Bulletin of the American Physical Society
52nd Annual Meeting of the APS Division of Plasma Physics
Volume 55, Number 15
Monday–Friday, November 8–12, 2010; Chicago, Illinois
Session TP9: Poster Session VII: Basic Plasma Physics: Turbulence, Simulations, Flows, Sheaths, and Shocks; CMod Tokamak; Turbulence and Transport; MiniConference: Solar Wind Turbulence 
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Room: Riverside West 

TP9.00001: BASIC PLASMA PHYSICS: TURBULENCE, SIMULATIONS, FLOWS, SHEATHS, AND SHOCKS 

TP9.00002: Poincare recurrence and intermittent destruction of the Kelvin wave cascade in turbulence George Vahala, Jeffrey Yepez, Linda Vahala, Min Soe, Bo Zhang, Sean Ziegeler Spacecraft data for solar wind turbulence shows a more sophisticated magnetic energy spectra than the simple k$^{5/3}$ Kolmogorov spectrum of fluid turbulence. In particular data shows that while the low wave number magnetic energy spectrum follows the Kolmogorov k$^{5/3}$ cascade, there is a clear break in the spectral exponent with the spectrum having a somewhat steeper power law decay at the kinetic ion scales. A unitary lattice algorithm, based on interleaved unitary collisionstream operators, is implemented to study turbulence of the nonlinear Schrodinger equation. Because of the near perfect parallelization of this unitary algorithm simulations were performed on 5760$^{3}$ grids, yielding multiscale physics seen in the multicascade behavior of the incompressible kinetic energy. Very short Poincare recurrence times have been seen with the intermittent destruction of the Kelvin wave cascade. [Preview Abstract] 

TP9.00003: Unitary Mesoscopic Algorithms for 2D Quantum and Classical Turbulence Bo Zhang, George Vahala, Linda Vahala, Min Soe The nonlinear Schrodinger (NLS) equation plays an important role in physics: from plasma wave and soliton propagation to turbulence in BoseEinstein condensates. There is much interest in unravelling the differences between 2D and 3D turbulence  in fluids, plasmas and BECs. In fluid turbulence there is a marked difference between: in 2D, there is an inverse cascade of energy and a direct cascade of enstrophy while in 3D only a direct cascade of energy. MHD, the cascades are similar in both 2D and 3D. To examine the effects of dimensionality on quantum turbulence we device an almost perfectly scalable unitary lattice gas algorithm to solve the NLS equation. Unlike classical or plasma turbulence, a vortex in quantum turbulence is a welldefined topological singularity. For various initial conditions we examine the spectra for both 2D and 3D turbulence on grids that scale from quantum to classical scales. [Preview Abstract] 

TP9.00004: Entropic Lattice Boltzmann Algorithms for MHD Turbulence Linda Vahala, George Vahala, Min Soe To achieve high resolution simulations of MHD turbulence, one must have highly parallelized algorithms that scale to hundreds of thousands of cores. Direct lattice Boltzmann algorithms are such explicit schemes  but they are typically restricted in the achievable Reynolds numbers due to numerical instabilities. Here we examine entropic generalizations of LB by introducing a scalar distribution for the magnetic field With the magnetic field arising as a first moment we can enforce positive definiteness on the magnetic scalar distribution and hence an entropic representation. This will permit simulations to be performed at arbitrary high magnetic Reynolds number  limited only by the number of cores available. Results will be presented for the OrszagTang vortex. Moreover large eddy simulation (LES) closures can be incorporated into LB without destroying the parallelization of the algorithm as macroscopic gradients are local moments in the LB representation. LB does not loose its parallelization when handling arbitrary boundary conditions. A semientropic LB scheme (using a vector distribution for \textbf{B}) will also be considered. [Preview Abstract] 

TP9.00005: The effect of diamagnetic drifts on the dynamics of turbulent transport D.E. Newman, R. Sanchez, Debasmita Samaddar Recently, much progress has been made toward understanding the fundamental dynamics of turbulent transport in the presence of sheared flows. The insights have come from following Lagrangian trajectories using both gyrokinetic simulations of ITG turbulence [1] and fluid models of driftwave turbulence [2]. In this work, using the same tools, the impact of simple diamagnetic drifts on the dynamics of the transport is investigated using numerical simulations of 2Dturbulence in slab geometry with the BETA code. By itself, a diamagnetic drift velocity can have a significant an impact on the transport dynamics both with and across flow. However when coupled with a sheared flow additional dynamics are observed which could lead to interesting profile control tools if separately controlled. These new dynamics are in part the result of coherent structure formation localized to particular regions of the flows. The transport dynamics and possible uses will be discussed. \\[4pt] [1] R. Sanchez, D.E. Newman, et al PRL 101, 205002 (2008) \\[0pt] [2] D.E. Newman, et al, Proc. of the 35th EPS Conf on Plasma Physics, ECA Vol. 32, p. 1.044 (2008) [Preview Abstract] 

TP9.00006: Parallelization in time of numerical simulations of driftwave turbulence using the parareal algorithm Raul Sanchez, Debasmita Samaddar, David Newman The simulation of turbulent fusion plasmas is very computationally intensive due to the large disparity of timescales that play a role in the dynamics. It is widely accepted that first principles simulations of ITERrelevant plasmas are currently unfeasible, and will remain so for quite sometime unless some important algorithmic advances are made. Even shorter simulations of a more restricted range of timescales, such as those based on gyrokinetics, are usually limited to tens of thousands of CPUs due to interprocessor communication, not scaling up to the 100,000+ CPUs that current supercomputers offer. In this contribution we test successfully a recently proposed scheme to parallelize in time the integration of systems of PDEs on a driftwave turbulence code [1]. The lessons learnt from this exercise suggest that an additional parallelization path exists to enable longer simulations, more complete physics models and a better utilization of existing computational resources. \\[4pt] [1] D. Samaddar, D.E. Newman and R. Sanchez, J. Comput. Phys. 229, 6558 (2010) [Preview Abstract] 

TP9.00007: Strongly driven drift modes independent of resistivity in finite beta plasmas ChingPui Hung, Adil Hassam We study drift waves (DW) in collinear magnetic field, beta $\sim $ O(1) systems (e.g., FRCs), wherein the sonic and Alfven drift branches are strongly coupled. For isothermal perturbations, we find that finite beta is strongly stabilizing. With temperature perturbations, we find a rapidly growing instability, mediated by the Braginskii thermal force but not requiring resistivity. The growth rate peaks at the drift frequency. This mode has been described by Mikhailovskii but has not been well studied. The nonlocal and nonlinear theory of this mode is investigated. A finite beta 3D 2fluid code with Hall terms and thermal force has been developed. The linear thermal force DW is confirmed. The code is also used to investigate dispersion characteristics and the ensuing turbulence. The code will also be used to study the interplay between DWs and the plasma thermoelectric effect. The latter effect generates a B x grad[T] current in magnetized plasmas and is of the same order as the plasma resistivity limited current in finite beta plasmas. It is of interest to study how drift wave turbulence would influence the thermoelectric effect and viceversa. [Preview Abstract] 

TP9.00008: On the measurement of Lagrangian correlation functions in drift wave fluctuations Fred Skiff, Vikram Patel, Xing Li, Shunjiro Shinohara, Taisei Motomura We explore the possibility of measuring Lagrangian correlation functions in drift wave turbulence in a magnetized plasma cylinder. The connection between Lagrangian and Eulerian correlation functions is known to be complex. For example it is possible for the same process to exhibit chaotic Lagrangian trajectories and at the same time to have a completely integrable Eulerian flow. Using laserinduced fluorescence it is possible to realize the measurement of both Eulerian and Lagrangian correlation functions depending on the degree of optical pumping. We explore the effects of optical pumping on the Eulerian limit (weak optical pumping) as well as what can be learned in the limit of strong optical pumping where the signal is best interpreted in the Lagrangian sense (``optical tagging''). Preliminary data are obtained in a singly ionized Argon plasma with density of 10$^{9}$  10$^{10}$ cm$^{3}$ an electron temperature of typically 4 eV and an ion temperature of typically 0.1 eV. LIF data are collected using both diode laser light at 668 nm and dye laser light at 611nm to excite metastable fluorescence lines. [Preview Abstract] 

TP9.00009: Tests of Nonlinear Interactions Between Alfv\'{e}n Waves Using Gyrokinetic Simulation Kevin Nielson, Gregory Howes Nonlinear interactions between Alfv\'{e}n waves are the fundamental action responsible for plasma turbulence, governing energy transport across a wide range of scales and in nearly any plasma environment. MHD theory predicts that turbulent transport in magnetized plasmas occurs as the result of nonlinear interactions between Alfv\'{e}n waves propagating oppositely along the mean magnetic field. This theory suggests a mechanism for these interactions and predicts interaction rates and products. These results from MHD theory have influenced the development of Alfv\'{e}nic turbulence theory, but the MHD approximation does not hold in many plasmas of scientific interest, making it difficult to test the theory by experiment. We present results of a study employing gyrokinetic simulations that test the hypotheses of MHD Alfv\'{e}nic turbulence theory. These simulations, performed with the astrophysical gyrokinetics code AstroGK, enable the construction of MHD approximating conditions without relying explicitly on the assumptions of MHD theory. [Preview Abstract] 

TP9.00010: Investigation of Instabilities in a Harris Current Sheet Using a Gyrokinetic Electron and Fully Kinetic Ion Particle Simulation Xueyi Wang, Wei Kong, Yu Lin, Liu Chen, Xiang Lv, Wenlu Zhang, Zhihong Lin A novel gyrokinetic electron and fully kinetic ion (GeFi) particle simulation model has been developed for the purpose of investigation of collisionless magnetic reconnection. In this model, the rapid electron cyclotron motion is removed, while retaining the finite electron Larmor radii, waveparticle interaction, and offdiagonal components of the electron pressure tensor. In this talk, we (1) present our recent improvement of scheme by adopting the potential formulations for both electrons and ions and (2) show simulations of currentsheet driven instabilities in a Harris sheet using GeFi code. The simulation is carried out for finite guide field and with a realistic mi/me. Code is benchmarked against our eigentheory of the tearing instability and the results are compared with the asymptotic matching results of Drake and Lee. For the currentsheet driven instability, in addition to the quasielectrostatic modified twostream instability/whistler mode on the edge, a new mode is found in the sheet center, which may contribute to the anomalous resistivity in reconnection. [Preview Abstract] 

TP9.00011: Statistical Theory for Energy Distribution in Gyrokinetic Turbulence P.W. Terry, D.R. Hatch, J.H. Kim Recent gyrokinetic simulations reveal that ITG turbulence excites a large number of damped modes in the wavenumber range of the instability. These dissipative structures engage in an equipartition of dissipated power across the modes of a singular value decomposition (SVD). Energy injected by the instability is simultaneously distributed among all modes. Equipartition is enforced by the large multiplicity of couplings among damped modes, the uniformity of coupling strengths from mode to mode, the propensity for ergodization in individual triads, and the relatively large damping rates. Through the concept of turbulent dissipative contact among separate decompositions, we derive the probability distribution function of dissipated power in any mode and the entropy of the system. We study the effect of different basis decompositions on equipartition. Because the system is dissipative but turbulent, energy not lost to dissipation in a turbulent decorrelation time progresses to smaller scales via a wavenumber cascade. At high $k$ the dissipation rate becomes smaller than the turbulent correlation rate, yielding a power law spectrum asymptotically. [Preview Abstract] 

TP9.00012: Gyrokinetic Simulations of Edge Pedestal Turbulence Scott Parker, Weigang Wan, Yang Chen, GunYoung Park, C.S. Chang, Norbert Podhorszki, Scott Klasky Firstprinciple simulations of edge pedestal microinstability are performed with the global gyrokinetic turbulence code GEM. The density, temperature and magnetic equilibrium profiles are obtained from both numerical simulation and experiments. The turbulence from simulation results peaks at the position of strongest pressure gradient and the bottom of Er. The dominant linear instability appears to be caused by the strong density gradient. As a result, the Hmode pedestal is linearly more unstable than Lmode. However, the nonlinear steadystate flux level of Hmode is indeed lower than Lmode. The linear instability requires kinetic electrons but is not due to trapped electrons, and it is nearly insensitive to ion and electron temperature gradients. The dominant instability is likely to be electron drift wave. In a systematic study, we find that there are two ``branches,'' lown and highn, of the pedestal instability. The electromagnetic effect is destabilizing in the lown branch and stabilizing in the highn branch. In a set of simulations with fixed pedestal height but varying pedestal width, the linear growth rate is first lowered then increased as the pedestal width get thinner and thinner, a phenomenon consistent with kinetic ballooning mode (KBM). [Preview Abstract] 

TP9.00013: Study of Shear Flow Effect on turbulence by GTC Zhixuan Wang, Zhihong Lin Shear flow, which can be generated by external field or turbulence of the plasma itself, is by now generally accepted as one of the most important factors to form transport barriers, both at the edge and further into the plasma core, and thus to enhance plasma confinement for ignition. However, the mechanism which leads shear flow to less transport, especially the transport from Alfven turbulence, is not well understood yet. A Gyrokinetic Particle Simulation (GTC) is applied to study such effects. Ion Acoustic wave, Drift wave and Doppler Effect by flow are now recovered from simulation with good agreement with theory. The code will be used to study the nonlinear effect of shear flow on different modes in tokamak geometry. [Preview Abstract] 

TP9.00014: Modeling Plasma Turbulence and Flows in LAPD using BOUT++ B. Friedman, T.A. Carter, D. Schaffner, P. Popovich, M.V. Umansky, B. Dudson A Braginskii fluid model of plasma turbulence in the BOUT code has recently been applied to LAPD at UCLA [1]. While these initial simulations with a reduced model and periodic axial boundary conditions have shown good agreement with measurements (e.g. power spectrum, correlation lengths), these simulations have lacked physics essential for modeling selfconsistent, quantitatively correct flows. In particular, the model did not contain parallel plasma flow induced by sheath boundary conditions, and the axisymmetric radial electric field was not consistent with experiment. This work addresses these issues by extending the simulation model in the BOUT++ code [2], a more advanced version of BOUT. Specifically, endplate sheath boundary conditions are added, as well as equations to evolve electron temperature and parallel ion velocity. Finally, various techniques are used to attempt to match the experimental electric potential profile, including fixing an equilibrium profile, fixing the radial boundaries, and adding an angular momentum source. \\[4pt] [1] Popovich et al., http://arxiv.org/abs/1005.2418 (2010).\\[0pt] [2] Dudson et al., \textit{Computer Physics Communications 180} (2009). [Preview Abstract] 

TP9.00015: Flows, turbulence, and transport in the Large Plasma Device D.A. Schaffner, T.A. Carter, B. Friedman, P. Popovich We report on measurements of spontaneous flows, turbulence, Reynold's stress and particle flux in the Large Plasma Device (LAPD) at UCLA. Measurements of perpendicular and parallel flow using a sixsided Mach probe reveal a shearlayer flow in the cathode edge region whose peak flow increases with magnetic field and broadly distributed faredge perpendicular flows that scale inversely with magnetic field. ~The role of boundary effects and turbulent Reynolds stress in establishing the flow profile is investigated. Reynolds stress is measured with a seven tip vorticity probe; characteristics of the turbulence are measured using triple Langmuir probe. ~The connection among shear flow, turbulence and spatial correlation lengths is examined through crosscorrelation techniques, which also serves to establish the relationship between these quantities and gradient driven instabilities such as driftAlfven or KelvinHemholtz. These results are especially useful for comparisons to ongoing fluid simulations using the BOUT and BOUT++ 3D Braginskii fluid codes. [Preview Abstract] 

TP9.00016: Electron Temperature Gradient Turbulence: Validation in the Columbia Linear Machine Experiments Xiangrong Fu, Wendell Horton, Amiya Sen, Yong Xiao, Zhihong Lin The electron temperature gradient (ETG) mode, which is a dominant mechanism for turbulent electron thermal transport in plasmas, is produced and verified by a recent experiment conducted in the Columbia linear machine[1]. They report modes at $\sim 0.3  0.5 \;\rm MHz$, with azimuthal wave numbers $m\sim 1416$ and parallel wave number $k_\parallel \sim 0.003\; \rm cm^{1}$. We study these results using a gyrofluid simulation code DTRANS and a gyrokinetic simulation code GTC[2]. The results show that in the linear phase, the dispersion relation is consistent with kinetic theory for a slab ETG model and the radial structure of the fluctuation agrees with the experiment. We also investigate the saturation of ETG mode using the ${\bf E}\times {\bf B}$ turbulent mixing and coupling to low frequency modes. It turns out that low frequency driftion acoustic waves as in [1] interact with high frequency ETG modes to extract energy and saturate the ETG fluctuations. \\[4pt] [1] X. Wei, V. Sokolov, and A. K. Sen, Physics of Plasmas 17, 042108(2010). \\[0pt] [2] I. Holod, W. L. Zhang, Y. Xiao, and Z. Lin, Physics of Plasmas 16, 122307(2009). [Preview Abstract] 

TP9.00017: SelfRegulation Dynamics of Drift WaveZonal Flow Turbulence in a Linear Magnetized Plasma Jinlin Xie, Ran Chen, Changxuan Yu, Adi Liu, Tao Lan, Soubiao Zhang, Guanghai Hu, WanDong Liu The LowFrequency Zonal Flow is studied experimentally with the Langmuir probe arrays in a linear magnetized plasma device. In a weakly developed drift turbulence, the 3D mode characteristics of $m\simeq{n}\simeq0, k_r\simeq0.16 cm^{1}$ and a very nearzero mode frequency are obtained through spectrum analysis ,indicating the feature of zonal flow. The threewave coupling between ZF and AT is shown through bispectrum analysis. Furthermore, the selfregulation dynamics are studied in such a drift wavezonal flow (DWZF) turbulence through changing axial magnetic field, accompanying with the change of turbelence energy. Finally, the shearing effect of the DW by the ZF is also examined. [Preview Abstract] 

