Session YP12: Poster Session IX (Supplemental and Postdeadline)

Design and optimization of a gas-puff nozzle for staged Z-pinch experiments using computational fluid dynamics simulations

Previous experimental work on staged Z-pinches demonstrated that gas liners can efficiently couple energy and implode uniformly a target-plasma. A 1.5 MA, 1 $\mu $s current driver was used to implode a magnetized, Kr liner onto a D$+$ target, producing 10$^{10}$ neutrons per shot and providing clear evidence of enhanced pinch stability. Time-of-flight data suggest that primary and secondary neutrons were produced. MHD simulations show that in Zebra, a 1.5MA and 100ns rise-time current driver, high fusion gain can be attained when the optimum liner and plasma target conditions are used. In this work we present the design and optimization of a liner-on-target nozzle to be fielded in Zebra and demonstrate high fusion gain at 1 MA current level. The nozzle is composed of an annular high atomic number gas-puff and an on-axis plasma gun that will deliver the ionized deuterium target. The nozzle optimization was carried out using the computational fluid dynamics (CFD) code fluent and the MHD code Mach2. The CFD simulation produces density and temperature profiles, as a function of the nozzle shapes and gas conditions, which are then used in Mach2 to find the optimum plasma liner implosion-pinch conditions.   

On reliable quantification of Richtmyer-Meshkov flows

We report an integrated study including experiments, Smooth Particle Hydrodynamics simulations, and theoretical and data analyses to reliably quantify Richtmyer-Meshkov (RM) flows induced by moderate shocks. The RM evolution is analyzed for realistic gases with different densities (Atwood numbers 0.68, 0.95) driven by moderate shocks (Mach 2.86, 1.95) in case of relatively small amplitude of the initial perturbation (0.06, 0.08 of the perturbation wavelength). Our study includes the systematic consideration of the effects of gamma, the initial perturbation amplitude, and the interference of the perturbation waves. We analyze quantitative and qualitative features of RM dynamics, including the vector and scalar flow fields, the bulk and interface velocities, the large-scale interfacial structures and small-scale non-uniformities (reverse jets, hot spots) in the bulk. We argue that a systematic interpretation of RM dynamics from the data and a reliably quantification the RM evolution requires a synergy of the experiments, simulation, and theory.   

Rayleigh-Taylor mixing in supernova experiments

We report a scrupulous analysis of data in supernova experiments that are conducted at high power laser facilities in order to study core-collapse supernova SN1987A. Parameters of the experimental system are properly scaled to investigate the interaction of a blast-wave with helium-hydrogen interface, and the induced Rayleigh-Taylor (RT) mixing of the denser and lighter fluids with time-dependent acceleration. We analyze all available experimental images of RT flow in supernova experiments, and measure delicate features of the interfacial dynamics. A new scaling is identified for calibration of experimental data to enable their accurate analysis and comparisons. By proper accounting for the imprint of the experimental conditions, the data set size and statistics are substantially increased. New theoretical solutions are identified to describe asymptotic dynamics of RT flow with time-dependent acceleration by applying theoretical analysis. Good qualitative and quantitative agreement is achieved of the experimental data with the theory and simulations. Our study indicates that in supernova experiments, the RT flow is in the mixing regime, the interface amplitude contributes substantially to the characteristic length scale for energy dissipation; the mixing flow may keep order.   

Axisymmetric equilibria with pressure anisotropy and plasma flow

A generalised Grad-Shafranov equation that governs the equilibrium of an axisymmetric toroidal plasma with anisotropic pressure and incompressible flow of arbitrary direction is derived. This equation includes six free surface functions and recovers known Grad-Shafranov-like equations in the literature as well as the usual static, isotropic one. The form of the generalised equation indicates that pressure anisotropy and flow act additively on equilibrium. In addition, two sets of analytical solutions, an extended Solovev one with a free boundary and an extended Hernegger-Maschke one for a plasma surrounded by a fixed boundary possessing an X-point, are constructed, particularly in relevance to the ITER and NSTX tokamaks. Furthermore, the impacts both of pressure anisotropy and plasma flow on these equilibria are examined. It turns out that depending on the maximum value and the shape of an anisotropy function, the anisotropy can act either paramagnetically or diamagnetically. Also, in most of the cases considered both the anisotropy and the flow have stronger effects on NSTX equilibria than on ITER ones.   

HELENA code with incompressible parallel plasma flow

It has been established that plasma rotation in connection to both zonal and equilibrium flow can play a role in the transitions to the advanced confinement regimes in tokamaks, as the L-H transition and the formation of Internal Transport Barriers. For incompressible rotation the equilibrium is governed by a generalized Grad-Shafranov (GGS) equation and a decoupled Bernoulli-type equation for the pressure. For parallel flow the GGS equation can be transformed to one identical in form with the usual Grad-Shafranov equation. In the present study on the basis of the latter equation we have extended HELENA, an equilibrium fixed boundary solver integrated in the ITM-TF modeling infrastructure. The extended code solves the GGS equation for a variety of the two free-surface-function terms involved for arbitrary Afv\'en Mach functions. We have constructed diverted-boundary equilibria pertinent to ITER and examined their characteristics, in particular as concerns the impact of rotation. It turns out that the rotation affects noticeably the pressure and toroidal current density with the impact on the current density being stronger in the parallel direction than in the toroidal one. Also, the linear stability of the equilibria constructed is examined   

Unified Statistics and Plausible Extension to Anisotropic Effect

Generalizing the classical probability and imprecise probability to the notion of ``neutrosophic probability'' in order to be able to model Heisenberg's Uncertainty Principle of a particle's behavior, Schr\"{o}dinger's Cat Theory, and the state of bosons which do not obey Pauli's Exclusion Principle (in quantum physics). Neutrosophic probability is close related to neutrosophic logic and neutrosophic set.   

Generic Stellarator-like Magnetic Fusion Reactor

The Generic Magnetic Fusion Reactor paper, published in 1985, has been updated, reflecting the improved science and technology base in the magnetic fusion program. Key changes beyond inflation are driven by important benchmark numbers for technologies and costs from ITER construction, and the use of a more conservative neutron wall flux and fluence in modern fusion reactor designs. In this paper the generic approach is applied to a catalyzed D-D stellarator-like reactor [1]. It is shown that an interesting power plant might be possible if the following parameters could be achieved for a reference reactor: R/\textless a\textgreater $\approx $ 4, confinement factor, f$_{\mathrm{ren}} = $ 0.9 - 1.15, \textless $\beta $\textgreater $\approx $ 8.0 -- 11.5 {\%}, Z$_{\mathrm{eff}}\approx $ 1.45 plus a relativistic temperature correction, fraction of fast ions lost $\approx $ 0.07, B$_{\mathrm{m}} \quad \approx $ 14 -- 16 T, and R $\approx $ 18 -24 m.\\[4pt] [1] J. Sheffield and D.A. Spong, ``Generic Stellarator-like Magnetic Fusion Reactor,'' submitted to Fusion Science and Technology, June 2015.   

Phase-mixing self-injection into wakefield acceleration structure driven in a rising density gradient

We model the phase-mixing self-injection of electrons into the plasma-wakefield acceleration structures driven in a longitudinally rising density gradient. In several laser-plasma acceleration experiments a long tail of accelerated electrons of different energies is experimentally observed. Self-injection is the process where some of the plasma electrons lose coherence with the wave due to non-linearities. The non-linearity is inherently and intentionally induced in the plasma oscillations due to the variation of the restoring force along the rising density gradient. These electrons then get trapped in and propagate with the accelerating phase of the plasma-wave. The onset of trapping is shown to scale with the gradient of the rising density and the amplitude of oscillations using the phase-mixing model. We computationally verify the phase-mixing model in planar geometry using PIC codes. The trapping of electrons in cylindrical electron plasma oscillations in the non-linear regime is verified with scaling similar to the planar geometry phase-mixing model. A full theory of longitudinal phase-mixing of radial oscillations is currently underway. The importance of this work for laser-plasma acceleration lies in consistently accelerating just the desired mono-energetic bunch.   

Fusion Breeding for Sustainable, Mid Century, Carbon Free Power

If ITER achieves Q$\sim$10, it is still very far from useful fusion. The fusion power, and the driver power will allow only a small amount of power to be delivered, $\alt$50MW for an ITER scale tokamak. It is unlikely, considering ``conservative design rules'' that tokamaks can ever be economical pure fusion power producers [1]. Considering the status of other magnetic fusion concepts, it is also very unlikely that any alternate concept will either. Laser fusion does not seem to be constrained by any conservative design rules, but considering the failure of NIF to achhieve ignition, at this point it has many more obstacles to overcome than magnetic fusion. One way out of this dilemma is to use an ITER size tokamak, or a NIF size laser, as a fuel breeder for searate nuclear reactors. Hence ITER and NIF become ends in themselves, instead of steps to who knows what DEMO decades later. Such a tokamak can easily live within the consrtaints of conservative design rules. This has led the author to propose ``The Energy Park''; a sustainable, carbon free, economical, and environmently viable power source without prolifertion risk. It is one fusion breeder fuels 5 conventional nuclear reactors, and one fast neutron reactor burns the actinide wastes.\\[4pt] [1] W. Manheimer, J. Fus. Energy, June, 210   

Superfluid He-explained to SecundoPiaTurins through Self-Organized Criticality/SOC

