Bulletin of the American Physical Society
56th Annual Meeting of the APS Division of Plasma Physics
Volume 59, Number 15
Monday–Friday, October 27–31, 2014; New Orleans, Louisiana
Session BP8: Poster Session I: MHD, Energetic Particles, Predictive Modeling, Plasma Surface Interactions; Diagnostic Measurements & Analysis; NonNeutral, AntiMatter & Strongly Coupled Plasmas; Plasma Technology 
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Room: Preservation Hall 

BP8.00001: MHD, ENERGETIC PARTICLES, PREDICTIVE MODELING, PLASMA SURFACE INTERACTIONS 

BP8.00002: Expansion of a MHD equilibrium About a Magnetic Axis Harold Weitzner Earlier work, Phys. Plasmas, 21,022515 (2014) showed that a formal expansion of a nonsymmetric ideal MHD equilibrium in a topological torus was possible to all orders the parameter corresponding to the amplitude of the ``helical'' field components. Selected field components were not arbitrary, but had to be chosen appropriately. This analysis did not allow the toroidal domain in which the expansion was carried out to include a magnetic axis. The present work examines the nature of nonsymmetric equilibria in the neighborhood of a magnetic axis in a topological toroidal domain. An expansion is carried out in the distance from the magnetic axis for two simple cases. In the first the axis is a straight line, and in the second the axis is a space curve. The expansions to all orders are carried out and conditions for the expansions to exist are given. Again for selected cases equilibria appear possible. [Preview Abstract] 

BP8.00003: Magnetic flux coordinates for highbeta tokamak equilibria with flow Atsushi Ito , Noriyoshi Nakajima Magnetic flux coordinates are useful for the study of stability of toroidal plasmas. A set of the magnetic flux coordinates are constructed from an analytic solution for the reduced magnetohydrodynamic equilibrium equations for highbeta tokamaks in the presence of toroidal and poloidal flows comparable to the poloidal sound velocity. The set of magnetic flux coordinates are found by solving the algebraic equations for the relation between the cylindrical and magnetic flux coordinates that are obtained by extending those for the static equilibria. As an application, the pressure profile in the magnetic coordinates is examined. The poloidal profiles of the pressure on each constant radial coordinate show that the pressure maxima are located in the outer midplane for subsonic poloidal flow and in the inner midplane for supersonic poloidal flow. The flux surface average of the pressure does not strongly depend on the poloidal flow velocity, but it is peaked near the magnetic axis for subsonic poloidal flow while it is broad for supersonic poloidal flow, compared with that for the static equilibrium. [Preview Abstract] 

BP8.00004: Theory and computation of general force balance in nonaxisymmetric tokamak equilibria JongKyu Park , Nikolas Logan , Zhirui Wang , Kimin Kim , Allen Boozer , Yueqiang Liu , Jonathan Menard Nonaxisymmetric equilibria in tokamaks can be effectively described by linearized force balance. In addition to the conventional isotropic pressure force, there are three important components that can strongly contribute to the force balance; rotational, anisotropic tensor pressure, and externally given forces, i. e. $\vec{{\nabla }}p+\rho \vec{{v}}\cdot \vec{{\nabla }}\vec{{v}}+\vec{{\nabla }}\cdot \mathord{\buildrel{\lower3pt\hbox{$\scriptscriptstyle\leftrightarrow$}}\over {\Pi }} +\vec{{f}}=\vec{{j}}\times \vec{{B}}$, especially in, but not limited to, high $\beta $ and rotating plasmas. Within the assumption of nested flux surfaces, Maxwell equations and energy minimization lead to the modifiedgeneralized Newcomb equation for radial displacements with simple algebraic relations for perpendicular and parallel displacements, including an inhomogeneous term if any of the forces are not explicitly dependent on displacements. The general perturbed equilibrium code (GPEC) solves this force balance consistent with energy and torque given by external perturbations. Local and global behaviors of solutions will be discussed when $\vec{{\nabla }}\cdot \mathord{\buildrel{\lower3pt\hbox{$\scriptscriptstyle\leftrightarrow$}}\over {\Pi }} $ is solved by the semianalytic code PENT and will be compared with MARSK. Any firstprinciple transport code calculating $\vec{{\nabla }}\cdot \mathord{\buildrel{\lower3pt\hbox{$\scriptscriptstyle\leftrightarrow$}}\over {\Pi }} $ or $\vec{{f}}$, e. g. POCA, can also be incorporated without demanding iterations. This work was supported by DOE Contract DEAC0209CH11466. [Preview Abstract] 

BP8.00005: Improving the quality of the experimental reconstructions as the initial equilibrium state for the NIMROD code Jacob King , Scott Kruger High quality equilibria are essential for extendedMHD modeling with the initialvalue NIMROD code [Sovinec et al., JCP 195, 355 (2004)]. Typically the spatial resolution requirements for extendedMHD modeling, which must resolve singularlayer physics and highly anisotropic diffusion, are more stringent than the resolution of equilibrium reconstructions from experimental discharges. With the current workflow, reconstructed fields are mapped onto the NIMROD finiteelement grid, and the disparity between the coarse resolution reconstruction and the fine resolution FE grid can create artificial smallscale artifacts. ExtendedMHD modeling, which contains many highorder differential operators, can be corrupted by the mapping errors. We describe efforts to resolve the GradShafranov equation with openflux regions using the NIMEQ solver [Howell and Sovinec, CPC 185, 1415 (2014)] to generate a new equilibrium while using the mapped results for both an initial guess and to specify the boundary conditions. Effects on computations with and without the resolving for force balance will be described. [Preview Abstract] 

BP8.00006: Inclusion of parallel fluid flow in the KITES 3D MHD equilibrium code Daniel Raburn The KITES (Kyoto ITerative Equilibrium Solver) code is being developed for the calculation of flowing MHD (magnetohydrodynamic) equilibria in nonsymmetric devices. [Daniel Raburn and Atsushi Fukuyama, Plasma and Fusion Research: Regular Articles, 7:240381 (2012).] An update on the code is presented, including preliminary results on the calculation of equilibria with purely parallel flow. [Preview Abstract] 

BP8.00007: Effects of density gradient caused by multipulsing CHI on twofluid flowing equilibria of spherical torus plasmas T. Kanki , M. Nagata Twofluid dynamo relaxation is examined to understand sustainment mechanism of spherical torus (ST) plasmas by multipulsing CHI (MCHI) in the HIST device. The steeper density gradient between the central open flux column (OFC) and closed flux regions by applying the second CHI pulse is observed to cause not only the \textbf{\textit{E}}x\textbf{\textit{B}} drift but also the ion diamagnetic drift, leading the twofluid dynamo. The purpose of this study is to investigate the effects of the steep change in the density gradient on the ST equilibria by using the twofluid equilibrium calculations. The toroidal magnetic field becomes from a diamagnetic to a paramagnetic profile in the closed flux region while it remains a diamagnetic profile in the OFC region. The toroidal ion flow velocity is increased from negative to positive values in the closed flux region. Here, the negative ion flow velocity is the opposite direction to the toroidal current. The poloidal ion flow velocity between the OFC and closed flux regions is increased, because the ion diamagnetic drift velocity is changed in the same direction as the\textbf{\textit{ E}}x\textbf{\textit{B}} drift velocity through the steeper ion pressure gradient. As a result, the strong shear flow and the paramagnetic toroidal field are generated in the closed flux region. Here, the ion flow velocity is the same direction as the poloidal current. The radial electric field shear between the OFC and closed flux regions is enhanced due to the strong dependence on the magnetic force through the interaction of toroidal ion flow velocity and axial magnetic field. The twofluid effect is significant there due to the ion diamagnetic effect. [Preview Abstract] 

BP8.00008: The observation of Synchronous Oscillation prior to Disruption in the HL2A tokamak Di Hu An evident class of MHD activities before disruption has been observed during the density limit induced disruptions of the HL2A tokamak discharge. It is named ``SOD,'' the Synchronous Oscillations prior to Disruption, which is characterized by the synchronous oscillations between ECE signal, the core SXR signal, Mirnov signal, and H line radiation crossing the divertor region. It is observed in the parameter regime which typically corresponds to radiationinduced disruptions. It is also found that during SODs, most of the plasma current is enclosed within the q=2 surface, making the resistive kink mode instable. It has been found that the 2/1 mode and its higher order harmonics are dominant during SODs, and it is the decrease of mode frequency and the final mode locking that leads to the disruptions. The electron temperature perturbation structure shows that plasma is dominant by resistivekink with gradual phase shift in the core plasma region and a single island in the cool, highly resistive boundary layer. There is little indication of the existence of multihelicities islands prior to the disruption. This suggests that it is the nonlinear growth of this 2/1 kink and its higher order harmonics, rather than the overlapping of multiple islands, ultimately triggered disruption. [Preview Abstract] 

BP8.00009: Hiro and Evans currents in Vertical Disruption Event Leonid Zakharov The notion of Tokamak MagnetoHydrodynamics (TMHD), which explicitly reflects the anisotropy of a high temperature tokamak plasma is introduced. The set of TMHD equations is formulated for simulations of macroscopic plasma dynamics and disruptions in tokamaks. Free from the Courant restriction on the time step, this set of equations is appropriate for high performance plasmas and does not require any extension of the MHD plasma model. At the same time, TMHD requires the use of magnetic field aligned numerical grids. The TMHD model was used for creation of theory of the Wall Touching Kink and Vertical Modes (WTKM and WTVM), prediction of Hiro and Evans currents, design of an innovative diagnostics for Hiro current measurements, installed on EAST device. While Hiro currents have explained the toroidal asymmetry in the plasma current measurements in JET disruptions, the Evans currents explain the tile current measurements in tokamaks. The recently developed Vertical Disruption Code (VDE) have demonstrated 5 regimes of VDE and confirmed the generation of both Hiro and Evans currents. {\bf\em The results challenge the 24 years long misinterpretation of the tile currents in tokamaks as ``halo'' currents, which were a product of misuse of equilibrium reconstruction for VDE}. [Preview Abstract] 

BP8.00010: Separation of Evans and Hiro currents in VDE of tokamak plasma Sergei A. Galkin , V.A. Svidzinski , L.E. Zakharov Progress on the Disruption Simulation Code (DSC3D) development and benchmarking will be presented. The DSC3D is onefluid nonlinear timedependent MHD code, which utilizes fully 3D toroidal geometry for the first wall, pure vacuum and plasma itself, with adaptation to the moving plasma boundary and accurate resolution of the plasma surface current. Suppression of fast magnetosonic scale by the plasma inertia neglecting will be demonstrated. Due to code adaptive nature, selfconsistent plasma surface current modeling during nonlinear dynamics of the Vertical Displacement Event (VDE) is accurately provided. Separation of the plasma surface current on Evans and Hiro\footnote{L.E. Zakharov, Phys. Plasmas, 15, 062507 (2008)}$^,$\footnote{L.E. Zakharov, S.A. Galkin, S.N. Gerasimov, Phys. Plasmas 19, 055703 (2012)} currents during simulation of fully developed VDE, then the plasma touches invessel tiles, will be discussed. [Preview Abstract] 

BP8.00011: Simulations of vertical disruptions with VDE code: Hiro and Evans currents Xujing Li The recently created numerical code VDE for simulations of vertical instability in tokamaks is presented. The numerical scheme uses the Tokamak MHD model, where the plasma inertia is replaced by the friction force, and an adaptive grid numerical scheme. The code reproduces well the surface currents generated at the plasma boundary by the instability. Five regimes of the vertical instability are presented: \begin{enumerate} \item Vertical instability in a given plasma shaping field without a wall; \item The same with a wall and magnetic flux $\Delta\Psi^{X}_{pl}<\Delta\Psi^{wall}_{X}$ (where $X$ corresponds to the Xpoint of a separatrix); \item The same with a wall and magnetic flux $\Delta\Psi^{X}_{pl}>\Delta\Psi^{wall}_{X}$; \item Vertical instability without a wall with a tile surface at the plasma path; \item The same in the presence of a wall and a tile surface. \end{enumerate} The generation of negative Hiro currents along the tile surface, predicted earlier by the theory and measured on EAST in 2012, is wellreproduced by simulations. In addition, the instability generates the forcefree Evans currents at the free plasma surface. {\bf The new pattern of reconnection of the plasma with the vacuum magnetic field is discovered.} [Preview Abstract] 

BP8.00012: Surface Currents during a Major Disruption P. Bolgert , C.S. Ng , J. Breslau , A. Bhattacharjee Understanding the surface current on the plasmavacuum interface during a disruption event is important for predicting the subsequent evolution of the instability and its interaction with the wall, with serious implications for ITER. Even in the linear regime, these surface currents are controversial and poorly understood, with disagreements over both their nature and sign. Previously, most analytical studies have used stepfunction background plasma profiles, for example, the linearized reduced MHD disruption model of Strauss et al. (PoP 17, 082505 (2010)). In this study we extend that model by replacing stepfunction profiles with more realistic profiles characterized by a strong but finite gradient along the radial direction. It is found that the resulting ``surface current'' is localized in the region of strong gradient but can also have an internal structure with peaks of both signs. We benchmark our results using the M3D code, finding quantitative agreement in the structure of the currents as well as the kink mode growth rate. The role of plasma resistivity in these simulations is explained. We also present preliminary M3D results showing the nonlinear evolution of these surface currents. [Preview Abstract] 

BP8.00013: Wall touching kink mode calculations with the M3D code J.A. Breslau In recent years there have been a number of results published [13] concerning the transient vessel currents and forces occurring during a tokamak VDE, as predicted by simulations with the nonlinear MHD code M3D [4]. The nature of the simulations is such that these currents and forces occur at the boundary of the computational domain, making the proper choice of boundary conditions critical to the reliability of the results. The M3D boundary condition includes the prescription that the normal component of the velocity vanish at the wall. It has been argued [5] that this prescription invalidates the calculations because it would seem to rule out the possibility of advection of plasma surface currents into the wall. This claim has been tested by applying M3D to an idealized case  a kinkunstable plasma column  in order to abstract the essential physics from the complications involved in the attempt to model real devices. While comparison of the results is complicated by effects arising from the higher dimensionality and complexity of M3D, we have verified that M3D is capable of reproducing both the correct saturation behavior of the free boundary kink and the ``Hiro'' currents arising when the kink interacts with a conducting tile surface interior to the ideal wall. [1] H.R. Strauss, R. Paccagnella, and J. Breslau, \textit{Phys. Plasmas} \textbf{17}, 082505 (2010). [2] H. Strauss, R. Paccagnella, J. Breslau, L. Sugiyama, and S. Jardin, \textit{Nucl. Fus}. \textbf{53}, 073018 (2013). [3] H. Strauss, L. Sugiyama, R. Paccagnella, J. Breslau, and S. Jardin, \textit{Nucl. Fus}. \textbf{54}, 043017 (2014). [4] W. Park, \textit{et al}, \textit{Phys. Plasmas} \textbf{6, }1796 (1999). [5] L.E. Zakharov, Phys. Plasmas \textbf{17}, 124703 (2010). [Preview Abstract] 

BP8.00014: Toroidal current asymmetry and boundary conditions in disruptions Henry Strauss It was discovered on JET [1] that disruptions were accompanied by toroidal asymmetry of the plasma current. The toroidal current asymmetry $\Delta I_\phi$ is proportional to the vertical current moment $\Delta M_{IZ},$ with positive sign for an upward vertical displacement event (VDE) and negative sign for a downward VDE. It was claimed [2] that this could only be explained by Hiro current. It is shown that instead it is essentially a kinematic effect produced by the VDE displacement of a 3D magnetic perturbation. This is verified by M3D simulations. The simulation results do not require penetration of plasma into the boundary, as in the Hiro current model [2]. It is shown that the normal velocity perpendicular to the magnetic field vanishes at the wall, in the small Larmor radius limit of electromagnetic sheath boundary conditions [3]. Plasma is absorbed into the wall only via the parallel velocity, which is small, penetrates only an infinitesimal distance into the wall, and does not affect forces exerted by the plasma on the wall.\\[4pt] [1] S.N. Gerasimov et al. Nucl. Fusion \textbf{54} 073009 (2014). \break [2] L. E. Zakharov, Phys. Plasmas \textbf{15} 062507 (2008). \break [3] H. R. Strauss, Physics of Plasmas \textbf{21}, 032506 (2014). [Preview Abstract] 

BP8.00015: Plasma surface and wall eddy currents and their connection to Halo currents during disruptions in tokamaks Vadim Yanovskiy , Roberto Paccagnella The behaviour of plasma surface currents and resistive wall eddy currents is analysed analytically within a cylindrical model for pressureless ideal plasma with flat and parabolic equilibrium current profiles. This mimics possible conditions in tokamak plasmas during disruptions between the thermal and the current quench phases. Earlier studies [1, 2] predict that plasma surface currents have to be taken into account for explanation of the Halo currents intensity and distribution. Our results show that this is true only in a very narrow window of edge safety factor $q_{a} $ and that in a wide region of $q_{a} $ the wall eddy currents are comparable or much larger than the plasma skin currents. The study reveals ranges of plasma and wall parameters for which the surface currents could play a role in Halo currents dynamics. Some comparison of the results with previous works [1, 2] on this topic is also presented. \\[4pt] [1] Zakharov L 2008 \textit{Phys. Plasmas} \textbf{15} 062507\\[0pt] [2] Zakharov L 2011 \textit{Phys. Plasmas} \textbf{18} 062503 [Preview Abstract] 