TP9.00018: Gyrokinetic inverse cascade in the subLarmor range: An analysis in the style of Fj{\o}rtoft, 1953 Gabriel Plunk, Tomo Tatsuno It is known that an inverse cascade of energy occurs in twodimensional neutral fluid turbulence and also, under certain conditions, in magnetized plasma turbulence. The reason for this phenomenon in both cases is due to the existence of two quadratic invariants that are {\em mutuallyconstraining} in the sense that the spectral redistribution of one is constrained by the other. The homogeneous gyrokinetic equation has two collisionless quadratic invariants when restricted to two dimensions in positionspace. In this letter, we consider the consequences of this fact for scales smaller than the thermal Larmor radius, where turbulent fluctuations exist, with equal importance, in the position and velocity space dependence of the kinetic distribution function. Using a spectral formalism for position and velocity space, we find that the gyrokinetic invariants are mutually constraining with respect to spectral redistribution of energy. We adapt the analysis of Fj{\o}rtoft (1953) to investigate the consequences of this fact. We find that inverse cascade is possible, but differs from the conventional inverse cascade of fluid turbulence in several ways. In certain scenarios, we argue that a dramatic nonlocal inverse cascade will occur, whereby fluctuations at scales much smaller than the Larmor radius can transfer energy directly to the Larmor scale. In the other extreme, we argue that the inverse cascade can be completely shut down. [Preview Abstract] 

TP9.00019: Freely decaying turbulence of twodimensional electrostatic gyrokinetics T. Tatsuno, G.G. Plunk, W. Dorland, A.A. Schekochihin Electrostatic gyrokinetic turbulence in weaklycollisional magnetized plasmas exhibits a turbulent cascade of an entropy invariant to fine scales in phase space [1]. In two dimensions, the existence of an additional independent collisionless invariant causes a concurrent phasespace cascade, where the second invariant {\em inversely} cascades to large scales. In this presentation, we report the detailed characteristics of the freely decaying turbulence in the twodimensional (2D) electrostatic gyrokinetics. By applying methods from 2D NavierStokes turbulence [2], we present a classification in terms of a dimensionless number (an analogue of the Reynolds number that is characteristic to the phasespace turbulence), and derive various decay laws in each region of the classification. We also show clear evidence of the inverse cascade by the diagnostics of the triad interaction in the wavenumber space using the AstroGK code [3]. \\[4pt] [1] T. Tatsuno \textit{et al}., Phys.\ Rev.\ Lett.\ \textbf{103}, 015003 (2009).\\[0pt] [2] J. R. Chasnov, Phys.\ Fluids \textbf{9}, 171 (1997).\\[0pt] [3] http://sourceforge.net/projects/gyrokinetics/ [Preview Abstract] 

TP9.00020: Mode conversion at density irregularities in the LAPD Kristopher Kersten, Cynthia Cattell, Bart Van Compernolle, Walter Gekelman, Pat Pribyl, Steve Vincena Mode conversion of electrostatic plasma oscillations to electromagnetic radiation is commonly observed in space plasmas as Type II and III radio bursts. Much theoretical work has addressed the phenomenon, but due to the transient nature and generation location of the bursts, experimental verification via \emph{in situ} observation has proved difficult. The Large Plasma Device (LAPD) provides a reproducible plasma environment that can be tailored for the study of space plasma phenomena. A highly configurable axial magnetic field and flexible diagnostics make the device well suited for the study of plasma instabilities at density gradients. We present preliminary results of mode conversion studies performed at the LAPD. The studies employed an electron beam source configured to drive Langmuir waves towards high density plasma near the cathode discharge. Internal floating potential probes show the expected plasma oscillations ahead of the beam cathode, and external microwave antenna signals reveal a strong band of radiation near the plasma frequency that persists into the low density plasma afterglow. [Preview Abstract] 

TP9.00021: Energy Dissipation in 3D ETGDriven Fluid Turbulence Juhyung Kim, Paul W. Terry Recent efforts to characterize the saturation of microturbulence indicate that there is significant dissipation by nonlinearly excited damped eigenmodes. In a 2D ETG fluid model, damped modes coexisting at low $k_y$ with unstable modes dissipate energy during and after the transition to the nonlinear state through a strong nonlinear correlation between potential and pressure.\footnote{J.H. Kim and P.~W. Terry. Submitted to Phys. Plasmas, 2010.} In this work, energy dissipation is numerically investigated in a 3D ETG fluid model in fluxtube geometry. While dissipation by damped modes is expected to be significant, the relative contributions by damped modes to various types of dissipation, including cross correlations and collisions, are not clear in the presence of Landau damping. The characteristics of energy dissipation in the transition to nonlinear state and the nonlinear steady state will be presented with the detailed analysis of energy transfer channels resolved in wavenumber space to distinguish high wave number dissipation, energy dissipation by damped modes and Landau damping. [Preview Abstract] 

TP9.00022: Measurement of Radial Electron Thermal Transport due to ETG Modes in a Basic Experiment Vladimir Sokolov, Amiya Sen Production and identification of electron temperature gradient (ETG) mode have been successfully demonstrated in a basic experiment in Columbia Linear Machine CLM [1]. Using a dc bias heating scheme of the core plasma, we are able to produce sufficiently strong ETG modes in CLM experiments. A unique miniature triple probe was used for local measurement of electron temperature and plasma potential fluctuations. Their crosscorrelation yields the local radial electron thermal flux. A preliminary measurement of electron thermal conductivity indicates $\chi_{\bot e}$ is about $\sim 3 m^2/s \sim 10 \chi_{\bot e,GB}$. This result appears to agree with a value of nonlocal thermal conductivity obtained from a rough theoretical estimation [2]. This research was supported by U.S. Department of Energy Grant No. DEFG0298ER54464. \\[4pt] [1] X. Wei, V. Sokolov and A.K. Sen, Phys. Plasmas, 17, 042108 (2010). \\[0pt] [2] H.L. Berk et al, Nucl. Fusion, 33, 263 (1993). [Preview Abstract] 

TP9.00023: Nonlinear Coupling between Zonal Modes and Damped Modes Kirit Makwana, Juhyung Kim, Paul Terry, David Hatch A simple fluid ITG model is simulated to study nonlinear coupling between zonal modes (ky=0, zero frequency modes) and damped modes. It is observed that the cross correlation terms dominate the energy dynamics, with the unstable modes supplying all the energy and the damped modes removing a significant portion of it. The remainder is removed by high ``k'' dissipation. However, even the dissipation has significant damped mode effects. Phase mixing analysis shows that transfer of energy from the unstable to damped modes via the zonal modes is more efficient compared to direct transfer of energy from unstable to damped modes. This is confirmed in simulations, which show that when zonal flows are included in the dynamics, 1) there is significantly more energy in the ky = 0 fluctuation component, and 2) the energy transfer channel from unstable modes to zonal modes to damped modes captures almost all of the energy injected by the instability. When zonal flows are not included, damped modes still saturate the instability but the transfer from the unstable modes is less efficient and requires a larger fluctuation level. [Preview Abstract] 

TP9.00024: Investigation of Chaotic Fluctuations in a Linear Helicon Plasma under Changing Magnetic Field and Radial Electric Field Shuangwei Xie, Mark Gilmore, Christopher Watts, Tiffany Hayes, Lincan Yan Experiments conducted in a linear helicon plasma (HelCat) device show evidence of deterministic chaos in edge fluctuations under DC biasing on a set of concentric rings which terminate the plasma column. At low bias or without bias, a low frequency coherent instability is present in the density gradient region, consistent with a resistive drift mode. At higher bias, there is an increase in azimuthal flow and flow shear, and a new instability is observed which could be a KelvinHelmholtz instability or interchange mode. Additionally, a parallel forward flow (away from the source) at the plasma center and backward flow at the plasma edge are observed. This return sheared flow may be an inflow due to increased radial fluctuationinduced transport at the plasma edge, and may play a role in the chaotic dynamics. Increasing magnetic field also affects these instabilities and their nonlinear dynamics. Experimental results and two fluid modeling are presented. [Preview Abstract] 

TP9.00025: Understanding Flow Profiles in a Large Scale Helicon Plasma With Electrode Biasing M. Gilmore, T.R. Hayes, S. Xie, L. Yan, C. Watts Experiments on flow shear/turbulence interactions are being conducted in the linear HelCat device, using both concentric ring and grid electrodes to bias the plasma. Flow profiles exhibit complicated changes with bias in both the azimuthal and parallel directions. Azimuthal flows are dominated by ``static'' E$_{r }$x B$_{z}$ rotation, but also have a fluctuationdriven (zonal) flow contribution, due to Reynolds stress at the edge. Biasing is found to change the fluctuation dynamics, including fully suppressing fluctuations under some conditions. Strong parallel downstream flow (away from the source) in the plasma center is observed, while a sheared return flow is seen at the edge. Under biasing, the return flow is reduced and eventually reversed. It appears that this return parallel flow may be an inflow driven by increased turbulent radial transport at the plasma edge, rather than a direct effect of biasing currents. As drift wave transport is suppressed, this parallel return inflow reduces. Experimental and initial twofluid modeling results are presented. [Preview Abstract] 

TP9.00026: Development of a drift wave turbulence transport model for a linear plasma device D. Brugger, A.S. Ware, M. Gilmore, S. Xie, E. Schuster, Q. Wang This work investigates modeling of transport and flow generation in a linear plasma device using a 1D transport code. Drift wave turbulence models have been analyzed to derive models for the growth rate, nonlinear saturation mechanism, and Reynolds stress parameterization in the transport model. The goal is to model the HELCAT experiment including the use of biased concentric rings as control elements for the radial electric field profile. By varying the bias voltages, the local ExB flow can be modified. The effect will be identical to a source of \textit{ExB} flow in the limit of zero beta (i.e., when diamagnetic flows are negligible). By varying the momentum sources a sheared radial electric field can be generated that can suppress turbulent particle and heat transport. The impact of ion temperature effects, axial flow and plasma boundary conditions are investigated. Comparisons with density and flow profiles from HELCAT experiments will be undertaken. [Preview Abstract] 

TP9.00027: NonModelBased Optimal Fluctuation Mitigation by E$\times $B Actuation in HELCAT Qiaoqiao Wang, Eugenio Schuster, Shuangwei Xie, Mark Gilmore, Andrew Ware Turbulence, and turbulencedriven transport are ubiquitous in magnetically confined plasmas, where there is an intimate relationship between turbulence, transport, destabilizing mechanisms like gradients and currents, and stabilizing mechanisms like shear. We investigate active control of fluctuations via manipulation of flow profiles in a magnetized laboratory plasma device (HELCAT). Fluctuations and particle transport are monitored by electrostatic probes, and E$\times $B flow profiles controlled via biased ring electrodes. A nonmodelbased optimization algorithm is implemented to seek control inputs that minimize a cost function related to the fluctuation amplitude. The algorithm is also able to identify radial poloidal flow profiles associated with low RMS fluctuations. The longterm goal is to develop modelbased feedback controllers to regulate the radial poloidal flow profiles around the identified lowfluctuation profiles. [Preview Abstract] 

TP9.00028: Clarification of symmetry breaking mechanism in intrinsic rotation of tokamak plasmas S. Yi, J.M. Kwon, T. Rhee, P.H. Diamond, J.Y. Kim Intrinsic rotation of tokamak plasmas is considered to be generated by nondiffusive stress (i.e. residual stress) induced by asymmetric $k_{\vert \vert } $ turbulence spectrum. To study the symmetry breaking mechanisms in intrinsic rotation, we have performed numerical simulations of intrinsic rotation by ITG turbulence using the gKPSP code, a deltaf global PIC code for tokamak. It is found that not only distortion of turbulence spectrum by $E\times B$ shear but also spatial diffusion of wave momentum driven by turbulence intensity gradient play an important role in the symmetry breaking mechanism, as expected from a theory [1]. It is hard to recognize individual contribution of $E\times B$ shear and turbulence intensity gradient to the residual stress because their evolution is strongly coupled with the preypredator feature [2]. To clarify their role, a comprehensive analysis including their nonlinear coupling is performed. The key symmetry breaking mechanism is identified for various physics situations. \\[4pt] [1] P.H. Diamond, et al., Phys. of Plasmas 15, 012303 (2008). \\[0pt] [2] P.H. Diamond, et al., PRL 72, 2565 (1994). [Preview Abstract] 

TP9.00029: On the Efficiency of Intrinsic Rotation Generation in Tokamaks Y. Kosuga, P.H. Diamond, O.D. Gurcan A theory of the plasma flow generation process efficiency is presented. A measure of the \textit{efficiency} of the plasma to produce mesoscale and mean flow from heat flux is introduced by analogy with engines, using entropy budget due to thermal relaxation and flow generation. The efficiency is defined as the ratio of entropy destruction rate due to flow generation and entropy production rate due to $\nabla T$ relaxation (i.e. related to turbulent heat flux). The efficiencies for two different cases, i.e. for the generation of turbulent driven $E\times B$ shear flow (zonal flow) and for toroidal intrinsic rotation are considered for a stationary state, achieved by balancing entropy production rate and destruction rate order by order in $O(k_\parallel/k_\perp)$ where $k$ is a wave number of a mode. The efficiency of intrinsic toroidal rotation is derived and shown to be $e_{IR}\sim0.01$. The scaling form of the efficiency of intrinsic rotation generation is also derived and shown to be $\rho_*^2(q^2/\hat s^2)(R^2/L_T^2)=\rho_*^2(L_s^2/L_T^2)$, which suggests a machine size scaling and an unfavorable plasma current scaling through the shear length. [Preview Abstract] 

TP9.00030: MHD wind tunnel M.R. Brown, T. Gray, X. Zhang, D. Dandurand Preliminary results are presented from a highvelocity, turbulent MHD wind tunnel at the SSX facility. The prototype wind tunnel has dimensions $L = 1~m$ and $R = 0.08~m$. Flow is measured with a cylindrical Mach probe calibrated both with magnetic timeofflight and ion Doppler spectroscopy. Magnetic structure and turbulence are measured with arrays of magnetic probes. In a typical experiment, a magnetized plasma plume is injected at one end at $v \ge 50~km/s$ then the plasma turbulently evolves down the wind tunnel and relaxes to a final state. We measure a relaxed final state with helical twist corresponding to the injected helicity and with $\lambda R = 3.15$, where the fields are minimum energy solutions to the Taylor state: $\nabla \times {\bf B} = \lambda {\bf B}$. The cylindrical copper boundary is baked and cleaned in a $He$ glow discharge to maintain excellent vacuum conditions. Typical plasma parameters are $T_i = 25~eV, T_e = 10~eV, n_e \le 10^{21}~m^{3}, B = 0.25~T$. Merging experiments with plasma plumes injected from both ends are planned. Results of the merging studies will be presented if available. [Preview Abstract] 

TP9.00031: Noisedriven plasma flow in HasegawaMima equation ChangBae Kim The generation of intrinsic flows amid turbulence in hot plasmas is of great importance in the nuclear fusion experiments. Instead of working out plasma dynamics of all scales we concentrate on the evolution of largescale fluctuations. Influence of the microscopic turbulence on the macroscopic dynamics is modeled as a noise. For pedagogical purposes, spontaneous appearance of the flow is studied with driven HasegawaMima equation (HME) by external noise. If the noise has a paritynonconserving (PNC) property, it is shown that an advective term associated with a uniform flow is inherently generated in the HME. Thus, the plasma transport appears in the form of both convective (nondiffusive) and enhanced diffusive flux. Numerical simulation of the noise driven HME of coarse scale is performed to confirm the result of the analytical theory and to verify the robustness of the noisedriven flow. The result will be discussed at the presentation. [Preview Abstract] 

TP9.00032: A JFNKbased implicit moment algorithm for selfconsistent, multiscale, plasma simulation Dana Knoll, William Taitano, Luis Chacon JacobianFreeNewtonKrylov method (JFNK) is an advanced nonlinear algorithm that allows solution to a coupled systems of nonlinear equations [1]. In [2] we have put forward a JFNKbased implicit, consistent, time integration algorithm and demonstrated it's ability to efficiently step over electron time scales, while retaining electron kinetic effects on the ion time scale. Here we extend this work by investigating a JFNK based implicitmoments approach for the purpose of consistent scalebridging between the fluid description and kinetic description in order to resolve the transition region. Our preliminary results, based on a reformulated Poisson's equation (RPE) [3], allows solution to the VlasovPoisson system for varying grid resolutions. In the limit of local coarse grid size (grid spacing large compared to Debye length), the RPE represents an electric field based on the moment system, while in the limit of local grid spacing resolving the Debye length, the RPE represents an electric field based on the standard Poisson equation. The technique allows smooth transition between the two regimes, consistently, in one simulation. [1] D.A. Knoll and D.E. Keyes,J. Comput. Phys., vol. 193 (2004) [2] W.T. Taitano, Masters Thesis, Nuclear Engineering, University of Idaho (2010) [3] R. Belaouar, N.Crouseilles and P. Degond,J. Sci. Comput., vol. 41 (2009) [Preview Abstract] 

TP9.00033: A Model for Molecular Hydrogen Ground State Rotational Populations in Kinetic Plasmas David Farley, Samuel Cohen A model has been developed to calculate the groundstate rotational populations of homonuclear diatomic molecules in kinetic gases, including the effects of electronimpact excitation, wall collisions, and gas feed rate. The equations are exact within the accuracy of the cross sections used and of the assumed equilibrating effect of wall collisions. It is found that the inflow of feed gas and equilibrating wall collisions can significantly affect the rotational distribution in competition with nonequilibrating electronimpact effects. The resulting steadystate rotational distributions are generally Boltzmann for N$>$2 with a rotational temperature between the wall and feed gas temperatures. The N=0,1,2 rotational level populations depend sensitively on the relative rates of electronimpact excitation versus wall collision and gas feed rates. [Preview Abstract] 

TP9.00034: An energyconserving nonlinearly converged implicit particleincell (PIC) algorithm G. Chen, L. Chac\'on, D.C. Barnes Conventional explicit PIC methods have to resolve shorttime and smallscale plasma dynamics, suffering from very stringent temporal and spatial stability constrains. An implicit approach can in principle remove these restrictions and solve for longtime and largescale dynamics. However, a large system of algebraic equations needs to be solved. In this work, we use a Jacobianfree NewtonKrylov method to invert an electrostatic VlasovAmp\`{e}re system. Unlike earlier attempts to implicit PIC, our approach selfconsistently couples particles and fields, achieving simultaneous convergence on the full system. We show that the implicit formulation enables an exact total energy conservation principle. We have found that the accuracy of the simulation for a large timestep is crucially dependent on enforcing charge conservation and adequately resolving particle orbits. These are accomplished by particle subcycling and orbit averaging, with the energy conservation preserved. We present results of standard test cases such as Langmuir wave, Landau damping, twostream instability and ion acoustic wave, compared with those from explicit simulations. [Preview Abstract] 