Through Mike Carrell:``Arata \& Zhang/AZ's coldFusion excess Heat \& He Production" normatively describe precedes by Arata \& Chang: ``Establishment of the "solid Fusion":"..moreover at this time, nuclear fusion reaction was generated inside the solid with synchronous creation of both much 2H4 \& thermal Energy". Nuclear fuel used are ZrO2-Pd(nanoPd), ZrO2.Pd alloy (7[g])+pure(100\%) D2 \& Pd-Zr-Ni alloy (18.4[g]) +... After strange avalanche behavior of superfluid He3 offers a unique `testing ground' for rapid transition, to bioinspired computing, neurobiology \& plasma physics quotes: ``SOC is a class of dynamical systems, whose macroscopic behaviour displays the spatial and/or temporal scale-invariance characteristics of a critical point of ``phase transition"-Wikipedia:SOC. Further are e.g to e-Marlin Early Science Meeting offers Secundo Pia Turins devoties, for avalanche dynamic in a pile of rice[V.Frette,et.al] \& slowly sprinkled to cause ``avalanches" of Per Bak's sand-Pile experiment at least involving F Lavoise,et.al: ``New Methods characterizing Avalanche behavior to determine powder Flow" 2002 denotes MO Tjia, HL The, Suparno S, Sutrisno: ``Karakterisasi Struktur PP, PS \& PVC dengan NMR", DIP-ITB no. 4872181-1981 to fractions the expenditure in UI/NJOP of Elders-parentals of we   

High- and low-symmetric coherent structures and dimensional crossover in Richtmyer-Meshkov flows

We study the three-to-two dimensional crossover for the nonlinear structures appearing in the nonlinear regime of Richtmeyer Meshkov instability (RMI). This large-scale coherent structure is an array of bubbles and spikes that is periodic in the plane normal to the direction of an initial shock (impulsive acceleration). The flow is assumed to be anisotropic in the plane with the symmetry group p2mm. For the bubbles, there is a two-parameter family of regular asymptotic solutions. Stability of these solutions is studied. The transitions to the flows with the group p4mm and pm as well as properties of the dimensional crossover are analyzed. We find that 3D bubbles in RMI tend to conserve a near-symmetric-shape, and cannot be transformed into 2D bubbles continuously. We discuss the mechanism of secondary instabilities in anisotropic RM flows and the discontinuity of the dimensional crossover, as well as their dependence of the density ratio.   

Generation of electromagnetic emission during the injection of dense supersonic plasma flows into arched magnetic field

Interaction of dense supersonic plasma flows with an inhomogeneous arched magnetic field is one of the key problems in near-Earth and space plasma physics. In this work a new experimental approach is suggested to study interaction of supersonic (ion Mach number up to 2.7) dense (up to $10^{15} cm^{-3}$) plasma flows with inhomogeneous magnetic field (an arched magnetic trap with a field strength up to 3.3 T) which opens wide opportunities to model space plasma processes in laboratory conditions. Fully ionized plasma flows with density from $10^{13} cm^{-3}$ to $10^{15} cm^{-3}$ are created by plasma generator on the basis of pulsed vacuum arc discharge and injected into open magnetic trap across magnetic field lines. The filling of the arched magnetic trap with plasma and further magnetic field lines break by dense plasma flow was accompanied by pulsed electromagnetic emission at electron cyclotron frequency range, which can generated by electrons in the place of intensive deceleration of plasma flow in magnetic field.   

L-H transitions driven by ion heating in scrape-off layer turbulence (SOLT) model simulations

The original SOLT model now includes the evolution of ion pressure consistent with drift-ordering. It is a two-dimensional, electrostatic reduced model wherein closure relations, obtained by integrating the equations along the B-field, model parallel physics that includes sheath-mediated current and heat flux in the scrape-off-layer and electron drift waves inside the separatrix. Low (L) and high (H) confinement regimes are observed in SOLT simulations, depending on the strength of an ion pressure (i.e., ion heating) source localized inside the separatrix: With increasing heating, particle and energy confinement times at first decrease in the L-mode then rise in the H-mode. The L-H transition is marked by distinct changes in sheared-flow profiles. The addition of ion pressure dynamics enables modeling the \textit{self-consistent} interaction between the ion diamagnetic drift and the radial electric field (mean and zonal flows). The roles of these sheared flows in mediating the L-H transition are explored. A new diagnostic, based on the density correlation function, is applied to study blob velocities in different regimes.   

Characterization of an inductively coupled plasma source with convergent nozzle

The inductively heated plasma generator (IPG6-B) located in the CASPER labs at Baylor University has recently been characterized for both air, nitrogen and helium. A primary area of research within the intended scope of the instrument is the analysis of material degradation under high heat fluxes such as those imposed by a plasma during atmospheric entry of a spacecraft and at the divertor within various fusion experiment. In order to achieve higher flow velocities and respectively higher heat fluxes, a new exit flange has been designed to allow the installation of nozzles with varying geometries at the exit of the plasma generator. This paper will discuss characterization of the plasma generator for a convergent nozzle accelerating the plasma jet to supersonic velocity. The diagnostics employed include a cavity calorimeter to measure the total plasma power, a Pitot probe to measure stagnation pressure and a heat flux probe to measure the local heat flux. Radial profiles of stagnation pressure and heat flux allowing the determination of the local plasma enthalpy in the plasma jet will be presented.   

Induced Single-Photon ionization Transparency

Induced single-photon ionization transparency is studied by using a hybrid quantum-classical model, tracking and moving each particle using molecular dynamics. Two short XUV pulses interact with the cluster which cause negligible inverse bremsstrahlung heating. The first pulse is of sufficient intensity, forming a warm-dense nanoplasma in the cluster, that it completely saturates the single-photon ionization channel. A second XUV pulse at the same wavelength then probe the cluster to test if the channel is actually saturated. If enhanced photo-ionization mechanisms contribute significantly to the ionization of the cluster, then the second pulse will create a significant change in the ionization of the cluster. Otherwise, the second XUV pulse will not interact with the cluster. Measuring the time-of-flight ion signal, the kinetic energy distribution of the ions and electrons, allows us to distinguish between saturated versus unsaturated single-photon ionization channel. In either case, an enhancement will be seen due to there being clusters not interacting with the spatial peak of the pulse and thus not saturating from the first pulse. This will be accounted for in the model, allowing for the determination of the role enhanced photo-ionization plays in XUV-cluster interactions.   

Exact magnetized particle orbits in a parabolic potential and their relation to ExB drifts, diocotron motion, Brillouin limit, stochasticity, axis v. non-axis encirclement, and canonical angular momentum

Analytic solutions are presented for the orbit of a charged particle in the combination of a uniform axial magnetic field and a parabolic electrostatic potential. These trajectories are shown to correspond to the sum of two individually rotating vectors with one vector rotating at a constant fast frequency and the other rotating in the same sense but with a constant slow frequency. These solutions are related to the diocotron mode, to Penning trap orbits, and to stochastic orbits. If the lengths of the two rotating vectors are identical, the particle has zero canonical angular momentum in which case the particle orbit will traverse the origin. Axis-encircling orbits are where the length of the vector associated with the fast frequency is longer than the vector associated with the slow frequency. Non-axis encircling orbits are the other way around.   

Study of staircase formation in Hasegawa-Wakatani turbulence, using a multi-field, $K-\epsilon$ based model

Staircase formation is a generic form of secondary pattern formation instability in out-of-equilibrium, turbulent systems. Inhomogeneous mixing of potential vorticity across its background gradient can result in highly structured staircases in the PV profile, by weakening the background PV in some regions and sharpening it in others. We study the staircase formation in the density profile of a Hasegawa-Wakatani system, in which turbulence can be driven by both the density gradient and the flow shear. Total potential enstrophy of this system is explicitly conserved, up to the enstrophy production and dissipation terms. We use a 3-field model, which evolves the mean density profile, the mean vorticity profile, and the turbulent potential enstrophy. Both analytical and numerical techniques are used to study the equilibrium solutions and their stability, as well as the dynamics of this model.   

Multi-code benchmark of global gyrokinetic electromagnetic instabilities

Considering the recent major extensions of global gyrokinetic codes towards a comprehensive and self-consistent treatment of electromagnetic (EM) effects, corresponding verification tests are obvious and necessary steps to be taken. While a number of (semi-)analytic test cases and benchmarks exist in the axisymmetric limit, microinstabilities and particularly EM turbulence are rarely addressed. In order to remedy this problem, a hierarchical linear gyrokinetic benchmark study is presented starting with electrostatic ion temperature gradient microinstabilities with adiabatic electron response and progressing finally to the characterization of fully EM instabilities as a function of $\beta$. The inter-code comparison involves contributions from Eulerian Vlasov, Lagrangian PIC, and Semi-Lagrange codes at least in one level of this verification exercise, thus confirming a high degree of reliability for the implementations that has rarely been achieved before in this context. Additionally, possible extensions of this benchmark into the physically more relevant nonlinear turbulence regime will be discussed, e.g., relaxation problems or gradient-driven setups.   

NUBEAM simulation for off-axis NBI design in KSTAR

The off-axis neutral beam injection (NBI) is being required for the off-axis current drive with capability of providing broaden current and pressure profile to achieve high performance steady state operation in KSTAR tokamak. The off-axis NBI design has two off-axis neutral beam injectors with maximum beam energy of 100 keV and the same tangency radius as the central beam in existing on-axis NBI in KSTAR. Characteristics of beam heating and current drive of off-axis NBI is simulated using NUBEAM code. The NUBEAM code calculates the current drive, the torque, the power absorption to ion and electron, and the beam loss using a Monte Carlo modeling of fast ion species. The predictive study of the high performance steady state operation scenario using off-axis NBI and RF heating is also presented using fast iterative integrated transport code, FASTRAN   

Experimental Investigation of the Wake-Mediated Interaction Forces Between Dust Particles in a Flowing Plasma

An anisotropic spatial dependence of the wake-mediated interaction forces between dust particles in a plasma flow was studied experimentally. The measurements were performed at CASPER for the vertically aligned chain self-organized from 11 microparticles inside a glass box placed on the lower electrode of a RF gas discharge chamber. The experiment was conducted in argon plasma at 137 mTorr and monodisperse MF particles having diameters of 8.93 microns were used. To recover the wake-mediated interaction forces we improved the method based on solving the inverse Langevin problem of the dynamics of many interacting particles. To determine 3D trajectories of the particles we used a stereoscopic video surveillance system. Spatial profiles of the forces with which upstream particles act on downstream ones and vice versa were obtained. The difference between the interparticle interaction forces in the opposite directions indicates its non-reciprocal nature and can be associated with the wake. The peak position of the wake-field and the space charge concentrated in it were evaluated by the force profile analysis.   

