of a 117.5 GHz gyrotron on DIII-D.

A new gyrotron operating at 117.5 GHz and generating in excess of 1.5 MW for short pulses has been installed at DIII-D and is being prepared for operations. The tube was designed and manufactured by CPI in Palo Alto, CA. At the limit of the CPI test set, the gyrotron generated pulses up to 10 sec in length at about 550 kW output power. The GA installation permits full output power at pulse lengths up to 5 sec, the administrative limit, to be used in testing. This will be the first gyrotron in the DIII-D complex to be operated for conditioning from the outset using FPGA based pulse control. This allows the tube to be restarted after a fault in many cases relevant to the conditioning activity. The progress of the conditioning program with the new pulse control hardware will be compared with previous \textit{ab initio} testing and the current status will be presented.   

Dependence of Helicon Antenna Loading on the Antenna/Plasma Gap and n$_{\mathrm{\vert \vert }}$ in DIII-D Experiments

A comprehensive set of measurements of the plasma loading of a 12-element antenna array, designed to launch helicon waves (i.e., very-high-harmonic fast waves), were performed on DIII-D in 2016. The antenna, operated in the 466 -- 486 MHz band, is prototypical of a wider array for a 1-MW-level experiment planned for 2018-9. The dependence of the antenna loading on antenna/plasma gap is of great practical significance, as the gap must be kept greater than a minimum distance to suppress deleterious plasma-material interactions, while the loading must be high enough to retain good efficiency of power transfer to the plasma. While the loading in all examined plasma regimes, including both limited and diverted L-mode discharges and H-mode discharges, decayed exponentially with increasing gap in agreement with simple theory, the characteristic decay length was in all cases larger than expected, motivating the development of a more realistic model. Furthermore, the characteristic decay length did not depend on the launched n$_{\mathrm{\vert \vert }}$, though the absolute level of loading at a given gap increased as \textbar n$_{\mathrm{\vert \vert }}$\textbar was decreased from 4 to 2. After the antenna was removed from DIII-D, measurements of the loading produced by a 100 $\Omega $/sq resistive film were carried out on the bench. Both the antenna/film gap and n$_{\mathrm{\vert \vert }}$ were scanned varied and the results compared with calculations done with the QuickWave FDTD electromagnetics solver. Very good agreement was found in this case.   

Full wave simulations of helicon wave losses in the scrape-off-layer of the DIII-D tokamak

Helicon waves have been recently proposed as an off-axis current drive actuator for DIII-D. Previous modeling using the hot plasma, full wave code AORSA, has shown good agreement with the ray tracing code GENRAY for helicon wave propagation and absorption in the core plasma. AORSA, and a new, reduced finite-element-model show discrepancies between ray tracing and full wave occur in the scrape-off-layer (SOL), especially at high densities. The reduced model is much faster than AORSA, and reproduces most of the important features of the AORSA model. The reduced model also allows for larger parametric scans and for the easy use of arbitrary tokamak geometry. Results of the full wave codes, AORSA and COMSOL, will be shown for helicon wave losses in the SOL are shown for a large range of parameters, such as SOL density profiles, n$_{\mathrm{\vert \vert }}$, radial and vertical locations of the antenna, and different tokamak vessel geometries.   

Prospects for Off-axis Current Drive via High Field Side Lower Hybrid Current Drive in DIII-D

An outstanding challenge for an economical, steady state tokamak is efficient off-axis current drive scalable to reactors. Previous studies have focused on high field side (HFS) launch of lower hybrid waves for current drive (LHCD) in double null configurations in reactor grade plasmas[P.T. Bonoli IAEA (2016)]. The goal of this work is to find a HFS LHCD scenario for DIII-D that balances coupling, power penetration and damping. The higher magnetic field on the HFS improves wave accessibility, which allows for lower n$_{||}$waves to be launched. These waves penetrate farther into the plasma core before damping at higher T$_e$ yielding a higher current drive efficiency. Utilizing advanced ray tracing and Fokker Planck simulation tools (GENRAY+CQL3D), wave penetration, absorption and drive current profiles in high performance DIII-D H-Mode plasmas were investigated. We found LH scenarios with single pass absorption, excellent wave penetration to r/a~0.6-0.8, FWHM r/a=0.2 and driven current up to 0.37 MA/MW coupled. These simulations indicate that HFS LHCD has potential to achieve efficient off-axis current drive in DIII-D and the latest results will be presented.   

High Field Side Lower Hybrid Current Drive Launcher Design for DIII-D

Efficient off-axis current drive scalable to reactors is a key enabling technology for a steady-state tokamak. Simulations of DIII-D discharges have identified high performance scenarios with excellent lower hybrid (LH) wave penetration, single pass absorption and high current drive efficiency. The strategy was to adapt known launching technology utilized in previous experiments on C-Mod (poloidal splitter) and Tore Supra (bi-junction) and remain within power density limits established in JET and Tore Supra. For a 2 MW source power antenna, the launcher consists of 32 toroidal apertures and 4 poloidal rows. The aperture is 60 mm x 5 mm with 1 mm septa and the peak $n_{||}$ is 2.7+/-0.2 for 90 phasing. Eight WR187 waveguides are routed from the R-1 port down under the lower cryopump, under the existing divertor, and up the central column with the long waveguide dimension along the vacuum vessel. Above the inner strike point region, each waveguide is twisted to orient the long dimension perpendicular to the vacuum vessel and splits into 4 toroidal apertures via bi-junctions. To protect the waveguide, the inner wall radius will need to increase by ~2.5 cm. RF, disruption, and thermal analysis of the latest design will be presented.   

Real Time Computer Control of Neutral Beam Energy and Current During a DIII-D Tokamak Shot.

A new control system has been implemented on DIII-D neutral beams which has been used during the 2016 and 2017 experimental campaign to directly change the beam acceleration voltage (V) and beam current (I) by the Plasma Control System (PCS) during a shot. Small changes in the beam voltage of 1-2 kV can be made in 1 msec or larger changes of up to 20kV in 0.5 seconds. The beam current can be modified by as much as \textpm 20{\%} at a fixed beam voltage. Since both can be independently and simultaneously changed it is possible to change beam power (IV) at fixed voltage, keep constant power while sweeping beam voltage, or to maintain minimum beam divergence during a beam voltage sweep by changing I simultaneously to keep a constant beam perveance. The limitations of the variability will be presented with required changes in equipment to extend either the speed or range of the controls. Some of the effects on fast ion plasma instabilities or other plasma mode changes made possible by this control will also be presented (see also D.C. Pace, this conference).   

Investigation of Neutral Beam Arc Chamber Failure During Helium Operations at DIII-D

The Neutral Beam system on the DIII-D tokamak consists of eight ion sources using the Common Long Pulse Source (CLPS) design. During helium operation, desired for research regarding the ITER pre-nuclear phase, it has been observed that the ion source arc chamber performance steadily deteriorates, eventually failing due to electrical breakdown across the insulation. This poster presents the details and preliminary results of an experimental effort to replicate the problem in a bench top ion source with similar plasma parameters. The initial aim of the experiment is to test the hypothesis that during helium operation there is increased tungsten evaporation and sputtering due to ion bombardment of the hot cathodes, leading to the deposition of filament material on the insulation and subsequent short circuits. Ultimately the aim of the experiment is to find methods to ameliorate the problems associated with helium operation at DIII-D.   

Overview of the HIT-SI3 spheromak experiment

The HIT-SI and HIT-SI3 spheromak experiments ($a=$23~cm) study efficient, steady-state current drive for magnetic confinement plasmas using a novel method which is ideal for low aspect ratio, toroidal geometries. Sustained spheromaks show coherent, imposed plasma motion and low plasma-generated mode activity, indicating stability. Analysis of surface magnetic fields in HIT-SI indicates large $n=$0 and 1 mode amplitudes and little energy in higher modes. Within measurement uncertainties all the $n=$1 energy is imposed by the injectors, rather than being plasma-generated. The fluctuating field imposed by the injectors is sufficient to sustain the toroidal current through dynamo action whereas the plasma-generated field is not (Hossack \textit{et al.}, Phys. Plasmas, 2017). Ion Doppler spectroscopy shows coherent, imposed plasma motion inside $r\approx $10~cm in HIT-SI and a smaller volume of coherent motion in HIT-SI3. Coherent motion indicates the spheromak is stable and a lack of plasma-generated $n=$1 energy indicates the maximum $q$ is maintained below 1 for stability during sustainment. In HIT-SI3, the imposed mode structure is varied to test the plasma response (Hossack \textit{et al}., Nucl. Fusion, 2017). Imposing $n=$2, $n=$3, or large, rotating $n=$1 perturbations is correlated with transient plasma-generated activity.   

Progress on FIR interferometry and Thomson Scattering measurements on HIT-SI3

Spatially resolved measurements of the electron temperature (T$_{\mathrm{e}})$ and density (n$_{\mathrm{e}})$ will be fundamental in assessing the degree to which HIT-SI3 demonstrates closed magnetic flux and energy confinement. Further, electron temperature measurements have not yet been made on an inductively-driven spheromak. Far infrared (FIR) interferometer and Thomson Scattering (TS) systems have been installed on the HIT-SI3 spheromak. The TS system currently implemented on HIT-SI3 was originally designed for other magnetic confinement experiments, and progress continues toward modifying and optimizing for HIT-SI3 plasmas. Initial results suggest that the electron temperature is of order 10 eV. Plans to modify the TS system to provide more sensitivity and accuracy at low temperatures are presented. The line-integrated n$_{\mathrm{e}}$ is measured on one chord by the FIR interferometer, with densities near 5x10$^{\mathrm{19}}$ m$^{\mathrm{-3}}$. Four cylindrical volumes have been added to the HIT-SI3 apparatus to enhance passive pumping. It is hoped that this will allow for more control of the density during the 2 ms discharges. Density measurements from before and after the installation of the passive pumping volumes are presented for comparison.   