BP8.00016: Initial Computations of Vertical Displacement Events with NIMROD Kyle Bunkers , C.R. Sovinec Disruptions associated with vertical displacement events (VDEs) have potential for causing considerable physical damage to ITER and other tokamak experiments. We report on initial computations of generic axisymmetric VDEs using the NIMROD code [Sovinec, $\textit{et. al.}$, JCP \textbf{195}, 355 (2004)]. An implicit thinwall computation has been implemented to couple separate internal and external regions without numerical stability limitations. A simple rectangular crosssection domain generated with the NIMEQ code [Howell and Sovinec, CPC (2014)] modified to use a symmetry condition at the midplane is used to test linear and nonlinear axisymmetric VDE computation. As current in simulated external coils for large$R/a$ cases is varied, there is a clear $n=0$ stability threshold which lies below the decayindex criterion for the currentloop model of a tokamak to model VDEs [Mukhovatov and Shafranov, Nucl. Fusion \textbf{11}, 605 (1971)]; a scan of wall distance indicates the offset is due to the influence of the conducting wall. Results with a vacuum region surrounding a resistive wall will also be presented. Initial nonlinear computations show large vertical displacement of an intact simulated tokamak. [Preview Abstract] 

BP8.00017: 3D MHD Simulations of Tokamak Disruptions Simon Woodruff , James Stuber Two disruption scenarios are modeled numerically by use of the CORSICA 2D equilibrium and NIMROD 3D MHD codes. The work follows the simulations of pressuredriven modes in DIIID [1] and VDEs in ITER [2]. The aim of the work is to provide starting points for simulation of tokamak disruption mitigation techniques currently in the CDR phase for ITER. Pressuredriven instability growth rates previously observed in simulations of DIIID are verified; Halo and Hiro currents produced during vertical displacements are observed in simulations of ITER with implementation of resistive walls in NIMROD. We discuss plans to exercise new code capabilities and validation.\\[4pt] [1] S.E. Kruger et al Plasma Physics of Plasmas, 12, 056113 (2005)\\[0pt] [2] R. Paccagnella et al Nucl. Fusion 49 035003 (2009) [Preview Abstract] 

BP8.00018: MHD Pedestal Formation in TimeDependent Simulations Luca Guazzotto , Riccardo Betti , Steve Jardin Finite toroidal and poloidal flows are routinely observed in the edge plasma region of tokamak experiments. MHD theory predicts that when the poloidal velocity is transonic with respect to the poloidal sound speed ($c_{sp} \equiv c_s B_p/B$, where $B_p$ is the poloidal field) a transient will develop. After the end of the transient, a steadystate MHD pedestal in plasma density and pressure is left, with the height of the pedestal depending on the poloidal location. The formation of the MHD pedestal was demonstrated with timedependent simulations with the resistiveMHD code SIM2D. In the present work, we explore the effect of additional physics on the formation of the pedestal. The advanced model implemented in M3DC1 is used to validate and extend SIM2D calculations. Since M3DC1, contrary to SIM2D, was not developed to study transonic transients, this also gives a strong independent verification of the correctness of the MHD pedestal model. Special focus is given to poloidal viscosity, which is already implemented in M3DC1 and is being implemented in SIM2D. Analytic calculations complement and support numerical results. [Preview Abstract] 

BP8.00019: Nonlinear MHD effects on the structure of ELMs and edge instabilities Linda Sugiyama Toroidal fusion plasmas with steep edge pressure gradients exhibit many different types of electromagnetic instabilities in the plasma edge, ranging from large Type I ELM crash to saturated interELM modes to small coherent oscillations without ELMs. Experimental observations find coherent spatial structures that typically have moderate toroidal numbers $n\sim 10$, which are poorly explained by the MHD linear eigenmode spectrum. While nonMHD effects may be important in some cases, within MHD alone strong toroidal and nonlinear mode coupling can produce such mode numbers for larger amplitude modes, when the full MHD model and plasma configuration are used. MHD also easily produces strong lown harmonics (typically $n=1$, but also higher) that have been observed in recent experiments. The lown harmonics tend to be relatively larger in the magnetic field compared to density or temperature; most experiments have analyzed the magnetics. Strong $n=1$ manifests as a band of higher$n$ fieldaligned filaments that wraps once around the outboard plasma edge from top to bottom. Nonlinear effects are analyzed for a number of plasmas from different experiments with differing edge conditions and types of instability to attempt to determine what sets the dominant mode numbers. [Preview Abstract] 

BP8.00020: The effect of strong radial variation of the diamagnetic frequency on twofluid stabilization of edge localized MHD instabilities Tyler Cote , Chris Hegna , Ping Zhu The conventional theory for twofluid stabilization of ballooning instabilities in tokamaks assumes the diamagnetic frequency is constant throughout the radial structure of the ballooning mode. However, this approximation is not valid in the pedestal region where large density and temperature gradient variation is present. In this work, we apply WKB theory to solve for the radial structure of the ballooning eigenmode\footnote{R. L. Dewar et al, Nucl. Fusion \textbf{21}, 493 (1981)} in the presence of a radially varying diamagnetic frequency\footnote{R. J. Hastie et al, Phys. Plasmas \textbf{7}, 4561 (2000)} for a class of MHD equilibria with edge pedestal regions. Generally, the radial variation of diamagnetic frequency reduces the stabilizing influence of twofluid physics. Quantification of this effect will be presented for a number of equilibria. Future work will include comparisons of the ballooning theory with linear twofluid calculations using the extended MHD code NIMROD. [Preview Abstract] 

BP8.00021: Toroidal Simulations of Sawteeth with Diamagnetic Effects Matthew Beidler , Paul Cassak , Stephen Jardin The sawtooth crash in tokamaks limits the core temperature, adversely impacts confinement, and seeds disruptions. Adequate knowledge of the physics governing the sawtooth crash and a predictive capability of its ramifications has been elusive, including an understanding of incomplete reconnection, i.e., why sawteeth often cease prematurely before processing all available magnetic flux. There is an indication that diamagnetic suppression could play an important role in this phenomenon. While computational tools to study toroidal plasmas have existed for some time, extendedMHD physics have only recently been integrated. Interestingly, incomplete reconnection has been observed in simulations when diamagnetic effects are present [1]. In the current study, we employ the threedimensional, extendedMHD code M3DC1 [2] to study the sawtooth crash in a toroidal geometry. In particular, we describe how magnetic reconnection at the q$=$1 rational surface evolves when selfconsistently increasing diamagnetic effects are present. We also explore how the termination of reconnection may lead to corerelaxing idealMHD instabilities.\\[4pt] [1] J. A. Breslau, S. C. Jardin, and W. Park, Phys. Plasmas 14, 056105 (2007).\\[0pt] [2] N. M. Ferraro and S. C. Jardin, J. Comp. Phys. 228, 77427770 (2009). [Preview Abstract] 

BP8.00022: Investigations on Sawtooth Reconnection in ASDEX Upgrade Tokamak Discharges Using the 3D Nonlinear Twofluid MHD Code M3DC1 Isabel Krebs , Stephen C. Jardin , Valentin Igochine , Sibylle Guenter , Matthias Hoelzl We study sawtooth reconnection in ASDEX Upgrade tokamak [Herrmann et al., Fusion Sci. Technol. 44(3) (2003)] plasmas by means of 3D nonlinear twofluid MHD simulations in toroidal geometry using the highorder finite element code M3DC1 [S.C. Jardin et al., J. Phys.: Conf. Ser. 125 (2008)]. Parameters and equilibrium of the simulations are based on typical sawtoothing ASDEX Upgrade discharges. The simulation results are compared to features of the experimental observations such as the sawtooth crash time and frequency, the evolution of the safety factor profile and the 3D evolution of the temperature. 2D ECE imaging measurements during sawtooth crashes in ASDEX Upgrade indicate that the heat is transported out of the core through a narrow poloidally localized region [Igochine et al., Phys. Plasmas 17 (2010)]. We investigate if incomplete sawtooth reconnection can be seen in the simulations which is suggested by soft Xray tomography measurements in ASDEX Upgrade showing that an (m=1,n=1) perturbation is typically observed to survive the sawtooth crash and approximately maintain its radial position [Igochine et al., Phys. Plasmas 17 (2010)]. [Preview Abstract] 

BP8.00023: Modeling Giant Sawtooth Modes in DIIID using the NIMROD code Scott Kruger , Thomas Jenkins , Eric Held , Jacob King Ongoing efforts to model giant sawtooth cycles in DIIID shot 96043 using NIMROD are summarized. In this discharge, an energetic ion population induced by RF heating modifies the sawtooth stability boundary, supplanting the conventional sawtooth cycle with longerperiod giant sawtooth oscillations of much larger amplitude. NIMROD has the unique capability of being able to use both continuum kinetic and particleincell numerical schemes to model the RFinduced hotparticle distribution effects on the sawtooth stability. This capability is used to numerically investigate the role played by the form of the energetic particle distribution, including a possible highenergy tail drawn out by the RF, to study the sawtooth threshold and subsequent nonlinear evolution. Equilibrium reconstructions from the experimental data are used to enable these detailed validation studies. Effects of other parameters on the sawtooth behavior (such as the plasma Lundquist number and hotparticle $\beta$fraction) are also considered. Ultimately, we hope to assess the degree to which NIMROD's extended MHD model correctly simulates the observed linear onset and nonlinear behavior of the giant sawtooth, and to establish its reliability as a predictive modeling tool for these modes. [Preview Abstract] 

BP8.00024: Selforganized stationary states of inductively driven tokamaks S.C. Jardin , N. Ferraro , I. Krebs , J. Chen We report on a mechanism for preventing the current and temperature profiles from peaking in a stationary state tokamak. For certain parameters, regardless of the initial state, the plasma profiles will evolve into a selforganized state with the safety factor q slightly above 1 and constant in a central volume. This large shear free region is unstable to interchange modes for any pressure gradient, and the instability drives a strong (1,1) helical flow. This flow has the property that \textbf{V x B }is the gradient of a potential, so it does not affect the magnetic field evolution. However, the driven flow appears in the temperature evolution equation and dominates over the thermal conductivity in the center of the discharge. The net effect is to keep the central temperature (and resistivity) profiles flat so that the resistive steady state preserves the self organized state with q slightly above 1 and constant in the central volume. This mechanism was discovered with the M3DC1 toroidal 3D MHD code, and could possibly explain the mechanism at play in nonsawtoothing discharges with q$_{\mathrm{0}}$ just above 1 such as hybrid modes in DIIID and ASDEXU and longlived modes in NSTX and MAST. [Preview Abstract] 

BP8.00025: Study of extended MHD effects on interchange modes in spheromak equilibria E.C. Howell , C.R. Sovinec A study of extended MHD effects on linear interchange modes is performed using the NIMROD code [Sovinec \& King JCP 2010]. A linear cylindrical equilibrium model is adapted from [Jardin NF 1982] to allow finite toroidal current at the edge. These equilibria are representative of SSPX discharges where currents are driven on the open field to keep the safety factor above $\frac{1}{2}$ across the profile [McLean et al POP 2006]. These spheromaks have weak magnetic shear, and interchange stability is an important consideration. The Suydam parameter, $D$, is scaled to study resistive and ideal interchange modes. The calculated MHD growth rate increases with $D$. The resistive interchange scaling $\gamma \sim \eta ^{1/3}$ is observed for $D < \frac{1}{4}$. Calculations using the full extended MHD model are performed for a range of hall parameters $\Lambda$. This model includes gyroviscosity, the hall term, equilibrium diamagnetic flows, and the crossfield diamagnetic heat flux. Two fluid effects in the full model are always destabilizing at large $\Lambda$. However, some cases exhibit a range of $\Lambda$ where the growth rate for the full model is reduced relative to the MHD growth rate. [Preview Abstract] 

BP8.00026: Magnetic islands and singular currents at rational surfaces in threedimensional MHD equilibria Joaquim Loizu , Stuart Hudson , Amitava Bhattacharjee , Per Helander Ideal MHD predicts the existence of singular current densities forming at rational surfaces in nonaxisymmetric equilibria. These current singularities consist of a PfirschSchl\"{u}ter component that arises as a result of finite pressure gradient and a deltafunction current that presumably prevents the formation of islands that would otherwise develop in a nonideal plasma. While analytical formulations have been developed to describe such currents, a numerical proof of their existence has been hampered by the assumption of smooth functions made in conventional MHD equilibrium models such as VMEC. Recently, a theory based on the energy principle was developed that incorporates the possibility of nonsmooth solutions to the MHD equilibrium problem and bridges the gap between Taylor's relaxation theory and ideal MHD. Leveraging a numerical implementation of this \emph{multiregion, relaxed MHD} model, we provide a numerical proof of the formation of singular currents in nonaxisymmetric ideal MHD equilibria. For each numerical result we perform careful convergence studies and analytical benchmarks. Finally, we discuss the implications for the MHD stability of nonaxisymmetric, toroidally confined plasmas. [Preview Abstract] 

BP8.00027: Perturbed particle orbits and kinetic plasma response in nonaxisymmetric tokamaks Kimin Kim , J.K. Park , A.H. Boozer , N.C. Logan , Z.R. Wang , J.E. Menard Nonaxisymmetric magnetic fields interact with the drift trajectories of ions and electrons to create an anisotropic plasma pressure. The force produced by the gradient of this anisotropic pressure produces a torque, the Neoclassical Toroidal Viscosity (NTV), which tends to relax the plasma rotation to a specific offset rotation, and modifies the energy required to perturb the plasma. Complexities, such as resonances of the ExB drift with particle bounce frequencies, finite orbit width, and full collisional effects, require full numerical simulation to determine the NTV and the perturbation energy. The POCA deltaf drift kinetic particle code has been used to: (1) demonstrate the existence of the bounce resonances with the ExB drift and show that they often dominate the magnitude of the NTV, (2) show the NTV of perturbations with different toroidal mode numbers are generally decoupled, and (3) verify a quadratic NTV dependence on the asymmetric magnetic field. Such results imply the pressure anisotropy is linear in the magnetic perturbation and can produce a significant change in the applied nonaxisymmetric field. Progress on integrating this pressure anisotropy into a perturbed equilibrium solver to obtain selfconsistent solutions is presented. [Preview Abstract] 

BP8.00028: Effects of remaining magnetic islands in resonant magnetic perturbations C.C. Chang , J.C. Lu , Y. Nishimura , C.Z. Cheng Effects of remaining magnetic islands in stochastic magnetic field is investigated. A guiding center orbit following code is employed.\footnote{C. C. Chang, Y. Nishimura, and C. Z. Cheng, Contrib. Plasma Phys. {\bf 54}, 479 (2014).} The island remnants play an important role in characterizing the radial particle and heat transport. By increasing the trapped particle fraction, the transport level is reduced due to the conservation of second adiabatic invariants.\footnote{G.~F.~Chew, M.~L.~Goldberger, and F.~E.~Low, Proc. Royal Soc. London {\bf A 236}, 112 (1956).} Three dimensional particle motion is projected onto one dimensional radial profile to compare with a 1D transport model. Furthermore, particle source is incorporated into the kinetic simulation to retain the global profile as in realistic tokamak discharge.\footnote{T.~E.~Evans, R.~A.~Moyer, K.~H.~Burrell, {\it et al.}, Nature Physics {\bf 2}, 419 (2006).} This work is supported by National Science Council of Taiwan, NSC 1002112M006021, 1032112M006007, and NCKU Top University Project. [Preview Abstract] 

BP8.00029: Model of Tearing Mode Suppression by Resonant Magnetic Perturbations in a Tokamak Wenlong Huang , Ping Zhu The conventional error field theory has been extended to model the interaction between tearing mode and resonant magnetic perturbation (RMP) in a tokamak approximated by a screw pinch configuration. The model is applied to the analysis and understanding of the mechanism underlying the tearing mode suppression induced by resonant magnetic perturbation as observed in recent tokamak experiments and simulations [1,2]. Numerical solutions of the model demonstrate that at lower strength, RMPs are able to reduce the tearing mode amplitude. As the RMP strength increases, the tearing mode is locked in phase and its amplitude jumps to a higher level. Model analysis further reveals that both the tearing mode suppression and the mode locking are achieved through the modulation of the tearing mode rotational frequency using RMPs. The model predictions for the parameter regimes of tearing mode suppression and locking have been examined, and comparisons with recent experimental observations and simulations will be discussed. \vskip 0.1in \noindent [1] B. Rao~{\it et al.} Phys. Lett. A 377, 315 (2013). \vskip 0.in \noindent [2] Q. Hu~{\it et al.} Phys. Plasmas 20, 092502 (2013). [Preview Abstract] 