TP9.00035: A fully implicit Hall MHD algorithm based on the ion Ohm's law Luis Chac\'on Hall MHD is characterized by extreme hyperbolic numerical stiffness stemming from fast dispersive waves. Implicit algorithms are potentially advantageous, but of very difficult efficient implementation due to the condition numbers of associated matrices. Here, we explore the extension of a successful fully implicit, fully nonlinear algorithm for resistive MHD,\footnote{L. Chac\'on, {\em Phys. Plasmas}, {\bf 15} (2008)} based on Jacobianfree NewtonKrylov methods with physicsbased preconditioning, to Hall MHD. Traditionally, Hall MHD has been formulated using the electron equation of motion (EOM) to determine the electric field in the plasma (the socalled Ohm's law). However, given that the centerofmass EOM, the ion EOM, and the electron EOM are linearly dependent, one could equivalently employ the ion EOM as the Ohm's law for a Hall MHD formulation. While, from a physical standpoint, there is no {\em a priori} advantage for using one Ohm's law vs. the other, we argue in this poster that there is an algorithmic one. We will show that, while the electron Ohm's law prevents the extension of the resistive MHD preconditioning strategy to Hall MHD, an ion Ohm's law allows it trivially. Verification and performance numerical results on relevant problems will be presented. [Preview Abstract] 

TP9.00036: Particle algorithms as reductions of phase space Evstati Evstatiev, Bradley Shadwick ParticleInCell (PIC) algorithm for simulation of plasmas has become a basic tool for investigating laserplasma interactions, MHD phenomena, etc. Historically, there have been two ``branches'' of the PIC algorithm, energy conserving and momentum conserving. The momentum conserving algorithm has been more widely adopted so far, however, energy conserving algorithms (including implicit schemes) are being investigated actively. Many physics phenomena depend crucially on the energy conserving property; for example, waveparticle resonance is sensitive to the energy distribution of particles and thus some numerical artifacts, e.g., grid heating, lead to large variation of the simulation results. In this presentation we revisit the connection between momentum and energy conserving algorithms. We show that they essentially are different reductions from the same initial continuous model. We derive a hierarchy of particle algorithms with properties depending on the approximations made; we show what conditions lead to energy or momentum conservation, or how to derive particle algorithms, which conserve both energy and momentum. We present simulations substantiating the above theory. [Preview Abstract] 

TP9.00037: Modeling HighVoltage Breakdown for Single and Multistack Dielectric Insulators Manuel Aldan, John Verboncoeur, Y.Y. Lau, John Booske Breakdown from DC through microwave in dielectricinsulator configurations with one or more segments will be investigated using an improved 2D PIC simulation model [1]. The goal of this work is to develop the capability to predict and control the breakdown threshold under a wide range of parameters and geometries. Effects considered include secondaryemission [2], spaceand surfacecharge, ambient and desorbed gas, and surfaceplasma generation for single and multiplelayer [3] insulators with applied fields from DC to THz frequencies. Comparison between simulation and experiment will be conducted where possible. \\[4pt] [1] Taverniers, S., et al., ICOPS 2009 Proc., 2009.\\[0pt] [2] Vaughan, J.R.M., IEEE TED, Vol. 36, No. 9, 1989, pp.19631967.\\[0pt] [3] Leopold, J.G., et al., Proc. 2010 PMHVC. [Preview Abstract] 

TP9.00038: An Arbitrary Curvilinear Coordinate PIC Method Chris Fichtl, John Finn, Keith Cartwright We demonstrate the feasibility of a new approach to the PIC method in which a grid generation strategy is coupled to a generalization of the PIC algorithm on the logical domain. Our grid generation strategy conforms to objects of arbitrary shape, eliminating such problems as stairstepping along curved boundaries, and thus allows us to simulate complicated physical structures very accurately. We then use the mappings from the physical to the logical domain to run our PIC code. We have developed a semiimplicit particle mover for based on a generalization of the leapfrog method to arbitrary (including nonorthogonal) grids. We show our mover is symplectic and thus preserves phasespace area exactly. Extensive testing has shown that it also conserves energy to high accuracy. The electrostatic fields are solved on the logical domain using a preconditioned conjugate gradient method. We show test case results for several standard physics examples on multiple physical domains. [Preview Abstract] 

TP9.00039: Kinetic properties of the particleincell simulation of a Lorentz plasma Y.R. LinLiu, T.Y. Lin, S.H. Chen The phenomenon of numerical thermalization in the standard particleincell (PIC) simulation of Vlasov plasmas has been extensively studied at the early stage of its development [1] and was considered well understood. However, it was recently reported [2] that the wellestablished scaling law for the thermalization time could be compromised by the presence of an additional stochastic force acting on the particles, which is used to simulate collisional processes in a weakly ionized gas. In the present work, we are interested in the problem of electronion collisions in a fully ionized plasma. We investigate the thermal relaxation phenomenon in the PIC simulation of a Lorentz plasma in one dimension [3]. The pitchangle scattering of the electrons by the stationary ion background is modeled by a MonteCarlo algorithm. The numerical results obtained indicate that the thermal relaxation time is proportional to $N_{D}$ (the number of particles per Debye length), and not $N_{D}^{2}$ as in the standard PIC simulations. Our results appear to complement those found by the previous study [2]. \\[4pt] [1] C. K. Birdsall and A. B. Langdon, \textit{Plasma Physics via Computer Simulation} (McGrawHill, New York, 1985). \\[0pt] [2] M. M. Turner, Phys. of Plasmas \underline {13}, 033506 (2006). \\[0pt] [3] R. Shanny, J. M. Dawson, and J. M. Greene, Phys. of Fluids \underline {10}, 1281 (1967). [Preview Abstract] 

TP9.00040: Particleincell Simulations with ChargeConserving Current Deposition on Graphic Processing Units Xianglong Kong, Michael Huang, Chuang Ren, Viktor Decyk We present an implementation of a fully relativistic, electromagnetic PIC code, with chargeconserving current deposition, on graphics processing units (GPUs) with NVIDIA's massively multithreaded computing architecture CUDA. A particlebased computation thread assignment was used in the current deposition scheme and write conflicts among the threads were resolved by a thread racing technique. A parallel particle sorting scheme was also developed and used. The implementation took advantage of fast onchip shared memory. The 2D implementation achieved a one particlestep process time of 2.28 ns for cold plasma runs and 8.53 ns for extremely relativistic plasma runs on a GTX 280 graphic card, which were respectively 90 and 29 times faster than a single threaded stateofart CPU code. A comparable speedup was also achieved for the 3D implementation. [Preview Abstract] 

TP9.00041: Controlling hot electrons by wave amplification and decay in compressing plasma Paul Schmit, Ilya Dodin, Nathaniel Fisch Through particleincell simulations, it is demonstrated that a part of the mechanical energy of compressing plasma can be controllably transferred to hot electrons by preseeding the plasma with a Langmuir wave that is compressed together with the medium. Initially, a wave is undamped, so it is amplified under compression due to plasmon conservation. Later, as the phase velocity also changes under compression, Landau damping can be induced at a predetermined instant of time. Then the wave energy is transferred to hot electrons, shaping the particle distribution over a controllable velocity interval, which is wider than that in stationary plasma. For multiple excited modes, the transition between the adiabatic amplification and the damping occurs at different moments; thus, individual modes can deposit their energy independently, each at its own prescribed time. [Preview Abstract] 

TP9.00042: A FullyImplicit, IonElectron, VlasovPoisson Algorithm William Taitano, Dana Knoll, Luis Chacon The JacobianFreeNewtonKrylov method (JFNK) is an advanced non linear alogorithm that allows solution to a coupled systems of nonlinear equations [1]. We put forth a new JFNKbased implicit plasma simulation algorithm. We have studied this algorithm within the context of a twospecies VlasovPoisson system where the Vlasov equations are solved in an Eulerian frame [2]. We have investigated the route of nonlinearelimination/kinetic enslavement to reduce the size of block Jacobian matrix in order to solve the fieldkinetic system implicitly. The nonlinear elimination/kineticenslavement technique allows reduction in the size of nonlinear system but still retains high order temporal accuracy and strong nonlinear coupling. Our new algorithm make implicit timedependent, coupled, fieldkinetic systems more attractive. As will be shown, a fully implicit run was able to achieve 22 times speedup compared to the explicit run for our ionacousticshowckwave simulation [2].\\[4pt] [1] D.A. Knoll and D.E. Keyes, {\em J. Comput. Phys.} vol. 193 (2004)\\[0pt] [2] W.T. Taitano, Masters Thesis, Nuclear Engineering, University of Idaho (2010) [Preview Abstract] 

TP9.00043: Performance evaluation of relativistic electromagnetic particle in cell algorithms in CPU and GPU Ricardo Fonseca, Paulo Abreu, Viktor Decyk The complexity of the phenomena involved in several relevante plasma physics scenarios, where highly nonlinear and kinetic processes dominate, makes purely theoretical descriptions impossible. Further understanding of these scenarios requires detailed numerical modelling, but fully relativistic particleincell codes such as OSIRIS [1] are computationally intensive. Recently graphics processing units (GPUs), offering peak theoretical performances of $\sim $ 1 TFlop/s for general purpose calculations, have received significant attention as an atractive alternative to CPUs for plasma modeling. In this work we perform a detailed performance evaluation of an electromagnetic fully relativistic particle in cell code in both GPUs and CPUs for production runs, focusing on the relative strengths and weaknesses of both architectures for all major algorithm sections, including particle push, current deposition, field solver, and also diagnostics. \\[4pt] [1] R. A. Fonseca et al., LNCS 2331, 342, (2002) [Preview Abstract] 

TP9.00044: Multidimensional effects on relativistic electrons in an oblique shock wave Mieko Toida, Kenta Shikii Particle simulations have revealed [1] that prompt electron acceleration to ultrarelativistic energies can occur in a magnetosonic shock wave propagating obliquely to an external magnetic field with the propagation speed of the shock wave $v_{\rm sh}$ close to $c \cos \theta$, where $\theta$ is the propagation angle of the shock wave. In such a wave, some electrons are reflected near the end of the main pulse of the shock wave, get trapped and are energized in the main pulse region. Once electrons are trapped, they cannot readily escape from the wave because of the electromagnetic fields they themselves produce [2]. Although the extensive studies have examined electron trapping and acceleration by a shock wave, the theory and simulations were onedimensional. In this study, we investigate multidimensional effects using twodimensional (two spatial coordinates and three velocities), particle simulations. It is found that some electrons can be detrapped from the main pulse because of magnetic fluctuations propagating along the shock front. It is furthermore demonstrated that after detrapping, some electrons can be accelerated to much higher energies because they can enter and exit the shock wave several times as a result of their gyromotions. The generation of magnetic fluctuations due to whistler waves is also discussed. \\[0pt] [1] N. Bessho and Y. Ohsawa, Phys.\ Plasmas {\bf 6} 3076 (1999).\\[0pt] [2] M. Toida and K. Shikii, Phys.\ Plasmas {\bf 16} 112305 (2009). [Preview Abstract] 

TP9.00045: Kinetic effects and their role on the properties of magnetized shocks Anne Stockem, Luis O. Silva, Ricardo A. Fonseca The formation and generation of shocks is a topic of broad interest in many fields of physics, but the role of the kinetics effects and the properties of the particle distribution across the shock front have not been explored in detail. Using particleincell simulations to study electronpositron magnetized collisionless shocks, generated from a reflecting wall in the presence of an initially perpendicular magnetic field, we explore the features of the particle distribution in the upstream, downstream, and shock transition region. In particular, we identify deviations from a Maxwellian distribution. The impact of these deviations on the shock properties (shock velocity, jump conditions) are also examined analytically. The relevance of these results for astrophysical shocks is also discussed. [Preview Abstract] 

TP9.00046: Strong Radiation Driven Shocks in Cassio James Cooley In this paper we present results of a sensitivity study for strong shocks in the HED code Cassio. Cassio is an Eularian radiationhydrodynamics code being developed at Los Alamos to study HED physics. The radiation transport cna be eitehr grey diffusion, multigroup diffusion or IMC. The materials models include threetemperature radiation, electron and ions and wither analytic of tabular EOS. We examine the behavior of strong shocks and explore not only the hydrodynamic convergence behavior but also the effect of other physics modeling choices on shock evolution. [Preview Abstract] 

TP9.00047: Ion Collection by a Sphere in a Magnetized Collisional Plasma Christian Bernt Haakonsen, Ian H. Hutchinson Ion collection by dust grains and probes in plasmas with a neutral background are of relevance to both space and terrestrial plasmas. It has recently been shown that moderate chargeexchange collisionality can enhance the ion current to a collecting sphere beyond that given by orbital motion limited (OML) theory. In the collisionless case a background magnetic field reduces ion collection, but how a magnetic field affects the collisional current enhancement remains unknown. The hybrid particleincell (PIC) code sceptic3D is used to study collisional current enhancement in the presence of a magnetic field. Figures are presented showing the dependence of the collected current on both magnetic field strength and collisionality, and illustrative examples are used to provide physical insight into the magnetic field and collisional effects on ion collection. Further, a preview is given of future work on the fully 3D problem of ion collection in drifting magnetized plasmas. [Preview Abstract] 

TP9.00048: High Frequency Input Admittance of Continuum Regime Langmuir Probe H.L. Rappaport Measurement of probe complex input impedance, or admittance, has been suggested as a way to increase the amount of information obtained from Langmuir probes [1]. In this poster, a spherical probe immersed in a weakly ionized homogeneous plasma is considered in the regime in which the probe radius is small compard with the Debye length. When the magnitude of the probe potential exceeds the plasma temperature in volts, the low frequency AC input admittance of the negatively biaed probe is given by the ion conductivity times 4$\pi$ times the probe radius plus the admittance associated with the probe vacuum capacitance. The real part of the input admittance falls rapidly when the drive frequency exceeds the reciprocal of the time it takes ions to diffuse a distance on the order of the probe radius. An analytic solution to this problem found by applying the method of matched asymptotic expansions to the describing differential equation is given. Probe circuit models and boundary conditions are reviewed.\\[4pt] [1] D.N. Walker, R.F. Fernsler, D.D. Blackwell, and W.E. Amatucci, Phys. Plasmas 15, 123506 (2008). [Preview Abstract] 

TP9.00049: Analysis of plasma interaction with a rough surface Natalia Krasheninnikova Over the years, a lot of research has been done in an attempt to understand the physics of plasmawall interaction, in particular the role of sheath  a boundary between the hot plasma and surface materials, through which the majority of the interactions are taking place. In relatively recent years it became clear that the quality of the wall's surface tremendously influences the physics of plasmawall interactions. In particular the wall's roughness is thought of playing an important role in the formation of ``hot spots'', sputtering, erosion, arching, thermionic emissions, which have been experimentally observed for years. Present work investigates the effects of the surface roughness on the plasmawall interactions. Collisionless plasma immersed in magnetic field is interacting with a nonflat surface, with the roughness parameters H and W varying relative to the thermal ion gyroradius. Steadystate particle and field profiles are analyzed and the scaling of penetration length is discussed. [Preview Abstract] 

TP9.00050: The effect of magnetic flux expansion on plasma sheath/presheath Z.H. Guo, X.Z. Tang, H. Berk Significant magnetic flux expansion can help spread the plasma heat load over a greater area of tokamak divertor plate. It also appears in the expander of an axisymmetric magnetic mirror, which for its favorable magnetic curvature, helps stabilize the global interchange modes in the central cell. For a weakly collisional plasma, the flux expansion introduces a mirror force accelerating the electron and ion flows downstream, which likely induces an ambipolar parallel electric field. This is in addition to the conventional presheath electric field which accelerates the ion to satisfy the Bohm criteria near the wall. We perform kinetic simulations in two spatial and three velocity dimensions to understand (1) the role of mirror force in the parallel and perpendicular thermal energy transfer, and (2) the combined role of mirroracceleration and parallel electric field on the parallel flow acceleration in the presheath and sheath. The detailed sheath/presheath plasma profiles and the ambipolar electric field will be investigated. Worked supported by OFES. [Preview Abstract] 

TP9.00051: Sheath dynamics in a fusion plasma with oblique magnetic fields X.Z. Tang, N.S. Krasheninnikova, Z.H. Guo To understand the plasma/surface interaction, one must know how plasma sheath modifies the characteristics of the upstream plasma as it approaches the wall surface. This is not only important to decipher the wall response to the ion bombardment flux, but also necessary for quantifying inward impurity transport and assessing the fate of dust particulates anticipated in a tokamak reactor. The magnetic field typically intercepts the tokamak wall at an oblique angle. Here we present a systematic, kinetic simulation study on how the inclination angle of the magnetic field affects the sheath plasma and its dynamics in both the highrecycling (collisional) and lowrecycling (nearly collisionless) regimes. Specifically we will show its effect on wall potential and plasma potential in the sheath and presheath, the characteristics of the normaltothewall and paralleltotheBfield particle and energy flux in the sheath/presheath region. The new findings provide an interesting comparison with the standard Chodura model. The implication on dust motion and survivability in a tokamak reactor will be explained, along with the implied constraint on divertor designs. [Preview Abstract] 

TP9.00052: Electron heat transport at the interface between hot and cold plasmas Grigory Kagan, Xianzhu Tang, Andrei Simakov In high energy density plasma experiments where compression is used to form a central hot target plasma, an interface between the hot but low density and cold but dense plasmas often appears. Evaluation of energy transport, especially electron thermal conduction, across this interface, if it is sufficiently sharp, could be complicated by an electric field localized about the boundary between the plasmas. The field emerges through a mechanism, which is somewhat similar to that of the sheath formation and due to the hot electrons traveling at much greater velocities than their cold counterparts. Such a strong electric field can further modify the distribution function of electrons and therefore their thermal conductivity. To calculate this field we treat hot electrons kinetically, assuming that their mean free path is greater than the interface width. On the other hand, the cold electron bulk is collisional and therefore described by usual fluid equations. By including the sheathlike effects into consideration, we are then able to find a more appropriate expression for the rate of the heat exchange between the hot and cold plasmas. [Preview Abstract] 

TP9.00053: Lowtemperature control of plasmaassisted nanofiber heating Hamid Mehdipour, Kostya Ostrikov Three model, sheath, growth, and heat models are coupled to investigate the direct dependencies of the carbon nanofiber growth and heating on the plasma parameters in a lowtemperature plasma. Using the models, the effects of variation in the plasma sheath parameters and substrate potential on the plasma heating effects in catalyzed growth of carbon nanofiber have been investigated. Numerical results have shown that variations in some parameters such as the electron temperature, electron number density, and substrate potential, which change the sheath width, mainly affect the growth rate and carbon nanofiber heating at low catalyst temperatures and the other parameters such as gas pressure and the ratio of the hydrocarbon/etching gas density to total gas density, change the carbon nanofiber growth at all temperatures and substantially increases the temperature of catalyst particle, attached to carbon nanofiber end, respect to the temperature at substrate interface with substrateholding platform. These results are also consistent with the available experimental results of the selectively control of plasmaassisted nanostructure heating and the catalyzed growth of some highaspectratio structures. [Preview Abstract] 

