Bulletin of the American Physical Society
2009 APS April Meeting
Volume 54, Number 4
Saturday–Tuesday, May 2–5, 2009; Denver, Colorado
Session S1: Sherwood Poster Session II (2:00pm  5:00pm) 
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Room: Plaza Exhibit 

S1.00001: Nonlinear Dynamics of AlfvenVortex Current Loops Cynthia Correa, Wendell Horton, Xiangrong Fu, Swadesh Mahajan, Hideaki Miura Solar coronaphotosphere and magnetosphereionosphere observations (HINODE and CLUSTER) show welldefined dynamics $({\bf v}={\bf \hat z} \times \nabla \phi)$ of currentcarrying Alfvenvortex flux tubes $d {\bf \psi}$. Using theory and simulations we investigate the nonlinear dynamics and heating rates that may be expected from electron Landau damping of kinetic Alfven waves launched by oscillating photospheric current loops and convective instabilities from inverted electron densitytemperature gradients. Computer experiments on vortex dynamical alignment and the generation of zonal flows and zonal magnetic fields are carried out. Theoretical generalizations of the Rossby wavedrift wave vortex solutions are given and explored numerically. [Preview Abstract] 

S1.00002: Analytic and computational investigation of the effect of finite parallel heat transport on the formation of magnetic islands in 3D plasma equilibria Mark Schlutt, C.C. Hegna, E. Held A resistive MHD model is used to investigate pressureinduced magnetic islands in 3D equilibria. We revisit previous analytic isolated island calculations while allowing for finite parallel heat transport, to derive an equation for equilibrium island widths. Finite parallel heat transport can alter the impact of resistive interchange and bootstrap current contributions to magnetic island formation. However, PfirschSchl\"uter currents driven by resonant components in $\frac{1}{B^{2}}$ are largely unaffected by transport processes. 3D MHD equilibria are modeled using NIMROD. A vacuum equilibrium helical magnetic field is loaded into the geometry of a straight stellarator. The symmetry of the vacuum field with a dominant magnetic harmonic can be spoiled by adding small magnetic perturbations. These perturbations alter the magnetic spectrum, and produce magnetic islands and regions of stochasticity. Numerical simulations are performed that include the effect of a heating source and selfconsistent anisotropic transport in a variety of magnetic configurations. The effect of finite parallel heat transport on the island formation and saturation processes is examined. [Preview Abstract] 

S1.00003: Parametric Studies of Lower Hybrid Wave Propagation in Tokamak Plasmas Using an Electromagnetic Field Solver P.T. Bonoli, J.C. Wright, A.S. Richardson, A.E. Schmidt, C.K. Phillips, E. Valeo A parallel electromagnetic field solver TORICLH [1] valid in the lower hybrid range of frequencies (LHRF) has been developed and applied to fusion plasmas characteristic of the Alcator CMod tokamak [B$_{0}$ = 5.3 T, n$_{e}$(0) $\approx $ (17) $\times $ 10$^{19}$ m$^{3}$, T$_{e}$(0) $\approx $ (24) keV, and $f_{0}$ = 4.6 GHz]. In this poster we present parametric scans of density, electron temperature, and parallel wave number aimed at elucidating the importance of fullwave effects at internal reflection layers (caustics) and cutoffs near the plasma edge. In particular, we study fullwave predictions in the weak and strong damping regimes, where it is found they are in qualitative agreement with traditional ray tracing calculations in the single pass damping limit, but then deviate in the weak absorption regime due to differences in the reconstructed wave fronts at edge cutoffs. [1] J. C. Wright, E. J. Valeo, C. K. Phillips \textit{et al}, Communications in Computer Physics \textbf{4}, 545 (2008). [2] J. C. Wright \textit{et al}, submitted to Physics of Plasmas (2009). [Preview Abstract] 

S1.00004: Systematic \emph{ab initio} Hall MHD numerical study of threedimensional magnetic field relaxation in a closed system. V.S. Lukin, W. Lowrie, G.J. Marklin, A.H. Glasser, C.D. Cothran, M.R. Brown We study the relaxation of an initial spheromak magnetic field configuration in a closed elongated perfectly conducting cylindrical can to the lowest energy Taylor state characteristic of such a domain. A threedimensional implicit high order finite (spectral) element code HiFi is used to conduct the simulations in both viscous singlefluid and Hall MHD regimes. It is shown that in the presence of magnetic field dissipation the system consistently relaxes to the fully threedimensional lowest energy state, calculated independently by an eigenvalue PSITET code and confirmed experimentally at the Swarthmore Spheromak Experiment. However, we also show that the rate of relaxation is significantly greater and the dynamics is different in the presence of the twofluid Hall terms in the Ohm's Law, with all else being equal. Additionally, the dependence of the relaxation rate and dynamics on the ion inertial scale and viscous coefficients is systematically investigated. [Preview Abstract] 

S1.00005: Full f Gyrokinetic Simulation of Tokamak Plasma Turbulence Using ELMFIRE Susan Leerink, Salomon Janhunen, Timo Kiviniemi, Tuomas Korpilo, Markus Nora, Jukka Heikkinen, Victor Bulanin, Evgeniy Gusakov, Francisco Ogando Gyrokinetic particleincell simulation on a transport and microinstability time scale is performed with the ELMFIRE code for a small tokamak FT2 with kinetic electrons. Turbulent modes are characterized based on their poloidal phase velocity, and tentative comparison with the Doppler reflectometric measurement is done for the poloidal mode rotation. Cyclone base case comparison with adiabatic electrons reveals the need for a sophisticated adiabaticity model in the presence of finite ion orbits. Progress in the simulation of the edge pedestal in LH transition conditions for a mediumsized tokamak is reported. [Preview Abstract] 

S1.00006: NIMROD simulations of ICC devices Charlson C. Kim We present ongoing NIMROD simulations of Plasma Science and Innovation (PSI) Center supported experiments. This poster focuses on two experiments; the Levitated Dipole EXperiment (LDX) and flux injection from coplanar gun. It has been proposed that nonlinear saturation of interchange instabilities in the LDX experiment lead to a robust, marginally stable profile. NIMROD simulations of interchange instabilities in a dipole field are used to examine this conjecture. Our simulations begin with a vacuum dipole field and `grow' a plasma with a heat source. Anisotropic heat conduction and the heat source produces a steady state plasma pressure profile. These profiles are then used to study interchange instabilities and their nonlinear evolution. Simulations of flux injection from a coplanar gun examine the parameter space of `gun lambda' ($\displaystyle\lambda_{gun}=\frac{\mu_0 I_{gun}}{\psi_{gun}}$ ratio of injected current to initial flux) and flux distribution, $\psi(r)$, to characterize optimal parameters for maximum flux amplification and/or closed flux generation. We are particularly interested in robust spheromak formation. Visualization tools that are useful to diagnosing these 3D simulations will be highlighted. [Preview Abstract] 

S1.00007: Multiscale Phenomena in Gyrokinetic Turbulence Simulations W.W. Lee, R. Kolesnikov, S. Ethier, R. Ganesh Through a simple iterative procedure for obtaining the higher order $ {\bf E} \times {\bf B}$ drift and $d{\bf E}/dt$ (polarization) drift associated with a single particle motion, we will show that the commonly used gyrokinetic VlasovPoisson equations are valid in the long wavelength limit of $k_\perp \rho_i \sim o(\epsilon)$ and $k_\perp L \sim o(1)$, where $\rho_i$ is the ion gyroradius, $L$ is the scale length of the background inhomogeneity and $\epsilon$ is a smallness parameter. This conclusion differs from some recent investigations that questioned the validity of these equations in the long wavelength limit. Moreover, using the gyrokinetic turbulence code (GTC) based on these original gyrokinetic equations in global toroidal geometry, we will show that the velocity space nonlinearity associated with parallel acceleration not only gives rise to the formation of global zonal flows with $k_\perp L \sim o(1)$, but also enhances the fluctuations of the long wavelength low $m$ global geodesic acoustic modes (GAM). The amplitude of these modes and the resulting ion thermal flux in the nonlinearly saturated state remain unchanged even if the global relaxation of the background profiles is taken into account in the $\delta f$ simulation. The effect on the zonal flows from the terms of $o(k_\perp^2 \rho_i^2)$ and $k_\perp L \sim o(1)$ due to the difference between the guiding center and the gyrocenter densities in the presence of spatial inhomogeneities for the background Maxwellian will also be discussed. [Preview Abstract] 

S1.00008: Unified Treatment of Model and General Plasma Shape for Neoclassical and Gyrokinetic Calculations J. Candy This work describes a unified method to treat model and general fluxsurface shape in gyrokinetic and neoclassical transport calculations. In all cases the equilibria are guaranteed to be exact solutions of the GradShafranov equation on each flux surface. In the case where model equilibria are considered, we provide a modest extension (adding finite elevation and squareness) of the original method usually attributed to Miller, whereas for general equilibria, a Fourier method is developed. The unified formulation makes use of and extends the intuitively appealing concepts of a midplane minor radius and effective field, originally introduced by Waltz. In the limit that the model and general fluxsurface shapes approach one another, the two methods give identical results. This work may serve to standardize the overall approach to shaped plasma geometry, reducing the probability of haphazard implementations and thereby simplifying the task of code verification. [Preview Abstract] 

S1.00009: Plasma Equilibria With Stochastic Magnetic Fields J.A. Krommes, A.H. Reiman Plasma equilibria that include regions of stochastic magnetic fields are of interest in a variety of applications, including tokamaks with ergodic limiters and highpressure stellarators. Such equilibria are examined theoretically, and a numerical algorithm for their construction is described.$^{2,3}$ \vphantom{% \footnote{A. Reiman et al., Pressureinduced breaking of equilibrium flux surfaces in the W7AS stellarator, Nucl.\ Fusion \textbf {47}, 5728 (2007).} % \footnote{J. A. Krommes and A. H. Reiman, Plasma equilibrium in a magnetic field with stochastic regions, submitted to Phys.\ Plasmas.}% }% The balance between stochastic diffusion of magnetic lines and small effects$^2$ omitted from the simplest MHD description can support pressure and current profiles that need not be flattened in stochastic regions. The diffusion can be described analytically by renormalizing\footnote{J. A. Krommes, Fundamental statistical theories of plasma turbulence in magnetic fields, Phys.\ Reports \textbf {360}, 1351.} stochastic Langevin equations for pressure and parallel current $j_\parallel$, with particular attention being paid to the satisfaction of the periodicity constraints in toroidal configurations with sheared magnetic fields. The equilibrium field configuration can then be constructed by coupling the prediction for $j_\parallel$ to Amp\'ere's law, which is solved numerically. [Preview Abstract] 

S1.00010: Projection of Saturated Nonlinear Gyrokinetic Distribution Functions onto Linear Eigenmodes David Hatch, Paul Terry, William Nevins, Frank Jenko It is becoming increasingly apparent that the dynamics of plasma microturbulence are determined by the interaction of multiple linear eigenmodes, largely in the wavenumber range of the instability. This can occur both when multiple unstable modes interact and when stable eigenmodes are excited, facilitating saturation and reducing transport. The GENE code is equipped with an eigenmode solver making it possible to reveal the properties of more than just the most unstable eigenmode. In limited cases it is possible to project a nonlinear distribution function onto the complete gyrokinetic eigenmode basis. In more general cases, the contribution of multiple eigenmodes can be determined by use of elements of the reciprocal dual basis. Results of such eigenmode projections will be presented, and the effect of stable eigenmodes on saturation will be discussed. [Preview Abstract] 