BP8.00030: Linear and Nonlinear Response of a Rotating Tokamak Plasma to a Resonant ErrorField Richard Fitzpatrick An indepth investigation of the effect of a resonant errorfield on a rotating, quasicylindrical, tokamak plasma is preformed within the context of resistiveMHD theory. General expressions for the response of the plasma at the rational surface to the errorfield are derived in both the linear and nonlinear regimes, and the extents of these regimes mapped out in parameter space. Torquebalance equations are also obtained in both regimes. These equations are used to determine the steadystate plasma rotation at the rational surface in the presence of the errorfield. It is found that, provided the intrinsic plasma rotation is sufficiently large, the torquebalance equations possess dynamically stable lowrotation and highrotation solution branches, separated by a forbidden band of dynamically unstable solutions. Moreover, bifurcations between the two stable solution branches are triggered as the amplitude of the errorfield is varied. A low to highrotation bifurcation is invariably associated with a significant reduction in the width of the magnetic island chain driven at the rational surface, and vice versa. General expressions for the bifurcation thresholds are derived, and their domains of validity mapped out in parameter space. [Preview Abstract] 

BP8.00031: Convective Radial Energy Flux Due To Resonant Magnetic Perturbations Francisco Alberto Marcus , Peter Beyer , Guillaume Fuhr , Arnaud Monnier , Sadruddin Benkadda With the resonant magnetic perturbations (RMPs) consolidating as an important tool to control the transport barrier relaxation, the mechanism on how they work is still a subject to be clearly understood. In this work we investigate the equilibrium states in the presence of RMPs for a reduced MHD model using 3D electromagnetic fluid numerical code (EMEDGE3D) with a single harmonic RMP (single magnetic island chain) and multiple harmonics RMPs in cylindrical and toroidal geometry. Two different equilibrium states were found in the presence of the RMPs with different characteristics for each of the geometries used. For the cylindrical geometry in the presence of a single RMP, the equilibrium state is characterized by a strong convective radial thermal flux and the generation of a mean poloidal velocity shear. In contrast, for toroidal geometry the thermal flux is dominated by the magnetic flutter. For multiple RMPs, the high amplitude of the convective flux and poloidal rotation are basically the same in cylindrical geometry, but in toroidal geometry the convective thermal flux and the poloidal rotation appear only with the islands overlapping of the linear coupling between neighbouring poloidal wavenumbers $m$, $m1$, $m+1$. [Preview Abstract] 

BP8.00032: The effect of small 3D magnetic perturbations on linear microinstability properties C.C. Hegna Small externally applied nonaxisymmetric magnetic perturbations can significantly alter the edge properties of tokamaks. In this work, we model the effect of the applied 3D fields on the flux surface deformation and show that these can alter key geometric properties of interest to microinstabilities. Shielding physics is assumed to be operative so that flux surface integrity is retained. Local 3D equilibrium theory is employed using a perturbative approach to calculate flux surface deformations consistent with magnetostatic force balance [1]. Prior work has shown applied 3D fields can significantly alter ideal ballooning stability boundaries due to order unity 3D field induced changes to the local shear [2]. The impact of 3D fields on ion temperature gradient and trapped electron mode growth rates are quantified using analytically derived proxy functions.\\[4pt] [1] C. C. Hegna, \emph{Phys. Plasmas} {\bf 7}, 3921 (2000).\\[0pt] [2] T. M. Bird and C. C. Hegna \emph{Nucl. Fusion} {\bf 53}, 013004 (2013). [Preview Abstract] 

BP8.00033: A CrossBenchmarking and Validation Initiative for Tokamak 3D Equilibrium Calculations A. Reiman , A. Turnbull , T. Evans , N. Ferraro , E. Lazarus , J. Breslau , A. Cerfon , C.S. Chang , R. Hager , J. King , M. Lanctot , S. Lazerson , Y. Liu , G. McFadden , D. Monticello , R. Nazikian , J.K. Park , C. Sovinec , Y. Suzuki , P. Zhu We are pursuing a crossbenchmarking and validation initiative for tokamak 3D equilibrium calculations, with 11 codes participating: the linearized tokamak equilibrium codes IPEC and MARSF, the timedependent extended MHD codes M3DC1, M3D, and NIMROD, the gyrokinetic code XGC, as well as the stellarator codes VMEC, NSTAB, PIES, HINT and SPEC. Dedicated experiments for the purpose of generating data for validation have been done on the DIIID tokamak. The data will allow us to do validation simultaneously with crossbenchmarking. Initial crossbenchmarking calculations are finding a disagreement between stellarator and tokamak 3D equilibrium codes. [Preview Abstract] 

BP8.00034: Energetic Ion Effects on Tearing Mode Stability in Tokamak Equilibria Michael Halfmoon , Dylan Brennan The 2/1 tearing mode is found to be damped or stabilized by energetic ions in a slowing down distribution, where the interaction between the ions and the mode is similar to their interaction in ideal MHD, which has been extensively studied. This damping effect is mainly due to trapped particle precession resonance and causes the tearing mode to have a finite real frequency. This study focuses on the pressuredriven, slow growing tearing modes; which are the first modes to be driven unstable as pressure increases. The layer physics modifies the mode interaction, and affects the frequency of the mode. In these simulations, a series of equilibria with fixed safety factor and varying pressure are analyzed using a $\delta $f hybridkinetic MHD code in NIMROD. Our equilibrium consists of a Dshaped poloidal cross section, a peaked pressure profile, and safety factor with finite shear to the magnetic axis. Also, a high aspect ratio toroidal model based on Hu {\&} Betti's work is investigated analytically to gain insight to the physics of modeparticle interactions. We combine our computational and analytic tools in an effort to explain this damping and stabilizing effect. [Preview Abstract] 

BP8.00035: Nonlinear simulation of the fishbone instability Malik Idouakass , Matteo Faganello , Herbert Berk , Xavier Garbet , Sadruddin Benkadda We propose to extend the OdblomBreizman precessional fishbone model [1] to account for both the MagnetoHydroDynamic (MHD) nonlinearity at the $q=1$ surface and the nonlinear response of the energetic particles contained within the $q=1$ surface. This electromagnetic mode, whose excitation, damping and frequency chirping are determined by the selfconsistent interaction between an energetic trapped particle population and the bulk plasma evolution, can induce effective transport and losses for the energetic particles, being them alphaparticles in nextfuture fusion devices or heated particles in present Tokamaks. The model is reduced to its simplest form, assuming a reduced MHD description for the bulk plasma and a twodimensional phasespace evolution (gyro and bounce averaged) for deeply trapped energetic particles. Numerical simulations have been performed in order to characterize the mode chirping and saturation, in particular looking at the interplay between the development of phasespace structures and the system dissipation associated to the MHD nonlinearities at the resonance locations.\\[4pt] [1] Odblom et al., Phys. Plasmas, 9, 155 (2002). [Preview Abstract] 

BP8.00036: Analytical theory of BAE gap modification due to a magnetic island Carson Cook , Chris Hegna , Donald Spong The Betainduced Alfven Eigenmode (BAE) gap is a break in the frequencies of the shear Alfven continuum. This gap is important because a discrete Alfven eigenmode can exist within the gap frequency range and will not be affected by continuum damping. In order for the BAE gap to appear, finite beta and curvature effects must be present. Under these conditions, there is a coupling between the equation for shear Alfven waves involving inertia and bending energy terms and the sound wave equation. The presence of a magnetic island has been shown to cause an upshift in the BAE gap frequency [1]. In the absence of an island the minimum of the continuum frequencies is located at the resonant rational surface; the island moves the location of the minimum to the island separatrix as a result of the coupling between helical mode numbers. The physical mechanism for this shift will be described employing analytical modeling. The shear Alfven spectrum is obtained globally through analytical methods, inside and outside the separatrix, for the first time. A WKB approximation is used in this analysis, and good agreement is found with previous numerical results.\\[4pt] [1] A. Biancalani, L. Chen, F. Pegoraro, and F. Zonca, Plasma Phys. Control. Fusion 53, 025009 (2011). [Preview Abstract] 

BP8.00037: Onedimensional energetic particle quasilinear diffusion for realistic TAE instabilities Vinicius Duarte , Katy Ghantous , Herbert Berk , Nikolai Gorelenkov Owing to the proximity of the characteristic phase (Alfv\'{e}n) velocity and typical energetic particle (EP) superthermal velocities, toroidicityinduced Alfv\'{e}n eigenmodes (TAEs) can be resonantly destabilized endangering the plasma performance. Thus, it is of ultimate importance to understand the deleterious effects on the confinement resulting from fast ion driven instabilities expected in fusiongrade plasmas. We propose to study the interaction of EPs and TAEs using a line broadened quasilinear model, which captures the interaction in both regimes of isolated and overlapping modes. The resonance particles diffuse in the phase space where the problem essentially reduces to one dimension with constant kinetic energy and the diffusion mainly along the canonical toroidal angular momentum. Mode structure and wave particle resonances are computed by the NOVA code and are used in a quasilinear diffusion code that is being written to study the evolution of the distribution function, under the assumption that they can be considered virtually unalterable during the diffusion. A new scheme for the resonant particle diffusion is being proposed that builds on the 1D nature of the diffusion from a single mode, which leads to a momentum conserving difference scheme even when there is mode overlap. [Preview Abstract] 

BP8.00038: Alpha particle redistribution produced by internal kink modes Hugo Ferrari , Ricardo Farengo , Pablo GarciaMartinez , Marie Christine Firpo , Wahb Ettoumi , Agustin Lifschitz The redistribution of alpha particles due to internal kink modes is studied. The exact particle trajectories in the total fields, equilibrium plus perturbation, are calculated. The equilibrium has circular cross section and the plasma parameters are similar to those expected in ITER. The alpha particles are initially distributed according to a slowing down distribution function and have energies between 18 keV and 3:5 M eV . The (1,1), (2,2) and (2,1) modes are included and the effect of changing their amplitude and frequency is studied. When only the (1,1) mode is included the spreading of high energy (E $\ge$ 1 MeV ) alpha particles increases slowly with the energy and mode frequency. At lower energies the redistribution is more sensitive to the mode frequency and particle energy. When a (2; 1) mode is added the spreading increases significantly and particles can reach the edge of the plasma. Trapped particles are the most affected and the redistribution parameter can have maxima above 1 MeV, depending on the mode frequency. These results can have important implications for ash removal. [Preview Abstract] 

BP8.00039: Role of phase locking in nonlinear dynamics of fishbones and EPMs Fulvio Zonca , Liu Chen , Zhiyong Qiu Fishbones [1] and, more generally, Energetic Particle Modes (EPM) [2], are discrete nonnormal modes excited out of the shear Alfv\'en wave (SAW) continuous spectrum. Their frequency is the characteristic one of resonant EPs and maximizes waveEP power exchange, exceeding SAW continuum damping. These properties are maintained during the nonlinear evolution of the system, due to the intrinsic nonperturbative response of EPs to the fluctuating SAW fields and their selfconsistent interplay with the perturbed EP source. This dynamic behavior is given by ``phase locking'' between resonant EPs and SAW fluctuations, as demonstrated in this work; and can be generally described by a Dyson equation for the emission and reabsorption of SAW fluctuations by the EP population [3]. Here, we apply this theoretical framework to nonlinear fishbone and EPM dynamics in fusion plasmas; and discuss their description as complex Nonlinear Schr\"odinger Equation, for which we provide solutions in simple yet practically relevant limiting cases [3].\\[4pt] [1] L. Chen et al. Phys. Rev. Lett. {\bf 52}, 1122 (1984).\newline [2] L. Chen, Phys. Plasmas {\bf 1}, 1519 (1994).\newline [3] L. Chen and F. Zonca, submitted to Rev. Mod. Phys. (2014). [Preview Abstract] 

BP8.00040: Finitebeta effects of nonMaxwellian fast ions in gyrokinetics George Wilkie , Ian Abel , William Dorland The presence of relatively small concentrations of fast ions is known to have a significant effect on the Alfv\'enic physics of fusion plasmas. These fast ions have large gyroradii and are usually nonMaxwellian, so the lowcollisionality ordering of gyrokinetics is an approprite tool. Here, we use the \texttt{GS2} gyrokinetics code to study finitebeta nonlinear effects in the presence of nonMaxwellian fast ions. [Preview Abstract] 

BP8.00041: Predictive models for fast ion profiles relaxation in burning plasmas Nikolai Gorelenkov , W.W. Heidbrink , J. Lestz , M. Podesta , M. Van Zeeland , R.B. White The performance of the burning plasmas is limited by the confinement of superalfvenic fusion products, alpha particles, which are capable to resonate with the Alfv\'enic eigenmodes (AEs). Two techniques based on linear AE stability theory are developed to evaluate the AE induced fast ion relaxation. The first is the reduced quasilinear technique or critical gradient model (CGM) where marginally unstable (or critical) gradient of fast ion pressure is due to unstable AEs. It allows the reconstruction of fast ion pressure profile and compute their losses. The second technique is called hybrid that is also based on NOVAK linear stability computations of TAE (or RSAE) mode structures and growth rates. AE amplitudes are computed from the nonlinear theory perturbatively and used in numerical runs. With the help of the guiding center code ORBIT the hybrid model predicts the relaxation of the fast particle profiles. We apply these models for NSTX and DIIID plasmas with the neutral beam injections in order to validate the models. Both methods are relatively fast ways to predict the fast ion profiles in burning plasmas and can be used for plasma modeling prior to building experimental devices such as ITER. [Preview Abstract] 

BP8.00042: A hybrid simulation model for runaway electron interaction with the tearing mode Chang Liu , Dylan Brennan , Allen Boozer The runaway electron problem is one of the key issues in disruption studies. It is predicted that in future large tokamak devices like ITER the runaway beam can be significantly large and energetic, which can cause serious damage to the device. In experiments increasing magnetic turbulence can suppress runaway electrons, which is due to the increase of runaway electron radial transport when the magnetic fields become stochastic. On the other hand, a large amount of runaway current can change the MHD stability, causing MHD instabilities, which can affect the magnetic field structure. It is therefore important to study the interaction of runaway electrons and MHD instabilities selfconsistently. We are working towards a hybrid simulation using a driftkinetic, MonteCarlo particle code for the runaway electrons and NIMROD for the background plasma. Our simulation will be selfconsistent, which means it will include a coupling of the runaway electrons to the MHD equations through the current. The kinetic simulation of the runaway electrons, even uncoupled from the MHD, can be used to analyze existing experiments on runaway electrons. In addition, we present a selfconsistent fluid treatment of the runaway current coupled to MHD, which captures much of the essential physics. [Preview Abstract] 

BP8.00043: Resistivity and sheared rotation effects on the toroidal external kink mode A.J. Cole , D.P. Brennan , J.M. Finn We present PESTIII analysis of the toroidal external kink with plasma resistivity and sheared rotation for a range of equilibria varying elongation, driven unstable by increasing $\beta$. The results show that the typical ordering for marginally stable $\beta$ values is $\beta_{\textrm{rp,rw}}<\beta_{\textrm{rp,iw}}<\beta_{\textrm{ip,rw}}<\beta_{\textrm{ip,iw}}$, where rp,ip signify resistive or ideal plasma, and iw,rw indicate ideal wall or resistive wall (nowall). The two resistive plasma $\beta$ limits are significantly lower than the two ideal plasma values. We vary aspects of the tearing layer physics by means of a variational principle with Pad\'e approximants, and compare with a general computational solution for the layers to gain insight. We also include pressure gradient and local velocity shear within the layers. Global rotation shear $\Omega'$ is included in the form of a relative rotation of the $q=2,~3,\cdots$ surfaces and we investigate the resultant effect on the poloidal mode number spectrum. We then present a model for active feedback control, which is the toroidal generalization building on recent results in cylindrical mode control theory [D.P. Brennan and J.M. Finn and submitted to Physics of Plasmas (2014)]. [Preview Abstract] 

BP8.00044: Verification of the Resistive DCON Code A.H. Glasser , Z.R. Wang , J.K. Park The ideal MHD axisymmetric toroidal stability code DCON has been extended to treat resistive instabilities, with resonant surfaces at rational safety factor values of $q = m/n$. DCON solves the ideal MHD equations using a singular Galerkin method to obtain matching data for the ideal outer region. Robust convergence is achieved by a careful choice of basis functions: $C^1$ Hermite cubics to resolve nonresonant solutions; a highorder power series in the neighborhood of each singular surface to resolve large and small resonant solutions; distributed with a gridpacking algorith with high resolution near the singular surfaces and adequate grid to resolve the nonresonant region. The degenerate case for $\beta = 0$ has been derived and coded up for verification, in addition to the nondegenerate case $\beta > 0$. The DELTAR code computes corresponding inner region matching data for the resistive MHD equations of Glasser, Greene, and Johnson. The MATCH code matches the inner and outer region data to obtain global eigenvalues and eigenfunctions. The VACUUM provides data for a vacuum region outside the plasma region. The MARSF code, which solves the same equations by a straighthrough method, is used to verify the accuracy of the DCON solution. Results will be presented. [Preview Abstract] 