TP9.00054: Sheath instability around an electronemitting object Gian Luca Delzanno, Giovanni Lapenta In this work, we analyze the stability of the electrostatic sheath of an electron emitting object, for sheath profiles characterized by a potential barrier. We show that such profiles can be unstable to the RayleighTaylor instability, driven by the favorable combination of the density gradient (of the emitted electrons) and electric field in the sheath [1]. We present an analytical theory based on a simplified fluid model which elucidates various aspects of the instability. We also present nonlinear results from a kinetic PIC code, showing that this instability is associated with periodic oscillations of the sheath profiles. [1] G.L. Delzanno, G. Lapenta, Sheath stability of an electron emitting, positively charged wall, in preparation (2010). [Preview Abstract] 

TP9.00055: Novel Electromagnetic Propulsion System Using HighDensity Helicon Plasma Taisei Motomura, Eiji Ohno, Hirotsugu Katanami, Yosuke Sakei, Takahiro Yasutake, Junichiro Mori, Shunjiro Shinohara, Tohru Hada We have been conducting an experimental study on advanced electromagnetic propulsion system using highdensity plasma, applying the helicon waves for efficient plasma production and the rotating magnetic field (RMF) for plasma acceleration via Lorentz force induced by a nonlinear azimuthal current [1,2]. Since the proposed scheme is completely electrodeless, the issue of electrodes erosion is absent, hence a very long operation lifetime can be expected. Using the Large Mirror Device (LMD) installed at Kyushu University [3], the electron density and the ion flow velocity are measured by Langmuir and Mach probes, respectively, with and without applying the RMF. The penetration conditions of the RMF into the plasma are estimated by using the magnetic probe. The initial results will be presented in detail.\\[4pt] [1] M. Inomoto, IEEJ Trans. FM. \textbf{128}, 319 (2008).\\[0pt] [2] I. R. Jones, \textit{et al}., J. Plasma Phys. \textbf{26}, 441 (1981).\\[0pt] [3] S. Shinohara, \textit{et al}., Jpn. J. Appl. Phys. \textbf{35}, 4503 (1996). [Preview Abstract] 

TP9.00056: ABSTRACT WITHDRAWN 

TP9.00057: CMOD TOKAMAK 

TP9.00058: Electron Transport Dominated Regimes in Alcator CMod M. Porkolab, J. Dorris, P.T. Bonoli, P. Ennever, C. Fiore, M. Greenwald, A. Hubbard, Y. Ma, M.L. Reinke, J. Rice, J. Rost, N. Tsujii, L. Lin, J. Candy, R. Waltz, P. Diamond, C.J. Lee In ohmically heated low density plasmas where $\tau _{E} \quad \propto $ n$_{e}$, the socalled neoAlcator regime, TRANSP results indicate that $\chi _{i}<< \quad \chi _{e}$, while nonlinear gyrokinetic analysis for the measured profiles predicts the opposite inequality [1]. This regime is of great interest for transport studies since Ti $<$ Te, and the electron and ion transport channels can be separated and studied separately. At the same time, measurements of turbulent fluctuations with Phase Contrast Imaging diagnostic (PCI) indicated reasonable agreement with GYRO predictions at frequencies 80250 kHz, corresponding to core ITG turbulence. The turbulent spectrum at lower frequencies could not be identified since the PCI technique does not allow separation of the core plasma fluctuations from those at the edge. Here we present measurements and analysis from a more extensive set of plasma regimes than previously. Of particular current interest is the role of electron drift wave turbulence driven by ohmic electron drift, U [2], since in these low density regimes U/C$_{s} \quad \le $ 6, and experimentally we find that the global confinement $\tau _{E}$ $\propto $ C$_{s}$/U where C$_{s}$ = (T$_{e}$/m$_{i})^{1/2}$. [1] L. Lin, Invited talk, APSDPP, 11, 2009, Atlanta, GA. [2] C.J. Lee, P. Diamond, M. Porkolab, presented at TTF workshop, 2010. [Preview Abstract] 

TP9.00059: Experimental study of plasma shaping effect in Alcator CMod Ohmic low confinement regime* Y. Ma, A. Hubbard, S. Wolfe, C. Fiore, M. Greenwald, M. Porkolab, J. Rice, A. Dominguez, T. Golfinopoulos, N. Tsujii, J. Hughes, E. Marmar Previous studies on TCV tokamak suggest that shaping parameters ($\kappa $, $\delta )$ could play a role in the plasma confinement. This study presents the experimental observations in Alcator CMod Ohmic Lmode plasmas at different line averaged densities (0.4$\sim $1.0 n20) as the shaping parameters being scanned. The shape of T$_{e}$, T$_{i,}$ n$_{e}$ profiles measured from Thomson scattering, ECE and Xray spectroscopy diagnostics are compared to extract the degree of profile similarities in these discharges. Sawtooth activities (intensity, period, inversion radius) are characterized from ECE measurements in various shaping configurations. Spectra of plasma fluctuations are monitored by PCI, Omode reflectometers and magnetic probes. Local particle and heat transport are calculated from 2 dimensional power balance analysis code TRANSP using experimental measurements and to be compared with global confinement scaling and anomalous transport models (e.g. TGLF). Perturbative transport studies will be explored in the future studies. *Supported by USDoE award DEFC0299ER54512 [Preview Abstract] 

TP9.00060: Developing predictive capability for the Hmode pedestal: Experimental contributions from Alcator CMod J.W. Hughes, R.M. Churchill, I. Cziegler, A. Dominguez, A.E. Hubbard, B. Lipschultz, Y. Ma, J.L. Terry, N. Tsujii, R.J. Groebner, P.B. Snyder Experiments on Alcator CMod characterize the edge pedestal in several high confinement regimes, as part of a community experimental and theoretical effort to improve predictive capability for the pedestal. Pedestal structure in both transiently evolving and stationary enhanced D$_\alpha$ Hmodes is studied and examined alongside edge fluctuations ({\it e.g.} quasicoherent modes), allowing us to seek evidence for transportdriven mechanisms limiting pedestal width and gradients. The pedestal structure in Hmodes with edgelocalized modes (ELMs) is likely to be governed both by transport and by intermittent ELM relaxation. ELMy Hmodes are diagnosed and used to test directly models for pedestal height/width, {\it e.g.} EPED. Pedestal profiles, fluctuations and ELM activity in these Hmode regimes are compared to those in Imode, in which a temperature and a pressure pedestal are maintained in the absence of a particle barrier ({\it i.e.} edge $L_n/L_T\gg 1$), and which can provide additional insight into physics governing pedestal formation and structure. [Preview Abstract] 

TP9.00061: GYRO simulations of turbulently driven 'intrinsic rotation' in Cmod plasmas D.R. Mikkelsen, M. Bitter, K.W. Hill, Y. Podpaly, J.E. Rice, J.W. Hughes, Y. Ma, J. Candy, R.E. Waltz In some CMod plasmas with no externally applied torque, the radial profile of the toroidal rotation speed indicates that ``intrinsic rotation'' is generated in the plasma core. GYRO simulations of LMode and Imode plasmas are used to learn if the turbulent transport of toroidal angular momentum might cause intrinsic rotation by removing angular momentum, thereby spinning up the plasma in the opposite direction. Two of the three plasmas have strong radial gradients in the measured toroidal rotation; the third is a ``control'' case. In GYRO simulations there is an inward flow of momentum when the input has no radial gradient of the toroidal rotation speed. We estimate the gradient that GYRO 'predicts' by varying the input gradient until we bracket the target state of zero momentum flux. The sign of the rotation speed gradient predicted by GYRO agrees with experiment, and the magnitude is generally within a factor of two  GYRO tending to be lower, but not everywhere. For the ``control'' case GYRO predicts an intrinsic rotation gradient a factor of 35 smaller than for the other cases. [Preview Abstract] 

TP9.00062: Momentum transport calculations on Alcator CMod in the LH mode transition Yuri Podpaly, John Rice, David Mikkelsen, Matthew Reinke, Kenneth Hill, Manfred Bitter Intrinsic rotation and momentum transport during the LH transition has been the topic of great interest over the last few years as a possible means of controlling plasma instabilities. Alcator CMod is uniquely situated to study these transitions at ITER like densities and magnetic fields. During the LH mode transition, rotation measurements have been made from the core to approximately r/a $\sim $0.7, and the location of the source of momentum in the plasma was found to match the location of the largest pressure gradient difference between the L and the Hmode. Further refinements of that research are presented here with time and space dependent diffusive and convective transport values and analysis comparing total pressure gradient to temperature gradient values. Power balance and gyrokinetic code calculation results on these transitions are shown as well. [Preview Abstract] 

TP9.00063: Comparison of impurity transport in Alcator CMod with fluid models of drift wave turbulence W.L. Rowan, I.O. Bespamyatnov, X. Fu, K.W. Gentle, W. Horton, K.T. Liao, S. Futatani, C.L. Fiore Using a new theory, we investigate the influence of the impurity density and impurity density gradient on turbulent particle transport. Heavy impurities (argon is the example here) appear to have the strongest influence while light impurities (boron, for example) may simply transport as passive tracers when in the presence of a significant quantity of heavy impurity. The theory describes how collisional and trapped electron drift wave dynamics are modified by impurities and how the turbulence transports the impurities in a background hydrogenic plasma. The collisional regime is described using a HasegawaWakatani system of equations. The trapped electron mode is modeled with a generalized form of the TerryHorton system of equations. Measured positive and negative impurity gradients can be predicted, but new experiments will be required to verify the implications of the theory. [Preview Abstract] 

TP9.00064: Insitu wavelength calibration and temperature control for the CMod highresolution xray crystal imaging spectrometer Luis F. DelgadoAparicio, Y. Podpaly, M.L. Reinke, C. Gao, J. Rice, S. Scott, M. Bitter, K. Hill, P. Beiersdorfer, D. Johnson, J.R. Wilson An xray crystal imaging spectrometer with high spectral and spatial resolution is currently being used on Alcator CMod to infer time histories of temperature and velocity profiles. An insitu wavelength calibration using a 1 $\mu$m palladium filter in between the crystal and the detectors of choice is being proposed as a natural wavelengthmarker using the transmission changes across the LII and LIII edges at 3722.9 mA and 3907.1 mA, respectively. Recent results also indicate that the crystal temperature should be kept constant within a fraction of a degree since the thermal expansion of the quartz crystal will change the interplanar ($2d$) spacing and introduce fictitious velocity measurements of several km/s. A detailed temperature scan indicates a thermal expansion coefficient ($\alpha_{\perp}$) of $13.5\times10^{6}$ $/^{\circ}$C and thus a false Doppler shift of $4.05\cdot\Delta T[^{\circ}$C$]$ km/s. [Preview Abstract] 

TP9.00065: Innerwall Impurity Density Measurements on Alcator CMod R.M. Churchill, B. Lipschultz Recent findings on Alcator CMod imply a poloidal impurity density asymmetry in the pedestal region, inferred from boron ($B^{5+}$) velocity measurements at the inner and outerwall combined with neoclassical transport theory. In an effort to confirm these findings, the direct measurement of the boron density was made at the innerwall pedestal using simultaneous spectroscopic views of boron charge exchange recombination spectroscopy (CXRS) ($B^{4+},\, n=76,\,\lambda=494.467nm$) and Balmer$\alpha$ ($D^{0+},\, n=32,\,\lambda=656.6nm$). Since the innerwall CXRS measurement utilizes a deuterium gas puff as the source of neutrals to induce charge exchange, detailed modeling is required in order to calculate the neutral density profile from the Balmer$\alpha$ measurement. Additionally, due to the low interaction energies the $B^{5+}+D^{0+}(n=2)\rightarrow B^{*(4+)}+D^{1+}$ is the dominant boron CX process, so a collisionalradiative model is required to calculate the $n=2$ deuterium density from the $n=3$ density derived from the Balmer$\alpha$ measurement. The radial shape of the resulting boron density profile agrees with the profile predicted by the impurity density asymmetry. Supported by USDoE award DEFC0299ER54512. [Preview Abstract] 

TP9.00066: Correlation Reflectometry Results and Analysis on Alcator CMod A. Dominguez, E.S. Marmar, G.J. Kramer, E.J. Valeo A swept frequency Omode reflectometry system has been operational on the Alcator CMod tokamak since the 2009 campaign. The system has a midplane view of the plasma from the low field side and covers the frequency range of 112GHz140GHz, corresponding to electron density cutoffs of 1.562.43 $[10^{20}m^{3}]$. In conjunction with two fixed frequency Omode reflectometry channels at 112GHz and 140GHz, it is possible to determine reflectometry radial decorrelation lengths in the plasma. These lengths can be mapped to the turbulent radial decorrelation lengths with the use of a 2D synthetic diagnostic code[1]. Results and analysis will be presented for density fluctuations in the radial region inside r/a $\sim$ 0.7. \\[4pt] [1] E.J. Valeo, G.J. Kramer, R. Nazikian, Plasma Phys. Control. Fus. 44 (2002) L1 [Preview Abstract] 

TP9.00067: Analysis tools for turbulence studies at Alcator CMod C. Burns, S. Shehata, A.E. White, I. Cziegler, A. Dominguez, J.L. Terry, D.C. Pace A new suite of analysis tools written in IDL is being developed to support experimental investigation of turbulence at Alcator CMod. The tools include GUIs for spectral analysis (coherence, crossphase and bicoherence) and characteristic frequency calculations. A userfriendly interface for the GENRAY code, to facilitate inbetween shot raytracing analysis, is also being developed. The spectral analysis tool is being used to analyze data from existing edge turbulence diagnostics, such as the Omode correlation reflectometer and Gas Puff Imaging, during Imode, ITB and EDA Hmode plasmas. GENRAY and the characteristic frequency tool are being used to study diagnostic accessibility limits set by wave propagation and refraction for Xmode Doppler Backscattering and Correlation Electron Cyclotron Emission (CECE) systems that are being planned for core turbulence studies at Alcator CMod. [Preview Abstract] 

TP9.00068: Correlation ECE and Doppler Backscattering Diagnostics for Alcator CMod A.E. White, A. Hubbard, P. Phillips, J. Irby, M. Greenwald, D.R. Mikkelsen, N.T. Howard A Correlation Electron Cyclotron Emission (CECE) diagnostic and an Xmode reflectometer system are being developed to measure long wavelength ($k_{\theta}\rho_s$) core electron temperature fluctuations and density fluctuations, respectively, at Alcator CMod. These new diagnostics will allow for detailed twofield core turbulence measurements and validation studies. Adjustable optics will allow the reflectometer to be configured as a Doppler backscattering system. Global, nonlinear gyrokinetic turbulence simulations (GYRO) and synthetic diagnostics are used to model the diagnostics' expected responses to turbulence in a variety of operating regimes. The challenges associated with the high frequency systems required for core turbulence studies at CMod and the feasibility of combining these complementary diagnostics into a single transmission system will be assessed. Accessibility limits, expected wavenumber sensitivity and waveguide/antennae configurations are discussed. [Preview Abstract] 

TP9.00069: Measurements of plasma sheath heat flux in the Alcator CMod divertor Dan Brunner, Brian LaBombard, Jim Terry, Matt Reinke Heat flux is one of the most important parameters controlling the lifetime of firstwall components in fusion experiments and reactors. The sheath heat flux coefficient $\left(\gamma\right)$ is a parameter relating heat flux (from a plasma to a material surface) to the electron temperature and ion saturation current. Being such a simple expression for a kinetic process, it is of great interest to plasma edge fluid modelers. Under the assumptions of equal ion and electron temperatures, no secondary electron emission, and no net current to the surface the value of $\gamma$ is approximately 7 [1]. Alcator CMod provides a unique opportunity among today's experiments to measure reactorrelevant heat fluxes (100's of MW/m$^2$ parallel to the magnetic field) in reactorlike divertor geometry. Motivated by the DoE 2010 joint milestone to measure heat flux footprints, the lower outer divertor of Alcator has been instrumented with a suite of Langmuir probes, novel surface thermocouples, and calorimeters in tiles purposefully ramped to eliminate shadowing; all within view of an IR camera. Initial results indicate that the experimentally inferred values of $\gamma$ are found to agree with simple theory in the sheath limited regime and diverges to lower values as the density increases. [Preview Abstract] 

TP9.00070: Kinetic studies of divertor heat fluxes in Alcator CMod A.Y. Pankin, G. Bateman, A.H. Kritz, T. Rafiq, G.Y. Park, C.S. Chang, D. Brunner, J.W. Hughes, B. LaBombard, J. Terry The kinetic XGC0 code [C.S. Chang et al, Phys. Plasmas 11 (2004) 2649] is used to model the H mode pedestal and SOL regions in Alcator CMod discharges. The selfconsistent simulations in this study include kinetic neoclassical physics and anomalous transport models along with the ExB flow shear effects. The heat fluxes on the divertor plates are computed and the fluxes to the outer plate are compared with experimental observations. The dynamics of the radial electric field near the separatrix and in the SOL region are computed with the XGC0 code, and the effect of the anomalous transport on the heat fluxes in the SOL region is investigated. In particular, the particle and thermal diffusivities obtained in the analysis mode are compared with predictions from the theorybased anomalous transport models such as MMM95 [G. Bateman et al, Phys. Plasmas 5 (1998) 1793] and DRIBM [T. Rafiq et al, to appear in Phys. Plasmas (2010)]. It is found that there is a notable pinch effect in the inner separatrix region. Possible physical mechanisms for the particle and thermal pinches are discussed. [Preview Abstract] 

TP9.00071: MHD activity during the prethermal quench phase of gas jet mitigated disruptions on Alcator CMod Geoffrey Olynyk, Matthew Reinke, Dennis Whyte, Robert Granetz, Ian Hutchinson, Valerie Izzo Using multiple AXUV diode arrays on Alcator CMod, radiated energy during gas jet mitigated disruptions has been shown to be toroidally asymmetric, with the ratio of energy on opposite looking diode arrays ranging from 1.1 to 2.6 [Reinke et al., \emph{Bull. Am. Phys. Soc.} {\bf 54}(15), UO4.00003]. Asymmetry of this magnitude during mitigated disruptions on ITER would lead to melting of the beryllium first wall [M. Sugihara et al., \emph{Nucl. Fus.} {\bf 47}(4), 337352]. Using a toroidal array of poloidal field pickup coils, there is shown to be a link between the growth rates of lown MHD modes during the pre thermal quench (preTQ) phase of the mitigated disruption and the radiation asymmetry during the TQ. This is also evidence for the role of MHD activity in triggering the TQ. The implications of this correlation for reducing the radiation asymmetry are discussed. [Preview Abstract] 