Two-fluid (plasma-neutral) Extended-MHD simulations of spheromak configurations in the HIT-SI experiment with PSI-Tet

A self-consistent, two-fluid (plasma-neutral) dynamic neutral model$^{\mathrm{1}}$ has been implemented into the 3-D, Extended-MHD code PSI-Tet. A monatomic, hydrogenic neutral fluid reacts with a plasma fluid through elastic scattering collisions and three inelastic collision reactions: electron-impact ionization, radiative recombination, and resonant charge-exchange. Density, momentum, and energy are evolved for both the plasma and neutral species. The implemented plasma-neutral model in PSI-Tet is being used to simulate decaying spheromak configurations in the HIT-SI experimental geometry, which is being compare to two-photon absorption laser induced fluorescence measurements (TALIF) made on the HIT-SI3 experiment. TALIF is used to measure the absolute density and temperature of monatomic deuterium atoms. Neutral densities on the order of 10$^{\mathrm{15}}$ m$^{\mathrm{-3}}$ and neutral temperatures between 0.6-1.7 eV were measured towards the end of decay of spheromak configurations with initial toroidal currents between 10-12 kA. Validation results between TALIF measurements and PSI-Tet simulations with the implemented dynamic neutral model will be presented. Additionally, preliminary dynamic neutral simulations of the HIT-SI/HIT-SI3 spheromak plasmas sustained with inductive helicity injection will be presented. Lastly, potential benefits of an expansion of the two-fluid model into a multi-fluid model that includes multiple neutral species and tracking of charge states will be discussed. $^{\mathrm{1}}$E.T. Meier, U. Shumlak, \textit{Phys. Plasmas} \textbf{19}, 072508 (2012).   

NIMROD Simulations of the HIT-SI and HIT-SI3 Devices

The Helicity Injected Torus with Steady Inductive helicity injection (HIT-SI) experiment uses a set of inductively driven helicity injectors to apply non-axisymmetric current drive on the edge of the plasma, driving an axisymmetric spheromak equilibrium in a central confinement volume. Significant improvements have been made to extended MHD modeling of HIT-SI, with both the resolution of disagreement at high injector frequencies in HIT-SI in addition to successes with the new upgraded HIT-SI3 device. Previous numerical studies of HIT-SI, using a zero-beta eMHD model, focused on operations with a drive frequency of 14.5 kHz, and found reduced agreement with both the magnetic profile and current amplification at higher frequencies (30-70 kHz). HIT-SI3 has three helicity injectors which are able to operate with different mode structures of perturbations through the different relative temporal phasing of the injectors. Simulations that allow for pressure gradients have been performed in the parameter regimes of both devices using the NIMROD code and show improved agreement with experimental results, most notably capturing the observed Shafranov-shift due to increased beta observed at higher $f_{inj}$ in HIT-SI and the variety of toroidal perturbation spectra available in HIT-SI3.   

NIMROD simulations and physics assessment of possible designs for a next generation Steady Inductive Helicity Injection HIT device

The Helicity Injected Torus - Steady Inductive 3 (HIT-SI3) experiment forms and maintains spheromaks via Steady Inductive Helicity Injection (SIHI) using discrete injectors that inject magnetic helicity via a non-axisymmetric perturbation and drive toroidally symmetric current. Newer designs for larger SIHI-driven spheromaks incorporate a set of injectors connected to a single external manifold to allow more freedom for the toroidal structure of the applied perturbation. Simulations have been carried out using the NIMROD code to assess the effectiveness of various imposed mode structures and injector schema in driving current via Imposed Dynamo Current Drive (IDCD). The results are presented here for varying flux conserver shapes on a device approximately 1.5 times larger than the current HIT-SI3 experiment. The imposed mode structures and spectra of simulated spheromaks are analyzed in order to examine magnetic structure and stability and determine an optimal regime for IDCD sustainment in a large device. The development of scaling laws for manifold operation is also presented, and simulation results are analyzed and assessed as part of the development path for the large scale device. 1. T. Jarboe et al., "Imposed-Dynamo Current Drive (IDCD)." APS Meeting Abstracts. 2012.   

Using Algebraic Space Curves to Investigate Magnetic Helicity and Its Application to the Spheromak

The goal of this research is to study magnetic helicity and the topology of magnetic flux tubes using the homotopy groups of braids, knots, links and tangles.  Flux tubes are represented as real algebraic curves in three dimensional space.  We are interested in developing a stochastic, dynamic group of curves representing knotted, braided, and tangled flux tubes that evolve around and converge onto a torus.  The group will be modeled using a computer algebra system.  Using our model, we propose to define helicity, writhe and linking number parameters to analyze their relation to the time for magnetic relaxation and confinement.     

Progress of STPX Discharges and Diagnostic Systems

The Spheromak Turbulent Physics Experiment (STPX) at Florida A{\&}M University is currently ramping up plasma operations and diagnostic testing. STPX is a large radius (1.5m), magnetic confinement device, capable of creating fusion-relevant and astrophysical-related spheromak plasmas. We have measurements and simulations of the formation banks and bias magnetic field coils. dB/dt coils provided by WVU have been calibrated and a Langmuir triple probe developed by Auburn University is providing density and temperature measurements with a saturation coil array providing a rough density profile. A CO$_{\mathrm{2}}$ interferometer has been installed to corroborate the density measurements and a mechelle spectrometer is providing spectral line data. CORSICA simulations of STPX plasmas have begun.   

Electron density measurements in STPX plasmas

Diagnostics have been installed to measure the electron density of Spheromak Turbulent Physics Experiment (STPX) plasmas at Florida A. {\&} M. University. An insertable probe, provided by Auburn University, consisting of a combination of a triple-tipped Langmuir probe and a radial array consisting of three ion saturation current / floating potential rings has been installed to measure instantaneous plasma density, temperature and plasma potential. As the ramp-up of the experimental program commences, initial electron density measurements from the triple-probe show that the electron density is on the order of 10$^{\mathrm{19}}$ particles/m$^{\mathrm{3}}$. For a passive measurement, a CO$_{\mathrm{2}}$ interferometer system has been designed and installed for measuring line-averaged densities and to corroborate the Langmuir measurements. We describe the design, calibration, and performance of these diagnostic systems on large volume STPX plasmas.   

Plasma driven by helical electrodes

We present a plasma state driven by helically symmetric electrodes $(m,n)$ in the presence of a uniform axial magnetic field in a periodic cylinder[1], with applications as an electrical transformer or for tailoring the current profile in a tokamak or RFP. For strong drive there is a $(m,n)$ state with mean-field current density and flat $q_0 \approx m/n=1$ in the interior. It has large helical flows, a bi-directional parallel current density $\lambda$, and an $O-$ line encircled by all of the field lines. We show a Cowling-like theorem $\langle\eta\lambda B^{2}\rangle=0$ and discuss the relationship with magnetic helicity. The transient stage is discussed. Integration of the current density streamlines is used to quantify primary-to-secondary leakage for the transformer application. Results varying $(m,n)$ the plasma length are presented. Sensitivity studies to (a) boundary conditions, (b) resistivity profile, and (c) electrode shape are presented. Results with finite $(m,n)$ radial magnetic field are introduced, showing high transformer efficiencies. 3D studies of finite length plasmas are presented. [1] C. Akcay, J. M. Finn, R. A. Nebel and D. C. Barnes, "Electrostatically driven helical plasma state", Phys. Plasmas 24, 052503 (2017).   

3D Resistive MHD Simulations of Formation, Compression, and Acceleration of Compact Tori

We present results from extended resistive 3D MHD simulations (NIMROD [1]) pertaining to a new formation method for toroidal plasmas using a reconnection region that forms in a radial implosion, and results from the acceleration of CTs along a drift tube that are accelerated by a coil and are allowed to go tilt unstable and form a helical minimum energy state. The new formation method results from a reconnection region that is generated between two magnetic compression coils that are ramped to 320kV in 2$\mu$s. When the compressing field is aligned anti-parallel to a pre-existing CT, a current sheet and reconnection region forms that accelerates plasma radially inwards up to 500km/s which stagnates and directed energy converts to thermal, raising temperatures to 500eV. When field is aligned parallel to the pre-existing CT, the configuration can be accelerated along a drift tube. For certain ratios of magnetic field to density, the CT goes tilt-unstable forming a twisted flux rope, which can also be accelerated and stagnated on an end wall, where temperature and field increases as the plasma compresses. We compare simulation results with adiabatic scaling relations. [1] C. Sovinec et al Journal of Computational Physics, 195, 355 (2004).   

UEDGE Simulations for Power and Particle Flow Analysis of FRC Rocket

The field-reversed configuration (FRC) is under consideration for use in a direct fusion drive (DFD) rocket propulsion system for future space missions. To achieve a rocket configuration, the FRC is embedded within an asymmetric magnetic mirror, in which one end is closed and contains a gas box, and the other end is open and incorporates a magnetic nozzle. Neutral deuterium is injected into the gas box, and flows through the scrape-off layer (SOL) around the core plasma and out the magnetic nozzle, both cooling the core and serving as propellant. Previous studies have examined a range of operating conditions for the SOL of a DFD using UEDGE, a 2D fluid code; discrepancies on the order of $\sim$5\% were found during the analysis of overall power balance. This work extends the analysis of the previously-studied SOL geometry by updating boundary conditions and conducting a detailed study of power and particle flows within the simulation with the goals of modeling electrical power generation instead of thrust and achieving higher specific impulse.   