S1.00011: Studies of transport and stability for optimized pulsed poloidal current drive (PPCD) operation in reversed field pinches Gian Luca Delzanno, John Finn We have combined 1D transport simulations of PPCD with linear stability studies for a spectrum of tearing and ideal MHD modes. We have specified a zero beta plasma with a fixed profile of parallel resistivity, with applied toroidal and poloidal electric fields at the edge to simulate PPCD. The first studies use a model in which the poloidal electric field and the toroidal electric field are specified as in Ref. [1]. The linear stability is monitored for modes with m=0 and with m=1 and a wide spectrum of n, producing linear growth rates as functions of time. In order to optimize the process, by maximizing the time over which the modes are stable, we introduce a procedure in which a global ``stability factor'' is minimized, holding the total toroidal current constant, and use this to determine the optimal waveforms of toroidal and poloidal electric field at the boundary. For these optimal waveforms, the stable time interval is computed and compared with the prescribed scheme discussed above. Comparisons with different stability factors are shown. \\[4pt] [1] J. Reynolds, PhD dissertation, University of Wisconsin, 2007. [Preview Abstract] 

S1.00012: Global Gyrokinetic Simulations of Toroidal Momentum Transport I. Holod, Z. Lin Global gyrokinetic simulations of toroidal momentum transport are performed, using the nonlinear gyrokinetic particleincell code GTC. The total momentum flux can be presented as a sum of diffusive and residual stress fluxes. To identify these components we have considered cases with constant and radially sheared angular velocity. In the presence of ITG turbulence, the inward flux of momentum is observed for the rigid rotation cases. This flux is proportional to background velocity and can be identified as a momentum pinch. For the sheared rotation cases, the competition between diffusive and offdiagonal fluxes takes place. The intrinsic Prandtl number is found to be in the range Pr=0.20.7, which is consistent with quasilinear estimates based on the obtained fluctuation spectra. We have shown that Pr$<$1 is due to the fact that resonant energy is typically larger than thermal energy. The effect of kinetic electrons is studied in both CTEM and ITG plasma turbulences. The offdiagonal momentum flux under CTEM turbulence shows qualitative difference compare to ITG case; in particular it weakly depends on background plasma rotation or its gradient, and thus can be treated as a residual stress flux. In case of ITG turbulence we observe the enhancement of momentum flux, compare to the case with adiabatic electrons. [Preview Abstract] 

S1.00013: Helicityinjected current drive and open flux instabilities in spherical tokamaks D.P. Brennan, P.K. Browning, J. Gates, R.A.M. Van der Linden The toroidal current driven by instabilities and relaxation processes in a cylindrical Spherical Tokamak (ST) geometry with coaxial injected flux is estimated by use of the linear ideal stability boundary of equilibria with a high current on the open driven flux and a lower current on the closed flux. Previous results for spheromaks (1D and 2D) and STs (1D) have predicted stabilization if the closed flux plasma current is sufficiently large, suggesting that the current drive mechanism is selflimiting. For 2D ST equilibria new features appear in the stability maps as the axial length and toroidal field strength are varied. These include changes in the shape of stability boundaries, and resonance effects which extend stability boundaries into the stable region. The results provide driven current estimates with varying geometric length ratio R/L and imposed toroidal field strength; these results have implications both for existing spherical tokamaks, and the design of future devices. [Preview Abstract] 

S1.00014: Modeling of RF/MHD coupling using NIMROD, GENRAY, and the Integrated Plasma Simulator Thomas Jenkins, D.D. Schnack, C.R. Sovinec, C.C. Hegna, J.D. Callen, F. Ebrahimi, S.E. Kruger, J. Carlsson, E.D. Held, J.Y. Ji, R.W. Harvey, A.P. Smirnov We summarize ongoing theoretical/numerical work relevant to the development of a selfconsistent framework for the inclusion of RF effects in fluid simulations; specifically considering resistive tearing mode stabilization in tokamak (DIIIDlike) geometry via ECCD. Relatively simple (though nonselfconsistent) models for the RFinduced currents are incorporated into the fluid equations, markedly reducing the width of the nonlinearly saturated magnetic islands generated by tearing modes. We report our progress toward the selfconsistent modeling of these RFinduced currents. The initial interfacing of the NIMROD* code with the GENRAY/CQL3D** codes (calculating RF propagation and energy/momentum deposition) via the Integrated Plasma Simulator (IPS) framework*** is explained, equilibration of RFinduced currents over the plasma flux surfaces is investigated, and studies exploring the efficient reduction of saturated island widths through time modulation and spatial localization of the ECCD are presented. *[Sovinec {\it et al.}, JCP {\bf 195}, 355 (2004)] **[www.compxco.com] ***[This research and the IPS development are both part of the SWIM project. Funded by U.S. DoE.] [Preview Abstract] 

S1.00015: Threedimensional computation of toroidal twofluid internal kink C.R. Sovinec, E.C. Howell, P. Zhu An important outcome of the fourfield model is the transition from currentsheet to xpoint reconnection during the nonlinear stage of the 1/1 mode in a cylinder [1]. A signature of the transition is a nonlinearly enhanced growth rate computed from the kinetic energy. The results have been confirmed with a full twofluid model [2]. Here, we generalize the fullmodel singlehelicity cylindrical analysis to three dimensions and toroidal geometry using the NIMROD code. Cylindrical 3D computations maintain helical symmetry; no secondary instabilities arise. Toroidal results are similar, at least in the absence of equilibrium diamagnetic rotation. The nonlinearly increased growth rate in kinetic energy and transition to xpoint reconnection are obtained. A sharp but shortlived drop in n=1 magnetic energy also occurs with the twofluid model at the peak of the n=1 kinetic energy. [1] A. Y. Aydemir, Phys. Fluids B 4, 3469 (1992). [2] K. Germaschewski, Bull. Am. Phys. Soc. 53, no. 14, 80 (2008). [Preview Abstract] 

S1.00016: Relativistic Quasilinear Theory for Electron Transport by Radio Frequency Waves in Toroidal Plasmas A.K. Ram, Y. Kominis, K. Hizanidis We derive the relativistic quasilinear diffusion equation for momentum and spatial diffusion of electrons due to RF waves and nonaxisymmetric magnetic field perturbations in a tokamak. In contrast to previous studies, the diffusion operator is derived without assuming that the underlying electron dynamics is Markovian. We allow for the dynamical phase space to be a mix of correlated regular orbits and decorrelated chaotic orbits, so that the diffusion operator is time dependent. The diffusion equation evolves the distribution function on the same time scale as the diffusion operator. A consequence of our assumption is that there is no resonant delta function in the operator. The singular delta function that has plagued previous studies is not amenable to numerical implementation. The nonaxisymmetric magnetic field perturbations included in our studies can be due to magnetic islands as in neoclassical tearing modes. We use the Lie perturbation technique to obtain the nonsingular diffusion operator which includes resonant and nonresonant momentum space diffusion leading to current generation, and nonresonant spatial diffusion leading to modifications of the current profile. [Preview Abstract] 

S1.00017: Size distribution of microclusters in laserirradiated plasmas Alexey Arefiev, Boris Breizman, Mikhail Tushentsov Laser interactions with a mixture of a gaseous plasma and microclusters depend strongly on the clustersize distribution, which is usually difficult to measure. We present a concept for recovering this distribution from measurements of a timedependent refraction index of the medium. The underlying idea is that the absorbed power in a pumpprobe experiment, measured as a function of the delay between the pulses, carries information about the clustersize distribution. The absorption in a single cluster is due to the plasma resonance at the critical density and the power absorption for a given cluster size can be obtained by rescaling the results for a benchmark case. The timedependent power absorption for a medium with a given clustersize distribution is then a convolution of the sizedistribution and the rescaled absorption curve. This relation can be inverted to recover the cluster distribution from the experimentally measured absorption. We demonstrate feasibility of this technique by analyzing the data from recent pumpprobe experiments at the University of Texas. [Preview Abstract] 

S1.00018: Similarities and differences between Beta Alfv\'{e}n Eigenmodes and Geodesic Acoustic Modes Christine Nguyen, Xavier Garbet, Andrei Smolyakov, Joan Decker, Guido Huysmans, Patrick Maget In this work, we make use of a gyrokinetic formalism to investigate and compare two particular modes induced by geodesic curvature, which have been experimentally observed to be excited by suprathermal particles, the Beta Alfv\'{e}n Eigenmode (BAE) and the Geodesic Acoustic Mode (GAM). First, the earlier predicted degeneracy of BAEs and GAMs is analyzed with a particular attention given to the electron response, which is likely to be adiabatic for BAEs and hydrodynamic for GAMs. It is observed that those different electron responses imply different electromagnetic effects. However, when the GAM is taken in the electrostatic limit, the dispersion relation of those modes is found degenerate due to the ideal magnetohydrodynamic property of BAEs: E//=0. Next, we investigate the excitation of those modes. Landau damping, expected to be the main damping process of the two modes, is computed both in the linear and nonlinear regimes and compared to the fast particle excitation processes, which are different for BAEs and for GAMs. Nguyen C. \textit{et al}, Phys. Plasmas~\textbf{15},~112502, 2008. [Preview Abstract] 

S1.00019: Numerical modeling of turbulence in magnetized plasmas Jean C. Perez, Stanislav Boldyrev We investigate the structure of turbulence in strongly magnetized plasmas through extensive high resolution numerical simulations. Such turbulence plays a significant role in laboratory plasma experiments, solar wind, as well as the interstellar medium. At large scales, above any characteristic plasma scale, the plasma is modeled as a Magnetohydrodynamic (MHD) fluid, while at smaller scales reduced models are used to capture two fluid effects. These models have been derived to describe various regimes observed in laboratory experiments, including tokamak devices in the quest for nuclear fusion. Most numerical turbulence studies of these models have been limited to the fieldperpendicular plane under the assumption that the strong magnetic field renders the dynamics two dimensional. However, recent analytic and numerical results indicate that even in the presence of a strong largescale magnetic field, the fieldparallel dynamics play a crucial role in MHD turbulence. We investigate the turbulence cascade transition from the large MHD scales to smaller scales and correctly capture the parallel dynamics in the small scale regime. [Preview Abstract] 

S1.00020: Theoretical explanation for edge localized modes and their connection to blob transport Linjin Zheng, H. Takahashi, E. Fredrickson Theoretical explanation for edge localized modes is presented. We show that there is a positive feedback process between the external MHD modes and the SOL current. The initial magnetic perturbation at the pedestal causes radial transport, that discharges the pedestal heat and particles to the SOL and results in the bursting of the SOL current. In turn, the SOL current bursting can induce a stronger magnetic perturbation at the pedestal. This positive feedback causes the edge MHD modes to grow nonlinearly and sharply even near the linear MHD marginal stability limit, leading to the ELM burst. We also discuss the connection with the blob transport. It is pointed out that the excitation of the SOL current may generate the filament structure and thermally detach it from the core plasma due to the formation of magnetic island and its surrounding stochastic region. We think that the unbalanced plasma and magnetic pressure due to the filament curvature may be a direct explanation to the blob transport toward the wall. We analogize the blob force unbalance to the tokamak plasma without the vertical magnetic field applied  missing the inward force due to the curl product of the vertical field and the toroidal current to balance the outward force. Research supported by DOE grant DEFG0204ER54742 and DEAC0276CH03073. [Preview Abstract] 

