Bulletin of the American Physical Society
55th Annual Meeting of the APS Division of Plasma Physics
Volume 58, Number 16
Monday–Friday, November 11–15, 2013; Denver, Colorado
Session BP8: Poster Session I: Turbulence, Tokamak, Z-Pinch, DIII-D I |
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Room: Plaza ABC |
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BP8.00001: TURBULENCE AND TRANSPORT |
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BP8.00002: Area preserving map models of gyro-averaged ExB chaotic transport J. Fonseca, D. del-Castillo-Negrete Area preserving maps have been extensively used to model 2-dimensional chaotic transport in plasmas. Here we focus on drift-wave maps describing chaotic transport in ${\bf E}\times {\bf B}$ zonal flows perturbed by electrostatic drift waves. Going beyond previous studies, we include finite Larmor radius (FLR) effects by gyro-averaging the corresponding Hamiltonian of the map. In the limit of zero Larmor radius, the gyro-averaged map reduces to the standard Chirikov map in the case of monotonic ${\bf E}\times {\bf B}$ shear flows, and to the standard non-twist map in the case of non-monotonic ${\bf E}\times {\bf B}$ shear flows. Like in the case of continuous ${\bf E}\times {\bf B}$ drift wave models,\footnote{ D. de-Castillo-Negrete and J.J. Martinell, Commun. Nonlinear. Sci. Numer. Sim. {\bf 17}, 2031 (2012); J.J. Martinell and D. de-Castillo-Negrete, Phys. of Plasmas {\bf 20}, 022303 (2013).} we show that in the gyro-averaged maps, FLR effects lead to chaos suppression, bifurcation of the shearless curve, and a complex phase space topology. Dynamical systems methods are used to quantify the dependence on the Larmor radius of the threshold for the destruction of transport barriers, and the transport properties of an ensemble of test particles with a Maxwellian distribution [Preview Abstract] |
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BP8.00003: Reconnection and transport in a two-frequency nontwist map model of a reversed magnetic shear tokamak Alexander Wurm The magnetic field line structure of reversed magnetic shear tokamaks has been modeled by an area-preserving nontwist map that includes non-integrable perturbations from an ergodic magnetic limiter [1]. An expansion around the equilibrium shearless curve (corresponding to the main transport barrier in the model) showed that the map is locally equivalent to the standard nontwist map with an additional perturbation due to the limiter [2]. Here I report on recent studies of separatrix reconnection, a global bifurcation that changes the phase space topology in the vicinity of the central barrier, and its consequences for global transport.\\[4pt] [1] K. Ullmann and I.L. Caldas, Chaos, Solitons and Fractals, {\bf 11}, 2129 (2000).\\[0pt] [2] J.S.E. Portela, I.L. Caldas, R.L. Viana, and P.J. Morrison, Internat. J. Bifur. Chaos Appl. Sci. Engrg. {\bf 17}, 1589 (2007). [Preview Abstract] |
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BP8.00004: An Universal Mechanism of Saturation of ITG/ETG Modes via Coupling to Ion Acoustic Modes Vladimir Sokolov, Amiya K. Sen New experimental results in the Columbia Linear Machine indicate that both Ion Temperature Gradient (ITG) and Electron Temperature Gradient (ETG) modes are nonlinearly saturated via coupling to ion acoustic modes. The 3-wave coupling of two high frequency ITG or ETG mode radial harmonics (at $ \sim 140kHz$ or $\sim 2.4MHz $ respectively) and one low frequency ion acoustic mode (at $ \sim 10kHz \backslash \sim 40kHz $ ) is validated via bi-coherence studies. Direct measurements of axial and azimuthal wave numbers of the low frequency mode prove that it is the ion acoustic mode. A novel feedback diagnostic also experimentally verifies this scenario. The 3-wave coupling model (two radial harmonics of ITG or ETG and one ion acoustic mode) yielded a theoretical saturation level of ITG $ \backslash $ ETG mode $ \sim 3 \% \backslash \sim 7 \% $, which roughly agrees with experiments. This mechanism may be valid for any drift wave with the radial harmonics structure due to profile variation of $ \omega_T^\star $. This research was supported by U.S. Department of Energy Grant No. DE-FG02-98ER-54464. [Preview Abstract] |
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BP8.00005: Whistler turbulence inverse cascade: Three-dimensional particle-in-cell simulations S. Peter Gary, R. Scott Hughes, Joseph Wang, Ouliang Chang Three-dimensional particle-in-cell (PIC) simulations of whistler turbulence have been carried out in a magnetized, homogeneous, collisionless plasma of initial $\beta_e =$ 0.10. The simulations begin with anisotropic bi-Maxwellian electron velocity distributions with $T_{\perp e}/T_{\parallel e} >$ 1, leading to the growth of the whistler anisotropy instability. The simulations follow the temporal evolution of the field fluctuations as they grow and saturate with largest amplitudes at $kbzero$ and $k_{\parallel} c/\omega_{pe} \simeq$ 1.0. The counter-propagating enhanced fluctuations drive an inverse cascade to longer wavelengths at $k_{\parallel} c/\omega_{pe} <<$ 1 with $k_{\perp} > k_{\parallel}$. Computations have been done at various values of the electron electron temperature anisotropy, and physical interpretations for the results of these simulations will be provided. [Preview Abstract] |
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BP8.00006: Linear non-normality as the cause of nonlinear instability in LAPD Brett Friedman, Troy Carter, Maxim Umansky A BOUT$++$ simulation using a Braginskii fluid model reproduces drift-wave turbulence in LAPD with high qualitative and quantitative agreement. The turbulent fluctuations in the simulation sustain themselves through a nonlinear instability mechanism that injects energy into k$_{\mathrm{\vert \vert }}=$0 fluctuations despite the fact that all of the linear eigenmodes at k$_{\mathrm{\vert \vert }}=$0 are stable [1]. The reason for this is the high non-orthogonality of the eigenmodes caused by the non-normality of the linear operator, which is common in fluid and plasma models that contain equilibrium gradients [2]. While individual stable eigenmodes must decay when acted upon by their linear operator, the sum of the eigenmodes may grow transiently with initial algebraic time dependence. This transient growth can inject energy into the system, and the nonlinearities can remix the eigenmode amplitudes to self-sustain the growth. Such a mechanism also acts in subcritical neutral fluid turbulence, and the self-sustainment process is quite similar [3], indicating the universality of this nonlinear instability.\\[4pt] [1] Friedman et al., Phys. Plasmas, 19, 2012.\\[0pt] [2] Camargo et al., Phys. Rev. E, 58 (1998).\\[0pt] [3] Trefethen et al., Science, 261 (1993). [Preview Abstract] |
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BP8.00007: Effects of Electrode Biasing and Sheared Magnetic Field on Edge Fluctuations in a Linear Plasma Device M. Gilmore, T.R. Hayes, J. Plank A study of the effects of electrode biasing and magnetic field strength, B, and topology on edge fluctuations is being conducted in the linear HelCat (Helicon-Cathode) device. Two types of electrodes have been utilized - a set of concentric rings that terminate the plasma, and a semitransparent grid near the source. It is found that drift fluctuations can be reduced, or even fully suppressed, by biasing either electrode with respect to the wall, whereas biasing between the rings {\&} grid to drive parallel current has no effect. The dynamics of fluctuations transition non-monotonically from coherent at low B to turbulent at high B, with some fields showing no fluctuations, while others show clear evidence of chaos. The bias voltage required to affect the dynamics of the fluctuations, including full suppression, also varies non-monotonically with B. High ($\sim$ 10--15xTe) grid bias is found to cause $\sim$ 100{\%} density fluctuations across the entire plasma (except in the source region) on a time scale $\sim$ 10L/Cs, which may be due to a bistable potential profile in the presence of an electron sheath. Additionally, a single turn coil is being installed on axis to generate magnetic shear. Preliminary results on the effects of shear source operation and on fluctuation dynamics will be presented. [Preview Abstract] |
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BP8.00008: Turbulence scaling study in an MHD wind tunnel on the Swarthmore Spheromak Experiment D.A. Schaffner, A. Wan, J. Owusu-Boateng, M.R. Brown, V.S. Lukin The turbulence of colliding spheromaks are explored in the MHD wind tunnel on the SSX. Fully ionized hydrogen plasma is produced by two plasma guns on opposite sides of a 1m by 15cm copper cylinder. Modification of B-field, $T_{i}$ and $\beta$ are made through stuffing flux variation of the plasma guns. Presented here are turbulent $f$-/$k$-spectra and correlation times/lengths of B-field fluctuations as measured by a 16 channel B-dot radial probe array at the chamber midplane. Power-law fits to spectra show scaling that is robust to changes in stuffing flux; fits are on the order of $f^{-3}$ and $k^{-2.1}$ for all flux variations. Dissipation range modification of the spectra is observed; changes to the $f$-spectra slopes occur around $f=f_{ci}$ while changes in $k$-spectra slopes appear around $\sim 5\rho_i$. Dissipation range fits are made with an exponentially modified power-law model [Terry et al, PoP 2012]. Fluctuations in axial velocity are made using a Mach probe. Both B-field and velocity fluctuations persist on the same timescale in these experiments. Mach velocity $f$-spectra show power-laws similar to that for B-field. Comparison of spectra from MHD and Hall MHD simulations of SSX performed within the HiFi modeling framework are made to the experimental results. [Preview Abstract] |
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BP8.00009: Reconnection- driven MHD turbulence on the SSX plasma wind tunnel Michael Brown, David Schaffner, Adrian Wan, Jeffrey Owusu-Boateng High velocity merging experiments in the SSX plasma wind tunnel configuration generate high Reynolds number ($R_M \sim 1000$), high beta ($\beta \sim 0.5$), MHD turbulence. The turbulent plasma is fully ionized and fully magnetized ($\rho_i = 2~mm \ll R = 8~cm$). Typical merged plasma parameters are $T_i = 50~eV, T_e= 10~eV, n_e = 10^{21}~m^{-3}, B = 0.5~T$. Magnetic structure and fluctuations are measured with a 16 channel high-resolution probe array ($4~mm$ spatial resolution, $30~MHz$ bandwidth). The turbulent MHD plasma is generated by multiple reconnection events and persists for many Alfv\'en times. The goal of this research is to study the universality of statistical measures of MHD turbulence. Reconnection-generated MHD turbulence in SSX shows a power-law spectrum and correlation function similar to that observed in the solar wind. Future plans include launching the turbulent plasma in a gas-filled expansion volume and imaging the resulting turbulence with a high-speed Xybion camera. [Preview Abstract] |
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BP8.00010: Lattice Boltzmann Representations of MHD Turbulence George Vahala, Linda Vahala, Min Soe, Christopher Flint Lattice Botlzmann algorithms are an ideally parallelized method for the solutions of macroscopic nonlinear equations of physics -- like resistive MHD. In its simplest LB representation one introduces a scalar distribution for the density-velocity fields and a vector distribution for the magnetic field. An important feature is that gradients of certain macroscopic fields can be represented by local moments of the mesoscopic distribution functions. In particular, div B $=$ 0 can be exactly enforced to machine accuracy, without any divergence cleaning. One of the problems facing the explicit LB code is numerical instabilities. Methods to permit strong turbulence simulations include: (a) moving from a single BGK to multiple collisional relaxation, (b) quasi-equilibria and central moment enhanced LB representations. The LB turbulence modeling of Ansumali et. al. to Navier-Stokes turbulence will be extended to MHD in which in its noted that filtering and Chapman-Enskog limits do not commute. In the NS-case, it leads to unique Samgorinsky closure scheme, with definite filter width. [Preview Abstract] |
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BP8.00011: Energy partitioning between damped modes in gyrokinetic turbulence K.D. Makwana, P.W. Terry, M.J. Pueschel Damped modes are stable roots of the plasma dispersion relation. Gyrokinetic simulations have tens of thousands of damped modes spanning the non-periodic phase space dimensions. It has already been shown that these modes are excited nonlinearly to finite amplitude and play an important role in the saturation of turbulence. We take a closer look at the partitioning of energy between these modes. Both proper orthogonal decomposition modes and linear eigenmodes are utilized. As the damping rate increases, the modes develop fine scale structure, and after some threshold they become unresolved. A metric is devised to identify the well-resolved modes. The energy dissipation and amplitude attenuation rates of damped modes are calculated. They show a systematic scaling with mode number (or damping rate) in the range of resolved modes. This indicates a strong dependence of energy partitioning on damping rate. The effects of resolution and collisionality on this scaling are investigated. We also find that the unstable mode transfers energy to all the damped modes simultaneously, in parallel, leading to a nonlocal transfer process in phase space. It is hoped that a simplified theory of damped modes in gyrokinetics can emerge out of these studies. [Preview Abstract] |
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BP8.00012: The observations of Low Frequency Zonal Flow in electrode biasing experiments on J-TEXT tokamak H.G. Shen, D.F. Kong, H.L. Zhao, J. Wu, T. Lan, W.D. Liu, C.X. Yu, Y. Sun, H. Liu, Z.P. Chen, G. Zhuang The long-distance correlations features of potential and density fluctuations during electrode biasing (EB) have been investigated using Langmuir probe arrays in the edge of J-TEXT tokamak. During the positive edge EB, both floating potential and density fluctuations in the high frequency ambient turbulence (AT) region are suppressed and radial particle flux is decreased. But no obvious change occurs during the negative edge EB. In the positive EB cases, toroidal and poloidal long-distance correlations of floating potentials increase in the low frequency regions of f\textless 3kHz and no distinct long-distance correlations is found in density fluctuations. It shows that this low frequency long-distance correlation mode is low frequency zonal flow (LFZF). In the meantime, strong E$_{\mathrm{r}}$xB shearing is observed when applying a positive EB. The results also suggests that the LFZF may be induced by AT and then regulate the AT amplitude. [Preview Abstract] |
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BP8.00013: Investigating the Interaction Between Magnetohydrodynamic Instabilities and Microturbulence S.D. James, C. Holland, O. Izacard, D.P. Brennan The effects of microturbulence on the evolution of magnetohydrodynamic (MHD) instabilities are known to be important. In turn, the MHD instabilities themselves can influence the dynamics of the turbulent fields. Microturbulence involves very small spatial and temporal scales while the global evolution of MHD instabilities involves spatial and temporal scales several orders of magnitude larger. Accurately capturing these discrepancies is a challenging computational problem. We present results for a 3-field model, which self-consistently couples turbulent density and vorticity fluctuations to magnetic flux via Ohm's law. We have developed new code, TURBO, to capture the evolution of a magnetic island in an unstable equilibrium and calculate resistive and viscous effects due to the turbulence. Comparisons with analytic approximations for a turbulent resistivity and viscosity are also presented. We discuss our approach for extending this work to a 5-field model, which includes the ion temperature gradient (ITG) mode. [Preview Abstract] |
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BP8.00014: Observation of intermittency with varying toroidal magnetic field in a simple toroidal plasma Shekar Thatipamula, Surabhi Jaiswal, Umesh Kumar, Rajaraman Ganesh, Yogesh Saxena, Raju Daniel In a simple toroidal plasma, self-consistent poloidal flow generation with varying toroidal magnetic field is observed. The toroidal magnetic field is varied in strength and topology. In our previous work, a rapid transition from coherent to turbulent fluctuations in plasma parameters was observed on varying toroidal magnetic field strength from $220\hspace{0.1cm}G$ to $440\hspace{0.1cm}G$. In the present work, the toroidal magnetic field is varied in strength, topology, and the statistical properties of fluctuations are investigated [Carreras et al, Phys. Plasmas 3, 2664 (1996)]. The successive variation in toroidal magnetic field strength around $220\hspace{0.1cm}G$ is limited to a low magnitude, typically $45\hspace{0.1cm}G$, to study the transition in intermittency carefully. Further, the external vertical magnetic field is varied with toroidal magnetic field fixed at $220\hspace{0.1cm}G$ and transition in fluctuations is investigated. A comparison of probability distribution functions and deviation from Gaussianity with varying toroidal magnetic field strength and topology is made and the results will be presented. [Preview Abstract] |
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BP8.00015: Magnetic field generation by non-Gaussian, non-random turbulent motion Raul Sanchez, David E. Newman It is well known that a turbulent velocity field generates perturbations of the electric current and magnetic field that, under certain conditions, may generate an average,large-scale magnetic field. Such generation process is of great importance to account for the generation of large-scale magnetic fields in stars, planetary and laboratory plasmas. Traditionally, one attacks this generation process theoretically by assuming a random velocity field with near-Gaussian fluctuations. This simplifying ansatz allows to express the effective electromotive force appearing in Faraday's law in terms of a piece that is proportional to the large-scale magnetic field itself (the so-called $\alpha$-term), and a second one that is proportional to its curl (the $\beta$ term), if certain conditions regarding the symmetry of the system are met. Physically, the $\alpha$-term represents a measure of the mean helicity of the turbulent flow. The $\beta$-term, an enhanced magnetic diffusivity. In this contribution, we depart form this traditional view and explore instead the consequences of considering Levy-distributed, Lagrangianly-correlated velocity fields, that have been currently identified as of relevance in regimes of near-marginal turbulence or in the presence of strong, stable sheared flows [Preview Abstract] |
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BP8.00016: Analyses of core heat transport in plasmas with different toroidal rotation profiles in JT-60U Emi Narita, Mitsuru Honda, Nobuhiko Hayashi, Hajime Urano, Shunsuke Ide, Takeshi Fukuda It has been reported that in H-mode plasmas, toroidal rotation in the co direction with respect to the plasma current is more favorable for energy confinement than that in the counter direction. Effects of toroidal rotation on core temperature profiles have been pointed out, whereas the improved confinement has been found to be due to an increase in the pedestal temperature with co-toroidal rotation and profile resilience. In JT-60U, roles of toroidal rotation have been studied using neutral beam injection changes [1]. In this study, core heat transport of these plasmas with different toroidal rotation profiles is investigated with several transport models implemented in the transport code TOPICS [2]. These transport models give the anomalous heat diffusivity and are tested against conventional H-mode plasmas in JT-60U. The calculations are performed with the $E\times B$ shear effect. The relationship between heat transport and toroidal rotation is examined with a flux-tube gyrokinetic code, which we will present in the paper.\\[4pt] [1] H. Urano {\it{et al.}}, Nucl. Fusion \textbf{48}, 085007 (2008).\\[0pt] [2] N. Hayashi and JT-60 Team, Phys. Plasmas \textbf{17}, 056112 (2010). [Preview Abstract] |
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BP8.00017: Regulation of ETG turbulence by TEM driven zonal flows Yuuichi Asahi, Akihiro Ishizawa, Tomohiko Watanabe, Hiroaki Tsutsui, Shunji Tsuji-Iio Anomalous heat transport driven by electron temperature gradient (ETG) turbulence is investigated by means of gyrokinetic simulations. It is found that the ETG turbulence can be suppressed by zonal flows driven by trapped electron modes (TEMs). The TEMs appear in a statistically steady state of ETG turbulence and generate zonal flows, while its growth rate is much smaller than those of ETGs. The TEM-driven zonal flows with lower radial wave numbers are more strongly generated than those driven by ETG modes, because of the higher zonal flow response to a density source term. An ExB shearing rate of the TEM-driven zonal flows is strong enough to suppress the long-wavelength ETG modes which make the main contribution to the turbulent transport. [Preview Abstract] |
