Bulletin of the American Physical Society
54th Annual Meeting of the APS Division of Plasma Physics
Volume 57, Number 12
Monday–Friday, October 29–November 2 2012; Providence, Rhode Island
Session NP8: Poster Session V: Nonneutral, Dusty, and Stronglycoupled Plasmas II; Plasma Sources and Boundaries; Space and Astrophysical Plasmas; Spherical Torus, MHD Stability, LTX, HICD 
Hide Abstracts 
Room: Hall BC 

NP8.00001: NONNEUTRAL DUSTY AND STRONGLYCOUPLED PLASMAS II 

NP8.00002: Diagnosing Energy and Angular Momentum Deposition Using Diocotron Mode Frequency Shifts A.A. Kabantsev, C.F. Driscoll Monitoring frequency variations$ f_1 (t)$ of a small amplitude $m_\theta =1$ diocotron mode in pure electron plasmas determines the energy and angular momentum deposited by a variety of damped plasma waves. The finite length and temperature model\footnote{Fine, Driscoll, Phy. Plas {\bf 5} 601 (1997)} of $f_1$ determines the frequency variations due to plasma radius $R$ and temperature $T$, arising from thermal pressure on the ends. For energy $\Delta T$ and angular momentum input resulting in $\Delta R$, the model gives $\Delta f_1 / f_1 \approx 1.2 (R_w / L) [\Delta T / e^2 N  \Delta R / R ]$. Typical plasma and wall sizes give $R / R_w ~\sim 0.3$, $L / R \sim 30$, so $R_w / L \sim 0.1$. With accuracy $\Delta f_1 / f_1 \leq 10^{4}$, we have confidently measured the energy deposits $( \Delta T )$ from Landau damped $m_\theta = 0$ plasma waves with $\Delta n / n \leq 10^{2}$; as well as both the energy deposits $( \Delta T )$ and angular momentum $( \Delta R )$ deposits from collisionally damped $m_\theta = 1$ trappedparticle diocotron modes with $D / R_W \leq 10^{2}$. In prior work, the $m=2$ frequency has been used to diagnose the plasma expansion, as $2 \dot{R} / R =  \dot{f}_2 / f_2$. Together, these two modes give a rather complete nondestructive diagnostic. [Preview Abstract] 

NP8.00003: Spatial Landau Damping of Diocotron Modes Caused by a Particle Flux C.F. Driscoll, A.A. Kabantsev, T.M. O'Neil Diocotron modes exhibit a novel {\it algebraic} (not exponential) damping when there is a flux of particles through the spatial resonance layer. Here, a magnetized pure electron column with density $n(r)$ and drift rotation $f_E (r)$ exhibits $m=1,2$ diocotron mode frequencies $f_m \sim \langle f_E \rangle$$[(m1) + (R_p / R_w )^{2m} ]$. {\it Exponential} mode damping is predicted (and observed) due to spatial Landau damping at the resonance layer where $f_E (r_s ) = f_m$; but with small $n ( r_s ) $ this damping may saturate due to waveparticle trapping. In contrast, when background asymmetries cause (slow) plasma expansion and a (weak) radial particle flux $\Gamma$ through $r_s$, the diocotron mode damps to zero algebraically with time, as $A_m (t) = A_m (0)  \gamma_m t$. Experiments and nascent theory show damping rates proportional to the radial particle flux $\Gamma$ through the relevant separatrix, with $\gamma_m \sim \Gamma$. For $m=1$, $\Gamma$ represents particles lost to the wall; but for $m=2$, even a small plasma expansion can cause strong damping. This algebraic damping will be compared to the exponential growth (or damping) observed from resistive (or feedback) wall voltages, from neutral collisions, and from axial ejection (or injection) of electrons. [Preview Abstract] 

NP8.00004: Squeeze Effects on Plasma Wave Damping A. Ashourvan, D.H.E. Dubin We present a theory for the damping of cylindrically symmetric plasma modes due to a cylindrically symmetric squeeze potential of magnitude $\phi_s$ applied to the center of a nonneutral plasma column. Squeeze divides the plasma into passing and trapped particles; the latter cannot pass over the squeeze. Damping of the mode in collisionless theory is caused by Landau resonances at energies $E_n$ for which the bounce frequency $\omega_b(E_n)$ and the wave frequency $\omega$ satisfy $\omega=n\omega_n(E_n)$. Particles experience a nonsinusoidal wave potential along their bounce orbits due to the squeeze potential. As a result, squeeze induces bounce harmonics with $n\gg 1$ in the perturbed distribution. The harmonics allow resonances at energies $E_n\le T$ and cause a substantial damping at phase velocities much larger than thermal velocity, which is not expected for unsqueezed plasma. In the regime $\omega/k\gg\sqrt{T/m}$ ($k$ is the wave number) and $T\gg\phi_s$, the resonance damping rate has a $\phi^2_s$ dependence. This behavior is consistent with the observed experimental results. [Preview Abstract] 

NP8.00005: Electron Acoustic Waves in Pure Ion Plasmas F. Anderegg, M. Affolter, C.F. Driscoll, T.M. O'Neil, F. Valentini Electron Acoustic Waves (EAWs) are the lowfrequency branch of nearlinear Langmuir (plasma) waves: the frequency is such that the complex dielectric function $(D_r , D_i )$ has $D_r = 0$; and ``flattening'' of $ f(v)$ near the wave phase velocity $v_{ph}$ gives $D_i=0$ and eliminates Landau damping. Here, we observe standing axisymmetric EAWs in a pure ion column.\footnote{F. Anderegg, {\it et al.}, Phys. Rev. Lett. {\bf 102}, 095001 (2009).} At low excitation amplitudes, the EAWs have $v_{ph} \simeq 1.4 \bar{v}$, in close agreement with nearlinear theory. At moderate excitation strengths, EAW waves are observed over a range of frequencies, with $1.3 \bar{v} < {v}_{ph} < 2.1 \bar{v}$. Here, the final wave frequency may differ from the excitation frequency since the excitation modifies $f (v)$; and recent theory analyzes frequency shifts from ``corners'' of a plateau at $v_{ph}$.\footnote{F. Valentini et al., arXiv:1206.3500v1.} Large amplitude EAWs have strong phaselocked harmonic content, and experiments will be compared to samegeometry simulations, and to simulations of KEEN\footnote{B. Afeyan et al., Proc. Inertial Fusion Sci. and Applications 2003, A.N.S. Monterey (2004), p. 213.} waves in HEDLP geometries. [Preview Abstract] 

NP8.00006: Cyclotron Resonances in a NonNeutral Multispecies Ion Plasma M. Affolter, F. Anderegg, C.F. Driscoll, D.H.E. Dubin Shifts of cyclotron mode frequencies away from the single particle $\Omega_c$ are observed to be proportional to the $E \times B$ rotation frequency in nonneutral ion plasmas. These cylindrical ion plasmas consist of Mg24$^+$, Mg25$^+$, and Mg26$^+$, with H$_3$O$^+$, O$_2^+$ and H$_2^+$ impurities. Laser cooling of the majority species, Mg24$^+$, enables temperature control over the range $10^{5} < T < 1.$eV, as well as determination of cyclotron mode frequencies from launched wave absorption. At moderately low temperatures, the $m=1$ and $m=2$ cyclotron frequency shifts are well described by cold fluid theory for an equilibrium square profile.\footnote{E. Sarid, F. Anderegg and C.F. Driscoll, Phys. Plasmas {\bf 2}, 2895 (1995).} However, at $T < 10^{3}$ eV centrifugal mass separation can cause order unity changes in these shifts. For $T \geq 1$ eV, the observed frequency shifts are reduced substantially. Prior high temperature experiments$^1$ saw majority species shifts consistent with cold fluid theory, and theoretically unexplained minority species shifts $\Delta f \sim 2f_{\mathrm Dio}$. Comparisons will be made with nascent theory to determine the effects of temperature and profile shape on these cyclotron modes. [Preview Abstract] 

NP8.00007: Cyclotron Modes in a MultiSpecies Nonneutral Plasma Column D. Dubin A kinetic theory of electrostatic modes near the cyclotron frequency $\Omega_c$ of a given plasma species is developed for a multispecies nonneutral plasma column, keeping terms in the perturbed distribution up to order $1 / \Omega_c^2$, and including the effects of finitelarmor radius $r_c$ up to order $r_c^2$. The theory requires perturbatively solving for particle orbits to order $1 / \Omega_c^4$, and for the equilibrium distribution to order $1 / \Omega_c^3$. At this order this distribution is not Maxwellian if the plasma temperature or rotation frequency is not uniform.\footnote{O'Neil, Driscoll, Phys Fl {\bf 22} 266 (1979)} For $r_c \rightarrow 0$ the theory reproduces coldfluid theory, which predicts a single mode for each azimuthal mode number and each species.\footnote{Gould, LaPointe, PRL {\bf 67} 3685 (1991)} The mode frequencies depend on species concentration, making them a useful diagnostic. However, at low temperature, centrifugal separation of the species causes frequency shifts that complicate the concentration diagnostic. In addition, the frequency spectrum is broadened by spatial Landau damping at radii where the transverse cold fluid dielectric vanishes. These singularities are regularized by finite $r_c$, giving a set of closelyspaced Bernstein modes.$^2$ [Preview Abstract] 

NP8.00008: Collisional Relaxation of a Strongly Magnetized, TwoIsotope, Pure Ion Plasma C.Y. Chim, T.M. O'Neil, D.H.E. Dubin The collisional relaxation of a strongly magnetized pure ion plasma\footnote{P.J. Hjorth and T.M. O'Neil, Phys. Fluids \textbf{26}, 2128(1983); M.E. Glinsky, {\it et al.}, Phys. Fluids B \textbf{4}, 1156 (1992).}
that is composed of two species with slightly different mass is discussed.
We assume the ordering $\Omega_{C1},\Omega_{C2}\ll\Omega_{C1}\Omega_{C2}\ll v / b $,
where $\Omega_{C1}$ and $\Omega_{C2}$ are the two cyclotron
frequencies, $ v $ is the thermal velocity, and $ b $ is the
classical distance of closest approach.
We find that the total cyclotron action for the two species $I_1$ and $I_2$
are adiabatic invariants conserved on the timescale of a few collisions,
so the Gibbs distribution relaxes to the form $\exp[H/T\alpha_1 I_1\alpha_2 I_2]$,
where $\alpha_1$ and $\alpha_2$ are thermodynamic variables like the temperature $T$.
On a timescale longer than the collisional timescale, the two species share action
so that $\alpha_1$ and $\alpha_2$ relax to a common value $\alpha$.
During this process, $ 

NP8.00009: Electrostatic Beams Formed from SingleComponent Plasmas N.C. Hurst, J.R. Danielson, T.R. Weber, C.M. Surko Research on novel plasma manipulation techniques is enabling a new class of positron (antielectron) beams for a variety of applications. Desirable characteristics include narrow energy spreads and finely focused beams (i.e., beams with small transverse spatial extent). Previously, we demonstrated that such beams can be extracted by carefully lowering the confining potential of a plasma in a PenningMalmberg trap.\footnote{Weber, Danielson, and Surko, {\it Phys. Plasmas} {\bf 16}, 057105 (2009).} While useful, these beams are necessarily in a region of high magnetic field. Recently, we have used test electron plasmas to show that these beams can be efficiently extracted from a 4.8 T magnetic field into a magnetic fieldfree region using a combination of adiabatic and nonadiabatic field changes. These beams were subsequently focused using an electrostatic (einzel) lens.\footnote{Weber, Danielson, and Surko, {\it Rev. Sci. Inst.} {\bf 82}, 016104 (2011).} The inclusion of a ``spider'' of highly permeable material is being explored as a way to minimize the momentum ``kicks'' due to the nonadiabatic transition, and hence to create highquality, magneticfield free beams. These beams are expected to be useful, for example, in positron microscopy and for a range of other matteran [Preview Abstract] 