S1.00021: Correlating heatflux profiles on divertor plate with input beam power for the DIIDD tokamak using the FACETS code Ammar Hakim, Richard Groebner, Scott Kruger, Alexander Pletzer, Srinath Vadlamani, John Cary, Thomas Rognlien, Ronald Cohen We present results from coupled coreedge simulations of tokamak transport equations using the FACETS code. In particular, we correlate the heatflux profile on the divertor plate with the input heating beam power for the DIIID tokamak. For the core transport equations we use a new core solver developed as part of the FACETS project. The solver uses a fully implicit multigrid method to advance the nonlinear transport equations. The beam heating profiles for the ions and electrons are obtained from experimental DIIID discharges and computed using the ONETWO code. For the edge transport we use the twodimensional fluid code UEDGE. The solutions in the core region is coupled to the edge regions using an implicit coupling scheme. Computational diagnostics are used to extract the heat flux profiles on the divertor plate. Correlations of the peak heat flux on the divertor plate with input beam power are made. These results are compared to experimental correlations obtained from DIIID data. [Preview Abstract] 

S1.00022: Towards fullBraginskii implicit extended MHD Luis Chacon Recently, viable algorithms have been proposed for the scalable, fullyimplicit temporal integration of 3D resistive MHD\footnote{L. Chac\'on, {\em Phys. Plasmas}, {\bf 15}, 056103 (2008)} and coldion extended MHD\footnote{L. Chac\'on, {\em J. Physics: Conf. Series}, {\bf 125}, 012041 (2008)} models. While significant, these achievements must be tempered by the fact that such models lack predictive capabilities in regimes of interest for magnetic fusion. Short of including kinetic closures, a natural evolution path towards predictability starts by considering additional terms as described in Braginskii's fluid closures in the collisional regime. Here, we focus on the inclusion of two fundamental elements of relevance for fusion plasmas: anisotropic parallel electron transport, and warmion physics (i.e., ion finite Larmor radius effects, included via gyroviscosity). Both these elements introduce significant numerical difficulties, due to the strong anisotropy in the former, and the presence of dispersive waves in the latter. In this presentation, we will discuss progress in our fully implicit algorithmic formulation towards the inclusion of both these elements. [Preview Abstract] 

S1.00023: Resistive Wall Mode Studies in NIMROD Andrea Montgomery, Chris Hegna, Andrew Cole, Scott Kruger Resistive wall kink stability is considered using a resistive MHD model. Resistive wall boundary conditions are implemented in NIMROD for a periodic cylinder with flat pressure and current equilibrium profiles. Simulation results are compared with analytic solutions [J. M. Finn, Phy. Plasmas \textbf{2}, 198 (1995).] The NIMROD code is used to study the effects of rigid plasma rotation on resistive wall modes. The effects of rotation on ideal plasma resistive wall modes and resistive tearing modes are compared and contrasted. Further plans include generalization of this work to more realistic tokamak equilibria. [Preview Abstract] 

S1.00024: Helical ChandresekharKendall (CK) Modes and 3D Relaxation States Xianzhu Tang, Allen Boozer CK modes are eigensolutions to the forcefree equation with homogeneuos boundary conditions. These forcefree eigensolutions are uniquely determined by the chamber geometry, and play an essential role in determining the relaxed states of a driven plasma, which may or may not be a Taylor state. Previous work on the relaxation theory have demonstrated that resonant coupling be the physical mechanism underlying the formation of spherical tokamak, spheromak, and reversed field pinch by helicity injection. Although much of the design constraint and optimization for laboratory applications have been understood using only the axisymmetric CK modes in an axisymmetric chamber, as the target magnetic configurations are axisymmetric, helical CK modes can play a subtle role in determining the operating boundary and the degrees of intrinsic nonaxisymmetry in the experiments. Here we present the numerical computation of these helical CK modes and elucidate the two physical mechanisms by which 3D relaxation states are determined in toroidal experiments with a special emphasis on reversed field pinch. [Preview Abstract] 

S1.00025: Global geometrical constraints on Lagrangian dynamics: guiding center plasma models in 3D$^*$ Linda Sugiyama Hamiltonian and Lagrangian methods emphasize local dynamic relationships. In three or more dimensions, geometrical properties of vector fields may impose independent, global existence conditions. For strongly magnetized plasmas, the guiding center model of charged particle motion superimposes a rapid gyration around the magnetic field lines onto the smoother, gyroaveraged motion of a guiding center, ordered in small gyroradius $\epsilon = \rho_i/L$. Beyond first order, equations of motion can be formally derived by noncanonical Hamiltonian or Lagrangian methods$^1$. In fully 3D magnetic fields, existence breaks down at second order$^2$ if the magnetic torsion $\tau=\hat{\mathbf{b}}\cdot\nabla\times\hat{\mathbf{b}}$ is nonzero, where $\hat{\mathbf{b}}=\mathbf{B}/$B. No consistent set of locally orthogonal coordinates aligned to $\mathbf{B}$ at every point exists and the gyroangle is undefined (unlike in 2D fields, including toroidal axisymmetry). Ordering the magnetic field timevariation to be slow relative to the gyration introduces further geometrical approximations. The coordinate system existence condition generalizes to $n\ge 3$ dimensions, where it applies to questions such as to the connection of the large scale 4D spacetime of general relativity to small scale, locally orthogonal theories, such as quantum phenomena.\\ $^*$Work supported by the U.S. Department of Energy.\\ $^1$R.J. Littlejohn, \emph{J. Plasma Phys.} \textbf{29} 111 (1983); references therein.\\ $^2$L.E. Sugiyama, \emph{Phys. Plasmas} \textbf{15} 092112 (2008). [Preview Abstract] 

S1.00026: Global Gyrokinetic Electron Temperature Gradient Turbulence and Associated Electron Heat Transport in NSTX Plasmas W.X. Wang, S. Ethier, S.M. Kaye, E. Mazzucato, D. Smith, W.W. Lee, T.S. Hahm, G. Rewoldt, J. Manickam, W.M. Tang, M. Adams Global, nonlinear simulations of electron temperature gradient (ETG) turbulence for experimental discharges have been carried out for the first time for direct validation against highk measurements of electron gyroradius scale fluctuations in NSTX. Qualitative agreement in the density fluctuation spectrum between the experiment and the simulation is obtained with exponential power 2.6 in k$_{r}$ and 5.3 in k$_{\theta }$ in the simulation, compared to 4.5 in k$_{perp}$ in the experiments. The nonlinear generation of zonal flows with fine radial scale is observed during ETG turbulence development. However, zonal flows are too weak to break up radially elongated streamers in the nonlinear phase of ETG turbulence. The identification of streamers will be a good opportunity for future highk diagnosis to validate nonlinear ETG simulation models. The ETG turbulence spreading is found to be small (a few tens electron gyroradii). Comparison of density fluctuation amplitudes based on synthetic diagnosis between simulations and measurements, will be discussed. Also presented is the phase space structure of the electron heat flux to elucidate the roles of resonant and nonresonant electrons. Work supported by U.S. DOE Contract DEAC0276CH03073 and SciDAC GPSTTBP. [Preview Abstract] 

S1.00027: Anisotropic Heat Transport in the Presence of Resonant Magnetic Perturbations Eric Held, Scott Kruger Heat transport in the Hmode tokamak edge is significantly modified by the presence of resonant magnetic perturbations. Application of collisional transport models to this problem ignores the fact that temperatures at the top of the edge pedestal may be several keV. Here, we compare the effective radial heat transport predicted by local (diffusive) and nonlocal \footnote{E. D. Held, J. D. Callen, C. C. Hegna, C. R. Sovinec, T. A. Gianakon,and S. E. Kruger, Phys Plasmas, 11, 2419 (2004).} (integral) forms for the parallel heat flux. Accurately predicting this effective radial heat transport becomes important when significant magnetic field line stochasticity is present, as in the case of overlapping magnetic perturbations. For such cases, the integral form for the parallel heat transport correctly assesses the effects of temperature perturbations all along the magnetic field line and yields predictions that vary substantially from the diffusive closure, which relies only on the local temperature gradient. Quantitative comparisons of effective radial transport are given for single helicity and multiple helicity magnetic perturbations in cylindrical and toroidal geometry, with emphasis given to a toroidal case with a narrow pedestal width and a high temperature at the top of the pedestal. [Preview Abstract] 

S1.00028: Proper Orthogonal Decomposition methods for particlebased transport calculations in plasmas Diego delCastilloNegrete, D. Spong, S. Hirshman The Proper Orthogonal Decomposition (POD) is a powerful technique to analyze large data sets by projecting the data into an optimal set of loworder modes that capture the main features of the data. POD methods have been widely used in image and signal processing and also in the study of coherent structures in neutral fluids. However, the use of these techniques in plasma physics is a relatively new area of research. Here we discuss recent novel applications of POD methods to particlebased transport calculations in plasmas. We show that POD techniques provide an efficient method to filter noise in the reconstruction of the particle distribution function. As a specific application we consider Monte Carlo simulations of plasma collisional relaxation and guidingcenter transport in magnetically confined plasma in toroidal geometry [1]. We also discuss recent results on the application of POD methods to PICcodes in the context of the VlasovPoisson system, and the use of POD methods in projective integration. In particular, we show how POD modes can be used as effective macroscopic variables to accelerate MonteCarlo calculations. [1] D. delCastilloNegrete, et al. \textit{Phys. of Plasmas} 15, 092308 (2008). [Preview Abstract] 

S1.00029: Parallel heat flux closures in toroidal plasmas Mukta Sharma, J.Y. Ji, E.D. Held Closures for the parallel conductive heat flux are derived using a ChapmanEnskoglike approach that maintains a maximal ordering between parallel streaming, particle trapping and collisional effects. The distribution function is written as the sum of a dynamic Maxwellian and a kinetic distortion, $F=\sum_{l} P_l (v_\ /v) F_l$, where the parallel gradient operator acts on both the coefficients, $F_l$, and the Legendre polynomials, $P_l (v_\ (x)/v)$. A moment approach is used to treat ${\hat b} \cdot {\vec \nabla} B$ terms as well as the linearized Coulomb collision operator \footnote{J.Y. Ji and E. D. Held, Phys. Plasmas {\bf 13}, 102103 (2006).} The Lorentz scattering term acting on $F$ inverted along with the free streaming term and the coupled ODE system for the $F_l$'s is diagonalized. Integrating the separated ODEs along magnetic field lines and taking the necessary moments yields the desired closures. This general approach allows examination of the closures in all collisionality regimes and captures the physics of a substantial reduction in the heat flow due to the trapping of particles in magnetic wells. Results are compared with previous bounceaveraged theories. [Preview Abstract] 

S1.00030: Numerical Studies of TwoFluid Tearing and Dynamo in a Cylindrical Pinch J.R. King, C.R. Sovinec, V.V. Mirnov The nonlinear evolution of twofluid tearing modes in a cylindrical pinch is investigated with the NIMROD code. The structure and dynamo of single and multihelicity nonreversed nonlinearly saturated states are examined and compared with singlefluid results. Computations show that the saturated island size and the combined nonlinear Hall and MHD dynamo structure are independent of the ion sound gyroradius, and the Hall dynamo is broad relative to a linear prediction. The individual Hall and MHD dynamo contributions exhibit oscillatory structures away from the rational surface that cancel when the total dynamo is calculated. Mode coupling and modal energy exchange is examined in the multihelicity cases. Consistent with analytical predictions [1], linear results show rotation of the twofluid tearing instability due to the relatively strong fieldline curvature; nonlinear twofluid rotation is investigated. [1] V.V. Mirnov, et al., Proc. of 21st IAEA Fusion Energy Conf, TH/P318 (2006) [Preview Abstract] 