Results from an 8 Joule RMF-FRC Plasma Translation Experiment for Space Propulsion

Field-Reversed Configuration (FRC) thrusters are attractive for advanced in-space propulsion technology as their projected performance, low specific mass, and propellant flexibility offer significant benefits over state-of-the art thrusters. A benchtop experiment to evaluate FRC thruster behavior using a Rotating Magnetic Field (RMF) formation method was constructed at the Air Force Research Laboratory. This experiment generated an RMF-FRC in a conical geometry and accelerated the plasma into a field-free drift region, using 8 J of input energy. Downstream plasma probes in a time-of-flight array measured the exhaust contents of the plasma plume. Results from this diagnostic demonstrated that the ejected mass and ion exit velocities fell short of the desired specific impulse and momentum. Two high-speed cameras were installed to diagnose the gross plasma behavior from two perspectives. Results from these images are presented here. These images show that the plasma generated in the formation region for several different operating conditions was highly non-uniform and did not form a stable closed-field topology that is expected from RMF-FRC plasmas.   

High Efficiency push-pull class E amplifiers for fusion rocket engines

In a Field Reversed Configuration fusion reactor, ions in the plasma are heated by an antenna operating at RF frequencies. This paper presents how push-pull class E amplifiers can be used to efficiently drive this antenna in the MHz range, from 0.5MHz to 4 MHz, while maintaining low harmonic content in the output signal. We offer four different configurations that present a trade-off between efficiency and low harmonic content. The paper presents theoretical values and breadboard results from these configurations, which operate at a power of around 100W. For a practical design, multiple amplifiers would be linked in parallel and would power the RF antenna at around 1MW. These designs provide multiple different options for reactor systems that could be used in a variety of applications, from power plants on the ground to rocket engines in space.   

Particle-in-cell studies of fast-ion slowing-down rates in cool tenuous magnetized plasma using LSP

We present particle-in-cell (PIC) simulations of fast-ion slowing down rates in cool, weakly-magnetized plasma (where $\rho_{e} < \lambda_{De}$ and $v_{fi} > v_{th,e}$) using the fully electromagnetic PIC code LSP. These simulations use explicit algorithms, resolving $\rho_{e}$ and $\lambda_{De}$ spatially and the electron cyclotron and plasma frequencies temporally. Scaling studies of the slowing-down time, $\tau_{sd}$, {\it {versus}} fast-ion charge and background plasma density are in good agreement with unmagnetized slowing-down theory; a small anisotropy is observed between $\tau_{sd}$ in the perpendicular- and parallel-field directions. Furthermore, scaling of the fast-ion charge is confirmed as a viable way to reduce the required computational time for each simulation. The implications of slowing down processes in this regime are described for one magnetic-confinement fusion concept, the small field-reversed configuration device.   

SiC MOSFET Switching Power Amplifier Project Summary

Eagle Harbor Technologies has completed a Phase I/II program to develop SiC MOSFET based Switching Power Amplifiers (SPA) for precision magnet control in fusion science applications. During this program, EHT developed several units have been delivered to the Helicity Injected Torus (HIT) experiment at the University of Washington to drive both the voltage and flux circuits of the helicity injectors. These units are capable of switching 700 V at 100 kHz with an adjustable duty cycle from 10 -- 90{\%} and a combined total output current of 96 kA for 4 ms (at max current). The SPAs switching is controlled by the microcontroller at HIT, which adjusts the duty cycle to maintain a specific waveform in the injector. The SPAs include overcurrent and shoot-through protection circuity. EHT will present an overview of the program including final results for the SPA waveforms.   

Study of Dislocation Loops in Ion-Irradiated Tungsten Using X-Ray Diffuse Scattering

As the material of choice for the divertor wall in tokamak fusion reactors, tungsten is exposed to high levels of radiation. As a result, a large amount of defects form inside the crystal, leading to significant changes in its thermal-mechanical properties. Therefore, it is important to understand the types and sizes of radiation-induces defects. X-ray diffuse scattering around Bragg peaks has been developed as a technique to solve this problem. By applying this technique to ion-irradiated tungsten, we have obtained quantitative data on the size-distribution of dislocation loops under different radiation levels.   

Abstract Withdrawn

Recent study has shown that diamagnetism may be suppressed in low temperature plasma due to neutrals depletion [1]. Diamagnetism and neutrals depletion in low temperature plasma are explored here theoretically. Cylindrical plasma is considered with radial cross-field transport. Conditions are found for either diamagnetism or neutrals depletion being dominant. An unexpected non-monotonic variation of the plasma density with the plasma particle flux is demonstrated. It is shown that as plasma generation (and particle flux) increase, the plasma density first increases, as expected, but then, as particle flux is increased further, the plasma density surprisingly decreases. The decrease follows a decrease of plasma confinement due to increased plasma diamagnetism. In addition, it is shown that an increase of the magnetic field as the plasma density is kept constant results in a decrease of neutrals depletion, as suggested previously [2], while an increase of the magnetic field as the plasma particle flux is kept constant results in constant neutrals depletion. [1] S. Shinohara, D. Kuwahara, K. Yano, and A, Fruchtman, Phys. Plasmas 23, 122108 (2016). [2] L. Liard, J.-L. Raimbault, and P. Chabert, Phys. Plasmas 16, 053507 (2009).   

Characterization of the Electron Energy Distribution Function in a Penning Discharge

Slow and fast sweeping Langmuir probe diagnostics were implemented to measure the electron energy distribution function (EEDF) in a cross-field Penning discharge undergoing rotating spoke phenomenon. The EEDF was measured using the Druyvesteyn method [1]. Rotating spoke occurs in a variety of ExB devices and is characterized primarily by azimuthal light, density, and potential fluctuations on the order of a few kHz, but is theoretically still not well understood [2] [3]. Characterization of a time-resolved EEDF of the spoke would be important for understanding physical mechanisms responsible for the spoke and its effects on Penning discharges, Hall thrusters, sputtering magnetrons, and other ExB devices. In this work, preliminary results of measurements of the EEDF using slow and fast Langmuir probes that sweep below and above the fundamental spoke frequency will be discussed. This work was supported by the Air Force Office of Scientific Research (AFOSR). [1] Godyak, V. A., Demidov, V. I. (2011). J of Physics D, 44(23), 233001. [2] Ellison, C. L., Raitses, Y., Fisch, N. J. (2012). Plasmas, 19(1), 013503. [3] Raitses, Y., Kaganovich, I., Smolyakov, A. IEPC/ISTS, Kobe, Japan (2015).   

Removal of DLC film on polymeric materials by low temperature atmospheric-pressure plasma jet

Diamond-like carbon (DLC) thin film has various excellent functions. For example, high hardness, abrasion resistance, biocompatibility, etc. Because of these functionalities, DLC has been applied in various fields. Removal method of DLC has also been developed for purpose of microfabrication, recycling the substrate and so on. Oxygen plasma etching and shot-blast are most common method to remove DLC. However, the residual carbon, high cost, and damage onto the substrate are problems to be solved for further application. In order to solve these problems, removal method using low temperature atmospheric pressure plasma jet has been developed in this work. The removal effect of this method has been demonstrated for DLC on the SUS304 substrate. The principle of this method is considered that oxygen radical generated by plasma oxidize carbon constituting the DLC film and then the film is removed. In this study, in order to widen application range of this method and to understand the mechanism of film removal, plasma irradiation experiment has been attempted on DLC on the substrate with low heat resistance. The DLC was removed successfully without any significant thermal damage on the surface of polymeric material.   

Cross-field electron transport inside an insulating cylinder of a baffled probe.

Plasma-immersed wall experiments have been performed in a magnetized xenon plasma in a cross-field Penning configuration with density around 10$^{\mathrm{12}}$ cm$^{\mathrm{-3}}$ and an electron temperature around a few eV. A cylinder with an open end and diameter of 1.4 mm was placed across field lines so that electrons were blocked from reaching a wire recessed behind the shield while ions were unimpeded. The reduction of electron current to the wire causes it to float closer to the plasma potential, possibly making a device that can passively measure plasma potential. However, the measured electron current was much higher than expected even when the wire was recessed several electron gyroradii behind the baffle. Possible mechanisms for this electron conduction causing the short circuiting to the bulk plasma have been studied with numerical approaches and with a dedicated experiment designed to isolate this short circuit effect. The obtained results may be important for cross-field transport in a variety of other configurations in magnetized, low-temperature plasmas.   

Experimental and Numerical Study of the Carbon Arc: Plasma Properties in the Region of Nanotube Synthesis

A carbon arc for nanomaterial synthesis was comprehensively studied using spectroscopic techniques and electrical measurements and modeled by specially modified computationally fluid dynamic (CFD) code ANSYS. The carbon arc plasma is generated and sustained by ablation of the graphite anode. In this study the plasma and carbon composition is fully characterized in the synthesis region that is important for understanding of synthesis of carbon nanomaterials by the arc method. We applied planar laser induced fluorescence (LIF) diagnostic to obtain instantaneous distribution of C$_{\mathrm{2}}$ in carbon arc. In addition, the arc was characterized by optical emission spectroscopy (OES) and fast filtered imaging. Results of the current work revealed two main arc plasma regions defined as the arc core and the arc periphery different by composition of carbon species. The core represents the dense and hot plasma region conducting most of the discharge current which is self-consistently sustained. The arc periphery is colder and characterized by intensive formation of carbon molecules. The resulting radial distribution of carbon molecules has a distinguished hollow profile structure which is preserved regardless of the arc stochastic motion realized in some modes. These results are in agreement with results of two dimensional CFD simulations of the carbon arc under operating conditions used in experiments.   

Development of SSUBPIC code for modeling the neutral gas depletion effect in helicon discharges

The SSUBPIC (steady-state unstructured-boundary particle-in-cell) code is being developed to model helicon plasma devices. The envisioned modeling framework incorporates (1) a kinetic neutral particle model, (2) a kinetic ion model, (3) a fluid electron model, and (4) an RF power deposition model. The models are loosely coupled and iterated until convergence to steady-state. Of the four required solvers, the kinetic ion and neutral particle simulation can now be done within the SSUBPIC code. Recent SSUBPIC modifications include implementation and testing of a Coulomb collision model (Lemons et al., JCP, 228(5), pp. 1391-1403) allowing efficient coupling of kineticly-treated ions to fluid electrons, and implementation of a neutral particle tracking mode with charge-exchange and electron impact ionization physics. These new simulation capabilities are demonstrated working independently and coupled to "dummy" profiles for RF power deposition to converge on steady-state plasma and neutral profiles. The geometry and conditions considered are similar to those of the MARIA experiment at UW-Madison. Initial results qualitatively show the expected neutral gas depletion effect in which neutrals in the plasma core are not replenished at a sufficient rate to sustain a higher plasma density.   