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BP8.00018: Nonlinear cross-field coupling on the route to broadband turbulence Christian Brandt, Saikat C. Thakur, Lang Cui, Jordan J. Gosselin, Jose Negrete Jr., Chris Holland, George R. Tynan In the linear magnetized plasma device CSDX (Controlled Shear De-correlation eXperiment) drift interchange modes are studied coexisting on top of a weak turbulence driven azimuthally symmetric, radially sheared plasma flow. In helicon discharges (helicon antenna diameter $15{\rm\, cm}$) with increasing magnetic field ($B\leq 0.24{\rm\, T}$) the system can be driven to fully developed broadband turbulence. Fast imaging using a refractive telescope setup is applied to study the dynamics in the azimuthal-radial cross-section. The image data is supported by Langmuir probe measurements. In the present study we examine the development of nonlinear transfer as the fully developed turbulence emerges. Nonlinear cross-field coupling between eigenmodes at different radial positions is investigated using Fourier decomposition of azimuthal eigenmodes. The coupling strength between waves at different radial positions is inferred to radial profiles and cross-field transport between adjacent magnetic flux surfaces. Nonlinear effects like synchronization, phase slippages, phase pulling and periodic pulling are observed. The effects of mode coupling and the stability of modes is compared to the dynamics of a coupled chain of Kuramoto oscillators. [Preview Abstract] |
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BP8.00019: Experiment to measure fast ion transport by magnetic fluctuations Adam Preiwisch, William Heidbrink, Heinz Boehmer, Roger McWilliams, Troy Carter, Walter Gekelman, Shreekrishna Tripathi, Bart Van Compernolle, Steve Vincena Fast ion transport in a linear magnetic field is studied at the upgraded Large Plasma Device. Recent developments allow for the generation of turbulent magnetic flux ropes, produced by a hot LaB6 cathode situated in the main chamber.$^{\mathrm{1}}$ A large-gyroradius, energetic lithium ion beam (300 $\le $ E$_{\mathrm{fast}}$ / T$_{\mathrm{i}} \quad \le $ 1000) is passed through the turbulent region and collected by a collimated analyzer downstream, yielding a detailed plane profile of the fast ion distribution.$^{\mathrm{2}}$ Magnetic fluctuations, density, and temperature profiles are also obtained via probes. Enhanced fast-ion transport is clearly observed in the form of beam broadening. Early analysis shows broadband ion saturation current and magnetic fluctuations attributed to the flux ropes. A follow up experiment is currently under way to address whether the increased transport is primarily attributed to magnetic fields, associated electric fields, or increased Coulomb scattering. [Preview Abstract] |
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BP8.00020: Numerical simulation of 3D Kinetic Alfv\'{e}n Turbulence Qian Xia, Stanislav Boldyrev, Jean Perez In our model for strong kinetic Alfv\'{e}n plasma turbulence, the spectrum of Kinetic-Alfv\'{e}n waves was found to scale as $k^{-8/3}$ at scales smaller than the ion gyroscale. This was close to the recent magnetic fluctuation observation at sub-proton scales. It also showed that the scaling would be changed with different viscosity setup. It suggested that von K\'{a}rm\'{a}n similarity is not valid beyond the inertial range. In this region, the dynamic of the outer scale (MHD) and the smaller scale (electron inertial range) may affect the spectrum. Hyperviscosity results showed that the electron Landau damping was not the reason for the steepening of the spectrum. [Preview Abstract] |
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BP8.00021: Initial results of magnetic nozzle induced plasma flows in the Controlled Shear Decorrelation eXperiment - Upgrade (CSDX-U) Jordan J. Gosselin, Saikat Chakraborty Thakur, George R. Tynan The lifetime of the plasma facing components (PFCs) in a tokamak, governed primarily by material erosion and redeposition, has been identified as a crucial research topic [1,2]. While some work has been done that shows evidence of the entrainment of impurities in linear machines [3] and in tokamaks [4-7], detailed, controlled studies of entrainment in plasma flows are harder to come by. In an effort to study the effects of the background flow on impurity transport, the Controlled Shear Decorelation eXperiment (CSDX: a linear helicon source operated plasma machine) has been upgraded with independently variable magnets. Using a magnetic nozzle, we can control the plasma flow speed. Here we shall show preliminary results of controlled background plasma flows in CSDX.\\[4pt] [1] J. Roth et al., Journal of Nuclear Materials 390-391, 1-9 (2009)\\[0pt] [2] V. Phillips, Physica Scripta 2006, 24 (2006)\\[0pt] [3] E. Hollmann et al., Journal of Nuclear Materials 415, S425-S429 (2011)\\[0pt] [4] S. Gangadhara and B. LaBombard, Plasma Physics and Controlled Fusion 46, 1617 (2004)\\[0pt] [5] M. Groth et al., Physics of Plasmas 14, 056120 (2007)\\[0pt] [6] G.F. Matthews, Journal of Nuclear Materials 337-339, 1-9 (2005)\\[0pt] [7] B. LaBombard et al, Nuclear Fusion 44,1047 (2004) [Preview Abstract] |
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BP8.00022: Effective mass in Rosenbluth-Hinton type zonal flows W. Sengupta, A.B. Hassam The temporal buildup of sub-bounce frequency tokamak zonal flows, in response to an external perpendicular force, $F_\perp$, is considered. In the collisionless regime, the trapped particle (TP) response is the well-known rapid toroidal precession at the speed $(q/\epsilon)u_E$, where $u_E$ is the ExB drift. The untrapped particles respond mainly as poloidal and oscillating ``Pfirsch Schluter'' flows. The effective mass of the system, defined by $M(d/dt)u_E = F_\perp$, is shown to include the factor $1 + 2q^2 + 1.6q^2/\sqrt{\epsilon}$, where $1.6q^2/\sqrt{\epsilon}$ is the Rosenbluth-Hinton (RH) factor. However, additional factors of $O(q^2/\epsilon^{3/2})$, representing the kinetic energy of TPs may also be present.The system is analogous to two mass beads on a rigid massless rod pushed perpendicularly, with the beads free to slide on the rod, but one bead constrained to a linear 1-D channel. A similar effective mass is obtained. The mathematical origin of this extra factor is a shift, proportional to E, of the usual energy coordinates in phase space. Importantly, this shift contributes to the effective mass even in the linearized E problem and can be interpreted as a first order linear shift in the Jacobian. Comparisons will also be made to RH zonal flows in collisional regime. [Preview Abstract] |
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BP8.00023: Turbulence dynamics during the transition to fully developed broadband turbulence in the Controlled Shear Decorrelation eXperiment - Upgrade (CSDX-U) Saikat Chakraborty Thakur, Christian Brandt, Lang Cui, Jordan Gosselin, Adam Light, Chris Holland, George Tynan Recent upgrades to the linear plasma device Controlled Shear Decorrelation Experiment (CSDX) at UCSD (maximum B$_{\mathrm{z}}$ upgraded from 1000 G to 2400 G and helicon source diameter increased from 10 cm to 15 cm) have revealed a rich array of turbulence dynamics at previously inaccessible conditions. Here we report the detailed dynamics during the transition from nonlinearly coupled but distinct eigenmodes at less than 900 G to fully developed broadband turbulence at 2400 G in argon plasma. Diagnostics include properly biased Langmuir probe arrays, Mach probes, optical emission spectroscopy and fast framing camera. We observe a slow smooth increase in the nonlinear dynamics of the system from 400 G to about 1300 G, followed by a very sharp transition (within 100 G) to a centrally peaked density with stiff profiles and very bright blue core mode. Thereafter there is another slow increase in the nonlinear dynamics until fully developed broadband turbulence is achieved at 2400 G. [Preview Abstract] |
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BP8.00024: Transient turbulence in beta-plane and quasi-Keplerian Taylor-Couette flows E.M. Edlund, E. Chertkov, E.P. Gilson, H. Ji The transfer of energy between small-scale turbulent structures and large-scale flows and waves in the presence of gradients of potential vorticity is thought to be central to the regulation of angular momentum transport in accretion disks and energy transport in tokamak plasmas. Experiments conducted at PPPL in the HTX device, a modified Taylor-Couette apparatus, explore the connections between potential vorticity and turbulent transport through two different types of studies. In the first, quasi-Keplerian rotation is established and then perturbed by an array of jets mounted on the inner cylinder to test the stability of these flows with respect to a subcritical transition to turbulence. In the second, sloped axial boundaries impose a gradient in potential vorticity under solid body rotation. Turbulent fluctuations are then introduced by the jets and the temporal evolution of the flows is observed. Recent results from these studies will be presented with commentary on the implications for transport in accretion disks and tokamak plasmas. [Preview Abstract] |
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BP8.00025: Recent Results from the Princeton MRI Experiment Ethan Schartman, Hantao Ji, Austin Roach, Eric Edlund, Erik P. Gilson, Tom Zick, Peter Sloboda, Jeremy Goodman, Frank Jenko, Angelo Limone Turbulent angular momentum transport is required to explain observationally inferred accretion rates in many astrophysical disks. The turbulent mechanism is believed to be the MagnetoRotational Instability (MRI) which uses weak magnetic fields to destabilize rotating shear flows of conductive fluids in which the angular velocity decreases with radius. The Princeton MRI Experiment is a modified Taylor-Couette device which uses GaInSn to study rotating MHD flows. A campaign to detect the MRI is underway. The MRI is expected to alter the mean azimuthal velocity by only a few percent, and will compete with alteration of the boundary layers due to the magnetic field. Thus making unambiguous detection of the MRI challenging. Scaling studies in Reynolds and Elsasser numbers were conducted below the stability threshold for the MRI to characterize the influence of the boundaries. Simulations indicate that the radial components of velocity and magnetic field may provide more robust signatures of the MRI. The ultrasonic velocimetry diagnostic has been modified to be more sensitive to radial velocity and a new internal magnetic probe was added. Results from the scaling studies and new diagnostics will be presented. Effects of oxide loading of the flow dynamics will also be discussed. [Preview Abstract] |
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BP8.00026: Development of a Swirling Gas/Plasma Experiment for Studying Angular Momentum Transport in Accretion Disks Enrique Merino, William Berrios, Samuel Greess, Hantao Ji Fast angular momentum transport in accretion disks is a lasting problem in astrophysics. Classically estimated viscosity of neutral fluid is too small to account for the fast accretion rate accompanied by angular momentum transport. Magnetorotational instability (MRI) and nonlinear hydrodynamic instabilities are proposed to be responsible mechanisms to generate the required turbulence. In addition to ongoing experiments using water, liquid metals and plasmas, a new experimental scheme is being developed at Princeton. High-speed gas is injected tangentially to the large radius in a cylindrical container. The gas gradually spirals-in and is pumped out from the container's center. This principle was successfully tested on a small scale prototype. To overcome large viscous forces, a 2nd generation prototype has been built. To provide information on the rotation profile of this swirling gas, a fog cloud is introduced. Motion is recorded by a hi-speed camera and using Particle Imaging Velocimetry, radial profiles of rotation speeds can be measured. Other improvements in this new device include addition of a three-axis translation mechanism, high-power heater and high-flow gas system. Technical designs and preliminary results will be presented and discussed, including near-future plans. [Preview Abstract] |
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BP8.00027: Modification of intermittency with sheared flow in the Large Plasma Device Giovanni Rossi, Troy Carter, David Schaffner, Danny Guice, Roger Bengtson Azimuthal flow and flow shear are controlled in the edge of the Large Plasma Device (LAPD) using a biasable limiter. Reduction of turbulent particle transport with increasing shearing rate is observed in LAPD.\footnote{D.A. Schaffner \textit{et. al.}, Phys. Rev. Lett. \textbf{109}, 135002 (2012).} Intermittency (as measured by skewness of the fluctuation amplitude PDF) increases with edge flow (in either direction) and reaches a minimum when spontaneous edge flow is reduced to near zero using biasing. This trend is counter to the observed changes in turbulent particle flux, which peaks at low flow/shear and decreases at high shear. Two-dimensional cross-conditional averaging confirms the intermittency to be associated with detached, filamentary structures (``blobs'') with a clear dipolar potential structure and a geometry also dependent on the magnitude of sheared flow. The structures are born in the region of strong pressure gradient in the LAPD edge, with the birth rate and blob lifetime correlating with the strength of the gradient. More detailed measurements are made to connect the occurrence of these blobs to observed flow-driven coherent modes and their contribution to radial transport loss. [Preview Abstract] |
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BP8.00028: Statistical properties of electrostatic turbulence XGC1 data Varun Tangri, T. Rafiq, A.H. Kritz, Seung-Hoe Ku, Jianying Lang, C.S. Chang, J. Seo Statistical properties of data from electrostatic ITG turbulence in gyrokinetic XGC1 simulations are examined for evidence of Self-Organized Criticality and intermittency in order to develop a better understanding of the dynamics of edge and core turbulence. The following quantities are computed at various radial locations: a) Speed of inward and outward propagating fronts; b) Non-Gaussian Distribution count; c) Fraction of total ion heat flux above a chosen base value; d) Power spectrum; e) Hurst parameter using both R/S and Aggregate Variance methods; and f) Skewness and kurtosis. These results are obtained using turbulence intensity, ion heat flux and temperature fluctuation data. Propagating fronts (avalanches) are observed to be moving with the speed of a few hundred m/s. High skewness and kurtosis are observed at some radial locations. The relation of Gaussian curvature to non-Gaussian nature of turbulence in XGC1 data is investigated. Turbulence intensity flux distribution with a long left tail is observed when turbulence intensity flux fluctuation is negative. This shows a small number of 'rare' events carry a ``burst'' of turbulence intensity inward. The relation between inward propagation of turbulent intensity and opening and closing of zonal flows will be elucidated. [Preview Abstract] |
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BP8.00029: Study of gyrokinetic edge blobs and vorticity merge dynamics in the SciDAC Center for Edge Physics Simulation C.S. Chang, J. Lang, S. Ku, P.H. Worley, E.F. D'Azevedo Importance of blobs and vorticity merge physics for edge plasma transport has been theorized or conjectured for over a decade. However, a first-principles understanding has been difficult due to the complexity of the diverted edge geometry and the multiscale nature of edge physics. The full-f gyrokinetic code XGC1 has shown, for the first time, the generation of blobs from nonlinear electrostatic turbulence interaction with mean ExB shearing action, and their 3D motions across the pedestal and separatrix. Inward propagating holes are generated together. Many interesting physics phenomena have been found to be related to the blob and hole dynamics; which include vorticity merge to strengthen the neoclassical ExB shearing rate, inward particle pinch, inward momentum pinch, particle and thermal transport, and divertor heat load footprint. [Preview Abstract] |
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BP8.00030: Momentum transport due to overlapping tearing modes in tokamaks and reversed field pinches A.J. Cole, J.M. Finn, C.C. Hegna, P.W. Terry Quasilinear calculations related to momentum transport due to a spectrum of stable driven tearing modes in RFPs and tokamaks in the presence of sheared rotation will be presented. The RFP and tokamak cases are treated in the limit that the tearing layers, but not the islands, overlap. The summation over mode contributions to the total Maxwell plus Reynolds force density on the plasma is converted into an integral over wavenumber. This process yields a multimode force density on the plasma that is related to the net force on a layer stemming from a single mode, but involves coefficients that depend on the resonant mode spectrum and the magnetic shear. The multimode effects appear to the plasma as a velocity-shear dependent viscous diffusion from Reynolds stress plus a Maxwell drag. Results are presented for both resistive-inertial and visco-resistive tearing regimes. Work supported by the US DoE under grants DE-FG02-85ER53212, DE-FG02-86ER53218, and contract number DE-AC52-06NA25396. [Preview Abstract] |
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BP8.00031: Gyrokinetic simulation of spontaneous plasma fueling from inward particle pinch J. Lang, C.S. Chang, S. Ku, D.P. Stotler Plasma fueling from edge to core, as have been consistently observed in tokamak experiments, have yet to be explained theoretically. Recently, it has been shown that electrostatic plasma turbulence may be able to drive an inward particle pinch of colder particles,\footnote{W Wan \textit{et al}, Phys. Plasmas \textbf{18}, 056116 (2011); W Wan \textit{et al}, Phys. Plasmas \textbf{17}, 040701 (2010).}$^,$\footnote{C. Angioni \textit{et al.}, Phys. Plasmas \textbf{16}, 060702 (2009).} while warmer particles are driven outward. However, these transport studies were performed in $\delta $f codes in which the source of the colder particles could not sustain for steady-state consistency. Neutral ionization and charge exchange effects are expected to play an important role in the inward particle pinch by providing particle sources and strong local cooling. We will present full-f gyrokinetic studies of global electrostatic turbulence together with neutral particle transport in realistic divertor geometry. Our primary simulation results have shown that the global nonlinear turbulence can propagate these effects from the plasma edge to the core and that the kinetic electron dynamics bring simulated particle pinch magnitude closer to the experimental observation.\footnote{M. Xu \textit{et al.}, IAEA 2012.} It is also found that the generation of nonlinear quasi-coherent structures (resembling blobs and holes) in the strongly ExB-sheared edge pedestal plays a significant role in the cold particle pinch physics. More complete simulations, data analysis and detailed comparison with experiment will be provided. [Preview Abstract] |
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BP8.00032: Experimental validation by global gyrokinetic particle simulation Yong Xiao, Taige Zhang, Zhihong Lin It is observed in modern gyrokinetic simulations that the heat and particle transport arising from the EXB turbulent motion is approaching to the anomalous transport level in tokamak experiments. However, most of these gyrokinetic simulations are carried out by some simplifications, such as circular cross section, approximate local temperature and density and their gradients, local flux-tube limit, etc. Eliminating these simplifications is very likely to improve the predictability of the numerical simulations. The new features lately developed in the global gyrokinetic particle simulation code GTC, such as kinetic electrons, electromagnetic effects, non-circular plasma shape and global instability drives, enable the GTC code to simulate the turbulent transport with better fidelity when comparing to real experiments. The GTC simulation is compared with DIII-D experiment and GYRO simulation with a result of consistent turbulent transport level between them. We also provide a first estimate of turbulent transport level in EAST experiment. Many important physics issues in the global turbulent transport, such as the dominance of trapped electron modes, turbulence spreading, electron transport mechanism and zonal flow effects can be addressed by the new features of the GTC code with a closer relevance to the tokamak experiments. [Preview Abstract] |