TP9.00072: Stimulation of MHD Modes in Alcator CMod T. Golfinopoulos, R. Granetz, B. LaBombard, Y. Lin, R.R. Parker, J. Sears, S.J. Wukitch Active MHD (AMHD) spectroscopy involves stimulating MHD modes by external means to study the modes or diagnose the plasma. In many AMHD experiments, drive frequency is swept across a $100200$ kHz range in which modes are expected; this allows for robust techniques to detect resonant poles in the presence of direct pickup from the driver. However, there is flexibility in the drive mechanism. At Alcator, we have employed a parametric excitation method, amplitudemodulating the ICRF wave (80 MHz) with envelope signals in the AE frequency range (100's kHz). This builds off the ICRF beat technique used in JET in 1996 and ASDEX Upgrade in 2006, but is unique in its use of a single antenna, improving coherence. An advantage of this approach is its ability to couple to the plasma core. It also has high input power, though efficiency is limited by the ManleyRowe relations. In initial experiments, we excited weak, stable modes in the toroidal Alfv\'{e}n eigenmode band gap. We plan to explore this and other methods for coupling to various MHDlike modes, especially CMod's Quasi Coherent mode. [Preview Abstract] 

TP9.00073: Progress on the CMod FIR Polarimeter System P. Xu, J.H. Irby, W.F. Bergerson, D.L. Brower, W.X. Ding, S. Shiraiwa, S. Wolfe A poloidally viewing FIR polarimetry diagnostic is being developed for the Alcator CMod Tokamak. The primary diagnostic components are a twowave FIR laser at 117.73 microns and newly developed detectors whose performance characteristics will be described. Faraday rotation will be used both to refine the qprofile measurement by adding constraints to EFIT , and to study density and magnetic field fluctuations. A threechord system has been installed, one chord of which is being tested during the FY10 CMod campaign. The FIR laser source is affected by both stray magnetic fields and mechanical vibrations present in the experimental cell thereby impacting the measurement. Methods developed to mitigate and correct for these effects will be discussed. Initial Faraday data will be compared with expectations from numerical simulation. [Preview Abstract] 

TP9.00074: Detection and application of Doppler and motional Stark features in the DNB emission spectrum in the high magnetic field of the Alcator CMod tokamak Igor Bespamyatnov, William Rowan, Kenneth Liao, Robert Mumgaard, Robert Granetz, Steve Scott The spectral region in the vicinity of the D$_{\alpha }$ line is to be studied with a high resolution spectrometer. This region contains spectral lines emitted by atoms in the diagnostic neutral beam (DNB) and plasma atoms and ions. Spectrally isolated emission serves as a measure of the properties of emitting particles and surrounding medium. In CMod, the main obstacle for application of these techniques is that at high magnetic fields (58T) the spectral separation due to motional Stark splitting is similar to the spectral Doppler shifts of lines emitted by DNB atoms of energies 50, 25 and 18 keV. This results in partial blending of observed spectral lines and consequent masking of Doppler or Stark effect. High spectral resolution ($\sim $ 1A) and complex spectral fitting technique are needed for isolation of different components. Results of this work will be used in the further development of Beam Emission Spectroscopy (BES) system installed at CMod and in support for the current Motional Stark Effect (MSE) diagnostic. [Preview Abstract] 

TP9.00075: Status and recent MSE results on Alcator CMod Steven Scott, Robert Mumgaard, Robert Granetz, Roman Shugayev Thermal birefringence within invessel lenses has been identified as the cause of a spurious drift in the calibration of the MSE diagnostic on Alcator CMod. Significant upgrades have been implemented to reduce thermal gradients in the invessel components including a goldplated radiative heat shield and a unique lens mount to thermally isolate the MSE periscope. Experimental results on the effectiveness of these upgrades are presented. An automated calibration system has been designed and constructed to enable a thorough invessel calibration of MSE during brief uptoair periods. This system was utilized during the Spring 2010 maintenance period to perform multiple parameter scans, including 2D scans of optical loss across the objective lens and 3D scans (2D position and angleofincidence) across the PEMs. Based on these measurements, the optical loss due to vignetting in the MSE optics is estimated at 20\%. An overview of the current MSE system performance, opportunities for improvements and MSE qprofile measurements from recent current drive experiments are presented. [Preview Abstract] 

TP9.00076: Design considerations for realtime MSE background subtraction on Alcator CMod Robert Mumgaard, Steven Scott, William Rowan, Igor Bespamyatnov, Ken Liao, Steve McClain, Russell Chipman MSE measurements of the qprofile in Alcator CMod are difficult at high density and in Hmode plasmas due to increased partiallypolarized background light in the MSE wavelength range. This background is highly variable both spatially and temporally, making traditional beamonbeamoff background interpolation insufficient. A realtime background subtraction is proposed: spectral studies [See poster 18, Bespamyatnov] have identified a spectral region free of impurity lines adjacent to the MSE measurement region where the polarized background signal can be measured as a proxy for the MSE background signal. A polychromater design that utilizes multiple tunable narrow bandpass filters to simultaneously measure the MSE signal and partially polarized background is presented. Issues pertaining to design and calibration of this instrument and its relevance to diagnostic challenges on ITER are discussed. [Preview Abstract] 

TP9.00077: Analysis of Lower Hybrid Current Drive Modification of Sawtooth in Alcator CMod P.T. Bonoli, A.E. Hubbard, A.E. Schmidt, J.C. Wright, C.E. Kessel, D.B. Batchelor, L.A. Berry, R.W. Harvey Experiments were performed in Alcator CMod, where the onset time for sawteeth was delayed significantly (up to 0.5 s) relative to ohmically heated plasmas, through the injection of offaxis LH current drive power [1]. The LH driven current density profiles in these experiments are being simulated using a ray tracing code (GENRAY) and Fokker Planck code (CQL3D) [2] in order to ascertain the consistency of the simulated current density profiles with the requirements for sawtooth stabilization. Comparisons of simulated LHRFgenerated hard xray spectra with experimental measurements will be shown. We will also discuss time dependent simulations of these experiments using an advanced parallel computing framework [3]. \\[4pt] [1] C. E. Kessel \textit{et al}, Bull. of the Am. Phys. Soc. \textbf{53}, Poster PP6.00074 (2008). \\[0pt] [2] R. W. Harvey and M. G. McCoy, Proc. of the IAEA Tech. Comm. Mtg on Sim. and Mod. of Therm. Plasmas, Montreal, Canada (1992). \\[0pt] [3] D. Batchelor \textit{et al}, J. of Phys. Conf. Series \textbf{125}, 012039 (2008). [Preview Abstract] 

TP9.00078: Investigation of ion toroidal rotation induced by Lower Hybrid waves in Alcator CMod using integrated numerical codes Jungpyo Lee, John Wright, Paul Bonoli, Ron Parker, Peter Catto, Yuri Podpaly, John Rice, Matt Reinke, Felix Parra Ion toroidal rotation in the counter current direction has been measured in CMod during lower hybrid (LH) RF power injection. Toroidal momentum input from the LH waves determines the initial increase of the counter current ion toroidal rotation. Due to the fast build up time of the plateau ($<$ 1msec), the electron distribution function is assumed to be in steady state. We calculate the toroidal momentum input of LH wave to electrons by iterating a full wave code (TORICLH) with a Fokker Plank code (CQL3D) to obtain a self consistent steady state electron distribution function. On the longer time scale, comparable to the transport time ($\sim$100msec), ion rotation is changing due to the constant momentum transfer from electrons to ions and the radial flux of ion toroidal momentum by Reynolds stress and collisional viscosity. We suggest a way to evaluate the viscosity terms for the low flow level rotation bya modifielectrostatic gyrokinetic code. [Preview Abstract] 

TP9.00079: The development of a 4.6 GHz reflectometer in Alcator CMod S.G. Baek, A. Dominguez, S. Shiraiwa, R. Parker, P. Bonoli, E. Marmar, J. Wright, G. Wallace, G. Kramer The development of a 4.6 GHz reflectometer system to detect LH waves in Alcator CMod plasmas is presented together with preliminary experimental results. Hard Xray data of the 2008 Alcator CMod campaign indicated an anomalous decrease of photon generation in high density plasmas during LHCD experiments, suggesting LH waves did not propagate inside the plasma separatrix. Calculations and simulations show that the nonlinear interaction between a reflectometer probe beam and LH waves in the region where wave matching conditions are satisfied generates backscattered, frequency shifted signals. To measure these signals, the high frequency stages of existing 60 GHz and 75 GHz Omode reflectometer channels were modified, and intermediate frequency and power detecting stages have been added. The ray tracing code, GENRAY, and full wave simulations, e.g., TORIC and LHEAF, will be used to optimize plasma conditions for maximum response of frequency shifted signals. Both 1D and 2D transient analysis using the finite element solver, COMSOL, is also presented. Supported by USDoE award DEFC0299ER54512. [Preview Abstract] 

TP9.00080: Recent results from lower hybrid current drive experiments on Alcator CMod R.R. Parker, S.G. Baek, O. Meneghini, C. Lau, Y. Podpaly, M. Porkolab, J.E. Rice, A.E. Schmidt, S. Shiraiwa, G.M. Wallace, S.J. Wukitch, J.R. Wilson A novel coupler designed to optimize LHRF power delivered to Alcator CMod plasmas is now in operation. New diagnostics have also been added to better understand the conversion of waveguide modes in the grill antenna to slow LH waves, and the penetration and damping of the waves as they pass beyond the separatrix. These include a set of 32 RF probes located near the plasmagrill interface, an Xmode reflectometer for measuring the density profile near the grill, and a twofrequency Omode reflectometer for detecting LH waves beyond the separatrix via Bragg scattering. The latter, supplemented by Xray and cyclotron emission profiles, is expected to be helpful in understanding the disparity in measured current drive efficiency at high density relative to predictions from raytracing and fullwave simulations. This paper surveys the results obtained with the new coupler, including coupling and current drive efficiency, plasma rotation and comparison with results of simulations. [Preview Abstract] 

TP9.00081: High Density ScrapeOffLayer Absorption of Lower Hybrid Waves on the Alcator CMod Tokamak I. Faust, G.M. Wallace, M. Reinke, R.R. Parker, O. Meneghini, A.E. Schmidt, S. Shiraiwa, J.R. Wilson The goal of the LHCD system on Alcator CMod is to investigate current profile control under plasma conditions relevant to burning plasma experiments. Bremsstrahlung from fast electrons in the core plasma drops suddenly at a density below the density limit previously observed on other tokamaks ($\omega/\omega_{LH} \sim 2$). Electric currents in the SOL between the inner and outer divertors increase across the same density range that the core bremsstrahlung emission drops while SOL Lyman$\alpha$ emissivity profiles shift outward, indicating absorption of LH waves in the SOL. The experimental xray data are compared to a ray tracing/FokkerPlanck model including collisional absorption in the SOL, which shows good agreement with the experiment across a wide range of densities. The model identifies possible strategies to circumvent the density limit such as increasing the temperature and decreasing the density in the SOL. [Preview Abstract] 

TP9.00082: Absorption of lower hybrid waves in the scrape off layer and possible implications for ITER G.M. Wallace, P.T. Bonoli, A.E. Hubbard, B.L. LaBombard, O. Meneghini, R.R. Parker, A.E. Schmidt, S. Shiraiwa, D.G. Whyte, J.C. Wright, S.J. Wukitch, M. Goniche, R.W. Harvey, A.P. Smirnov, J.R. Wilson The goal of the lower hybrid current drive (LHCD) system on Alcator CMod is to investigate current profile control at ITER relevant values of magnetic field, plasma density, and LHCD frequency. Experimental observations of an LHCD density limit show that current drive in CMod drops suddenly at a density near the upper range expected in ITER steadystate scenarios. Measurements on CMod indicate that the LH power is deposited in the SOL at high density. These data are compared to a model including collisional absorption in the SOL, which shows good agreement across a wide range of densities. These results show that strong absorption of LH waves in the SOL is possible and must be considered in simulations of LHCD at high density. Simulations of LHCD on ITER with several possible SOL profiles will be presented. Supported by USDoE awards DEFC0299ER54512 and DEAC0209CH11466. [Preview Abstract] 

TP9.00083: Full wave modeling of offaxis LHCD using the LHEAF code on Alcator CMod S. Shiraiwa, O. Meneghini, S. Scott, R.R. Parker, G. Wallace, S. Wolfe We will present LHEAF full wave simulation results of Alcator CMod LHCD experiments. LHEAF is a full wave simulation code for LHCD based on the finite element method, which allows simulations of the hot core plasma, the SOL plasma, and the launcher in a seamless manner. The LHEAF FokkerPlanck module has been upgraded to a 3D FokkerPlanck code to compare code results with Alcator CMod experiments. Simulation results of stable LHCD discharges show good agreement with the current profile obtained by an equilibrium reconstruction. On the other hand, the code predicts hollower current profile than observed on the discharges which had n=1,m=2 MHD instabilities, implying that those instabilities limited further broadening of the current profile. We will also discuss interesting wave spectrum broadening observed in code simulations in the multipass regime, which may be difficult to reproduce using a traditional ray tracing technique. [Preview Abstract] 

TP9.00084: First Results from Alcator CMod SOL Reflectometer Cornwall Lau, Greg Hanson, John Wilgen, Yijun Lin, Steve Wukitch The study of antennaplasma interactions during RF heating and current drive is greatly influenced by the SOL density profile. A sweptfrequency Xmode reflectometer has recently being built for Alcator Cmod to measure the SOL density profiles at top, middle and bottom locations in front of the new Lower Hybrid Launcher and adjacent to one of the twostrap ICRF antennas. The system operates between 100 and 146 GHz and covers a density range of approximately 10$^{16}$to 10$^{20}$m$^{3}$ at 55.4T at sweep rates from 10 $\mu $s to 1 ms. First data from the reflectometer will be presented. SOL density profiles will be shown for different plasma conditions, such as various ICRF and LHRF power, L or H regimes, and different line averaged densities. Comparison between the reflectometer and other density profile diagnostics on Alcator CMod will also be presented. [Preview Abstract] 

TP9.00085: Quantitative assessment of RF sheath rectification in Alcator CMod with emissive, bdot, and ion sensitive probes Roman Ochoukov, Dennis Whyte, Bruce Lipschultz, Brian LaBombard, Stephen Wukitch Radio frequency (RF) rectification of the plasma sheath is currently being studied as a possible mechanism that leads to prohibitively high molybdenum levels in the plasma core of RF heated discharges in the Alcator CMod tokamak. We installed emissive, ion sensitive, and 3D bdot probes to quantify the presence of RF sheaths in RF heated Alcator CMod plasma discharges on surfaces magnetically connected to the active RF antenna. Two probe sets were mounted on fixed limiter surfaces and one set of probes was mounted on a reciprocating (along the major radius) probe, the Surface Science Station. Preliminary results showed that RF rectification of the plasma sheath correlated with the local plasma density with little to no correlation to the local RF fields. Plasma density scans also revealed a thresholdlike appearance of the RF sheaths above a certain plasma density value. The strongest RF sheath potentials were observed on magnetic field lines directly mapped to the active RF antenna. [Preview Abstract] 

TP9.00086: CXRSbased diagnostic for fast ion detection in the core of the Alcator CMod Tokamak K.T. Liao, W.L. Rowan, I.O. Bespamyatnov Charge exchange recombination spectroscopy (CXRS) will be used to measure the spatial and temporal distribution of fast ions within the core plasma. Fast ions are generated in CMod by minority absorption of injected waves in the ion cyclotron range of frequencies. Typically, the minority is H in a D plasma or possibly He3 in D. Emission from the fast ions is excited by charge exchange with the neutral atoms in a diagnostic neutral beam. [see W.W. Heidbrink, et al., Plasma Phys. Control. Fusion 47, 1855 (2004)] In the new diagnostic, the spectra are captured with 1 cm spatial resolution into approximately 30 poloidal or toroidal channels, spectrally analyzed with a high throughput spectrograph that is modified to reduce scattered light from edge emission lines, and detected with a camera with 10 ms temporal resolution. The capabilities of the diagnostic are explored through simulation of the spectrum and measurements of the emission background. For CMod, the diagnostic is uniquely capable of detecting fast ions in the plasma core and thus contributing to RF physics as well as to fast ion transport. Expected fast ion ``signaltonoise'' will be presented. [Preview Abstract] 

TP9.00087: ICRF Mode Conversion Flow Drive on Alcator CMod Yijun Lin, J.E. Rice, S.J. Wukitch, M.L. Reinke, M. Greenwald, A.E. Hubbard, E.S. Marmar, Y. Podpaly, M. Porkolab, N. Tsujii ICRF mode conversion flow drive (MCFD) may be a candidate for the external control of plasma rotation in large tokamaks like ITER. Recently, we have carried out a detailed study of MCFD on CMod, including its dependence on plasma and RF parameters [1]. The observed change in the toroidal rotation ($\Delta $V) is always in the coI$_{p}$ direction. The flow drive efficiency depends on the $^{3}$He concentration in D($^{3}$He) plasmas. It is strongly affected by density ($\sim $ 1/n$_{e})$, generally increases with I$_{p}$ and decreases with RF frequency. At +90$^{o}$ and dipole antenna phases, we find that $\Delta $V is proportional to P$_{RF}$ up to the maximum available RF power. The rotation at 90$^{o}$ antenna phase is more complicated. In low density Lmode plasmas, $\Delta $V $\sim $110 km/s has been achieved. Results in Hmode plasmas appear to follow a similar parametric scaling, but the observed $\Delta $V in Hmode has been small because of the high density and unfavorable 1/n$_{e}$ scaling. These results may help extrapolate MCFD to other fusion devices.\\[4pt][1] Y. Lin et al, 23$^{rd}$ IAEA Fusion Energy Conference, 2010, EXW/41. [Preview Abstract] 

TP9.00088: ICRF Antenna Optimization for Alcator CMod M.L. Garrett, S.J. Wukitch, W. Beck, P. Koert, Y. Lin, R. Parker Two major challenges for ICRF utilization are reducing impurity generation and increasing reliability at high voltages. In Alcator CMod, we are designing a rotated 4strap antenna where we seek to lower Eparallel and improve voltage handling. Simulations were conducted to analyze the effect of antenna orientation on the parallel electric field, which is thought to influence impurity production. In addition, simulations were carried out on antenna box and limiter structures with particular emphasis on parallel electric field reduction through image current modification. Antenna septum and limiter thickness, position, and separation were varied. The effect of slotting antenna limiters and antenna box walls was also investigated. Previous experiments suggest that improved voltage handling may be obtained through the use of refractory metals compared with copper. A test stand has been designed and built to characterize ICRF relevant voltage breakdown as a function of: antenna material, neutral pressure, and magnetic field orientation. Results from simulations and experiments will be presented along with details of the new antenna design. [Preview Abstract] 