Investigation of Dusts Effect and Negative Ion in DC Plasmas by Electric Probes

Dust is typically negatively charged by electron attachment whose thermal velocities are fast compared to that of the heavier ions. The negatively charged particles can play a role of negative ions which affect the quasi-neutrality of background plasma. To investigate effect of metal dusts and negative ion on plasma and materials, metal dusts are injected into background Ar plasma which is generated by tungsten filament using dust dispenser on Cubical Plasma Device (CPD). The CPD has following conditions: size$=$24x24x24cm$^{\mathrm{3}}$, plasma source$=$DC filament plasma (n$_{\mathrm{e}}\approx $ 1x10x10$^{\mathrm{10}}$, T$_{\mathrm{e}}\approx $ 2eV), background gas$=$Ar, dusts$=$tungsten powder (diameter $\approx $1.89micron). The dust dispenser is developed to quantitate of metal dust by ultrasonic transducer. Electronegative plasmas are generated by adding O$_{\mathrm{2}}+$ Ar plasma to compare negative ion and dust effect. A few grams of micron-sized dusts are placed in the dust dispenser which is located at the upper side of the Cubical Plasma Device. The falling particles by dust dispenser are mainly charged up by the collection of the background plasma. The change in parameters due to negative ion production are characterized by measuring the floating and plasma potential, electron temperature and negative ion density using electric probes.   

Control of radical and ion production in chlorine plasma

Chlorine gas is widely used in the nanochip industry for ion etching of silicon wafers. As feature sizes on chips shrink, greater control of ion production is needed. Despite its popularity as an etching gas, it is difficult to control the dissociation and densities of ions and radicals. In this work, rare gas actinometry is used to determine an absolute number density for Cl$_{\mathrm{2}}$. Plasma parameters are then varied to control chlorine densities. We focus on obtaining the measurements using an argon or krypton dopant while confirming previous work done with xenon. Density measurements are achieved by comparing the relative peak intensities produced in an inductively coupled chlorine plasma mixed with 5{\%} rare gas. The plasma is sampled using line-of-sight spectroscopy in the source and across a blank silicon wafer. The benefit of creating a scheme for these rare gases is that argon and krypton provide stronger spectral lines and are cheaper than xenon. This work demonstrates a method for chlorine ion and radical production that will allow the precise control needed for nanochip etching.   

Electron density measurement of non-equilibrium atmospheric pressure plasma using dispersion interferometer

Medical applications of non-equilibrium atmospheric plasmas have recently been attracting a great deal of attention [1], where many types of plasma sources have been developed to meet the purposes. For example, plasma-activated medium (PAM), which is now being studied for cancer treatment [2], has been produced by irradiating non-equilibrium atmospheric pressure plasma with ultrahigh electron density to a culture medium [3]. Meanwhile, in order to measure electron density in magnetic confinement plasmas, a CO$_2$ laser dispersion interferometer has been developed and installed on the Large Helical Device (LHD) at the National Institute for Fusion Science, Japan [4]. The dispersion interferometer has advantages that the measurement is insensitive to mechanical vibrations and changes in neutral gas density. Taking advantage of these properties, we applied the dispersion interferometer to electron density diagnostics of atmospheric pressure plasmas produced by the NU-Global HUMAP-WSAP-50 device, which is used for producing PAM.\\ $[1]$ H. Tanaka et al., Rev. Mod. Plasma Phys. 1, 3 (2017). [2] H. Tanaka et al., IEEE Trans. Plasma Sci. 42, 3760 (2014). [3] M. Iwasaki et al., Appl. Phys. Lett. 92, 081503 (2008). [4] T. Akiyama et al., J. Inst. 10, P09022 (2015)   

Characterization of a plasma photonic crystal using a multi-fluid plasma model

Plasma photonic crystals have the potential to significantly expand the capabilities of current microwave filtering and switching technologies by providing high speed ($\mu s$) control of energy band-gap/pass characteristics in the GHz through low THz range. While photonic crystals consisting of dielectric, semiconductor, and metallic matrices have seen thousands of articles published over the last several decades, plasma-based photonic crystals remain a relatively unexplored field. Numerical modeling efforts so far have largely used the standard methods of analysis for photonic crystals (the Plane Wave Expansion Method, Finite Difference Time Domain, and ANSYS finite element electromagnetic code HFSS), none of which capture nonlinear plasma-radiation interactions. In this study, a 5N-moment multi-fluid plasma model is implemented using University of Washington's WARPXM finite element multi-physics code. A two-dimensional plasma-vacuum photonic crystal is simulated and its behavior is characterized through the generation of dispersion diagrams and transmission spectra. These results are compared with theory, experimental data, and ANSYS HFSS simulation results.   

Particle-in-Cell Modeling of Magnetron Sputtering Devices

In magnetron sputtering devices, ions arising from the interaction of magnetically trapped electrons with neutral background gas are accelerated via a negative voltage bias to strike a target cathode. Neutral atoms ejected from the target by such collisions then condense on neighboring material surfaces to form a thin coating of target material; a variety of industrial applications which require thin surface coatings are enabled by this plasma vapor deposition technique. In this poster we discuss efforts to simulate various magnetron sputtering devices using the Vorpal PIC code in 2D axisymmetric cylindrical geometry. Field solves are fully self-consistent, and discrete models for sputtering, secondary electron emission, and Monte Carlo collisions are included in the simulations. In addition, the simulated device can be coupled to an external feedback circuit. Erosion/deposition profiles and steady-state plasma parameters are obtained, and modifications due to self consistency are seen. Computational performance issues are also discussed.   

Plasma Modeling with Speed-Limited Particle-in-Cell Techniques

Speed-limited particle-in-cell (SLPIC) modeling is a new particle simulation technique [G. R. Werner and J. R. Cary, arXiv:1511.08225 (2015)] for modeling systems wherein numerical constraints, e.g. limitations on timestep size required for numerical stability, are significantly more restrictive than is needed to model slower kinetic processes of interest. SLPIC imposes artificial speed-limiting behavior on fast particles whose kinetics do not play meaningful roles in the system dynamics, thus enabling larger simulation timesteps and more rapid modeling of such plasma discharges. The use of SLPIC methods to model plasma sheath formation and the free expansion of plasma into vacuum will be demonstrated. Wallclock times for these simulations, relative to conventional PIC, are reduced by a factor of 2.5 for the plasma expansion problem and by over 6 for the sheath formation problem; additional speedup is likely possible. Physical quantities of interest are shown to be correct for these benchmark problems. Additional SLPIC applications will also be discussed.   

Hydrodynamic Model for Density Gradients Instability in Hall Plasmas Thrusters

There is an increasing interest for a correct understanding of purely growing electromagnetic and electrostatic instabilities driven by a plasma gradient in a Hall thruster devices [1-2]. In Hall thrusters, which are typically operated with xenon, the thrust is provided by the acceleration of ions in the plasma generated in a discharge chamber [3-4].The goal of this paper is to study the instabilities due to gradients of plasma density and conditions for the growth rate and real part of the frequency for Hall thruster plasmas [5]. Inhomogeneous plasmas prone a wide class of eigen modes induced by inhomogeneities of plasma density and called drift waves and instabilities. The growth rate of the instability has a dependences on the magnetic field, plasma density, ion temperature and wave numbers and initial drift velocities of the plasma species. References [1] E. Ahedo, J. M. Gallardo, and M. Marti\textasciiacute nez-S\'{a}nchez. Phys. Plasmas 10, 3397 (2003). [2] L. Garrigues, G. J. M. Hagelaar, C. Boniface, and J. P. Boeuf. J. Appl. Phys. 100, 123301 (2006). [3] E. Y. Choueiri. Phys. Plasmas 8, 1411 (2001). [4] S. Singh and H. K. Malik. J. Appl. Phys. 112, 013307 (2012). [5] H. K. Malik and S. Singh. Phys. Rev. E 83, 036406 (2011).   

Numerical Simulation of Discharge in the Ion Thruster Using BUMBLEBEE-EP Code.

Due to high efficiency, high specific impulse, long lifetime and high reliability, ion thrusters have already become the research focus of the electrical propulsion. Up to now, the numerical simulation of the ionization characteristics in the discharge chamber of ion thruster was mainly based on electrostatic model, which cannot give the important information on the electromagnetic radiation features and the self-consistent interaction between charged particles and time-varying electromagnetic fields. The 2D3V PIC/MCC code `BUMBLEBEE-EP' was developed based on the electromagnetic model for the research of ion thruster. In this paper, the discharge process of the ion thruster was simulated using BUMBLEBEE-EP. The complete Maxwell's equations were solved and the effects of the electromagnetic fields on the charged particles were taken into account in the self-consistent way. The spatiotemporal distribution of the charged particles and electromagnetic fields were obtained in detail.   

Three-Dimensional FEM-PIC Simulation of Ion Extraction with CEX Collision.

Electric propulsion has the characters of high specific impulse and total efficiency, which results in a reduction in the amount of propellant required for a given space mission or application compared to other conventional propulsion methods. Over the past few decades, its use in spacecraft has grown steadily worldwide, and the modeling and simulation techniques have been playing a more and more important role in developing advanced electric thrusters. In this paper, the ion extraction in the optics system of ion thruster was described, which solves particle trajectory, CEX collision, space charge, the Poisson's equation self-consistently, as the three dimensional FEM-PIC method. The single and seven grid apertures models were considered, respectively. The spatiotemporal distributions of the total ion beam current and the generation of CEX ions were obtained, and the effects of CEX collision on ion extraction process were discussed.   