BP8.00045: Neoclassical Tearing Modes characterization in JET ILW operation Matteo Baruzzo , Barry Alper , Clemente Angioni , Yuriy Baranov , Paolo Buratti , Francis Casson , Tim Hender , Paola Mantica , Chiara Marchetto , Laura Lauro Taroni , Marco Valisa After several years of operation with the ITER Like Wall a comprehensive evidence on the effect of Neoclassical Tearing Modes on discharge stability and confinement has been collected. NTMs appearance is coincident with a flattening of the electron temperature profile within the island (the effect with the Cwall), but it is sometimes correlated with enhanced core plasma radiation and eventually radiative collapse. A mechanism for W accumulation in presence of magnetic island has been outlined in [1], where the island is responsible of connecting two radial regions characterized by different transport regimes. In this work the statistics of W accumulation measured with bolometry and Soft Xray will be correlated with the island radial position and island width as measured by fast Electron Cyclotron Emission for different toroidal mode numbers and in different tokamak operational scenarios. \\[4pt] [1] C Angioni et al. 2014, to be published in Nuclear Fusion. [Preview Abstract] 

BP8.00046: GTC Simulation of Tearing Modes in Fusion Plasmas Dongjian Liu , Ihor Holod , Wenlu Zhang , Zhihong Lin In Tokamak discharge, Tearing modes are very important modes which may cause the disruption and sawtooth crash. For the reason, an effective physics model and corresponding simulation code are needed to study these modes. We have modified the fluidkinetic hybrid electron model used in Gyrokinetic Toroidal Code (GTC) and developed both resistive and finite mass electron fluid model for tearing mode simulations. Using the model in GTC, we have successfully recovered linear behavior of both the classical resistive tearing mode and the collisonless tearing mode, and verified the capability of GTC to study this mode. The modified GTC may supply a more powerful implement for kineticMHD study of Tokamak plasma. [Preview Abstract] 

BP8.00047: Studies of NSTX equilibria with beta above the n$=$1 nowall limit using new toroidal resistive wall boundary condition in NIMROD A.L. Becerra , C.C. Hegna , C.R. Sovinec , S.E. Kruger , J.R. King , S.A. Sabbagh We make use of the generalized thin resistive wall boundary condition recently implemented in NIMROD to study the linear and nonlinear RWM stability properties of a series of reconstructed NSTX equilibria. The boundary condition operates by matching the magnetic field inside the computational domain with external fields found using the GRIN vacuumfield solver at the wall, and is valid for toroidal geometries with poloidal asymmetry as well as for cylindrical geometries. A time series of NSTX equilibrium reconstructions from a single shot with a range of normalized beta above and below the nowall limit is used to benchmark this boundary condition by comparing the beta computed for RWM onset with the stability limit predicted by DCON. Scans with varying wall parameters are also performed to demonstrate the approximately linear relationship between growth rate and wall resistivity, and to determine the wall parameters that are the best match to the NSTX device. The stability of these equilibria for n\textgreater 1 is also tested, with both linear and nonlinear runs. [Preview Abstract] 

BP8.00048: Magnetic Field Line Stickiness in Tokamaks Caroline G.L. Martins , Marisa Roberto , Ibere L. Caldas , Philip J. Morrison We analyze a Hamiltonian model with five wire loops that delineate magnetic surfaces of tokamaks with poloidal divertors. Nonaxisymmetric magnetic perturbations are added by external coils, similar to the correction coils that have been installed or designed in present tokamaks. We obtain the footprints and deposition patterns on the divertor plates, and, additionally, we show that while chaotic lines escape to the divertor plates, some of them are trapped, for many toroidal turns, in complex structures around magnetic islands, giving rise to evidence of stickiness characteristic of chaotic Hamiltonian systems [Caroline G. L. Martins et al. IEEE Transactions on Plasma Science (accepted), 2014]. In order to identify sticky structures, we perform a finite time rotation number calculation [J. D. Szezech Jr. et al. Phys. Lett. A, 377, 452, 2013]. Finally, we introduce a random collisional term to the field line mapping to investigate the effect of particle collisions on stickiness. The results indicate that the reported trapping may affect the transport in present tokamaks [Caroline G. L. Martins et al. Physics of Plasmas (Submitted), 2014]. [Preview Abstract] 

BP8.00049: Hamiltonian and Action Principle Formalisms for Gyroviscous models Manasvi Lingam , Philip J. Morrison A general procedure for constructing action principles for continuum models via the generalized Hamilton's principle of mechanics is described. In [1], this procedure is employed to construct a class of actions, which includes several hydrodynamics and magnetohydrodynamics(MHD) models. The conditions under which the conservation of energy, linear and angular momentum hold are presented. The generalized formalism is used to develop a simple model with intrinsic angular momentum. In [2], the action principle for a specific 2D gyroviscous MHD model is developed, which is identical to a reduced version of Braginskii's fluid equations. The procedure explains the origin of the gyromap, used in deriving previous gyrofluid models. A systematic reduction procedure yields the Hamiltonian structure of this model through the noncanonical Poisson bracket. The construction procedure yields classes of Casimir invariants, which are then used to derive variational principles for equilibria with flow and gyroviscosity. It is shown that the model can be modified to obtain other reduced models in the literature. \\[4pt] [1] M. Lingam and P.J. Morrison, ``The gyroviscous fluid'' (in preparation)\\[0pt] [2] P. J. Morrison, M. Lingam and R. Acevedo, arXiv:1405.2326 (to appear in Physics of Plasmas) [Preview Abstract] 

BP8.00050: Extended MHD simulations of RayleighTaylor instability with real frequency in a 2D slab Ryosuke Goto , Hideaki Miura , Atsushi Ito , Masahiko Sato , Tomoharu Hatori Small scale effects such as the Finite Larmor Radius (FLR) effect and the Hall term can change the linear and nonlinear growth of the high wave number unstable modes of the pressure driven instability considerably. Here we consider a simple RayleighTaylor (RT) instability in a 2D slab, and study the effect of the Hall term and the FLR effect to the RT instability by means of numerical simulations of the Braginskiitype extended MHD equations [1]. As we have reported earlier, the linear growth rates of the high wave number modes are highly reduced when the Hall term and the FLR effect are added simultaneously [2]. However, there appears little real frequency in the previous work. Since the diamagnetic drift associated with the real frequency is considered to affect the growth of the linear and nonlinear evolutions, we provide a new equilibrium in which appearance of the real frequency is expected and carry out numerical simulations. Influences of the real frequency on the growth rates as well as on the nonlinear mixing width for some combinations of the Hall and the FLR parameters are going to be presented. \\[4pt] [1] S. I. Braginskii, Rev. Plasma Phys., 1, 205 (1965).\\[0pt] [2] R. Goto et al., to appear in the Plasma Fusion Research (2014). [Preview Abstract] 

BP8.00051: Building Action Principles for Extended MHD Models Ioannis Keramidas Charidakos , Manasvi Lingam , Philip Morrison , Ryan White , Alexander Wurm The general, nondissipative, twofluid model in plasma physics is Hamiltonian, but this property is sometimes lost in the process of deriving simplified twofluid or onefluid models from the twofluid equations of motion. One way to ensure that the reduced models are Hamiltonian is to derive them from an action. We start with the general twofluid action functional for an electron and an ion fluid interacting with an electromagnetic field, expressed in Lagrangian variables. We perform a change of variables and make various approximations (eg. quasineutrality and ordering of the fields) and small parameter expansions directly in the action. The resulting equations of motion are then mapped to the Eulerian fluid variables using a novel nonlocal LagrangeEuler map. The correct Eulerian equations are obtained after we impose locality. Using this method and the proper approximations and expansions, we recover Lust's general twofluid model, extended MHD, Hall MHD, and Electron MHD from a unified framework. The variational formulation allows us to use Noether's theorem to derive conserved quantities for each symmetry of the action. References: I.Keramidas Charidakos, M.Lingam, P.J.Morrison, R.White, A. Wurm ``Action Principles for Extended MHD Models'' (to be submitted) [Preview Abstract] 

BP8.00052: Simulation and analytic analysis of radiation driven islands at the density limit D.P. Brennan , C. Liu , D.A. Gates , L. DelgadoAparicio , R. White The effect of radiative cooling on the onset and evolution of magnetic islands is investigated with nonlinear resistive MHD simulations and reduced theoretical analysis. ~The configuration is a cylindrical tokamak with a m/n$=$2/1 island and includes three dimensional resistivity and anisotropic heat conduction in the simulations. ~The radiative cooling is implemented as a temperature perturbation inside the island, which modifies the island structure and drives the island more unstable. ~Analytic reduction of the saturated island size and structure supports the simulation results. ~The results offer intuitive understanding of experimental observations of radiation driven magnetic islands, which may explain density limit disruptions. [Preview Abstract] 

BP8.00053: Tridimensional Ribbon Burning Modes in Igniting Plasmas* B. Coppi The fusion burn conditions of magnetically confined plasmas are investigated usually by one dimensional or 1 +1/2 D codes, when referring to toroidal configurations. This means that the fusion burning process is being described as an axisymmetric and a poloidally symmetric process in a toroidal configuration. On the other hand when the presence of magnetic shear in the considered confinement configuration and the effects of anisotropic thermal conductivities, relative to the confining magnetic field, are taken into account a new kind of thermonuclear instability can be found in plasmas close to ignition conditions [1]. Deuteriumtritium plasmas are considered in particular. The relevant mode involving the growth of electron temperature perturbations is tridimensional and radially localized around a given rational magnetic surface. Clearly, the onset and evolution of this kind of ``ribbon'' modes have to be considered in order to envision and predict how a condition of global ignition [1] can be reached. *Sponsored in part by the U.S. DOE. \\[4pt] [1] B. Coppi, \textit{Comments Pl. Phys. and Cont. Fus}. \textbf{3}, 2 (1977). [Preview Abstract] 

BP8.00054: Numerical Analysis of Drift Resistive Inertial Ballooning Modes A.H. Kritz , V. Tangri , T. Rafiq , A.Y. Pankin Three numerical techniques employing differentiation matrices are used to investigate the linear analysis of drift resistive inertial ballooning modes (DRIBM). The techniques applied avoid numerical stability issues associated with the frequently used shooting method. Hermite and Sinc spectral methods and a finite difference method are applied to compute the DRIBM eigenvalues and eigenvectors. It is shown that the spectral methods converge more rapidly than the finite difference method. In the DRIBM, model incorporated in the MultiMode transport model, the strong ballooning approximation is used [T. Rafiq \textit{et. al.,} Phys. Plasmas \textbf{20}, 032506 (2013)]; whereas, in the numerical analysis of these modes presented here, a strong ballooning limit approximation is not utilized. It is shown that for conditions appropriate for the edge region of a DIIID plasma (where contributions to transport associated with DRIBM are significant), the Multimode DRIBM component (utilizing a strong ballooning limit) and the numerical analysis that does not involve a strong ballooning approximation yield similar growth rates for the most unstable mode. This result follows from the fact that in the tokamak edge region the ballooning modes are strongly localized. The techniques utilized in this paper for calculating eigenvalues are quite general and are relevant to investigate other modes that can be analyzed using the ballooning mode formalism. [Preview Abstract] 

BP8.00055: ABSTRACT WITHDRAWN 

BP8.00056: Parallel electron heat flow along a spatially varying magnetic field JeongYoung Ji , Eric Held We solve a system of general moment equations to obtain the parallel electron heat flow in an inhomogeneous magnetic field. Magnetic field gradient terms are kept and treated using both finite difference and Fourier series methods. Convergence in the heat flow is demonstrated as the number of moments is increased in regimes of high to moderate collisionality. Properties of the moment equations in the collisionless limit are also discussed. The heat flow shows local enhancement and reduction due to magnetic variations when compared to the integral parallel heat flow closure. [Preview Abstract] 

BP8.00057: A selfconsistent model of an isothermal tokamak Steven McNamara , Matthew Lilley Continued progress in liquid lithium coating technologies have made the development of a beam driven tokamak with minimal edge recycling a feasibly possibility. Such devices are characterised by improved confinement [1] due to their inherent stability and the suppression of thermal conduction. Particle and energy confinement become intrinsically linked and the plasma thermal energy content is governed by the injected beam. A selfconsistent model of a purely beam fuelled isothermal tokamak is presented, including calculations of the density profile [2], bulk species temperature ratios and the fusion output. Stability considerations constrain the operating parameters and regions of stable operation are identified and their suitability to potential reactor applications discussed.\\4pt] [1] R. Majeski et al., Phys. Rev. Lett. 97, 075002 (2006) \newline [2] P. J. Catto {\&} R. D. Hazeltine, Phys. Plasmas 13, 122508 (2006) [Preview Abstract] 

BP8.00058: PSICenter Validation Studies B.A. Nelson , C. Akcay , A.H. Glasser , C.J. Hansen , T.R. Jarboe , G.J. Marklin , R.D. Milroy , K.D. Morgan , P.C. Norgaard , U. Shumlak , D.A. Sutherland , B.S. Victor , C.R. Sovinec , J.B. O'Bryan , E.D. Held , J.Y. Ji , V.S. Lukin The Plasma Science and Innovation Center (PSICenter  http://www.psicenter.org) supports collaborating validation platform experiments with 3D extended MHD simulations using the NIMROD, HiFi, and PSITET codes. Collaborators include the Bellan Plasma Group (Caltech), CTH (Auburn U), HBTEP (Columbia), HITSI (U Wash  UW), LTX (PPPL), MAST (Culham), Pegasus (U WiscMadison), SSX (Swarthmore College), TCSU (UW), and ZaP/ZaPHD (UW). The PSICenter is exploring application of validation metrics between experimental data and simulations results. Biorthogonal decomposition (BOD) is used to compare experiments with simulations. BOD separates data sets into spatial and temporal structures, giving greater weight to dominant structures. Several BOD metrics are being formulated with the goal of quantitive validation. Results from these simulation and validation studies, as well as an overview of the PSICenter status will be presented. [Preview Abstract] 

BP8.00059: Evolving magnetic equilibria in anomalous turbulent transport simulations Jungpyo Lee , Antoine Cerfon , Edmund Highcock , Michael Barnes The evolution of poloidal and toroidal magnetic fluxes in a tokamak are determined by Faraday's law in which electric field needs to be consistent with 1D radial transports of density, temperature, and toroidal angular momentum. Consistency is required because the transport of the thermodynamic variables depends on the 2D magnetic equilibrium that changes depending on the radial pressure profile. For neoclassical transport, consistency is achieved through a proper treatment of the parallel electric field and Ohm's law [Hinton and Hazeltine, (1976), Hirshman and Jardin (1979)]. Recently, consistency for the anomalous turbulent transport has been studied analytically using a Lagrangian formulation of gyrokinetics [Sugama et. al. (2014)]. In this poster, we propose a simple numerical model to evolve both the magnetic equilibrium and the radial profile of density, temperature, and toroidal angular frequency due to turbulent transport with a fixed q (safety factor) profile. The constraint of fixed q profile makes the evolution selfconsistent only if the transport time scale is much smaller than the resistive current diffusion time scale. In this model, we use the transport code TRINITY coupled with the local gyrokinetic code GS2 and the qsolver version of the GradShafranov code ECOM. [Preview Abstract] 

BP8.00060: Predictive Modeling of Tokamak Density, Temperature and Toroidal Rotation Profiles T. Rafiq , A.H. Kritz , A.Y. Pankin , X. Yuan The predictive TRANSPort and integrated modeling code, PTRANSP, is used to compute electron density, temperature, toroidal velocity and radial electric field profiles. The MultiMode anomalous transport model, MMM7.1, or the Trapped GyroLandau Fluid model, TGLF, is used along with the new numerical transport solver, PTSOLVER, in carrying out the simulations. An option to evolve the electron density profiles has been recently introduced to PTSOLVER. The effects associated with this new option on the plasma profiles in the predictive PTRANSP simulations that advance the coupled density, energy, and momentum equations are presented. The selfconsistent evolution of the equilibrium is computed using the TEQ or ISOLVER module. Neoclassical transport is calculated using the ChangHinton model. Neutral beam heating and current drive are obtained using the NUBEAM module and ion cyclotron heating and current drive are obtained using the full wave TORIC module. Results are presented for Lmode and Hmode discharges in order to illustrate the extent to which the MMM7.1 and TGLF transport models yield profiles that are consistent with experimental data. The comparison is quantified by calculating the RMS deviations and Offsets. The plasma parameter dependencies associated with the anomalous transport resulting from the use of the MMM7.1 and TGLF models are illustrated. [Preview Abstract] 