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BP8.00033: ABSTRACT WITHDRAWN |
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BP8.00034: Heat pulse propagation is 3-D chaotic magnetic fields D. del-Castillo-Negrete, D. Blazevski Perturbative transport studies provide valuable time dependent information to construct and test transport models in magnetically confined plasmas. In these studies, the transient response of the plasma to externally applied small perturbations is followed in time. Here we present a numerical study of the radial propagation of edge heat pulse perturbations in the presence of 3-dimensional chaotic magnetic fields in cylindrical geometry. Based on the strong transport anisotropy encountered in magnetized plasmas ($\chi_\parallel/\chi_\perp \sim ~10^{10}$ in fusion plasmas, where $\chi_\parallel$ and $\chi_{\perp}$ are the parallel and perpendicular conductivities) we limit attention to the extreme anisotropic, purely parallel, $\chi_\perp=0$, case. Using the Lagrangian-Green's function method\footnote{D. del-Castillo-Negrete and L. Chacon, Phys. Rev. Lett. {\bf 106} (2011); Phys. Plasmas {\bf 19}, 056112 (2012)} we study the dependence of the pulse speed and radial penetration on the level of stochasticity of the magnetic field in regular, and reversed magnetic shear configurations. Of particular interest is the slowing down of the heat pulse due to weak chaos, islands, and shearless cantori.\footnote{D. Blazevski and D. del-Castillo-Negrete, Phys. Rev. E {\bf 87} 063106 (2013)} [Preview Abstract] |
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BP8.00035: Determination of correlation functions from experimental measurements Fred Skiff, Sean Mattingly We look at the problem of comparing theory and experiment with phase-space resolved correlation functions \textless f(x,v,t)f(x',v',t')\textgreater . The first problem is extracting the correlations from the measurements. We will outline two approaches; the first involves suppressing photon statistics fluctuations by averaging and the second involves extracting the correlations from the PDFs of the photon statistics themselves. Secondly there is the problem that the theoretical expressions are expressed in transform space and the measurements are made at discrete times and locations with finite experimental precision. We will outline the range accessible to the current measurement techniques. [Preview Abstract] |
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BP8.00036: GYROKINETIC DESCRIPTION |
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BP8.00037: Effects of magnetic islands on drift wave instability Peng Jiang Static magnetic islands have been added into GTC (gyrokinetic toroidal code) simulation of drift wave instability. First, we investigate the ion density flattening inside the islands in the absence of turbulence. We find that the density profile of the high field side has more flattening than that of the low field side. This phenomena is mainly due to the trapped ions in the low field side. After verification of the density profile change due to the static magnetic islands, the behavior of ion temperature gradient (ITG) in the presence of static magnetic islands is investigated in GTC simulation. It is shown that the island perturbation causes the toroidal mode coupling. The toroidal mode spectrum becomes broader in the presence of static magnetic islands. [Preview Abstract] |
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BP8.00038: ABSTRACT WITHDRAWN |
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BP8.00039: Gkeyll: High-Order Discontinuous Galerkin Solver for (Drift/Gyro) Kinetic Simulations of Edge Plasmas Ammar Hakim, Greg Hammett, Eric Shi A new high-order discontinuous Galerkin (DG) code for the solution of drift- and gyrokinetic equations in edge plasma is under development. Gkeyll implements extensions of recently developed DG schemes to general Hamiltonian systems, including to the case of discontinuous potentials. The collisionless part of the dynamics is evolved with an energy conserving DG discretization. Diffusion operators are handled with a consistent recovery-based algorithm. It is shown that traditional penalty and local DG schemes for diffusion are inconsistent, and can lead to large errors in predicting high-order moments of the solution. An energy and momentum conserving Lenard-Bernstein collision operator is implemented. The velocity space drag and diffusion operators, as well as the boundary conditions, need to be handled carefully to conserve the discrete particles, momentum and energy. Extension of Gkeyll to multiple dimension are presented, and initial tests of the code in 1D/2V and 2D/2V are shown. In addition, application of the code to computing heat-loads on divertor plates using a variety of 1D/1V kinetic models will be shown. [Preview Abstract] |
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BP8.00040: 1D2V Gyrokinetic Simulations of Parallel Transport in a Scrape-Off Layer Plasma using Discontinuous Galerkin Algorithms E.L. Shi, A. Hakim, G.W. Hammett We have performed 1D2V gyrokinetic simulations of ELM pulse propagation along a scrape-off layer plasma and measured the resulting time profile of the heat deposition on the divertor plate. The ELM modeling problem is based on a case studied in recent literature, and results using kinetic ions and electrons will be presented. The model is implemented in Gkeyll, a prototype code exploring discontinuous Galerkin (DG) algorithms for modeling the edge plasma in fusion devices and basic plasma experiments like LAPD. To handle the effect of collisions, the model uses a Lenard-Bernstein collision operator, which conserves total number, momentum, and kinetic energy. The diffusive term in the collision operator is implemented using a recovery-based DG method. We will also present results from a test problem of ion-acoustic wave damping in a collisional plasma used to study resolution requirements and to benchmark with Braginskii's transport coefficients. [Preview Abstract] |
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BP8.00041: Tests of Maxwellian-Weighted Basis Functions in a Discontinuous Galerkin Kinetic Code G.W. Hammett, A. Hakim, E.L. Shi Discontinuous Galerkin (DG) algorithms have been very actively studied and used in the applied math and computational fluid dynamics communities in the past decade. They combine certain attractive properties of finite element methods (like high accuracy per interpolation point) and finite volume methods (like locality of calculation for parallel computers and flexibility for limiters). Higher-order methods also have more floating point operations per data point, and so can be more efficient on modern computers that are often bandwidth limited. The flexibility of DG allows one to consider various types of Maxwellian-weighted basis functions while preserving important conservation properties of the underlying system. One can think of this either as a modified inner-product norm or a Petrov-Galerkin approach. Here we explore some ways of using Maxwellian-Weighted Basis functions and test them on paradigm problems using the Gkeyll code, which is being developed for edge gyrokinetic simulations. In addition to the formal order of accuracy in the asymptotic limit as a grid is refined, we are also interested in robust reasonable solutions on coarser grids. [Preview Abstract] |
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BP8.00042: Gyrokinetic simulations with a general equilibrium distribution function George Wilkie, Edmund Highcock, Ian Abel, William Dorland Applying the gyrokinetic framework to study the dynamics of fast particles requires a transport-scale equilibrium distribution that is not Maxwellian, and whose functional form may not be known a priori. The GS2 gyrokinetics code has been modified to accommodate an arbitrary equilibrium distribution and this capability has been validated. The need to resolve the tail of the distribution for fast particles introduces numerical challenges that are resolved by implementing a generalized quadrature scheme that retains spectral accuracy of velocity-space integrals. Preliminary simulation results are presented. [Preview Abstract] |
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BP8.00043: MEASUREMENT AND DIAGNOSTICS |
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BP8.00044: Millimeter Wave Interferometry and Fabry-Perot Spectroscopy on the Madison Plasma Dynamo Experiment K. Flanagan, M. Clark, C. Cooper, W. Ding, J. Milhone, W. Peng, F.L. Roesler, J. Wallace, D. Weisberg, C.B. Forest New non-invasive optical diagnostics for use on the Madison Plasma Dynamo Experiment (MPDX) allow for measurements of line-averaged density through interferometry and ion velocity and temperature through Fabry-Perot spectroscopy. Both the interferometer and the Fabry-Perot spectrometer are capable of scanning multiple chords through the plasma. Through inversion techniques, these chords can be used to construct profiles of electron density, ion temperature, and ion velocity. The interferometer consists of a millimeter wave source with two detunable outputs, two fundamental mixers with low-noise amplifiers, and an analog phase detector. A millimeter wave beam provides an easily measurable phase shift of approximately one fringe at typical MPDX densities of $10^{11}-10^{12}$ cm$^{-3}$. The Fabry-Perot spectrometer collects light from a single chord through the plasma and passes it through an etalon, which images the typical ring structure onto a high performance CCD camera. Through a ring summing technique developed by Roesler et. al., we can determine the ion velocity and temperature on both MPDX and PCX. We will present detailed descriptions of both diagnostics and their implementation on MPDX in addition to preliminary density, ion temperature, and ion velocity measurements. [Preview Abstract] |
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BP8.00045: A 10MHz Fiber-Coupled Photodiode Imaging Array for Plasma Diagnostics Samuel Brockington, Andrew Case, F. Douglas Witherspoon HyperV Technologies has been developing an imaging diagnostic comprised of arrays of fast, low-cost, long-record-length, fiber-optically-coupled photodiode channels to investigate plasma dynamics and other fast, bright events. By coupling an imaging fiber bundle to a bank of amplified photodiode channels, imagers and streak imagers of 100 to 10,000 pixels can be constructed. By interfacing analog photodiode systems directly to commercial analog to digital convertors and modern memory chips, a prototype pixel with an extremely deep record length (128k points at 40 Msamples/s) has been achieved for a 10 bit resolution system with signal bandwidths of at least 10MHz. Progress on a prototype 100 Pixel streak camera employing this technique is discussed along with preliminary experimental results and plans for a 10,000 pixel imager. Work supported by USDOE Phase 1 SBIR Grant DE-SC0009492. [Preview Abstract] |
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BP8.00046: Continuous Wave Ring-Down Spectroscopy Diagnostic for Measuring Argon Ion and Neutral Velocity Distribution Functions in a Helicon Plasma Dustin McCarren, Robert Vandervort, Mark Soderholm, Jerry Carr Jr., Matthew Galante, Richard Magee, Earl Scime Cavity Ring-Down Spectroscopy CRDS is a proven, ultra-sensitive, cavity enhanced absorption spectroscopy technique. When combined with a continuous wavelength (CW) diode laser that has a sufficiently narrow line width, the Doppler broadened absorption line, i.e., the velocity distribution functions (IVDFs), can be measured. Measurements of IVDFS can be made using established techniques, such as laser induced fluorescence (LIF). However, LIF suffers from the requirement that the initial state of the LIF sequence have a substantial density. This usually limits LIF to ions and atoms with large metastable state densities for the given plasma conditions. CW-CRDS is considerably more sensitive than LIF and can potentially be applied to much lower density populations of ion and atom states. In this work we present ongoing measurements of the CW-CRDS diagnostic and discuss the technical challenges of using CW-CRDS to make measurements in a helicon plasma. [Preview Abstract] |
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BP8.00047: Two-photon Laser Induced Fluorescence on Xenon for Neutral Density and Temperature Measurements Drew Elliott, Matthew Galante, Earl Scime, Mark Soderholm, Robert Vandervort Many noble gasses are ideal species for plasma generation because of their relatively low ionization energies, very low electron affinities, and because the neutral and ion electronic configurations are easily probed spectroscopically. Laser induced fluorescence of a ground state neutral atom is particularly useful because it enables absolute signal calibration. We have identified a new two-photon-absorption laser-induced-fluorescence (TALIF) scheme for neutral xenon. The initial 5p$^{6}$ ground state is pumped to the 5p$^{5}$ 7f state ($\Delta $J$=$2) by two photons of wavelength approximately 209nm, which then decays to the 5p$^{5}$ 6s state through single photon emission at 543nm. Since the excitation is from the ground state, measurements of the fill gas provide absolute calibration. The pulsed TALIF laser (approx. 1MWatt) with a very narrow line width (approx. 1cm$^{-1})$ enables the Doppler broadened line shape (superimposed on the isotopic splitting) to be measured. These measurements are obtained with confocal optics necessitating only a single lens and a single view port. We present spatially and temporally resolved neutral density and neutral temperature profiles in a xenon helicon plasma. [Preview Abstract] |
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BP8.00048: Fluctuation Measurements at New Spatial Scales Ryan Hood, Sean Mattingly, Jorge Berumen, Dereth Drake, Fred Skiff We present preliminary measurements from a laser induced fluorescence detection system used to resolve ion density fluctuations on spatial scales approaching the ion Debye length $\sim$0.5 mm. The detection system consists of a pair of moveable periscopes which collimate light collected from a small measurement region ($\sim$0.1 cm$^{3})$ along the axis of a magnetized singly ionized Argon plasma column. The light is imaged onto a pair of 16-channel linear photomultiplier arrays with digitized photon counting on all 32 channels at 1 MHz or on 8 channels at 4 MHz. The viewing regions may be resolved spatially either along or radial to the magnetic field axis depending on the orientation of the entrance slit. Plasma fluctuations resolved in ion velocity have never been observed at this scale. Measurements may provide insight into transport phenomena, which are fundamentally linked to plasma fluctuations. [Preview Abstract] |
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BP8.00049: Synthetic analysis results for Microwave Imaging Reflectometry on the DIII-D Tokamak Xiaoxin Ren, Christopher Muscatello, Benjamin Tobias, Calvin Domier, Xing Hu, Neville Luhmann Microwave Imaging Refletometry (MIR) is a radar like system to measure the density fluctuations of the plasma in both poloidal and radial directions. A fully synthetic analysis of MIR based on a DIII-D plasma is conducted by applying sophisticated simulation tools. The 2D full-wave reflectometry code FWR2D is coupled to optical design software to propagate the probe beam and to detect the instrumental response of the reflected signal. The transmitting optics are designed such that the wavefront of the probing beam matches the shape of the cutoff surface to keep the best imaging quality. Correlation between the cutoff fluctuation and the measured phase fluctuation is calculated to check the imaging quality. The simulation results reveal that MIR has the ability to decode fluctuations with wavenumbers less than 2.5 cm$^{\mathrm{-1}}$ and radial density variations up to 3{\%}, with a distance correlation value equal to or above 0.6. MIR is proven to be a robust density fluctuation measurement tool based on a series of sensitivity studies, for example incidence angle of receiver sightlines and focal position offset from the cutoff. [Preview Abstract] |
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BP8.00050: Preliminary Results for Coded Aperture Plasma Diagnostic Magnus Haw, Pakorn Wongwaitayakornkul, Paul Bellan A 1D coded aperture camera has been developed as a prototype for a high speed, wavelength-independent, lenseless, plasma imaging diagnostic. Images are obtained via a coded or masked aperture that projects an invertible transform of the object onto a detector. The mask was made by printing the 1D code pattern on transparency sheets. The detector is a 48-element photodiode array sensitive to visible light. The system has a 38x2cm field of view, a vertical spatial resolution of 8mm, and a temporal resolution of 10ns. Visible light images of the Caltech MHD-driven jet experiment agree with simultaneous 2D images obtained with a conventional camera. Further work will involve increasing resolution and acquiring X-ray and EUV scintillators for imaging in those wavelengths. [Preview Abstract] |
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BP8.00051: Measurements of ultrafast laser-driven ionization and extreme gas nonlinearity Sina Zahedpour, Yu-Hsiang Cheng, Jared Wahlstrand, Howard Milchberg A 2D spectral interferometry method for measuring high laser field phenomena such as laser-driven ionization and high field nonlinearity is introduced. The method is based on Single-shot Supercontinuum Spectral Interferometry, in which a chirped supercontinuum is used to probe the time-dependent refractive index induced by a pump pulse. A thin gas target ensures uniform intensity and minimizes refraction of the probe beam due to refractive index gradients. An imaging spectrometer allows measurement of the spatial dependence of the response along one direction. To measure in 2D, a motorized mirror scans the probe beam across the spectrometer slit. The technique has 3 micron spatial and 5 fs temporal resolution. The effective interaction length is measured interferometrically, allowing absolute calibration of the refractive index change. We present measurements of the absolute ionization rates of noble and molecular gases and their high field nonlinear response. [Preview Abstract] |
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BP8.00052: Platform for Interfacing Synthetic Diagnostics with Analysis of Fusion Experiments and Simulation Codes Lei Shi, William Tang, Ernest Valeo, Benjamin Tobias, Stephane Ethier, Weixing Wang, Seung-Hoe Ku, Choong-Seock Chang, Ahmed Diallo Synthetic diagnostics have been widely used for interpreting experimental results and for validating numerical simulations. Since the individual synthetic diagnostic codes are usually developed independently, interfacing them with fusion experiments and simulation codes is a necessary but tedious task. We present here a new Python package containing useful modules for developing, testing, and benchmarking synthetic diagnostics with interfaces to data obtained from the NSTX and DIII-D experiments, and with simulation data from the GTS and XGC1 global particle-in-cell codes. A synthetic ECE imaging code and a synthetic reflectometry code (known as FWR2D) are also included as modules in this analysis infrastructure. [Preview Abstract] |
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BP8.00053: A New and Novel Way of Looking at Waves Through Probes Katherine Pacha There are many ways to look at waves and other turbulent phenomena in plasmas and in nature. One way is through the use of probes. Probes have been around since the late 19th and early 20th centuries (at that time they were called sounding electrodes). They aid in every aspect of diagnostics but they have some drawbacks at times. These drawbacks can affect a number of things such as measurements. However, these can be limited with some work. What will be discussed is a new and novel way of using a simply designed probe (along with soft where) to give better insights into this phenomena. [Preview Abstract] |