Multi-Fluid Simulations of Field Reversed Configuration Formation

The use of field reversed configuration (FRC) have been studied extensively for fusion application but here we investigate them for propulsion purposes. FRCs have the potential to produce highly variable thrust and specific impulse using different gases as propellant. Aspects of the FRC formation physics, using a rotating magnetic field (RMF) at low power, are simulated using a multi-fluid plasma model. Results are compared with experimental observations with emphasis in the development of instabilities and robustness of the field reversal. The use of collisional radiative models are used to help compare experiment versus simulation results. Distribution A: Approved for public release; distribution unlimited; Clearance No. 17445.   

Current Driven Instabilities and Anomalous Mobility in Hall-effect Thrusters

Due to the extreme cost of fully resolving the Debye length and plasma frequency, hybrid plasma simulations utilizing kinetic ions and quasi-steady state fluid electrons have long been the principle workhorse methodology for Hall-effect thruster (HET) modeling. Plasma turbulence and the resulting anomalous electron transport in HETs is a promising candidate for developing predictive models for the observed anomalous transport. In this work, we investigate the implementation of an anomalous electron cross field transport model for hybrid HET simulations such a HPHall. A theory for anomalous transport in HETs and current driven instabilities has been recently studied by Lafleur et al. This work has shown collective electron-wave scattering due to large amplitude azimuthal fluctuations of the electric field. We will further adapt the previous results for related current driven instabilities to electric propulsion relevant mass ratios and conduct a preliminary study of resolving this instability with a modified hybrid (fluid electron and kinetic ion) simulation with the hope of integration with established hybrid HET simulations.   

Improvement of Thrust Characteristics of Helicon Plasma Thruster using Local Gas Fueling Method.

A helicon plasma thruster is proposed as a long-lifetime electric thruster which has non-direct contact electrodes. Here, a neutral particle, e.g., H2, Ar, and Xe works, as a fuel gas. In most cases, these gases are supplied into a discharge tube by the use of a simple nozzle. Therefore, the neutral particle fills a discharge tube homogenous. However, there are two problems in this configuration. First, there is a limitation of an electron density increase, due to a neutral particle depletion in the central region of the high-density helicon plasma [1]. This limitation reduces the thrust performance directly. Second, the high-density plasma causes an erosion of an inner discharge tube wall. For the future MW class thruster, this problem will become serious because the particle and heat fluxes of the plasma will increase drastically. To solve above-mentioned problems, we have proposed local fueling methods for the high-density helicon plasma. In this presentation, we will show the methods and experimental results using a fueling tube, inserted in a plasma directly. [1] A. Fruchtman, Plasma Sources Sci. Technol. 17 (2008) 024016.   

High Frequency, Low Pressure, Plasma Generation using Extremely Small Diameter Tube

Electrodeless electric propulsion method has a very long life compared with conventional electric propulsion method, because electrode and plasma do not have a direct contact each other, leading to no wear of the electrode [1]. In addition, miniaturization of the plasma generation unit is desired as one of important propulsion objectives. The generation of electrodeless plasma in a quartz tube with an inner diameter down to only 3 mm has already been succeeded by changing rf frequency, but there remains a problem of a high pressure (Lower limit 100 Pa range) operation [2]. Therefore, plasma generation under lower pressure (Lower limit 2 Pa range) by improving the experimental setup external parameters were performed. Here, the plasma characteristics was investigated, using the SHD device [3]. Furthermore, rf plasma generation has been performed with a diameter of only 1 mm. [1] S. Shinohara et al., IEEE Trans. on Plasma Sci. 42 (2014) 1245. [2] T. Nakagawa et al., Plasma Fusion Res. 10 (2015) 3401037. [3] D. Kuwahara et al., Rev. Sci. Instrum. 84 (2013) 103502.   

Plasma Acceleration by Rotating Magnetic Field Method using Helicon Source

Electrodeless plasma thrusters are very promising due to no electrode damage, leading to realize further deep space exploration. As one of the important proposals, we have been concentrating on Rotating Magnetic Field (RMF) [1] acceleration method [2,3]. High-dense plasma (up to 10$^{\mathrm{13}}$ cm$^{\mathrm{-3}})$ can be generated by using a radio frequency (rf) external antenna, and also accelerated by an antenna wound around outside of a discharge tube. In this scheme, thrust increment is achieved by the axial Lorentz force caused by non linear effects. RMF penetration condition into plasma can be more satisfied than our previous experiment [4], by increasing RMF coil current and decreasing the RMF frequency, causing higher thrust and fuel efficiency. Measurements of AC RMF component s have been conducted to investigate the acceleration mechanism and the field penetration experimentally. [1] I. R. jones, \textit{Phys. Plasmas} \textbf{6} (1990) 1950. [2] S. Shinohara \textit{et al.}, \textit{IEEE Trans. on Plasma Sci.} \textbf{42} (2014) 1245. [3] S. Otsuka \textit{et al.}, \textit{Plasma Fusion Res.} 10 (2015) 3401026. [4] T. Furukawa \textit{et al.}, \textit{Phys. Plasmas} \textbf{24} (2017) 043505.   

Electrodeless Plasma Acceleration Using $m=$ 0 Coil

We have been investigating electrodeless plasma acceleration method by the Lorentz force, using $m=$ 0 coil ($m$ is an azimuthal mode number) without electrode erosion condition, which leads to a deep space exploration in future [1,2]. The Lorentz force of $j$-theta * $B$r is composed of two factors; the $m=$ 0 coil can generate the azimuthal current $j$-theta by supplying an AC current (over 100 A) and the externally magnet make the static radial magnetic field $B$r in divergent field configuration. In the past $m=$ 0 coil experiment using the SHD [3], we have found increases of ion velocity and electron density by a factor of 2.5 and 3, respectively. In this research, detailed measurement have been done as to ion velocity, electric density and the azimuthal current to clarify the effect of $m=$ 0 coil method on plasma acceleration. [1] S. Shinohara \textit{et al.}, IEEE Trans. Plasma Sci. \textbf{42} (2014) 1245. [2] T. Ishii \textit{et al.}, JPS Conf. Proc. \textbf{1} (2014) 015047. [3] D. Kuwahara \textit{et al}., Rev. Sci. Instrum. \textbf{84} (2013) 103502.   

Graphene as a Coating for Plasma Facing Components

This research explores the protection by graphene of plasma facing materials bombarded with energetic ions of helium. Few studies have shown that graphene can act as a protective layer against sputtering due to energetic ions. In the presence of such irradiation, plasma facing components (PFC's) tend to develop surface morphologies that lead to the sputtering of wall material, potentially diminishing the lifetime of the PFC's and plasma performance. Since plasmas have broad applications and the quality of transferred and grown graphene is different, we have used a chemical vapor deposition method to grow on other substrates. We have also shown that graphene can reduce changes on surface morphology due to energetic helium. After irradiation, in the case of graphene-covered tungsten, our results show that, compared to the uncovered W, graphene suppresses these morphologies that form on the surface of hot W. Using Raman spectroscopy as a diagnostic, the graphene coating shows little sign of damage after being irradiated, indicating that there is little to no sputtering of carbon impurities from the surface. We have determined that the mass losses in W have been reduced significantly, which may lead to an improved plasma performance and longer PFC lifetimes.   

Thermomechanical and chemical properties of porous W/liquid Li hybrid systems as plasma-facing self-healing surfaces

The environmental conditions at the plasma-material interface of a future nuclear fusion reactor interacting will be extreme. The incident plasma will carry heat fluxes of the order of 100's of MWm$^{\mathrm{-2}}$ and particle fluxes that can average 10$^{\mathrm{24}}$ m$^{\mathrm{-2}}$s$^{\mathrm{-1}}$. The fusion reactor wall would need to operate at high temperatures near 800 C and the incident energy of particles will vary from a few eV ions to MeV neutrons. A hybrid system, inspired by self-healing solid-state concepts, combines the ductile phase of liquid Li within a solid phase porous W. The liquid Li serves to control hydrogen retention and provide vapor shielding, within the framework of a tunable porosity to optimize edge plasma conditions [2]. Additionally, the porous interface can also provide for effective defect sinks for high duty cycle neutron damage. The surface chemistry of liquid Li on a porous surface varied with D irradiation is studied and its effect on retention. Prior results with refractory alloys have demonstrated effective wetting properties [3]. These hybrid systems, as well as traditional W samples, are bombarded with 500eV D$_{\mathrm{2}}^{\mathrm{+}}$ and Ar$^{\mathrm{+}}$ at 230$^{\mathrm{o}}$C and 300$^{\mathrm{o}}$C. The Li, O, and C XPS peaks were examined and compared to controls. Additionally, the porous W is characterized for thermo-mechanical properties.   

Non-equilibrium electron energy distribution in oxygen plasma: observation with optical emission spectroscopy

Partially ionized inductively-coupled RF oxygen plasmas are in widespread use for materials processing, and non-invasive diagnostics are of interest for the optimization and control of the degrees of ionization and dissociation. Our initial study involves a 2-5\% admixture of argon for optical emission spectroscopy (OES) of the oxygen plasma glow. The Ar 420.1/419.8 nm line intensity ratio, previously used in other mixtures to compute electron temperature, when $<1$, is also an indicator of a significant population of high energy ($>35$ eV) electrons;\footnote{J. B. Boffard {\it et al.}, PSST {\bf 24} (2015))} the latter is observed under conditions of low power and high pressure in the oxygen plasma. We tentatively attribute the increase in energetic electrons to a transition to capacitive coupling, leading to electron acceleration to high energy in the sheaths adjacent to the powered electrode, which in this system is a spiral flat antenna separated from the plasma by a dielectric window. Investigations of OES methods involving additional species, including other trace rare gases,\footnote{V. M. Donnelly, J. Phys. D {\bf 37} (2004).} O, and O$_2^+$, to determine oxygen plasma properties such as non-Maxwellian electron energy distributions will also be described.   