BP8.00061: An improved bootstrap current formula for edge pedestal plasma Robert Hager , C.S. Chang An improved version of a bootstrap current formula based on the results of the neoclassical guidingcenter particleincell code XGC0 [Koh et al., Phys. Plasmas $\bf{19}$, 072505 (2012)] is presented. The original formula improved the accuracy of the predicted bootstrap current in the edge pedestal, where the ion orbit width can be comparable to the pressure gradient scale length, the passing particle region is narrow, and the ions experience orbit loss. We improved two aspects of this formula. We corrected the asymptotic behavior of the bootstrap current coefficients at higher collisionality from what was inherited from the Sauter formula [O. Sauter et al., Phys. Plasmas $\bf{6}$, 2834 (1999)]. We also improved the jumpy aspectratio dependence of the transition between an enhanced (NSTX) and reduced (DIIID) bootstrap current regime found by Koh et al. In addition, we elucidate the physical origins of the improvement and of the difference from a local analysis that includes the importance of finite ion orbit excursion effects on the electron current in the edge pedestal. [Preview Abstract] 

BP8.00062: The Material Plasma Exposure eXperiment (MPEX) J. Rapp , T.M. Biewer , T.S. Bigelow , J. Canik , J.B.O. Caughman , R.C. Duckworth , R.H. Goulding , D.L. Hillis , J.D. Lore , A. Lumsdaine , W.D. McGinnis , S.J. Meitner , L.W. Owen , G.C. Shaw , G.N. Luo Next generation plasma generators have to be able to access the plasma conditions expected on the divertor targets in ITER and future devices. The Material Plasma Exposure eXperiment (MPEX) will address this regime with electron temperatures of 1  10 eV and electron densities of 10$^{21}$  10$^{20}$ m$^{3}$. The resulting heat fluxes are about 10 MW/m$^{2}$. MPEX is designed to deliver those plasma conditions with a novel Radio Frequency plasma source able to produce high density plasmas and heat electron and ions separately with Electron Bernstein Wave (EBW) heating and Ion Cyclotron Resonance Heating (ICRH). Preliminary modeling has been used for predesign studies of MPEX. MPEX will be capable to expose neutron irradiated samples. In this concept targets will be irradiated in ORNL's High Flux Isotope Reactor (HFIR) or possibly at the Spallation Neutron Source (SNS) and then subsequently (after a sufficient long cooldown period) exposed to fusion reactor relevant plasmas in MPEX. The current state of the predesign of MPEX including the concept of handling irradiated samples will be presented [Preview Abstract] 

BP8.00063: Initial Operation of the ProtoMPEX High Intensity Plasma Source J.B.O. Caughman , R.H. Goulding , T.M. Biewer , T.S. Bigelow , S.J. Diem , P.V. Pesavento , J. Rapp , H.B. Ray , G.C. Shaw , G.N. Luo The Prototype Materials Plasma Experiment (ProtoMPEX) is a linear highintensity rf plasma source that combines a highdensity helicon plasma generator with electron and ion heating. It is being used to study the physics of heating overdense plasmas, as well as exploring source interactions with a downstream target. The helicon plasma is produced by coupling 13.56 MHz rf power at levels up to 100 kW. Microwaves at 28 GHz (up to $\sim$ 200 kW) are coupled to the electrons in the overdense helicon plasma via Electron Bernstein Waves (EBW). Ion cyclotron heating ($\sim$ 30 kW) is via a magnetic beach approach. Tungsten baffles are used to help control neutral pressure between the helicon source and a tungsten target. Plasma diagnostics include Thomson Scattering and a retarding field energy analyzer to determine plasma parameters near the target, while a microwave interferometer and Langmuir probes are used to determine plasma parameters near the source and elsewhere in the system. High plasma densities have been produced in He (\textgreater 3x10$^{19}$/m$^{3})$ and D (\textgreater 1.5x10$^{19}$/m$^{3})$, and operation in magnetic field strengths up to 1T has been demonstrated. Details of the experimental results will be presented, as well as future plans for studying plasma surface interactions and rf antenna plasma interactions. [Preview Abstract] 

BP8.00064: Preliminary results of Laserbased diagnostics for protoMPEX G. Shaw , T.M. Biewer , G.N. Luo , M. Martin , R. Martin , B. Wirth Oak Ridge National Laboratory (ORNL) Laboratory Directed Research and Development (LDRD) funding enabled the initial installation of laser based, Thomson Scattering (TS), Rayleigh Scattering (RS), and Laser Induced Breakdown Spectroscopy (LIBS) diagnostics on the prototype MaterialPlasma Exposure eXperiment (protoMPEX). TS measures the electron temperature and density while RS measures the neutral density. LIBS is performed by focusing laser radiation onto a target surface, ablating the surface, forming a plasma plume, and analyzing the plume to determine the surface matter composition. The design elements and preliminary measurements for the TS, RS, and LIBS will be discussed, along with considerations for further optimization. [Preview Abstract] 

BP8.00065: Determining the Spatial Coherence of Modes in a Linear Plasma Using Filterscopes H. Ray , T.M. Biewer , D. Fehling , E.A. Unterberg , G.N. Luo Oak Ridge National Laboratory's (ORNL) prototype Material Plasma Exposure eXperiment (ProtoMPEX) is a linear plasma device dedicated to the understanding of plasma material interaction (PMI) physics. A photo multiplier tube (PMT) based diagnostic system called a filterscope examines the visible light emission from ProtoMPEX in the radial (r) and axial (z) directions. Each of the filterscope's twelve PMTs has a calibrated D filter for plasma edge and target region analysis. Fiber optics located at various r and zpositions along ProtoMPEX will transmit the brightness of the plasma as a function of time to the filterscope. Analysis of the data will include performing a Fast Fourier Transform (FFT) to determine the dominant modes in the spectral emission and characterizes these modes in relation to the facilities operating parameters. Pairs of measurements are also analyzed to determine the spatial coherence of the signals, which include phase shifts and relative differences, in order to determine mode localization. [Preview Abstract] 

BP8.00066: Digital Holography for Plasma Facing Component (PFC) Erosion Measurement C.E. (Tommy) Thomas Jr. , T.M. Biewer , L.R. Baylor , S.K. Combs , S.J. Meitner , D.L. Hillis , E.M. Granstedt , R. Majeski , R. Kaita One of the more serious engineering problems facing magnetic fusion energy reactors is the plasma/firstwall or plasma/divertor interface. Hot particles striking these PFC's could easily force replacement in less than a year. Insitu quantitative realtime erosion diagnostics to help understand the erosion process are not currently available. Single wavelength Digital Holography (DH) has been developed to a considerable level of sophistication and dualwavelength (synthetic wavelength) DH has the potential to be a reliable vibrationresistant erosion diagnostic. Ambiguity free measurements at kHz rates of up to 1 cm of erosion with $\sim$ 1 micron resolution into the PFC and diffraction limited resolution transverse to the PFC are possible. Development of DH as an insitu realtime PFC erosion diagnostic will be discussed and example data from singlewavelength DH will be presented. [Preview Abstract] 

BP8.00067: Monte Carlo TRIM simulations, with evolving target and surface morphology, in support of plasma simulations and devices Kyle Lindquist , Davide Curreli , Kishor Kalathiparambil , David Ruzic Simulations using fractal and dynamic versions of the BCA code TRIM (Fractal TRIDYN) are reported. The sputtering yields from the simulations are being used to support experiments and simulations of plasma devices. The use of linear plasma scenarios can provide an intermediate point of understanding before attempting full tokamak systems. Specifically, we are targeting experiments, like those at PISCESB, of light, low energy ions (H/D/T/He) incident on beryllium targets. The sputtering yield of Be by D and He has been shown at PISCESB to be about 6 and 13 times smaller, respectively, than traditional TRIM results would predict. We show what combinations of surface roughness, target composition, and incident ion composition can produce the observed sputtering yields. The current model for sputtering in the SOLPS code uses the Bohdansky formula. The surface roughness feature of Fractal TRIDYN can be used to improve upon this. Shown are database results and the rough surface fitting parameters that are being used to implement an improved curve fit for the Bohdansky model. [Preview Abstract] 

BP8.00068: Effects of hydrogen surface processes on hydrogen retention in plasma facing components Jerome Guterl , Roman Smirnov , Sergei Krasheninnikov Hydrogen retention and recycling on metallic plasmafacing components (PFCs) are among the keyissues for future fusion devices due to both safety and operational reasons. For tungsten, which has been chosen as divertor material in ITER, parameters of hydrogen desorption from Wsurfaces, experimentally measured for fusionrelated conditions, show a large discrepancy [1]. Indeed, various complex phenomena may affect hydrogen desorption (e.g atomic islands, roughness, surface reconstruction, impurities, ect). In this work, we investigate effects of hydrogen desorption from W surfaces on hydrogen retention in W material. Two regimes of hydrogen surface desorption (readsorptionlimited and recombinationlimited) can be identified and may affect the kinetic order of desorption. Within these desorption regimes, it is shown that release of hydrogen from W material in fusionrelated conditions may be surfacelimited at low temperature and diffusionlimited at high temperature. Analyses of hydrogen release regimes for thermodesorption experiments and plasma operations in fusion reactors show that surface processes may strongly affect retention and release of hydrogen from W material. In this context, effects of W surface coverage with oxygen on hydrogen desorption are discussed since high concentrations of oxygen on PFCs surfaces are expected in future fusion devices. \\[4pt] [1] R. Causey, Journal of Nuclear Materials 300 91117 (2002) [Preview Abstract] 

BP8.00069: Development of an analytical hydrogen isotope exchange model in fusion relevant plasma facing components Joseph Barton , Yongquang Wang , Russell Doerner , George Tynan A simple model for H isotope retention depth profiles in W is developed, which can easily be extended to other plasma facing components (PFCs). This retention model is subsequently used to model how the depth profile changes after H isotope exchange. We calculate how trapping defects in W trap D (or H) inventory as W is being exposed to plasma. The model characterizes each trapping site by a trapping rate and a release rate, where the only free parameters are the distribution of these trapping sites in the material. The filled trap concentrations for each trap type are modeled as a diffusion process because postmortem D depth profiles indicate that traps are filled well beyond the ion implantation zone (34 nm with 100 eV ions). Using this retention model, an isotope exchange rate is formulated. The retention model and isotope exchange rate are compared to low temperature (100 $^{\circ}$C) isotope exchange experiments in W with good agreement. Experimental retention profiles were measured using the D($^{3}$He,p)$\alpha $ nuclear reaction after plasma treatment. We additionally discuss how a uniform damage profile up to 1 micron in W induced by Cu ions using incident energies of 0.5, 2, and 5 MeV affect retention in W and the retention model. [Preview Abstract] 

BP8.00070: Temperature effects in accumulation of deuterium and helium at the grain boundaries of a nanograined tungsten Igor Kaganovich , Predrag Krstic , Edward Startsev It has been known that defects in tungsten, in particular at the grain boundaries, are preferable sites for deuterium and helium retention. For the case of the nanograined boundaries, we study by classical molecular dynamics the cumulative retention of deuterium and helium at impact energies below 100 eV as functions of tungsten temperature at models of the dislocation boundaries. We obtain a strong preference of the retention of the impact particles at the boundaries at high temperature of 1000K. [Preview Abstract] 

BP8.00071: Retention property of deuterium for fuel recovery in divertor by using hydrogen storage material Saori Mera , Akira Tonegawa , Yoshihito Matsumura , Kohnosuke Sato , Kazutaka Kawamura Magnetic confinement fusion reactor by using Deuterium and Tritium of hydrogen isotope as fuels is suggested as one of the future energy source. Most fuels don't react and are exhausted out of fusion reactor. Especially, Tritium is radioisotope and rarely exists in nature, so fuels recovery is necessary. This poster presentation will explain about research new fuel recovery method by using hydrogen storage materials in divertor simulator TPDSheet IV. Samples are tungsten coated with titanium; tungsten of various thickness, and titanium films deposited by ion plating on tungsten substrates. The sample surface temperature is measured by radiation thermometer. Retention property of deuterium after deuterium plasma irradiation was examined with thermal desorption spectroscopy (TDS). As a result, the TDS measurement shows that deuterium is retained in titanium. Therefore, Titanium as a hydrogen storage material expects to be possible to use separating and recovering fuel particles in divertor. [Preview Abstract] 

BP8.00072: Molecular dynamics simulations of growth and coalescence of helium nanobubbles in tungsten Roman Smirnov , Sergei Krasheninnikov , Jerome Guterl It was experimentally observed that filamentary nanostructures, called fuzz, can grow on tungsten surfaces irradiated with plasma containing helium. Although the mechanism of the fuzz growth is not clearly understood, experiments show that formation of helium nanobubbles in tungsten always precedes fuzz creation. In this work we investigate mechanisms of growth and coalescence of helium bubbles using molecular dynamics code LAMMPS. We demonstrate that the growth process is governed by crystal symmetries and properties of generated dislocations forming helium nanobubbles of nonspherical geometry. This produces complex stress field in the tungsten lattice around the bubble with distinct compression and tension regions. We show that helium transport in the stressed lattice in bubble vicinity can be dominated by drift from the compression to tension regions. Helium transport coefficients in tungsten are also obtained. Modeling of two closely positioned helium nanobubbles demonstrates that their coalescence proceeds preferentially by lateral growth. The implications of the obtained results on fuzz formation mechanism are discussed. [Preview Abstract] 

BP8.00073: Effect of Li coatings on coarsegrained W exposed to high flux He plasmas at high temperatures Anton Neff , Jean Paul Allain , Thomas Morgan Tungsten is appealing as a plasma facing component (PFC) because of its high sputter threshold, high melting temperature, and good thermal conductivity. However, when exposed to He ions at low energy and high flux, like those in a tokamak divertor, the surface microstructure changes detrimentally, creating bubbles, holes, and fuzz. Recent studies show that adding impurities (C and Be) to the He plasma can inhibit the growth of fuzz. Additionally, lithium as a PFC coating in multiple tokamaks has improved plasma performance. We investigated the effect that a thin $\sim$500 nm Li coating had on the formation of these surface defects in W. Samples were exposed in the linear plasma device Magnum PSI, at fluxes of $\sim$1024 m$^{2}$s$^{1}$ and T$_{surf}$ $>$700$^{\circ}$C. After irradiation, the surface of the samples were characterized with scanning electron microscopy (SEM). These results will be presented along with XPS and SIMS results investigating the survivability of the Li coating under these conditions. [Preview Abstract] 

BP8.00074: Disruption Studies and Simulations in Ignitor* G. Ramogida , F. Villone , G. Rubinacci , B. Coppi The prediction of plasma disruption features and evaluation of the associated EM loads played an important role in the development of Ignitor [1]. The kind and number of expected plasma disruptions drove the development of the plasma scenarios and the design of invessel components, as these events produced by far the largest EM loads the components must withstand. A strong integration of physics and engineering expertise was required to estimate the range of expected variation, based on the experimental data from existing machines, of the main parameters of the disruptions: thermal and current quench times, evolution of the plasma current, li, safety factor limits, halo current fraction and width, and radiated heat fraction. The MAXFEA axisymmetric 2D MHD code was used to evaluate the effects on the induced currents and EM loads caused by variation of the disruption parameters. Further, the detailed evolution of the plasma was simulated using the CarMa0NL code, which is able to selfconsistently couple a nonlinear axisymmetric plasma evolution with volumetric 3D conductors. This allows the evaluation of the effects of the nonaxisymmetric components of the machine such as the plasma chamber ports. *US DOE partly sponsored.\\[4pt] [1] B. Coppi, et al. \textit{Nucl. Fus}. 53, 104013 (2013). [Preview Abstract] 

BP8.00075: DIAGNOSTIC MEASUREMENTS \& ANALYSIS 

BP8.00076: Two Photon Absorption Laser Induced Fluorescence of Helium Ions in a Microwave Assisted Helicon Source Earl Scime The spectroscopic measurement of helium ion velocity distribution functions in a low temperature plasma is problematic for a number of reasons. First and foremost is the difficulty in accessing the UV and soft xray transitions to the ground state. Conventional laser induced fluorescence on ions in plasmas is routinely performed in argon, neon, xenon, and barium. Twophoton absorption laser induced fluorescence (TALIF) on neutrals has been demonstrated in hydrogen, nitrogen, and oxygen plasmas. We have successfully performed LIF on helium atoms and have had some hints of success with laser absorption spectroscopy on excited states of helium ions, the n $=$ 5 to n $=$ 6 transition in the infrared (1012 nm). Here we report a new approach using TALIF to access the n $=$ 2 to n $=$ 6 transition of singly ionized helium. The fluorescence path at 656 nm completes the threelevel sequence. To obtain the electron temperatures necessary to create a sufficient population of metastable helium ions trapped in the 2S state, we have increased the electron temperature of a helicon plasma with 1.2 kW of microwaves at 2.45 GHz. Here we report emission spectroscopy measurements that confirm the increase in excited state population densities and preliminary TALIF measurements on helium ions. [Preview Abstract] 