S1.00031: Linear Gyrokinetic Simulations of Electrostatic Ion Temperature Gradient Driven Instability In a Toroidal Reverse Field Pinch Varun Tangri, Paul Terry, R.W. Waltz We address linear Ion Temperature Gradient (ITG) driven microturbulence in a real RFP geometry using GYRO[1], a code extensively used for simulations of microinstabilities in tokamak geometry. The parameters in the RFP suggest an ultralow q, negative shear regime with average bad curvature that has been rarely investigated. We show that this regime has unique mode structure and scaling properties. The code GYRO has been modified to simulate ITG in a collisionless, linear, electrostatic limit. We compute the growth rate spectrum, and analyze its dependence on density and temperature scalelengths. We also make comparisons with simple calculations and potential relevance of the slab and toroidal branches. [1] J. Candy and R.E. Waltz, J. Comp. Phys. 186, 545 (2003) [Preview Abstract] 

S1.00032: MHD simulations of ELMs using the BOUT++ code B.D. Dudson, M.V. Umansky, X.Q. Xu, P.B. Snyder, H.R. Wilson The new BOUT++ code [1] is an extensible tool for studying non linear plasma phenomena such as ELMs. It is capable of solving an arbitrary number of scalar and vector fluid equations in curvilinear geometry, and has been benchmarked against analytically solvable problems, and other codes in Xpoint geometry. Here we present linear simulations of 3field reduced MHD for plasmas with circular crosssection, and compare with the ELITE linear MHD code [2,3]. These show good agreement in both the mode structure and growth rates, giving confidence that BOUT++ can reproduce the ideal ballooning mode. Suppression of ballooning modes by diamagnetic and flowshear effects is demonstrated. Nonlinear development of ballooning modes has been studied, showing eruption of filaments from the plasma edge, which are observed to accelerate outwards. Finally, the effect of nonasymmetric perturbations will be studied, in both the linear and nonlinear regimes to understand the effect of resonant magnetic perturbations on ELMs. [1] B.D.Dudson et. al. Preprint arXiv.org:0810.5757 [2] P.B.Snyder et. al. Phys. Plas. 9 (2002) 2037 [3] H.R.Wilson et. al. Phys. Plas. 9 (2002) 1277 [Preview Abstract] 

S1.00033: Gyrokinetic particle simulation of edge turbulence in HL2A tokamak Feng Liu, Yong Xiao, Wenlu Zhang, Jiaqi Dong, Ihor Holod, Kaijun Zhao, Zhihong Lin Strong correlation between high frequency microturbulence and low frequency geodesic acoustic mode (GAM) has been observed in the edge plasmas of the HL2A tokamak$^{1}$, suggesting possibility of turbulence generation of GAM and GAM modulation of turbulence. In this work, we use the gyrokinetic toroidal code (GTC)$^{2}$ to study the nonlinear interaction between turbulence and GAM (and zonal flows) in realistic parameters of HL2A edge plasmas with collisions and steep pressure gradients. Initial GTC linear simulation finds strongly unstable trapped electron mode (TEM). Effects of collisions will be studied and nonlinear simulation results will be reported. Work supported by SciDAC GPS Center. [Preview Abstract] 

S1.00034: Potential energy surfaces for hydrocarbon molecules and ions Bastiaan J. Braams, Amit R. Sharma, Joel M. Bowman Studies of reaction dynamics and molecular spectroscopy rely on the concept of a potential energy surface (PES): the potential energy of the molecule or reaction complex as a function of the configuration of nuclei. In practice such a PES must be available in an analytical form that can be quickly evaluated and that has been fitted to the results of (expensive) electronic structure calculations. We have been constructing potential energy surfaces for hydrocarbon molecules and complexes C$_m$H$_n$, $m\le4$ and at most 8 atoms total, neutral or once charged, in full dimensionality and with due respect for the invariance under exchange of identical nuclei. The poster will describe our family of surfaces and will highlight applications to the spectroscopy of methane and of the vinyl radical (C$_2$H$_3$). [Preview Abstract] 

S1.00035: Comparisons of anomalous and collisional radial transport with a continuum kinetic edge code K. Bodi, S. Krasheninnikov, R. Cohen, T. Rognlien Modeling of anomalous (turbulencedriven) radial transport in controlledfusion plasmas is necessary for longtime transport simulations. Here the focus is continuum kinetic edge codes such as the (2D, 2V) transport version of TEMPEST, NEO, and the code being developed by the Edge Simulation Laboratory, but the model also has wider application. Our previously developed anomalous diagonal transport matrix model with velocitydependent convection and diffusion coefficients allows contact with typical fluid transport models (e.g., UEDGE). Results are presented that combine the anomalous transport model and collisional transport owing to ion drift orbits utilizing a Krook collision operator that conserves density and energy. Comparison is made of the relative magnitudes and possible synergistic effects of the two processes for typical tokamak device parameters. [Preview Abstract] 

S1.00036: Gyrokinetic $\delta\! f$ particle simulation of energetic particles driven modes Jianying Lang, Yang Chen, Scott Parker, Guoyong Fu We reduce the global GEM code [1] from a fully kinetic model with gyrokinetic ions and drift kinetic electrons to a hybrid model with gyrokinetic ions and massless fluid electrons to study the ToroidicityInduced Alfven Eigenmodes (TAEs) at finite plasma pressure. For benchmark purpose, this hybrid model is further reduced to a two fluid model. Using a lown global TAE as a test case, we observed the existence of a global discrete eigenmode in the two fluid simulation. The observed mode frequency is within the gap and close to the lower continuum which agrees well with the expected TAE frequency. This simulation result shows very good agreement with an eigenmode analysis based on the two fluid model. In the presence of the gyrokinetic hot ions, this TAE is driven unstable with the growth rate scaling linearly with the hot ion pressure $\beta_{hot}$. Turning on the gyrokinetic bulk ions, we observed the kinetic Alfven mode structure and the growth rate of the unstable TAE being reduced, which is expected because of the kinetic damping effect. We are currently comparing the damping rate obtained from the gyrokinetic simulations to theoretical calculation. [1] Y. Chen and S. Parker, J. of Comp. Phys. 220, 839 (2007). [Preview Abstract] 

S1.00037: Electron transport due to global Alfv\'en eigenmodes in NSTX Nikolai Gorelenkov, Allen Boozer, Eric Fredrickson, Dan Stutman, Roscoe. B. White We inverstigate theoretically and numerically the possible electron transport induced by multiple instabilities of Global Alfv\'en Eigenmodes (GAE) in a toroidal plasma. Such anomalous eletron transport was observed in NSTX recently when NBI power was increased to $P_{NBI}=6MW$ in both H and Lmode discharges. With the frequency range of $0.51MHz$ GAEs may resonantly interact with bulk ($\sim 12keV$ energy) primarily trapped electrons. Because of strong beam ion drive GAEs are not damped on electrons, but are excited to a strong amplitudes, $\delta n_{e}/n_{e}\sim 10^{4}$. ORBIT simulations show that the overlap of electron phase space resonant structures due to multiple GAE instabilities may induce stochastic electron diffusion. Our calculations suggest that GAEs with observed amplitudes may lead to electron heat diffusivity, $\chi_{e}\ge 10m^{2}/sec$, comparable to those inferred from the power balance analysis. The above mechanism potentially could have significant implications for fusion. [Preview Abstract] 

S1.00038: Dust Devil Dynamics Wendell Horton, Cynthia Correa, Hideaki Miura, Bruce Rodenborn The theory and simulation tools of fusion plasma physics are used to describe the dynamics of dust devils. The GradShafranov equation governs the poloidal flow stream function and gives a class of solutions for steady axisymmetric flows. The high core velocity is limited by viscous dissipation with a modified Burger's vortex model. Since the Reynolds number is not large, these structures are well represented on vector computers in contrast to collisionless plasmas. Electrically charged sand grains ($10100 \mu m$) are integrated as passively convected by the winds and results in vertical electric fields that assist the vortices in lifting materials off the ground and into the vortex. The rotating charged dust produces a magnetic field. Thus, some of the important properties of high temperature plasmas are manifested in these common, small scale coherent structures. [Preview Abstract] 

S1.00039: SteadyState Flows in TwoFluid Models of NSTX and DIIID Plasmas N.M. Ferraro, S.C. Jardin, J. Chen Accurate axisymmetric steadystates of a comprehensive twofluid model are calculated for plasmas in diverted NSTX and DIIID geometries using the M3DC$^1$ code [1]. It is found that gyroviscosity may have a significant effect on the flows in steadystate when a localized density source is present. The model implemented in M3DC$^1$ selfconsistently includes the effects of flows, anisotropic viscosity, anisotropic thermal conductivity, and resistivity. Results for ohmically driven plasmas are presented. New capabilities of M3DC$^1$ allow the threedimensional linear stability of axisymmetric equilibria to be calculated; these capabilities and preliminary stability results are discussed. Also discussed are recent and future extensions to M3DC$^1$, including heuristic bootstrap current models, coupling to a physicsbased transport model, and nonlinear nonaxisymmetric capability. \par\vskip3pt\noindent [1] S. C. Jardin, J. Breslau, N. Ferraro, J. Comput. Phys, 226 (2007) 2146 [Preview Abstract] 

S1.00040: The nextgeneration ESL continuum gyrokinetic edge code R. Cohen, M. Dorr, J. Hittinger, T. Rognlien, P. Collela, D. Martin The Edge Simulation Laboratory (ESL) project is developing continuumbased approaches to kinetic simulation of edge plasmas. A new code is being developed, based on a conservative formulation and fourthorder discretization of fullf gyrokinetic equations in parallelvelocity, magneticmoment coordinates. The code exploits mapped multiblock grids to deal with the geometric complexities of the edge region, and utilizes a new flux limiter [P. Colella and M.D. Sekora, JCP 227, 7069 (2008)] to suppress unphysical oscillations about discontinuities while maintaining highorder accuracy elsewhere. The code is just becoming operational; we will report initial tests for neoclassical orbit calculations in closedflux surface and limiter (closed plus open flux surfaces) geometry. It is anticipated that the algorithmic refinements in the new code will address the slow numerical instability that was observed in some long simulations with the existing TEMPEST code. We will also discuss the status and plans for physics enhancements to the new code. [Preview Abstract] 

S1.00041: TEMPEST simulations of the neoclassical transport in a singlenull tokamak geometry X.Q. Xu, R.H. Cohen, T.D. Rognlien TEMPEST simulations were carried out for plasma transport and flow dynamics in a singlenull tokamak geometry. The core radial boundary ion distribution is a fixed Maxwellian $F_M$ with $N_0=N(\psi_0)$ and $T_{i0}=T_i(\psi_0)=300eV$, and exterior radial boundary ion distribution is Neumann boundary condition with $\partial F_i(\psi,\theta,E,\mu)/\partial\psi_{\psi_w}=0$ during a simulation. Given boundary conditions and initial profiles, the interior plasmas in the simulations should evolve into a neoclassical steady state. A volume source term in the private flux region is included, representing the ionization in the private flux region to achieve the neoclassical steady state. A series of TEMPEST simulations are conducted to investigate the scaling characteristics of the neoclassical transport and flow as a function of $\nu_{*i}$ via a density scan. Here $\nu_{*i}$ is the effective collision frequency, defined by $\nu_{*i}=\epsilon^{3/2}\nu_{ii}\sqrt{2}qR_0/v_{Ti}$, $\nu_{ii}$ is the ionion collision, and $v_{Ti}$ the ion thermal velocity. Simulation results show significant poloidal variation of density and ion temperature profiles due to the endloss machanism at the divertor plates. Each region (Edge, the SOL and private flux) achieves the dynamical steady state at its own time scale due to the different physical processes. The impact of selfconsistent electric field on transport and flow will be presented. [Preview Abstract] 