MINI-CONFERENCE POSTERS: BRIDGING THE DIVIDE BETWEEN SPACE AND LABORATORY PLASMA PHYSICS

Bridging the Divide Between Space and Laboratory Plasma Physics   

Laboratory Study of Wave Generation Near Dipolarization Fronts

Experiments conducted in the Space Physics Simulation Chamber at the Naval Research Laboratory (NRL) studying instabilities generated by small-scale plasma flows use plasma equilibrium that replicate those found in dipolarization fronts. It has previously been shown that these small-scale flows can generate waves in the lower hybrid range. Recent experiments at NRL have demonstrated that these flows can also generate electromagnetic waves in the whistler band. These waves are large amplitude, bursty waves that exhibit frequency chirps similar to whistler mode chorus. Recent results from these experiments will be presented.   

Exploring the role of Alfv\'en waves in heating the solar corona

The solar corona, the outer atmosphere of the Sun, is $\sim 200$ times hotter than the underlying visible surface of the Sun. Recent coronal observations find Alfv\'en wave damping at unexpectedly low heights in the corona, suggesting that Alfv\'en waves may contribute to the heating of the corona to temperatures of $\sim 10^{6}$ K. Dissipation of wave energy may occur due to gradients in the Alfv\'en speed along the coronal magnetic field lines. These gradients may cause wave reflection, which subsequently generates turbulence. Furthermore, the presence of gradients in the Alfv\'en speed across the magnetic field line may lead to phase mixing, which can promote additional nonlinear damping mechanisms. We are studying various wave dissipation processes under conditions similar to the solar corona, using the Large Plasma Device (LAPD) at the University of California, at Los Angeles. Here we will present the results of our initial experiments exploring the effectiveness of gradients in the Alfv\'en speed along the magnetic field in reflecting Alfv\'en waves and reducing the amplitude of Alfv\'en waves transmitted across a gradient   

Numerical Support for Applying Field-Particle Correlations to Space and Laboratory Plasmas

Determining the mechanisms that transfer energy between electromagnetic fields and plasma particles, eventually leading to heating, is an important task in the study of a wide variety of plasma systems. Many different mechanisms have been proposed to mediate the energy transfer, which can be broadly classified as resonant, non-resonant, and intermittent. Each mechanism will preferentially energize particles with different velocities; such distinct features make the identification of energy transfer mechanisms possible assuming the velocity-space structure of the phase-space energy density transfer can be measured. Based upon the structure of the field-particle interaction term in the Vlasov equation, we construct a correlation using field and particle distribution timeseries from a single point in space which tracks the phase-space energy density transfer. We present such field-particle correlations calculated using data from a variety of turbulent kinetic simulations with the aim of eventual application of these correlations to space and laboratory plasma observations. Even in the presence of strong turbulence, we show that field-particle correlations calculated from a single-point data set can be used to determine the mechanisms responsible for the energy transfer.   

Observational Evidence for Field-Particle Energy Transfer in the Earth’s Magnetosheath

One of the unanswered questions in space plasma turbulence is how the energy is dissipated at the small scale end of the turbulent cascade. To help address this, a technique was recently developed (Klein & Howes 2016 ApJL, Howes et al. 2017 JPP) to allow the field-particle energy transfer to be determined as a function of velocity space, enabling the different heating mechanisms to be distinguished, each of which has a characteristic signature. Here, we present the first application of this technique to data from the MMS mission in and around the Earth’s magnetosheath region. The velocity space energy transfer between the electromagnetic fields and plasma particles is measured and compared to theoretical predictions and numerical simulations of the different dissipation mechanisms, to determine which ones are taking place.   

Using Field-Particle Correlations to Show that Landau Damping Leads to Spatially Intermittent Particle Energization in Current Sheets

Understanding the removal of energy from turbulent fluctuations in a magnetized plasma and the consequent energization of the constituent plasma particles is a major goal of heliophysics and astrophysics. Previous work has shown that nonlinear interactions among counterpropagating Alfven waves---or Alfven wave collisions---are the fundamental building block of astrophysical plasma turbulence and naturally generate current sheets in strong turbulence. A nonlinear gyrokinetic simulation of a strong Alfven wave collision is used to examine the damping of the electromagnetic fluctuations and the associated energization of particles that occurs in self-consistently generated current sheets. A simple model explains the flow of energy due to the collisionless damping and the associated particle energization, as well as the subsequent thermalization of the particle energy by collisions. Using the recently developed field-particle correlation technique, we show that particles resonant with the Alfven waves in the simulation dominate the energy transfer, demonstrating conclusively that Landau damping plays a key role in the spatially intermittent damping of the electromagnetic fluctuations and consequent energization of the particles in this strongly nonlinear simulation.   

Velocity-space cross-correlation matrix measurements and potential applications to space plasmas

We summarize a recent laboratory measurement of a velocity - space cross correlation matrix. This matrix can be decomposed into a set of eigenmodes that can be compared to plasma kinetic fluctuation modes. The measurement is a local measurement that may be applied with any velocity-sensitive measurement technique. In the laboratory, this measurement is achieved with laser induced fluorescence. In the spirit of this miniconference, we discuss the criteria a velocity-sensitive measurement must fulfill for a velocity-space cross-correlation measurement to be taken \emph{in situ} in space plasma.   

Towards a turbulent magnetic dysnamo platform

It is known through astronomical observations that most of the Universe is ionized, magnetized, and often turbulent and filled with jets. One theorized process to create strong magnetic fields and jets is the turbulent magnetic dynamo. The magnetic dynamo is a fundamental process in plasma physics, taking kinetic energy and converting it to magnetic energy and is very important to planetary physics and astrophysics. We report on recent Omega EP experiments to produce platform with a turbulent plume of magnetized material with which to study the turbulent magnetic dynamo process. The laser interaction with the target can seed magnetic fields that can be advected into the plume and amplified to saturation by the turbulent magnetic dynamo process. The experimentally measured plume characteristics are compared to hydro code calculations.   

Kinetic Theory and Fast Wind Observations of the Electron Strahl

Measurements of the electron velocity distribution function (eVDF) in the solar wind exhibit a high-energy, field-aligned beam of electrons, known as the ``strahl''. We develop a kinetic model for the strahl population, based on the solution of the electron drift-kinetic equation at heliospheric distances where the plasma density, temperature, and the strength of the magnetic field decline as power-laws of the distance along a magnetic flux tube. We compare our model with the eVDF measured by the Wind satellite's SWE strahl detector. The model is successful at predicting the angular width of the strahl for the Wind data at 1 AU, in particular, the scaling of the width with particle energy and background density. Ref: Horaites et al (2017), "Kinetic Theory and Fast Wind Observations of the Electron Strahl," arXiv:1706.03464.   

Turbulent reconnection driven by kinetic instabilities in colliding laser-produced plasmas

Magnetic reconnection experiments are conducted in a low-collisionality regime at the OMEGA EP facility. Magnetic fields are generated in expanding plasmas by the Biermann battery effect. Collision of multiple plasma bubbles produces a magnetic reconnection current sheet and drives magnetic reconnection. A novel aspect of these experiments is that a gap is introduced between the targets lowering the plasma density at the reconnection layer, and allowing high resolution proton radiography. Proton radiography reveals, for the first time, a cascade of plasmoid instabilities from short wavelength to long wavelength. The initial short-wavelength tearing is strongly modified by plasma anisotropy driven by the counter-streaming flows forming the current sheet, and is a hybrid of Weibel and tearing instability. The results have implications for magnetic reconnection driven in low-collisionality, compressive systems such as planetary magnetospheres and the heliosheath. Results on particle energization during reconnection will be reported.   

Magnetic Reconnection during Turbulence: Statistics of X-Lines and Heating

Magnetic reconnection is a ubiquitous plasma phenomenon that has been observed in turbulent plasma systems. It is an important part of the turbulent dynamics and heating of space, laboratory and astrophysical plasmas. Recent simulation and observational studies have detailed how magnetic reconnection heats plasma and this work has developed to the point where it can be applied to larger and more complex plasma systems. We examine the statistics of magnetic reconnection in fully kinetic PIC simulations to quantify the role of magnetic reconnection on energy dissipation and plasma heating. We examine the distribution of reconnection rates at the x-points found in the simulation and find that their distribution is broader than the MHD counterpart, and the average value is approximately 0.1. Reconnection heating predictions are applied to the regions surrounding the identified x-points and this is used to study the role of magnetic reconnection in turbulent heating of plasma. The ratio of ion to electron heating rates is found to be consistent with magnetic reconnection predictions.   

Partition of Heating During Magnetic Reconnection: Role of Exhaust Velocity

Understanding how magnetic reconnection heats the plasma and how the energy is partitioned between electrons and ions is an important problem that has recently become under intense scrutiny in both space and laboratory studies of reconnection. In the strong magnetic shear limit of magnetic reconnection (low guide field), the production of counter-streaming beams due to magnetic field line contraction plays an important role in heating the plasma. The contraction velocity or outflow velocity controls both the magnitude of the heating and partition of the heating between electrons and ions. However, although it is known that often the outflow velocity is less than the upstream Alfven speed, an understanding of why this is so is lacking. We show that the outflow velocity in reconnection is reduced by the ion exhaust temperature and derive a scaling relationship for this effect. Both kinetic PIC simulations and satellite observations are used to test this scaling prediction. The reduction in outflow speed is shown to be due to the firehose instability, which is suppressed for large guide field cases where the outflow speed matches the inflowing Alfven speed. This scaling for the outflow is then applied to a general theory for plasma heating during magnetic reconnection.   