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BP8.00054: Measuring the ion energy distribution using a retarding field energy analyzer in a plasma material interaction test stand Michael Christenson, Soonwook Jung, Daniel Andruczyk, Davide Curreli, David Ruzic The Divertor Erosion and Vapor Shielding eXperiment (DEVeX) at the University of Illinois is a gas-puff driven, theta pinch plasma source that is used as a test stand for off-normal plasma events incident on materials in the edge and divertor regions of a tokamak. Ion temperatures and the resulting energy distribution are of vital importance in DEVeX, indicating the level of edge simulation. For this reason, a theta pinch has been applied as a source of external heating, along with a coaxial plasma accelerator as a pre-ionization source. In its most recent iteration, the accurate diagnosis of ion temperature will prove difficult using conventional methods, since diagnostics are difficult in a pulsed device for measuring the ion temperature range produced in DEVeX ($\sim$10-100 eV). A retarding field energy analyzer (RFEA) has been proposed to measure the ion energy distribution and will be compared to theoretical predictions for the ion temperature in the upgraded DEVeX system. Such a diagnostic tool would be less susceptible to external fields and would be suitable for ion temperatures on the order of 100 eV. The RFEA will serve as a diagnostic for the ThermoElectric-driven Liquid-metal plasma-facing Structures (TELS), and its further applications are discussed. [Preview Abstract] |
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BP8.00055: In-situ studies of stainless steel exposed to hydrogen plasmas in the Lithium Tokamak Experiment (LTX) Felipe Bedoya, Sean Gonderman, Jean Paul Allain, Robert Kaita, Matthew Lucia, Charles Skinner, Robert Ellis, Lane Roquemore, Richard Majeski The Materials Analysis Particle Probe (MAPP) is an in situ characterization device for diagnosing samples exposed to fusion reactor plasmas. X-ray photoelectron spectroscopy (XPS), ion scattering spectroscopy (ISS), thermal desorption spectroscopy (TDS) and direct recoil spectroscopy (DRS) will allow comprehensive shot-to-shot analysis of the samples. In the summer of 2013, MAPP was attached to a midplane port on LTX. The plasma-facing components (PFCs) in LTX are stainless steel, and MAPP enables evaluation of stainless steel samples before and after exposure to LTX plasmas. Initial studies compare XPS spectra from discharges with and without lithium PFC coatings. These results, combined with future measurements with TDS and ISS, provide unique insights into the relationship between the plasma behavior and the chemical structure of the first wall in fusion devices. [Preview Abstract] |
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BP8.00056: Using Ion Implanted Depth Markers to Measure Erosion and/or Deposition in Fusion Relevant Materials Jude Safo, Regina Sullivan, Dennis Whyte A method for measuring the net erosion and deposition of high-Z materials at high temperatures (\textgreater~1000 K) has been developed and tested. This was motivated by the success of a $^{7}$Li depth marker at making similar measurements in low-Z materials at relatively low temperature (\textless~600 K). At temperatures above 600K diffusion can cause the implanted low-Z depth marker to diffuse thus degrading the resolution and usefulness of this technique. Using high-Z depth markers greatly reduces this concern as these heavier species have much slower diffusion rates. Using Rutherford Backscattering Spectroscopy, (RBS), and/or Nuclear Reaction Analysis, (NRA), we can infer net erosion of the target. Preliminary analysis, using SIMNRA and SRIM identified $^{197}$Au as an ideal candidate for the depth marker species. A simulated RBS trace of 2200 keV Au implanted in Molybdenum (Mo) shows a distinctive peak that is distinguishable from the RBS signal due to the Mo bulk. Experiments have been performed to determine the optimal method of implanting, optimal implantation time, and charge state. The goals of the experiment are, in order, to optimize the implantation and RBS characterization of the Au depth marker at room temperature (300K) then compare with results at elevated temperatures. Research supported by US Air Force ASOFR Grant FA9550-11-1-0195. [Preview Abstract] |
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BP8.00057: Ionization Source Effects on near-Antenna Static and Dynamic Electric Field Measurements by Stark-Effect, Passive Emission Spectroscopy C.C. Klepper, S. Panayotis, B. Pegourie, J. Jacquot, L. Colas, J. Hillairet, R.C. Isler, E.H. Martin, J.B. Caughman, J.H. Harris, S.C. Shannon Radiofrequency electric fields (\textbf{E}$_{\mathrm{\mathbf{RF}}})$ are frequently modeled within the tenuous plasma around high-power launch antennas in the edge of fusion experiments. An experimental measurement of \textbf{E}$_{\mathrm{\mathbf{RF}}}$ in the plasma-antenna interface is valuable for assessing these models. Recently, \textbf{E}$_{\mathrm{\mathbf{RF}}}$ was determined in front of an LHCD launcher (3.7 GHz) in Tore Supra by fitting D$_{\mathrm{\beta }}$ line profiles to a fully-dynamic Stark-effect model and obtaining good agreement with full-wave modeling [1]. The measurement was localized within the sightline using the EIRENE neutrals model to estimate the location of peak D$_{\mathrm{\beta }}$ emission probability, which can be several cm from the plasma-antenna boundary. While facilitating the measurement of the dynamic fields at the LH antenna, this effect is shown to be unfavorable to direct measurement of static (rectified) electric fields, at ICRH antenna surfaces under similar conditions. New modeling capabilities [2] are used to estimate the spatial extent of such DC fields at the Tore Supra ICRH antenna and an upper limit to their value is estimated from D$_{\mathrm{\gamma }}$ profiles obtained near this antenna. [1]\textit{ C.C. Klepper, et al.,} \quad \textit{PRL} \textbf{110}, 215005 (2013)$.$[2]\textit{ J.Jacquot et al., proc. 20}$^{th}$\textit{ topic. conf. RF power in plasmas, Sorrento (Italy) 2013, I3.7 (AIP)} [Preview Abstract] |
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BP8.00058: High-Resolution and Frequency, Printed Miniature Magnetic Probes James Prager, Timothy Ziemba, Kenneth Miller, Julian Picard Eagle Harbor Technologies, Inc. (EHT) is developing a technique to significantly reduce the cost and development time of producing magnetic field diagnostics. EHT is designing probes that can be printed on flexible PCBs thereby allowing for extremely small coils to be produced while essentially eliminating the time to wind the coils. The coil size can be extremely small when coupled with the EHT Hybrid Integrator, which is capable of high bandwidth measurements over short and long pulse durations. This integrator is currently being commercialized with the support of a DOE SBIR. Additionally, the flexible PCBs allow probes to be attached to complex surface and/or probes that have a complex 3D structure to be designed and fabricated. During the Phase I, EHT will design and construct magnetic field probes on flexible PCBs, which will be tested at the University of Washington's HIT-SI experiment and in EHT's material science plasma reactor. [Preview Abstract] |
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BP8.00059: Vector Tomographic Reconstruction of 3D Plasma Flows with Ion Doppler Spectroscopy Keon Vereen, Setthivoine You A laboratory astrophysical jet experiment is being constructed to investigate the dynamics of canonical flux tubes. This poster will present a vector field diagnostic able to measure 3D ion flows from spectroscopic Doppler shifts based on vector tomographic reconstruction techniques [1]. The Ion Doppler Spectroscopy (IDS) setup consists of a 1.0m Czerny-Turner monochromator, a dual-inline frame Princeton Instruments PIMAX-3 (1024 x 1024) iCCD camera, collimating optics, matching optics, and a fiber bundle. The fiber bundle is designed to group 48 optical detector arrays of 14 chords each, totaling 672 lines of sight, into a 2D iCCD image. The mounting hardware is designed to position the fiber arrays spherically around the plasma.\\[4pt] [1] A. L. Balandin, Y. Ono and S. You, ``3D Vector tomography using vector spherical harmonics decomposition,'' \textit{Comput. {\&} Math. Appl., } vol. 63, (2012) 1433-1441. [Preview Abstract] |
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BP8.00060: Development of Fast Ionization Gauge for Time-Resolved Neutral Gas Density Measurements Eric Lavine, Setthivoine You A plasma experiment seeking to simulate a magnetically-driven jet launched by an accretion disk is under construction to improve understanding of plasma shear flow interactions with magnetic fields. The experimental setup replaces an accretion disk that would rotate in the vacuum chamber at impractical speeds with three independent concentric annular electrodes. To minimize the effect of asymmetries on jet launching and late-stage fuelling special attention must be paid to establishing azimuthal symmetry of the mass source at the boundaries. In order to accomplish this, a diagnostic with temporal resolution fast enough to track the evolution of the gas puff is needed. This poster describes the development of a custom fast ionization gauge (FIG) with $<$2$\mu s$ response time that will allow precise timing of gas valves to measure and control the symmetry in gas distribution for pressures of $10^{-6}$ to $10^{-3}$ torr. [Preview Abstract] |
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BP8.00061: Test, Construction, and Calibration of a Fast Valve Driver Unit (FVDU) and an Earth-isolated High Voltage Probe (HV probe) for a pulsed plasma experiment Yu Kamikawa, Jens von der Linden, Setthivoine You A fast valve driver unit (FVDU) and an optically isolated high voltage probe (HV probe) [1] were built for an experiment to generate laboratory astrophysical jets with a triple electrode plasma gun [2]. The FVDU controls fast pulse gas valves (Parker P/N: 9S4-A1-P2-9B13, 090-0270-090) by converting an optical trigger input into a square 6V pulse output of a desired duration (100$\mu$s to 1ms) with an initial 250V shot pulse. A potentiometer controls the duration of the square pulse, corresponding to the open time of the valve. The solar cell powered HV probe measures, once triggered by an optical pulse, the voltage across the electrodes without exposing sensitive data acquisition instruments to high voltage. A custom made capacitive voltage divider couples the signal to a solar powered LED, which optically transmit the signal to a receiver circuit. The voltage across the electrodes controls the current driven across the jet and the azimuthal rotation of the jet.\\[4pt] [1] X. Zhai and P. M. Bellan, Rev. Sci. Instrum.83, 104703 (2012)\\[0pt] [2] J. von der Linden, S. You, this meeting. [Preview Abstract] |
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BP8.00062: HEATING AND CURRENT DRIVE |
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BP8.00063: Slow Wave Excitation due to warm electrons in NSTX-U and tokamaks C.K. Phillips, E.F. Jaeger, L.A. Berry, P.T. Bonoli, E.J. Valeo, N. Bertelli, J.C. Hosea, R. Perkins, P.M. Ryan, G. Taylor, J.R. Wilson, J.C. Wright Recent theoretical studies and high spatial resolution numerical simulations of high harmonic fast wave heating (HHFW) in spherical toruses (ST) and of ICRF heating in tokamaks indicate that the launched fast waves may excite a short wavelength slow mode inside of the plasma discharge due to the presence of hot electrons that satisfy the condition $\omega $ \textless k$_{\mathrm{//}}$v$_{\mathrm{te}}$, where $\omega $ is the launched wave frequency, k$_{\mathrm{//}}$ is the local parallel component of the wave vector, and v$_{\mathrm{te}}$ is the local electron thermal speed [1]. The 3D structure of the wave fields in ST's and tokamaks will be presented for the HHFW and ICRF regimes as well as for the related kinetic Alfven waves [2] with $\omega $ \textless $\omega_{\mathrm{ci}}$. Difficulties with resolving these short wavelength slow modes will be discussed. This slow wave may provide another path for rf power absorption in tokamaks and ST devices. \\[4pt] [1] C.K. Phillips et al, AIP Conf. Proc. 1406, AIP, 2011, pg. 341\\[0pt] [2] T.H. Stix, Waves in Plasmas, [AIP, 1992], pg. 357 [Preview Abstract] |
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BP8.00064: Integrated Plasma Simulation of Sawtooth Modification via Lower Hybrid Current Drive in Tokamaks P.T. Bonoli, R.R. Parker, S. Shiraiwa, G.M. Wallace, J.C. Wright, R.W. Harvey, D.B. Batchelor, W. Elwasif, J. Chen, F. Poli, S.J. Jardin, C.E. Kessel An advanced lower hybrid RF (LHRF) actuator component was been implemented in the Integrated Plasma Simulator [1], and has been used to simulate modification of sawteeth via lower hybrid current drive (LHCD). The TSC transport code [2] is used to evolve the background plasma in conjunction with the Porcelli sawtooth model [3], and driven LH current density profiles are computed using the GENRAY ray tracing code which includes a scrape off layer and the CQL3D Fokker Planck code [4]. The integrated model has been tested against a series of experiments [5] in the Alcator C-Mod tokamak in which sawteeth were systematically delayed for increasingly longer periods of time as the level of LHCD was increased.\\[4pt] [1] D. Batchelor \textit{et al}, Journal of Physics: Conf. Series \textbf{125}, 012039 (2008).\\[0pt] [2] S. C. Jardin \textit{et al}, J. Comp. Phys. \textbf{66}, 481 (1986).\\[0pt] [3] F. Porcelli, Plasma Phys. Cont. Fusion 38 (1996) 2163.\\[0pt] [4] R. W. Harvey and M. G. McCoy, Proc. of the IAEA Tech. Comm. Meeting on Simulation and Modeling of Therm. Plasmas, Montreal, Canada (1992).\\[0pt] [5] C. E. Kessel \textit{et al}, Bull. Am. Phys. Soc. \textbf{53}, Poster PP6.00074 (2008). [Preview Abstract] |
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BP8.00065: Interference effects on quasilinear diffusion of lower hybrid waves John Wright, Paul Bonoli In cases of weak damping resulting in multi-pass behavior, lower hybrid (LH) ray tracing has been shown to predict a stronger LH wave-electron interaction than observed in experiment [1]. We have previously presented [2] a comparison with full wave simulations in which the full wave results demonstrated much closer agreement in magnitude of hard x-ray emissions than ray tracing. For an explanation of the different model predictions we look to interference effects manifested in the quasi-linear (QL) diffusion tensor ~$E_1\,f_1$. Ray tracing treats the contribution of each LH wave to QL diffusion independently whereas in full wave each partial wave constructively or destructively interferes with the distribution function perturbed by the entire spectrum. We remove the phase effects in the full wave QL calculation and compare to previous results. We conclude with a discussion on the causes of the prediction discrepancies from experiment in multi-pass regimes.\\[4pt] [1] A. Schmidt et al, Phys. Plasmas, 17 (2011).\\[0pt] [2] J. Wright et al, 19th RF Topical Conference (2011). [Preview Abstract] |
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BP8.00066: Benchmarking and application of integrated 3D time-domain RF sheath and plasma model David Smithe, Daniel D'Ippolito, James Myra Significant efforts have been made to quantitatively benchmark the sheath sub-grid model used in our time-domain simulations of plasma-immersed antenna and conducting wall near fields. These simulations include applications to highly detailed three-dimensional geometry, the presence of both fast and slow cold plasma waves, and the non-linear evolution of the sheath potential [1]. An important result from our benchmarking efforts is to highlight the importance and necessity of including the sheath plasma wave in these calculations. We present these detailed benchmarking cases in low-dimensionality, for comparison to analytic and simplified models [2]. These benchmarks also provides confidence in how we evolve the sheath's physical parameters. We present applications of the model to ICRF antennas in ITER and CMod tokamaks, as well as application to industrial plasmas. Finally, we discuss efforts to generalize the model to include plasma in contact with dielectric materials, as well as metallic materials. This work is supported by DOE grants DE-FC02-08ER54953, DE-FG02-09ER55006, and DE-FC02-05ER54823. \\[4pt] [1] D. N. Smithe, ``Finite-difference time-domain simulation of fusion plasmas at radiofrequency time scales,'' Physics of Plasmas 14, 056104 (2007).\\[0pt] [2] D. A. D'Ippolito, J. R. Myra, E. F. Jaeger, and L. A. Berry, ``Far Field Sheaths Due to Fast Waves Incident on Material Boundaries,'' Physics of Plasmas 15, 102501 (2008). [Preview Abstract] |
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BP8.00067: Glancing angle RF sheaths D.A. D'Ippolito, J.R. Myra RF sheaths occur in tokamaks when ICRF waves encounter conducting boundaries. The sheath plays an important role in determining the efficiency of ICRF heating, the impurity influxes from the edge plasma, and the plasma-facing component damage. An important parameter in sheath theory is the angle $\theta $ between the equilibrium B field and the wall. Recent work with 1D and 2D sheath models has shown that the rapid variation of $\theta $ around a typical limiter can lead to enhanced sheath potentials and localized power deposition (hot spots) when the B field is near glancing incidence [e.g. D.A. D'Ippolito et al., Plasma Phys. Control. Fusion 55, 085001 (2013)]. The physics model used to obtain these results does not include some glancing-angle effects, e.g. possible modification of the angular dependence of the Child-Langmuir law and the role of the magnetic pre-sheath [J.R. Myra et al., Nucl. Fusion 30, 845 (1990)]. Here, we report on calculations which explore these effects, with the goal of improving the fidelity of the rf sheath BC used in analytical and numerical calculations. [Preview Abstract] |
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BP8.00068: Scattering of radio frequency waves by density blobs A.K. Ram, K. Hizanidis, J. Valvis The scattering of ion cyclotron, lower hybrid, and electron cyclotron waves by density blobs embedded in the edge region of a fusion plasma is studied using a full-wave model [1]. The theory is similar to that for Mie scattering of electromagnetic waves by dielectric objects. The plasma, both inside the blob and outside, is assumed to be homogeneous and cold so that there are only two independent wave modes. The anisotropy induced by the magnetic field is such that the propagation characteristics and the polarization of the wave modes depend on the polar angle with respect to the direction of the magnetic field. Consequently, an incident plane wave is not only scattered by the blob, but also couples power to a different plasma wave. The blobs are assumed to be either cylindrical, with their axes aligned along the magnetic field, or spherical. The spectrum is affected by the size of the blobs, and the frequency and direction of propagation of the incident wave. We present the theoretical model along with numerical results, for all three frequency regimes, on the spectral characteristics of the scattered waves propagating into the plasma core.\\[4pt] [1] A. K. Ram, K. Hizanidis, and Y. Kominis, {\it Phys. Plasmas} {\bf 20}, 056110 (2013). [Preview Abstract] |
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BP8.00069: Development of the Finite Orbit Width version of the CQL3D code Yuri Petrov, Bob Harvey Further improvements for the Full Finite-Orbit-Width (FOW) version of the finite-difference CQL3D bounce-averaged Fokker-Planck (FP) code [1] have been made. This version adds neoclassical radial transport features into the FP coding, in contrast to the simplified Hybrid-FOW version. We emphasize that the Full-FOW version includes nonthermal and full-orbit, not small-orbit first order correction, neoclassical theory. The collision coefficients are averaged along guiding center orbits, with a proper transformation matrix from local coordinates to the midplane coordinates, where the FP equation is solved. All radial terms are included. The computation of the collision operator is parallelized in velocity-grid index, typically using 128 CPU cores, resulting in run times about 1-2 hours. Tests are performed for NSTX conditions with NBI heating. Comparison is done between the Full-FOW, Hybrid-FOW, and Zero-Orbit-Width models. \\[4pt] [1] R.W. Harvey and M. McCoy, ``The CQL3D Fokker Planck Code,'' www.compxco.com/cql3d [Preview Abstract] |
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BP8.00070: Investigating Stationary Phase Violations in Kinetic RF Simulation of Real Plasmas D.L. Green, L.A. Berry, E.F. Jaeger \renewcommand{\vec}[1]{\mathbf{#1}} The standard approach to linear, kinetic RF simulation in the ion-cyclotron and lower-hybrid frequency regimes in fusion plasmas utilizes the Fourier spectral method to capture the non-local plasma response [e.g., 1]. This response, i.e., the plasma current $\vec{j}_p$, is related to the wave electric field through a dielectric tensor $\bar{\sigma}$ for each Fourier mode $\vec{j}_p(\vec{k})=\bar{\sigma}(\vec{k})\cdot\vec{E}(\vec{k})$. $\bar{\sigma}$ is typically derived by solving the linearized Vlasov equation via the method of characteristics assuming stationary phase, constant amplitude electric field modes along those characteristics (i.e., a single $\vec{k}$ along unperturbed particle trajectories). This assumption is violated in real device magnetic field configurations. Here we examine the impact of variations in $\vec{k}$ along characteristics due to the poloidal magnetic field in Tokamak devices using the {\sc{Kinetic-j}} code [2]. We calculate $\vec{j}_p$ accounting for the variations in $\vec{k}$, compare with the analytic result, and discuss possible implications for present kinetic spectral RF codes. \\[4pt] [1] Jaeger E.F. et al., Phys. Rev. Lett. 90, 195001 (2003)\\[0pt] [2] Green D. L., http://meetings.aps.org/link/BAPS.2012.DPP.TP8.66 [Preview Abstract] |