NP8.00010: Novel Positronbeam Systems for Atomic Physics M.R. Natisin, J.R. Danielson, C.M. Surko Trapped positron plasmas are now routinely used to generate high resolution positron beams for a range of atomic physics experiments. Described here are the designs of two new positron beam systems intended for study of the nature and mechanisms of positron attachment to ordinary matter. Positrons attach to molecules in twobody collisions via the excitation of vibrational modes, resulting in huge enhancements in the annihilation rate. While this technique provides a way to measure binding energies,\footnote{Gribakin, Young, and Surko, {\it Rev. Mod. Phys.} {\bf 82}, 2557 (2010).} improved energy resolution is critical to further progress. The design of a new system using a cryogenically cooled buffer gas is described that is intended to meet this need (i.e., resolution $\le 10$ meV, FWHM, a factor of 4 improvement). The analogous process of positron attachment to atoms has not yet been studied experimentally. Also described here is the design of a tailored beam system, combined with a pulsed laser, intended to do this via photoinduced recombination.\footnote{Surko, Danielson, Gribakin, and Continetti, {\it NJP} {\bf 14}, 065004 (2012).} The example of positron binding to zinc (predicted binding energy $\sim$ 0.1 eV) is discussed. [Preview Abstract] 

NP8.00011: Multicell Electrode Structure for Offaxis Plasma Confinement J.R. Danielson, N.C. Hurst, C.M. Surko There are many potential applications of highcapacity and/or portable antimatter traps. One route towards this goal which we have been pursuing is the construction of a novel ``multicell'' trap acrchitecture, with the goal of storage of $\ge 10^{12}$ positrons using kV confinement potentials. Plasmas will be stored in separate PenningMalmberg traps (``cells'') arranged in parallel off the magnetic axis. This utilizes efficiently the magnetic field volume, while minimizing the required confinement voltages. Other enabling techniques will be discussed including the excitation of autoresonant diocotron modes to inject plasmas into the offaxi cells, as well as novel beams that can be created from this type of trapped plasma. New experiements testing the confinement in offaxis cells will be presented. Anticipated uses of this device, including an experiment to create an electronpositron plasma in a stellerator,\footnote{T. S. Pedersen, {\it et. al.}, {\it NJP} {\bf 14}, 035010 (2012).} will also be discussed. [Preview Abstract] 

NP8.00012: Status of the Magnetized Dusty Plasma Experiment (MDPX) E. Thomas, R. Fisher, S. LeBlanc, K. Wood, D. Artis, U. Konopka, R.L. Merlino, M. Rosenberg The Magnetized Dusty Plasma Experiment (MDPX) facility is a multiuser research project whose primary mission is to study the properties of a dusty plasma in which the magnetic force on the charged microparticles is comparable to the other confinement and interdust forces. The MDPX facility will be a flexible device with a range of experimental configurations. It will be capable of producing highly uniform magnetic fields above 4 T as well as operating in a variety of shaped magnetic geometries: from linear gradients up to 1 T/m to magnetic quadrupole configurations. The device uses an octagonal vacuum vessel design to maximize diagnostic access to the plasma. This presentation describes the current state of development of the MDPX facility as it advances towards its complete system integration by Summer, 2013. The presentation provides an overview of the final design of the superconducting magnet system, the updated design of the vacuum vessel, the plasma source, and the development of diagnostic systems. [Preview Abstract] 

NP8.00013: Using particle image velocimetry (PIV) measurements adapted from high speed imaging for groundbased, microgravity, and magnetized dusty plasmas M. Kretschmer, T. Antonova, E. Thomas, J. Williams, U. Konopka, P. Badyopadhyay, G.E. Morfill For over a decade, particle image velocimetry (PIV) techniques have been used to make measurements of microparticle transport, waves, and velocity distributions in dusty (complex) plasmas. With the increasing availability and usage of the high speed imaging techniques and continuing improvement in the PIV analysis algorithms, it is now possible to apply PIV analysis techniques to a wide variety of experimental systems. However, it remains critical to perform careful spatial calibrations and to understand the operational limits under which PIV can be applied. This presentation will discuss the application of twodimensional PIV measurements to four different experimental dusty plasma setups: groundbased tests of the PK4 experiment, parabolic flight measurements on PlasmaLab, groundbased tests of microDPX, and measurements of a magnetized dusty plasma. [Preview Abstract] 

NP8.00014: Circular, Spiral and Pointlike Filamentation of a Magnetized, Radio Frequency Discharge U. Konopka, P. Badyopadhyay, D. Sharma, E. Thomas, G.E. Morfill In a cylindrical radio frequency (rf), low pressure discharge experiment, we investigated the plasma homogeneity while an external magnetic field was varied from 0 to 2 Tesla. The plasma was quasi homogeneous for cases of zero or low magnetic fields. With increasing field, close to and above the ion magnetization limit, the discharge became more and more distorted. The emerging inhomogeneities became first noticeable as a set of circular shaped, plasma light emissions that were aligned to the electrode confinement geometry on the outside and centered on the electrodes. The filamentation structures were very stable in time but could slowly expand or contract in size depending on the exact conditions. At higher fields a transition to slowly rotating plasma spirals was observed, sometimes even double or triple spirals. At very high fields, beyond the ion magnetization threshold, the spirals themselves splitup into many, pointlike filaments aligned with the magnetic field. We demonstrate that the different kinds of filamentation can be explained by a combination of the cross magnetic field diffusion of the plasma and a spatially independent coupling of the RF power generation efficiency. [Preview Abstract] 

NP8.00015: Spatially resolved energy distribution measurements in a weaklycoupled dusty plasma Ross Fisher, Edward Thomas The phase space distribution (PSD) for the dust component of a fluidlike dusty plasma was measured using the stereoscopic particle image velocimetry (stereoPIV) diagnostic. The spatially resolved PSD measurements allowed the distributions of the drift, thermal, and gravitational potential energy densities to be directly calculated throughout the dust cloud structure. The three dimensional spatial distributions of the PSD components (the number density, drift velocity, and distribution width/shape) and the energy density distributions are shown. Additionally, it is shown that the trinormal probability distribution function provides a substantially better fit to the stereoPIV measurements than the canonical Maxwellian distribution. This work is supported by the NSF and NASA. [Preview Abstract] 

NP8.00016: Laserinduced fluorescence measurements of ion densities and flows near a dusty plasma Keith Wood, Ross Fisher, Edward Thomas The interaction between ions and charged microparticles in a dusty (complex) plasma is often one of the mechanisms that have a substantial contribution to the dynamics of the system. However, detailed measurements of ion behavior in the vicinity of dust particles remain elusive. Using the Magnetized Dusty Plasma Experiment (MDPX) test vacuum chamber at Auburn University, a onedimensional vertical dust string is created in an argon plasma within an openended glass box. It has been speculated that the ion focusing effect creates a positively charged region behind each dust particle, altering the electric field felt by the dust particle, which directly affects each of these properties. This presentation will describe experiments that use laserinduced fluorescence (LIF) to measure both the neutral and ion argon densities and flows in the region near the dust particles. The broader application of LIF measurements to the MDPX device will also be discussed. [Preview Abstract] 

NP8.00017: Intergrain forces in low Machnumber plasma wakes Ian Hutchinson Mutual interaction of dust grains depends upon their wake. How that wake and the intergrain forces evolve from the oscillatory structure at soundspeed plasma flow velocity to the symmetric shielding at zero flow, is here studied computationally. Rigorous simulation of interactions of two negatively charged grains smaller than the Debye length has been carried out using the Cartesiancoordinate Obliqueboundary Particle and Thermals in Cell (COPTIC) code, covering a wide range of subsonic plasma flow velocities. In plasmas with temperature ratio $T_e/T_i=100$, it is found that a single grain's oscillatory wake disappears for flow Mach numbers ($M$) less than approximately 0.3, which is the parameter regime where Landau damping is expected to be strong. Neutral collisions suppress potential oscillations above $M=0.3$, but not the trailing attractive potential peak caused by ion focussing. The transverse (grainaligning) force on a downstream particle in the wake of another is obtained rigorously from the code in threedimensional simulations. It shows general agreement with the force that would be deduced from the singlegrain wake potential gradient. Except for relatively large grains in the nonlinear collisional regime, the grainaligning force is very small for slow flow. [Preview Abstract] 

NP8.00018: Magnitude and Direction of FineParticle Gyrophase Drift Jeffrey Walker, Mark Koepke, Michael Zimmerman, William Farrell, Vladimir Demidov Gyrophaseresonant excursions of magnetizedorbit dust grains in inhomogeneous plasma, causing periodic chargestate changes, may occur in the presence of strong magnetic field and inhomogeneous plasma potential. Gyrophase drift [Northrup and Hill, 1983], resulting from nonzero noninfinite charging rate of a dust grain, results in a perpendicular modification to the usual ExB drift. In plasmas with structured inhomogeneity, this ultimately causes dust grains to leave regions of inhomogeneity and cease both ExBdrifting and gyrophase drifting. In our approach, the motion of a dust grain is computed numerically by a leapfrog method for the Orbit Motion Limited (OML) charging model while the grain executes its gyroorbit in plasma with either abrupt or gradual inhomogeneity. The causal link between chargingrate details and magnitude and direction of gyrophase drift is evaluated by applying an effective chargerate parameter in the OML charging model. This parameter can be used to demonstrate the sensitivity of the gyrophase drift vector prediction on any model's charging rate details. [Preview Abstract] 

NP8.00019: Fundamental mode of ultralow frequency electrostatic dustcyclotron surface waves in a magnetized complex plasma with drifting ions Seungjun Lee, MyoungJae Lee The electrostatic dustcyclotron (EDC) waves in a magnetized dusty plasma was reported that they could be excited by gravity in a collisional plasma [1]. Rosenberg suggested that EDC waves could be excited by ions drifting along the magnetic field in a collisional plasma containing dust grains with large thermal speeds [2]. The existing investigations, however, focus on EDC volume waves in which the boundary effects are not considered. In this work, we attempt to obtain some physical results concerning the fundamental mode of EDC surface wave and the stability of wave by utilizing a kinetic method. The EDC surface wave is assumed to propagate along an external magnetic field at the interface between the plasma and the vacuum. The plasma is comprised of drifting ions flowing along an external magnetic field. To derive the growth rate of surface waves, we employ the specular reflection boundary conditions. The EDC surface wave is found to be unstable when the ion drift velocity is larger than the phase velocity of the wave. In addition, the wave becomes to be more unstable if dust particles carry more negative charges.\\[4pt] [1] N. D'Angelo, Phys. Lett. A 323, 445 (2004).\\[0pt] [2] M. Rosenberg, Phys. Scr. 82, 035505 (2010). [Preview Abstract] 

NP8.00020: Solitary wave evolution in inhomogeneous electronpositron pair plasma having dust grains Rakhee Malik, Hitendra K. Malik, Subash C. Kaushik Main concern of the present article are to investigate the possible modes and their evolution as soliton in inhomogeneous electronpositron plasma having stationary negatively charged dust particles. The Kortewegde Vries (KdV) like equation with an additional term due to density gradients is deduced by employing reductive perturbation technique. An investigation on the existence and propagation of the modes in such a plasma model reveals that two types of modes are possible. The KdV equation is solved for its solitary wave solution. It is observed that both the modes evolve in the form of density hill type structures in the plasma, confirming that these solitary structures are compressive in nature. The amplitude and width of the soliton are studied regarding to plasma parameter such as positrontoelectron temperature ratio, density of positrons and dust density. It is observed that the tailing structure is not prominent in the present plasma model. [Preview Abstract] 