Role of electron trapping during reconnection in laboratory are space plasmas

Experiments in VTF catalyzed an analysis of electron trapping, showing that electron pressure anisotropy will develop in the reconnection region [1]. The results inspired a kinetic model for anisotropic electron distributions recorded by the Wind spacecraft in the deep magnetotail [2]. The model was subsequently used to formulate a closure to the electron fluid equations, where the resulting Equations of State [3] permit electron trapping to be retained in two-fluid simulations [4]. Trapping has fundamental implications for the reconnection process, where it is the main driver of electron jets [4,5]. In the talk I will present the trapping model and how the circle between research in the laboratory, simulations, theory and spacecraft observations, now is being closed with observations of the narrow electron jets in the Terrestrial Reconnection EXperiment (TREX) at UW-Madison [6]. \\[1ex] [1] Egedal, (2002) Physics of Plasmas, 9, 1095.\\[0ex] [2] Egedal et al., (2005) Phys. Rev. Lett., 94, 025006.\\[0ex] [3] Le et al., (2009) Phys. Rev. Lett., 102, 085001.\\[0ex] [4] Ohia et al., (2012) Phys. Rev. Lett, 109, 115004.\\[0ex] [5] Le et al., (2010) Geophys. Res. Lett., 37, L03106.\\[0ex] [6] Olson et al., (2016) Phys. Rev. Lett, 116, 255001.   

Electron Pressure Anisotropy in the Terrestrial Reconnection Experiment and the Magnetospheric Multiscale Mission

The NASA Magnetospheric Multiscale (MMS) Mission seeks to measure heating and motion of charged particles from reconnection events in the magnetotail and dayside magnetopause. MMS is paralleled by the Terrestrial Reconnection Experiment (TREX) at the Wisconsin Plasma Astrophysics Laboratory (WiPAL) in its study of collisionless magnetic reconnection. In the regimes seen by TREX and MMS, electron pressure anisotropy should develop, driving large-scale current layer formation [1]. MMS has witnessed anisotropy, but the spatial coverage of the data is too limited to determine how the pressure anisotropy affects jet and current layer creation [2]. Measurements of pressure anisotropy on TREX will be presented, and implications for reconnecting current layer structure in the magnetosphere, as measured by MMS, will be discussed. [1] J. Egedal \emph{et al.}, Nature Phys. (2012). [2] J.L. Burch \emph{et al.}, Space Sci. Rev. (2016).   

Accessing the Asymmetric Collisionless Reconnection Regime in the Terrestrial Reconnection Experiment (TREX)

Kinetic effects are expected to dominate the collisionless reconnection regime, where the mean free path is large enough that the anisotropic electron pressure can develop without being damped away by collisional pitch angle scattering. ~In simulations, the anisotropic pressure drives the formation of outflow jets [1]. These jets are expected to play a role in the reconnection layer at the Earth's magnetopause, which is currently being explored by Magnetospheric Multiscale Mission (MMS) [2]. Until recently, this regime of anisotropic pressure was inaccessible by laboratory experiments, but new data from the Terrestrial Reconnection Experiment (TREX) shows that fully collisionless reconnection can now be achieved in the laboratory. Future runs at TREX will delve deeper into this collisionless regime in both the antiparallel and guide-field cases. [1] Le, A. et al. JPP, 81(1). doi: 10.1017/S0022377814000907. [2] Burch, J. L. et al. Space Sci. Rev. 199,5. doi: 10.1007/s11214-015-0164-9.   

Energy conversion in the asymmetric reconnection diffusion region

The energy conversion in the diffusion region during asymmetric reconnection is studied using two-dimensional particle-in-cell (PIC) simulations. The energy partition is region-dependent and varies with the guide field strength. Without a guide field, within the central electron diffusion region, the input magnetic energy is mostly converted to electron thermal energies; half of the input energy to the region from the X-line to the peak ion outflow location is converted to the plasmas energy, with approximately equal partition between ions and electrons, similar to the laboratory results from the Magnetic Reconnection Experiment (MRX); over the entire ion diffusion region, about half of the energy goes to ions, and 20{\%} goes to electrons. Electrons obtain energies mainly from the reconnection electric field (E$_{\mathrm{r}})$, while the in-plane electrostatic fields (E$_{\mathrm{in}})$ have a net negative contribution. For the ion total energy gain in the diffusion region, about 2/3 is from E$_{\mathrm{in}}$ and 1/3 is from E$_{\mathrm{r}}$. Adding a guide field tends to reduce the plasmas energy gain. The energy partition in the diffusion region observed by the Magnetospheric Multiscale (MMS) Mission will be estimated and compared with the PIC and MRX results.   

Issues in Space Physics in Need of Reconnection with Laboratory Physics

Predicted space observations, such as the ``foot'' in front of collisionless shocks or the occurrence of magnetic reconnection in the Earth’s magnetotail leading to auroral substorms, have highlighted the fruitful connection of laboratory and space plasma physics. The emergence of high energy astrophysics has then benefitted by the contribution of experiments devised for fusion research to the understanding of issues such as that of angular momentum transport processes that have a key role in allowing accretion of matter on a central object (e.g. black hole). The theory proposed for the occurrence of spontaneous rotation in toroidal plasmas was suggested by that developed for accretion. The particle density values, $\simeq10^{15}$ cm$^{-3}$ that are estimated to be those of plasmas surrounding known galactic black holes have in fact been produced by the Alcator and other machines. Collective modes excited in the presence of high energy particle populations in laboratory plasmas (e.g. when the ``slide away'' regime has been produced) have found successful applications in space. Magnetic reconnection theory developments and the mode particle resonances associated with them have led to envision new processes for novel high energy particle acceleration.   

​ Kinetic instabilities and reconnection in flux ropes under laboratory and space conditions

​ Reconnection converts magnetic energy forming hot flows of matter and Poynting fluxes. Reconnection happens in laboratory either by design (in experiments designed to study it) or as byproduct of other experiments (e.g. sawtooths in tokamaks). Reconnection is also often observed in situ or remotely in space systems. Among the conditions leading to reconnection, the kinking of a flux rope is amongst the most observed: in the solar corona, the Earth magnetosphere and in laboratory plasmas. We consider here specifically two conditions of current interest. First, the conditions expected in the DIIID device where kinking can be induced with appropriare setup [1] and the flux ropes observed by the NASA mission MMS in the Earth magnetopause [2]. In both cases, flux ropes become unstable to a number of competing modes, drift modes and kink modes [3]. We investigate the relative importance and interplay of these two families of modes and their impact on reconnection. Our approach will be taking into account observational data and computer simulation making a direct comparison of the two. [1] DIII-D Frontier Science Campaign, https://tinyurl.com/ya5o9z7m [2]​ Øieroset, M., et al. Geophys. Res. Lett. 43.11 (2016): 5536 [3] ​Lapenta, G, et al. Nature Physics 11.8 (2015): 690.   

Formation and Evolution of Laser-Driven, High-Mach-Number Magnetized Collisionless Shocks

Recent experiments\footnote{Schaeffer \textit{et al.}, Phys. Rev. Lett. \textbf{119}, 025001 (2017)} demonstrated the laboratory generation of high-Mach-number, magnetized collisionless shocks through the interaction of a laser-driven piston plasma with a pre-formed magnetized ambient plasma. We present additional results on collisionless shock formation, structure, and evolution from new experiments and numerical simulations. These include angular filter refractometry and Thomson scattering measurements of the density and temperature of the piston and ambient plasmas and their interaction, and proton radiography measurements of the dynamics of the magnetic field. Related studies on the role of collisionless coupling, magnetic field overshoots, particle heating, and the MHD jump conditions in piston-driven shocks were undertaken with the 2D particle-in-cell code PSC. The results provide improved understanding of laboratory-generated magnetized collisionless shocks and their relationship to shocks in astrophysical systems.   

Magnetized jet creation using a ring laser and applications

We have recently demonstrated a new robust platform of magnetized jet creation using 20 OMEGA beams to form a hollow ring. We will present the latest experimental results and their theoretical interpretation, and explore potential applications to laboratory astrophysics, fundamental plasma physics and other areas. We will also discuss the scaling of this platform to future NIF experiments.   

Scaling Arguments for Magnetically Affected Shock Experiments

In this talk we will discuss general scaling arguments applicable to magnetically affected shock experiments and their inherent challenges. This genre of experiments is rapidly growing and holds enormous promise for the field of laboratory astrophysics, but universally faces two basic constraints. First, the conditions must be right for a shock to form, and, second, the magnetic field strength must be strong enough to affect the structure and/or evolution of the shock. We will present the ramifications of these constraints, their effect on recent experiments we fielded, and current efforts underway to overcome them. This work is funded by the U.S. Department of Energy, through the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, grant number DE-NA0002956, and the National Laser User Facility Program, grant number DE-NA0002719, and through the Laboratory for Laser Energetics, University of Rochester by the NNSA/OICF under Cooperative Agreement No. DE-NA0001944.   

Quasi-nonlinear approach to the Weibel instability

Astrophysical and high-energy-density laboratory plasmas often have large-amplitude, sub-Larmor-scale electromagnetic fluctuations excited by various kinetic-streaming or anisotropy-driven instabilities. The Weibel (or the filamentation) instability is particularly important because it can rapidly generate strong magnetic fields, even in the absence of seed fields. Particles propagating in collisionless plasmas with such small-scale magnetic fields undergo stochastic deflections similar to Coulomb collisions, with the magnetic pitch-angle diffusion coefficient representing the effective ``collision'' frequency. We show that this effect of the plasma ``quasi-collisionality'' can strongly affect the growth rate and evolution of the Weibel instability in the deeply nonlinear regime. This result is especially important for understanding cosmic-ray-driven turbulence in an upstream region of a collisionless shock of a gamma-ray burst or a supernova. We demonstrate that the quasi-collisions caused by the fields generated in the upstream suppress the instability slightly but can never shut it down completely. This confirms the assumptions made in the self-similar model of the collisionless foreshock.   