Development of ultra-fast 2D ion Doppler tomography using image intensified CMOS fast camera

The world fastest novel time-resolved 2D ion Doppler tomography diagnostics has been developed using fast camera with high-speed gated image intensifier (frame rate: 200kfps. phosphor decay time: $\sim1\mu$s). Time evolution of line-integrated spectra are diffracted from a f=1m, F/8.3 and g=2400L/mm Czerny-Turner polychromator, whose output is intensified and recorded to a high-speed camera with spectral resolution of $\sim$0.005nm/pixel. The system can accommodate up to 36 (9$\times$4) spatial points recorded at 5$\mu$s time resolution, tomographic reconstruction is applied for the line-integrated spectra, time-resolved (5$\mu$s/frame) local 2D ion temperature measurement has been achieved without any assumption of shot repeatability. Ion heating during intermittent reconnection event which tends to happen during high guide field merging tokamak was measured around diffusion region in UTST. The measured 2D profile shows ion heating inside the acceleration channel of reconnection outflow jet, stagnation point and downstream region where reconnected field forms thick closed flux surface as in MAST. Achieved maximum ion temperature increases as a function of $B_{rec}^2$ and shows good fit with MAST experiment, demonstrating promising CS-less startup scenario for spherical tokamak.   

On the numerical dispersion and the spectral fidelity of the Particle-In-Cell method

The Particle-In-Cell (PIC) method is widely used in plasma modeling. However, the PIC method exhibits grid type numerical instabilities, including the finite grid instability and the numerical Cherenkov instability that can render unphysical simulation results or disrupt the simulation. A faithful numerical dispersion of the electromagnetic PIC algorithm is obtained and analyzed to obtain the insight about the numerical instabilities inherent in such a computation model [1]. Using this dispersion, we investigate how the finite grid instability arises from the interaction of the numerical modes admitted in the system and their aliases. Compared with the gridless model [2, 3], we show that the lack of spectral fidelity relative to the real system due to the aliasing effect is a major cause of the numerical instabilities in the PIC model. \\[4pt] [1] M. D. Meyers et al., \textit{Journal of Computational Physics}, \textit{297}, 565--583, (2015).\\[0pt] [2] G. Vlad et al., \textit{Computer Physics Communications}, 134(1), 58--77, (2001).\\[0pt] [3] E. G. Evstatiev, B. A. Shadwick, \textit{Journal of Computational Physics}, 245, 376--398, (2013).   

R-Z Density Mapping and CFD Simulation of Gas Puff Nozzle Flow

Laser induced fluorescence (LIF) is a technique in which a tracer is added to the gas flow for measurement of its spatial and temporal density profile. The Nd:YAG EKSPLA laser ~20mJ/150ps at the fourth harmonic 266nm wavelength is focused down to a <1mm pencil beam to excite the acetone tracer. The use of anr ICCD gating camera is necessary because the 4ns short-lived fluorescence state is an order-of-magnitude dimmer than the 200us long-lived phosphorescence state. Mapping the density profile in time and space requires multiple shots. Once the temporal and spatial density profile is obtained, it can be used and benchmarked for two independent CFD software programs using transient solvers: OpenFOAM and FLUENT. The measurements and simulations serve as the initial conditions for (i) Gas Puff experiments that utilize special nozzle contours to inject the gas load between the electrode gap on pulsed-power machines and (ii) use with future MHD modeling efforts. Support for this work is provided by DOE/NNSA grant DE-NA0002075 and funded by the US Department of Energy, ARPA-E, Control Number 1184-1527   

Electron Transport and Tunneling Resistance between Carbon Nanotube Fibers

The carbon nanotube (CNT) has exceptional intrinsic properties in its mechanical strength and stiffness, low density, and electrical and thermal conductivity [1]. However, on a macroscopic level, these outstanding properties, especially the electrical conductivity, remain elusive. The CNT fibers contain a very large number of junctions and contacts. It is therefore important to understand the electron transport through the contact between individual CNTs as well as the contact between CNT and the substrate. Based on a simple transmission line model, we study the tunneling resistance for a parallel contact formed between two closely spaced CNTs. The localized contact resistance along the contact region is modeled by the tunneling resistance, which is calculated from a recent self-consistent model [2]. The results give insights on the macroscopic electrical conductivity of CNT fibers. \\[4pt] [1] N. Behabtu, et al., Science, 339, 182 (2013). \\[0pt] [2] P. Zhang, Sci. Rep., 5, 9826 (2015).   

Particle-In-Cell Simulations of Efficient Raman Amplification in High Intensity Regime

Backward Raman amplification (BRA) in plasma makes it possible to obtain the short pulse with higher output intensity beyond the existing CPA systems. Numerous analytic and simulation studies have been focused on this, together with some proof-of-principle experiments reported. However, most of the theoretical studies are done for one-dimensional geometry, which neglect the possible filamentation and diffraction of the pump and seed pulse. Here, by using the two-dimensional three-velocity particle-in-cell simulations, we explore in a very preliminary way to study certain higher dimensional aspects of the amplification process.   

Characterization of warm dense matter (WDM) from high intensity laser driven shockwaves

Understanding the transport physics of an intense relativistic electron beam in various plasma regimes is crucial for many high-energy-density applications, such as fast heating for advanced ICF schemes and ion sources. Most short pulse laser-matter interaction experiments for electron transport studies have been performed with initially cold targets where the resistivity is far from that in warm dense and hot dense plasmas. In order to extend fast electron transport and energy coupling studies in pre-assembled plasmas, we must first characterize those regime possibilities. We present initial experiments conducted on the OMEGA EP laser ($\sim$ 10$^{14}$ W/cm$^2$) to characterize WDM created from the shock compression of low density ($\rho $0 $\sim$ 330 mg/cc) CRF foams and solid Al foil targets. In foam targets, imaging x-ray Thomson scattering is used to measure spatial profiles of the temperature, ionization state and relative material density. The ASBO diagnostic and radiation hydrodynamics simulations deduce shock pressure in Al targets of various thicknesses. Details of the experiment and available data will be presented.   

Enhanced X-ray radiation from laser wakefield acceleration transition to plasma wakefield acceleration

The electromagnetic fields responsible for Laser Wakefield Acceleration (LWFA) also cause electrons to radiate bright X-ray pulses though betatron oscillations [1,2]. Using 3-D OSIRIS particle in cell simulations with a Monte Carlo synchrotron X-ray emission algorithm, the X-ray flux was also shown to increase dramatically for interaction distances beyond the dephasing length, where the main electron beams in the first ion bubble catch up the laser pulse front. Subsequently, it forms a secondary beam in the tail of the first bubble. Laser wakefield acceleration transitions to beam driven plasma wakefield acceleration [3], which results in the onset of the electron-hose instability [4] and thus significantly enhances the X-ray radiation.\\[4pt] [1] E. Esarey, B. A. Shadwick, P. Catravas, and W. P. Leemans, Phys. Rev. E 65, 056505 (2002).\\[0pt] [2] A. G. R. Thomas, Physics of Plasmas 17, 056708 (2010); A. G. R. Thomas and K. Krushelnick, Physics of Plasmas 16, 103103 (2009).\\[0pt] [3] P. E. Masson-Laborde, et al., Phys. Plasmas 21, 123113 (2014).\\[0pt] [4] D. H. Whittum, et al., Phys. Rev. Lett. 67, 991 (1991); Y.Y. Lau, Phys. Rev. Lett. 63, 1141 (1989).   

Comparison of spectral Boltzmann and Fokker-Planck solvers for plasma relaxation

The Fokker-Planck operator is an approximation of the Boltzmann collision operator for charged particles resulting from the dominance of small angle interactions. However for many relevant plasmas the larger angle collisions contained in the full Boltzmann equation have a nontrivial effect on the relaxation rate to equilibrium. I will compare deterministic numerical results for the Boltzmann and Fokker-Planck operators to show this difference, as well as an analytical result relating the error between the two models.   

Advanced Fuels Reactor using Aneutronic Rodless Ultra Low Aspect Ratio Tokamak Hydrogenic Plasmas

The use of advanced fuels for fusion reactor is conventionally envisaged for field reversed configuration (FRC) devices. It is proposed here a preliminary study about the use of these fuels but on an aneutronic Rodless Ultra Low Aspect Ratio (RULART)[1] hydrogenic plasmas. The idea is to inject micro-size boron pellets vertically at the inboard side (HFS, where TF is very high and the tokamak electron temperature is relatively low because of profile), synchronised with a proton NBI pointed to this region. Therefore, p-B reactions should occur and alpha particles produced. These pellets will act as an edge-like disturbance only (cp. killer pellet, although the vertical HFS should make this less critical, since the unablated part should appear in the bottom of the device). The boron cloud will appear at midplance, possibly as a MARFE-look like. Scaling of the p-B reactions by varying the NBI energy should be compared with the predictions of nuclear physics. This could be an alternative to the FRC approach, without the difficulties of the optimization of the FRC low confinement time. Instead, a robust good tokamak confinement with high local HFS TF (enhanced due to the ultra low aspect ratio and low pitch angle) is used. The plasma central post makes the RULART concept attractive because of the proximity of NBI path and also because a fraction of born alphas will cross the plasma post and dragged into it in the direction of the central plasma post current, escaping vertically into a hole in the bias~plate and reaching the direct electricity~converter,~such as in the FRC concept. [1] Ribeiro C, SOFE-15, Austin, US, June 2015.   

From Spintronics to CFD/ContractForDifferences

Involve the CFD/Computational Fluid Dynamics \& HCCI/Homogeneous Charge Compression Ignition - Marcine Frackowiak, dissertation, 2009, for CFD/Contract For Differences accompanied by ``One Man's Crusade to Exonerate Hydrogen for Hindenburg Disaster'' of Addison BAIN, APS News, v. 9, n.7 (July 2000) concludes ``ignition of the blaze" are responsible to those May, 1937 Accidents. Spintronics their selves include active control \& manipulation of spin degree of freedom ever denotes: the nano-obelisk of scanning electron microscopy of galliumnitride/GaN nanostructures-Yong-Hon Cho, et.al:``Novel Photonic Device using core-shell nanostructures", SPIE-newsroom,10.1117/2.1201503.005864. Herewith commercial activated carbon/C can be imaged directly using abberation-corrected transmission electron microscopy[PJF Harris,et.al: ``Imaging the Atomic Structures of activated C", J.Phys.Condens.Matt, 20 (2008) in fig b \& c- images networks of hexagonal rings can be clearly be seen depicts equal etchings of 340 px Akhenaten, Nefertiti \& their childrens.   