S1.00042: Collisionless and Collisional Tearing Mode in Gyrokinetics Ryusuke Numata, Tomoya Tatsuno, William Dorland, Barret Rogers We present numerical results of linear tearing mode simulations for collisionless and collisional regimes in a strong guide magnetic field limit using the \texttt{AstroGK} astrophysical gyrokinetics code. In the collisionless regime, the twofluid effect, instead of the resistivity, mediates reconnection. Mirnov {\it et al.} and Fitzpatrick {\it et al.} have derived linear and nonlinear versions of reduced twofluid models for the tearing mode in the presence of the guide field$^{1,2}$. We compare numerically obtained tearing mode growth rate with those theories. For the collisional regime, we compare gyrokinetic simulation results with the classical tearing mode theory by Furth, Kileen, and Rosenbluth, and with a fluid simulation. This benchmarks recently implemented resistivity term in the code. AstroGK can smoothly connect those two regimes. We also discuss the scaling of the growth rate against the collisionality in the intermediate regime, and how the kinetic effects play roles in the tearing mode. 1. V.~V. Mirnov, C.~C. Hegna, and S.~C. Prager, Phys. Plasmas {\bf 11}, 4468, (2004). 2. R. Fitzpatrick and F. Porcelli, Phys. Plasmas {\bf 11}, 4713 (2004). [Preview Abstract] 

S1.00043: Effect of screened resonant magnetic perturbations on the density profile F.L. Waelbroeck, I. Joseph, E. Nardon, F. Militello At low collisionality, Resonant Magnetic Perturbations (RMP) can suppress the edge localized modes (ELM), which present a threat to the ITER divertor.$^1$. Explanations of the suppression based on the effects of magnetic stochasticity face several difficulties: (1) while stability analyses show that the suppression is caused by a reduction of the edge pressure gradient, it is primarily the density rather than the temperature gradient that is reduced. (2) A steepening of the electrontemperature pedestal indicates the persistence of good magnetic flux surfaces. (3) There is no island spinup after removal of the RMP. (4) Signs of modepenetration are absent during rampup of the RMP. In fact, lowdensity locked modes are carefully avoided in RMP experiments because of their undesireable consequences, such as disruptions. Here, we use a 2fluid model to examine the quasilinear transport of particles caused by the convection cells generated near suppressed RMPs.$^2$ [1] T. Evans et al., Nucl. Fusion 48, 024002 (2008). [2] E. Nardon et al., Phys. Plasmas 14, 092501 (2007). [Preview Abstract] 

S1.00044: Gyrokinetic particle simulation of nonlinear generation of second harmonics of GAM H.S. Zhang, Z.Y. Qiu, I. Holod, W.L. Zhang, Y. Xiao, Y.J. Mao, X.G. Wang, L. Chen, Z. Lin Nonlinear generation of second harmonics of the geodesic acoustic mode (GAM) has been observed in DIIID tokamak. In this work, we use the gyrokinetic toroidal code (GTC) to study GAM nonlinear coupling. With a GAM amplitude in the range of experimental values, we observe the nonlinear generation of a second harmonics with a frequency of 2$\omega _{GAM}$ ($\omega _{GAM}$ is the linear GAM frequency). The second harmonics is dominated by an electrostatic potential with n=m=0 (n and m are toroidal and poloidal mode number, respectively), and a density perturbation with n=0 and m=1. The amplitude of the second harmonics is proportional to the intensity of the primary harmonics, as expected from a quadratic nonlinearity due to toroidal coupling of surface averaged potential and GAM density perturbation. Comparison of eigenmode structures from GTC simulation with DIIID measurements will be presented. [Preview Abstract] 

S1.00045: TimeDomain Simulation of RF Couplers on NERSC Supercomputers David Smithe, Johan Carlsson, Travis Austin We report on progress in simulating the behavior of RF couplers in tokamak devices with the ``TimeDomain Plasma with Sheath Boundaries'' simulation software [1]. Recent work focuses on the challenges of upscaling to more complicated coupler geometry, running on NERSC supercomputers, and improvements for full implicitness in the sheath model. Previously we have used CAD drawings and parametric models to simulation a LH coupler on the MST tokamak, and now are constructing edge geometry for NSTX and CMod ICRF couplers. Issues associated with importation and construction of accurate 3D edge and coupler geometries from drawings and documentation will be explored. We will also discuss results from 1D benchmark exercises of the sheath model [2], and possible techniques for extension of the model to include longrange effects. Finally, we consider the feasibility of other possible improvements to the overall model, including the use of testparticles to show nonlinear effects, and an analysis aimed at the possible inclusion of thermal effects in the timedomain plasma algorithm. [1] David N. Smithe, Phys. Plasmas 14, 056104 (2007); DOI:10.1063/1.2710784. [2] D.A. D'Ippolito and J.R. Myra, Phys. Plasmas 13, 102508 (2006). [Preview Abstract] 

S1.00046: Stabilization of ion temperature gradient driven modes by lower hybrid wave in a tokamak Animesh Kuley, V.K. Tripathi A gyro kinetic formalism has been developed to study lower hybrid wave stabilization of ion temperature gradient (ITG) driven modes, responsible for anomalous ion transport in the inner region of tokamak. The parametric coupling between lower hybrid and drift waves produce lower hybrid sideband waves. The pump and the sidebands exert a ponderomotive force on electrons, modifying the eigen frequency of the drift wave and influencing the growth rate. The longer wavelength drift waves are destabilized by the lower hybrid wave while the shorter wavelengths are suppressed.The requiste lower hybrid power is in the range $\sim$ 900kW at 4.6 GHz. [Preview Abstract] 

S1.00047: Transport Equations In Tokamak Plasmas J.D. Callen, C.C. Hegna, A.J. Cole Transport equations for tokamak plasmas are usually obtained by taking fluxsurface averages of the collisional Braginskii equations. However, tokamak plasmas are usually not in collisional regimes. Also, ad hoc terms are added for: neoclassical effects on the parallel Ohm's law (trapped particle effects on resistivity, bootstrap current); fluctuationinduced transport; heating, currentdrive \& flow sources and sinks; small nonaxisymmetries; etc. Here we develop selfconsistent second order in gyroradius fluidmomentbased transport equations, including poloidal and toroidal flow equations, in nearly axisymmetric tokamak plasmas. The derivation begins from fluid moments of the plasma kinetic equation transformed to poloidal magnetic flux coordinates, uses neoclassicalbased parallel viscosity closures, and includes all the added effects noted above, many of which produce nonambipolar radial particle fluxes. An evolution equation for toroidal plasma rotation results from setting the net radial current produced by the sum of these nonambipolar fluxes to zero. The net radial particle flux is then the sum of the usual intrinsically ambipolar fluxes (classical, neoclassical, etc.) plus the nonambipolar fluxes evaluated at the ambipolarityenforcing toroidal plasma rotation (radial electric field). The resultant transport equations will be presented and contrasted with the usual ones. [Preview Abstract] 

S1.00048: Synergy of Edge Turbulence and Zonal Flows in the Density Limit Raghvendra Singh, Predhiman Kaw, Rajiv Goswami, Mikhail Tokar, Pervez Guzdar Understanding of the density limit is of great interest, as it will significantly improve fusion power performance. It is well known that there occurs a dramatic deterioration of particle confinement at the edge of tokamaks as one approaches the Greenwald limit. We present a theoretical model on synergy of edge turbulence dominant by DRBM instability and zonal flows in determining the Greenwald density limit. The multiscale interaction of zonal flows with DRBM is presented. The predatorprey model for saturation of ZFs shows that the saturation level of the primary turbulence is determined by the damping of the secondary ZFs. We have determined conditions under which ZFs saturate by different mechanics such as by I) collision damping II) instability to tertiary modes III) nonlinear trapping of DRBM turbulence, giving coherent structures etc. A discussion of the relevant parameter spaces where various mechanisms dominate leading to the observed variety of phenomena will be presented. [Preview Abstract] 

S1.00049: NUBEAM Sources in FACETS A. Pletzer, D. McCune, K. Indireshkumar, A. Morris, A. Pankin, J.R. Cary The SciDAC project for the development of a Framework Application for Core Edge Transport Simulation (FACETS) aims at producing tokamak coretowall transport simulations on massively parallel architectures. Here, we report on the progress of integrating the new parallel, Plasma\_State based, MonteCarlo NUBEAM module into the FACETS framework to provide neutral beam and fusion source terms in the plasma core diffusion equations. NUBEAM has recently been improved to facilitate invocation from third party software (e.g. SWIM). This was achieved by consolidating 100s of input variables into separate structures according to machine specificity, shot specificity, or timeslice specificity. Thanks to a combination of autogenerated code and a newly developed methodology for exposing Fortran90 derived types to C, all derived type members of NUBEAM structures have become inmemory accessible to FACETS's C++ infrastructure. NUBEAM, which is the first volumetriccoupling component in FACETS, has been wrapped with methods complying to the FACETS standard interface definition for easy interchangeability of modules at run time. Examples of neutral beam computations instrumented with TAU/Paratools on leadership class machines will be presented, as well as first coupled coresource FACETS simulations. [Preview Abstract] 

S1.00050: Calculation of Nonambipolar Transport in Tokamaks Jongkyu Park, Allen Boozer, Jonathan Menard Small nonaxisymmetric perturbations of the magnetic field can greatly change the performance of tokamaks through nonambipolar transport. The recently generalized analytic calculations of the nonambipolar transport have shown that the consistency between theory and experiment can be significantly improved by two effects [J.K. Park, et al., ``Nonambipolar Transport by Trapped Particles in Tokamaks,'' Phys. Rev. Lett. (2009), To be published] : (1) The small fraction of trapped particles for which the bounce and precession rates of particles resonate. (2) The nonaxisymmetric variation in the field strength along the perturbed magnetic field lines rather than along the unperturbed magnetic field lines. Most apparent effects can be found in toroidal momentum transport, and thus by a torodial rotational damping associated with Neoclassical Toroidal Viscosity (NTV). Various experiments for NTV rotation braking in NSTX and DIIID will be compared with theoretical predictions, and the expected sensitivity of ITER to nonaxisymmetries will be presented. Also, the effects of nonaxisymmetic field on particle and heat transport will be discussed with regard to ELM suppressions. This work was supported by DOE contract DEAC0276CH03073 (PPPL), and DEFG0203ERS496 (CU). [Preview Abstract] 

S1.00051: Calculation of the NanbuTrubnikov Kernel: Implications for Numerical Modeling of Coulomb Collisions A.M. Dimits, B.I. Cohen, C.M. Wang, R.E. Caflisch, Y. Huang We investigate the accuracy of and assumptions underlying the numerical binary MonteCarlo collision operator due to Nanbu [K. Nanbu, Phys. Rev. \textbf{E 55} (1997)]. The numerical experiments that resulted in Nanbu's parameterized collision kernel are approximate realizations of the CoulombLorentz pitchangle scattering process, for which an analytical solution is available. It is demonstrated empirically that Nanbu's collision operator quite accurately recovers the effects of CoulombLorentz pitchangle collisions, or processes that approximate these even for very large values of the collisional time step. An investigation of the analytical solution shows that Nanbu's parameterized kernel is highly accurate for small values of the normalized collision time step, but loses some of its accuracy for larger values of the time step. Finally, a practical collision algorithm is proposed that for smallmassratio Coulomb collisions improves on the accuracy of Nanbu's algorithm. [Preview Abstract] 