NP8.00021: PLASMA SOURCES AND BOUNDARIES 

NP8.00022: Instabilities in ion rich sheaths J. Manuel Urrutia, Reiner Stenzel Ion rich sheaths are observed to become unstable when the electron supply is restricted. This instability has been studied for a spherical grid immersed in an ambient discharge plasma. When biased negatively ions are attracted into the sphere while electrons are restricted and the inside sheath of the grid becomes unstable. The charge density, hence plasma potential, oscillates below but near the ion plasma. Electrons inside the sheath lower the frequency and create harmonics and subharmonics. When the mesh size becomes comparable to the Debye length the 3D sheath structure creates additional low frequency sheath oscillations which produce sidebands to the instability spectrum. Related instabilities are also seen when the electron supply is restricted by a magnetic field parallel to the sheath. Relevance and applications will be explained. [Preview Abstract] 

NP8.00023: ABSTRACT WITHDRAWN 

NP8.00024: Theoretical and computational studies of the sheath of a planar, electron emitting wall Martina Giraudo, Gian Luca Delzanno, Enrico Camporeale We present an investigation of the properties of the sheath near an electron emitting wall in the electrostatic, collisionless limit. Electron emission is modeled with a drifting Maxwellian distribution function whose shift and thermal spread are changed parametrically in order to bridge from beamlike distributions to a Maxwellian at rest. We present an analytic equilibrium theory for this system based on the conservation of particle flux and energy, in connection with nonlinear ParticleInCell (PIC) simulations. The latter are conducted with CPIC [1], a new electrostatic PIC code that couples the standard PIC algorithm with strategies for generation and adaptation of the computational grid. We also present a linear theory study, based on Ref. [2], in an attempt to interpret some of the oscillations that can be present in the system when the sheath potential profile is nonmonotonic.\\[4pt] [1] G.L. Delzanno, E. Camporeale, et al., ``CPIC: a curvilinear ParticleInCell code for spacecraftplasma interaction studies,'' Proceedings of the 12st Spacecraft Charging and Technology conference, 2012. \\[0pt] [2] G.L. Delzanno, ``A paradigm for the stability of the plasma sheath against fluid perturbations,'' Phys. Plasmas 18, 103508 (2011). [Preview Abstract] 

NP8.00025: Oscillation, Collapse and Disappearance of Debye Sheaths Due to Secondary Electron Emission Michael Campanell, Alexander Khrabrov, Igor Kaganovich Most theories of PSI with secondary electron emission (SEE) implicitly assume a stable sheath exists. Ions are assumed to be drawn to the wall and the SEE is characterized by a fixed ``coefficient'' (e.g. G.D. Hobbs and J.A. Wesson, Plasma Phys. 9, 85 (1967)). We present simulations and basic theory showing a class of sheath instabilities that can arise under general conditions. Instabilities cause abrupt changes in the plasma, drive spontaneous oscillations, and dramatically increase crossBfield transport, wall flux and energy loss. (M.D. Campanell et. al. PRL 108, 235001 (2012)). Also, if the SEE yield of hot plasma electrons impacting the walls exceeds unity, the sheath and presheath may disappear completely because there is no need for ions to be drawn to the wall in order to maintain current balance (M.D. Campanell et. al. PRL 108, 255001 (2012)). Instead, the walls acquire a positive charge. The plasma potential is negative, the ion flux is zero and plasma electrons are unconfined. These three properties all differ from the ``space charge limited'' sheath often assumed to form when SEE yield exceeds 1. In the new ``inverse sheath'' regime, zero current is maintained only by pulling the ``extra'' secondaries back to the wall. [Preview Abstract] 

NP8.00026: Transport in a fieldaligned magnetized plasma and neutral gas boundary: the end of the plasma Christopher Cooper, Walter Gekelman A series of experiments at the Enormous Toroidal Plasma Device (ETPD) at UCLA study the Neutral Boundary Layer (NBL) between a magnetized plasma and a neutral gas in the direction of the confining field. A lanthanum hexaboride (LaB$_{6})$ cathode and semitransparent anode create a currentfree, weakly ionized (n$_{e}$/n$_{n}<$5{\%}), helium plasma (B$\sim $250 G, R$_{plasma}$=10cm, n$_{e}<$10$^{12}$cm$^{3}$, T$_{e}<$3eV, and T$_{i}\sim $T$_{n})$ that terminates on helium gas without touching any walls. Probes inserted into the plasma measure the basic plasma parameters in the NBL. The NBL begins where the plasma and neutral gas pressures equilibrate and the electrons and ions come to rest through collisions with the neutral gas. A fieldaligned electric field ($\Delta \phi $/kT$_{e}\sim $1) is established selfconsistently to maintain a currentfree termination and dominates transport in the NBL, similar to a sheath but with a length L$\sim $10$\lambda _{ei}\sim $10$^{2}\lambda _{en}\sim $10$^{5}\lambda _{D}$. A twofluid weaklyionized transport model describes the system. A generalized Ohm's Law correctly predicts the electric field observed. The pressure balance criteria and magnitude of the termination electric field are confirmed over a scaling of parameters. The model can also be used to describe the atmospheric termination of aurora or fully detached gaseous divertors. [Preview Abstract] 

NP8.00027: A gaspuffdriven theta pinch for plasmasurface interaction studies Soonwook Jung, Leigh Kesler, HyunHo Yun, Davide Curreli, Daniel Andruczyk, David Ruzic DEVeX is a theta pinch device used to investigate fusionrelated material interaction such as vapor shielding and ICRF antenna interactions with plasmapulses in a laboratory setting. The simulator is required to produce high heatflux plasma enough to induce temperature gradient high enough to study extreme conditions happened in a plasma fusion reactor. In order to achieve it, DEVeX is reconfigured to be combined with gas puff system as gas puffing may reduce heat flux loss resulting from collisions with neutral. A gas puff system as well as a conical gas nozzle is manufactured and several diagnostics including hot wire anemometer and fast ionization gauge are carried out to quantitatively estimate the supersonic flow of gas. Energy deposited on the target for gas puffing and staticfilled conditions is measured with thermocouples and its application to TELS, an innovative concept utilizing a thermoelectricdriven liquid metal flow for plasma facing component, is discussed. [Preview Abstract] 

NP8.00028: Electrodeless Plasma Source: Phase II Update James Prager, Timothy Ziemba, Kenneth Miller Eagle Harbor Technologies, in collaboration with the University of Washington, has developed a lowimpurity, electrodeless plasma source (EPS) for startup and source plasma injection for fusion science applications. In order to not interfere with the experiment, a preionizer/plasma source must meet a few critical criteria including low impurity production, low electromagnetic interference (EMI), and minimal disruption to the magnetic geometry of the experiment. This system was designed to be UHV compatible and bakable. Here we present the results of the EPS Phase II upgrade. The output plasma density was increased by two orders of magnitude to $>$10$^{17}$ m$^{3}$ in hydrogen with no magnetic field injected. EPS system integration with the HITSI experiment has begun. [Preview Abstract] 

NP8.00029: OneDimensional Analysis of ECRH Preionization for Plasma Startup in JT60SA Kazuyoshi Hada, Kazunobu Nagasaki, Kai Masuda, Ryota Kinjo, Shunsuke Ide, Akihiko Isayama Preionization using Electron Cyclotron Resonance Heating (ECRH) has been proposed to ensure reliable plasma breakdown in superconducting tokamaks where applicable loop voltage is low compared with conventional tokamaks. In this paper, we report results of onedimensional (1D) analysis of plasma startup assisted by ECRH in the JT60SA superconducting tokamak, which is now under construction. The 1D model consists of five temporal diffusiontype equations: electron and neutral density equations, electron and ion energy density equations, and a toroidal current equation. The calculation results show that the required ECRH power is estimated to be lower than the zerodimensional analysis results [1] because of localized power density, and that the plasma startup is dependent on the ECRH power absorption profile and the resonance location. The ECRH preionization is more effective for plasma startup when narrowing the ECRH power absorption radius and locating the resonance location close to the plasma core. We will also discuss the difference in plasma production between fundamental and higher harmonic ECRH.\\[4pt] [1] K. Hada \textit{et al.}, presented at JPS Annual Meeting, March 2427, 2012 [Preview Abstract] 

NP8.00030: SPACE AND ASTROPHYSICAL PLASMAS 

NP8.00031: Measurement and Simulation of the Electric Current in a kpcScale Jet P.P. Kronberg, R.V.E. Lovelace, G. Lapenta, SA Colgate, L. Sanna We present radio emission, polarization, and Faraday rotation maps of the radio jet of the galaxy 3C303. From these data we derive the magnetoplasma and electrodynamic parameters of this 50 kpc long jet. For one component of this jet we obtain for the first time a direct determination of a galacticscale electric current (3 $\times$ 1018 A), and its directionpositive away from the active galactic nucleus. Our analysis strongly supports a model where the jet energy flow is mainly electromagnetic.\\[4pt] P.P. Kronberg, R.V.E. Lovelace, G. Lapenta, S.A. Colgate, Measurement of the Electric Current in a KpcScale Jet, Astrophysical Journal Letters, 741, L15, doi:10.1088/20418205/741/1/L15, 2011. [Preview Abstract] 

NP8.00032: Solar wind obervations of electric and magnetic field spectra beyond the MHD inertial range John J. Podesta Advances in spacecraft instrumentation now permit accurate measurements of electric and magnetic fields to be performed in the solar wind at scales less than or equal to the thermal proton gyroradius $\rho_i$ and the proton inertial length $d_i$. In the solar wind the proton beta is on the order of unity and, therefore, $\rho_i\sim d_i$. Recent results show that in the regime of kinetic scales $k\rho_i < 1$ wavenumber spectra of magnetic field fluctuations and electron density fluctuations both exhibit power laws with the same spectral slope $\sim 2.7$ or $2.8$, consistent with predictions for kinetic Alfv\'en wave (KAW) turbulence. This assumes that the fluctuations are ``frozen into the flow,'' also known as Taylor's hypothesis, an assumption believed to be valid for KAW turbulence. Here, I present new electric and magnetic field measurements from the {\it Artemis} spacecraft which confirm previous search coil magnetometer measurements of solar wind magnetic field spectra from the {\it Cluster} spacecraft and which illustrate the improved electric field spectra at kinetic scales obtained with the electric field instrument on board the Artemis spacecraft (previously Themis B and C). The results are compared to theoretical predictions and high resolution numerical simulations [Preview Abstract] 

NP8.00033: ABSTRACT WITHDRAWN 

NP8.00034: Collective Escape of Cosmic Rays from their Acceleration Sites Mikhail Malkov, Patrick Diamond, Roald Sagdeev, Felix Aharonian, Igor Moskalenko Supernova remnant (SNR), as the major contributors to the galactic cosmic rays (CR), are believed to maintain an average CR spectrum by diffusive shock acceleration (DSA) regardless of the way they release CRs into the interstellar medium (ISM). However, the interactions of the CRs with nearby gas clouds crucially depend on the release mechanism. Recently, such interactions have been actively studied by observations in the gammaray band to probe the SNR as a particle accelerator. Motivated by these observations, we call into question two aspects of a popular paradigm of the CR injection into the ISM, according to which they passively and isotropically diffuse in the prescribed magnetic fluctuations as test particles. First, we treat the escaping CR and the Alfv\'en waves excited by them on an equal footing. Second, we adopt field aligned CR escape outside the source, where the waves become weak. An exact analytic selfsimilar solution for a CR ``cloud'' released by a dimmed accelerator will be presented. The observational consequences of this solution will be discussed. [Preview Abstract] 