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BP8.00071: Penetration and Scattering of Lower Hybrid Waves by Density Fluctuations Wendell Horton, M. Goniche, Y. Peysson, J. Decker, A. Ekedahl, X. Litaudon Lower Hybrid [LH] ray propagation in toroidal plasma is controlled by a combination of the azimuthal spectrum launched from the antenna, the poloidal variation of the magnetic field, and the scattering of the waves by the density fluctuations. The width of the poloidal and radial RF wave spectrum increases rapidly as the rays penetrate into higher density and scatter from the turbulence. The electron temperature gradient [ETG] spectrum is particularly effective in scattering the LH waves due to its comparable wavelengths and parallel phase velocities. ETG turbulence is also driven by the radial gradient of the electron current density giving rise to an anomalous viscosity spreading the LH-driven plasma currents. The scattered LH spectrum is derived from a Fokker-Planck equation for the distribution of the ray trajectories with diffusivity proportional to the fluctuations. The LH ray diffusivity is large giving transport in the poloidal and radial wavenumber spectrum in one - or a few - passes of the rays through the core plasma. [Preview Abstract] |
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BP8.00072: Nonlinear effects on lower hybrid waves current drive Dehui Li, Nong Xiang, Yu Lin, Xueyi Wang The quasi linear theory has been widely used to calculate lower hybrid wave current drive efficiency. For a sufficiently strong wave field, however, the nonlinear effects such as mode-mode couplings and perturbed particle orbits, should be taken into account. In this work, the nonlinear interactions of lower hybrid waves and plasmas are investigated via particle-in-cell simulations based on GEFI framework. It is found that as the wave amplitude increases, the resonance broadening due to the electron trapping and mode-mode coupling is observed. As a result, the driven current is greatly enhanced. [Preview Abstract] |
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BP8.00073: Active control of ECCD-induced tearing mode stabilization in coupled NIMROD/GENRAY HPC simulations Thomas Jenkins, Scott Kruger, Eric Held Actively controlled ECCD applied in or near magnetic islands formed by NTMs has been successfully shown to control/suppress these modes, despite uncertainties in island O-point locations (where induced current is most stabilizing) relative to the RF deposition region. Integrated numerical models of the mode stabilization process can resolve these uncertainties and augment experimental efforts to determine optimal ITER NTM stabilization strategies. The advanced SWIM model incorporates RF effects in the equations/closures of extended MHD as 3D (not toroidal or bounce-averaged) quasilinear diffusion coefficients. Equilibration of driven current within the island geometry is modeled using the same extended MHD dynamics governing the physics of island formation, yielding a more accurate/self-consistent picture of island response to RF drive. Additionally, a numerical active feedback control system gathers data from synthetic diagnostics to dynamically trigger \& spatially align the RF fields. Computations which model the RF deposition using ray tracing, assemble the 3D QL operator from ray \& profile data, calculate the resultant xMHD forces, and dynamically realign the RF to more efficiently stabilize modes are presented; the efficacy of various control strategies is also discussed. [Preview Abstract] |
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BP8.00074: Design of an HHFW antenna including high impedance surfaces for FTU Daniele Milanesio, Riccardo Maggiora The successful design of an Ion Cyclotron antenna mainly relies on the capability of coupling high power to the plasma (MW), feature that is currently reached by allowing rather high voltages (tens of kV) on the unavoidable unmatched part of the feeding lines. This requirement is often responsible of arcs along the transmission lines and other unwanted phenomena that considerably limit the usage of IC launchers. In this work, we suggest and describe a revolutionary approach based on high impedance surfaces, which allows to increase the antenna radiation efficiency and, hence, to highly reduce the imposed voltages to couple the same level of power to the plasma. High-impedance surfaces are periodic metallic structures (patches) displaced usually on top of a dielectric substrate and grounded by means of vertical posts usually embedded inside the dielectric, in a mushroom-like shape. In terms of working properties, high impedance surfaces are electrically thin in-phase reflectors, i.e. they present a high impedance, within a given frequency band, such that the image currents are in-phase with the currents of the antenna itself, thus determining a significant efficiency increase. This work documents the design by means of numerical codes of an antenna including high impedance surfaces to be tested on the FTU IBW port and fed by the FTU IBW generators at 433 MHz. The test on FTU, if successful, will confirm the possibility to adopt this approach for future HHFW antennas. [Preview Abstract] |
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BP8.00075: Parasitic oscillation study on CRPP X3 gyrotron Fengping Li, Jean-Philippe Hogge, Andreas Schlaich, Stefano Alberti, Miguel Silva Parasitic oscillations have a high impact to high power Gyrotron operation. They can degrade the beam quality, reduce the interaction efficiency and reduce the power production. Furthermore, it can cause the stability of the gyrotron operation which leads to unwanted oscillation modes and this unwanted oscillation modes can sometimes cause serious damage to gyrotron. In these paper the parasitic oscillation have been studied based the the 2s, 118 GHz X-3 gyrotron at CRPP. One frequency counter (70-170 GHz) with $\sim$20 ms sample ratio was used to monitor the entire pulse of the main modes. Two mixer systems were used to monitor the spectrum of the output RF. One mixer system is based on harmonic mixer with fast oscilloscope which can record $\sim$6GHz bandwidth spectrum with maximum time duration of 4 ms. Another is based on mixer and a 16 channel band-pass multiplex (in 4 GHz bandwidth) which can record pulse and CW signals. Parasitic oscillations were recorded and compared during different part of the pulse. The gyrotron operation parameters have been swept to check the change and evolution of these parasitic oscillations. [Preview Abstract] |
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BP8.00076: Recent Results using a 28 GHz EBW Heating and Current Drive System on MAST Tim Bigelow, John Caughman, Martin Peng, Stephanie Diem, Julian Hawes, Chris Gurl, Jonathan Griffiths, Vladimir Shevchenko, Paul Finburg, Joelle Mailloux, Gary Taylor Improvements to a high power 28 GHz gyrotron system have been made to the MAST Electron Bernstein Wave (EBW) heating, start up, and current drive system in the past few years as collaborative research between ORNL and CCFE. Recent EBW heating and CD experiments on MAST have improved upon previous RF generated plasma current levels. The goals of the research were to extend the initial EBW CD study [1] by increasing substantially the power level and pulse length of the gyrotron hardware and improve transmission line efficiency used in initial experiments. A dummy-load power level of up to 200 kW and a pulse length approaching 0.5 s has been achieved. Arcing, localized to the launcher box, has been observed to limit the launched power level to $\sim$80 kW for up to 450 ms. Several days of high power plasma operation have been recently completed with good progress in increasing the previously attainable solenoid-free plasma current levels. Up to 75 kA of plasma current was achieved at this injected power level. \\[4pt] [1] V. Shevchenko, et al, Nucl. Fusion \textbf{50} (2010), 022004. [Preview Abstract] |
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BP8.00077: Far-Field RF Sheaths due to Shear Alfv\'{e}n Waves in the LAPD Michael Martin, Bart Van Compernolle, Walter Gekelman, Pat Pribyl, Troy Carter, Daniel A. D'Ippolito, James R. Myra Ion cyclotron resonance heating (ICRH) is an important tool in current fusion experiments and will be an essential heating component in ITER. ICRH could be limited by deleterious effects due to the formation of radio frequency (RF) sheaths in the near-field (at the antenna) and in the far-field (e.g. in the divertor region). Far-field sheaths are thought to be caused by the direct launch of or mode conversion to a shear Alfv\'{e}n wave with an electric field component parallel to the background magnetic field at the wall.\footnote{D. A. D'Ippolito and J. R. Myra, \emph{Phys. Plasmas} \textbf{19}, 034504 (2012).} In this experiment a limiter plate was inserted into a cylindrical plasma in the LAPD (n$_{e}$ $\sim$ 10$^{10-11}$ cm$^{-3}$, T$_{e}$ $\sim$ 5 eV, B$_{0}$ = 1.2 kG) and RF sheaths were created by directly launching the shear Alfven wave. Plasma potential measurements were made with an emissive probe. DC plasma potential rectification was observed along field lines connected to the plate, serving as an indirect measure of RF sheath formation. 2-D maps of plasma properties and rectified plasma potential will be presented. This research is part of an ongoing campaign to study the formation and structure of RF sheaths. [Preview Abstract] |
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BP8.00078: Experimental Measurements of the Dynamic Electric Field Topology Associated with Magnetized RF Sheaths E.H. Martin, J.B.O. Caughman, S.C. Shannon, C.C. Klepper, R.C. Isler A major challenge facing magnetic fusion devices and the success of ITER is the design and implementation of reliable ICRH systems. The primary issue facing ICRH is the parasitic near-field which leads to an increased heat flux, sputtering, and arcing of the antenna/faraday screen. In order to aid the theoretical development of near-field physics and thus propel the design process experimental measurements are highly desired. In this work we have developed a diagnostic based on passive emission spectroscopy capable of measuring time periodic electric fields utilizing a generalized dynamic Stark effect model and a novel spectral line profile fitting package. The diagnostic was implemented on a small scale laboratory experiment designed to simulate the edge environment associated with ICRF antenna/faraday screen. The spatially and temporally resolved electric field associated with magnetized RF sheaths will be presented for two field configurations: magnetic field parallel to electric field and magnetic field perpendicular to electric field, both hydrogen and helium discharges where investigated. [Preview Abstract] |
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BP8.00079: The ion-ion hybrid Alfv\'{e}n resonator in ITER G.J. Morales, W.A. Farmer In magnetized plasmas with two ion species, the cold, ion-ion hybrid frequency alters the propagation of Alfv\'{e}n waves. For compressional modes propagating across the magnetic field, the ion-ion hybrid frequency acts as a resonance, which can be used for plasma heating. In contrast, the shear Alfv\'{e}n wave experiences a cutoff at locations where the wave frequency equals the ion-ion hybrid frequency. Since fusion plasmas must operate with two dominant ion species, Deuterium and Tritium, it is of interest to explore the role of this cutoff in such an environment. In a tokamak, the periodic variation in the strength of the magnetic field along a field-line results in two conjugate ion-ion hybrid points that could, in principle, give rise to a shear Alfv\'{e}n wave resonator. The present study examines various issues (curved field-lines, focusing and divergence of ray trajectories) that play a role in the formation of such a resonator in ITER plasmas, in which the high electron temperature requires that the electron response be treated adiabatically. [Preview Abstract] |
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BP8.00080: A full-wave numerical simulation code for RF heating in weakly-inhomogeneous plasmas C. Tsironis, A. Papadopoulos, A.K. Ram, K. Hizanidis, A. Samaras The numerical code FWTOR is a full-wave solver of electromagnetic wave propagation in weakly inhomogeneous plasmas. It is based on the finite-difference time-domain method (FDTD), and simulates, using a least resource-demanding algorithm, wave propagation in one, two, or three spatial dimensions. The code consists of four basic parts: (1) the wave propagation solver; (2) a computation of the magnetic equilibrium based on a Hamiltonian model for magnetic field-line tracing; (3) the plasma response function for electron cyclotron waves based on the linear, weakly-relativistic, hot plasma dielectric tensor; (4) the convolutional perfectly matched layer (CPML) boundary conditions. We are in the process of code parallelization (mixed open MP-MPI) and the implementation of a fully-inhomogeneous plasma tensor. We will then have the capability to extend our analysis of wave propagation to the lower frequency lower hybrid and ion cyclotron waves. The inhomogeneous plasma model is based on a formalism of the dielectric tensor obtained from the kinetic equation containing the spatial derivatives of the distribution function. A description of the various algorithms and the structure of the code along with some numerical results for electron cyclotron wave propagation will be presented. [Preview Abstract] |
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BP8.00081: New Technique of AC drive in Tokamak using Permanent Magnets Jackson Matteucci, Ali Zolfaghari This study investigates a new technique of capturing the rotational energy of alternating permanent magnets in order to inductively drive an alternating current in tokamak devices. The use of rotational motion bypasses many of the pitfalls seen in typical inductive and non-inductive current drives. Three specific designs are presented and assessed in the following criteria: the profile of the current generated, the RMS loop voltage generated as compared to the RMS power required to maintain it, the system's feasibility from an engineering perspective. All of the analysis has been done under ideal E{\&}M conditions using the Maxwell 3D program. Preliminary results indicate that it is possible to produce an over 99{\%} purely toroidal current with a RMS d$\Phi $/dt of over 150 Tm$^{\mathrm{2}}$/s, driven by 20MW or less of rotational power. The proposed mechanism demonstrates several key advantages including an efficient mechanical drive system, the generation of pure toroidal currents, and the potential for a quasi-steady state fusion reactor. The following quantities are presented for various driving frequencies and magnet strengths: plasma current generated, loop voltage, torque and power required. [Preview Abstract] |
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BP8.00082: Coupling and spatial structure of Alfven-ion-cyclotron waves in GAMMA 10 R. Ikezoe, M. Ichimura, M. Hirata, T. Yokoyama, T. Iimura, Y. Saito, Y. Iwamoto, T. Okada, S. Sumida, K. Watanabe, M. Yoshikawa, J. Kohagura, Y. Shima In the GAMMA 10 tandem mirror, anisotropy-driven Alfven wave, referred as Alfven ion-cyclotron (AIC) wave, have been spontaneously excited in high-beta discharges. Density fluctuation, which we measured with a reflectometer, shows fruitful interactions of AIC waves with externally applied ICRF waves and with themselves. These wave-wave coupling phenomena are found to be an important issue for mirror-confinement of high-energy ions in GAMMA 10; the amount of axially transported high-energy ions of greater than 6 keV measured with a semiconductor detector demonstrated significant modulation by the difference frequencies between simultaneously excited AIC waves (about 100 kHz). This indicates pitch-angle scattering due to the excited low-frequency Alfven waves. We present detailed characteristics of the coupling phenomena observed in GAMMA 10 and also spatial structure of the spontaneously excited AIC waves, which we have investigated by using a two-channel reflectometer. [Preview Abstract] |
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BP8.00083: Gas Puff Z-Pinches at 1-MA and 200-ns on COBRA David Hammer, Niansheng Qi, Elliott Rosenberg, Levon Atoyan, William Potter, Kate Blesener, Adam Cahill, Pierre-Alexandre Gourdain, John Greenly, Cad Hoyt, Bruce Kusse, Sergei Pikuz, Peter Schrafel, Tatiana Shelkovenko We report 6-cm diameter, double-shell gas puff Z-pinch experiments at 1 MA on the COBRA pulsed power generator, in which the implosion dynamics in puff-on-puff load configurations with and without a wire on the pinch axis were studied. Diagnostics used included: Planar Laser Induced Fluorescence Analyzer for measuring initial density profiles of the gas puff; a Laser Shearing Interferometer and a Laser Wavefront Analyzer for density profiles in the implosion and pinch phases; fiber-coupled, gated visible-light spectrometers for radially resolved imploding plasma spectra; gated XUV cameras for implosion dynamics; filtered pinhole x-ray cameras for imaging x-ray emission; and a double-crystal x-ray spectrometer for axially resolved pinch plasma densities and temperatures. From these, we derived the implosion velocity, ion charge states and then the imploding plasma temperatures, obtained the time evolution of the imploding plasma sheath structure and Magnetic Rayleigh-Taylor instability, and observed the most stable implosion with light-ions (Ne) imploding on heavy-ions (Ar), unstable implosions with heavy-ions (Ar) imploding on light-ions (Ne), and tighter, denser and less hot pinch plasma with a wire on axis. Details of the results will be presented. [Preview Abstract] |
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BP8.00084: Developing DIII-D to Address Critical Plasma Science for Fusion Energy R.J. Buttery, T.S. Taylor, M.R. Wade, D.N. HIll DIII-D is being equipped with new tools and upgrades to confront the scientific challenges required to prepare the next generation of fusion devices. An increase to dominant electron heating with high power ECH and balanced neutral beam will heat like fusion alphas to develop the scientific basis for burning plasma regime optimization. Improved 3-D field capabilities will resolve control of transients while maintaining plasma stability. Upgraded disruption mitigators will explore the science of safely quenching tokamak plasmas. These developments will provide the basis to develop robust high performance in ITER. To develop quasi-continuous operation for a future reactor, off axis current drive and total heating power is being raised, to study the optimization of self-consistent self-sustaining plasma regimes. And the physics basis for an improved divertor configuration is being developed, to be tested and optimized in an upgrade to DIII-D prior to implementation in an FNSF. These solutions will then be tested with a reactor relevant wall, emergent from a parallel US materials program. This will enable DIII-D to address the crucial challenges for ITER, FNSF and fusion energy. [Preview Abstract] |
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BP8.00085: Stability and Confinement of ITER Baseline Scenario Plasmas in DIII-D T.C. Luce, T.W. Petrie, G.L. Jackson, F. Turco, W.M. Solomon Recent experiments extended plasma conditions typical of the ITER baseline scenario for $Q=10$ operation ($q_{95}=3$, $\beta_N=1.8$) in the direction of low applied torque and low collisionality while maintaining $T_e=T_i$. These are key parameters where the worldwide H-mode database differs significantly from conditions expected in ITER, due to the use of co-injected neutral beam (co-NBI) heating. Here, balanced NBI and electron cyclotron heating (ECH) are used. Assessment of the global confinement using the IPB98y,2 scaling indicates confinement is good ($H_{98y2}\geq 1.0$) at low torque ($<$1~Nm). The stability of these plasmas is different from those with co-NBI, with most becoming unstable to $n=1$ tearing modes that lock to the lab frame and grow, leading to loss of confinement. Since the $n=1$ mode often appears soon after the plasma reaches the target $\beta_N$, the issue may be access to stable conditions or the absence thereof. Stability is enhanced when the ELMs and edge conditions are modified by deuterium flow on the outboard side of the plasma for radiative divertor operation, which may indicate a key role of the pedestal current density in the $n=1$ tearing mode stability at $q_{95}=3$. [Preview Abstract] |