TP9.00089: Impurities Associated with ICRF on CMod S.J. Wukitch, H. Barnard, D. Brunner, M.L. Reinke, G. Wright, M. Garrett, Y. Lin, B. Lipschultz, B. LaBombard, D.G. Whyte In CMod experiments, a boron (B) film is applied to minimize the core molybdenum (Mo) content associated with ion cyclotron range of frequency heating; however, experiments suggested a high B erosion rate. A $\sim $100 $\mu $m boron film has been sprayed onto the Mo tile surfaces with the expectation that 2030 $\mu $m of the B would be locally eroded during a campaign. Following the campaign, the B coating was found not to be significantly eroded except in locations where peeling and melting occurred. The peeling appears to be the result of poor bonding and the melt damage was localized to the outboard midplane of the plasma limiters. Thus, the high erosion rate reflects degradation of localized spots rather than sputtering of large surface areas. Conditions favoring melting limiter surfaces are discharges with low density and high ICRF power. To cause surface melting, the energy delivered to the tile is a small fraction of the injected energy ($<$1{\%}); however, the precise mechanism responsible is yet to be identified. [Preview Abstract] 

TP9.00090: TURBULENCE AND TRANSPORT 

TP9.00091: Gyrokinetic simulation of short wavelength residual zonal flows E.S. Yoon, T.S. Hahm, S. Ku It is widely recognized that zonal flow plays a crucial role in saturating the level of turbulence. Therefore, estimation of residual (i.e., undamped) zonal flow level is important in predicting turbulence transport. There has been considerable theoretical progress on this topic [1,2,3]. In particular, Wang and Hahm [3] formulated an analytic expression for residual zonal flows which is valid for arbitrary wavelength, taking into account of both neoclassical and classical polarization shielding of both species. This is in broad agreement with the previous gyrokinetic simulation results by Jenko et al. [4]. In this work, we examine various parametric dependences of residual zonal flow level in wide wavelength range using gyrokinetic simulation, and compare with the analytic predictions [3]. [1] M.N. Rosenbluth and F.L. Hinton, Phys. Rev. Lett. \textbf{80}, 724 (1998) [2] Y. Xiao and P.J. Catto, Phys. Plasmas \textbf{13}, 102311 (2006) [3] L. Wang and T.S. Hahm, Phys. Plamsas \textbf{16}, 062309 (2009) [4] F. Jenko, W. Dorland, M. Kotschenreuther, and B.N. Rogers, Phys. Plasmas \textbf{7}, 1904 (2000) [Preview Abstract] 

TP9.00092: Experimentally Relevant Benchmarks for Gyrokinetic Codes Ronald Bravenec Although benchmarking of gyrokinetic codes has been performed in the past, e.g., The Numerical Tokamak, The Cyclone Project, The Plasma Microturbulence Project, and various informal activities, these efforts have typically employed simple plasma models. For example, the Cyclone ``base case'' assumed shiftedcircle flux surfaces, no magnetic transport, adiabatic electrons, no collisions nor impurities, $\rho_{i}$ $<< \emph{a}$ ($\rho_{i}$ the ion gyroradius and $\emph{a}$ the minor radius), and no \textbf{E}$\times $\textbf{B }flow shear. This work presents comparisons of linear frequencies and nonlinear fluxes from GYRO and GS2 with none of the above approximations except $\rho_{i}$ $<< \emph{a}$ and no \textbf{E}$\times $\textbf{B }flow shear. The comparisons are performed at two radii of a DIIID plasma, one in the confinement region ($\emph{r/a}$ = 0.5) and the other closer to the edge ($\emph{r/a}$ = 0.7). Many of the plasma parameters differ by a factor of two between these two locations. Good agreement between GYRO and GS2 is found when neglecting collisions. However, differences are found when including ei collisions (Lorentz model). The sources of the discrepancy are unknown as of yet. Nevertheless, two collisionless benchmarks have been formulated with considerably different plasma parameters. \\Acknowledgements to J. Candy, E. Belli, and M. Barnes. [Preview Abstract] 

TP9.00093: Gyrofluid Simulations of Intrinsic Rotation Generation in Reversed Shear Plasmas with Internal Transport Barriers Hogun Jhang, S.S. Kim, J.M. Kwon, L. Terzolo, J.Y. Kim, P.H. Diamond It is accepted that the intrinsic rotation is generated via the residual stress, which is nondiffusive components of the turbulent Reynolds stress, without external momentum input. The physics leading to the onset of intrinsic rotation in L and H mode plasmas have been elucidated elsewhere. However, the physics responsible for the generation and transport of the intrinsic rotation and its relationship to the formation of internal transport barriers (ITBs) in reversed shear (RS) plasmas have not been explored in detail, which is the main subject in the present work. The revised version of the global gyrofluid code TRB is used for this study. It is found that the large intrinsic rotation ($\sim$1030\% of the ion sound speed depending on ITB characteristics) is generated near the ITB region and propagates into the core. The intrinsic rotation increases linearly as the temperature gradient at ITB position increases, albeit not indefinitely. Key parameters related to the symmetry breaking, such as turbulent intensity and its gradient, the flux surface averaged parallel wavenumber are evaluated dynamically during the ITB formation. In particular, the role of reversed shear and the qprofile curvature is presented in relation to the symmetry breaking in RS plasmas. [Preview Abstract] 

TP9.00094: Hysteresis and Back Transitions in Internal Transport Barriers S.S. Kim, Hogun Jhang, L. Terzolo, J.Y. Kim, J.M. Kwon, P.H. Diamond, M. Malkov, T.S. Hahm Understanding and control of the transport barrier formation and back transition are essential to achieve the optimized plasma operation and performance in tokamak plasmas. Back transition dynamics, in particular, is complicated due to the phenomenon of hysteresis, whereby the barrier state persists when the driving power is lowered below the initial threshold value. Here we report new results from theoretical and computational studies of hysteresis in internal transport barrier (ITB) with reversed magnetic shear. A revised version of the global gyrofluid TRB code has been used to study ITG turbulence. ITB formation, back transition, and hysteresis are manifested during slow rampups/downs of the central heating power. Comparisons are made of the similarity/difference in the characteristics of hysteresis when the control parameter is lowered dynamically. The strength of hysteresis is quantified as functions of ion Nusselt number, qprofile shape and lower order rational q surface. In addition to the computational study, an analytical study of a twofield model of pressure and density dynamics is presented for a reversed shear ITB plasma by extending a previous theory that is applied to the edge pedestal. [Preview Abstract] 

TP9.00095: The characteristics of density fluctuations induced by geodesic acoustic modes in the edge of plasmas T. Lan, A.D. Liu, H.L. Zhao, D.F. Kong, W.D. Liu, C.X. Yu, L.W. Yan, W.Y. Hong, K.J. Zhao, J.Q. Dong, J. Cheng, J. Qian, Q.W. Yang, X.R. Duan, W. Zhang, J.F. Chang, X. Gao, B.N. Wan, J.G. Li The geodesic acoustic mode (GAM) induced density fluctuations were measured by the toroidally and poloidally departed Langmuir triple probe arrays in the edges of HL2A (Chengdu) and HT7 (Hefei) tokamaks. Some theoretical predictions about the mode features of GAM density fluctuations are verified in our experiments: the toroidal mode number of GAM density fluctuations is $n=0$; the amplitude is consistent with the theoretical prediction in a factor of 2; the GAM density and potential fluctuations are in antiphase at the top of plasma crosssection. The nonlinear interactions between GAM and ambient turbulence (AT) are also investigated. The cross phase between envelope of high frequency AT and GAM density fluctuations is nearly $\pi/2$ radians, which supports the conclusions that the envelope modulation of density fluctuations is due to the GAM shear effect. [Preview Abstract] 

TP9.00096: Poloidal rotation in strongly magnetized plasmas C.J. McDevitt, P.H. Diamond, O.D. Gurcan, T.S. Hahm Poloidal flows play a critical role in the regulation and stabilization of numerous modes within tokamak devices which are known to have detrimental effects on plasma confinement. In this work, a novel mean field formulation of poloidal rotation is developed, with emphasis on the elucidation of mechanisms through which microturbulence drives poloidal flows. In particular, a kinetic generalization of a Taylor identity appropriate to a strongly magnetized plasma is derived, providing an explicit link between the poloidal Reynolds stress and the transport of potential vorticity. A quasilinear calculation of the flux of potential vorticity is carried out, yielding diffusive, turbulent equipartition and thermoelectric convective components. Selfconsistency is enforced via the quasineutrality relation, revealing that for the case of a stationary small amplitude wave population, deviations from neoclassical predictions of poloidal rotation can be closely linked to the growth/damping profiles of the underlying drift wave microturbulence, in accord with expectations from wave energy balance at stationarity. Applications of the above theory to poloidal spin up in the vicinity of a transport barrier will be discussed. [Preview Abstract] 

TP9.00097: Interspecies Energy Transfer and Turbulent Heating in CTEM L. Zhao, P.H. Diamond We reconsider the classic problem of calculating ``turbulent heating'' and the interspecies transfer of energy in drift wave turbulence. The total heating is composed of the parallel quasilinear and nonlinear terms, as well as ion polarization and diamagnetic terms. The parallel quasilinear terms effect a collisionless transfer of energy from electrons to ions with ion Landau damping mediating the resulting heating. The nonlinear contribution describes the ion heating associated with beat wave Landau damping. Ion polarization and diamagnetic terms account for the net Reynolds work of the turbulence on the zonal flow. At steady state, these must balance collisional zonal flow damping, thus driving ion heating through zonal flow friction. This process of energy transfer via zonal flows has not previously been accounted for in analyses of energy transfer. Note that these are at least two ``channels'' for turbulent electronion energy transfer, namely one via Landau resonance heating and one via zonal flow frictional heating. Ongoing work is concerned with the ratios of these two heating channels in CTEM, including trapped electron beat heating. [Preview Abstract] 

TP9.00098: Current Driven Drift Wave Turbulence C.J. Lee, P.H. Diamond, M. Porkolab Recent and ongoing analyses [1] have indicated that the ``usual suspects'' for the mechanism of electron thermal transport, such as ITG, ETG, CTEM modes, etc., cannot explain results from modest density, $T_e>T_i$ plasmas in either OH or ECH heating regimes. Interestingly, such plasmas exhibit very large toroidal current drift parameters $v_d/c_s$, thus naturally suggesting revisitation of current driven drift waves. In this work, we examine the linear and nonlinear theory of current driven drift wave turbulence. Special attention is focused on the eigenfunction structure and spectral centroid shift induced by finite current. Note that the spatial asymmetry is a signature of current drive and has implications for flow generation and intrinsic rotation as well. We further explore nonlinear saturation mechanisms. In particular, the implications of spectral asymmetry for zonal flow generation and possible synergy or competition between $\mathbf{E} \times \mathbf{B}$ shear and currentinduced shifts, and the effects of electron scattering, both in space and velocity; specifically magnetic shearinduced resonance broadening effects on the electron response and its implication for saturation levels.\\[4pt] [1] L. Lin, M. Porkolab et al., PPCF, 2009 [Preview Abstract] 

TP9.00099: Boundary Layer and Streamer Flows in Interchangeunstable plasmas Mikhail Malkov, Patrick Diamond We describe the interchange instability in the simplest two dimensional Boussinesq fluid approximation. First, using a closure procedure proposed earlier, we reduce the original twodimensional system to a system of moment equations for the flow velocity and temperature. In the ideal fluid limit, the time asymptotic analysis of these equation predicts an unstable grow of streamers or zonal flows, depending on the initial conditions. By taking finite viscosity and thermoconductivity into account and returning to the original twodimensional Boussinesq system, we analyze the emerging flow patterns. The link between streamer and boundary layer flows in convective cells, which are responsible for transporting heat between the opposite walls, is studied in the limit of low viscosity and thermoconductivity for various Prandtl numbers. [Preview Abstract] 

TP9.00100: Isotopic Dependence of Fine Scale Zonal Flows T.S. Hahm, Lu Wang, E.S. Yoon This work addresses the isotopic dependence of the fine scale zonal flow (ZF) dynamics which are generated from fine scale (shorter than $\rho _i $, but significantly larger than $\rho _e )$ electron drift wave turbulence (DWT) which is related to either collisionless TEM or current driven drift waves (CDDW), or inverse cascade of ETG modes. We find that the fine scale zonal flows in deuterium (D) plasmas can be stronger than those of hydrogen (H) plasmas, and therefore lead to lower turbulence and transport and better confinement. We have analytically calculated the RosenbluthHinton (RH) residual level of zonal flows, taking into account both ion and electron dynamics using bouncekinetics. Since the average ion gyroradius is different for different ion species for the same temperature, a transition from the ion classical polarization shielding dominated regime to the electron neoclassical shielding dominated regime occurs at different values of $k_r \rho _e $ for different ion species. As a consequence, RH ZFs for D plasmas can be stronger than those for H plasmas for $k_r \rho _e $ around 0.01. Based on this observation, we conclude that a significant isotopic dependence of confinement can result from the fine scale zonal flows generated from fine scale DWT. [Preview Abstract] 

TP9.00101: Analysis of interaction mechanism of offresonant mode in reversed shear plasma Shinsuke Tokunaga, Masatoshi Yagi, SanaeI. Itoh, Kimitaka Itoh, Patrick Diamond It is known that offresonant modes around qminimum position in reversed magnetic shear configuration in tokamak bury the resonant surface gap and essentially change the transport to be smooth over the zeroshear region. Such role of the offresonant mode has been a problem in reproducing ITB with gyrofluid simulation. The offresonant ITG mode in vicinity of qminimum position was reported to be slablike one coupled with surrounding toroidal ITG mode. However, how they are coupled in the region where toroidal mode coupling is weak has not been stated. In this study, interaction between offresonant modes and the other modes is investigated. Radial electric field source was introduced into a gyrofluid code to examine the ExB flow shear effect flexibly on the interaction related to offresonant mode. It was confirmed that the ExB flow shear with amplitude in the same order as spontaneous zonal flow provided by the electric field source is insufficient to suppress the offresonant mode. The analysis of coupling mechanism between offresonant slablike ITG mode and toroidal resonant modes is in progress. [Preview Abstract] 

TP9.00102: Modeling on toroidal angular momentum transport with turbulent Reynolds stress in tokamak plasmas Wonjae Lee, Ki Min Kim, Hyunseok Kim, YongSu Na Turbulent momentum transport is regarded as an important issue since it could account for the intrinsic toroidal rotation and the inward propagation of momentum in tokamaks. The effects of offdiagonal flux of toroidal angular momentum in tokamak plasmas are investigated by 1.5D core transport simulation using ASTRA. The plasma current and angular momentum transport equations are calculated with evolutions of the density and temperature profiles obtained from experiments. A simple momentum transport model [1] is implemented to take into account shear suppressed momentum diffusion, turbulent pinch, and residual stress terms. The theory based model considering turbulent pinch and residual stress shows better agreements with the measured toroidal velocity profile than the model only considering diffusion term, from which the effects of turbulent Reynolds stress are discussed.\\[4pt] [1] O. D. Gurcan et al., Phys. Plasmas, 17, 032509 (2010) [Preview Abstract] 

TP9.00103: Heavy Particle Mode: IRegime, Magnetic Fluctuations and Toroidal Geometry Effects$*$ T. Ma, B. Coppi, T. Golfinopoulos, T. Zhou The ``signature'' mode excited in the IRegime [1] involves both density and magnetic field fluctuations. Referring to a plane geometry, the ``heavy particle'' mode [2] that we propose as the candidate to explain the mode features has a longitudinal phase velocity ${\rm{v}}_{thI}^2 \sim {{\omega ^2 } \mathord{\left/ {\vphantom {{\omega ^2 } {k_\parallel ^2 < }}} \right. \kern\nulldelimiterspace} {k_\parallel ^2 < }}{\rm{v}}_{thi}^2 < {\rm{v}}_{the}^2$ where ${\rm{v}}_{thI}^2 = {{2T_I } \mathord{\left/ {\vphantom {{2T_I } {m_I }}} \right. \kern\nulldelimiterspace} {m_I }}$ and ${m_{I}}$ is the heavy particle (impurity) mass [3]. The main mode driving factor is the impurity pressure gradient near the edge of the plasma column combined with a significant ion temperature gradient[3]. Thus, the mode can be triggered by a heat pulse emitted from the central region. The theory has predicted correctly the direction (electron diamagnetic velocity) of the mode transverse phase velocity and the resulting transport of impurities toward the edge region of the plasma column. A theoretical formulation [4] based on a toroidal geometry is necessary to include the important effects, on the mode, of the curvature and the gradient of the magnetic field. *Sponsored in part by the U.S. D.O.E. [1] E. Marmar \textit{et al. Bull. Am. Phys. Soc.} {\bf54}, 97 (2009). [2] B. Coppi, H.P. Furth, M.N. Rosenbluth and R.Z. Sagdeev, \textit{Phys. Rev. Lett.} {\bf17}, 377 (1966). [3] B. Coppi and T.C. Zhou, MITLNS H.E.P. Report 09/04 (2009). [4] B. Coppi, \textit{Phys. Rev. Lett.} {\bf39}, 939 (1977). [Preview Abstract] 