NP8.00035: Dissipation Mechanisms of Kinetic Plasma Turbulence Jason TenBarge Turbulence plays an important role in space and astrophysical plasmas by mediating the transfer of energy from largescale motions to the small scales at which the turbulence can be dissipated. However, the dominant physical mechanisms that dissipate the smallscale turbulent motions remain unidentified. The dynamics at the dissipative scales are typically weakly collisional in diffuse astrophysical plasmas, such as the solar wind, so the mechanisms responsible for the dissipation and plasma heating are described by kinetic plasma physics. Two mechanisms have been proposed to be the dominant dissipation processes for plasma turbulence: collisionless waveparticle interactions and dissipation in smallscale current sheets. We investigate the relative importance of dissipation via collisionless waveparticle damping versus dissipation in smallscale current sheets in weakly collisional plasma turbulence via threedimensional, nonlinear gyrokinetic and particleincell simulations. [Preview Abstract] 

NP8.00036: Gyrokinetic Particle Simulation of Kinetic Alfv\'{e}n Wave Turbulence Onnie Luk, Xi Cheng, Peter Porazik, Zhihong Lin The previous studies of spectral cascade in Alfv\'{e}nic turbulence clearly show signs of plasma heating, and there are several highlydebated explanations to this phenomenon. We have developed a nonlinear gyrokinetic particle simulation to study the perpendicular spectral cascade caused by Landau damping of kinetic Alfv\'{e}n wave, which is one of those possible heating mechanisms. The current nonlinear gyrokinetic code includes scalar potential and vector potential. We will propose a new formulation that implements compressional magnetic perturbation into the existent code to form a complete, selfconsistent nonlinear simulation. [Preview Abstract] 

NP8.00037: ABSTRACT WITHDRAWN 

NP8.00038: Magnetic Field Generation Processes Involving Gravity and Differential Rotation. Solitary Plasma Rings Formation around Black Holes Bruno Coppi A clear theoretical framework to describe how magnetic fields are generated and amplified is provided by the magnetogravitational modes that involve both differential rotation and gravity and for which other factors such as temperature gradients can contribute to their excitation. These modes are shown to be important for the evolution of plasma disks surrounding black holes.\footnote{B. Coppi, \textit{Phys. Plasmas} \textbf{18}, 032901 (2011)} Nonlinear and axisymmetric plasmas and associated field configurations are found under stationary conditions that do not involve the presence of a preexisting ``seed'' magnetic field unlike other configurations found previously.\footnote{Ibid.} The relevant magnetic energy density is of the order of the gravitationally confined plasma pressure. The solitary plasma rings that characterize these configurations are localized radially over regions with vanishing differential rotation and can be envisioned as the saturated state of magnetogravitational modes. The ``source'' of these configurations is the combination of the gravitational force and of the plasma density gradient orthogonal to it. [Preview Abstract] 

NP8.00039: Magnetogenesis through a Relativistic Biermann Effect Evan Miller In a 2010 Physical Review Letter, Mahajan and Yoshida proposed a relativistic correction to the wellknown Biermann Battery. The Biermann Battery allows for the generation of magnetic fields in a plasma fluid from orthogonal gradients in temperature and entropy ($\frac{\partial B}{\partial t} \propto \nabla T \times \nabla \sigma$). The proposed correction would result in an additional term, proportional to the gradient of velocity squared crossed with the gradient of entropy ($\frac{\partial B}{\partial t} \propto \nabla v^2 \times \nabla \sigma$). This new effect can in some cases provide the dominate source of magnetic field growth, even when the fluid is only mildly relativistic. This could in turn help explain the dynamics of certain relativistic plasmas, including modern laser plasmas and astrophysical jets. It is possible it could even provide a primordial source for the seed fields needed to explain the cosmological magnetic fields that appear to permeate most galaxies. In my poster, I will explain the theory underlying this new correction and present simulations demonstrating magnetic field growth in a variety of test cases, performed using both a particleincell code and a fluid model. [Preview Abstract] 

NP8.00040: Multilevel multidomain simulations: a new approach to multiscale multiphysics descriptions Arnaud Beck, M.E. Innocenti, Giovanni Lapenta, Stefano Markidis There are a number of modeling challenges posed by space weather numerical simulations. Most of them arise from the multiscale and multiphysics aspects of the problem. The multiple scales dramatically increase the requirements, in terms of computational resources, because of the need to carry large scale simulations with the proper smallscales resolution. Lately, many suggestions have been made to overcome this difficulty by using various refinement methods which consist in splitting the domain into regions of different resolutions. The multiple physics are generally treated in a similar way: interfaces separate the regions where different equations are solved. We present here an innovative approach based on the coexistence of several levels of description, which differ either by their resolutions or by their physics. Instead of interacting through interfaces, these levels are all entirely simulated and are interlocked over the complete extension of their overlapping area. This scheme has been applied to a twodimensional implicit Particle in Cell code. Some results of magnetic reconnection simulations are presented and we also discuss the optimal implementation of this scheme on very large clusters. [Preview Abstract] 

NP8.00041: Resonant and diffusive transport of relativistic electrons in Earth's radiation belts Dimitris Vassiliadis, Mattias Tornquist, Xi Shao, Mark Koepke Electron transport at fieldline resonances and cavity modes is a textbook case of adiabatic motion. Often however such structures are absent so particle scattering is modulated by interplanetary and internal disturbances featuring broadband spectra and resulting in diffusive transport. We discuss the types of relativistic electron transport occurring when FLR structures coexist with stochastic fields. First, testparticle simulations driven with powerlaw wave spectra are used to show that the diffusion coefficient is a function of the integrated wave power and the spectral index. Second, the excitation of an FLR by compressionalmode waves is simulated in a 2D box model. The combined fields of driver waves and the resonance are used to drive particle transport, and competition between resonant and diffusive scattering depends on driver amplitude and resonance dissipation. Third, globalmagnetospheric MHD simulations driven with measured solar wind are used to reconstruct magnetic storm events. Solar wind variations often have nearpowerlaw spectra, and produce lowfrequency magnetospheric compressional fluctuations. These waves are used to drive guidingcenter electron dynamics in the equatorial plane. Competition between modes of transport is a function of the wave amplitude, polarization, and spectral index; and of the decay rate of stationary resonances on the magnetospheric dayside and flanks. We discuss the fundamental transport types in each case. [Preview Abstract] 

NP8.00042: Compressional Mode ULF Waves Excitation and Relativistic Electron Acceleration during a Geomagnetic Storm Event Xi Shao, L.C. Tan, A.S. Sharma, S.F. Fung, Mattias Tornquist, Dimitris Vassiliadis There has been increasing evidence indicating the importance of magnetospheric ULF waves in the Pc5 frequency range in enhancing relativistic electron fluxes in the outer radiation belt. These ULF waves can be divided into two groups: poloidal modes and toroidal modes. In theory, electron acceleration by poloidalmode wave should be more effective than by toroidal mode wave due to that electron drift motion is mainly along the azimuthal direction overlapping with compressional (poloidal) mode wave electric field. We found evidence of relativistic electron acceleration by the compressionalmode ULF waves during a storm sudden commencement event on September 25, 2001. In this event, the energetic electron flux measured by LANL shows modulations of lowenergy electrons and acceleration of highenergy electrons by the compressional mode electric field oscillations over 23 hours. The energy threshold of accelerated electrons at the geosynchronous orbit agrees well with the theory of driftresonant interaction of magnetospheric electrons with compressionalmode ULF waves. Global MHD simulation of the event through NASA/CCMC will also be presented. [Preview Abstract] 

NP8.00043: The FarleyBuneman Instability in the Solar Chromosphere Chad A. Madsen, Yakov S. Dimant, Meers M. Oppenheim, Juan M. Fontenla Strong currents drive the FarleyBuneman Instability (FBI) in the Eregion ionosphere creating turbulence and heating. The solar chromosphere is a similar weakly ionized region with strong local Pedersen currents, and the FBI may play a role in sustaining the thin layer of enhanced temperature observed there. The plasma of the solar chromosphere requires a new theory of the FBI accounting for the presence of multiple ion species, higher temperatures and collisions between ionized metals and neutral hydrogen. This paper discusses the assumptions underlying the derivation of the multispecies FBI dispersion relation. It presents the predicted critical electron drift velocity needed to trigger the instability. Finally, this work argues that observed chromospheric neutral flow speeds are sufficiently large to trigger the multispecies FBI. [Preview Abstract] 

NP8.00044: Global stability of MHD disk equilibria with sheared flows: a unified perspective Bertrand Lefebvre, Amitava Bhattacharjee, Fatima Ebrahimi The velocity sheardriven magnetorotational instability (MRI) is believed to contribute to turbulence and momentum transport in accretion disks. It is one of a broader class of velocity sheardriven instabilities, in which the stable continuum is generically converted into a sequence of overstable discrete modes. Such instabilities were treated mathematically and numerically by Bondeson et al. [PoP 30, 2167 1987], who focused on fusion applications and considered primarily the effect of sheared axial flows. In order to develop a unified perspective, we first extend the plasma column equilibria studied by Bondeson et al. to include a sheared azimuthal flow. In addition to Suydam modes destabilized by the flow in the vicinity of $\mathbf{k}\cdot\mathbf{B}=0$ surfaces, we find an MRIlike instability driven by the azimuthal flow. Second, we consider a Couette flow with a sheared equilibrium magnetic field as well as a small axial velocity added to the azimuthal flow. Such a generic equilibrium can have different stability properties than predicted by standard analyses, with nonaxisymmetric modes linearly growing faster than axisymmetric ones. These general classes of instabilities are potentially important for MRIgenerated turbulence in accretion disks and laboratory experiments. [Preview Abstract] 

NP8.00045: Global simulations of dynamo in flowing plasmas  applications to laboratory and astrophysical plasmas Fatima Ebrahimi, A. Bhattacharjee The alpha dynamo effect is numerically examined for magnetically and flowdriven turbulence. It has been shown that the alpha effect can be rigorously written in the form of a total divergence of the helicity flux from fluctuations and dissipative terms (Bhattacharjee and Hameiri 1986). For the first time, we have confirmed this functional form from direct numerical simulations of the magnetorotational instability (MRI) as well as reconnecting instabilities. When turbulence is dominated by tearing modes, the total divergence term is shown to be related to ``hyperresistivity.'' In plasmas unstable to the MRI, we demonstrate that the same total divergence form leads to a very different dynamo. We compute this MRIdriven turbulent dynamo, and show from global simulations that it differs from the VishniacCho form (V\&C 2001), used in recent astrophysical dynamo studies. Indeed, their form is found to be subdominant to other contributions to the total divergence form, which depend upon the source of free energy for the instability. These numerical calculations of the total divergence form of the turbulent helicity flux are fundamental for understanding the role of boundary conditions on the dynamo problem in laboratory as well as astrophysical plasmas. Supported by DOE and NSF. [Preview Abstract] 

NP8.00046: FLASH Hydrodynamic Simulations of Experiments to Explore the Generation of Cosmological Magnetic Fields Anthony Scopatz, Milad Fatenejad, Norbert Flocke, Gianluca Gregori, Don Lamb, Dongwook Lee, Jena Meineke, Petros Tzeferacos, Klaus Weide Magnetic fields are ubiquitous throughout the universe. However, the origin and strength of these fields are not fully understood. A promising mechanism for the origin of seed fields is the asymmetric shocks that occur in hierarchical structure formation when smaller halos merge to form galaxies and galaxies merge to form clusters of galaxies. The seed fields are generated by the Biermann battery mechanism. The COSMOLAB team are conducting experiments to investigate the generation of magnetic fields by asymmetric shocks. These experiments involve laser illumination of a foil target, driving a shock into a gasfilled chamber, and a variety of plasma and magnetic field diagnostics. Hydrodynamiconly simulations are useful because the shockgenerated magnetic fields are not dynamically important. In this paper, we describe hydrodynamic simulations of the experiment conducted using the FLASH code. The scientific objective of these simulations is to explore the sensitivity of the properties of the jetlike shock to target composition, thickness, and lateral extent. [Preview Abstract] 