BP8.00077: Improving Resolution of Confocal Laser Induced Fluorescence in Argon Helicon Plasma Mark Soderholm , Robert Vandervort , Earl Scime , John McKee , Dustin McCarren Laser Induced Fluorescence (LIF) provides measurements of flow speed, temperature and when absolutely calibrated, density of ions or neutrals in a plasma. Traditionally, laser induced fluorescence requires two ports on a plasma device. One port is used for laser injection and the other is used for fluorescence emission collection. Traditional LIF is tedious and time consuming to align. These difficulties motivate the development of an optical configuration that requires a single port and remains fully aligned at all times; confocal LIF. Our confocal optical design employs a single two inch diameter lens to both inject the laser light and collect the stimulated emission from an argon plasma. A dichroic mirror is used to separate the injected laser light from the collected emission. The measurement location is scanned radially by manually adjusting the final focusing lens position. In the initial version of the confocal optical system, measurements were poorly resolved radially because they were integrated over a fairly large path length ($\sim$ 4 cm) centered at the focal point. Here we present collected data from a modified configuration that significantly improves the special resolution of confocal measurements. The confocal measurements are compared to traditional, twoport, LIF measurements over the same radial range. [Preview Abstract] 

BP8.00078: Continuous Wave Cavity RingDown Spectroscopy and Laser Induced Fluorescence Measurements of Argon Ion Velocity Distribution Functions in a Helicon Plasma Dustin McCarren , Robert Vandervort , Mark Soderholm , Earl Scime LIF is an established and powerful technique, but suffers from the requirement that the initial state of the LIF sequence have a substantial density. This usually limits LIF to ions and atoms with large metastable state densities for the given plasma conditions. Cavity ring down spectroscopy (CRDS) is a proven, ultrasensitive, cavity enhanced absorption spectroscopy technique and when combined with a continuous wavelength (CW) diode laser that has a sufficiently narrow line width, the Doppler broadened absorption line, i.e., the target specie velocity distribution function (VDFs), is measured. CWCRDS is designed for measurements of ion and atom states inaccessible to conventional techniques such as LIF. However, being a line integrated technique, CWCRDS lacks the spatial resolution of LIF. We present a comparison of CWCRDS and spatially resolved LIF measurements of the VDFs in an argon plasma using the 668.614 nm (in vacuum) line of Ar II. [Preview Abstract] 

BP8.00079: Direct Measurements of the Spatial and Velocity Dependence of the Ion Density Fluctuation Spectrum of a Laboratory Plasma with Two Independent LIF Schemes Sean Mattingly , Jorge Berumen , Feng Chu , Ryan Hood , Fred Skiff By using two independently tunable lasers, each with its own collection optics and Ar II LIF transition scheme, we are able to investigate plasma ion density fluctuations as a function of not only spatial scales but also as a function of ion velocities as sampled on different points of a single Doppler  broadened spectral emission line. We do this by measuring the two point correlation $C(x,v, x', v', \tau) = \langle f(x, v, t) f(x', v', t  \tau) \rangle_t$. With the current system, the two carriages determine $x$ and $x'$, while the velocities selected by each laser determine $v$ and $v'$. Using the two lasers to make two point correlations in phase space demonstrates effects that are not fully understood. In this experiment, we explore the striking difference in correlations when, in the past, the particle orbits overlap in space versus when they do not overlap. This is performed on a small cylindrical laboratory plasma with $n \sim 10^9 cm^{3}, T_e \sim 5eV, T_i \sim 0.06 eV$, and a $1 kG$ axial magnetic field. LIF is performed on ions at two locations aligned with the magnetic field line with a viewing volume comparable to the size of the Larmor radius. Results and interpretations from these experiments are presented and discussed. [Preview Abstract] 

BP8.00080: Electron and ion currents to a planar probe oriented at an arbitrary angle to the magnetic field in a cesium Q machine plasma Michael J. McKinlay , Sean M. Harding , Robert L. Merlino Current collection to a planar Langmuir probe in a magnetized Q machine plasma was investigated. The Q machine was operated in the singleended mode with cesium ions having densities in the range of 10$^{\mathrm{14}}$ to 10$^{\mathrm{15}}$ m$^{\mathrm{3}}$, electron and ion temperatures, T$_{\mathrm{e}}\approx $T$_{\mathrm{i}}\approx $0.2 eV, and magnetic fields from 0.06 T to 0.48 T. The probe was a disk of 9.5 mm diameter, and the side facing away from the plasma source was insulated. The effect of varying the angle between the magnetic field and the probe's surface normal vector on the ion and electron saturation currents and the floating potential was the focus of this study. The effect of varying the probe normalmagnetic field angle on the excitation and quenching of currentdriven electrostatic ion cyclotron waves was also observed. [Preview Abstract] 

BP8.00081: Design and Operation of a TwoColor Interferometer to Measure Plasma and Neutral Gas Densities in a LaserTriggered Spark Gap Switch J.F. Camacho , E.L. Ruden , M.T. Domonkos , A. SchmittSody , A. Lucero A MachZehnder imaging interferometer, operating with 1064nm and 532nm wavelength beams from a shortpulse laser and a frequencydoubled branch, respectively, has been designed and built to simultaneously measure plasma free electron and neutral gas densities profiles within a lasertriggered spark gap switch with a 5mm gap. The switch will be triggered by focusing a separate 532nm or 1064nm laser pulse along the gap's axis to trigger lowjitter breakdown. Illuminating the gap {\it transverse} to this axis, the diagnostic will generate interferograms for each wavelength, which will then be numerically converted to phaseshift maps. These will be used to calculate independent lineintegrated free electron and neutral density profiles by exploiting their different frequency dispersion curves. The density profiles themselves, then, will be calculated by Abel inversion. Details of the interferometer's design will be presented along with density data obtained using a variety of fill gasses at various pressures. Other switch parameters will be varied as well in order to characterize more fully the performance of the switch. [Preview Abstract] 

BP8.00082: Development of a dual $\bf v$ and $\dot{\bf B}$ diagnostic for fast reconnection Douglass Endrizzi , Jan Egedal , Joseph Olson , Cary Forest , John Wallace The Terrestrial reconnection experiment (TREX) under construction at the Wisconsin Plasma Astrophysics Facility will study magnetic reconnection in a low$\beta$, collisionless plasma. A probe to simultaneously measure the velocity and magnetic fields during a fast reconnection event is being constructed. An array of 3D $\dot{\bf B}$ probes and 2D Mach probes will measure at a $\sim$2 cm spatial resolution and MHz frequencies. Using a digitally controlled drive, the probe will be able to sweep the full radial length (1.5 m) of the experiment and through an angle of $\sim$1 radian, thus providing significant coverage of the anticipated event region. Measurements and results from the probe will be presented. [Preview Abstract] 

BP8.00083: Comparison of imaging and probe measurements in a linear plasma column A.D. Light , S.C. Thakur , C. Brandt , Y. Sechrest , G.R. Tynan , T. Munsat The advent of fast imaging diagnostics, which provide twodimensional measurements on relevant plasma time scales, has proven invaluable for interpreting plasma dynamics in laboratory devices. Despite its success, imaging remains a qualitative aid for many studies, because intensity cannot often be mapped onto a single physical variable for use in a theoretical model. This study explores the relationship between visiblelight and electrostatic probe measurements in the Controlled Shear Decorrelation Experiment (CSDX). CSDX is a wellcharacterized linear machine producing dense plasmas relevant to the tokamak edge ($T_e \sim 3$ eV, $n_e \sim 10^{13}$/cc). Visible light from ArI and ArII line emission is collected at high frame rates using a fast digital camera. Floating potential and ionsaturation current are measured by an array of electrostatic probe tips. We construct a detailed comparison between imaging and probe measurements of fluctuations, including temporal, spatial, and spectral properties. In addition, we combine probe and imaging techniques to identify modes in a multiinstability regime. [Preview Abstract] 

BP8.00084: EUV and visible light imaging of magnetic reconnection associated with RayleighTaylor instability in MHD driven jets KilByoung Chai , Paul Bellan A highspeed EUV movie camera has been developed for imaging magnetic reconnection in the Caltech MHDdriven jet experiment. In order to achieve high temporal resolution, a highspeed visible camera (up to 2x10$^{8}$ fps) is utilized with a fastdecaying YAG:Ce scintillator crystal that converts EUV radiation into visible light. A customdesigned, broadband Si/Mo multilayer mirror having central wavelength at 36 nm is used to form an image on the scintillator crystal. The jet 3D structure is imaged in visible light by a twobranch fiber bundle which simultaneously captures end and side view images. The fiber bundle is coupled to the highspeed visible light movie camera. Comparison of EUV and visible light movies shows that the EUV images are similar to visible light images at early times. However, the EUV images differ from the visible light images when a RayleighTaylor instability occurs. A small segment near the apex of the kinked jet becomes extremely bright in EUV but dark in visible light. Future plans include further investigation of this bright spot, plasma evolution and upgrade of optical sensitivity by better optical coupling to the scintillator crystal. [Preview Abstract] 

BP8.00085: Upgrade Plans for the CMod FIR Polarimeter R. Watterson , D. Garnier , J. Irby , D.L. Brower , P. Xu , W.F. Bergerson , W.X. Ding , W. Guttenfelder , E.S. Marmar The 3chord FIR polarimeter presently deployed on CMod is capable of responding to both fast changes in the plasma equilibrium and high frequency fluctuations. It operates under ITERlike plasma conditions and magnetic fields, and uses an optical layout similar to that proposed for ITER. The details of this system and some results from the CMod 2012 campaign will be presented, along with the design of the upgrade that is now being implemented. The new system will provide horizontal chords near the midplane and low loss etalon windows to improve both the signal level and our ability to study magnetic fluctuations. The laser table has been relocated from the CMod cell to a shielded and climate controlled location, and improvements have been made to its acoustic isolation. New collimation optics, and a beamline needed to convey the FIR beams into the tokamak port have been designed. Improvements to the detector electronics will also be discussed, as will initial testing of the laser system and reference detectors during CMod operation. [Preview Abstract] 

BP8.00086: FaradayEffect PolarimeterInterferometer System for current density measurement on EAST Haiqing Liu , Yinxian Jie , Weixing Ding , David Lyn Brower , Zhiyong Zou , Weiming Li , Jinping Qian , Yao Yang , Long Zeng , Ting Lan , Gongshun Li , Liqun Hu , Baonian Wan A multichannel farinfrared laserbased \textbf{PO}larimeter\textbf{INT}erferometer (\textbf{POINT}) system utilizing the threewave technique is under development for current density and electron density profile measurements in the EAST tokamak. Novel molybdenum retroreflectors are mounted in the inside wall for the doublepass optical arrangement. A Digital Phase Detector with 250 kHz bandwidth, which will provide realtime Faraday rotation angle and density phase shift output, have been developed for use on the POINT system. System time response ($\sim$ 1 microsecond) and phase resolution (\textless 0.1$^{\circ})$ allows resolution of fast equilibrium changes associated with MHD events. Initial calibration indicates the electron lineintegrated density resolution is less than 5 $\times$ 10$^{16}$m$^{2}$ ($\sim$ 2$^{\circ}$), and the Faraday rotation angle rms phase noise is \textless 0.1$^{\circ}$. Initial results of POINT system will be presented. [Preview Abstract] 

BP8.00087: Plasma spectroscopy using optical vortex laser Shinji Yoshimura , Mitsutoshi Aramaki , Kenichiro Terasaka , Yasunori Toda , Uwe Czarnetzki , Yutaka Shikano Laser spectroscopy is a useful tool for nonintrusive plasma diagnostics; it can provide many important quantities in a plasma such as temperature, density, and flow velocity of ions and neutrals from the spectrum obtained by scanning the frequency of narrow bandwidth laser. Obtainable information is, however, limited in principle to the direction parallel to the laser path. The aim of this study is to introduce a LaguerreGaussian beam, which is called as optical vortex, in place of a widely used HermiteGaussian beam. One of the remarkable properties of the LaguerreGaussian beam is that it carries an angular momentum in contrast to the HermiteGaussian beam. It follows that particles in the laser beam feel the Doppler effect even in the transverse direction of the laser path. Therefore it is expected that the limitation imposed by the laser path can be overcome by using an optical vortex laser. The concept of optical vortex spectroscopy, the development of the laser system, and some preliminary results of a proofofprinciple experiment will be presented. [Preview Abstract] 

BP8.00088: Measurements of the ion temperature and ion energy distribution in a linear pulsed plasmamaterial interaction test stand Michael Christenson , Soonwook Jung , Casey Bryniarski , Kishor Kalathiparambil , Daniel Andruczyk , David Ruzic Critical components in understanding interactions between the highly transient plasma and target materials in the ThermoElectricdriven Liquidmetal plasmafacing Structures (TELS) device are the ion temperature and subsequent energy distribution, since the ions are nearly as energetic as the electrons under such extreme conditions. An electrostatic energy analyzer has been proposed and modified to extract this information under different pulse conditions in an effort to gain insight about plasma transport to the target region. The electrostatic analyzer was chosen as the most practical method for evaluating ion information in TELS, since it is suitable for measuring temperatures on the order of 10 to 100 eV. Accounting for high displacement current, recent results indicate ion temperatures on the order of 19.95 $\pm $ 1.39 eV when applying a guiding magnetic field to improve transport, which are in good agreement with theoretical and experimental predictions subject to specific pulse conditions. The development and modification of the electrostatic analyzer are discussed in conjunction with recent modifications to the TELS device, including the addition of compact toroid magnetic fields used to generate a reversed field configuration. [Preview Abstract] 

BP8.00089: Investigation of XRay Thomson Scattering Using A Statistical Approach Laura Johnson We present a statistical method of computing xray Thomson scattering signals. This model uses average atom wave functions for both bound and continuum electrons, which are computed in a spherically symmetric, selfconsistent potential. The wave functions are used to obtain electron distributions for a statistical approach to computing the scattering signals. We compare the differences between using distortedwave continuum electrons and freewave electrons in both the statistical approach and the impulse approximation. The results are compared to various experiments including experimental data taken at Cornell's Laboratory of Plasma Studies. [Preview Abstract] 

BP8.00090: Simulation of Laser Induced Fluorescence (LIF) Signals in a Plasma F. Chu , F. Skiff Velocityspace diffusion and electric mean fields play important roles in the transport phenomena in the turbulent plasma. One way to explore how they determine transport is through the optical testparticle diagnostics, which is based on using ionic electronic states as a means of tagging particles. It requires a means of changing and measuring the state densities by optical pumping and LIF. In order to interpret the LIF signals, which provide the information on particle orbits, we introduce a transfer function that specifies the probability of finding a particle at position x and velocity v at time t, given that the particle was at position x' and velocity v' at time t'. We model the signal at first without the presence of waves in the plasma, studying only the roles that optical pumping and velocityspace diffusion play in the resulting LIF signals. Then we consider how meanfield waves affect the distributions of metastable states. Finally we combine the two factors to construct the complete theory. We note that even ``ordinary'' LIF using a single laser and detection system can benefit from the testparticle approach under conditions where there is significant optical pumping or where the metastable lifetime is not long compared to a wave period. [Preview Abstract] 

BP8.00091: NONNEUTRAL, ANTIMATTER \& STRONGLY COUPLED PLASMAS 

BP8.00092: Nonlinear Interactions of TrivelpieceGould Waves Arash Ashourvan , Daniel H.E. Dubin We study nonlinear TrivelpieceGould waves in a cold, finite length plasma model. Analytical expressions for the forms and frequencies of both traveling and standing cnoidal waves are obtained, and parametric resonances between waves are studied and compared to numerical solutions of the 1D fluid equations. For waves with $k_{m} < k_{\bot}$, where $k_{m}$ and $k_{\bot}$ are the axial and perpendicular wave numbers respectively, 3wave resonance conditions can be satisfied. Using perturbation theory we obtain a reduced system of evolution equations for slowly varying mode amplitudes in a 3 wave interaction. We use them to study the parametric resonance between a dominant $m=2$ mode and a small amplitude $m=1$ mode, including the effect of higher harmonics. We obtain an instability threshold amplitude $A_{2}^{\mathrm{th}}$ for mode $m=2$. For $A_{2} > A_{2}^{\mathrm{th}}$ mode $m=1$ becomes unstable and grows exponentially, whereas for $A_{2} < A_{2}^{\mathrm{th}}$, mode $m=1$ exhibits beat wave oscillations. We find that if enough harmonics are kept in the theory, $A_{2}^{\mathrm{th}}$ converges to a value independent of the number of harmonics. On the other hand, for a short plasma with $k_{1} \sim k_{\bot}$, 3wave resonances cannot occur but conditions allow 4wave resonances, especially in the short wavelength scales $(k_{m} > k_{\bot}$). In our simulations we observe mode instabilities that have signatures of this 4wave interaction. [Preview Abstract] 