Analysis of Tokamak Fusion Test Reactor (TFTR) Prototype of International Thermonuclear Experimental Reactor (ITER)$^{\ddag }$

TFTR \textit{produced world record of 10 million watts of controlled fusion power}$^{1}$ (CFP-1994) was summarized in \textit{Review}$^{1}$\textit{. We} present evidence$^{3}$ that: (1) TFTR input vs. output was 40 to 10 MW i.e. a power \underline {loss}. (2) Review claims no \underline {experimental} evidence for thermonuclear CFP production (only a calculation). (3) Ultra-high vacuum (UHV) required for $\tau_{E} \quad =$ 0.2 s is 10$^{-9}$ torr. TFTR had no UHV pumps, resulting in 10$^{-3}$ torr, restricting $\tau_{E}$ \textless 10$^{-6}$ s, \textless \textless thermalization time; 0.1 s., hence DT plasma did not occur\textbf{.} (4) Carbon ions were presented as D-T plasma. (5) Unknown neutron detector on unexplained neutron diamagnetic effect, measured ``fusion neutron power'' without particle energy identification, energy or coincidence. (6) 8 of 9 parameters claimed were inferred not measured. Quadratic test of TFTR data results$^{2}$ in \underline {zero thermonuclear fusion power contribution} to 10 MW: SFP $=$ (0 $\pm$ 1){\%}. $^{\ddag }$Submitted to \textit{Physics of Plasmas} $^{\dag }$Deceased \\[4pt] [1] McGuire K.M., et al.: Review of D-T results from TFTR, \textit{Phys. Plasmas} \underline {2}, 2176 (May, 1995)\\[0pt] [2] T. Hester, D.W. Scott, B.C. Maglich, Absence of Exp. Evi. Thermo. Power Production TFTR, http://world-scientific-education.net   

Too big to see: overlooked plasma-destroying reaction with cross section10$^{12}$ times that for fusion necessitates redesign of ITER*

Existence of \textit{charge transfer} collisions (CT) was overlooked in ITER design$^{1,2}$ although CT cross section$^{3}$, $\sigma_{CT}$ $\sim$ 10$^{9}$ b, is $\sim$ 10$^{12}$ times that for fusion, $\sigma_{DT}$ $\sim$ mb, at T $=$ 10 KeV. CT de-confines plasma by neutralizing ions. Since $\sigma_{CT} \quad =$ 100 $\sigma_{IO}$, ion $\tau_{CT}$ $\sim$ $\tau_{E} \quad =$ 3x10$^{-7}$ s \textless \textless thermalization time $\sim$ 0.1 s; \underline {plasma cannot form}. $\tau_{E}$ $\sim$ 1 s requires operating vacuum p $\sim$ 10$^{-9}$ torr, base 10$^{-11}$ torr. CT oversight brings 4 serious but corrigible errors: --Operating at T $=$ 10-30 KeV below Critical ion energy$^{4,5}$ E$_{c}$ $\sim$ 200 KeV, CT prevents plasma formation$^{6}$. Above E$_{c}$, ion dominates $\tau_{E} \quad =$ 24 s achieved$^{-8}$ with 700 KeV D$^{+}$.--No UHV system; base 10$^{-7}$ torr$^{2}$. Based on tenet that $\sigma_{CT}$/$\sigma _{io}$$\sim$ 10$^{-2}$, opposite to measured$^{3} \quad \sigma _{CT}$/ $\sigma_{io}$ $\sim$ 10$^{2}$, ionization \textit{by itself}, acts as UHV ion pump; data show it is compressor.--Neutral injection of 10$^{22}$ D/T s$^{-1}$ will result in pressure $\sim$ 1 torr, a ``poison.''--ITER goal n$\tau $$\sim$ 10$^{20}$ m$^{-3}$ s$^{-1}$ presented as Lawson$^{9}$ is ``1{\%} burn-up'' criterion; real n$\tau $$\sim$ 10$^{22}$ m$^{-3}$s$^{-1}$. *Preprint presented to Fusion Energy Sci. Committee, USDOE 11/11/14. $^{\dag }$Deceased (1) Nucl. Fusion \underline {49} 065012 (2009). (2)\textit{Pumping Systems for ITER}, 3/01 (2001). (3)Physics Scripta, 23, 143 (81). (4) Evid. Crit. Energy, www.world-scientific-education.net (5) Ibid Am. Phys. Soc. March Meeting 2015, Abstract T34.00004. (6) Exp. Evidence Absence Thermonuc. Fus. Power prod. In TFTR, www.world-scientific-education.net. (7) \textit{Phys. Rev. Lett.} \underline {54}, 769 (85). (8) NIM A 271 1-288 (88). (9) Proc. Phys. Soc. B70, 6, (57).   

Characteristics of a diffuse brush-shaped plasma plume produce by a dielectric barrier discharge at atmospheric pressure

Atmospheric pressure non-thermal plasmas generated by gas discharges have attracted much attention because chemically active species are abundant in these plasmas. They have enormous application potentials in various fields of science and technology. The scale is not desirable for the diffuse discharge generated by existing technologies, such as dielectric barrier discharge or plasma jet. The challenge that low-temperature plasma research encounters is how to generate large scale plasma at atmospheric pressure. With argon used as working gas, a barrier discharge device composed of two diverging wire electrodes is developed to generate a diffuse brush-shaped plasma plume outside a wedged gap. The parameter range for plume generation and its discharge characteristics are studied through electrical and optical methods. The spatial and temporal evolution is implemented by fast photography to investigate the formation mechanism of the plume. It is found that the large-scale plume is a superposition of micro-discharge filaments gliding along the argon flow, which operate in a glow discharge regime. Optical emission spectrum has been collected from the diffuse plume to investigate the excited electron temperature, the vibrational temperature and the gas temperature of the diffuse plume. Results indicate that the plasma is in non-equilibrium condition.   

Particle simulation of filamentary formation in dielectric barrier discharge.

Dielectric barrier discharge (DBD) is well known for its extensive industrial applications. Recently, new attention has been paid to DBD as a system of rich nonlinear dynamics to study the self-organized filamentary patterns. Though a number of experimental studies have been implemented, the involved physics is still not completely clear, partially due to the limitation of the available space and time-resolved diagnostics. Computer simulation has proven to be an effective tool to give insights into the discharge mechanism. So far, most simulations presented are based on fluid models. However, since the plasma is non-equilibrium in DBD where the particle velocities may deviate from the Maxwellian distribution, self-consistent kinetic simulations are required. In this paper, two successive filamentary discharges in DBD have been studied by use of two-dimensional particle-in-cell simulation with Monte Carlo collisions included (PIC-MCC). The formation of multiple filaments and the involved electric fields, electric potentials, plasma densities, and particle temperatures are presented. Results show that both of the surface charges and space charges play significant roles in the discharges. The total electric field in the gas gap has been completely reversed before the ac voltage hit zero, due to the accumulation of the surface charges, which triggers the next discharge. The space charges always exist between two successive discharges, which provides the `seed charges' for reignition of the filaments. This modeling has revealed significant details of the discharge behaviors, which greatly improved our understanding of DBD mechanisms.   

Continued Development of Python-Based Thomson Data Analysis and Associated Visualization Tool for NSTX-U

MultiPoint Thomson Scattering (MPTS) is an established, accurate method of finding the temperature, density, and pressure of a magnetically confined plasma. Two Nd:YAG (1064 nm) lasers are fired into the plasma with a effective frequency of 60 Hz, and the light is Doppler shifted by Thomson scattering. Polychromators on the NSTX-U midplane collect the scattered photons at various radii/scattering angles, and the avalanche photodiode voltages are saved to an MDSplus tree for later analysis. IDL code is then used to determine plasma temperature, pressure, and density from the captured polychromator measurements via Selden formulas.[1] Previous work[2] converted the single-processor IDL code into Python code, and prepared a new architecture for multiprocessing MPTS in parallel. However, that work was not completed to the generation of output data and curve fits that match with the previous IDL. This project refactored the Python code into a object-oriented architecture, and created a software test suite for the new architecture which allowed identification of the code which generated the difference in output. Another effort currently underway is to display the Thomson data in an intuitive, interactive format.   

Cycloid motions of aggregates in a dust plasma

Hypocycloid and epicycloid motions of aggregates consisted of one large and one small grains are experimentally observed in a rf dust plasma. The cycloid motions are regarded as combination of a primary circle and a secondary circle. Measurements with high spatiotemporal resolution show that the secondary circle is determined by the initial angle velocity of the dropped aggregate. The primary circle originates from the asymmetry of the aggregate. The small grain in the aggregate always leads the large one as they travelling, which results from the di?erence of the resonance frequency of the two grains. Comparison experiments with regular microspheres show that the cycloid motions are distinctive features of aggregates immersed in a plasma.   

Design point and scenario development for a compact Spherical Tokamak with Double Null Divertor

We present the design point of a high field spherical tokamak (R$=$45cm, BT\textgreater 2T, Ip$=$2MA, kappa$=$2.5) developed with the CORSICA equilibrium, stability and transport code. The tokamak equilibrium is determined as a series of fiducial states: after merging; limited; diverted and flat top with a transition to pedestal profiles and H-mode confinement. Vertical stability has been optimized by having two copper passive plates which unusually can be cooled to liquid nitrogen temperatures. Scenarios are developed for the compression, current ramp and flat-top phases. Cases where all of the heating energy goes to the: ions, electrons and a 50/50 split are examined, and power requirements are assessed to gain access to keV temperatures. We discuss implications for follow on devices including use of high temperature superconductors and a ST burning plasma experiment.   