NP8.00047: Numerical simulations of anisotropic plasmas using a modified ZEUSMP Benjamin Chandran, Varun Tangri, Aveek Sarkar, Jean Perez, Prateek Sharma Three dimensional linear and nonlinear simulations of collisionless onefluid plasmas with pressure anisotropy are presented using the Chew GoldbergerLow (CGLMHD) and doubleisothermal models. For this purpose, the code ZEUSMP [J. C. Hayes \textit{et. al.} The APJ Supplement Series \textbf{165} (2006) 188.] has been modified. Major modifications include a changed method of characteristics, new compressive and noncompressive forces, and a ``hard wall'' limit on pressure anisotropy that is intended to mimic the effects of plasma microinstabilities that limit the temperature anisotropy. For purposes of validation, more than 100 test simulations of linear waves (Alfven, slow and fast), instabilities (firehose and mirror) and nonlinear vortices (OrszagTang) are presented for a number of initial conditions and parameters. Finally, this model is used to investigate the way that Alfvenwave turbulence leads to a spreading of the temperatureanisotropy probability distribution in the solar wind. Analysis is completed with a detailed analysis of the fluctuation data. [Preview Abstract] 

NP8.00048: Gyrokinetic simulation of the mirror instability and comparison with quasilinear results and hybrid simulations Peter Porazik, Jay Johnson, Peter Yoon, Pavel Travnicek Nonlinear evolution of the mirror instability is studied using gyrokinetic particle simulation in threedimensional uniform slab. Plasma beta and temperature anisotropy are chosen for which the quasilinear numerical solutions show that the mirror instability dominates over the electromagnetic ion cyclotron instability, and the gyrokinetic simulation results for these parameters are compared to quasilinear numerical solutions, and to hybrid simulations. Final structures in planes parallel and perpendicular to the magnetic field are also addressed. The motivation of the present study is to help guide the interpretation of observations and improve efficiency of future simulation models. [Preview Abstract] 

NP8.00049: Electron KelvinHelmholtz Instability and Generation of Demagnetized Electron Rings Paul Cassak, Homa Karimabadi, Vadim Roytershteyn, William Daughton, Jack Scudder, Burlen Loring Recent simulations of reconnection indicate the formation of long demagnetized electron layers which can become unstable to secondary island formation. When the current sheet is asymmetric, these layers can also develop velocity shear in the electrons. While there has been significant work on ion scale velocity shear driven KelvinHelmholtz (KH) instabilities, there has been little work on electron scale KH. Here we consider such a configuration using full particle and twofluid simulations. We find that in the fully kinetic simulations, electron KH leads to formation of rings of current. The comparison between fully kinetic and twofluid simulations will be presented and the relevance of KH to formation of flux ropes will be discussed. [Preview Abstract] 

NP8.00050: Rethinking Electrostatic Solvers in Particle Simulations for the Exascale Era Jan Deca, Stefano Markidis, Giovanni Lapenta, Erik J\'arleberg, Rossen Apostolov, Erwin Laure In preparation to the exascale era, an alternative approach to calculate the electrostatic forces in Particle Mesh (PM) methods is proposed. While the traditional techniques are based on the calculation of the electrostatic potential by solving the Poisson equation, in the new approach the electric field is calculated by solving Amp\`ere's law. When the Ampere's law is discretized explicitly in time, the electric field values on the mesh are simply updated from the previous values. In this way, the electrostatic solver becomes an embarrassingly parallel problem, making the algorithm extremely scalable and suitable for exascale computing platforms. An implementation PM code with the new electrostatic solver is presented to show that the proposed method produces correct results. It is a very promising algorithm for exascale PM simulations. [Preview Abstract] 

NP8.00051: Space plasmastructure interaction: simulation with verification Oleg Batishchev Space plasma interaction with artificial and natural objects in the presence of EMfields is a strongly nonlinear phenomenon with many kinetic effects taking place at once. Experimental data are limited to passive observations and scarce active experiments using satellites. New adaptive multiscale model is being extended into 3D3V Eulerian formulation [1]. A parallel verification using laboratory experiments is being developed as well. We report current status of this combined program. \\[4pt] [1] O. Batishchev, SemiAnalytical Adaptive Vlasov  FokkerPlanck  Boltzmann Methods, pp.237315, in book Eulerian Codes for the Numerical Solution of the Kinetic Equations of Plasmas (Ed. M. Shoucri), Nova Science, 2010. [Preview Abstract] 

NP8.00052: Particleincell simulations of electron energization from low Mach number quasiperpendicular shocks in solar flares Eric Blackman, Jaehong Park, Chuang Ren, Jared Workman Low Mach/high beta fast mode shocks can occur in the magnetic reconnection outflows of solar flares. These shocks, which occur above flare loop tops, may provide electron energization responsible for some of the hard Xrays detected by YOHKO and the RHESSE, and radio emission. There has been a dearth of work on understanding the microphysics of these low Mach number shocks. We present new 2D particleincell simulations of low Mach/high beta shocks for the general quasiperpendicular geometry of field and shock normal to compare with the results for the purely perpendicular case considered in Park et. al. (2012)[Phys.Plasmas 19,062904]. Our aim is to study shock structure and particle acceleration. We find that the modifiedtwostream instability sustains the shock and accounts for the entropy creation downstream. We observe the electron Whistler instability in the transition region due to the temperature anisotropy. To have enough simulation electrons above the threshold energy for shockdriftacceleration (SDA), we inject a twotemperature Maxwellian distribution represented by two separate species, which is approximated to a kappa distribution with $\kappa$=10. From particle tracking and the particle energy distribution, we find copious highenergy electrons experiencing SDA. [Preview Abstract] 

NP8.00053: Numerical modeling of artificial ionospheric layers driven by highpower HFheating Bengt Eliasson, Xi Shao, G. Milikh, E.V. Mishin, K. Papadopoulos We present a multiscale dynamic model for the creation and propagation of artificial plasma layers in the ionosphere observed during highpower high frequency (HF) heating experiments at HAARP. Ordinary mode electromagnetic waves excite parametric instabilities and strong Langmuir turbulence near the reflection point. The coupling between high frequency electromagnetic and Langmuir waves and lowfrequency ion acoustic waves is numerically simulated using a generalized Zakharov equation. The acceleration of plasma electrons is described by a FokkerPlanck model with an effective diffusion coefficient constructed using the simulated Langmuir wave spectrum. The propagation of the accelerated electrons through the nonuniform ionosphere is simulated by a kinetic model accounting for elastic and inelastic collisions with neutrals. The resulting ionization of neutral gas increases the plasma density below the acceleration region, so that the pump wave is reflected at a lower altitude. This leads to a new turbulent layer at the lower altitude, resulting in a descending artificial ionized layer that moves from near 230 km to about 150 km. The modeling results reproduce artificial ionospheric layers produced for similar sets of parameters during the highpower HF experiments at HAARP. [Preview Abstract] 

NP8.00054: Planetary and stellar auroral magnetospheric radio emission David Speirs, Robert A. Cairns, Robert Bingham, Barry J. Kellett, Sandra L. McConville, Karen M. Gillespie, Irena Vorgul, Alan D.R. Phelps, Adrian W. Cross, Kevin Ronald A variety of astrophysical radio emissions have been identified to date in association with nonuniform magnetic fields and accelerated particle streams [1]. Such sources are spectrally well defined and for the planetary cases [1,2] show a high degree of extraordinary (Xmode) polarisation within the source region. It is now widely accepted that these emissions are generated by an electron cyclotronmaser instability driven by a horseshoe shaped electron velocity distribution. Although the generation mechanism is well established, a satisfactory explanation does not yet exist for the observed field aligned beaming of the radiation outwith the source region [2]. In the current context, the results of PiC simulations will be presented investigating the spatial growth of the horseshoemaser instability in an unbounded interaction geometry, with a view to studying the wave vector of emission, spectral properties and RF conversion efficiency. In particular, the potential for backwardwave coupling is investigated as a viable precursor to a model of upward refraction and fieldaligned beaming of the radiation [3].\\[4pt] [1] A.P. Zarka, Advances in Space Research, 12, pp. 99 (1992).\\[0pt] [2] R.E. Ergun et al., Astrophys. J., 538, pp. 456 (2000)\\[0pt] [3] J.D. Menietti et al., J. Geophys. Res., 116, A12219 (2011). [Preview Abstract] 

NP8.00055: Laboratory measurement of cyclotron radiation inhibition by background plasma relevant to the polar magnetosphere Sandra L. McConville, Martin King, Mark Koepke, David Speirs, Karen Gillespie, Alan Phelps, Adrian Cross, Kathleen Matheson, Alan Cairns, Irena Vorgul, Robert Bingham, Barry Kellett, Kevin Ronald Auroral Kilometric Radiation (AKR) emitted at polar regions of magnetised planets such as Saturn and Earth arises as particles descend and accelerate through an auroral density cavity (partial plasma depletion region, f$_{pe}\sim $9kHz and n$_{p}\sim $10$^{6}$m$^{3})$ into the increasing magnetic field at the poles. Adiabatic conservation of the magnetic moment increases the pitch angle of each electron causing an increase in perpendicular velocity, resulting in a horseshoe shaped distribution function in velocity space. This distribution has been shown to be unstable to a cyclotron resonance maser type interaction and produces radiation with spectral peaks at $\sim $300kHz, GW's of power and with wave propagation in the Xmode. A scaled laboratory experiment allows magnetic compression of an electron beam to represent the action of the Earth's magnetic field on the particles. A Penning trap was incorporated into the experimental apparatus to allow generation of background plasma. Results showed that the background plasma affected the EM wave generation, characterised by reduced intensity, intermittent radio emission compared to the stable emission observed in the absence of plasma. [Preview Abstract] 

NP8.00056: Variational Symplectic Algorithm for Whistler Wave Ray Tracing in the Inner Magnetosphere Chris Crabtree, Leonid Rudakov, Gurudas Ganguli, Manish Mithaiwala Whistler wave ray tracing in the inner magnetosphere using the full cold plasma dispersion relation is prone to producing drifts in frequencies that lead to inaccurate ray dynamics especially in the presence of both field aligned density structures (such as ducts and plasmapause boundaries) and sharp radial gradients in multispecies plasmas (such as ionospheric layers). The computation of accurate and quick ray trajectories are especially important for developing solutions to the wave kinetic equation including nonlinear (NL) effects such as induced scattering [1] where a large number of rays need to be time advanced and energy redistributed among rays. To facilitate such a calculation we have transformed the usual canonical ray tracing equations to an extended phase space Lagrangian framework and extended the variational symplectic integrator (VSI) [2] used for guidingcenter dynamics to the ray tracing equations. The VSI conserves exactly a discrete Lagrangian structure and most importantly leads to bounds in the frequency drift that can develop.\\[4pt] [1] C. Crabtree, L. Rudakov, G. Ganguli, M. Mithaiwala, V. Galinsky, V. Shevchenko, Phys. Plasmas 19, 032903, (2012).\\[0pt] [2] H. Qin and X. Guan, Phys. Rev. Lett. 100, 035006 (2008). [Preview Abstract] 