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BP8.00086: High Internal Inductance as a Steady-State Scenario J.R. Ferron, T.C. Luce, C.T. Holcomb, J.M. Park An optimized high $\ell_i$ discharge is being investigated as a candidate steady-state operating scenario. Increased plasma internal inductance, $\ell_i$, is motivated by better confinement and higher ideal-stability-limited normalized beta ($\beta_N$). Stable operation at high $\beta_N$, even with relatively low H-mode pedestal pressure, could be possible with sufficient confinement and without a requirement for a conducting wall or $n\geq 1$ feedback coils. Increased $\beta_N$, and thus bootstrap current fraction ($f_{BS}$), results in lower $\ell_i$, so an optimized steady-state scenario is expected to have moderate $\beta_N\approx 4$, $f_{BS}\approx 0.5$ and $\ell_i\approx 1$. The externally-driven current is required near the axis where it can be produced efficiently. In experiments, non-stationary discharges with parameters exceeding these values ($f_B\approx 0.8$, $\beta_N >4$ but below the calculated no-wall ideal stability limit) have been produced. Noninductive overdrive of the plasma current was verified through freezing of the ohmic coil current. Based on these discharges, an ideal MHD stable, stationary solution for DIII-D has been modeled using FASTRAN and TGLF. [Preview Abstract] |
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BP8.00087: MARS-K Modeling Validation for Rotation and Fast-Ions Impact on RWM Stability in DIII-D Plasmas F. Turco, J.M. Hanson, G.R. Navratil, Y. Liu, M.J. Lanctot, A.D. Turnbull New MARS-K modeling results have been obtained to validate the theory that links the stabilization of the RWM to the presence of toroidal rotation and kinetic resonances. A $\beta_N$ scan previously analyzed with MARS-F (ideal MHD only), whose results showed a peak in plasma response amplitude at the $\beta_N$ no-wall limit, has been modeled including kinetic wave-particle resonances and non-resonant fast-ion damping. The damping physics increases the accuracy of the match with experimental data by a factor of $\sim$2 up to $\sim$80\% of the no-wall limit. The cases at and above the limit are overestimated. New experimental data have been obtained in a rotation scan, extending the range of explored rotations by a factor of $\sim$2. The downward trend of the response amplitude stops at $\sim$60 km/s and an increasing slope is present at higher rotation. MARS-K correctly reproduces experimental trend, but the amplitude is overestimated by a factor of $\sim$2, consistently with the results of the high $\beta_N$ cases. [Preview Abstract] |
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BP8.00088: Analysis and Simulation of ITER Steady-State Discharges on DIII-D S.J. Diem, M. Murakami, J.M. Park, A.C. Sontag One of the primary goals of the ITER project is to demonstrate a reactor scale steady-state operation for future tokamaks. This is a challenging task which requires simultaneous operation with fully noninductive current drive, a fusion gain of $Q\geq 5$ and IBS for discharges approximately 3000s in length. Previously, DIII-D has demonstrated fully noninductive scenario in ITER-like shaped plasmas at relatively high $q_{95}\sim 6.5$ and moderate $\beta_N\sim 3$ but with low fusion performance ($G=\beta_N H_{89}/q_{95}^2\sim 0.15$). Recent high $q_{min}$ experiment and modeling indicate that the goal of $G=0.3$ predicted for $Q=5$ operation on ITER can be achieved noninductively at reduced $q_{95}$ and at higher $\beta_N$. An optimum choice of $q_{95}$ and $\beta_N$ for the ITER steady-state mission will be discussed based on the experimental scaling from ITER demonstration discharges on DIII-D, as well as predictive FASTRAN scenario modeling using TGLF coupled to the Integrated Plasma Simulator. FASTRAN is a new iterative numerical procedure that integrates a variety of models (transport, heating, CD, equilibrium and stability) and has been shown to reproduce most features of DIII-D high beta discharges with a stationary current profile. [Preview Abstract] |
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BP8.00089: Response of DIII-D Discharges in ITER Baseline Scenario Regime to Incremental Heating Power R.I. Pinsker, G.L. Jackson, D.C. Pace, B.A. Grierson, J.C. Hosea, A. Nagy, R. Perkins, W.M. Solomon, G. Taylor, M. Porkolab, M.E. Austin, S. Diem, P.M. Ryan, F. Turco Experiments on DIII-D have been performed in which discharges in the ITER Baseline Scenario regime have been perturbed with 1-2 MW of additional heating power. With a base of $\sim$3 MW of neutral beam (NB) power, incremental electron cyclotron heating (ECH), fast waves (FWs) at 90 MHz and 60 MHz, or additional NB power has been introduced into a quasi-stationary phase of the flattop. The responses of the thermal profiles, D-D neutron rate, total stored energy, etc. to the different forms of heating power show that both incremental EC and FW power engender increases in heat, particle, and momentum diffusivity in response to the changes in power deposition profiles and $T_e/T_i$. This is manifested as a flattening of the central density profile and a slowing of the toroidal rotation velocity. TRANSP shows that the neutron rate is as expected for incremental NB and EC, while some FW power damps on NB ions and enhances the neutron rate significantly. [Preview Abstract] |
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BP8.00090: Electron Temperature Critical Gradient and Transport Stiffness on DIII-D C.C. Petty, S.P. Smith, T.C. Luce, R. Prater, T.L. Rhodes, G. Wang, L. Zeng, C.H. Holland, M.E. Austin, G.R. McKee, Z. Yan Experiments on DIII-D have measured the electron temperature critical gradient by varying the electron cyclotron heating (ECH) profile on a shot-by-shot basis using five gyrotrons, while a sixth gyrotron was modulated to simultaneously measure the electron transport stiffness. In L-mode plasmas at a normalized radius around $\rho$=0.6-0.7, the electron temperature critical scale length decreased from $L_{Te}$=0.26 m at a plasma current of 0.8 MA to $L_{Te}$=0.19 m at 1.2 MA. The electron transport stiffness, a parameter obtained by fitting the data to a critical gradient model, was weaker by up to a factor of 5 at the higher plasma current. Plasmas with co-neutral beam injection in addition to ECH had similar dependences of the critical $L_{Te}$ and transport stiffness on plasma current. The measured electron temperature critical gradients, transport stiffness and turbulence characteristics will be compared to transport simulations by the GYRO and TGLF codes, especially in regard to understanding the origin of the ``edge shortfall'' in the predicted heat flux that occurs for many L-mode plasmas. [Preview Abstract] |
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BP8.00091: ELM-free, Quiescent H-mode Operation in DIII-D Under Reactor-Relevant Conditions Using Non-Axisymmetric Magnetic Fields K.H. Burrell, A.M. Garofalo, W.M. Solomon, M.E. Fenstermacher Application of static, non-axisymmetric magnetic fields (NAMFs) to DIII-D plasmas allows sustained quiescent H-mode (QH-mode) operation under reactor-relevant conditions of beta, collisionality and torque from neutral beam injection (NBI). QH-mode is an ideal plasma for next step devices, exhibiting H-mode confinement levels while operating without edge localized modes at constant density and radiated power. Peeling-ballooning mode stability theory suggests, and previous studies confirm, that QH-mode operation requires sufficient radial shear in the toroidal rotation near the plasma edge. In past experiments, this rotation shear was predominantly produced by torque from counter-directed NBI. In recent experiments, counter torque due to neoclassical toroidal viscosity produced by the NAMFs gave rise to the necessary edge rotational shear, even overcoming small amounts of co-NBI torque. Experiments in the 2013 campaign have investigated techniques for creating QH-mode plasmas with zero net NBI torque from Ohmic plasmas, opening a path to QH-mode operation with reactor-relevant torque throughout the shot. [Preview Abstract] |
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BP8.00092: Structure and Behavior of the Edge Harmonic Oscillation in Quiescent H-Mode Plasmas on DIII-D G.R. McKee, Z. Yan, K.H. Burrell, A.M. Garofalo, B.A. Grierson, W.M. Solomon The edge harmonic oscillation (EHO) is a steady-state, pedestal-localized instability that is observed in high-performance, ELM-free Quiescent H-mode plasmas. The spatiotemporal characteristics of the EHO have been measured in QH-mode plasmas with a 2D BES array that measures low-k density fluctuations. The skewness of the fluctuation distribution increases radially from -0.5 to +1 near the separatrix, consistent with the radially varying and highly non-sinusoidal harmonic structure. These fluctuation characteristics are qualitatively consistent with an outward particle transport driven by the EHO. The density fluctuation ($\tilde{n}/n$) profile peaks inside the pedestal, near $\rho=\,$0.90-0.95, and is observed from $\rho=0.85$ to the separatrix; the fundamental frequency is typically in the range of 5-15 kHz. The radial structure of the oscillation has a monotonically varying phase shift of approximately 180 degrees across the outer plasma region that changes direction with plasma current, suggesting that the mode structure is impacted by the high edge toroidal rotation velocity. [Preview Abstract] |
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BP8.00093: Interpretive and Predictive Transport Analysis in DIII-D ITER Baseline and QH-Mode Discharges B.A. Grierson, R.V. Budny, W.M. Solomon, X. Yuan, J. Candy, T.C. Luce, C.C. Petty Development of a set of predictive modeling tools requires models to be continually benchmarked against experimental measurements. In order to support a predictive capability for future fusion reactors the accuracy of predictive modeling tools must be verified and validated. In this work, selected DIII-D discharges from inductive ITER baseline and QH-mode scenarios are investigated with interpretive analysis and predictive transport models. TRANSP is used in an interpretive mode to determine heating sources and transport fluxes during steady phases of the discharges. TGYRO-TGLF is used to examine steady-state transport solutions whereby profiles are calculated based on flux-matching gradients. Time-dependent predictive modeling will be done with PTRANSP, using the PT$\underline{~}$SOLVER solution with the TGLF transport model [Preview Abstract] |
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BP8.00094: Intense Bursts of Millimeter-wave Emission in QH-mode Plasmas on the DIII-D Tokamak L. Yu, C.W. Domier, N.C. Luhmann, Jr., B.J. Tobias, W.M. Solomon, M.E. Austin Intense bursts of millimeter-wave emission have been observed during low collisionality QH-mode plasmas on the DIII-D tokamak. These bursts are synchronized to the edge harmonic oscillation (EHO) and the rising edge of longer period oscillations observed in filterscope data. Enhanced electron transport precedes the bursting and we hypothesize that this bursting is due to some of the resulting electron orbits being in resonance with the 3D structure of the EHO. We present a 3D model for the EHO and we locate the bursting on this structure. This is compared to the orbits of trapped electrons. [Preview Abstract] |
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BP8.00095: Fast Ion Confinement in High Beta, Steady-State Scenario Plasmas W.W. Heidbrink, X. Chen, J.R. Ferron, M.A. Van Zeeland, B.A. Grierson, C.T. Holcomb Fast-ion confinement is studied for $q_{min}$ between 1.2-2.8 in plasmas with normalized $\beta > 2.6$. Fast-ion D-alpha (FIDA), neutron, and neutral-particle diagnostics measure the confined fast ions. Tearing modes and a ``sea'' of unstable Alfv\'en eigenmodes (AE) are observed. In preliminary analysis, the degradation in fast-ion confinement increases with $q_{min}$; increased AE activity appears responsible. Predictions of a model that assumes that AE-induced fast-ion transport is stiff are compared with the data. [Preview Abstract] |
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BP8.00096: Neutron Detection With Ultra-Fast Digitizer and Pulse Identification Techniques on DIII-D Y.B. Zhu, W.W. Heidbrink, D.A. Piglowski A prototype system for neutron detection with an ultra-fast digitizer and pulse identification techniques has been implemented on the DIII-D tokamak. The system consists of a cylindrical neutron fission chamber, a charge sensitive amplifier, and a GaGe Octopus 12-bit CompuScope digitizer card installed in a Linux computer. Digital pulse identification techniques have been successfully performed at maximum data acquisition rate of 50MSPS with on-board memory of 2GS. Compared to the traditional approach with fast nuclear electronics for pulse counting, this straightforward digital solution has many advantages, including reduced expense, improved accuracy, higher counting rate, and easier maintenance. The system also provides the capability of neutron-gamma pulse shape discrimination and pulse height analysis. Plans for the upgrade of the old DIII-D neutron counting system with these techniques will be presented. [Preview Abstract] |
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BP8.00097: H-mode Particle Transport Measurement and Comparison to TGLF in DIII-D L. Zeng, E.J. Doyle, L. Schmitz, T.L. Rhodes, W.A. Peebles, S. Mordijck, G.M. Staebler, C.C. Petty H-mode particle transport has been measured in DIII-D using an upgraded high resolution profile reflectometer and gas-puff perturbative transport techniques. It is observed that the electron density peaking is insensitive to collisionality in DIII-D. Initial analysis indicates the ne peaking factor decreases in H-mode plasmas with dominant ECH heating, versus NBI-only heated cases. In addition, longer density decay times are observed with dominant ECH heating compared with NBI-only. In some of these cases, particle transport changes are associated with changes in the dominant turbulence mode from ITG to TEM. It is also observed that the density decay time associated varies with the magnitude of the NBI input torque, implying a correlation between particle and momentum transport. The quantitative particle transport rates are under analysis, and will be compared to TGLF modeling. Turbulence measurement results will be presented also. The results will help to understand turbulence mechanism of particle transport and the relation to momentum transport. [Preview Abstract] |
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BP8.00098: Effect of Robin Boundary Conditions on Analysis and Simulation of Turbulent Transport Using TGLF, MMM95, and GLF23 H.E. St. John, A.D. Turnbull, L.L. Lao Turbulent transport predictions using transport models show that results are often sensitive to the choice of Dirichlet boundary values used as well as the location of the plasma edge assumed for core transport simulations. However, experimental data does not support the discontinuous slope of temperature profiles at the boundary that often result from simulations using this boundary condition. Experimental profiles appear to be best reproduced when such discontinuities are absent. This suggests that a linear combination of boundary derivative and boundary value at the core simulation boundary is more appropriate. Here, we develop this general Robin condition for the coupled set of nonlinear transport equations and apply the results to a number DIII-D L- and H-mode experimental discharges including time evolved simulations with TGLF, MMM95 and GLF23 as well as rapid power balance analyses methods. [Preview Abstract] |
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BP8.00099: Theory and Simulation of Quasilinear Transport from External Magnetic Field Perturbations in a DIII-D Plasma R.E. Waltz, N.M. Ferraro The linear response profiles for the 3D perturbed magnetic fields, currents, ion velocities, plasma density, pressures, electric potential due to external resonant magnetic field perturbations (RMP) are obtained from the collisional two-fluid M3DC1 code. A newly developed RMPtran code computes the resulting quasilinear ExB and magnetic radial transport flows in all channels: ion and electron particle and energy, as well as toroidal angular momentum (TAM). The relative mix of ambipolar ExB and non-ambipolar magnetic particle transport and resulting JxB torque is of particular interest. Surprisingly much of the core RMP island JxB torque braking plasma rotation is returned to accelerate the plasma edge. Our main focus is on delineating the mechanisms for the RMP density pump-out where the radial convection of TAM is competitive with the magnetic braking of plasma rotation. Enhancement of the two-fluid crossfield resistivity, heat diffusivity, and viscosity represents the effects of turbulence on the low-n RMP transport. High-n turbulent transport is to be taken from the TGLF transport model. [Preview Abstract] |
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BP8.00100: Physics-model-based Actuator Trajectory Optimization and Feedback Control of the Plasma Safety Factor Profile and Internal Energy Dynamics in DIII-D J.E. Barton, E. Schuster, M.L. Walker, D.A. Humphreys Simulation and experimental results in DIII-D are presented to demonstrate the potential of integrated physics-model-based $q$ profile and internal energy control algorithms for systematic attainment and repeatability of discharges. Both simulations and experiments demonstrate improved profile control accuracy relative to open loop (feedforward) control alone, by using a combined feedforward~+ feedback scheme. The scheme is constructed by embedding a nonlinear, first-principles-driven, physics-based model of the plasma dynamics into the control design process. Firstly, a tool to numerically design actuator trajectories that steer the plasma to a desired operating state (feedforward) is developed with the objective of supporting the traditional trial-and-error experimental process of advanced scenario planning. Secondly, an algorithm to track a desired $q$ profile and internal energy evolution (feedback) is developed with the goal of adding robustness to the control scheme. [Preview Abstract] |
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BP8.00101: Comparison of Data-Driven and First-Principles Model-Based Control Approaches for Regulation of the Poloidal Flux Profile and $\beta_N$ in DIII-D Advanced Tokamak Scenarios W. Wehner, W. Shi, E. Schuster, M.L. Walker, D.A. Humphreys Modeling of the coupled evolution of the poloidal flux profile and $\beta_N$ in response to the heating and non-inductive current drive systems (neutral beam and electron cyclotron powers) as well as to the total inductive plasma current is carried out in this work with the ultimate goal of employing the developed models for control design. The modeling process follows two distinct approaches: data-driven modeling and first principles modeling. Using each model separately to design and test a controller for the regulation of the poloidal flux profile and $\beta_N$ around desired operating points, the advantages and limitations of the two approaches are compared. This study represents one of the first steps towards defining the modeling needs for successful model-based current-profile control in present and future devices. Results from numerical and experimental testing in the DIII-D tokamak are presented. [Preview Abstract] |
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BP8.00102: Off-diagonal Terms Connection Between Particle and Momentum Transport in DIII-D Plasma X. Wang, S. Mordijck, E.J. Doyle, O. Meneghini Understanding particle and momentum transport in tokamaks is essential to predict density and rotation profiles. Previous work [1] has indicated that there is a connection between changes in momentum transport as well as particle transport across ITG-TEM domains and its relation to the peaking of density profiles. On DIII-D, recent experiments were unable to reproduce those results [1] in H-mode plasmas. In order to study the role of the rotation profile on the changes in particle transport, we varied the input torque through the neutral beams, from co to counter. We compare linear instability growth rates with changes in density fluctuations and we investigate the off-diagonal contribution of the rotation profile on the changes in particle transport. Using TGLF, we calculate the perturbed D and v coefficients and compare them to experimental measurements and theoretical predictions for inward turbulent pinch and outward diffusion.\par \vskip6pt \noindent [1] C.~Angioni, et al., Nuclear Fusion {\bf 52}, 114003 (2012). [Preview Abstract] |