TP9.00104: Heavy Particle Mode as the Signature of the IRegime* T. Zhou, B. Coppi Key features [1] of the IRegime investigated by the Alcator CMod can be explained by the excitation of a new heavy particle (e.g. impurity) mode [2] at the plasma edge. This mode involves both density and magnetic fluctuations. The impurity is treated as collisional. Considering a plane geometry, the dispersion relation has a unstable root for $\eta_i\equiv (dT_i/dr) n_i/(T_i dn_i/dr)>2/3$ and $dn_I/dr>0$. The marginal stability point is reached for a maximum $d n_I/dr$ such that $\omega^I_{**}=\omega_{IA}=\omega$, where $\omega^I_{**}\equiv c k_y T_I (dn_I/dr)/(Ze B n_I)$ and $\omega_{IA}\equiv(5/3) k^2 T_I/m_I$. The instability condition is $\omega^I_{**}<\omega_{IA}$. $\rm{Re}\, \omega/\omega^I_{**}>0$ indicates that the mode phase velocity($v_{ph}$)is in the electron diamagnetic direction, a feature consistent[3]with the observation that the plasma spontaneous rotation is in the ion diamagnetic direction. This predicted direction of $v_{ph}$ has been confirmed by the experiments. The impurity flux evaluated from the quasilinear theory is $\langle\hat{n}_I \hat{v}_{Ex}\rangle=n_i\langle\widehat{T}_i \hat{v}_{Ex}\rangle/(Z T_i) \simeq n_i (dT_i/dr)/(Z T_i k^2 v_{th i} \lambda_i) \left[12/(3\eta_i)\right] \cdot\langle \hat{v}_{Ex}^2\rangle >0$ for $\eta_i>2/3$, where $\lambda_i$ is the effective main ion mean free path. This shows that both the main ion thermal energy and the impurity are transported outwards. These features are consistent with a mode with frequency $\sim 200\, kHz$ observed in the I Regime and with the fact that impurities are confined at the edge in this regime. *Sponsored by the DOE. [1] E. Marmar, B. Lipschultz, A. Dominguez, et al., Bull. Am. Phys. Soc. {\bf 54} (2009) 97 [2] B. Coppi, H. Furth, M. Rosenbluth and R. Sagdeev, Phys. Rev. Lett. {\bf{17}} (1966) 377379 [3] B. Coppi, Nucl. Fusion {\bf{42}} (2002) 14 [Preview Abstract] 

TP9.00105: Interaction of energetic ions with the background microtubulence in a tokamak Jugal Chowdhury, Weixing Wang, Stephane Ethier, Janardhan Manickam, Rajaraman Ganesh Interaction of energetic ions with the background microturbulence induced by pressure gradient driven modes such as ion temperature gradient (ITG) driven mode and trapped electron mode (TEM) is investigated using the global Gyrokinetic Tokamak Simulation (GTS) code [1]. The energetic ions are treated as testparticles, which respond to the perturbed fields, but do not contribute to them. The radial transport of energetic particles is estimated with respect to its characteristic dependence on the ratio of e$\phi/T_E$ in different turbulence regimes. The phase space evolution of the energetic particles is analyzed and its effect on energeticparticledrivenmodes will be discussed. Interactions of these energetic ions with particular (n,m) mode, where n and m being the toroidal and poloidal mode numbers, are studied with focus on the identification of resonant and nonresonant contributions to the energetic particle transport in both ITG and TEM regimes.\\[4pt] [1] W. X. Wang et al., Phys. Plasmas 13, 092505 (2006). [Preview Abstract] 

TP9.00106: Nonlocal transport across zonal shear flows A. Kullberg, D. delCastilloNegrete, G.J. Morales, J.E. Maggs In the diffusive transport model, the flux is completely determined by the local value of the gradient. Despite the relative success of this approach, there are situations in which the local fluxgradient assumption does not hold. In particular, in the presence of nonlocal transport, the flux at a point might depend on the gradients throughout the entire domain. Evidence of this type of transport includes perturbative experiments in tokamaks, numerical simulations of turbulent transport, and generalized random walk theoretical models. The goal of this presentation is to study nonlocal transport in the presence of zonal shear flows. Zonal flows play a key role in the dynamics and transport in magnetically confined plasmas and it is of significant theoretical and practical importance to understand their impact on nonlocal transport. Our study is based on a simplified 2dimensional advection nonlocal diffusion model consisting of a poloidal zonal flow coupled to a radial nonlocal transport channel. Extending previous work we model nonlocal transport using truncated fractional derivatives that allow the incorporation of finite size effects. Numerical and analytical results on nonlocal transport across the zonal flow are presented, along with a numerical study of truncation effects in fluctuationdriven transport. [Preview Abstract] 

TP9.00107: Finite Larmor radius effects on chaotic transport in ${\bf E} \times {\bf B}$ zonal flows Julio Martinell, Diego delCastilloNegrete Finite Larmor radius (FLR) effects on chaotic test particle transport are studied in the context of Hamiltonian dynamical systems. Based on a marginal stability assumption, the Hamiltonian is modeled as the superposition of a nonmonotonic zonal shear flow and regular neutral drift wave modes. FLR effects are incorporated through a gyroaverage of the ${\bf E} \times {\bf B}$ Hamiltonian. We provide numerical evidence of the following novel FLR effects on chaotic transport: (i) Bifurcation leading to the creation of additional shearless regions in the zonal flow profile; (ii) Double heteroclinichomoclinic separatrix reconnection; and (iii) Chaotic transport suppression and transport barrier formation. Of particular interest is the dependence on the Larmor radius of the destruction of shearless transport barriers leading to global transport. To compute this we use indicator points based on the symmetry properties of the Poincare map. [Preview Abstract] 

TP9.00108: Local and nonlocal parallel heat transport in general magnetic fields Diego delCastilloNegrete, Luis Chacon A novel approach that enables the study of purely parallel transport in magnetized plasmas is proposed. The approach is based on a Lagrangian Green's function method applicable to general magnetic fields (2D and 3D from integrable to completely chaotic), and with local or nonlocal parallel heatflux closures. The approach is free from numerical pollution, and preserves temperature positivity by construction. The method is used to study: (i) local and nonlocal temperature flattening in magnetic islands; (ii) the fractal structure of the devil staircase temperature profile in weakly chaotic fields; and (iii) effective radial transport in fully chaotic 3D fields. For (iii), selfsimilar evolution of the form $T=(\chi_{\parallel} t)^{\gamma/2} f(\eta)$ is observed with similarity variable $\eta=(\psi<\psi>)/(\chi_{\parallel} t^{\gamma/2})$ where $\psi$ is a radial flux function. Different to the wellknow local transport case (RechesterRosenbluth), it is shown that in the case of nonlocal parallel transport $f$ is an algebraic decaying, $f \sim \eta^{3}$, nonGaussian function, and $\gamma=1$. Recent work on the extension of the method to include perpendicular transport and heat sources is presented. The approach is algorithmically scalable, and secondorder accurate in time on the slowperpendiculartime scale. Numerical examples of relevance to magnetic fusion geometries will be presented. [Preview Abstract] 

TP9.00109: Impurity dynamics in plasma turbulence: multiscale analysis, intermittency, and nondiffusive transport S. Futatani, D. delCastilloNegrete, N. Dubuit, X. Garbet, S. Benkadda Impurity transport in tokamak plasmas is investigated using a threedimensional fluid global code. The impurities are treated as an active scalar and the selfconsistent interaction between the impurity concentration and the turbulence is studied in detail. A multiscale analysis based on proper orthogonal decomposition methods reveals that the impurity concentration gives rise to strong intermittency in the ${\bf E} \times {\bf B}$ flow and the ion temperature flux. The probability density functions of fluctuations exhibit a transition from Gaussian (for low Z impurities) to exponential (for high Z impurities). Spatiotemporal fluxgradient cross correlation functions are used to characterize the level of nondiffusive, nonlocal transport in the system. [Preview Abstract] 

TP9.00110: Tensor Product Decomposition of Gyrokinetic Microturbulence Data David Hatch, Diego del Castillo Negrete, Paul Terry Gyrokinetic microturbulence simulations generate large amounts of data. Typical simulations involve distribution functions in five or six dimensions plus time, which, for a very modest simulation, would require computer memory on the order of terabytes to store. As a result, data output is usually limited to electromagnetic fields and certain moments of the distribution function for a subset of time points. It would be desirable to develop methods to efficiently represent the gyrokinetic distribution function with the aim of compressing the data and extracting the relevant information. In this presentation we propose the use of tensor product decomposition (TPD) methods to achieve this task. In its simplest version (order2 tensors) TPD reduces to the singular value decomposition (SVD) of the corresponding matrix. For higher order tensors of interest to gyrokinetic simulations we discuss the use of high order SVD (HOSVD) and generalized low rank approximation of matrices (GLRAM) methods. [Preview Abstract] 

TP9.00111: Bifurcation to improved confinement driven by intrinsic rotation Felix Parra, Michael Barnes, Edmund Highcock, Alexander Schekochihin, Steve Cowley, Colin Roach We study the effect of sheared flow on the turbulent transport of energy and momentum employing the gyrokinetic flux tube code GS2. The results show two features, namely, (i) given the value of the heat flux, there is a maximum temperature gradient that is achieved for a finite velocity shear; and (ii) the ratio of turbulent momentum and energy diffusivities is constant for a wide range of flow shear values. Based on this knowledge, we investigate the equilibrium of a tokamak heated by neutral beams. Considering only turbulent transport, bifurcations to enhanced confinement are not possible because for given energy and momentum depositions there is only one solution. If neoclassical transport is included, under specific circumstances there are up to three simultaneous solutions. It is possible to transit to enhanced confinement solutions, but to do so it is necessary to decrease the energy input. We propose a new mechanism that drives bifurcations to enhanced confinement solutions based on new terms in the momentum equation. These new terms are also the drive of intrinsic rotation. [Preview Abstract] 

TP9.00112: Edgecore interaction of ITG turbulence in Tokamaks: Is the Tail Wagging the Dog? S. Ku, C.S. Chang, G. DifPradalier, P.H. Diamond A fullf XGC1 gyrokinetic simulation of ITG turbulence, together with the neoclassical dynamics without scale separation, has been performed for the wholevolume plasma in realistic diverted DIIID geometry. The simulation revealed that the global structure of the turbulence and transport in tokamak plasmas results from a synergy between edgedriven inward propagation of turbulence intensity and the coredriven outward heat transport. The global ion confinement and the ion temperature gradient then selforganize quickly at turbulence propagation time scale. This synergy results in inwardoutward pulse scattering leading to spontaneous production of strong internal shear layers in which the turbulent transport is almost suppressed over several radial correlation lengths. Coexistence of the edge turbulence source and the strong internal shear layer leads to radially increasing turbulence intensity and ion thermal transport profiles. [Preview Abstract] 

TP9.00113: Benchhmark of NIMROD kinetic electron closures with the NEO code Eric Held, Scott Kruger, Emily Belli, James Callen The need to close the extended magnetohydrodynamic equations to include perturbed bootstrap current physics in response to magnetic island formation has long been recognized. In this work we discuss a numerical solution of the secondorder\footnote{J. Ramos, private communication} driftkinetic equation (DKE) which supplies the bootstrap current closure for the perturbed Ohms Law in simulations of slowly growing, neoclassical tearing modes. Important aspects of this numerical solution include the conservative properties of the adopted ChapmanEnskog like approach as well as the fully implicit solution for the electron DKE which is staggered in time from the advancing fluid equations. The complexity of the analytic formulation and numerical implementation makes verification of this closure paramount. To this end, we compare axisymmetric NIMROD calculations with the results of NEO\footnote{E. A. Belli, J. M. Candy PPCF 50, 095010 (2008).}, which numerically solves the DKE in 2D geometry, and with various analytic formulas. [Preview Abstract] 

TP9.00114: Secondorder ion driftkinetic equation J.J. Ramos A novel form of ion driftkinetic equation is presented, well suited to close the fluid description of slow macroscopic dynamics in lowcollisionality, magnetically confined plasmas. It features secondorder accuracy in the gyroradius expansion, with diamagneticscale ordering of frequencies and flow velocities. This secondorder driftkinetic equation is derived in the moving reference frame of the ion macroscopic flow, which facilitates the precise consistency with the complementary fluid system, as well as the rigorous treatment of the electric field. Examples of intended applications are the precursor of the ``sawtooth'' internal disruption and the ``neoclassical tearing mode'' in fusionrelevant tokamak temperature regimes. With these applications to slow excursions from well confined equilibria in mind, the distribution function is assumed to be close to a Maxwellian. The Maxwellian part carries the density, mean flow and temperature in ChapmanEnskoglike fashion. The resulting driftkinetic equation for the nonMaxwellian perturbation is shown to be automatically consistent with the required condition that the density, random parallel velocity and random kinetic energy moments of such nonMaxwellian part be equal to zero. [Preview Abstract] 

TP9.00115: The importance of ionelectron collisions and temperature evolution in ion transport JeongYoung Ji, E.D. Held Ionelectron collisions have been ignored by the small mass ratio approximation in studies of ion transport processes, including Braginskii's closure theory. However, recent analytical calculations\footnote{J.Y. Ji and E. D. Held, Phys. Plasmas {\bf 13}, 102103 (2006); {\bf 15}, 102101 (2008)} show that the ionelectron collision terms must be retained whenever the ion temperature is comparable to or higher than the electron temperature. For equal electron and ion temperatures, the ion transport coefficients are moderately modified by the ionelectron collision operator. When the ion temperature is higher than the electron temperature, temperature change terms in the moment equations must also be kept. The ion coefficient formulas from 3 moment (Laguerre polynomial) calculations, precise to less than 0.4\% error from the convergent values, are discussed for the relevant case that includes both the ionelectron collision and temperature change terms. [Preview Abstract] 

TP9.00116: Drift Hamiltonian Guiding Center Orbits with Full Electromagnetic Fields in Axisymmetric Geometry Guy Cooper, W.A. Cooper, J.P. Graves A Hamiltonian/Lagrangian formulation of the guiding center drift orbits is extended to include full perturbed electromagnetic fields in axisymmetric tokamak geometry. Previous work only admitted perturbed fields with finite parallel component of the vector potential.$^1$ A background magnetohydrodynamic equilibrium state with anisotropic pressure is considered which allows a more consistent treatment of energetic particle physics. The contribution of radial equilibrium magnetic field in the covariant representation, usually ignored in most formulations of Hamiltonian drift orbit analysis, is retained. The manipulation of the drift Lagrangian and the imposition of a gauge transformation that relates the radial projection of the perturbed vector potential to its toroidal component constitute very important steps to identify the canonical angular variables and momenta$^{1,2}$ in the Boozer coordinate frame.$^3$ The radial drift motion and the evolution of the parallel gyroradius are subsequently determined. The drift equations are presented in a form amenable to implementation in the VENUS$+\delta f$ code. \\ \begin{footnotesize} \noindent $^1$G.~A.~Cooper {\em et al.},Phys.~Plasmas \textbf{14} (2007) 102506. \newline $^2$S.~Wang, Phys.~Plasmas \textbf{13} (2006) 052506. \newline $^3$A.~H.~Boozer, Phys.~Fluids \textbf{23} (1980) 904. \end{footnotesize} [Preview Abstract] 

TP9.00117: Gyrofluid simulations of turbulence in the Trinity transport code Kate Despain, William Dorland, Michael Barnes In order to fully understand the effect of turbulence on the evolution of background profiles in fusion devices, the transport code Trinity was developed to tie together these processes that live on disparate temporal and spatial scales. Such an approach leads to potential computational savings on the order of hundreds (Barnes, et al. PoP 2010). In order to increase the computational savings, we have incorporated the use of the recently updated gyrofluid code gryffin into the Trinity framework decreasing computational size by a factor of a hundred or so. We have furthered enhanced savings by running gryffin calculations on GPUs creating a potential 25 times speed up. Such a computational savings allows for the exploration of novel fusion device configurations. We present initial numerical results. [Preview Abstract] 

TP9.00118: Momentum balance and radial electric fields in axisymmetric and nonaxisymmetric toroidal plasmas Hideo Sugama, Tomohiko Watanabe, Masanori Nunami, Shin Nishimura It is investigated how symmetry properties of toroidal magnetic configurations influence mechanisms of determining the radial electric field such as the momentum balance and the ambipolar particle transport. Both neoclassical and anomalous transport of particles, heat, and momentum in axisymmetric and nonaxisymmetric toroidal systems are taken into account. Generally, in nonaxisymmetric systems, the radial electric field is determined by the neoclassical ambipolarity condition. For axisymmetric systems with updown symmetry and quasisymmetric systems with stellarator symmetry, it is shown by using a novel parity transformation that the particle fluxes are automatically ambipolar up to $O(\delta^2)$ and the determination of the radial electric field $E_s$ requires solving the $O(\delta^3)$ momentum balance equations, where $\delta$ denotes the ratio of the thermal gyroradius to the characteristic equilibrium scale length. In axisymmetric systems with large ExB flows on the order of the ion thermal velocity $v_{Ti}$, the radial fluxes of particles, heat, and toroidal momentum are dependent on $E_s$ and its radial derivative while the time evolution of the $E_s$ profile is governed by the $O(\delta^2)$ toroidal momentum balance equation. [Preview Abstract] 

TP9.00119: Electron turbulence driven nondiffusive transport and intrinsic rotation in tokamaks W.X. Wang, T.S. Hahm, P.H. Diamond, S. Ethier, G. Rewoldt, W.M. Tang Global gyrokinetic simulations have found that mesoscale phenomena and associated nonlocal transport are largely enhanced in the trapped electron mode (TEM) turbulence regime due to strong coherent waveparticle interaction at the trapped electron precession frequency. Robust radial pinches in toroidal flow, heat and particles, which emerge ``in phase'' in collisionless TEM turbulence, are found to play remarkable roles in determining plasma transport. Particularly, toroidal flow perturbations, which are generated locally (in the center of the plasma in the simulation case) by the turbulence, are found to propagate radially. This result amazingly reproduces the experimental phenomenon of radially inward penetration of perturbed flows created by modulated beams in peripheral regions [1], and thus is highly illuminating. The revealed universal, nonlinear flow generation process due to the residual stress produced by the fluctuation intensity and the intensity gradient, acting with the zonalflowshearinduced k$_{//}$ symmetry breaking [2,3] offers an ideal mechanism to drive intrinsic rotation via waveparticle momentum exchange [4]. This turbulence driven intrinsic rotation scales close to linearly with plasma gradients and the inverse of the plasma current in various turbulence regimes, reproducing empirical scaling obtained in multiple fusion devices. [Preview Abstract] 

TP9.00120: Studies of turbulence and fast ion interactions in TORPEX simple magnetized plasmas A. Fasoli, I. Furno, K. Gustafson, D. Iraji, B. Labit, J. Loizu, G. Plyushchev, P. Ricci, Ch. Theiler We present high resolution data together with fluid models and numerical simulations, which advance the understanding of electrostatic turbulence and its effect on transport of bulk plasma and fast ions in the TORPEX simple magnetized device. The dominant instabilities are determined by the ratio of the vertical magnetic field to the toroidal field. For B$_{v}$/B$_{T}>$3{\%}, ideal interchange instabilities are observed, which nonlinearly develop radially propagating blobs. The radial blob velocity is limited by crossfield ion polarization currents and by parallel currents to the sheath in the small and large blob size limits, respectively. The effect of the blobs on the particle, heat and toroidal momentum transport are investigated in detail and complemented by data form a fast framing camera coupled to an image intensifier and a movable gas puff system. The effect of turbulence on fast ions is studied using movable fast ion source and detector in the interchange dominated regime. A theory validation project is conducted, based on comparisons of observables that are defined identically in the 2D and 3D simulations and in the data. [Preview Abstract] 