NP8.00057: Coexistence of Whistler Waves with Kinetic Alfven Wave Turbulence for the HighBeta Solar Wind Plasma Manish Mithaiwala, Leonid Rudakov, Gurudas Ganguli, Chris Crabtree It is shown that the dispersion relation for whistler waves is identical for a high or low beta plasma. Furthermore in the highbeta solar wind plasma whistler waves meet the Landau resonance with electrons for velocities less than the thermal speed, and consequently the electric force is small compared to the mirror force. As whistlers propagate through the inhomogeneous solar wind, the perpendicular wave number increases through refraction, increasing the Landau damping rate. However, the whistlers are not damped since the background kinetic Alfven wave turbulence creates a plateau by quasilinear diffusion in the solar wind electron distribution at small velocities [Rudakov et al., 2011]. The diffusion coefficient for whistlers in a high beta plasma is determined from mirror force. For a whistler spectrum similar to that of KAW, it is found that for whistler energy density of only $\sim $10$^{3 }$of the kinetic Alfven waves, the quasilinear diffusion rate due to whistlers and KAW are comparable. Thus very small amplitude whistler turbulence can have a significant consequence on the evolution of the solar wind electron distribution function. L. Rudakov, M. Mithaiwala, G. Ganguli, and C. Crabtree. Phys. Plasmas \textbf{18}, 012307 (2011); http://dx.doi.org/10.1063/1.3532819 [Preview Abstract] 

NP8.00058: Magnetic Topology of PseudoStreamers in the 2010 August 12 Eruption Events Viacheslav Titov, Zoran Mikic, Tibor Torok, Jon Linker, Olga Panasenco A sequence of apparently coupled eruptions was observed on 2010 August 12 by SDO and STEREO. The eruptions were closely synchronized, even though some of them occurred very far from each other. Trying to identify a plausible reason for such synchronization, we study the largescale structure of the background magnetic field. The latter was computed from the photospheric magnetic field observed at the appropriate time period by using the potential field sourcesurface model. For the resulting configuration, we determine its structural skeleton, which includes all separatrix and quasiseparatrix surfaces. Analyzing them, we reveal three pseudostreamers in the regions where the eruptions occurred. Of special interest to us are the magnetic null points and separator field lines associated with these pseudostreamers. We propose that magnetic reconnection at such nulls and separators played likely a key role in establishing the physical link between the successive eruptions. [Preview Abstract] 

NP8.00059: SPHERICAL TORUS, MHD STABILITY, LTX, HICD 

NP8.00060: Nonsolenoidal Startup through Local Helicity Injection in the Pegasus Toroidal Experiment M.W. Bongard, J.L. Barr, M.G. Burke, R.J. Fonck, E.T. Hinson, J.M. Perry, A.J. Redd, D.J. Schlossberg, N.L. Schoenbeck, P.C. Shriwise, K.E. Thome Nonsolenoidal plasma startup via local helicity injection is governed by helicity balance and Taylor relaxation constraints. Local helicity injection capabilities at Pegasus have been increased, supporting an expansion of the existing operational space towards I$_{p}\sim $ 0.3 MA and characterization of helicity dissipation mechanisms during plasma startup, growth, and sustainment. After discharge initiation with an active current source, helicity injection may be provided by passive electrodes to continue its evolution and extend pulse length. Local magnetic measurements confirm that a local field null is transiently created by injected current streams prior to relaxation into a tokamaklike state and sustained helicity injection. Bursts of MHD activity during the growth phase are correlated with rapid equilibrium changes, redistribution of the toroidal current density, and observations of strong ion heating (T$_{i }\sim $ 1 keV). The impedance of active injectors and thereby their helicity input rate appears constrained by a doublelayer space charge limit at low currents and the Alfv\'{e}nLawson limit for intense electron beams at high currents. Facility and diagnostic upgrades include an expanded poloidal field coil system for improved plasma control, new divertor coils, new plasma gunelectrode injector assemblies, a Thomson scattering system, expanded gas fueling techniques, and support for doubling the toroidal field. [Preview Abstract] 

NP8.00061: MHD During Relaxation and Growth of DC Helicity Injection Plasmas on Pegasus J.L. Barr, M.W. Bongard, R.J. Fonck, A.J. Redd, S.M. Reiss Nonsolenoidal plasma startup via DC helicity injection in Pegasus uses injected current streams that become unstable and relax to a tokamaklike configuration consistent with Taylor relaxation. Previous work had suggested that the current streams perturb the vacuum poloidal magnetic field to create a field null prior to relaxation. Local magnetic measurements using an insertable Hall Probe array diagnostic confirm the creation of this field null less than 1 ms prior to relaxation. Helicity injection plasmas are often accompanied by bursty n = 1 magnetic activity that presumably transports driven current into the plasma core, but the precise mechanism for the current drive is still under investigation. The MHD bursts quickly diminish after helicity injection drive is stopped. This MHD quiescence continues after the introduction of Ohmic induction, and the plasma continues without the tearing modes that usually limit Pegasus Ohmic operation. This is consistent with equilibrium reconstructions that show helicity injection drives J(r) profiles that are modestly frozenin for the following Ohmic phase. The Hall Probe has been redeployed to a midplane location to ease analysis for local current density and magnetic measurements to investigate the relationship between the n = 1 MHD activity and current drive associated with DC helicity injection. [Preview Abstract] 

NP8.00062: Limiting Currents of Pegasus HelicityInjection Sources E.T. Hinson, R.J. Fonck, B.T. Lewicki, A.J. Redd, G.R. Winz DC helicity injection startup and current growth schemes call for sources of current injection at the tokamak edge. Since helicity injection rate scales with injection voltage, knowledge of the physics governing the impedance of the current injectors is needed for a predictive model of the helicity injection rate. In Pegasus, two types of injector are implemented  a plasma cathode electron gun, and a bare molybdenum electrode. The electron gun operates immersed in plasma, and draws current densities J $\sim $1 kA/cm$^{2}$ from an arc discharge of similar current density. It manifests two regimes of operation, one with I $\propto $ V$^{3/2}$, and a higherpower mode where I $\propto $ V$^{1/2}$ holds. At voltages and currents below $\sim $100 V / 1 kA, the threehalves power mode manifests a perveance of $\sim $1 A/V$^{3/2}$. At higher currents and voltages, the I $\propto $ V$^{1/2}$ characteristic has the magnitude of a few Alfv\'{e}n currents, I$_{A}$. It is hypothesized that the lowpower mode is a spacecharge limited current mode, due to a $\sim $10 $\mu $m thick double layer at the 2 cm$^{2}$ gun aperture. The transition into the halfpower mode is indicative of a change from a spacecharge limited to a magnetically limited regime. Current in both regimes is observed to increase linearly with neutral fueling to the gun. The electrode in Pegasus also manifests a spacecharge limited, I $\propto $ V$^{3/2}$ mode when the plasma is decoupled from the electrode. This current roughly scales with electrode area, as expected. [Preview Abstract] 

NP8.00063: Magnetic Reconnection and Ion Flows During PointSource DC Helicity Injection on the Pegasus Toroidal Experiment M.G. Burke, M.W. Bongard, R.J. Fonck, D.J. Schlossberg, G.R. Winz A passive ion temperature polychromator has been deployed on Pegasus to study power balance and nonthermal ion distributions that arise during point source helicity injection. Spectra are recorded from a 1 m F/8.6 CzernyTurner polychromator whose output is recorded by an intensified highspeed camera. During helicity injection, stochastic magnetic fields keep T$_{e}$ low and thus low ionization impurities penetrate to the core. Under these conditions, high core ion temperatures are measured (T$_{i}$ $\approx $ 1.2 keV, T$_{e}\approx $ 0.1 keV) using spectral lines from CIII, NIII, and BIV. This rapid ion heating is seen to coincide with internal MHD activity. The ion temperature closely follows the injection bias voltage, indicating that power from the guns is strongly coupled to the ions through this MHD activity. Bidirectional toroidal ion flows of $\sim $60 km/s have been observed on the BIV line during helicity injection when looking near the front of the injectors. The flow is on the order of the Alfv\'{e}n velocity, as predicted by SweetParker reconnection, and is indicative of magnetic reconnection occurring near the injectors. When looking away from the helicity injectors, the bidirectional flow appears to be replaced by strong toroidal rotation, suggesting that ion acceleration during helicity injection is asymmetric and 3D in nature. [Preview Abstract] 

NP8.00064: Improved Density Control in the Pegasus Toroidal Experiment using Internal Fueling K.E. Thome, M.W. Bongard, J.A. Cole, R.J. Fonck, A.J. Redd, G.R. Winz Routine density control up to and exceeding the Greenwald limit is critical to key Pegasus operational scenarios, including nonsolenoidal startup plasmas created using singlepoint helicity injection and high $\beta $ Ohmic plasmas. Confinement scalings suggest it is possible to achieve very high $\beta $ plasmas in Pegasus by lowering the toroidal field and increasing n$_{e}$/n$_{g}$. In the past, Pegasus achieved $\beta \quad \sim $ 20{\%} in high recycling Ohmic plasmas without running into any operational boundaries.\footnote{ Garstka, G.D. \textit{et al.}, Phys. Plasmas \textbf{10}, 1705 (2003)} However, recent Ohmic experiments have demonstrated that Pegasus currently operates in an extremely lowrecycling regime with R $<$ 0.8 and Z$_{eff }\sim $ 1 using improved vacuum conditioning techniques, such as Ti gettering and cryogenic pumping. Hence, it is difficult to achieve n$_{e}$/n$_{g}>$ 0.3 with these improved wall conditions. Presently, gas is injected using lowfield side (LFS) modified PV10 valves. To attain high n$_{e}$/n$_{g}$ operation and coincidentally separate core plasma and local current source fueling two new gas fueling capabilities are under development. A centerstack capillary injection system has been commissioned and is undergoing initial tests. A LFS movable midplane needle gas injection system is currently under design and will reach r/a $\sim $ 0.25. Initial results from both systems will be presented. [Preview Abstract] 

NP8.00065: Energy Confinement and Helicity Dissipation Studies Using Thomson Scattering on the Pegasus Toroidal Experiment D.J. Schlossberg, A.S. Dowd, R.J. Fonck, N.L. Schoenbeck, G.R. Winz The Pegasus Toroidal Experiment provides several unique operating regimes that require characterization of plasma density and temperature by Thomson scattering. High$\beta $, high I$_{p}$/I$_{TF}$ regimes at low B$_{T}$ present discharges that require accurate plasma profiles for equilibrium reconstructions. Investigations of nonsolenoidal startup using pointsource DC helicity injection necessitate characterizing resistive helicity dissipation, accessible via measurement of T$_{e}$ and n$_{e}$ profiles. Furthermore, the usefulness of this method for startup of future fusion devices hinges on confinement scaling during helicity injection. By measuring temperature and density profiles before, during, and after Taylor relaxation, the dominant energy confinement scalings and related helicity dissipation rates for this startup technique can be evaluated. To address these issues, a new multipoint Thomson scattering diagnostic has been deployed on Pegasus. It will provide 1224 spatial points radially across the plasma with a high degree of flexibility to provide measurements within the varied plasma regimes. First results from the newly installed Thomson scattering system will be shown for some of these regimes. [Preview Abstract] 

NP8.00066: Design and Operation of a Frequency Doubled Nd:YAG Thomson Scattering System with Transmission Grating ICCD Spectrometer N.L. Schoenbeck, A.S. Dowd, R.J. Fonck, D.J. Schlossberg, G.R. Winz A novel Thomson scattering system has been deployed on the Pegasus Toroidal Experiment. It provides a relatively lowcost, simplified design. Scattering is achieved using a 7 ns, 2 J frequency doubled Nd:YAG laser operating at 532 nm. The laser focuses to $\sim $3 mm diameter within the plasma via a 7 m beamline. The beamline contains cameras as beam finders and remotely adjustable mirrors for shottoshot alignment. A custom multielement lens collects scattered photons from 15 cm $<$ R$_{maj}<$ 85 cm with 1.2 cm radial resolution. Eight fiber optic bundles provide 8 spatial points for sampling the laser or background light. Each set of 8 channels is measured in a single spectrometer that utilizes a high efficiency ($\sim $80{\%}) volume phase holographic grating and a high quantum efficiency ($>$ 40{\%}) image intensified CCD (ICCD) camera. Three spectrometers provide a total of 24 channels. Two interchangeable gratings exist to cover low (T$_{e}$ = 10100 eV) and high (T$_{e}$ = 0.101 keV) electron temperature regimes on Pegasus. The spectrometer is optimized for n$_{e}$ from mid10$^{18}$ to mid10$^{19}$ m$^{3}$. The signaltonoise expected is $\sim $0.5 of an equivalent system using Nd:YAG at 1064 nm and avalanche photodiode detectors. [Preview Abstract] 