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BP8.00103: Initial UF-CHERS Measurements of Ion Temperature Fluctuations as a Function of Electron Temperature Gradient D. Truong, R.J. Fonck, G.R. McKee, Z. Yan, S.P. Smith The Ultra Fast CHarge Exchange Recombination Spectroscopy (UF-CHERS) diagnostic on DIII-D measures local, long-wavelength ion temperature and toroidal velocity fluctuations at turbulence-relevant spatiotemporal scales. The optical system consists of 2 spatial channels, with 8 spectral channels each, set 1 cm apart radially (within a turbulence correlation length). UF-CHERS measures photons emitted from the n=8-7 transition of C VI at 529.05 nm during the charge exchange recombination reaction between injected neutral beam deuterium atoms and intrinsic carbon ions. Unique features include high optical throughput, low-noise, high-gain, high efficiency APD detectors, and a 1 MHz sampling rate; all designed to measure turbulent ion thermal fluctuations. In an experiment exploring the calculated shortfall of transport and turbulence at high gyroBohm normalized flux in L-mode plasmas, varying ECH power was applied between $\rho$=0.6 and $\rho$=0.8 to change the gradient scale length and local heat flux to examine transport behavior near $\rho$=0.7. This experiment provided a suitable test case for UF-CHERS and measurements were obtained as a function of electron temperature gradient; initial results will be presented. [Preview Abstract] |
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BP8.00104: Progress on Bayesian Inference of the Fast Ion Distribution Function L. Stagner, W.W. Heidbrink, X. Chen, W. Salewski, B.A. Grierson The fast-ion distribution function (DF) has a complicated dependence on several phase-space variables. The standard analysis procedure in energetic particle research is to compute the DF theoretically, use that DF in forward modeling to predict diagnostic signals, then compare with measured data. However, when theory and experiment disagree (for one or more diagnostics), it is unclear how to proceed. Bayesian statistics provides a framework to infer the DF, quantify errors, and reconcile discrepant diagnostic measurements. Diagnostic errors and weight functions that describe the phase space sensitivity of the measurements are incorporated into Bayesian likelihood probabilities. Prior probabilities describe physical constraints. This poster will show reconstructions of classically described, low-power, MHD-quiescent distribution functions from actual FIDA measurements. A description of the full weight functions will also be shown. [Preview Abstract] |
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BP8.00105: High Resolution ECE Measurements on DIII-D M.E. Austin, D. Truong In DIII-D plasmas, electron cyclotron emission (ECE) measurements with high spatial resolution, $\sim$1 cm or less, are possible due to typically large optical depth. To take advantage of this, a new set of eight channels has been added to the ECE radiometer with narrow bandwidth, closely spaced, fixed frequency filters to look at small scale $T_e$ fluctuations. The high resolution ECE system uses signals from the three existing IF bands of the radiometer. Full band coverage is accomplished by mixing higher IF frequencies down into the 2-4 GHz filter range. Channel filters are 200 MHz wide, with centers separated by 250 MHz; these will provide resolved measurements down to 0.6-0.8 cm depending on the local electron temperature and $B_T$ scale length. Calculations of the relativistically broadened emission widths will be given. Typical uses of the channels will be to map out the spatial dependence of Alfv\'enic eigenmodes, geodesic acoustic modes, and externally applied magnetic perturbations. First data has been obtained and initial measurements of $T_e$ structures will be presented. [Preview Abstract] |
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BP8.00106: Commissioning a Megawatt-class Gyrotron with Collector Potential Depression J. Lohr, M. Cengher, Y.A. Gorelov, D. Ponce, R. Prater A 110 GHz depressed collector gyrotron has been installed on the DIII-D tokamak. The commissioning process rapidly achieved operation at full parameters, 45 A and 94 kV total voltage, with 29 kV depression. Although short pulse, 2 ms, factory testing demonstrated 1.2 MW at 41\% electrical efficiency, long pulse testing at DIII-D achieved only 33\% efficiency at full power parameters, for pulse lengths up to 10 s. Maximum generated power was $\sim$950 kW, considerably below the 1.2 MW target. During attempts to increase the power at 5 s pulse length, it was noted that the collector cooling water was boiling. This led to the discovery that 14 of the 160 cooling channels in the collector had been blocked by braze material during manufacture of the tube. The locations of blocked channels were identified using infrared imaging of the outside of the collector during rapid changes in the cooling water temperature. Despite these difficulties, the rf beam itself was of very high quality and the stray rf found calorimetrically in the Matching Optics Unit, which couples the Gaussian rf beam to the waveguide, was only 2\% of the generated power, about half that of our previous best quality high power beam. Details of the power measurements and collector observations will be presented. [Preview Abstract] |
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BP8.00107: Performance of the DIII-D ECH System M. Cengher, J. Lohr, Y.A. Gorelov, D. Ponce The six gyrotron ECH system on DIII-D is performing with good reliability while being upgraded. The total power injected into DIII-D has reached 3.4 MW, with pulse length up to 5 s. The power generated by the individual gyrotrons, the power injected into the tokamak, and the total energy injected into DIII-D will be shown for the present year on a shot-to-shot basis. The efficiency of a new transmission line for the most recently installed gyrotron was measured. This gyrotron injects up to 720 kW of power into DIII-D, for 915 kW of generated power. The polarization was checked and the results are shown in agreement with the computed values. The gyrotron ``Tinman'' was moved to a tank, formerly occupied by the poorly performing ``Han'' gyrotron, which developed an internal water leak. The re-measured transmission efficiency for this line is -0.96 dB. The use of TIMCON event controller to set ECH timing and aiming is expected to lead to a decrease in the time necessary to install the setup for a new shot, eliminate possible operator errors, and provide better coordination with other aspects of the experiment. The data processing includes calculation of the toroidal and poloidal ECH aiming angles and X-mode content for the steerable mirrors that are moved during the plasma shot. [Preview Abstract] |
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BP8.00108: Upgrades and Additions for the ECH System on \mbox{DIII-D} Y.A. Gorelov, J. Lohr, M. Cengher, D. Ponce Six MW-class, 110 GHz gyrotrons have been in routine operation on DIII-D since 2008. One of these gyrotrons, which had low rf production and higher than normal collector power loading, failed due to a collector water leak. Nevertheless, the number of 110 GHz gyrotrons remained the same, as the first new 110 GHz CPI gyrotron with depressed collector potential design was installed and used in the 2013 experimental campaign. The DIII-D ECH transmission line system now comprises seven evacuated transmission lines up to 80 meters in length with transmission efficiencies from 69\%-79\% and four dual launchers. New stands are being fabricated and installed for two additional depressed collector gyrotrons, one with designed power of 1.2 MW at 110 GHz and the other with 1.5 MW at 117.5 GHz. One gyrotron was relocated to accommodate the new additions. High voltage power supplies, the water-cooling system and new waveguide lines for these gyrotrons are being built. One of the 110 GHz 1.0 MW gyrotrons in DIII-D was used as a source for heat exchanger tests. The rf beam was routed to a mobile test unit (MTU) trailer and shows expected expansion of beam radius vs distance from the waveguide end. Experiments were completed using 50-500 kW injected into the MTU lab at pulse lengths from 5-300 ms [Preview Abstract] |
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BP8.00109: Application of High Harmonic Fast Waves to Off-Axis Current Drive in DIII-D R. Prater, R.I. Pinsker, C.P. Moeller, M. Porkolab, V.L. Vdovin High harmonic fast waves, also called ``whistlers'' or ``helicons,'' may be an effective means of driving current off-axis in high performance discharges in \mbox{DIII-D}. Modeling using the GENRAY ray tracing code APP shows that fast waves launched with frequency 500~MHz tend to spiral around the magnetic axis. If the electron beta is above 1.7\%, the waves are damped around $\rho=0.5$ for a broad range of conditions. The fast wave current drive in the test discharge is 2 to 4 times larger per MW than that from the electron cyclotron heating or neutral beam injection systems on DIII-D. Interestingly, the current drive location and magnitude are nearly independent of the launched $n_{||}$ over the range 2 to 4. Use of a moderately large value, $n_{||}=3$, reduces the possibility of mode conversion to the slow wave. A traveling wave antenna is expected to be effective at launching the wave with a narrow spectrum of $n_{||}$, which also helps avoid mode conversion. A test of the physics of high harmonic fast wave current drive is planned for DIII-D. [Preview Abstract] |
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BP8.00110: Imaging Runaway Electrons in Slide-Away and Killer Pellet Discharges in DIII-D R.A. Moyer, E.M. Hollmann, V.A. Izzo, N.W. Eidietis, P.B. Parks, E.J. Strait, J.C. Wesley, C. Paz-Soldan, N. Commaux, R. Granetz Runaway electrons (REs) produced by acceleration of slide-away electrons in very low density ohmic discharges, and by rapid shutdown induced by argon pellets, have been studied by imaging synchrotron emission (SE) from 700-1000 nm, providing new data on the equilibrium and formation physics of RE beams. Trace levels of quiescent RE current (QRE) are produced in ohmic discharges with $n_e=4\times10^{18}/m^3$. The synchrotron emission forms 1 or 2 crescents near the q=1.5 and 2 surfaces, which survive fast transients due to low density locked modes. 2mm argon pellets with velocity $\sim$185 m/s produce REs when the pellet is strongly ablated upon reaching the core, forming $\sim$0.5 s long plateaus of several hundred kA when the RE seeds are formed inside $\rho\sim$0.35. Discharges in which the pellet survives, passing completely through the plasma to hit the centerpost, do not form enough RE seeds to provide an imageable synchrotron emission in the 700-1000 nm range. [Preview Abstract] |
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BP8.00111: Ideal MHD Continua, Mercier Stability, Sturmian Sequences, and Interchange Modes in Tokamak A.D. Turnbull, D.P. Brennan, J.M. Finn Numerical investigations are used to systematically study the dependence of unstable mode eigenvalues and mode structures as they are stabilized and pass into the continuum as physical parameters are varied. It is well known that the ideal MHD spectrum consists of a pair of stable continua corresponding to the shear Alfv\'en and acoustic waves, and a discrete unstable component [1]. Additional discrete modes can also exist within frequency gaps in the continua. In a special case, typically when the equilibrium is interchange unstable according to the Mercier criterion, a Sturmian sequence of unstable modes is predicted in 1D with an accumulation point at the edge of the shear Alfv\'en continuum [1]. In this case, the existence of Sturmian sequences is verified in 2D and their relation to the Mercier trial modes and to the continuum is analyzed. The sequence continuously transforms from a global kink into localized interchanges and ultimately singular continuum-like modes with increasing eigenmode number.\par \vskip6pt \noindent [1] J.P.\ Goedbloed and S.\ Poedts, Principles of Magnetohydrodynamics (Cambridge, 2004). [Preview Abstract] |
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BP8.00112: Feedback-Driven Mode Rotation Control by Electro-Magnetic Torque M. Okabayashi, E.J. Strait, A.M. Garofalo, R.J. La Haye, Y. In, J.M. Hanson, D. Shiraki, F. Volpe The recent experimental discovery of feedback-driven mode rotation control, supported by modeling, opens new approaches for avoidance of locked tearing modes that otherwise lead to disruptions. This approach is an application of electro-magnetic (EM) torque using 3D fields, routinely maximized through a simple feedback system. In DIII-D, it is observed that a feedback-applied radial field can be synchronized in phase with the poloidal field component of a large amplitude tearing mode, producing the maximum EM torque input. The mode frequency can be maintained in the 10 Hz to 100 Hz range in a well controlled manner, sustaining the discharges. Presently, in the ITER internal coils designed for edge localized mode (ELM) control can only be varied at few Hz, yet, well below the inverse wall time constant. Hence, ELM control system could in principle be used for this feedback-driven mode control in various ways. For instance, the locking of MHD modes can be avoided during the controlled shut down of multi hundreds Mega Joule EM stored energy in case of emergency. Feedback could also be useful to minimize mechanical resonances at the disruption events by forcing the MHD frequency away from dangerous ranges. [Preview Abstract] |
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BP8.00113: Validation of the Combined TGLF and NEO Transport Models on DIII-D J.E. Kinsey, R.W. Harvey, Yu.V Petrov, G.M. Staebler, C.C. Petty, E.A. Belli Recently, the ExB shear physics in the Trapped Gyro-Landau Fluid (TGLF) transport model was improved resulting in better agreement with GYRO nonlinear gyrokinetic turbulence simulations. The XPTOR transport code has been upgraded with the new version of TGLF. Here, we report on the results of predicting the density and temperature profiles in DIII-D H-mode discharges using the new TGLF model and compare the results to those obtained previously with TGLF-09. We also show the results of including kinetic carbon effects in TGLF and using the NEO drift-kinetic model for the neoclassical calculations. Previous TGLF modeling studies used the Chang-Hinton model. Building on these results we recompute the neutral beam deposition profile using the CQL3D code and examine the impact of finite orbit width (FOW) effects on the heating profile and the subsequent impact on our TGLF/NEO model predictions. In our validation study we focus on DIII-D discharges with varying degrees of toroidal rotation thus providing a dataset with varying mixes of turbulent and neoclassical transport. [Preview Abstract] |
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BP8.00114: Z-PINCH AND DENSE PLASMA FOCUS |
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BP8.00115: ABSTRACT WITHDRAWN |
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BP8.00116: ABSTRACT WITHDRAWN |
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BP8.00117: ABSTRACT WITHDRAWN |
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BP8.00118: VISAR Unfold Analysis of Load Current in MagLIF Experiments Mark Hess, Ryan McBride, Matthew Martin An accurate prediction of the load current is essential in the performance of MagLIF [1] experiments on the Z-Machine at Sandia. At present, the most accurate diagnostic for measuring load current on the Z-machine is the well-established VISAR technique. The VISAR diagnostic measures the velocity of a thin aluminum foil placed near the load, which is subject to the magnetic pressure produced by the load current, using a laser interferometer. The load current unfold analysis is highly nonlinear due to the equation of state/conductivity models, along with the MHD equations governing the foil. Nevertheless, an accurate load current unfold from the VISAR measurement is possible using an MHD code, in conjunction with an optimization algorithm. We will review the VISAR unfold analysis, and show recent current unfolds of MagLIF experiments in comparison to load current measurements using B-dot probes. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.\\[4pt] [1] S.A. Slutz et al, Phys. Plasmas 17, 056303 (2010). [Preview Abstract] |
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BP8.00119: Laser-only experiments in support of the MagLIF scheme Adam Harvey-Thompson, Stephen Slutz, Adam Sefkow, David Bliss, Matthias Geissel, Matthew Gomez, Eric Harding, Daniel Sinars, Ian Smith, Gennady Fiksel, Mingsheng Wei The MagLIF inertial confinement fusion scheme involves imploding a cylindrical liner with the 24 MA, 100 ns rise-time current pulse delivered by the Z generator which compresses a D2 fuel that is magnetized with an external magnetic field and preheated with an energy source -- currently the 2.5 kJ Z-Beamlet laser. For this scheme to be successful, laser energy has to be coupled effectively into the fuel and electron thermal conduction needs to be suppressed by the applied magnetic field. Laser only experiments at ZBL and Omega EP can potentially test these aspects of the scheme, exploring the physics and aiding target design. Completed and planned experiments are discussed. [Preview Abstract] |
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BP8.00120: Fundamental magneto-Rayleigh-Taylor Instability Growth Experiments D.B. Sinars, K.J. Peterson, R.A. Vesey, C. Jennings, M.C. Herrmann, R.D. McBride, M.R. Martin, S.A. Slutz Sandia is investigating a magnetized liner inertial fusion concept that uses cylindrical Be or Al liners to compress magnetized and preheated fusion fuel. As part of this work, we have been studying the growth of instabilities in initially solid liners driven with 20-24 MA, 100-ns current pulses on the Z pulsed power facility. The magneto-Rayleigh-Taylor instability in particular can disrupt the plasma liner during its implosion. Previous experiments studied instability growth starting either from intentionally seeded single-mode perturbations or from diamond-turned best-finish surfaces. Here we report on experiments studying (1) the growth of intentionally seeded multi-mode perturbations, and (2) the growth from polished best-finish surfaces where the tooling mark orientation is changed from being predominantly azimuthal to axial. [Preview Abstract] |
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BP8.00121: ABSTRACT WITHDRAWN |
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BP8.00122: Experimental Results from Plasma Shell on Deuterium Gas-puff Z-pinch on the Current Level of 3 MA K. Rezac, D. Klir, P. Kubes, J. Kravarik, A. Shishlov, A. Labetsky, V. Kokshenev, N. Ratakhin The experiments with a plasma shell on deuterium gas-puff Z-pinch were carried out on the GIT-12 generator at IHCE in Tomsk. We diagnosed Z-pinch shots with deuterium linear mass of about 100 $\mu$g/cm. The outer shell of the load was formed by 48 plasma guns positioned on diameter of 350 mm, the diameter of the nozzle producing deuterium inner shell gas-puff was 80 mm. Results obtained from X-ray and neutron diagnostics, especially neutron time-of-flight signals, where 15 MeV neutrons (in radial direction) and 22 MeV neutrons (in axial direction) were registered, are presented. Obtained implosion velocity of the gas-puff had the value of $4.5 \times 10^{7}$cm/s, neutron yield from D(d,n)$^3$He reaction was in order of $10^{12}$ neutrons/shot on a current level of about 2.7 MA. The time correlations of the TOF diagnostics with other diagnostics such as electrical characteristics, an MCP frames, and a visible streak camera are also presented. [Preview Abstract] |
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BP8.00123: Hybrid X-pinch Experiments on a MA Linear Transformer Driver* S.G Patel, D.A. Yager-Elorriaga, A.M. Steiner, R.M. Gilgenbach, N.M. Jordan, D.A. Chalenski, Y.Y. Lau X-pinch experiments have been conducted on the Linear Transformer Driver (LTD) at the University of Michigan. The x-pinch consists of a single wire separated by conical electrodes between two current return plates. The LTD was charged to $+$/-70 kV resulting in approximately 0.5 MA passing through a 35$\mu$m Al wire. Multiple, short x-ray bursts were detected over the 400 ns current pulse. Ultimately the x-pinch will be located in parallel with a planar foil in order to backlight the Magneto-Rayleigh-Taylor instability. A smaller 100 kA driver is also in development and may be used to independently energize the x-pinch. The x-pinch chamber has been constructed and the results of these experiments will be presented. \\[4pt] *This work was supported by DoE award number DE-SC0002590, NSF grant number PHY 0903340, and US DoE through Sandia National Labs award numbers 240985 and 76822 to the U of Michigan. S.G Patel and A.M Steiner are supported by NPSC funded by Sandia National Labs. D.A. Yager-Elorriaga is supported by an NSF fellowship under grant number DGE 1256260. [Preview Abstract] |