S1.00052: A study of minorityion gyroresonance crossing using wave packets Yanli Xiao, E.R. Tracy, A.N. Kaufman We compare the results of raybased and fullwave methods for the problem of mode conversion in nonuniform plasma. The case studied uses the model developed by Ye and Kaufman [1] to treat a magnetosonic wave crossing a cold minorityion gyroresonance layer. We launch a wave packet in the magnetosonic channel and follow its evolution, in order to study the effects of its crossing the layer. This allows us to observe the emission of the reflected wave packet after a time delay (the linear `ioncyclotron echo'), as well as to directly observe the evolution of the minorityion current density. From the fullwave output, we compute the energy density as a function of position and time, and compare it to the raybased predictions. [1] H. Ye and A. N. Kaufman, PhysRevLett 60 (1988) 1642. [Preview Abstract] 

S1.00053: Driftkinetic electron description with lowcollisionality and slowdynamics orderings J.J. Ramos, J.D. Callen, C.C. Hegna An electron driftkinetic formalism is developed, with the aim of obtaining a closure of the fluid equations for slow macroscopic instabilities in lowcollisionality plasmas, including applied RF wave sources. The analysis follows an expansion in the ratio between the ion sound gyroradius and the macroscopic lengths, under a lowcollisionality ordering scheme whereby the ratios between ion collision and cyclotron frequencies and between electron and ion masses are taken as second order. This results in a hierarchy of time scales such that, relative to the ion cyclotron frequency, the electron collision frequency and the MHD frequencies are first order, the ion collision frequency and the diamagnetic drift frequencies are second order, and the transport time scales are third order. Besides, a slowdynamics ordering is assumed, with the macroscopic flows comparable to the diamagnetic drift velocities and the time derivatives comparable to or smaller than the diamagnetic drift frequencies. A new nontrivial result is obtained in the second or diamagnetic drift order. The analysis is carried through the third order, where the main collisional transport effects take place. [Preview Abstract] 

S1.00054: Trapped Particle Instabilities in the Kinetically Stabilized Tandem Mirror J. Pratt, H.L. Berk, W. Horton The kinetically stabilized tandem mirror (KSTM) is an innovative design to stabilize MHD modes in an axially symmetric tandem mirror machine (Post, J. Fus. Energy 2007). Originally proposed by Ryutov (Ryutov, Proc. of Course and Workshop, Varenna, Italy, 1987), this stabilizer has been empirically verified in the Gas Dynamic Trap (Ivanov, Anakeev et.al. Trans. Fusion Technology. 39, 127, 2001). The KSTM uses the momentum flux of escaping particles that sample good magneticfieldlinecurvature region outside the central confinement region. Charged ion beams at relatively low energy are externally injected from the ends into the expander region at an energy that is consistent with a stable MHD prediction and acceptable power loss for fusion. If stable, the KSTM would be extremely useful for limiting radial diffusion since the chaotic step size is minimized. We confirm that MHD stability is achieved in the KSTM. We examine the effect of the trapped particle instability discussed in Berk, Rosenbluth, et al. Sov. J. Plasma Phys. 1983 on overall stability. In this case stability is very sensitive to the electron connection between the stabilizer and the end plug. [Preview Abstract] 

S1.00055: Relevance of High Density Plasma Regimes for Fusion Reactors$*$ F. Bombarda, B. Coppi High density regimes (with peak values around $10^{21} \rm m^{3}$) in magnetically confined plasmas have been observed and investigated within the Alcator program at first, and later within the Frascati Torus program. In particular, record low values of the ion thermal conductivity and high degrees of purity($Z_{eff}\simeq1$) were achieved when peaked density profiles were produced either spontaneously or by the ignition of pellets. It was recognized early on that the large $\it{n}\tau$ values attainable in these regimes are suitable to achieve ignition conditions in devices such as Ignitor that are feasible with existing technologies. Plasma regimes with similar confinement characteristics have been produced in the LHD machine, characterized by relatively low magnetic fields and a helical configuration, by means of repeated pellet injection techniques. Assuming that the good characteristics of these plasmas can be preserved at the temperatures where ignition can occur, the helical configuration characterizing LHD makes it possible to avoid the need of a steady state current drive system, a problem that remains unsolved for meaningful fusion burn regimes with axisymmetric configurations. Experiments on fusion burning plasmas to be developed in parallel along the high field compact line represented by Ignitor and the helical line represented by LHD are envisioned.\\ $*$Sponsored in part by ENEA of Italy and by the U.S. D.O.E. [Preview Abstract] 

S1.00056: Numerical Simulation of Giant Sawteeth in Tokamaks using the NIMROD Code D.D. Schnack, S.E. Kruger, C.R. Sovinec, C. Kim, A.D. Turnbull It is well known that a minority population of energetic particles can stabilize the $n=1$ sawtooth mode in tokamaks even when the onaxis safety factor is well below unity [1]. When destabilized, the resulting crash can lead to degradation of confinement, the generation of NTM and ELMs, and a significant loss of stored energy. Extensive linear studies have been performed recently to analyze the sawtooth activity in DIIID discharge \#96043 through a sequence of equilibria reconstructed from experimantal data [2]. The results were consistent with the observed sawtooth crash. Here we begin a computational study of the nonlinear consequences of the crash of a giant sawtooth using the NIMROD Extended MHD code [3]. Two sets of calculations are considered. The first is a model toroidal equilibrium; the second is the series of equilibrium reconstructions considered in Ref. 2. Initial linear results for both MHD and extended MHD, including energetic particle effects, are presented. 1. R. B. White, P. H. Rutherford, and P. Colestock, Phys. Rev. Letters \textbf{60}, 2038 (1988); D. J. Campbell, D. F. H. Start, J. A. Wesson, et al., Phys. Rev. Letters \textbf{60}, 2148 (1988). 2. M. Choi, A. D. Turnbull, V. S. Chan, et al., Phys. Plasmas \textbf{14}, 112517 (2007). 3. C. R. Sovinec, et al., J. Phys. Conf. Ser. \textbf{16}, 25 (2005). [Preview Abstract] 

S1.00057: Lowdimensional model of fluctuations observed in MCX I. UzunKaymak, P.N. Guzdar, A.B. Hassam, S.H. Choi, C. Teodorescu, R.F. Ellis Magnetic fluctuations in the Maryland Centrifugal eXperiment (MCX) plasma recorded by an azimuthal array of sixteen coils in the edge region of the plasma have indicated that there is primarily convection of a low azimuthal mode number (dominantly m=2) fluctuation by the azimuthally rotating plasma. However the frequency spectrum of this mode is broad and is almost of the same order as the ``rotation'' frequency. Furthermore bicoherence studies indicate a dominant interaction between these modes and a low frequency m=0 mode. Earlier we utilized a 2D (radial and azimuthal) MHD code to investigate the dynamics of the primary interchange instability which can be unstable in a rotating mirror geometry. These studies showed that due to the sheared flow only low mode number interchange modes can be unstable. Here we present results from a Galerkin truncated model for a single unstable interchange mode coupled to zonal flow and quasilinear flattening of the pressure profile yields a system of seven ODEs. This lowdimensional model surprisingly captures many of the observed spatiotemporal features. The broadband frequency spectrum is attributed to the rotating plasma being in a ``chaotic'' state. [Preview Abstract] 

S1.00058: Wall Force in Tokamak Disruptions Henry Strauss, Roberto Paccagnella, Joshua Breslau Disruptions in tokamaks produce forces on conducting structures surrounding a tokamak. These forces are a serious concern for the operation of ITER, especially the toroidally asymmetric forces. We continue numerical resistive MHD studies of disruptions reported previously [1]. The model includes a resistive wall in order to allow the magnetic field to penetrate. We carry out numerical simulations with the M3D [2] code, in which the disruption consists of a vertical displacement event (VDE) combined with an external kink, resistive wall mode, or a pressure driven instability. The radial force exerted by the magnetic field on the wall is proportional to the magnetic pressure difference across the wall. Studies are being carried out to determine how the toroidally asymmetric wall force is related to other features of the disruption, such as the toroidal peaking factor (TPF) and halo current fraction. \par\noindent [1] R. Paccagnella, H. Strauss, J. Breslau, submitted to Nucl. Fusion (2008); B.A.P.S. 53, CP6.00067 (2008) \par\noindent [2] W. Park, E. V. Belova, G. Y. Fu, X. Z. Tang, H. R. Strauss, L. E. Sugiyama, Phys. Plasmas 6, 1796 (1999) [Preview Abstract] 

S1.00059: Unitary Lattice Simulations of Reconnection in Quantum Turbulence George Vahala, Jeffrey Yepez, Linda Vahala, Min Soe A unitary mesoscopic lattice algorithm is developed for the 3D GrossPitaesvkii equation, a Hamiltonian system. The equivalent moment representation is that of an ideal barotropic compressible fluid in which vortex reconnection occurs without viscosity. The internal energy plays an important role in the vortex development. For sufficiently small internal energies, the Hamiltonian system exhibits fast Poincare recurrence time even though there are strong vortex entanglements at intermediate times (c.f., Arnold Cat map). At higher internal energies, the Poincare recurrence time becomes extremely large and on 2880 x 2880 x 2880 grids, the incompressible kinetic energy spectrum exhibits a limited region of Kolmogorov scaling followed by weaker power law for larger k. Vortex loops are born not only from the vortex cores themselves but also from regions between the interacting vortex cores. These loops play a major role in the reconnection. [Preview Abstract] 

S1.00060: Plasmas with High Energy Particles and Relevant Magnetic Reconnection Processes* P. Buratti, B. Coppi Plasma macroscopic modes producing magnetic reconnection with finite frequencies of oscillation that have a phase velocity in the direction of the ion diamagnetic velocity have been identified in collisionless plasmas with strong neutral beam heating produced by the DIIID and the JET machines. Modes with this feature had been proposed$^1$ to account for the observation of ``high$\mathit m$ fishbones'' in plasmas with high energy particle populations$^2$, as they can resonate with the magnetic curvature drift frequencies of these populations. The theoretical model$^1$ introduced for the relevant reconnection layer was based on the presence of a ``finite inductivity'' prevailing over the effects of finite electrical resistivity$^3$. In view of a more recent theory$^4$, the excitation of electron temperature gradient driven modes producing strings of microscopic islands can be considered as a natural candidate to justify the envisioned finite inductivity through the coupling of these microreconnecting modes to the macroscopic modes. *Sponsored in part by ENEA of Italy and in part by the U.S. D.O.E. $^1$B. Coppi, Bull. Am. Phys. Soc. $\bf{45}$, 366 (2000). $^2$K. Toi, $\it et. al.,$ IAEA Fusion Energy 1998, F1CN69EXP1/19. $^3$B. Coppi, $\it{Phys. Fluids}$ $\bf{8}$, 2273 (1965). $^4$B. Coppi, in ``Collective Phenomena in Macroscopic Systems'' pg. 59, Eds. G. Bertin $\it{et.al.,}$ Publ. World Scientific (2007). [Preview Abstract] 