Additive manufacture (3d printing) of plasma diagnostic components and assemblies for fusion experiments

Additive manufacturing (or 3D printing) is now becoming sufficiently accurate with a large range of materials for use in printing sensors needed universally in fusion energy research. Decreasing production cost and significantly lowering design time of energy subsystems would realize significant cost reduction for standard diagnostics commonly obtained through research grants. There is now a well-established set of plasma diagnostics, but these expensive since they are often highly complex and require customization, sometimes pace the project. Additive manufacturing (3D printing) is developing rapidly, including open source designs. Basic components can be printed for (in some cases) less than 1/100th costs of conventional manufacturing. We have examined the impact that AM can have on plasma diagnostic cost by taking 15 separate diagnostics through an engineering design using Conventional Manufacturing (CM) techniques to determine costs of components and labor costs associated with getting the diagnostic to work as intended. With that information in hand, we set about optimizing the design to exploit the benefits of AM.   

Thermionic plasma injection for the Lockheed Martin T4 Compact Fusion Reactor experiment

Lockheed Martin's Compact Fusion Reactor (CFR) concept relies on diamagnetic confinement in a magnetically encapsulated linear ring cusp geometry. Plasma injection into cusp field configurations requires careful deliberation. Previous work has shown that axial injection via a plasma gun is capable of achieving high-beta conditions in cusp configurations [Park, J., et al., Phys. Rev. X 5, 021024 (2015)]. We present a pulsed, high power thermionic plasma source and the associated magnetic field topology for plasma injection into the caulked-cusp magnetic field. The resulting plasma fueling and cross-field diffusion is discussed. \copyright 2015 Lockheed Martin Corporation. All Rights Reserved.   

X-Ray Diagnostics on the Lockheed Martin T4 Experiment

The Lockheed Martin T4 Experiment is a magnetically encapsulated linear ring cusp confinement device designed to study the physics relevant to the Compact Fusion Reactor program. The diagnostic suite includes a hard x-ray detector ($\sim$ 1 -- 100 keV) and a soft x-ray grazing incidence monochromator ($\sim$ 5 -- 1200 eV). X-ray emission spectra were used to identify plasma impurities. Specific emission lines were used to determine ion temperature via Doppler broadening and electron temperature via line intensity ratios. An overview of both x-ray systems and analysis of results from the 2015 experimental campaign will be presented.   

Preliminary density and temperature measurements in Lockheed Martin's magnetically encapsulated linear ring cusp confinement configuration

Lockheed Martin's T4 experiment confines deuterium plasma with a magnetically encapsulated linear ring cusp configuration. Electron-Cyclotron Resonance Heating (ECRH) is used to generate and heat the plasma. An initial set of commissioning experiments at low-beta were performed on the device, across a range of ECRH powers and neutral gas pressures. Langmuir probe measurements were taken to determine the density and electron temperature of the plasma at these conditions, and to examine fluctuations in these parameters. The internal structure of the plasma was investigated using radial location sweeps of the probe. A 95 GHz microwave interferometer was used to independently measure line-averaged density, and results were compared to the probe data.   

Magnetic diagnostics on the Lockheed Martin T4 Experiment

The Lockheed Martin T4 Experiment is a magnetically encapsulated linear ring cusp confinement device designed to study the physics relevant to the Compact Fusion Reactor program. As part of the diagnostics suite, an invasive three-axis magnetic probe and several flux loops have been constructed and installed. The probe was designed to reduce electrostatic pick-up by differentially amplifying two counter-wound coils for each axis. The flux loops are designed to detect plasma diamagnetism after accounting for the flux due to the background magnetic field. This mandates that the temporal evolution of the background field must be properly taken into account in order to discern the plasma response. To this end, both hardware and software techniques have been employed. Diagnostic designs and preliminary measurements will be presented.   

Passive Spectroscopy Measurements of Deuterium Plasmas in the Lockheed Martin T4 Experiment

The T4 experiment is a magnetically encapsulated linear ring cusp device being developed at Lockheed Martin for the purpose of plasma confinement. To study the deuterium plasmas in the T4 experiment a suite of diagnostics are being implemented. Passive spectroscopy is a powerful and well established plasma diagnostic technique. A passive spectroscopy diagnostic is non-invasive and experimentally easy to set-up: essentially requiring viewports with lines of sight to the region of interest in the plasma. Analysis of the radiative spectra can be challenging, but provides insight into plasma parameters such as plasma composition, density and temperature. In this work we discuss the visible spectrum spectroscopy diagnostics on the T4 experiment and present preliminary measurements.   

Effect of initial conditions and Mach number on the Richtmyer-Meshkov instability in ICF like conditions

The qualitative and quantitative effect of initial conditions (linear and non-linear) and high Mach number (1.3 and 1.45) is studied on the turbulent mixing induced by the Richtmyer-Meshkov instability in idealized ICF conditions. The Richtmyer-Meshkov instability seeds Rayleigh-taylor instabilities in ICF experiments and is one of the factors that contributes to reduced performance of ICF experiments. Its also found in collapsing cores of stars and supersonic combustion. We use the Stony Brook University code, FronTier, which is verified via a code comparison study against the AMR multiphysics code FLASH, and validated against vertical shock tube experiments done by the LANL Extreme Fluids Team. These simulations are designed as a step towards simulating more realistic ICF conditions and quantifying the detrimental effects of mixing on the yield.   

A generalized model of atomic processes in dense plasmas

A generalized model of atomic processes in plasmas, FLYCHK, has been developed over a decade to provide experimentalists fast and simple but reasonable predictions of atomic properties of plasmas. For a given plasma condition, it provides charge state distributions and spectroscopic properties, which have been extensively used for experimental design and data analysis and currently available through NIST web site. In recent years, highly transient and non-equilibrium plasmas have been created with X-ray free electron lasers (XFEL). As high intensity x-rays interact with matter, the inner-shell electrons are ionized and Auger electrons and photo electrons are generated. With time, electrons participate in the ionization processes and collisional ionization by these electrons dominates photoionization as electron density increases. To study highly complex XFEL produced plasmas, SCFLY, an extended version of FLYCHK code has been used. The code accepts the time-dependent history of x-ray energy and intensity to compute population distribution and ionization distribution self-consistently with electron temperature and density assuming an instantaneous equilibration. The model and its applications to XFEL experiments will be presented as well as its limitations.   

Simulating Magnetic Reconnection Experiment (MRX) with a Guide Field using Fluid Code, HiFi

Magnetic reconnection is a phenomenon that occurs in plasmas when magnetic field lines effectively ``break'' and reconnect resulting in a different topological configuration. In this process, energy that was once stored in the magnetic field is transfered into the thermal velocity of the particles, effectively heating the plasma. MRX at the Princeton Plasma Physics Laboratory creates the conditions under which reconnection can occur by initially ramping the current in two adjacent coils and then rapidly decreasing with and without a guide magnetic field along the reconnecting current. We simulate this experiment using a fluid code called HiFi, an implicit and adaptive high order spectral element modeling framework, and compare our results to experimental data from MRX. The purpose is to identify physics behind the observed reconnection process for the field line break and the resultant plasma heating.   

Influence of ion orbit width on onset threshold of neoclassical tearing modes

The onset threshold of neoclassical tearing modes with finite ion orbit width is studied. The evolution of neoclassical tearing modes including the effect of ion orbit is derived analytically. When ion orbit width is comparable to island width, the effect of ion orbit is significant. It would increase the island width needed to flatten pressure in the island, and reduce the amplitude of ion perturbed bootstrap current. It is found that ion orbit effect tends to increase the onset threshold $\beta_{\theta }^{onset} $ for a given seed island. It also would increase the lowest threshold $\beta_{\theta ,\min } $ and the corresponding marginal island width. It has an important implications for the onset of neoclassical tearing modes with comparable ion orbit width and island width in ITER.   

Study of an indirect-drive ignition capsule with the main pulse shape of decompression and recompression

Hydrodynamics in the low-foot (LF) implosion$^{\mathrm{\thinspace [1][2]\thinspace }}$during the National Ignition Campaign is highly nonlinearity, which results in significant amount of CH(Si) ablator material mixing into the hot spot and low-mode non-uniformity of the shell areal density. The high-foot (HF) implosion $^{\mathrm{[3]}}$after the NIC largely suppresses mediate- and high- mode hydrodynamic instabilities, in which neutron yields go up an order of magnitude compared to the LF implosion, but the hot spot pressure is still low and the hot spot shape goes bad when the peak power is increased for larger implosion velocity$^{\mathrm{[4][5]}}$. In our new ignition capsule design$^{\mathrm{[6]}}$, first, the HF prepulse similar to the HF implosion on NIF is adopted for resisting the CH(Si) ablator mix problem; second, the new main pulse shape of decompression and recompression (DR) is proposed to improve performance of the HF implosion on NIF. In this scheme of the DR, the secondary auxiliary shock (SAS) is produced during the late of the main pulse by the recompression pulse to raise the shell density for improving the hot spot pressure. The decompression pulse is used for reducing ablative pressure in order to relax the limit of the peak drive power for SAS production. The SAS colliding with the rebound shock from the center also improves the hot spot pressure and temperature, which is very useful to stabilize the hydrodynamic instabilities during the deceleration stage of implosion for the hot spot ignition. Decompressing the outer part of the ablator thickens the shell to lessen feed-through of perturbations from the ablative to inner interfaces. In this presentation, good 1D and 2D performance of implosion of the DR scheme is reported, especially reduced growth of perturbations at the interface between the hot spot and the main DT fuel. [1] J.Lindl, O. Landen, J. Edwards, E. moses, and NIC team, Phys. Plasmas 21,020501(2014). [2] M. J. Edwards, P. K. Patel, J. D. Lindl ea al, Phys. Plasmas 20, 070501. [3] O. A. Hurricane, D. A. Callahan, D. T. Casey et al, Nature (London) 506, 343(2014). [4] T. Doppner, D. A. Callahan, O. A. Hurricane et al, Phys. Rev. Lett 115, 055001(2015). [5] T. Ma, O. A. Hurricane, D. A. Callahan ea al, Phys. Rev. Lett 114, 145004(2015). [6] Wang Li-Feng, WU Jun-Feng, YE Wen-Hua, FAN Zheng-Feng, HE Xian-Tu, Design of an Indirect-Drive pulse shape for $\sim $1.6MJ inertial confinement fusion ignition capsules, CHIN. PHYS. LETT. 31(4), 045201(2014). ye\textunderscore wenhua@iapcm.ac.cn   