NP8.00067: Divertor Coil Design and Implementation on Pegasus P.C. Shriwise, M.W. Bongard, J.A. Cole, R.J. Fonck, B.A. KujakFord, B.T. Lewicki, G.R. Winz An upgraded divertor coil system is being commissioned on the Pegasus Toroidal Experiment in conjunction with power system upgrades in order to achieve higher $\beta $ plasmas, reduce impurities, and possibly achieve Hmode operation. Design points for the divertor coil locations and estimates of their necessary current ratings were found using predictive equilibrium modeling based upon a 300 kA target plasma. This modeling represented existing Pegasus coil locations and current drive limits. The resultant design calls for 125 kAturns from the divertor system to support the creation of a double null magnetic topology in plasmas with $I_p \le 300$ kA. Initial experiments using this system will employ 900 V IGBT power supply modules to provide $I_{DIV} \le 4$ kA. The resulting 20 kAturn capability of the existing divertor coil will be augmented by a new coil providing additional Aturns in series. Induced vessel wall current modeling indicates the time response of a 28 turn augmentation coil remains fast compared to the poloidal field penetration rate through the vessel. First results operating the augmented system are shown. [Preview Abstract] 

NP8.00068: Upgrades to Power Systems and Magnetic Field Coils in the Pegasus Toroidal Experiment J.M. Perry, M.W. Bongard, M.R. Bradisse, R.J. Fonck, B.T. Lewicki, S.M. Swager A set of facility upgrades for Pegasus is currently underway to improve the control and performance of the power systems and the magnetic field coils, with the aim of increased helicitydriven current drive for noninductive startup. The plasma current achieved through helicity injection goes as $\sqrt {I_{TF} I_{inj} } $, the toroidal field rod current and injector bias current, respectively. To increase this quantity, the toroidal field power system will be upgraded. Eight new highcurrent IGBT bridges will replace the 6 bridges currently in place, bringing $I_{TF} $ from 288 kAturns to 600 kAturns. $I_{inj} $ is increased via a new 14 kA, 2.2 kV, singlequadrant IGCT switching power supply. The main poloidal field coil system is expanded to provide faster vertical field penetration of the vessel wall, thereby providing more flexible control of plasma position during startup and current growth. The $L/R$ time for these coils is reduced by $\sim $40{\%}. New divertor coils are being installed to provide more shaping flexibility and separatrixlimited operations. Overall power supply control will be improved and simplified by deployment of digital feedback controllers using Field Programmable Gate Arrays (FPGAs) to replace PWM analog feedback controllers. FPGAs will provide faster control frequencies, improved faulthandling capability, and streamlined recording of power system operations. [Preview Abstract] 

NP8.00069: Simulation of currentfilament dynamics and relaxation in the Pegasus ST J.B. O'Bryan, C.R. Sovinec Nonlinear numerical computation is used to investigate the relaxation of nonaxisymmetric currentchannels from washergun plasma sources into ``tokamaklike'' plasmas in the Pegasus ST. Resistive MHD simulations with the NIMROD code utilize ohmic heating, temperaturedependent resistivity, and anisotropic, temperaturedependent thermal conduction to reproduce critical transport effects. With sufficient injected current, adjacent passes of the current channel merge periodically, releasing axisymmetric current rings from the driven channel. The current rings provide a new phenomenological understanding for filament relaxation in Pegasus [O'Bryan, Sovinec, Bird. \textit{Phys. Plas.} submitted]. After largescale poloidalfield reversal, a hollow current profile and significant poloidal flux amplification accumulate over many reconnection cycles. When the current injection ceases, closed flux surfaces form quickly. Better electron thermal confinement with a twotemperature model produces a slower rate of decay for plasma current and internal energy than the singletemperature MHD model. [Preview Abstract] 

NP8.00070: Fast Ion Redistribution due to Fishbones in MAST Richard Lake, Simon Pinches, Rob Akers, Erwin Verwichte The confinement of fusion born $\alpha$particles for sufficient duration that they heat the bulk fuel ions and maintain thermonuclear burn is an important challenge in magnetically confined fusion. Fast ion driven plasma instabilities such as fishbones can lead to a significant fast ion redistribution and loss, degrading performance. Neutral beam injection in MAST drives fishbones that coincide with drops in the neutron rate. We present a detailed numerical study of the evolution of a single fishbone. Resonant regions of phase space are identified, which move as the frequency of the mode sweeps downward. The fishbone mode redistributes the fast ions, which is quantified by means of transport coefficients. The anomalous fast ion transport these coefficients represent is similar to that required by other codes modelling the same phenomena. Numerical representations of experimental diagnostics also allow a quantitative comparison with experimental observations. [Preview Abstract] 

NP8.00071: Electron Bernstein Wave Experiments in the Low Aspect ratio Torus Experiment Device Yuto Noguchi, Tadahiko Fukunaga, Masaki Uchida, Hitoshi Tanaka, Takashi Maekawa Two kinds of EBW experiments have been done on LATE using 2.45 GHz microwaves obliquely injected using open circular waveguide launchers. The vacuum vessel is a cylinder with a diameter of 100 cm and a height of 100 cm, and an 11.4 cm centerpost for center conductors for the Bt field with no central solenoid. In the first experiment we inject a relatively high power of 4060 kW from three 20kWmagnetrons, which noninductively starts up the discharge and finally maintains a toroidal current of 10 kA with a central plasma density 10 times the plasma cutoff density by EBW heating and current drive at the first propagation band. A wave injection with the optimal polarization for modeconversion to EBW via one launcher (other two launchers being with usual linear polarization parallel to the midplane) improves plasma performance in terms of density and current. In the second experiment we investigate various basic characteristics of EBW, including the modeconversion and subsequent propagation and absorption of EBW. Here, an 1.5 GHz microwave at 10 W is injected via OXB scheme into an ECR plasma maintained by a 2.45 GHz microwave at 1 kW. The wave field for 1.5GHz microwave is 2dimensionally measured on the midplane using probes attached to a twojoint robot arm. [Preview Abstract] 

NP8.00072: Observation of nonlinear phenomena of edge fluctuations in the TST2 spherical tokamak Yoshihiko Nagashima, Yuichi Takase, Akira Ejiri, Masateru Sonehara, Takuya Oosako Turbulence transport is one of the most important research themes in nature, fusion, and laboratory plasmas. TST2 is a medium size spherical tokamak device where we have good turnaround of experiments and flexible accessibility of Langmuir probes. In this study, we present progress in edge fluctuation measurement with a number of Langmuir probes in TST2. In previous work, a number of edge fluctuations have been observed in ohmically heated plasmas. Representative edge fluctuations are an MHD oscillation in the frequency of 10 kHz and turbulence fluctuations in the frequency range of 60100 kHz. Spatial structures of the fluctuations have been investigated, and we found significant nonlinear couplings among the fluctuations under a few observation conditions. Nonlinear energy transfer between MHD modes and turbulence is an important topic in fusion plasma study. However, we need careful consideration whether the nonlinear coupling implies the nonlinear energy transfer among the fluctuations. Experimental investigation of conditions under which the nonlinear couplings occurs is ongoing. Further investigation of various nonlinear phenomena will be addressed. [Preview Abstract] 

NP8.00073: Relationship between Magnetic Helicity Injection and Magnetic Reconnection in DoubleNull Startup of the UTST Spherical Tokamak Takenori Watanabe, Shuji Kamio, Qinghong Cao, Hirotomo Itagaki, Koichiro Takemura, Kotaro Yamasaki, Koji Ishiguchi, Takuma Yamada, Michiaki Inomoto, Yasushi Ono Magnetic helicity injection is a useful idea for explaining plasma current drive and startup of various magnetized plasmas such as Spherical Tokamaks (STs). Magnetic reconnection is directly related with the magnetic helicity injection, because it is essential to reorganization of magnetic field lines injected externally. We address how and why helicity injection is related with magnetic reconnection. An ST plasma is produced by using two pairs of external poloidal field coils in the University of Tokyo Spherical Tokamak (UTST) device. In the late phase of the formation, a single ST is connected to the coil flux, which enables magnetic helicity injection from the helicity source (the coil flux) into the helicity sink (the ST plasma). We measured the Yshaped reconnection region between the ST plasma and the poloidal coil using two dimensional pickup coil arrays in the rz plane. magnetic reconnection of common flux into private flux causes concentration of current density along the current sheet, forming a high eigenvalue area between the helicity source and the helicity sink. We made a parameter scan to study how crucial and effective the plasmoid ejection is for helicity injection and found that the plasmoid motion is a dynamic helicity injection process. [Preview Abstract] 

NP8.00074: Formation of Ultra High Beta Spherical Tokamak by Use of Merging Spheromak Plasmas Taichi Ito, Toru Ii, Michiaki Inomoto, Yasushi Ono We formed ultrahigh beta spherical tokamak plasmas using both of two spherical plasma merging and rampup of external toroidal field.\footnote{Y. Ono et al. Nucl. Fusion 43, 789, (2003).} The merging and reconnection heats ions significantly during magnetic reconnection in TS3 experiments. The maximum ion temperature $T_{i} \sim$ 250 eV is obtained in two merging spheromaks with counterhelicity and $T_{i} \sim$ 120 eV in those with cohelicity. While the reconnection heating decreases with the external guide toroidal field $B_{t}$, the confinement time of toroidal plasma tends to increase with external $B_{t}$. In order to confine the maximum ion thermal energy, we applied external $B_{t}$ to merging low$q$ plasmas such as spheromaks with co and counterhelicity after completion of reconnection, transforming the highbeta low$q$ toroid to an ultra highbeta ST in TS3$^{[1]}$ and TS4. This transformation increases the life times of low$q$ toroids by fact 23. It is noted that the highbeta ST has an absolute minimum $B$ profile with deep magnetic well. With increasing the rampup speed of external $B_{t}$, the magnetic well increases, but stays longer in low$q$ state unstable to MHD modes. [Preview Abstract] 

NP8.00075: Conceptual Study of the Steadystate of the Merging Startup ST DEMO Reactor Keii Gi, Toru Ii, Michiaki Inomoto, Yasushi Ono, Kenji Tobita We studied a new conceptual design of the advanced ST DEMO reactor with the merging startup [1], which has been developed in TS3, TS4, UTST and MAST. Its unique characteristics are low aspect ratio (A $<$ 2.0), highbeta ($\beta$ $>$ 30 [\%]) due to the significant heating of merging [2], high bootstrap current fraction ($f_{BS}$ $>$ 80 [\%]), stable highelongation ($\kappa$ $>$ 2.5) and rapid noninductive rampup by the plasma merging method. First, we calculated the appropriate parameters set by the 0D system code: TPC. Then, we produced the 2D axisymmetric MHD equilibrium consistent with the result of the 0D system code using the 2D free boundary equilibrium code: MEUDAS, interactively recalculating the parameters set by TPC. The experimentally obtained profiles in TS4 and MAST were used for our calculation model. We will also derive the current profile by ACCOME code (analyzer for current drive consistent with MHD equilibrium), and confirm the beta limit by the linear ideal MHD stability analysis code: ERATOJ to develop this conceptual study.\\[4pt] [1] Y. Ono et al., 19th IAEA Fusion Energy Conference, EX/P315 (2002).\\[0pt] [2] Y. Ono et al., Phys. Rev. Lett. 107, 185001 (2011). [Preview Abstract] 