S1.00061: General transport theory for a magnetized plasma in general magnetic geometry JeongYoung Ji, Mukta Sharma, Eric D. Held From linearized general moment equations, general transport equations are derived for a magnetized plasma in general magnetic geometry. The moment equations are not derived from the drift kinetic equation but from the full moment equations~\footnote{J.Y. Ji and E. D. Held, Phys. Plasmas {\bf 15}, 102101 (2008).} with the smallLarmorradius ordering. The transport equations appear in integral form of parallel and perpendicular thermodynamic drives. In the existence of nested flux surfaces, the general transport theory is compared with neoclassical transport theory. The nonlinear couplings of parallel moments to magnetic field gradient and thermodynamic drives are also discussed. [Preview Abstract] 

S1.00062: Edge Electron Heatings by the nonlinear Landau damping John R. Cary, Nong Xiang To heat an overdense plasma, for which the electron plasma frequency is a couple of times of the electron gyrofrequency, it has been proposed that the incident electromagnetic wave can be converted into an electron Bernstein waves (EBW) which does not have a cutoff in plasma, and the EBW will be absorbed at the electron cyclotron resonance in the plasma. In this work, the PIC simulations are conducted to study the nonlinear wave processes near the plasma edge. It is shown that if the incident frequency is larger than the second harmonic electron cyclotron frequency near the upper hybrid resonance (UHR), the incident wave may decay to an electron cyclotron wave whose frequency equals the electron gyrofrequency near the UHR, and an EBW at a lower frequency. As a result, a significant portion of the incident wave power will be absorbed at the plasma edge and electrons are strongly heated. This nonlinear Landau damping could much reduce the electron heating efficiency in the core plasma, and significantly affect the edge plasma properties. [Preview Abstract] 

S1.00063: Plasma Torque and NonAmbipolar Transport Allen Boozer Poloidal symmetry breaking in toroidal plasmas causes a damping of poloidal rotation and toroidal symmetry breaking a damping of toroidal rotation. These torques are transmitted by the magnetic field to the outside world. An upper limit exists on the torque that can be transmitted by a magnetic perturbation. This limit is enforced by shielding asymmetries from the plasma, which can be an important effect for toroidal asymmetries. The torque interaction of plasmas with magnetic fields can be either through an anisotropic pressure or by a drive for magnetic islands. The physics of both types of interactions are considered. Although the magnetic field is essential for transmitting the torque, it does not explicitly appear in the internal torque balance equations. This and other paradoxical effects are clarified. [Preview Abstract] 

S1.00064: Intrinsically Electromagnetic (MicroReconnecting) Modes and Electron Thermal Energy Transport Chris Crabtree, Bruno Coppi The main features of the microreconnecting mode~[1], whose relevant asymptotic limit requires a kinetic description, are i) it has a natural transverse (to the magnetic field) scale distance of the order of $d_e=c/\omega_{pe}$, ii) it produces strings of microscopic magnetic islands, iii) it does not require electron gyroradius effects, iv) it is driven by the transverse electron temperature gradient. The mode is charaterized by $\omega\sim k_{\} v_{te}$, $\omega$ being the mode complex frequency that is of the order of $k_{\perp}cT_e/(eBr_{Te})$, and $1/r_{Te}\equiv ({\rm d}\log T_e/{\rm d}r)$. The implied ordering, $\beta_e\sim 2r_{Te}^2/L_s^2$ where $\beta_e$, the ratio of electron thermal energy density to the magnetic energy density, is regarded as relevant to current experiments such as those carried out by the NSTX device where modes with transverse scale distances of the order of $d_e$ have been identified [2]. The considered mode does not produce an appreciable particle transport while the relevant effective thermal diffusion coefficient $D_{e\perp}^{th}$ is estimated to be of the order of $(d_e/r_{Te})cT_e/(eB)$. This mode, and the trapped electron mode, are the primary candidates to explain the observed anomalous electron thermal energy transport in modern high temperature toroidal plasmas. [1] B. Coppi, in \textit{Collective Phenomena in Macroscopic Systems}, p. 59, \textit{publ.} World Scientific (2007). [2] E. Mazzucato, R. E. Bell, J. C. Hosea, {\it et al.}, \textit{Am. Phys. Soc.}, \textbf{52}, 61 (2007). [Preview Abstract] 

S1.00065: Tests of quasilinear and tracer transport with gyrokinetic simulations R.E. Waltz, G.M. Staebler, A. Casati The GYRO gyrokinetic code tests the quasilinear transport approximation (QLTA) with a simulated nonlinear spectral intensity. There are two common forms of the QLTA which either use (1) the linear mode spectrum or (2) the complete frequency spectrum for the nonlinear spectral intensity. The first is tested via twostep linear then nonlinear simulations convoluting the quasilinear and nonlinear field intensity spectral weights, and the second via onestep simulations which have ion and electron ``plasma species'' at full and ``tracer species'' negligible densities. If the tracer and plasma gyrokinetic equations are identical, then so are their respective energy and particle diffusivities. Comparing tracer and plasma diffusivities when the tracer equation nonlinearity is deleted provides a quantifiable test of the second QLTA form. The twostep test preserves ambipolarity but includes only the leading linear modes at each wave number. Net quasilinear energy diffusivities are typically 1.41.8 larger and QLTA appears to breakdown most evidently for strongly pinched particle flows. [Preview Abstract] 

S1.00066: Lattice Boltzmann representations for MHD Turbulence Tao Wang, George Vahala, Linda Vahala Lattice Boltzmann (LB) representations are mesoscopic algorithms that exploit a simple collidestream scheme that is ideal for parallelization  even for nonperiodic boundary conditions. Moreover, in LB one can enforce $\nabla \cdot {\rm {\bf B}}=0$ to machine accuracy. Typically one has introduced a vector distribution function for the magnetic field to account for the asymmetry tensor in the magnetic field evolution as opposed to the symmetric stress tensor in velocity evolution. Here we investigate 2D MHD turbulence by working with a scalar magnetic distribution function representation. A major advantage of the scalar representation is the much reduced computational memory requirements, as well as simpler boundary condition enforcement. The OrszagTang vortex will be examined as well as some LES closure schemes using Elsasser variables. [Preview Abstract] 

S1.00067: Developing Validation Metrics for Simulations of Plasma Turbulence C. Holland, G.R. Tynan, G.R. McKee, M.W. Shafer, A.E. White, T.L. Rhodes, L. Schmitz, R. Prater, J.C. DeBoo, J. Candy, R.E. Waltz Robust model validation efforts require the use of metrics for quantifying the skill or fidelity of a given model in reproducing experimental results [1]. In this work, we propose a variety of different metric forms for evaluating the fidelity of gyrokinetic models of driftwave turbulence. The metrics are applied to GYRO simulations of DIIID Lmode plasmas at multiple radial locations, including data from a recent elongation scaling experiment. The relative performance of global and local GYRO fixedgradient simulations, as well as TGYRO fixedflux simulations, will be quantified. In addition, the impact of using an upgraded magnetic geometry interface for GYRO will be reported. Initial work on ensemble simulation algorithms for propagating experimental profile uncertainties through these turbulence models is also discussed. \par\vskip3pt\noindent [1] P.W. Terry et al., Phys. Plasmas 15 (2008) 062503. [Preview Abstract] 

S1.00068: Geodesic Acoustic Modes Induced by Energetic Particles Tianchun Zhou, Herbert Berk A global geodesic acoustic mode driven by energetic particles (EGAM) has been observed in JET[1, 2] and DIII D[3, 4]. The mode is to be treated fully kinetically. The descriptions of the background electrons and ions are based on standard high and low bounce frequency expansion respectively with respect to the mode frequency. However, the energetic ions must be treated without any expansion of ratio between their bounce frequency and the mode frequency since they are comparable. Under electrostatic perturbation, we construct a quadratic form for the wave amplitude, from which an integrodifferential equation is derived. In the limit where the drift orbit width is small comparison with the mode width, a differential equation for perturbed electrostatic field is obtained. Solution is obtained both analytically and numerically. We find that beam counterinjection enhances the instability of the mode [Preview Abstract] 

S1.00069: Gyrokinetic Simulation of Energetic Particles Turbulence and Transport in Fusion Plasmas Wenlu Zhang, Zhihong Lin, Ihor Holod, Yong Xiao, Andreas Bierwage, Donald Spong, Ming Chu The confinement of the energetic particles (EP) is a critical issue in the International Thermonuclear Experimental Reactor (ITER), since that ignition relies on the selfheating by the fusion products. Shear Alfven wave excitations by EP in toroidal systems, for example Toroidal Alfven Eigenmode (TAE) and Energetic Particle Mode (EPM) have been investigated as primary candidate for fluctuationinduced transport of EP in fusion plasma. In this work, TAE excitations by energetic particles are investigated in large scale firstprinciple simulations of fusion plasmas using the global gyrokinetic toroidal code (GTC) [Lin, Science 1998]. Comprehensive linear benchmarking results are reported between GTC, GYRO, fluid code TAEFL, and Magnetohydrodynamicgyrokinetic hybrid code HMGC. [Preview Abstract] 

S1.00070: Numerical Modeling of NBIdriven GAE modes E.V. Belova, N.N. Gorelenkov, E.D. Fredrickson Hybrid 3D code HYM is used to investigate beam ion effects on MHD modes in NSTX, aiming at simulations of NSTX shots where chirping frequency GAE/CAE modes have been observed. The thermal plasma is modeled using the MHD equations, and fullorbit deltaf kinetic description is used for the beam ions. For large neutral beam injection velocities and strong anisotropy in the pitchangle distribution, many Alfven modes are excited. The resonant particles satisfy Dopplershifted cyclotron resonant conditions. Growth rates of global Alfven eigenmodes (GAEs) are sensitive to details of the distribution function, in particular, the pitch angle distribution. Most unstable mode in HYM simulations compares well with experimental results for NSTX. Nonlinear simulations show that GAE instabilities saturate at low amplitudes due to particle trapping. The saturation amplitude is proportional to the square of the linear growth rate, except for the marginally unstable cases. The magnetic perturbations have shear Alfven polarization in the core, however the compressional component dominates at the edge, indicating possible coupling to the edgelocalized CAE modes. [Preview Abstract] 

S1.00071: Onaxis ideal internal kink modes in RFPs V.V. Mirnov, G. Fiksel Large scale, currentdriven, resistive MHD tearing modes are believed to determine the dynamics of the Reversed Field Pinch (RFP) operation. Ideal MHD modes are supposed to be stabilized by a strong magnetic shear and a close proximity of a highly conducting chamber wall. However, for a specific case of ideal internal cylindrical kink modes with the rational surfaces located at or near the axis of the cylinder the stabilizing effects of the magnetic shear and the conducting wall are significantly reduced. The possibility of destabilization of the onaxis ideal modes has been predicted in the past for the RFP plasma$^{1,2}$. We revisit and extend this problem by developing a nonstationary theory of onaxis ideal modes which can be applicable to experimentally observed sawtooth variations of the mean magnetic field in the Madison Symmetric Torus RFP experiment. The interrelationship between theoretical and experimental results is discussed. [1] D. C. Robinson, Nuclear Fusion, \textbf{18}, 7 (1978). [2] S. Ortolani, D. D. Schnack, ``\textit{Magnetohydrodynamics of Plasma Relaxation''}, World Scientific Publishing Co., Singapore (1993). [Preview Abstract] 