Driving Fast Flows with Volumetric Current Drive

Volumetric current drive has been shown to be an efficient method for driving fast flows with high Rm for studying the onset of flow-driven plasma instabilities. High performance plasmas are produced with 20 kW of electron cyclotron heating (ECH) and thermally emissive lanthanum hexaboride cathodes. Plasma flow is achieved by injecting current through the plasma across an externally applied weak magnetic field setting up a $J \times B$ body force on the plasma volume. Two scenarios for volumetric current drive have been demonstrated. The first injects current across a weak uniform axial magnetic field driving a Keplerian-like flow for magneto-rotational instability (MRI) studies. The second injects current across a weak quadrupole magnetic field for driving a von Karman-like flow for dynamo studies. First results measuring velocity and ion temperature profiles measured by a Fabry-Perot interferometer are shown. Detailed mach probe flow measurements show stronger flow shear in volumetric current drive compared to previous edge-driven plasma flow experiments.   

Equilibrium and Stability Properties of Low Aspect Ratio Mirror Systems: from Neutron Source Design to the Parker Spiral

Equilibrium reconstructions of rotating magnetospheres in the lab are computed using a user-friendly extended Grad-Shafranov solver written in Python and various magnetic and kinetic measurements. The stability of these equilibria are investigated using the NIMROD code with two goals: understand the onset of the classic ``wobble" in the heliospheric current sheet and demonstrating proof-of-principle for a laboratory source of high-$\beta$ turbulence. Using the same extended Grad-Shafranov solver, equilibria for an axisymmetric, non-paraxial magnetic mirror are used as a design foundation for a high-field magnetic mirror neutron source. These equilibria are numerically shown to be stable to the m=1 flute instability, with higher modes likely stabilized by FLR effects; this provides stability to gross MHD modes in an axisymmetric configuration. Numerical results of RF heating and neutral beam injection (NBI) from the GENRAY/CQL3D code suite show neutron fluxes promising for medical radioisotope production as well as materials testing. Synergistic effects between NBI and high-harmonic fast wave heating show large increases in neutron yield for a modest increase in RF power.   

Observations of magnetic pumping in the solar wind using MMS data

The turbulent cascade is believed to play an important role in the energization of the solar wind plasma. However, there are characteristics of the solar wind that are not readily explained by the the cascade, such as the power-law distribution of the solar wind speed. Starting from the drift kinetic equation, we have derived a magnetic pumping model, similar to the magnetic pumping well-known in fusion research, that provides an explanation for these features. In this model, particles are heated by the largest scale turbulent fluctuations, providing a complementary heating mechanism to the turbulent cascade. We will present observations of this mechanism in the bow shock region using data from the Magnetospheric MultiScale mission.   

Interaction of a Relativistic Electron Beam with Magnetized Plasma

The interaction between relativistic electron beams and a magnetized plasma is a fundamental and practical problem that is relevant to many challenging issues in space physics and astrophysics. For example, it is well known that energetic particles in the Earth’s radiation belts pose a danger to communication satellites. Compact electron beam sources may be used on future spacecraft to generate waves that would remove the energetic particles from the radiation belt region. A full understanding of the physics of these waves may also shed light on the mechanism for type II/III solar radio emissions. This talk will discuss experiments proposed to further advance understanding of the physical mechanisms governing beam-plasma interactions. The experiments and supporting simulations will investigate in detail the types of waves (whistler, Langmuir, etc.) produced by high-energy beams, beam stability, and feasibility for future space-based experiments. Experiments will be conducted on the Large Plasma Device (LAPD) at UCLA using a unique variable-energy electron beam recently developed at Los Alamos. We will discuss the proposed experimental setup as well as ongoing feasibility studies conducted using theoretical estimates and kinetic simulations.   

How to emit a high-power electron beam from a magnetospheric spacecraft?

The idea of using high-power electron beams to actively probe magnetic-field-line connectivity in space has been discussed since the 1970’s. It could solve longstanding questions in magnetospheric/ionospheric physics by establishing connectivity and causality between phenomena occurring in the magnetosphere and their image in the ionosphere [1]. However, this idea has never been realized onboard a magnetospheric spacecraft because the tenuous magnetospheric plasma cannot provide the return current necessary to keep the spacecraft charging under control. Recently, we have used Particle-In-Cell simulations to propose a spacecraft-charging mitigation scheme that would enable the emission of a high-power electron beam from a magnetospheric spacecraft [2]. In this work, we will present an overview of the concept and of our theoretical, computational and experimental effort to establish this idea conclusively. [1] G.L. Delzanno, J.E. Borovsky, M.F. Thomsen, B.E. Gilchrist, and E. Sanchez, J. Geophys. Res. Space Physics 121, 6769, 2016. [2] G.L. Delzanno, J.E. Borovsky, M.F. Thomsen, J.D. Moulton, and E.A. MacDonald, J. Geophys. Res. Space Physics 120, 3647, 2015.   

Modeling-challenge paradigm using design of experiments for spacecraft immersed in nonstationary, between-regimes, flowing plasma

A conducting sphere and cylinder under the conditions of nonstationary, between-regimes, flowing plasma is adopted as a test case for a modeling-challenge paradigm based on design of experiments (DOE) methodology that merges numerical simulation and testing. This model/simulation development platform facilitates a red-team/blue-team style challenge aimed at a tailored set of standard experimental conditions and measurements addressing specific questions in spacecraft-environment interactions and assessing the capability of models to describe those conditions. The goal is streamlining the Model/Simulation development process. A byproduct is an enhancement of the interrelationship between experiments in the laboratory and in space. Here, we conceptualize the advantage of the model-challenge over conventional validation in advancing whole-device modeling objectives in basic and applied plasma science.   

Laboratory observation of multiple double layer resembling space plasma double layer

Perceptible double layer consisting of more than one layers were produced in laboratory using a double discharge plasma setup. The confinement of oppositely charged particles in each layer with sharply defined luminous boarder is attributed to the self-organization scenario. This structure is generated in front of a positively biased electrode when the electron drift velocity ($\nu_{\mathrm{d}})$ exceeds 1.3 times the electron thermal velocity ($\nu_{\mathrm{te}})$. Stable multiple double layer structures were observed only between 1.3 $\nu_{\mathrm{te}} \quad \le \quad \nu _{\mathrm{d}} \quad \le $ 3 $\nu_{\mathrm{te}}$. At $\nu _{\mathrm{d}}=$1.3 $\nu_{\mathrm{te}}$, oscillations were excited in the form of large amplitude burst followed by a high frequency stable oscillation. Beyond $\nu_{\mathrm{d}}=$3 $\nu_{\mathrm{te}}$, multiple double layer begins to collapse which is characterized by an emergence in turbulence. Long range dependence in the corresponding electrostatic potential fluctuations indicates the role of self-organized criticality in the emergence of turbulence. The algebraic decaying tale of the autocorrelation function and power law behavior in the power spectrum are consistent with the observation.   

Experimental Simulation of Solar Wind Interactions with Magnetic Dipole Fields above Insulating Surfaces

Magnetic anomalies on the surfaces of airless bodies such as the Moon interact with the solar wind, resulting in both magnetic and electrostatic deflection of the charged particles and thus localized surface charging. This interaction is studied in the Colorado Solar Wind Experiment with large-cross-section ($\sim$300 cm$^2$) high-energy flowing plasmas (100-800 eV beam ions) that are incident upon a magnetic dipole embedded under various insulating surfaces. Measured 2D plasma potential profiles indicate that in the dipole lobe regions, the surfaces are charged to high positive potentials due to the collection of unmagnetized ions, while the electrons are magnetically shielded. At low ion beam energies, the surface potential follows the beam energy in eV. However, at high energies, the surface potentials in the electron-shielded regions are significantly lower than the beam energies. A series of studies indicate that secondary electrons are likely to play a dominant role in determining the surface potential. Early results will also be presented from a second experiment, in which a strong permanent magnet with large dipole moment (0.55 T, 275 A*m$^2$) is inserted into the flowing plasma beam to replicate aspects of the solar wind interaction with the earth’s magnetic field.   

How high energy fluxes may affect Rayleigh-Taylor instability growth in young supernova remnants

Energy-transport effects can alter the structure that develops as a supernova evolves into a supernova remnant. The Rayleigh Taylor instability is thought to produce structure at the interface between the stellar ejecta and the circumstellar matter, based on~simple models and hydrodynamic simulations. Simulations predict that RT produces structures at this interface, having a range of spatial scales. When the CSM is dense enough, as in the case of SN 1993J, the hot shocked matter can produce significant radiative fluxes that affect the emission from the SNR. Here we report experimental results from the National Ignition Facility to explore how large energy fluxes, which are present in supernovae such as SN 1993J, might affect this structure. We present data and simulations from Rayleigh-Taylor instability experiments in high- and low- energy flux experiments performed at the National Ignition Facility. We also will discuss the apparent, larger role of heat conduction when we closely examined the comparison between the experimental results, and the SNR observations and models. This work is~funded~by the~NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, grant number~DE-NA0002956.~   

Progress on the Development of Low Pressure High Density Plasmas on the Helicon Plasma Experiment (HPX)

The small Helicon Plasma Experiment (HPX) at the Coast Guard Academy Plasma Lab (CGAPL), continues to progress toward utilizing the reputed high densities (10$^{\mathrm{13}}$ cm$^{\mathrm{-3}}$ and higher) at low pressure (.01 T) [1] of helicons, for eventual high temperature and density diagnostic development in future laboratory investigations. HPX is designed to create repeatedly stable plasmas (\textasciitilde 20 - 30 ns) induced by an RF frequency in the 10 to 70 MHz range. HPX has constructed a protected Langmuir probe where raw data will be collected, compared to the RF compensated probe and used to measure the plasma's density, temperature, and behavior during experiments. Our 2.5 J YAG laser Thomson Scattering system backed by a 32-channel Data Acquisition (DAQ) system is capable 12 bits of sampling precision at 2 MS/s for HPX plasma property investigations are being integrated into the existing diagnostics and control architecture. Progress on the construction of the RF coupling system, Helicon Mode development, and magnetic coils, along with observations from the Thomson Scattering, particle, and electromagnetic scattering diagnostics will be reported.