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BP8.00124: Characteristics of soft x-ray spectra from ultra-fast micro-capillary discharge plasmas Jing Li, Gonzalo Avaria, Vyacheslav Shlyaptsev, Fernando Tomasel, Michael Grisham, Quincy Dawson, Jorge Rocca The efficient generation of high aspect ratio (e.g. 300:1) plasma columns ionized to very high degrees of ionization (e.g. Ni-like Xenon) by an ultrafast current pulses of moderate amplitude in ~micro-capillary channels is of interest for fundamental plasma studies and for applications such as the generation of discharge-pumped soft x-ray lasers. Spectra and simulations for plasmas generated in 500 um alumina capillary discharges driven by 35-40 kA current pulses with 4 ns rise time were obtained in Xenon and Neon discharges. The first shows the presence of lines corresponding to ionization stages up to Fe-like Xe. The latter show that Al impurities from the walls and Si (from injected SiH$_{4})$ are ionized to the H-like and He-like stages. He-like spectra containing the resonance line significantly broaden by opacity, the intercombination line, and Li-like satellites are analyzed and modeled. For Xenon discharges, the spectral lines from the Ni-like transitions the 3d$^{9}$4d(3/2, 3/2)$_{\mathrm{J=0}}$ to the 3d$^{9}$4p(5/2, 3/2)$_{\mathrm{J=1}}$ and to 3d$^{9}$4p(3/2, 1/2)$_{\mathrm{J=1}}$ are observed at gas pressures up to 2.0 Torr. [Preview Abstract] |
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BP8.00125: ZaP Flow Z-pinch extended source results and machine upgrade to ZaP-HD Michal Hughes, Uri Shumlak, Brian Nelson, Raymond Golingo, Chris Bowers, Shawn Doty, Sean Knecht, Michael Ross, Harrison Stankey, Sydney Swofford The ZaP Flow Z-Pinch project investigates the use of velocity shear to mitigate MHD instabilities. The existing experiment produces Z-pinch plasmas that are approximately 1 cm in radius and 100 cm long. Low magnetic fluctuations demonstrate a long-lived stable pinch lasting several flow-through times. The experiment presently has two regions of differing physics: an acceleration region that ionizes neutral gas and accelerates the plasma axially providing a plasma source with axial momentum and an assembly region forming the Z-pinch configuration and compressing the plasma to high density and temperature. Past run campaigns have modified the plasma source to investigate the resulting behavior of the pinch plasma. Previous results show that the lifetime of the plasma is limited by the current from the power supply and depletion of the plasma source. The supplied power has previously been increased to extend the current waveform. The source has an increased plenum to extend the supply from the accelerator, the stability period of the Z-pinch, and thus the plasma lifetime. Results are discussed focusing on the physics of the source and pinch stability. The results have guided the design of a new ZaP-HD experiment which is presented. [Preview Abstract] |
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BP8.00126: Development of a digital holographic interferometer for the ZaP-HD Flow Z-Pinch Michael Ross, Uri Shumlak, Brian Nelson, Ray Golingo, Chris Bowers, Shawn Doty, Michal Hughes, Sean Knecht, Matt Paliwoda, Harrison Stankey, Sydney Swofford The ZaP Flow Z-Pinch project investigates flow shear stabilization of MHD modes. The current experiment is being upgraded to a higher energy-density operating regime that will provide a platform to explore how shear stabilized Z-pinches could scale to HEDP and even fusion reactor conditions. The experiment's upgrade includes developing a digital holographic interferometer to measure electron density with fine spatial resolution. The holographic interferometer uses a pulsed laser with a consumer digital camera to generate and record holograms, which are then numerically reconstructed to obtain the phase shift caused by the interaction of the laser beam with the plasma. The numerical reconstruction provides a two-dimensional map of chord-integrated electron density. The interferometer's accuracy is being validated with comparisons to measurements from an existing four-chord HeNe interferometer. The new diagnostic will allow the ZaP team to search for plasma structures such as shocks that were previously unresolvable. It will also be able to resolve the density profile of the smaller, higher energy-density pinch plasma. [Preview Abstract] |
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BP8.00127: Magnetized plasma jets in experiment and simulation Peter Schrafel, John Greenly, Pierre Gourdain, Charles Seyler, Kate Blesener, Bruce Kusse This research focuses on the initial ablation phase of a thing (20 micron) Al foil driven on the 1MA-in-100ns COBRA through a 5mm diameter cathode in a radial configuration. In these experiments, ablated surface plasma (ASP) on the top of the foil and a strongly collimated axial plasma jet can be observed developing midway through current-rise. Our goal is to establish the relationship between the ASP and the jet. These jets are of interest for their potential relevance to astrophysical phenomena. An independently pulsed 200$\mu$F capacitor bank with a Helmholtz coil pair allows for the imposition of a slow (150$\mu$s) and strong ($\sim$1T) axial magnetic field on the experiment. Application of this field eliminates significant azimuthal asymmetry in extreme ultraviolet emission of the ASP. This asymmetry is likely a current filamentation instability. Laser-backlit shadowgraphy and interferometry confirm that the jet-hollowing is correlated with the application of the axial magnetic field. Visible spectroscopic measurements show a doppler shift consistent with an azimuthal velocity in the ASP caused by the applied B-field. Computational simulations with the XMHD code PERSEUS qualitatively agree with the experimental results. [Preview Abstract] |
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BP8.00128: Deducing surprisingly small thermal ion energy content from spectral line shapes in an imploding z-pinch plasma E. Kroupp, L. Gregorian, G. Davara, A. Starobinets, Y. Maron, A. Fruchtman, N.J. Fisch Spectral broadening of emission lines of singly to five-times ionized oxygen are used to investigate the ion density and flow in the plasma during the implosion phase of a $0.6~\mu$s, $220$~kA z-pinch experiment. Despite significant Doppler broadening of the lines, which indicates a large range of ion velocities, it can be deduced that this energy resides in fluid motion, rather than in thermal motion. The picture that emerges is that plasma, undergoing rapid implosion, supports large energies in turbulent fluid motion, but not in the relative motion of ions to each other or to electrons. [Preview Abstract] |
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BP8.00129: Study of Ablation and Implosion Stages of 1-MA Wire Array Z-Pinch using X-ray Laser-Based Backlighting Austin Anderson, Vladimir Ivanov, Daniel Papp, Bjorn Talbot, Alexey Astanovitskiy The ablation and implosion stages of wire array z-pinches were studied using laser-based x-ray imaging at the 1-MA Zebra pulse power generator at the University of Nevada, Reno. X-ray backlighting at the wavelength of 6.65 {\AA} was provided by hitting a Si target with the 50 TW Leopard laser. Laser-based radiography allows flexibility in both the timing and the position of the x-ray source. The issue of the method is the small energy of the laser pulse compared to radiation of the Z pinch. A spherically bent quartz crystal can give spatial resolution \textless~10 microns and spectral linewidth of the x-ray on the order of 10$^{-4}$. X-ray imaging allows viewing of the dense core of plasma column during the ablation stage. Wires with diameters 7.6-15 were resolved in test shots. Images of the wire-array at the ablation stage are discussed. [Preview Abstract] |
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BP8.00130: Energetic Electron Beams in Conical Wire Array Z-Pinches R. Presura, M.S. Wallace, S. Haque, A. Arias, N. Quiros Intense beams of energetic electrons are often inferred in z-pinch experiments. Using magnetic deflection and Faraday cup detection we diagnosed electron beams with energies in the range 0.1-1 MeV produced in conical wire array z-pinches and x-pinches. The experiments were performed on the 1 MA Zebra z-pinch at the Nevada Terawatt Facility. The divergence of the beams and variations in pointing from one emission episode to another reduced the accuracy of these measurements and are subject of further investigation. However, the temporal characteristics of the electron beams can be correlated with the x-ray emission of the z-pinches. Results of these measurements will be presented. [Preview Abstract] |
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BP8.00131: The Magnetic Field Distribution of Single Exploding Wire Aluminum Plasmas Kate Blesener, Sergei Pikuz, Tania Shelkovenko, David Hammer, Yitzhak Maron, Ramy Doron, Vladimir Bernshtam, Leonid Weingarten, Yuri Zarnitsky The exploding wires were driven by the 13 kA Low Current Pulser LCP3 at Cornell University, employing high-resolution time-gated emission spectroscopy at visible wavelengths to determine the plasma parameters as a function of radial position and time. The distribution of current through single exploding aluminum wires was determined through time resolved studies of the magnitude of the magnetic field as a function of position. To study the magnetic field we used the Zeeman Broadening technique developed at the Weizmann Institute of Science [1]. \\[4pt] [1] E. Stambulchik, \textit{et al.} Phys. Rev. Lett. \textbf{98}, 225001 (2007). [Preview Abstract] |
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BP8.00132: An Investigation of X-Pinch Dynamics by X-Ray Absorption Adam Cahill, Cad Hoyt, Sergei Pikuz, Tania Shelkovenko, David Hammer Previous studies of plasma pinches, such as x-pinches or hybrid pinches, have thoroughly characterized the radiating hot spot formed at the center of the plasma in terms of size, temperature, and density. However, much of the plasma volume surrounding the hot spot has remained relatively unstudied. We propose that a study of the surrounding plasmacanbe accomplished by means of absorption spectroscopy in spite of the high brightness of the x-pinch hot spot. Such an experiment has been designedforthe XP pulser at Cornell University. The XP pulser, which is capable of delivering 500kA of current in 100ns, is used to drive an x-pinch as a source of continuum radiation. This radiation is dispersed by an astigmatic mica crystal before interacting with another x-pinch serving as the objectplasma. The astigmatism of the crystal allows focusing to occur both at the sample location as well as at the detector for increased luminosity. To date, the experimental design for the study of plasma in an aluminum x-pinch has been completed. The object plasmaunder study willbe Al 5056, an Al alloy containing 5{\%} Mg. The H-like and He-like resonance andsatellite linesin the spectrum from the Mgwill be used as the basis for plasma diagnosis. Preliminary results from this experiment will be presented. [Preview Abstract] |
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BP8.00133: X-ray Thomson Scattering using the Hybrid X-pinch X-ray Source Cad Hoyt, Sergei Pikuz, Tania Shelkovenko, Dave Hammer Stringent photometric and bandwidth requirements have historically relegated X-ray Thomson scattering (XRTS) probe sources to high energy laser plasma sources or free electron lasers. Standard x-pinch configurations in which two or more fine wires cross and subtend an angle of about 30$^{\circ}$ forming an ``X'' between the anode and cathode of a pulsed power generatorcan produce extremely bright, subnanosecond bursts of continuum and line radiation from micron-scale sources. The hybrid x-pinch is a new configuration based on conical W-Cu alloy electrodes with a short 1-2mm gap that is bridged by a fine wire resulting in an easier to load setup with improved performance characteristics. We explore the possibility of utilizing the hybid x-pinch as a novel XRTS probe source by examining certain spectral and temporal attributes of a range of materials in a hybrid x-pinch configuration on the XP (500kA, 50ns) and COBRA(1MA, 100ns) pulsed power generators. We find that a Ti hybrid x-pinch produces \textgreater 10$^{12}$ photons/sr in Ti He-alpha radiation and satisfies the noncollective scattering bandwidth requirement. Measurements of photon fluence, bandwidth and applicability to the relevant scattering regime and initial scattering results will be presented. [Preview Abstract] |
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BP8.00134: Examination of the Feasibility of a Spark Gap - X-Pinch Hybrid for Point-Projection Radiography Gilbert Collins, Julio Valenzuela, Derek Mariscal, Farhat Beg We present an investigation into the feasibility of using a simple merging of the spark gap and X-pinch concepts as a substitute for conventional X-pinches for point-projection radiography. We demonstrate formation of an x-ray source between two pointed electrodes. Experiments are conducted on UC San Diego's 80kA peak, 50ns rise time, Marx-driven pulser. The ability to change the material and the spacing of the electrodes allows for control of the x-ray spectrum. Potential advantages include the reusability of the electrodes for successive pulses until the initial apexes of the electrodes are significantly altered due to ablation, and the simplicity of setup and design. [Preview Abstract] |
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BP8.00135: Recent Developments on the Pulsed Neutron Source and Diagnostics on Zebra Erik McKee At the Nevada Terawatt Facility, neutron diagnostics are being added to the x-ray and optical diagnostics already employed on the Zebra pulsed-power z-pinch generator. The Zebra generator can produce plasmas approaching solid density over 100 ns timescales. It is hypothesized that production of neutrons on Zebra are through beam-like collisions in MHD instabilities in the z-pinch where there exist localized, intense electric fields. These fields accelerate deuterons to energies where the fusion reaction cross section becomes significant to produce neutrons. Palladium wires are used as the constraining media for deuterium gas in the fabrication of targets used on Zebra which produces short pulses of fast neutrons. The MCNP Monte Carlo particle transport code will be used in conjunction with neutron activation diagnostic to model detector effects from background scatter events and detector geometry. The neutron detectors currently measuring neutron yield include isotope activation using Silver, Indium and bubble-gel detectors. Also presented are nTOF detector geometries inspired by the difficulty in measuring TOF neutron signals in a low neutron yield, high gamma yield environment on Zebra. We report on a neutron yield exceeding 10$^{10}$ neutrons per pulse measured using activation techniques and novel nTOF detector geometries being shaped by MCNP calculations to be fielded in the Zebra environment. Effort enabled by support from collaboration with LLNL and NSTec. [Preview Abstract] |
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BP8.00136: Formation of One-Dimensional Reverse Shocks in Collisionless Magnetized Plasma Flows Driven by Inverse Wire Array Z Pinches Lee Suttle, Sergey Lebedev, Matthew Bennett, Guy Burdiak, Gareth Hall, Nadine Kalmoni, Francisco Suzuki-Vidal, George Swadling, Roland Smith, Siddharth Patankar, Adam Frank, Andrea Ciardi Experiments presented here utilize ablation plasma flow from an inverse wire array z pinch at the MAGPIE facility, as a platform for studying reverse radiative shocks in well-defined and diagnosable 1D geometry. A supersonic and super-Alfvenic plasma flow (M,M$_{\mathrm{A}}\approx $6) of parallel and uniform trajectory is directed towards planar surface obstacles. The plasma stream contains frozen-in magnetic field ($R_{em}\approx $50, $B\approx $2T) orientated perpendicular to the flow. This is shown to affect the interaction region via the formation of a thin-layer ($\ll$ $\lambda_{ii})$ magnetic precursor shock-like formation at a distance from the obstacle comparable with the ion inertial length, and mediated by the build-up of field diffusing from the downstream stagnated plasma. Measurement of the plasma velocity and temperature is made by Thomson Scattering in the upstream flow and across the shock, with simultaneous measurement of electron density distribution with laser interferometery (532 {\&} 355nm). A 12-frame fast optical camera was used to measure dynamics of the shock formation while miniature inductive probes were used to diagnose the advected magnetic field. [Preview Abstract] |
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BP8.00137: Colliding supersonic plasma jets on the MAGPIE pulsed-power generator F. Suzuki-Vidal, S.V. Lebedev, L.A. Pickworth, J. Skidmore, G.F. Swadling, G. Burdiak, M. Bennett, S.N. Bland, J.P. Chittenden, P. de Grouchy, G.N. Hall, J. Music, S. Patankar, R.A. Smith, L. Suttle The dynamics of the interaction of supersonic, radiatively cooled plasma jets with applications to laboratory astrophysics are under study on the MAGPIE generator. Latest experiments focus on the interaction of jets with solid targets and counter-streaming jet collisions. In both cases the interaction is characterised by the formation of a ``static'' shock in which the magnetic field advected with the plasma flow seems to be playing a crucial role. The dynamics are studied by the means of time-resolved, fast-framing optical imaging, laser probing at 532 and 355 nm and Thomson scattering diagnostics. The experimental results are also compared with 3-D MHD simulations using the code GORGON. [Preview Abstract] |
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BP8.00138: Update on PHELIX Pulsed-Power Hydrodynamics Experiments and Modeling Christopher Rousculp, William Reass, David Oro, Jeffery Griego, Peter Turchi, Robert Reinovsky, Barbara Devolder The PHELIX pulsed-power driver is a 300 kJ, portable, transformer-coupled, capacitor bank capable of delivering 3-5 MA, 10 $\mu $s pulse into a low inductance load. Here we describe further testing and hydrodynamics experiments. First, a 4 nH static inductive load has been constructed. This allows for repetitive high-voltage, high-current testing of the system. Results are used in the calibration of simple circuit models and numerical simulations across a range of bank charges ($\pm$20 \textless\ V$_{\mathrm{0}}$ \textless\ $\pm$40 kV). Furthermore, a dynamic liner-on-target load experiment has been conducted to explore the shock-launched transport of particulates (diam. $\sim$ 1 $\mu $m) from a surface. The trajectories of the particulates are diagnosed with radiography. Results are compared to 2D hydro-code simulations. Finally, initial studies are underway to assess the feasibility of using the PHELIX driver as an electromagnetic launcher for planer shock-physics experiments. [Preview Abstract] |
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BP8.00139: Predictive Fully Kinetic Modeling of kJ and MJ Dense Plasma Focus Z-Pinches A. Link, J. Ellsworth, S. Falabella, H. McLean, B. Rusnak, A. Schmidt, J. Sears, V. Tang, D. Welch Dense plasma focus (DPF) Z-pinches are compact devices capable of producing MeV ion beams, x-rays, and (for D or DT gas fill) neutrons but the details of the mechanisms which give rise to these strong accelerating gradients are not well understood. We report on progress in developing predictive, fully kinetic simulations of DPF Z-Pinches using the particle-in-cell code LSP. These simulations include full-scale electrodes; both run-in and pinch phases; and post-pinch behavior. Here we present a comparison between simulations and experiments conducted on the LLNL 4 kJ tabletop DPF. Diagnostics allow us to measure neutron yield, plasma oscillations arising from instabilities, DPF ion beam energies, and the acceleration of an externally injected ion probe beam in the pinch region, which can be compared with simulations. We will further report on the initial work to extend these simulations from kJ to MJ-class devices. LLNL-ABS-640759 [Preview Abstract] |
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BP8.00140: MHD modeling of dense plasma focus electrode shape variation Harry McLean, Charles Hartman, Andrea Schmidt, Vincent Tang, Anthony Link, Jen Ellsworth, David Reisman The dense plasma focus (DPF) is a very simple device physically, but results to date indicate that very extensive physics is needed to understand the details of operation, especially during the final pinch where kinetic effects become very important [1]. Nevertheless, the overall effects of electrode geometry, electrode size, and drive circuit parameters can be informed efficiently using MHD fluid codes, especially in the run-down phase before the final pinch. These kinds of results can then guide subsequent, more detailed fully kinetic modeling efforts. We report on resistive 2-d MHD modeling results applying the TRAC-II code to the DPF with an emphasis on varying anode and cathode shape. Drive circuit variations are handled in the code using a self-consistent circuit model for the external capacitor bank since the device impedance is strongly coupled to the internal plasma physics. Electrode shape is characterized by the ratio of inner diameter to outer diameter, length to diameter, and various parameterizations for tapering. \\[4pt] [1] A. Schmidt, et. al., Phys. Rev. Lett, 109(2):205003, 2012 [Preview Abstract] |
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