S1.00072: Theory of the residual stress and the origins of intrinsic Chris McDevitt, Patrick Diamond, Ozgur Gurcan, T.S. Hahm We present recent results in the theory of turbulent momentum transport pertinent to the description of intrinsic rotation. A minimal model of intrinsic rotation is developed for Hmode plasmas based on an extended LH mode bifurcation model [1]. The primary novel components introduced into this model are a residual stress [2,3] (i.e. the portion of the momentum flux not proportional to $v_\phi$ or $v^\prime_\phi$) and a turbulent equipartition pinch [4]. This reduced model reproduces salient features of the ITPA Hmode database [5]. Furthermore, a quasilinear analysis of a phase space conserving gyrokinetic equation is utilized to identify a novel mechanism by which microturbulence may spinup a plasma from rest, in addition to the $\mathbf{E}\times\mathbf{B}$ shear driven mechanism discussed in Refs. [2,3]. This mechanism, which appears in the gyrokinetic formulation through the parallel nonlinearity, emerges due to charge separation induced by the polarization drift, and is not tied to $\mathbf{E} \times\mathbf{B}$ shear. Thus, this mechanism is likely relevant in regimes of weak $\mathbf{E}\times\mathbf{B}$ shear. [1] F. L. Hinton, Phys. Fluids B 3, 696 (1991), [2] O. D. Gurcan et al. Phys. Plasmas 14, 042306 (2007), [3] Dominguez et al. Phys. Fluids B 5, 3876 (1993), [4] T.S. Hahm et al. Phys. Plasmas 14, 072302 (2007), [5] J. E. Rice et al. Nucl. Fusion 47, 1618 (2007). [Preview Abstract] 

S1.00073: Relativistic Thomson scattering including depolarization E.B. Parke, V.V. Mirnov, D.J. Den Hartog Several analytic relativistic approximations that include the depolarization term have been derived for the Thomson scattered spectrum [K. V. Beausang and S. L. Prunty, Plasma Phys. Control. Fusion \textbf{50}, 095001 (2008)]. In general, the simplifying assumption is made that the detector of the scattered radiation collects only the component of the electric field along the direction of the incident wave electric field. This assumption is not valid for the Thomson scattering diagnostic system on the Madison Symmetric Torus (MST) reversedfield pinch, which collects all polarizations and is able to measure radiation scattered from highlyrelativistic electrons (Te $\ge $ 10 keV). We present relativistic analytic extrapolations derived for this case and analyze their accuracy. The results are of particular importance for analysis of data from the MST Thomson scattering diagnostic, as it is being extended to high repetition rate and will produce a large amount of Thomson scattered spectra for every MST shot. This data must be analyzed both quickly (with minimal computational resources) and accurately (correct measurement of the actual electron temperature). [Preview Abstract] 

S1.00074: Progress in kinetic MHD simulation of magnetic reconnection in Harris sheet equilibrium Jianhua Cheng, Yang Chen, Scott E. Parker We have previously developed a Lorentz force ion, fluid electron kinetic MHD hybrid model [D. Barnes, \emph{et al}, Phys. Plasmas {\bf{15}}, 055702 (2008)]. This model has been extended to gyrokinetic electrons. Here we focus on the implementation of an isothermal fluid electron model in the GEM turbulence code. A secondorder accurate implicit scheme that generalizes the previous implicit scheme for Vlasov ions and drift kinetic electrons [Chen and Parker, submitted] has been implemented. The generalized Ohm's law is solved for the Harris sheet equilibrium configuration by Fourier decomposing the electric field along the equilibrium field and solving for each Fourier component in the direction perpendicular to the current sheet using direct matrix inversion. This presentation focuses on the simulation of Alfv\'en waves, ion sound waves and the Whistler waves in a slab. Preliminary results for the 1D Harris sheet equilibrium with a guide field will be reported. [Preview Abstract] 

S1.00075: Neoclassical Ion Heat Transport in a Tokamak Pedestal Grigory Kagan, Peter J. Catto A strong electric field is inherent to a subsonic banana regime pedestal in a tokamak. This field changes the ion trapping condition, thereby modifying the neoclassical heat transport. In conventional theory the main contribution to the collisional heat flux comes from trappedpassing transitions across a boundary that is a cone centered at the origin in velocity space so that these transitions are due only to the pitchangle scattering component of the collision operator. In the pedestal this boundary is shifted away from the origin and becomes curved due to the strong electric field and finite ion drift departures from flux surfaces [1]. Consequently, a more complete collision operator must be employed that retains the trappedpassing transitions in a transparent manner so that ion neoclassical heat transport can be evaluated in the pedestal with finite orbit effects retained. In this work we employ such a collision operator and apply it to evaluate the banana regime neoclassical ion heat flux in the pedestal region of a tokamak. \textbf{References} 1 G. Kagan, P.J. Catto, Plasma Phys. Controlled Fusion 50, 085010 (2008) [Preview Abstract] 

S1.00076: Linear 3D Toroidal TwoFluid Stability Calculations Using M3D$C^{1}$ S. Jardin, J. Breslau, M. Chance, J. Chen, N. Ferraro, X. Luo, K. Jansen, M. Shephard The M3D$C^{1}$ code is a twofluid toroidal magnetohydrodynamic code based on highorder, compact finite elements with $C^{1}$ continuity on an unstructured adaptive trianglebased grid. The code is built upon many of the favorable features of the M3D approach to solving the MHD equations in a highly magnetized toroidal plasma. The vector fields use a physicsbased decomposition, allowing for two energyconserving subsets of the full equations (reduced MHD). The efficient splitimplicit time advance is closely related to the ideal MHD energy principle, and allows time steps several orders of magnitude in excess of the Courant condition based on the Alfven or whistler waves. The present emphasis is on benchmark calculations for the linearized two fluid MHD equations in 3D toroidal geometry. The computational model has a physically based resistivity profile such that the Lundquist number S varies from 10$^{8}$ in the plasma to $\sim $ 10$^{0}$ in the surrounding `vacuum' region. Special adaptive meshing algorithms allow high resolution in the resistivity rapid transition region and around mode rational surfaces. Comparisons are made with ideal MHD (PESTI) and resistive MHD (PESTIII) codes and the dependence of growth rates on dissipative parameters is presented. This work was supported by U.S. DoE contract DEAC0276CH03073. [Preview Abstract] 

S1.00077: Estimation of Electron Bernstein Emission in the TJII Stellarator J.M. Garc\'IaRega\~na, A. Cappa, F. Castej\'on, M. Tereshchenko In order to study experimentally the viability of first harmonic EBW heating in the TJII stellarator by means of the OXB tecnique [1], an EBE diagnostic was recently installed [2]. In the present work a theoretical estimation of the EBW radiation in the TJII plasmas have been carried out making use of the ray tracing code TRUBA [3]. The line of sight of the EBE diagnostic may be modified using an internal movable mirror and therefore, for comparison with the experimental results, the theoretical OXB emission window has been determined. Experimental density and temperature profiles obtained in NBI discharges are considered in the simulations.\\ \textbf{References:}\\ $\left[1\right]$ F. Castejon {\it et al}, \textit{Nucl. Fusion} {\bf 48}, 075011 (2008).\\ $\left[2\right]$ J. Caughman {\it et al}, \textit{Proc. 15th Joint Workshop on ECE and ECRH}, Yosemite, USA (2008).\\ $\left[3\right]$ M. A. Tereshchenko {\it et. al}, {\it Proc. 30th EPS Conference on Contr. Fusion and Plasma Phys.}, {\bf 27A}, P1.18 (2003). [Preview Abstract] 

S1.00078: Gyrokinetic Studies of ETG Turbulence in NSTX, and Comparisons of Advection Algorithms G.W. Hammett, J.L. Peterson, D.R. Mikkelsen, S.M. Kaye, R.E. Waltz, J. Candy Electron temperature gradient (ETG) driven turbulence has been predicted to be important in some parameter regimes\footnote{W. Dorland, F. Jenko, et al., Phys.\ Rev.\ Lett.\ {\bf 85}, 5579 (2000)}. Highk fluctuations have recently been measured\footnote{E. Mazzucato, D. R. Smith, et al., Phys.\ Rev.\ Lett. {\bf 101}, 075001 (2008)} in the National Spherical Torus Experiment (NSTX), at $k_\theta \rho_e \sim 0.10.4$, in the range of ETG turbulence. We are undertaking studies of ETG turbulence for NSTX cases using the GYRO gyrokinetic code. Among other results, we will show the dependence of some of the linear ETG properties on magnetic shear, $q$, and $Z_{eff} T_e/T_i$. Microtearing may also be important in some cases. On another topic, we will compare various advection algorithms on simple 1D and 2D test problems. The edge region in a magnetic fusion device has very steep density variations, which can cause problems for standard advection algorithms. Gibb's phenomena can lead to negative overshoots in the density solution; however, modern highorder upwind methods, developed initially for shock capturing, can preserve positivity of density, making them useful for edge gyrokinetic simulations. [Preview Abstract] 

S1.00079: Stability of a Tokamak Plasma's Edge Anthony Webster The edge of tokamak plasmas strongly affects the plasma's confinement, and can be subject to edgelocalised instabilities with the potential to erode plasma facing components in large tokamaks such as ITER. Therefore it would be helpful to be able to control the edge plasma properties as fully as possible, so as to maximise confinement while avoiding damaging instabilities. Surprisingly however, whereas the complicated plasma geometry associated with a separatrix has slowed progress towards a full understanding of a tokamak plasma's edge stability, there are seemingly well understood examples of ideal Magnetohydrodynamic (MHD) instabilities that provide the opportunity for techniques to be developed to control the edge plasma's properties  and as a likely consequence, the properties of its edge stability, confinement, and ELMs. Although our understanding of ideal MHD stability near a separatrix is becoming relatively mature (A.J. Webster {\&} C.G.Gimblett, Phys. Rev. Lett. in press), the description appears incomplete, as will be discussed. Nonetheless, our current understanding of plasma stability is sufficient to suggest simple methods (A.J. Webster, Phys. Plasmas. \textbf{16}, 012501, 2009), that in principle allow us to control the plasma's edge pressure gradient (as an example), and potentially the properties and consequences of ELMs. Such experiments should at least allow a greater understanding of the plasma's edge to be obtained. [Preview Abstract] 

S1.00080: Plasma Response to External Magnetic Perturbations M.S. Chu, L.L. Lao, M.J. Schaffer, T.E. Evans, Y.Q. Liu, M.J. Lanctot, H. Reimerdes Plasma response to an external perturbation is formulated as minimization of the total free energy of the plasma and the external coils [1]. For tokamaks, this minimization is achieved by directly solving the resultant Euler equations using the MARSF code [2] without resorting to the virtual casing principle. Neglecting the plasma response resulted in the vacuum response previously computed by the Surfmn code [3]. The vacuum response can be computed independently by using an analytic method. Results from MARSF and Surfmn are found to give excellent agreement with that obtained by the analytic method. For ideal plasma, the total perturbation field in the plasma results from the plasma response in addition to that of the vacuum field. Depending on the coil arrangement, plasma response could be dominated by the resonant or nonresonant components.\\[4pt] [1] M.S. Chu, et al., Nucl. Fusion \textbf{43} (2003) 441.\\[0pt] [2] Y.Q. Liu, et al., Phys. Plasmas \textbf{7} (2000) 3681.\\[0pt] [3] M.J. Schaffer, et al., Nucl. Fusion \textbf{48} (2008) 024004. [Preview Abstract] 
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