BP8.00093: Nonresonant Particle Heating due to Collsional Separatrix Crossings F. Anderegg , M. Affolter , D.H.E. Dubin , C.F. Driscoll We observe weak plasma heating when a pure ion column is ``sloshed'' back and forth across a partial trapping barrier, and coherent laser diagnostics characterize the resulting particle distributions. Here, an externally applied thetasymmetric ``squeeze'' potential creates a velocity separatrix between trapped and passing particles, and weak collisions at rate $\nu_c$ cause separatrix crossings. The trapped particles are repeatedly compressed and expanded (by $\delta L$) whereas the passing particles counterstream and Debye shield the resultant potential variations. The LIF diagnostics then clearly determine the separatrix energy $E_{sep} (r)$, since the trapped and passing particle distributions are inphase and outofphase with the plasma motion. The measured $E_{sep} (r)$ is in agreement with that calculated from a $(r,z)$ BoltzmannPoisson equilibrium solution. Theory predicts heating from separatrix crossings scaling as $\nu_c^{1/2} E_{sep}^2 ( \delta L / L )^2 $, distinct from bulk viscosity heating scaling as $\nu_c^1 $. Experimental scalings with density and temperature will allow direct comparison to theory. [Preview Abstract] 

BP8.00094: Nonlinear Coupling and Decay Instability of Plasma Waves M. Affolter , F. Anderegg , C.F. Driscoll , F. Valentini We measure the nonlinear coupling of plasma waves, for both the ``standard'' Langmuir waves with $\mbox{v}_{phase} \gg \mbox{v}_{bar} $, and for the unusual ``EAW'' (KEEN) waves with $\mbox{v}_{phase} \sim \mbox{v}_{bar} $. These are $\theta $symmetric standing modes on pure ion and (separately) pure electron plasma columns, with discrete wavenumbers $k_{z} =m_{z} (\pi /L_{p} )$. The nonlinear coupling rates are measured between large amplitude $m_{z} =2$ waves and small amplitude $m_{z} =1$ waves, which have a small detuning $\Delta \omega =2\omega_{1} \omega_{2} $. For Langmuir waves at small excitation amplitudes, this detuning causes the $m_{z} =1$ mode amplitude to ``bounce'' at rate $\Delta \omega $, with amplitude excursions $\Delta A_{1} \propto \delta n_{2} /n_{0} $ consistent with cold fluid theory and Vlasov simulations. At larger excitation amplitudes, theory and simulations predict phaselocked exponential growth of the $m_{z} =1$ mode. Experimentally we find the effects of detuning to be more pervasive than simple theory would suggest. Typically at these large amplitudes we observe strong amplitude bouncing, with a yet unexplained slower average growth. In contrast, EAW waves exhibit phasedlocked exponential growth or no growth at all, apparently due to ``frequency fungibility'' of the EAW waves. Measurements on higher temperature Langmuir waves with $\mbox{v}_{phase} \sim 4\mbox{v}_{bar} $ are being conducted to investigate the effects of waveparticle kinetics on the nonlinear coupling rates. [Preview Abstract] 

BP8.00095: Nonlinear Spatial Landau Damping of Plasma Waves Beating at Plasma Angular Velocity A.A. Kabantsev , C.F. Driscoll Experiments on pure electron plasmas characterize the nonlinear beat between two counterpropagating plasma waves, and the spatial Landau damping of the beat wave at the wave/rotation critical radius. The two plasma waves are $(m_{\theta } =1,k_{z} =1,\omega =\omega_{\ast } \pm \omega_{1} )$, giving the beat wave with $(m_{\theta } =2,\omega =2\omega_{\ast } )$. The beat wave is resonant with the plasma rotation $\Omega (r)$ at radius $r_{\ast } $ where $\Omega (r_{\ast } )=\omega_{\ast } $. The net effect of this resonance is an energy exchange through waveparticle interaction between the two primary plasma waves and the background plasma rotation. Initial excitation of only one of the waves leads first to its fast sharing of energy with the other wave, and then followed by a slower combined decay of both waves. In contrast, initial excitation of both waves to (approximately) the same amplitude leads to three alternative scenarios: 1) both plasma waves may show the slow and synchronous decay evolution; 2) one of the waves may decay faster, with temporarily arrested decay of the other; 3) it may switch back and forth (seemingly randomly) between the first two types of evolution. Interestingly, wave/particle energy flow can be \textit{reversed} when the plasma density profile is made to have a positive density gradient at $r_{\ast } $. In this case, spontaneous excitation (instability) of both $\omega =\omega _{\ast } \pm \omega_{1} $ plasma waves is observed. [Preview Abstract] 

BP8.00096: A Novel Damping Mechanism for Diocotron Modes Chi Yung Chim , Thomas M. O'Neil Recent experiments with pure electron plasmas in a MalmbergPenning trap have observed the algebraic damping of $m=1$ and $m=2$ diocotron modes.\footnote{A.A. Kabantsev \textit{et. al.}, Phys. Rev. Lett. \textbf{112}, 115003, 2014. See also the invited talk by C. F. Driscoll.} Transport due to small field asymmetries produces a low density halo of electrons moving radially outward from the plasma core, and the mode damping begins when the halo reaches the resonant radius, where $f=mf_{E\times B}(r)$. The damping rate is proportional to the flux of halo particles through the resonant layer. The damping is related to, but distinct from spatial Landau damping, in which a linear waveparticle resonance produces exponential damping. This poster explains with analytic theory and simulations the new algebraic damping due to both mobility and diffusive fluxes. The damping is due to transfer of canonical angular momentum from the mode to halo particles, as they are swept around the ``cat's eye'' orbits of resonant waveparticle interaction. Another picture is that the electrons in the resonant layer form a dipole $(m=1)$ or quadrupole $(m=2)$ density distribution, and the electric field for this distribution produces $E\times B$ drifts that symmetrizes the core and damps the mode. [Preview Abstract] 

BP8.00097: Enhanced Collision Rates in Correlated Plasmas C.F. Driscoll , F. Anderegg , D.H.E. Dubin , T.M. O'Neil Experiments on cryogenic pure ion plasmas corroborate the Salpeter collisional enhancement\footnote{E.E.~Salpeter \& H.M.~VanHorn, Astrophys. J. 155, 183 (1969)} factor $g ( \Gamma )$ when the correlation parameter $\Gamma \equiv e^2 / a T$ is large. This factor enhances the perptoparallel collision rate in the magnetized plasmas described here,\footnote{D.H.E.~Dubin, Phys. Plas. 15, 055705 (2008)} and also enhances the nuclear reaction rates in dense stellar interiors. The enhancement is caused by plasma screening of the repulsive Coulomb potential, enabling closer collisions for a given particle energy. The Salpeter theory assumes thermal equilibrium screening, whereas various dynamical theories suggest other factors. Prior experiments\footnote{F. Anderegg et al., PRL 102, 185001 (2009)} corroborate the predicted $g \sim \exp ( \Gamma )$ enhancement with enhancements as large as $g \sim 10^{11}$. Current theory is considering the effects of parallel collisions in multispecies ion plasmas, and cyclotron modes and energy exchange. Current experiments with improved laser cooling and plasma stability will provide more accurate tests of equilibrium theory in the sensitive regime of $\Gamma \leq 1$, and may also approach the (classical) pycnonuclear regime. [Preview Abstract] 

BP8.00098: Parallel Slowing from LongRange Collisions in a Magnetized Plasma Daniel H.E. Dubin This poster presents a new theory of the collisional drag rate $\nu$ parallel to the magnetic field in a plasma for which $r_c < \lambda_D$, where $r_c$ is the thermal cyclotron radius and $\lambda_D$ is the Debye length.\footnote{D. Dubin, Phys. Plasmas {\bf21}, 052108 (2014)} In such a plasma, longrange collisions with impact parameters $\rho > r_c$ make a dominant contribution to the drag. Such collisions are described by guiding centers moving in one dimension (1D) along the magnetic field. These 1D longrange collisions are not included in the classical collision rates. We show that such collisions separate into two classes: Boltzmann collisions where colliding particles can be treated as an isolated pair, and FokkerPlanck (FP) collisions where many weak interactions are occurring simultaneously. These collision classes are separated by a new fundamental length scale $d$ where $d^{\hspace{1. pt} 5} \equiv (e^2/T)^3 (T/m) \nu^{2}$ : FP or Boltzmann collisions dominate for $\rho > d$ or $\rho < d$ respectively. Furthermore, the drag due to Boltzmann collisions is enhanced by ``collisional caging'': colliding charges are influenced by surrounding charges to diffuse in relative velocity, reversing their 1D motion and colliding several times while remaining correlated. [Preview Abstract] 

BP8.00099: Numerical solution for linear cyclotron and diocotron modes in a nonneutral plasma column Daniel Walsh , Daniel H.E. Dubin This poster presents numerical methods for solution of the linearized VlasovPoisson (LVP) equation applied to a cylindrical singlespecies plasma in a uniform magnetic field. The code is used to study zindependent cyclotron and diocotron modes of these plasmas, including kinetic effects. We transform to polar coordinates in both position and velocity space and Fourier expand in both polar angles (i.e. the cyclotron gyro angle and $\theta$). In one approach, we then discretize in the remaining variables $r$ and v (where v is the magnitude of the perpendicular velocity). However, using centered differences the method is unstable to unphysical eigenmodes with rapid variation on the scale of the grid. We remedy this problem by averaging particular terms in the discretized LVP operator over neighboring gridpoints. We also present a stable Galerkin method that expands the r and v dependence in basis functions. We compare the numerical results from both methods to exact analytic results for various modes. [Preview Abstract] 

BP8.00100: Experimental Investigation of Rotational, Pumping, Magnetic Pumping and Toroidal Asymmetry Modes in a Toroidal Electron Plasma A.R. Doares , K. Wang , A.S. Patterson , M.R. Stoneking Electron plasma is confined with a purely toroidal magnetic field in the Lawrence NonNeutral Torus II ($R_{0} = $18 cm, \textit{a} $\sim$ 2 cm), for times ($\sim$ 1 s) that are much longer than any of the dynamical timescales of the system. The experiment can be operated as a variablelength partial torus or a full torus trap. The damping rate for the $m=$1 diocotron mode in a partial torus trap is found to depend on the equilibrium position (major radius) and on magnetic field (150 G  550 G). We report on efforts to explain these results in terms of rotational and magnetic pumping effects using 3D (PoissonBoltzmann) equilibria calculations. Novel full torus asymmetry modes are examined with multiple separatrices and a new charge tomography is developed to infer charge density from image charge measurements on the conducting boundary. [Preview Abstract] 

BP8.00101: Phase space dynamics of Landau damping with a truncated Maxwellian distribution Grant Hart , Emma Hoggan , Ross Spencer We have built a ParticleInCell (PIC) simulation that models a damped wave in a nonneutral plasma. In this simulation we can cut off the distribution function at an arbitrary velocity. As the cutoff velocity is passed through the resonant velocity, the change in plasma behavior demonstrates the effect of that group of plasma particles on the damping of the wave. Certain particles change from damping to antidamping as they change their phase relative to the wave in the resonant region. The frequency of the wave changes by about 2\% as the cutoff velocity passes through the resonance, much larger than expected from the change in the charge in the plasma. We are developing different ways of analyzing the data from this simulation to illuminate the different effects that occur. [Preview Abstract] 

BP8.00102: Effect of a central ``squeeze'' potential on asymmetryinduced transport D.L. Eggleston We report on initial experiments measuring the radial particle flux produced when a ``squeeze'' voltage ($V_{sq}\sim\pm 1$~V) is applied to the center ring (S3) of our cylindrical MalmbergPenning trap at the same time as the voltages producing our usual asymmetry potential $\phi_1(r)\cos{(kz)}\cos{(\omega t  l\theta)}$. Two results are of interest: 1) When a negative DC squeeze voltage is applied to S3, the flux produced by the asymmetry is reduced by a factor $e^{(V_{sq}/V_0)}$ where $V_0\approx 1.2$~V. Evidently, particles need to be able to transit the entire machine to produce transport. This is consistent with our transport model but the scale factor $V_0$ is much larger than expected. 2) When symmetric $\pm$ voltages are applied to the two azimuthallydivided halves of S3, DC or lowfrequency voltages increase the radial flux while highfrequency voltages decrease it. In similar experiments, others\footnote{Daniel H.E. Dubin et al., Phys. Plasmas {\bf 19}, 056102 (2012).} have attributed such transport changes to induced chaotic particle orbits, but we note that the squeeze voltage itself produces transport and the resulting modification of the plasma may also be a factor in changing the observed flux. We have not yet found a way to distinguish between these two effects. [Preview Abstract] 

BP8.00103: Recent Results on the Study of Transverse Beam Dynamics Using the LaserInducedFluorescence Diagnostic on the Paul Trap Simulator Experiment (PTSX) Hua Wang , Erik Gilson , Ronald Davidson , Philip Efthimion , Richard Majeski The Paul Trap Simulator Experiment (PTSX) is a compact Paul trap that simulates the nonlinear transverse dynamics of an intense charged particle beam propagating through an equivalent kilometerslong magnetic alternatinggradient (AG) focusing system. The recently developed laser inducedfluorescence (LIF) diagnostic allowed us to measure the time dependent, transverse phase space profiles of the charge bunch and better understand critical issues in charged particle beam dynamics including emittance growth, and halo particle formation. The LIF diagnostic system includes an excimer laser, a dye laser, a CCD camera system and a stable highdensity barium ion source. The measurements of the radial density profiles of the barium ion source using the LIF diagnostic are calibrated and compared to measurements using a charge collector. The design of the new barium ion source and the LIF diagnostic system will be discussed. The initial results of the radial density profiles measured by the LIF diagnostic will be presented. [Preview Abstract] 

BP8.00104: New Mechanism for SingleComponent Plasma Loss from Asymmetric Potentials N.C. Hurst , J.R. Danielson , C.J. Baker , C.M. Surko The manipulation of singlecomponent plasmas in a PenningMalmberg trap often requires the use of applied asymmetric potentials.\footnote{Huang, et. al., {\it Phys. Rev. Lett.} {\bf 78}, 875 (1997).}$^,$\footnote{\small Fajans, Gilson, Friedland, {\it Phys. Rev. Lett.} {\bf 82}, 4444 (1999).}$^,$\footnote{Hurst, Danielson, Baker, Surko, {\it Phys. Rev. Lett.}, {\bf 113} 025004 (2014).} While it has long been known that these asymmetries can cause plasma expansion,\footnote{Kriesel and Driscoll, {\it Phys. Rev. Lett.} {\bf 85}, 2510 (2000).} it is shown here that direct particle loss may also occur; and this is deleterious for many applications, especially antimatter storage. The plasma selfpotential and the applied potential superpose to form a separatrix, and this can result in the $E\times B$ drift of plasma particles out of the trap. A simple model is presented which captures the observed behavior. The analogy of this effect to the stripping of a 2D vortex by a shear flow will be discussed. [Preview Abstract] 

BP8.00105: Hawking radiation and classical tunneling Eugene Tracy , Dmitriy Zhigunov ``Hawking radiation'' is most familiar as a quantum field phenomenon in curved spacetimes that contain an event horizon. Unruh pointed out that acoustic waves in \textit{classical} fluids with \textit{nonuniform} background flows can exhibit analogous behavior. [1] The ``event horizon'' in that case consists of the set of spatial points where the flow speed and sound speed are equal. A WKB analysis [2] of the acoustic wave equation reveals that tunneling occurs at the ``event horizon,'' but it is not of the standard type. We have recast the Unruh model into a selfadjoint form using a formulation of linearized MHD due to Brizard [3]. A selfadjoint formulation of the linearized wave equation allows the use of variational methods. These provide a systematic means to derive conservation laws and, after discretization, symplectic integration schemes. \\[4pt] [1] G Volovik, M Novello, and M Visser, \textit{Artificial Black Holes} (World, 2002). \\[0pt] [2] ER Tracy, AN Kaufman, AJ Brizard, and AS Richardson, \textit{Ray Tracing and Beyond: Phase Space Methods in Plasma Wave Theory} (Cambridge, 2014). \\[0pt] [3] AJ Brizard, ``Hermitian structure for linearized ideal MHD equations with equilibrium flows,'' PLA \textbf{168} (1992) 357. [Preview Abstract] 

BP8.00106: Electron plasma behavior during autoresonant dioctron excitation C.J. Baker , J.R. Danielson , N.C. Hurst , C.M. Surko A novel multicell PenningMalmberg trap is currently being studied as a way to trap and store up to $10^{12}$ positrons using kV confinement potentials.\footnote{Danielson, Weber, Surko, {\it Phys. Plasmas} {\bf 13}, 123502 (2006).}$^,$\footnote{Danielson, Hurst, Surko, AIP Conf. Proc. {\bf 1521}, 101 (2013).} A test structure has been constructed to conduct preliminary experiments. It consists of a large diameter ``master'' cell and four smaller diameter ``storage'' cells, three of which are offaxis. To load the multicell trap, plasma in the master cell is moved offaxis to radial displacements $D \gg r_p$, where $r_p$ is the plasma radius, before being transferred axially into offaxis storage cells. Details of the radial transfer process, which relies upon the autoresonant excitation of the dioctron mode,\footnote{Fajans, Gilson, Friedland, {\it Phys. Rev. Lett.} {\bf 82}, 4444 (1999).} will be discussed, as well as the plasma behavior during the axial transfer process.\footnote{Hurst, Danielson, Baker, Surko, {\it Phys. Rev. Lett.}, {\bf 113} 025004 (2014).} [Preview Abstract] 