TP9.00121: Fast ion dynamics in the basic plasma physics experiment TORPEX Kyle Gustafson, Paolo Ricci, Alice Burckel, Gennady Plyushchev, Ivo Furno, Ambrogio Fasoli The transport of fast ions in interchange turbulence is examined in TORPEX, a basic plasma physics experiment with the essential elements of the scrapeoff layer (SOL). Extensive modeling in two and three dimensions has shown that TORPEX plasma is welldescribed by a driftreduced Braginskii fluid simulation (GBS). We follow fast ion trajectories using the full Lorentz force, specified by the GBS fields. A large ensemble of trajectories allows us to create a synthetic diagnostic, giving results that compare favorably with experimental measurements of current density using a fast ion source/detector pair. We also explore the properties of fast ion transport on timescales longer than those accessible to the experiment. We find that the rate of radial dispersion is strongly dependent on the ratio of ion energy to plasma (electron) temperature. The dispersion tends to be subdiffusive for $\rho_i \sim \Lambda$, where $\rho_i$ is the fast ion Larmor radius and $\Lambda$ is the scale length of the turbulence. The effective diffusivity is examined from the perspectives of (1) trajectory dispersion, (2) the fluxgradient Fick's Law relation, (3) velocity correlation, and (4) waitingtime/flightlength distributions. [Preview Abstract] 

TP9.00122: Turbulence and Turbulence Suppression in the Helimak K.W. Gentle, W.L. Rowan, K. Liao, B. Li The Helimak is an approximation to the infinite cylindrical slab, but with open field lines of finite length. Radiallysegmented isolated end plates allow application of radial electric fields that drive radial currents. Above a threshold in applied voltage (driven current), the fractional turbulent amplitude is greatly reduced, as is the radial turbulent particle transport in the region of applied bias. Stabilization is observed for both positive and negative bias. Concurrent measurements of the ion flow velocity are made by Doppler spectroscopy. The turbulence  density, potential, and temperature fluctuations and their relations, will be compared with simulations from a fluid model for this geometry. Comparisons of turbulence reduction with changes in radial correlation length and flow shear will be given. Although the radial correlation length is much smaller than the plasma, the turbulent structures have a large spatial scale of short lifetime. The amplitude reduction is associated with shrinkage in size of the most coherent structures. [Preview Abstract] 

TP9.00123: Simulations of turbulence reduction by the biasinduced flows in the Helimak Bo Li, Barrett Rogers, Paolo Ricci, Ken Gentle, Amitava Bhattacharjee Global fluid simulations of interchange turbulence are presented for the Helimak in which the open field lines are helices on a surface of constant radius. The threedimensional simulation is based on an electrostatic twofluid model that evolves the full plasma density, the electric potential, the electron temperature, and the parallel velocities. In the grounded nobias case, we find that interchange instabilities produce radially elongated ExB velocity eddies and turbulent radial transport in the badcurvature region. The plasma potential profiles produce the equilibrium radial electric fields and vertical EXB flows. Application of a bias voltage in the radial direction changes the global structures of plasma potential and flow velocity. Both negative and positive bias are studied. The sheared vertical EXB flows induced by the bias limit the radial extent of the turbulent eddies in the bad curvature region, and thus limit the radial crossfield transport. [Preview Abstract] 

TP9.00124: Neoclassical Calculations with Momentum Conservation Using the PENTA Code Jeremy Lore, D.A. Spong, A. Briesemeister The PENTA code calculates neoclassical radial and parallel flows of heat and particles, including the effects of collisional momentum conservation, for arbitrary toroidal geometries. As an input, PENTA uses transport coefficients calculated using a pitch angle scattering (PAS) collision operator, for example from the DKES code. In this sense PENTA acts as a momentum correction technique to transport quantities calculated from the PAS transport coefficients, which are often used in stellarator transport analyses. PENTA has recently been upgraded to account for arbitrary ion impurity species, and to include multiple methods of momentum correction for comparison and benchmarking. For non(quasi)symmetric configurations, the radial electric field is calculated from the nonambipolar particle fluxes. For (quasi)symmetric devices PENTA recaptures intrinsic ambipolarity, demonstrating its applicability to both 2D and 3D geometries. Momentum correction has been shown to have a significant effect on the calculated parallel flows in the HSX stellarator. [Preview Abstract] 

TP9.00125: Influence of the Plasma Shape on the Pinch Effect on Axisymmetric Tokamaks Enrique Castro, Pablo Martin Numerical calculations of Warepinch effect in general plasma configuration are considered. Though analytical treatment of Warepinch in plasma configurations including ellipticity and triangularity were presented previously, however, applications of these equations to actual tokamaks are very important and not presentations have been done until now using this technique. Curvilinear coordinates described in previous papers are used [14]. This work is justly dedicated to fill out this matter and numerical calculations have been carried out for different tokamaks with different geometry parameters. First, the effect of ellipticity is considered and later triangularity influences are also included in our calculations. Graphics results will be presented. \\[4pt] [1] P. Martin, E. Castro and M. Haines, \textit{Phys. Plasmas} 14, 052502 (2007) \\[0pt] [2] P. Martin and M. Haines, \textit{Phys. Plasmas} 5, 410 (1998) \\[0pt] [3] P. Martin \textit{Phys. Plasmas} 7, 2915 (2000) \\[0pt] [4] P. Martin and E. Castro, Proceedings of 35th Plasma Physics Conference, \underline {32} (2008) P 5.042 [Preview Abstract] 

TP9.00126: Plasma Shape Effect on Tokamak Electric Fields Pablo Martin, Enrique Castro This work considers the effects of tokamak plasma shape, mainly ellipticity and triangularity, on the different components of the electric field. The plasma shape parameters influence mainly the poloidal and transversal electric fields, however the effect on the toroidal electric field is also analyzed. Resistive MHD equations are used for this treatment, as well as, new differential equations obtained by applying the curl operator on the original equations. Curvilinear coordinates described in previous papers are used [1]. In our treatment first, the transversal, poloidal and toroidal velocities are obtained as a function of some geometric parameters and values along some radius lines. The electric field determination comes after that. Axisymmetric conditions are used. Though our treatment is general, some simplifications can be obtained when additional updown geometry symmetry is assumed. Application of our equation to different tokamaks is performed and compared with the results of previous authors. \\[4pt] [1] P. Martin, E. Castro and M. Haines, \textit{Phys. Plasmas}14, 052502 (2007) [Preview Abstract] 

TP9.00127: Effect of Superbanana Diffusion on Fusion Reactivity Fred Hinton The FokkerPlanck equation is solved numerically for the energy distribution of the particles in the tail of the distribution function, assuming a loss rate due to superbanana diffusion. Using a simple randomwalk estimate, this loss rate is proportional to a positive power (+7/2) of the particle energy. The rate of repopulation by Coulomb scattering is proportional to a negative power (3/2) of the particle energy, so the most energetic particles in the tail are most strongly depleted by superbanana diffusion. For ion temperatures relevant for fusion in magnetic confinement devices, it is the tail particles which are most needed for fusion, since the peak of the DT reaction rate is at roughly 100 kev. The numerically computed energy distribution for the tail particles is used to obtain an integrated fusion reactivity, using a standard fit to the DT reaction cross section. A plot of reactivity vs loss rate shows that the fusion reactivity is quite sensitive to loss by superbanana diffusion. [Preview Abstract] 

TP9.00128: Connection formula for bananadrift neoclassical toroidal viscosity A.J. Cole, C.C. Hegna, J.D. Callen Nonresonant magnetic perturbations can affect plasma rotation in toroidally confined plasmas through their modification to $B$. Variations along a field line induce nonambipolar radial transport and produce a global neoclassical toroidal viscous force [NTV]. In this work, a previously calculated WKBtype solution smoothly connecting the lowcollisionality ``$1/\nu$'' and ``$\nu\sqrt{\nu}$'' regimes is extended to include the superbanana plateau [sbp] regime [1]. The sbp effect occurs for particles whose toroidal $\vec{E}\times\vec{B}$ precessional drift vanishes. In this case, the relevant drift kinetic equation exhibits a ``turning point'' and the WKB method fails. We employ the connection formula method of Langer [2] which continuously varies between the previous WKB result and the superbanana regime without difficultly at the turning point. The resultant smoothed NTV is presented in terms of flows along flux surfaces. \\[4pt] [1] K. C. Shaing, S. A. Sabbagh, and M. S. Chu, PPCF \textbf{51}, 035009 (2009), and refs. cited therein. \\[0pt] [2] R. E. Langer, Phys. Rev. \textbf{51}, 669 (1937). [Preview Abstract] 

TP9.00129: Physics of zonal flow, density and field excited by finite beta drift waves Amita Das, Parvez Guzdar, Robert Kleva, Predhiman Kaw The excitation of zonal perturbations by finite beta drift waves can be investigated using the Floquet Theory. When the growth rate for this process is smaller than the drift frequency, the Floquet expansion can be truncated to a fourwave interaction involving the pump driftwave, the zonal perturbations and the sum and difference driftwave sidebands. This leads to nine coupled algebraic equations. First, a quadratic dispersion relation derived in our earlier work is discussed. The dispersion relation is recast into a standard form which helps identify the different physical processes responsible for the modulational instability providing a clearer picture of the role of finite beta effects in determining the parametric dependence of the growth rate on the dimensionless parameters. We compare results obtained by numerically solving the nine coupled equations with the simplified dispersion relation and show that in the range of validity of the theory the agreement for the growth rates computed by the two methods is very good. [Preview Abstract] 

TP9.00130: MINICONFERENCE: SOLAR WIND TURBULENCE 

TP9.00131: New Developments in the Theory of Incompressible MHD Turbulence with ${\mbox{\textit{Pr}}}_m = 1$ J.J. Podesta For incompressible MHD turbulence, the correlation lengths along directions parallel and perpendicular to the local mean magnetic field may be defined by isoenergy surfaces derived from second order structure functions. The correlation time of the turbulence may be defined in a similar manner by means of a temporal second order structure function. Moreover, there is a natural correspondence between the lengthscales of fluctuations with a given energy and the timescale of fluctuations of the same energy so that each isoenergy surface is associated with a unique pair of parallel and perpendicular correlation lengths \emph{and} a unique correlation time. In the case when the magnetic Prandtl number is unity, ${\mbox{\textit{Pr}}}_m \equiv \nu/\eta=1$, it is shown that the correlation time $\tau$ associated with an isoenergy contour of energy $E$ is equal to the energy cascade time of the turbulence in the sense that $E/\tau \sim \varepsilon$, where $\varepsilon$ is the energy cascade rate. For balanced MHD turbulence, both the Goldreich and Sridhar theory and the Boldyrev theory are shown to have this same property. I conjecture that the same property also holds for imbalanced MHD turbulence, that is, MHD turbulence with nonvanishing crosshelicity. These and other recent developments in the theory of incompressible MHD turbulence with ${\mbox{\textit{Pr}}}_m=1$ are discussed. [Preview Abstract] 

TP9.00132: Measurements of the normalized crosshelicity of solar wind turbulence spanning the entire inertial range J.J. Podesta MHD turbulence which is spatially homogeneous and stationary in time is characterized in part by its three dimensional energy spectrum (Fourier spectrum) and its crosshelicity spectrum. The ratio of the crosshelicity spectrum divided by the energy spectrum is the normalized crosshelicity spectrum $\sigma_c$ which takes values between $1$ and $+1$. Solar wind measurements of the energy spectrum, crosshelicity spectrum, and the normalized crosshelicity spectrum (reduced spectra) have been performed almost since the dawn of the space age 50 years ago. However, measurements of the crosshelicity and the normalized crosshelicity spanning the entire inertial range at 1 AU have only recently been performed for the first time using simultaneous 3second plasma and magnetic field data from the WIND spacecraft. The new measurements extend the frequency range of previous measurements by 1.5 decades (a factor of $\sim 30$). A large study of over 100 different intervals of solar wind data shows that the normalized crosshelicity is approximately constant throughout the inertial range and, moreover, that this result holds over a wide range of solar wind conditions including both high and lowspeed wind. This result has important implications for theories of imbalanced MHD turbulence as I show in an accompanying poster. [Preview Abstract] 

TP9.00133: Whistler Turbulence from ParticleinCell Simulations S. Peter Gary, Shinji Saito, Yasuhito Narita Twodimensional particleincell simulations of whistler turbulence in magnetized, homogeneous, collisionless plasmas of electrons and protons have been carried out. Enhanced magnetic fluctuation spectra are initially imposed at relatively long wavelengths, and, as in previous such simulations, the temporal evolution shows a forward cascade of magnetic fluctuation energy to shorter wavelengths and preferentially toward wavevectors relatively perpendicular to the background magnetic field ${\bf B}_o$. Two new results are reported here. First, the wavevector anisotropy is very different for each of the three components of the fluctuating magnetic field. Second, the magnetic fluctuation energy spectrum at relatively short wavelengths ($kc/\omega_{pe}\sim$ 1) is steeper than that predicted by EMHD simulations and theories at relatively long wavelengths. This steep spectrum may correspond to recent solar wind observations of magnetic turbulence spectra at short wavelengths. [Preview Abstract] 

TP9.00134: Dispersive magnetized waves in the solar wind plasma Dastgeer Shaikh, B. Dasgupta, P.K. Shukla We derive a generalized linear dispersion relation of waves in a strongly magnetized, compressible, homogeneous and isotropic quasineutral plasma. Starting from a twofluid model, describing distinguishable electron and ion fluids, we obtain a sixorder linear dispersion relation of magnetized waves that contains effects due to electron and ion inertia, finite plasma beta and angular dependence of phase speed. We investigate propagation characteristics of these magnetized waves in a regime where scale lengths are comparable with electron and ion inertial length scales. This regime corresponds essentially to the solar wind plasma, where length scales, comparable with ion cyclotron frequency, lead to dispersive effects. These scales in conjunction with linear waves present a great deal of challenges in understanding the highfrequency, smallscale dynamics of turbulent fluctuations in the solar wind plasma. [Preview Abstract] 

TP9.00135: Inhomogeneous two dimensional whistler turbulence Dastgeer Shaikh Whistler turbulence is investigated by including electron density perturbation in two dimensional fluid model. We find that electron density couples with the wave magnetic field and leads to to finite compressibility effects in whistler turbulence. Interestingly it is found from our simulations that despite strong compressibility effects, the density fluctuations couple only weakly to the wave magnetic field fluctuations. In a characteristic regime where largescale whistlers are predominant, the weakly coupled density fluctuations do not modify inertial range energy cascade processes. Consequently, the turbulent energy is dominated by the largescale eddies and it follows a Kolmogorovlike spectrum, where k is a characteristic wavenumber. [Preview Abstract] 

TP9.00136: Interaction of Charged Particles with Collisionless Shock Ensembles Mikhail Malkov, Patrick Diamond Collisionless shocks are ubiquitous in the solar wind plasma and their interaction with charged particles is an important, long standing problem. In the de HoffmannTeller frame, particle trajectories upstream and downstream are simple, yet the accurate conditions for particle transmission and reflection have been obtained only for the special cases of quasiperpendicular and quasiparallel shocks. In the former case the particle magnetic moment is conserved with a good accuracy, which determines the outcome (transmission/reflection) of a particle encounter with the shock. In the general case of an oblique shock, however, the magnetic moment alone is not sufficient and the angle of incidence is essential as well. First, we show that the process of multiple interaction of particles with an individual, infinitely thin collisionless shock may be formulated in terms of an iterated map involving solutions of the spherical triangles. Second, we consider particle interactions with an ensemble of such shocks, which result naturally from wave steepening and are often observed in the solar wind turbulence. [Preview Abstract] 

TP9.00137: Gyrokinetic Particle Simulation of Alfven Turbulence Xi Cheng, Zhihong Lin The issue of spectral cascade and plasma heating in Alfvenic turbulence is a major unsolved problem in plasma physics. Gyrokinetic particle simulation is applied in this work to study the cascade and heating in Alfvenic turbulence with fully selfconsistent nonlinear kinetic effects. A massively parallel particleincell 3D code with gyrokinetic ions and fluidkinetic hybrid electrons is used to study spectral cascading and dissipation of Alfvenic turbulence. A magnetic energy spectrum with index of ``5/3'' in the inertial range has been observed from the gyrokinetic simulation. The code will be used to study energy dissipation in the Alfvenic turbulence on the spatial scale of the order of ion gyroradius. [Preview Abstract] 

TP9.00138: Wandering magnetic field lines, turbulence and laboratory flux ropes T. Intrator, J. Sears, A. Lazarian Understanding the dynamics of flux ropes and their mutual interactions offers the key to many important solar phenomena including magnetic reconnection and turbulence. Kink dynamics and bursty driven dissipative reconnection processes may be important for example in the heating of the solar corona, bursty bulk flows, and magnetotail turbulence. Tangled magnetic field lines are ubiquitous, for example on the sun from differential solar rotation, in the corona, and in the magnetotail. We believe isolated Xlines in 3D space can generate jets and bursty bulk flows. Astrophysical weak MHD turbulence and 3D reconnection are likely related. There is little or no laboratory work on possible links between reconnection and turbulence, or the dynamics of intermittent, unsteady reconnection. We take advantage of a unique collaboration between a LANL experiment and theory computational capabilities at Univ Wisconsin and LANL, to shed light on the link between magnetic reconnection and turbulence. [Preview Abstract] 

TP9.00139: On the nature of the electromagnetic fluctuations in the dissipation/dispersion range of solar wind turbulence C. Salem, D. Sundkvist, S.D. Bale, C. Chaston We present a study of the nature of the electromagnetic fluctuations in the dissipation/dispersion range of solar wind turbulence, typically up to a few Hz. It has been shown that wavemodes in this range of frequencies become dispersive and are consistent with Kinetic Alfven Waves (KAW). However, strongly Dopplershifted KAW in the solar wind can show similar properties as slightly dopplershifted proton whister waves in the s/c frame. We explore here the possibility of distinguishing between both wavemodes. We analyze several lowbeta ambient solar wind intervals, using both electric and magnetic field data from Cluster. This analysis is performed in the s/c frame along with theoretical estimates based on the effect of Doppler shift on KAW and compressional proton whistler waves. The dispersive properties of KAW and whistler waves, as well as the E/B ratio, are determined both analytically and numerically in the plasma and the s/c frame. Those estimates are then directly compared to the data in the s/c frame. We propose this technique as an efficient diagnostics for wavemode identification in the dissipation/dispersion range of solar wind turbulence. [Preview Abstract] 
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