Gyrokinetic Study of L-H Transition with Profile Evolution

Recent simulations based on gyrokinetic toroidal code (GTC) and theory based on model eigen equation (H. S. Xie and Y. Xiao, arXiv:1503.04440) have found that the eigenstates of mirco-instabilities (trapped electron mode TEM or ion temperature gradient mode ITG) under strong and weak gradients are not the same. Under weak gradient, the most unstable mode is on the ground state, with conventional ballooning mode structure. When the gradient exceed a critical value, the most unstable mode jump to non-ground state. The mode structures of non-ground state are rich and unconventional, and thus can reduced the transport level, which can provide a explanation to the H-mode in the mirco-scale aspect. Nonlinear simulations (H. S. Xie, Y. Xiao and Z. Lin, 9th West Lake International Symposium on Plasma Simulation, May. 18-21, 2015, Hangzhou, China) verified this and have also found a turning point of the gradient. The turbulent transport coefficient would decrease with the gradient increasing when the gradient exceed a critical value. This provide a new route for the L to H transition without invoking shear flow or zonal flow. In the above works, the profiles are fixed. In this work, we will give some preliminary results on self-consistent simulations of L-H transition including the evolution of the radial plasma profiles.   

Ultrafast XRD of Heterogeneous Solid Hydrogen at LCLS

The high intensity and short pulse duration of the Linac Coherent Light Source (LCLS) at SLAC allows for single shot x-ray scattering studies from a jet of frozen hydrogen. The high repetition rate of LCLS allows us to build a detailed understanding of the cold structure of this jet. This provides a strong foundation for analysis of time resolved scattering data from the laser heated hydrogen jet. Angularly resolved x-ray diffraction at $5.5\mathrm{\ keV}$ is used to establish the structure of the cold $5\mathrm{\ \mu m}$ diameter solid hydrogen jet. The jet was composed of approximately $65\ \%\pm5\ \%$ HCP and $35\ \%\pm5\ \%$ FCC by volume with an average crystallite size on the order of hundreds of nanometers. Broadening in the angularly resolved spectrum provided strong evidence for anisotropic strain up to approximately $3\ \%$ in the HCP lattice. Finally, we found no evidence for orientational ordering of the crystal domains.   

Development of a low debris x-ray backlighter source via laser irradiation of a cluster gas medium

X-ray backlighter sources, typically based on laser irradiated solid targets, are of great importance for radiography of transient plasmas produced in high power laser-target interactions. Here we report on the development of an atomic cluster gas based x-ray source and assess its viability for x-ray point projection imaging motivated by the debris free, high repetition rate nature of laser-cluster gas interactions. The dependence on cluster size and atomic number of the anisotropic radial x-ray distribution, 100$\mu $m x-ray source size and multi-keV free electron temperatures produced by the interaction of a 1TW short pulse (500fs), high contrast laser system operating at 1054nm with high density Ar, Kr and Xe cluster gas media have been investigated. Previously, when propagated through a large (10mm) volume cluster gas medium at 10\textasciicircum 17 atoms/cc, \textgreater 95{\%} of the laser energy contained in a short pulse was absorbed launching a strong, radiative cylindrical blast wave. At 10\textasciicircum 19 atoms/cc, the absorption of the laser energy by the cluster gas medium was high (\textgreater 85{\%}). However, optical probing at 2$\omega $ showed that the laser energy was predominantly absorbed at the edge of the gas volume where the energy absorbed per unit length rapidly changed over a scale length of 2mm launching a radiative, elliptical blast wave.   

Simulation of low temperature atmospheric pressure corona discharge in helium

The main objective of this work was to construct a numerical model of corona discharge in helium at atmospheric pressure. Calculations were based on the two-dimensional hybrid model. Two different plasma-chemical models were considered. Models were built for RF corona and negative DC corona discharges. The system of equations was solved by the finite element method in the COMSOL Multiphysics. Main parameters of the discharge (the density of charged and excited particles and the electron temperature) and their dependence on the input parameters of the model (geometry, electrode voltage and power) were calculated. The calculations showed that the shape of the electron distribution near the electrode depends on the discharge power. The neutral gas heating data obtained will allow for the prediction of the temperature of the gases in atmospheric pressure helium plasma sources.   

Characteristics of the Betatron Radiation from the Direct-Laser Accelerated Electrons

The underlying scalings of the direct-laser accelerated electrons and the radiated photons are investigated. The dependence of the radiation properties on the plasma density and laser intensity is given analytically. It is shown that the electron dynamics and the emitted photons are strongly dependent on a self-similar parameter of $n_e/n_ca_0$. This controls the energy gain and the transverse betatron amplitude of the electrons, as well as the radiated photon number and photon energy. In addition, the total number of the photons is proportional to $a_0^2$ and the conversion efficiency of the photons from the accelerated electrons is proportional to $a_0^3$ for a fixed value of $n_e/n_ca_0$.   

Characteristics of the Betatron Radiation from the Direct-Laser Accelerated Electrons

The underlying scalings of the direct-laser accelerated electrons and the radiated photons are investigated. The dependence of the radiation properties on the plasma density and laser intensity is given analytically. It is shown that the electron dynamics and the emitted photons are strongly dependent on a self-similar parameter of $n_e/n_ca_0$. This controls the energy gain and the transverse betatron amplitude of the electrons, as well as the radiated photon number and photon energy. In addition, it is shown that the total number of the photons is proportional to $a_0^2$ and the conversion efficiency of the photons from the accelerated electrons is proportional to $a_0^3$ for a fixed value of $n_e/n_ca_0$. . .   

Statistical studies on two-point correlation length measurement for ion-scale turbulence.

To understand turbulence in a tokamak, it is essential to measure characteristics of turbulence such as radial, poloidal, and parallel correlation lengths, fluctuation level, and decorrelation time. Parallel correlation length at the hot core plasma has not been measured yet from any tokamaks, but in KSTAR there are two 2D diagnostics measuring density fluctuations on two poloidal cross-sections from different toroidal locations: BES (Beam Emission Spectroscopy) and MIR (Microwave Imaging Reflectometry). Therefore, we have potential to measure the parallel correlation length in KSTAR. As only two measurement points are available, we need to confirm that the correlation length measurement with the two points is reliable. Synthetic data satisfying stationary process and homogeneous state is generated. We find that the reliability of two-points correlation length measurement highly depends on the ratio of the separation distance between the two measurement points to the actual correlation length of the fluctuation. We confirm our quantitative results based on the synthetic data with the measured experimental data.   

Experimental investigation of impulsive magnetic reconnection induced by large amplitude electromagnetic fluctuations in the presence of a guide field

Impulsive enhancement of magnetic reconnection is one of the potential candidates to invoke various explosive events observed in nature and laboratory plasmas. In TS-3 laboratory experiment with a guide field of $B_{guide}/B_{rec}$ = 1--2.5, impulsive growth of the reconnection electric field was observed just behind the onset of large-amplitude electromagnetic fluctuations (f = 1.5--2 $f_{ci}$ and the amplitude was 0.1$B_{rec}$). It was found that both the fluctuation amplitude and the enhanced reconnection electric field during the fluctuation period showed positive correlation with the guide field. The normalized reconnection rate of about 0.03 before the onset of fluctuations was reasonably comparable with the classical reconnection rate of Sweet-Parker model. However, the reconnection rate rose up to 0.11 after the fluctuations onset, suggesting that the transition from slow steady reconnection to fast impulsive reconnection took place. Since the fluctuation amplitude was so large that the nonlinear terms of the induced electric field was not negligible. The electric field enhancement due to the nonlinear contribution from the observed fluctuation was 650 V/m, which showed good agreement with the experimentally observed electric field increment of about 800 V/m.   

Inverse Bremsstrahlung in Weakly Ionized Underdense Plasmas

Laser-induced air breakdown has attracted much attention in many applications such as laser ignition, laser breakdown spectroscopy. The breakdown and energy transfer are dominated by the properties of a weakly ionized plasma, which is characterized by a collision with the neutral gas. In order to predict threshold conditions of the laser breakdown precisely, it is necessary to understand the details of the laser energy absorption and ionization degree in the weakly ionized plasma. The coefficient of classical absorption were investigated for various degree of ionization.   

Effect of Radio Frequency Waves on Plasma Instabilities

The effect of Radio Frequency waves on low frequency plasma instabilities and turbulence is studied. It is shown that the ponderomotive force can stabilize or destabilize instabilities depending on the power deposition profile and no RF induced flow generation hypothesis is required. Its possible consequence on space and fusion plasma will be discussed.   

An investigation of short glow discharge in helium and the development of its applications for the analysis of gases.

DC glow discharge is the subject of constant attention, because it is widely used in practical applications. However, the main object of study remained positive column, the negative glow area has not been fully studied. The main objective of this work was to investigate the short glow discharge in helium. In this work current-voltage characteristics of short glow discharge and probe were obtained. Plasma parameters in the negative glow at different discharge currents and gas pressures were measured. It is shown that the temperature of the core group of electrons in negative glow is low and amounts to a few tenths electronvolts. The concentration of the main groups of electrons is typical for this discharge. Electron energy distribution function was calculated by the method of double numerical differentiation. Features in the form of peaks were found in the ion part of EEDF. These peaks correspond to the electrons which were born as a result of Penning ionization. These peaks may be used for identification of gas mixture.   

Hybrid modelling of open glow discharge with account of nonlocal ionization by fast electrons.