BP8.00107: Operation of a Multicell Trap J.R. Danielson , N.C. Hurst , C.J. Baker , C.M. Surko The multicell PenningMalmberg trap has been proposed as a way to obtain highcapacity and/or portable antimatter traps.\footnote{Danielson, et. al., {\it Phys. Plasmas} {\bf 13}, 123502 (2006).}$^,$\footnote{Danielson, et al., AIP Conf. Proc. {\bf 1521}, 101 (2013).} A new multicell teststructure is investigated, which has several offaxis cells as well as the capability of studying plasmas with kV space charge potentials. Experiments using test electron plasmas have demonstrated the injection of over 50\% of the plasma into an offaxis trap, and the confinement of plasmas with $2\times10^8$ particles in an offaxis cell for hours using rotating electric fields. Other results to be discussed include the limits of the injection process, stacking plasmas in the offaxis cells, and comparing asymmetryinduced transport in offaxis and onaxis cells. Nearterm goals include increasing offaxis injection efficiency, as well as the trapped particle number to $> 10^{10}$ in a single cell. These studies will test further the basic physics of the multicell concept and help refine the design a 21cell trap for $10^{12}$ positrons. [Preview Abstract] 

BP8.00108: Progress toward positronelectron pair plasma experiments J. Stanja , U. Hergenhahn , H. Niemann , N. Paschkowski , T. Sunn Pedersen , H. Saitoh , E.V. Stenson , Ch. Hugenschmidt , G.H. Marx , L. Schweikhard , J.R. Danielson , C.M. Surko Matterantimatter pair plasmas have been of great theoretical and astrophysical interest for a long time. A PositronElectron Experiment (APEX) aims for the creation and study of such a plasma in the laboratory. It will be operated at the NEPOMUC facility which provides a cold and highintensity positron beam. To achieve at least 10 Debye length within APEX's flux surfaces the beam needs to initially pass through several stages of manipulation. Presented here is an overview of work from the APEX team. Topics include $\vec{E}\times\vec{B}$ beam handling for separation into multiple beams in order to reduce the energy spread of the positron beam; injection and trapping of electrons in a prototype dipole field device with a permanent magnet; and design plans for the next generation of confinement device. [Preview Abstract] 

BP8.00109: Progress toward positron accumulation for use in pair plasmas E.V. Stenson , U. Hergenhahn , H. Niemann , N. Paschkowski , T. Sunn Pedersen , H. Saitoh , J. Stanja , G.H. Marx , L. Schweikhard , C. Hugenschmidt , J.R. Danielson , C.M. Surko A PositronElectron Experiment (APEX) is being developed to create and investigate magnetically confined matterantimatter pair plasmas in the laboratory. These plasmas, whose oppositely charged species have precisely equal mass, have long been a topic of theoretical and astrophysical interest. The accompanying Positron Accumulation Experiment (PAX) comprises a series of nonneutral plasma traps. PAX will provide a bridge between the parameters of the NEPOMUC (NeutronInduced Positron Source Munich) beam, from which APEX will receive its positrons, and the parameters needed to achieve at least 10 Debye lengths within APEX's flux surfaces. Presented here is an overview of work from the PAX team. Topics include the following: diagnostics for nonneutral plasmas, including a comparison of phosphor luminescence in response to electrons versus positrons, as well as work on a nonperturbative potential probe; progress to date on injection into and trapping within various subcomponents of the experiment (buffer gas trap, accumulator, and highfield trap); and a discussion of design considerations for the nextgeneration, multicell trap to be built for the highfield magnet. [Preview Abstract] 

BP8.00110: LowFrequency Rotating Wall Compression of ElectronAntiproton Plasmas Andrey Zhmoginov , Joel Fajans , Jonathan Wurtele , Andrea Gutierrez , Makoto Fujiwara , Thomas O'Neil Recent advances in antihydrogen production and trapping would be impossible without the means for compressing and mixing individual particle species [1]. Rotating wall technique based on applying harmonicallychanging potentials to segmented electrodes of an electrostatic plasma trap is one of the methods widely used for compressing nonneutral plasmas. The frequency of the rotating wall perturbation used for compressing electrons in a laboratory is typically of order of several MHz. However, it has recently been observed in ALPHA (CERN) that an efficient compression of twocomponent electronantiproton plasmas may occur at much lower frequencies. We show that the mechanism of such compression can be attributed to single particle resonances in contrast to excitation of collective plasma modes [2]. A model of resonant plasma compression based on kinetic theory is presented and shown to agree with experimental results in a stronglycollisional regime. Plasma evolution in the opposite weeklycollisional regime is also discussed. The most complicated intermediate case is analyzed using a 2D nbody code.\\[4pt] [1] G. B. Andersen, et al. (ALPHA Collaboration), Phys. Rev. Lett. 100, 203401 (2008) \newline [2] F. Anderegg, E. M. Hollmann, and C. F. Driscoll, Phys. Rev. Lett. 81, 48 [Preview Abstract] 

BP8.00111: Techniques to improve plasma properties for antihydrogen production in ALPHA T. Tharp , J. Fajans , H. Bostock , N. Madsen , W. Bertsche , T. Friesen Spectroscopic studies of antihydrogen in ALPHA depend on the reliable production of antihydrogen atoms in quantities large enough to achieve the necessary statistics for precision studies. The efficient production of antihydrogen requires the simultaneous trapping of antiproton and positron populations with high densities and very low temperatures. Presently, we report on two recent developments in the ALPHA2 apparatus: (1) Initial experiments have been performed to identify multiple regimes of plasma compression using electrostatic rotating wall boundary conditions, and (2) a system of cryogenic flaps is being developed to actively close off various sources of radiative heating in order to achieve colder plasma temperatures. [Preview Abstract] 

BP8.00112: Improvement to the Effective Potential Transport Theory Based on Enkog's Theory of Dense Gases Scott D. Baalrud , Jerome Daligault We recently proposed a method for extending traditional plasma transport theories to strong coupling using a binary collision model in which manybody correlation effects were included through an effective interaction potential [1]. By comparing with molecular dynamics simulations, this was shown to be quite successful at extending the binary collision approach well into the strongly coupled regime. However, one persistent feature was an approximately 30\% overestimation of the collision rate in the range $1 < \Gamma < 50$, were $\Gamma$ is the coupling parameter. Here we show that this can be corrected by applying the same scattering cross section to Enskog's kinetic equation for dense gases, rather than Boltzmann's equation for dilute gases. The salient new physics is an exclusion radius for the probability distribution of initial scattering positions that arises due to the strong Coulomb repulsion at close distances; i.e., by accounting for the finite size of particles. Although Enskog's equation was developed exclusively for hard spheres, we propose a connection between the PercusYevick equation for hard spheres and the hypernetted chain equation to find the appropriate exclusion radius for Coulomb systems.\\[4pt] [1] S.D.\ Baalrud, and J.\ Daligault, PRL 110, 235001 (2013). [Preview Abstract] 

BP8.00113: Diffusive Transport Properties Across Coupling Regimes G. Dharuman , M.S. Murillo , J. Verboncoeur , A. Christlieb Transport properties are poorly known across coupling regimes, therefore understanding them is of importance for theoretical and practical reasons. A useful tool is an ultracold plasma system because of the experimental capability to tune the system to attain Coulomb coupling $\Gamma $ ranging from 0.1 to 1 to 10 with the screening parameter $\kappa $ ranging from 0 to 4 to 8, spanning the regions of the phase diagram from weak to moderate to strongly coupled and screened systems. Strong coupling is possible if Disorder Induced Heating is mitigated which requires a correlated initial ion state [1]. Of particular interest is Rydberg blockaded gas of ultracold atoms where the local blockade effect results in correlations. Predictions of higher coupling in ultracold plasma created from a Rydberg blockaded gas have been reported [2]. In this work we examine the diffusive transport properties of ultracold plasma system using molecular dynamics simulations for experimentally realizable values of $\Gamma $ and $\kappa $ as discussed above.\\[4pt] [1] M. S. Murillo, Phys. Rev. Lett.~87 (2001).\\[0pt] [2] G. Bannasch et. al, Phys. Rev. Lett.~110 (2013). [Preview Abstract] 

BP8.00114: Semiclassical Ponderomotive Lagrangian for the Dirac Electron D.E. Ruiz , I.Y. Dodin The ponderomotive effect caused by a highfrequency electromagnetic field on a classical particle can be calculated conveniently, within a firstprinciple variational approach, as the Kerr effect experienced by the particle's quantum wave function in the semiclassical approximation. The previous calculations have been restricted to nonrelativistic scalar particles in weak fields [1]. Here we extend those results to relativistic vector particles in arbitrarily strong fields. In particular, we derive the ponderomotive Lagrangian for the Dirac electron in a relativisticallyintense laser wave propagating in vacuum. Classical waves in plasma can be described in a similar manner; hence our calculation also generalizes the recent ``ponderomotive'' theory of wavewave adiabatic coupling [1] to fully electromagnetic interactions.\\[4pt] [4pt] [1] I.~Y. Dodin and N.~J. Fisch, \textit{Ponderomotive forces on waves in modulated media}, Phys. Rev. Lett. \textbf{112}, 205002 (2014). [Preview Abstract] 

BP8.00115: PLASMA TECHNOLOGY 

BP8.00116: Issues and Solutions for Implementation of a Nanoparticle Plasma Jet Diagnostic on DIIID J.R. Thompson , I.N. Bogatu For ITER, runaway electron (RE) beams are considered a critical problem. Moreover, RE beam dynamics involves processes not yet fully understood or precisely diagnosed. FARTECH has proposed using a C$_{\mathrm{60}}$/C plasma jet as a novel diagnostic probe for RE beamplasma interaction on DIIID. The existing FARTECH prototype plasma jet system is expected to deliver up to $\sim $75 mg C$_{\mathrm{60}}$, at $\sim $4 km/s, and within $\sim $1 ms of triggering, resulting in a free and bound electron density $\sim $2.4x10$^{\mathrm{21}}$ m$^{\mathrm{3}}$, about 60 times larger than the typical DIIID predisruption operation value. Implementation of a 100 kJ pulsed power plasma jet system is nontrivial, with electromagnetic interference (EMI) and safety being two major issues. Microsecond timescale, high current drivers generate significant EMI from which other DIII D systems need to be shielded. Safety issues associated with high voltage and potential capacitor failure must also be addressed. We will present the status of our investigation into the principle solutions for the critical issues involved in the implementation of FARTECH's prototype C$_{\mathrm{60}}$/C plasma jet system on DIIID. [Preview Abstract] 

BP8.00117: Demountable, High field HighTemperature Superconductor TF coils for flexible steadystate fusion experiments Phillip Michael , Leslie Bromberg , Rui Vieira , Joseph Minervini , Christopher Galea , Sarah Hensley , Dennis Whyte The excellent properties of HTS materials (e.g., YBCO) at high fields and elevated temperatures (\textgreater 20 K), offer operational advantages for fusion machines, but results in challenges. For fusion devices, the ability to disassemble the TF coil is very attractive as it provides direct access to maintain the vacuum vessel, first wall and other components in a timely manner. High current conductors, made from multiple thin tapes, are not available but are being developed. Quench protection is a serious issue with HTS magnets, and novel means are needed to detect normal zones and to quickly discharge the magnet. Potential cables designs, demountable magnets and solutions to quench and protection issues for an HTS TF magnet for the Vulcan device (long term PMI studies) will be described. We also describe means for making continuous, persistent loops with HTS tapes. These loops offer an alternative to expensive monoliths for field control for complex geometries, such as stellaratorlike fields. [Preview Abstract] 

BP8.00118: High Field Magnet Developments for the Future of High Field Compact Experiments* G. Grasso , B. Coppi The adoption of ``All Superconducting Hybrid'' (ASH) magnets for the design of new high field confinement machines with relatively long plasma current pulses has been considered. These consist of MgB$_{2}$ superconducting coils, in the outer portion of the magnet, that operate at about 10 K like those adopted for the Ignitor[1] vertical field coils, but can produce up to 10T as in the case of the hybrid magnet with a copper core under construction at Grenoble. In the case of the envisioned ASH magnets the inner core will be made of high temperature superconductors capable of operating at very high fields. The inclusion of advanced solutions [1] such as that concerning the coupled toroidal magnet and central solenoid system for new advanced machines is envisioned. *Sponsored in part by the US DOE.\\[4pt] [1] B. Coppi, et al. \textit{Nucl. Fus}. \textbf{53} 104013 (2013). [Preview Abstract] 

BP8.00119: Surface morphology changes to tungsten under exposure to He ions from an electron cyclotron resonance plasma source David Donovan , Dean Buchenauer , Josh Whaley , Raymond Friddle , Graham Wright Exposure of tungsten to low energy (\textless 100 eV) helium plasmas at temperatures between 9001900 K in both laboratory experiments [1] and tokamaks [2] has been shown to cause severe nanoscale modification of the near surface resulting the growth of tungsten tendrils. We are exploring the potential for using a compact ECR plasma in situ with scanning tunneling microscopy (STM) to investigate the early stages of helium induced tungsten migration. Here we report on characterization of the plasma source for helium plasmas with a desired ion flux of $\sim$ 1x10$^{19}$ ions m$^{2}$ s$^{1}$ and the surface morphology changes seen on the exposed tungsten surfaces. Exposures of polished tungsten discs have been performed and characterized using SEM, AFM, and FIB cross section imaging. Bubbles have been seen on the exposed tungsten surface and in subsurface cross sections growing to up to 150 nm in diameter. Comparisons are made between exposures of warm rolled Plansee tungsten discs and ALMT ITER grade tungsten samples. \\[4pt] [1] M.J. Baldwin, R.P. Doerner, Nucl. Fusion 48 (2008) 035001; M.J. Baldwin, R.P. Doerner, J. Nucl. Mater. 404 (2010) 165.\\[0pt] [2] G.M. Wright, et al, Nucl. Fusion 52 (2012) 042003. [Preview Abstract] 

BP8.00120: Velocity Measurements of Thermoelectric Driven Flowing Liquid Lithium Matthew Szott , Wenyu Xu , Peter Fiflis , Ian Haehnlein , Aveek Kapat , Kishor Kalathiparambil , David N. Ruzic Liquid lithium has garnered additional attention as a PFC due to its several advantages over solid PFCs, including reduced erosion and thermal fatigue, increased heat transfer, higher device lifetime, and enhanced plasma performance due to the establishment of low recycling regimes at the wall. The Lithium Metal Infused Trenches concept (LiMIT) has demonstrated thermoelectric magnetohydrodynamic flow of liquid lithium through horizontal openfaced metal trenches with measured velocities varying from 3.7+/ 0.5 cm/s in the 1.76 T field of HT7 to 22+/ 3 cm/s in the SLiDE facility at UIUC at 0.059 T. To demonstrate the versatility of the concept, a new LiMIT design using narrower trenches shows steady state, thermoelectricdriven flow at an arbitrary angle from horizontal. Velocity characteristics are measured and discussed. Based on this LiMIT concept, a new limiter design has been developed to be tested on the midplane of the EAST plasma. Preliminary modelling suggests lithium flow of 6 cm/s in this device. Additionally, recent testing at the MagnumPSI facility has given encouraging results, and velocity measurements in relation to magnetic field strength and plasma flux are also presented. [Preview Abstract] 

BP8.00121: ABSTRACT WITHDRAWN 

BP8.00122: Silicon Carbide (SiC) MOSFETbased FullBridge for Fusion Science Applications Timothy Ziemba , Kenneth Miller , James Prager , Julian Picard , Akel Hashim Switching power amplifiers (SPAs) have a wide variety of applications within the fusion science community, including feedback and control systems for dynamic plasma stabilization in tokamaks, inductive and arc plasma sources, Radio Frequency (RF) helicity and flux injection, RF plasma heating and current drive schemes, ion beam generation, and RF preionizer systems. SiC MOSFETs offer many advantages over IGBTs including lower drive energy requirements, lower conduction and switching losses, and higher switching frequency capabilities. When comparing SiC and traditional siliconbased MOSFETs, SiC MOSFETs provide higher current carrying capability allowing for smaller package weights and sizes and lower operating temperature. Eagle Harbor Technologies (EHT) is designing, constructing, and testing a SiC MOSFETbased fullbridge SPA. EHT will leverage the proprietary gate drive technology previously developed with the support of a DOE SBIR, which will enable fast, efficient switching in a small form factor. The primary goal is to develop a SiC MOSFETbased SPA for fusion science applications. [Preview Abstract] 
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