Cage and open discharges as well as hollow cathode devices are used for creating negative glow plasma. In order to perform numerical simulations of such kind of plasma object properly it is necessary to account for nonlocal excitation and ionization induced by fast electrons emitted from cathode and accelerated up to energies 10$^{2}$-10$^{3\, }$eV in cathode voltage drop. In this work a numerical study of open discharge in argon is presented. Simulations were performed using simple hybrid model that incorporates nonlocal ionization by fast electrons into ``extended'' fluid framework. Electron energy balance is written with account of electron heating due to coulomb interaction between ``bulks'' (with energies less than 1eV) and ``intermediate'' electrons (with energies up to inelastic collisions energy threshold). Distributions of main discharge parameters, such charged particle densities, electron temperature, electric potential, current-voltage characteristics of the discharge were obtained. Comparison with experimental results showed good agreement and suggests good applicability of the model.   

Generation of low-temperature air plasma for food processing

The project is aimed at developing a physical and technical foundation of generating plasma with low gas temperature at atmospheric pressure for food industry needs. As known, plasma has an antimicrobial effect on the numerous types of microorganisms, including those that cause food spoilage. In this work an original experimental setup has been developed for the treatment of different foods. It is based on initiating corona or dielectric-barrier discharge in a chamber filled with ambient air in combination with a certain helium admixture. The experimental setup provides various conditions of discharge generation (including discharge gap geometry, supply voltage, velocity of gas flow, content of helium admixture in air and working pressure) and allows for the measurement of the electrical discharge parameters. Some recommendations on choosing optimal conditions of discharge generation for experiments on plasma food processing are developed.   

Investigation of electron transport properties of two-temperature~Argon-Helium thermal plasma

In the present work, two cases of thermal plasma have been considered; the ground state plasma in which all the atoms and ions are assumed to be in the ground state and the excited state plasma in which atoms and ions are distributed over various possible excited states. Electron transport properties (electrical conductivity~and electron thermal conductivity) of argon-helium (25-75{\%}) thermal plasma mixture have been studied within the framework of Chapman-Enskog method in temperature range from 5000K to 40000K at pressure p$=$5 atm for both the ground state (GS) and excited state (ES) cases. The influence of electronic excitation and non-equilibrium parameter $\theta =$ T$_{\mathrm{e}}$/T$_{\mathrm{h}}$ has been examined on higher-order contribution to electrical conductivity and electron thermal conductivity. It is observed that higher-order contributions of these transport properties are affected by both the non-equilibrium parameter $\theta $ and inclusion of electronically excited states (EES).   

Linear waves in~the near-surface plasma layer of the illuminated part of the Moon

A dusty plasma system in the near-surface layer of the illuminated~part of the Moon is described. The system involves photoelectrons, solar-wind electrons and ions, neutrals, and charged dust grains. Linear waves in the plasma near the Moon's surface are discussed. It is noticed that the velocity distribution of photoelectrons can be represented as a superposition of two distribution functions characterized by different electron temperatures: lower energy electrons are knocked out of lunar regolith by photons with energies close to the work function of regolith, whereas higher energy electrons are knocked out by photons corresponding to the peak at 10.2 eV in the solar radiation spectrum. The anisotropy of the electron velocity distribution function is distorted due to the solar wind motion with respect to photoelectrons and dust grains, which leads to the development of instability and excitation of high-frequency oscillations with frequencies in the range of Langmuir and electromagnetic waves. In addition, dust acoustic waves can be excited. A possibility of the dust-acoustic instability development due to the interaction of Earth's magnetosphere tail plasma and the dusty plasma in the near-surface layer of the illuminated part of the Moon is discussed. This work was supported in part by the Presidium of the Russian Academy of Sciences (under Fundamental Research Program no. 9, ``Experimental and Theoretical Study of the Solar System and Stellar Planet Systems'') and the Russian Foundation for Basic Research (project no. 15-02-05627-a).   

Bayesian modeling of JET Li-BES for edge electron density profiles using Gaussian processes

A Bayesian model for the JET lithium beam emission spectroscopy (Li-BES) system has been developed to infer edge electron density profiles. The 26 spatial channels measure emission profiles with \textasciitilde 15 ms temporal resolution and \textasciitilde 1 cm spatial resolution. The lithium I (2p-2s) line radiation in an emission spectrum is calculated using a multi-state model, which expresses collisions between the neutral lithium beam atoms and the plasma particles as a set of differential equations. The emission spectrum is described in the model including photon and electronic noise, spectral line shapes, interference filter curves, and relative calibrations. This spectral modeling gets rid of the need of separate background measurements for calculating the intensity of the line radiation. Gaussian processes are applied to model both emission spectrum and edge electron density profile, and the electron temperature to calculate all the rate coefficients is obtained from the JET high resolution Thomson scattering (HRTS) system. The posterior distributions of the edge electron density profile are explored via the numerical technique and the Markov chain Monte Carlo (MCMC) samplings.   

Control of plasma properties in a short direct current glow discharge with active boundaries

To demonstrate controlling electron and metastable density ratio and electron temperature by applying negative voltages to the active (conducting) discharge wall in a low-pressure plasma with nonlocal electron energy distribution function, modeling has been performed in a short (without positive column) dc glow discharge with a cold cathode. The applied negative voltage can modify trapping the low-energy part of the energetic electrons emitted from the cathode sheath and arising from the atomic and molecular processes in the plasma within the device volume. Those electrons are responsible for heating the slow, thermal electrons, while production of slow electrons (ions) and metastable atoms is mostly due to energetic electrons with higher energies. Increasing electron temperature results in increasing decay rate of slow, thermal electrons, while decay rate of metastable atoms and production rates of slow electrons and metastable atoms practically are unchanged. The result is in variation of electron and metastable density ratio and electron temperature with variation of the wall negative voltage.   

Linear waves in~the near-surface plasma layer of the illuminated part of the Moon

A dusty plasma system in the near-surface layer of the illuminated~part of the Moon is described. The system involves photoelectrons, solar-wind electrons and ions, neutrals, and charged dust grains. Linear waves in the plasma near the Moon's surface are discussed. It is noticed that the velocity distribution of photoelectrons can be represented as a superposition of two distribution functions characterized by different electron temperatures. The anisotropy of the electron velocity distribution function is distorted due to the solar wind motion with respect to photoelectrons and dust grains, which leads to the development of instability and excitation of high-frequency oscillations. In addition, dust acoustic waves can be excited. A possibility of the dust-acoustic instability development due to the interaction of Earth's magnetosphere tail plasma and the dusty plasma in the near-surface layer of the illuminated part of the Moon is discussed. This work was supported in part by the Presidium of the Russian Academy of Sciences (under Fundamental Research Program no. 9, ``Experimental and Theoretical Study of the Solar System and Stellar Planet Systems'') and the Russian Foundation for Basic Research (project no. 15-02-05627-a).   

2D Resistive Magnetohydrodynamics Calculations with an Arbitrary Lagrange Eulerian Code

Single fluid resistive MHD is useful for modeling Z-pinch configurations in cylindrical geometry. One such example is thin walled liners for shock physics or HEDP experiments driven by capacitor banks such as the LANL's PHELIX or Sandia-Z. MHD is also useful for modeling high-explosive-driven flux compression generators (FCGs) and their high-current switches. The resistive MHD in our arbitrary Lagrange Eulerian (ALE) code operates in one and two dimensions in both Cartesian and cylindrical geometry. It is implemented as a time-step split operator, which consists of, ideal MHD connected to the explicit hydro momentum and energy equations and a second order mimetic discretization solver for implicit solution of the magnetic diffusion equation. In a staggered grid scheme, a single-component of cell-centered magnetic flux is conserved in the Lagrangian frame exactly, while magnetic forces are accumulated at the nodes. Total energy is conserved to round off. Total flux is conserved under the ALE relaxation and remap. The diffusion solver consistently computes Ohmic heating. Both Neumann and Dirichlet boundary conditions are available with coupling to external circuit models. Example calculations will be shown.   

Optimization of cold K-alpha emission using copper foams

Experiments were conducted at the Trident Laser Facility to increase the conversion efficiency of short-pulse, copper K-alpha x-ray backlighter sources. New target designs using copper foams are in development to investigate the role of underdense/near-critical density targets on the optimization of cold K-alpha emission. K-alpha emission was measured using Highly Ordered Pyrolytic Graphic (HOPG) and imaged with a toroidally bent quartz crystal to determine uniformity, spatial resolution and conversion efficiency of the new designs. Results from this experiment will help inform the development of short-pulse Cu K-alpha back-lighters on facilities like Omega, OmegaEP and the NIF, with a particular emphasis on creating advanced narrow-band backlighter sources capable of producing strong signal to noise with high x-ray fluxes.   

Longtime evolution of two-stream instability driven by an ion beam pulse propagating in a background plasma

The longitudinal two-stream instability of an ion beam pulse propagating through a background plasma is investigated using a collisionless one-dimensional kinetic simulation, in which a particle-in-cell (PIC) method is used for the ion beam and a direct Vlasov simulation is used for the background plasma. Previous kinetic simulations [E. Startsev et al. Nucl. Instrum. Methods. Phys. Res. A \textbf{733}, 80 (2014); E. Tokluoglu and I. Kaganovich, Physics of Plasmas \textbf{22}, 040701 (2015)] have shown that two-stream instability may play a deleterious role in compressing the ion beam. As the initial beam instability grows, the plasma electrons are accelerated by the plasma wave and can move faster than the ion beam. The stream of accelerated electrons moves ahead of the ion beam pulse and affects the background plasma, which in turn generates a secondary electron-beam two-stream instability. The numerical results show that the process reaches a quasi steady state with the modulations in electron and ion beam densities.   

Laser Induced Plasma Spectroscopy to Diagnose Impurities on a Tokamak Divertor

In order to monitor dust and impurity deposition on the plasma facing components (PFCs) of a fusion device, the Laser Induced Plasma Spectroscopy (LIPS) is considered. It is a powerful spectroscopic technique to measure emission lines from the excited atoms by means of the high power laser pulse, and could be applied to diagnose dust and impurities deposition on the PFCs. We have measured LIPS spectra for the inner-divertor tile from 2011 KSTAR campaign. Characteristic emission lines for several key elements, such as iron, chrome are identified. Using those lines, plasma conditions for various laser parameters and their temporal evolution are characterized. It will be also presented that the depth profiling for the deposited elements on a surface of graphite tile. *This work is supported by the NRF (No. 2013M1A7A1A02043864), National Research Foundation of Korea (No. 2013R1A1A1007084) and the TBP research project of GIST.   

Collisionless microtearing modes in large aspect ratio Tokamaks with weak reversed shear configurations

Gyrokinetic simulations have found Collisionless Microtearing Modes (MTM) to be linearly unstable in sharp temperature gradient regions of tokamaks, typically with high magnetic shear. The collisionless MTM is driven by the magnetic drift resonance of passing electrons, aided by the closeness of Mode Rational Surfaces (MRS) arising due to the high shear. Here, the role of global safety factor profile variation on the MTM instability and global mode structure is studied, in particular in weak reverse shear (WRS) configurations in large aspect ratio tokamaks. At lower shear profiles, multiple MTM branches are found with tearing parity as well as mixed parity. The linear growth rates of MTM is found to be weakened and linearly unstable modes are found whose global mode structures of $\tilde{\varphi}$ and $\tilde{A}_\parallel$ exhibit Mixed Parity. For the same equilibrium profiles and parameters, AITG instability is also studied and global mode structures are compared with MTM. The growth rate spectrum is found to extend to shorter/mesoscale wavelengths in WRS. Several other characteristics of MTMs and AITG are recovered in the WRS configuration, such as the dependency on free energy source and on plasma $\beta$.   

Simulation of cold atmospheric plasma component composition and particle densities in air

Recently discharges in air at atmospheric pressure were the subject of numerous studies. Of particular interest are the cold streams of air plasma, which contains large amounts of chemically active species. It is their action can be decisive in the interaction with living tissues. Therefore, in addition to its physical properties, it is important to know the component composition and particle densities. The goal was to develop a numerical model of atmospheric pressure glow microdischarge in air with the definition of the component composition of plasma. To achieve this goal the task was divided into two sub-tasks, in the first simulated microdischarge atmospheric pressure in air using a simplified set of plasma chemical reactions in order to obtain the basic characteristics of the discharge, which are the initial approximations in the problem of the calculation of the densities with detailed plasma chemistry, including 53 spices and over 600 chemical reactions. \section{As a result of the model was created, which can be adapted for calculating the component composition of plasma of various sources. Calculate the density of particles in the glow microdischarges and dynamics of their change in time.}   

Simulation of cold atmospheric plasma component composition and particle densities in air

Recently discharges in air at atmospheric pressure were the subject of numerous studies. Of particular interest are the cold streams of air plasma, which contains large amounts of chemically active species. It is their action can be decisive in the interaction with living tissues. Therefore, in addition to its physical properties, it is important to know the component composition and particle densities. The goal was to develop a numerical model of atmospheric pressure glow microdischarge in air with the definition of the component composition of plasma. To achieve this goal the task was divided into two sub-tasks, in the first simulated microdischarge atmospheric pressure in air using a simplified set of plasma chemical reactions in order to obtain the basic characteristics of the discharge, which are the initial approximations in the problem of the calculation of the densities with detailed plasma chemistry, including 53 spices and over 600 chemical reactions. As a result of the model was created, which can be adapted for calculating the component composition of plasma of various sources. Calculate the density of particles in the glow microdischarges and dynamics of their change in time.   

Bright half-cycle optical radiation from relativistic wavebreaking

Wavebreaking injection of electrons into relativistic plasma wakes generated in near-critical density hydrogen plasmas by sub-terawatt laser pulses is observed to generate an extremely energetic and ultra-broadband radiation flash. The flash is coherent, with a bandwidth of $\Delta\lambda/\lambda\sim 0.7$ consistent with half-cycle optical emission of duration $\sim$ 1 fs from violent unidirectional acceleration of electrons to light speed from rest over a distance much less than the radiated wavelength. We studied the temporal duration and coherence of the flash by interfering it in the frequency domain with a well-characterized Xe supercontinuum pulse. Fringes across the full flash spectrum were observed with high visibility, and the extracted flash spectral phase supports it being a nearly transform-limited pulse. To our knowledge, this is the first evidence of bright half-cycle optical emission.   

Enhanced ion beam energy by relativistic transparency in laser-driven shock ion acceleration

We investigated the effects of relativistic transparency (RT) on electrostatic shock ion acceleration. Penetrating portion of the laser pulse directly heats up the electrons to a very high temperature in backside of the target, resulting in a condition of high shock velocity. The reflected portion of the pulse can yield a fast hole boring and density compression in near-critical density plasma to satisfy the electrostatic shock condition; 1.5 \textless M \textless 3.7. The high speed electrostatic shock reflects upstream ions up to velocity \textasciitilde 2v$_{sh}$. In 1D PIC simulation, we have clearly observed RT-based shock acceleration which generates significantly higher ion beam energy in comparison to that in a purely opaque plasma. In multi-dimensional systems, various instabilities should be considered such as Weibel-like instability, which causes filamentation during the laser penetration. From series of comparisons of linearly polarized and circularly polarized pulses for the RT-based shock, we observed the circularly polarized pulse is usually more advantageous in reducing the instability, possibly leading to better RT-based shock acceleration.   

Is turbulence indeed reduced in the tokamak edge pedestal? Mysteries of pedestal poloidal asymmetries revealed

It has been suggested that the L-H transition involves the reduction of turbulence by sheared radial electric fields. For H-mode pedestals, neoclassical collisional theory may thus be expected to properly treat low order phenomena, such as flows. However, Alcator H-mode edge pedestals exhibit significantly stronger poloidal asymmetry than predicted by the most comprehensive neoclassical models developed to date. We propose a novel self-consistent neoclassical theoretical model that allows us to explain these poloidal asymmetries in boron temperature and density, and hence potential. First, impurity temperature asymmetries can be driven by inertial effects, which are significant when impurities are allowed to reach sonic speeds. Second, a much stronger impurity density in-out asymmetry than given by magnetic field variation can be introduced by the poloidally varying impurity diamagnetic drift. This asymmetry is achieved by allowing the diamagnetic drift contribution to be comparable to the poloidal and toroidal flows used to measure the radial electric field. In conclusion, we provide a more realistic predictive model for pedestal observations without the need to invoke anomalous transport.   

UEDGE modeling of divertor geometry effects in NSTX

We report efforts toward the modeling of divertor geometry effects using the fluid code UEDGE and NSTX experimental equilibria with different X-point heights. A variation of the geometry generates a competition between the poloidal magnetic flux expansion, which reduces the peak of the deposited heat flux and homogenizes its profile at divertor plates, and the proximity of the X-point to the divertor plates, which decreases the connection length and increases the peak heat flux. Our simulations use fixed fraction of carbon impurity, poloidally and radially constant transport coefficients, and high recycling boundary conditions, with a scan of density and pressure boundary conditions, and impurity fraction. Our simulations support the experimental observation that the poloidal flux expansion dominates the deposit heat flux over the parallel connection length effect. In opposite to experimental observation, detachment seems independent to the elevation. Improvement of the model is required.   

MHD simulations of magnetized laser-plasma interaction for laboratory astrophysics

Laser-driven plasmas coupled with externally applied strong, steady-state, magnetic fields have applications that range from ICF to astrophysical studies of jet collimation, accretion shock dynamics in young stars and streaming instabilities in space plasmas. We have recently included the modelling of laser energy deposition in our three-dimensional, resistive two-temperature MHD code GORGON. The model assumes linear inverse-bremsstrahlung absorption and the laser propagation is done in the geometrical optics approximation. We present full scale numerical simulations of actual experiments performed on the ELFIE installation at LULI, including plasma generated from single and multiple laser plasmas embedded in a magnetic field of strength up to 20 T, and experiments and astrophysical simulations that have shown the viability of poloidal magnetic fields to directly result in the collimation of outflows and the formation of jets in astrophysical accreting systems, such as in young stellar objects.   

Time-resolved X-ray Absorption Spectroscopy for Electron Transport Study in Warm Dense Gold

The warm dense Matter represents states of which the temperature is comparable to Fermi energy and ions are strongly coupled. One of the experimental techniques to create such state in the laboratory condition is the isochoric heating of thin metal foil with femtosecond laser pulses. This concept largely relies on the ballistic transport of electrons near the Fermi-level, which were mainly studied for the metals in ambient conditions. However, they were barely investigated in warm dense conditions. We present a time-resolved x-ray absorption spectroscopy measured for the Au/Cu dual layered sample. The front Au layer was isochorically heated with a femtosecond laser pulse, and the x-ray absorption changes around L-edge of Cu, which was attached on the backside of Au, was measured with a picosecond resolution. Time delays between the heating of the `front surface' of Au layer and the alternation of x-ray spectrum of Cu attached on the `rear surface' of Au indicate the energetic electron transport mechanism through Au in the warm dense conditions.   

Characterization of plasma formation and outflow emission from different wire-based z-pinch experiments driven at the 350kA, 1kA/ns Llampudken pulsed power driver.

We present results on tungsten and aluminium wire-based z-pinch plasma experiments driven by the 350kA, 1kA/ns Llampudken generator at P Universidad Catolica de Chile. Our experiments are concentrated in the formation and subsequent emission of plasma from two different configurations: conical arrays and modified cylindrical arrays using different wire diameters within the load. The former produce collimated jet-like outflows by the zippering effect at the axis of the conical array, whereas the latter produce emission of an unstructured dense plasma object by the temporal variations on the global magnetic field topology of the cylindrical array. We present measurements of the ablation process in both configurations and the main features of the outflows obtained, such as plasma densities and propagation velocities. It is found that an appropriate mass per unit length in the load is particularly important for producing outflows from modified cylindrical arrays, and that high pressure background gas embedding the load hampers the emission of plasma outflows in conical arrays. In addition, the analysis of the dimensionless parameters that characterize each outflow will be presented.