NP8.00076: Overview of the Lithium Tokamak eXperiment (LTX) R. Kaita, L. BerzakHopkins, D.P. Boyle, E.M. Granstedt, J. Hare, C.M. Jacobson, M.A. Jaworski, T. Kozub, B. LeBlanc, M. Lucia, D.P. Lundberg, R. Majeski, E. Shi, J. Squire, J.C. Schmitt, D.P. Stotler, L. Zakharov, L.R. Baylor, T.M. Biewer, T.K. Gray, R. Maingi, S. Kubota, C.E. Thomas, K. Tritz, J. Clementson The Lithium Tokamak eXperiment (LTX) is a spherical tokamak for investigating the lowrecycling regime achieved with lithium plasmafacing components (PFCs). They consist of a stainless steel liner on copper plates that form a shell conformal to the last closed flux surface of the LTX design equilibrium. The liner is coated with lithium, and discharges up to 65 kA have been achieved. To create liquid lithium PFCs, a lithium filler is used to deposit liquid lithium directly onto the lower shell reservoirs. New diagnostic capabilities include upgraded passive chargeexchange recombination spectroscopy (ChERS) for ion temperatures and plasma flows, additional edge Thomson scattering channels, an extreme ultraviolet spectrometer, and a multichannel microwave reflectome [Preview Abstract] 

NP8.00077: Magnetic Analysis of LTX plasmas J.C. Schmitt, R. Majeski, R. Kaita, L. Berzak Hopkins, T. Kozub, J. Squire, L. Zakharov The Lithium Tokamak Experiment (LTX) is a spherical tokamak with a close fitting lowrecycling wall. The wall is conditioned prior to plasma operations by evaporating lithium onto stainless steellined copper shells. The 3/8'' copper shells are conformal to the last closed flux surface, cover about $\sim $85{\%} of the surface area, and have two poloidal and two toroidal breaks. The copper shells have high electrical conductivity, so changes in the coil and plasma currents induce longlived eddy currents with large spatial extent in the close fitting wall [1]. Digital signal processing techniques [2] will be applied to remove the effects of the coilinduced eddy currents. Lowest order calculations of the current centroid position, column width, beta and internal inductance will be presented. In the presence of the 3D shell eddy currents, a reliable 2D axisymmetric reconstruction is challenging. Poloidal field coil program simulations, including the effects of the 3D eddy currents, are started. Predictions of the simulations, experimental results and reconstructions of LTX plasmas will be compared.\\[4pt] [1] L. Berzak Hopkins, et al., Nuclear Fusion 52 (2012) 063025.\\[0pt] [2] Laqua and Schneider, Fusion Engineering and Design 48 (2000), 143. [Preview Abstract] 

NP8.00078: Development of liquid lithium plasma facing components on LTX M. Lucia, R. Majeski, R. Kaita, E. Kearns The Lithium Tokamak Experiment (LTX) will provide the first data from a tokamak with liquid lithium as the main (about 90\% surface coverage) plasma facing component (PFC). Until recently, lithium results on LTX had been restricted to solid coatings produced by evaporation onto cold shells. This poster describes initial efforts to develop and analyze active liquid lithium PFCs on LTX. A lithium fill system has been designed using a heated tungsten crucible assembly to rapidly deploy liquid lithium onto preheated LTX shells. In contrast with the earlier slow evaporation of lithium, this crucible releases its entire inventory at once, quickly filling the LTX shell reservoirs with liquid lithium. A system for testing dendritic tungsten as a candidate substrate for liquid lithium PFC has also been designed. Lithium was shown to wet the dendritic tungsten at about 350$^{\circ}$C, and the lithiumwetted surface can be characterized while it acts as a limiter during an LTX plasma shot. Finally, research in collaboration with Purdue University is underway to adapt the Materials Analysis Particle Probe (MAPP) to LTX. With its extensive diagnostic capabilities, MAPP will allow for \emph{in situ} study of surface physics inside LTX. [Preview Abstract] 

NP8.00079: Electron Temperature and Density Profiles for Low Recycling Wall Conditions in the Lithium Tokamak Experiment C.M. Jacobson, R. Kaita, B.P. LeBlanc, R. Majeski The Lithium Tokamak Experiment (LTX) is a spherical tokamak designed to study the lowrecycling regime through the use of a liquidlithium coated shell conformal to the last closed flux surface. Li is deposited onto the surface of the shells from internal crucible evaporators or is poured into the lower shell reservoir using a lithium filler system. The recycling rate $R=\Gamma_{\mathrm{wall}\rightarrow\mathrm{plasma}}/\Gamma_{\mathrm{plasma}\rightarrow\mathrm{wall}}$ is varied by the method of Li deposition, shell temperature, and slow passivation of the Li surface over time. A low recycling rate is expected to flatten core electron temperature profiles, raise edge temperatures, and strongly affect electron density profiles. A Thomson scattering diagnostic uses a 15 J, 30 ns FWHM pulsed ruby laser (694.3 nm) to measure $T_{e}$ and $n_{e}$ at 9 radial points on the horizontal midplane, spaced from the plasma axis to the outer edge at a single temporal point for each discharge, with two background light channels. Scattered light is imaged though a spectrometer to an intensified CCD. $T_{e}$ and $n_{e}$ profiles under various wall conditions are presented. Measurements are used in interpretive modeling of plasmas on LTX. [Preview Abstract] 

NP8.00080: Edge Thomson Scattering System for the Lithium Tokamak Experiment E. Shi, R. Kaita, C.M. Jacobson, B.P. LeBlanc, Q. Zang, R. Majeski An edge Thomson scattering system is currently being implemented on the Lithium Tokamak Experiment (LTX). The completed system will provide five edge spatial channels with 5 mm resolution. Scattered light from a 15 J, 30 ns FWHM pulsed ruby laser at 694.3 nm is imaged onto optical fibers by a singleelement lens and spectrally resolved into five different wavelength bands in the 680 nm to 750 nm range with filter polychromators and avalanche photodiode detectors. The output waveforms are digitized by fast sampling (250Ms/s) 12bit ADCs. This system is intended to measure edge densities and temperatures with varying amounts of lithium deposition on plasmafacing components, providing insight on the effect of a lowrecycling surface on the edge plasma. It can also be used to measure fluctuations in the emission from this region. Preliminary results will be presented. [Preview Abstract] 

NP8.00081: ABSTRACT WITHDRAWN 

NP8.00082: Recycling and Edge Impurities on the Lithium Tokamak eXperiment E.M. Granstedt, R. Kaita, R. Majeski, J. Squire, K. Tritz Measurements of neutral hydrogen emission demonstrate that the Lithium Tokamak eXperiment (LTX) has been able to achieve a range of hydrogen recycling conditions depending on the lithium wall conditioning. In particular, with a thin layer of a solid active lithium surface deposited by evaporation, LTX has excellent density control and neutral hydrogen emission drops to very low levels consistent with lowrecycling. Despite the stainlesssteel substrate, spectroscopic emission measurements suggest carbon wall fluxes are significant. RGA traces after lithium is evaporated suggest the lithium is reacting chemically with carbon. To better understand hydrogen recycling and wall impurity sources, neutral and impurity transport modeling is in process. Finally, experiments with a thick layer of liquid lithium in the lower shell reservoirs are underway. [Preview Abstract] 

NP8.00083: Passive CHERS measurements in the Lithium Tokamak Experiment (LTX) D.P. Boyle, T.M. Biewer, T.K. Gray, R. Maingi, R. Kaita, R. Majeski The Lithium Tokamak Experiment (LTX) is designed to achieve lowrecycling and reduced edge neutral density. This is predicted to significantly improve plasma momentum and ion energy confinement by reducing drag and energy losses due to charge exchange on edge neutrals. In order to measure the ion profiles, a charge exchange recombination spectroscopy (CHERS) diagnostic is undergoing a staged implementation on LTX. Initial passive toroidal and poloidal measurements have been made in discharges with solid lithium wall coatings, and toroidal line of sight measurements of ion temperature $T_{i} \approx$ 70 eV and toroidal rotation $v_{tor} \approx$ 45 km/s have been presented [1]. Analysis of the toroidal and poloidal measurements from additional discharges will be presented, including experiments with liquid lithium surfaces and measurements with higher spatial resolution toroidal optics. We will also present plans for a diagnostic neutral beam and further upgrades to the toroidal and poloidal views for both active and passive CHERS in 2013.\\[4pt] [1] T.K. Gray, et al. Rev. Sci. Instrum. (submitted 2012). [Preview Abstract] 

NP8.00084: Effect of Lithium PFCs on impurity ion content in LTX Jack Hare, Dennis Boyle, Robert Kaita, Richard Majeski, Joel Clementson, Peter Beiersdorfer The Lithium Tokamak Experiment (LTX) investigates Li coatings as the main plasmafacing component (PFC) which are expected to reduce ion impurity content in the plasmas. High densities of impurity ions, such as C, O, Fe, and even Li, may cool the plasmas by line radiation. Presently, solid lithium is used in LTX, but soon liquid Li will be tested as a PFC. To survey the ion impurity contents in LTX plasmas, an extreme ultraviolet (EUV) spectrometer has recently been installed, capable of distinguishing wavelengths in the range 40400 \AA. These EUV spectra are beneficial for impurity diagnostics since a multitude of low to highZ ions emit strong line radiation in this interval. The EUV spectrometer will study how the Li coatings affect the impurity content in LTX. [Preview Abstract] 

NP8.00085: FMCW Reflectometry for Electron Density Measurements on LTX S. Kubota, X.V. Nguyen, W.A. Peebles, R. Majeski, R. Kaita An FMCW (frequencymodulated continuouswave) reflectometer is being developed and installed on the Lithium Tokamak Experiment (LTX). The initial system will have two channels covering 13.533 GHz for (Omode) electron density measurements in the range of $0.2$$$$1.3$$\times$$10^{13}$ cm$^{3}$. The reflectometer is designed to provide electron density profile measurements for fueling studies using the molecular cluster injector (MCI), the supersonic gas injector (SGI), as well as external gas puffing. The ultrafast time resolution $\geq 4$ $\mu$s allows tracking of both the fast evolution of the density profile as well as fluctuations. A future third channel will extend the frequency range to 53 GHz for coverage up to $3.5$$\times$$10^{13}$ cm$^{3}$. The system design, along with simulations using ray tracing and 2D fullwave codes showing the measurement capabilities and data as available, will be presented. [Preview Abstract] 

NP8.00086: Latest Results from the LTX HighSpeed Digital Holography System C.E. (Tommy) Thomas Jr., E.M. Granstedt, C.M. Jacobson, D.P. Lundberg, R. Majeski, R. Kaita, L.R. Baylor, S.K. Combs, S.J. Meitner, D.A. Rasmussen During the last year research efforts for the LTX Digital Holography system have been concentrated on reducing noise and producing sample images. A highspeed CO$_{2}$ laser digital holography system (500 frames per second (FPS) at 256 x 256 pixels, 1500 FPS at 128 x 128 pixels, etc., to a maximum of 43,000 FPS at 64 x 4 pixels) has been built for highresolution imaging of electron density on the Lithium Tokamak Experiment (LTX). The laser operates at 9.1 microns by using an Oxygen18 isotope, and has a power output up to 20 W. A FLIR SC4000 IR camera is used to capture the digital holograms. An acoustooptic modulator (AOM) is used to ``shutter'' the laser so that effective camera integration times down to less than one microsecond are possible. The system will be used for imaging measurements on LTX during molecular cluster injection (MCI), supersonic gas injection (SGI), and external gas injection. Results of noise reduction efforts along with sample images and any LTX results will be presented. [Preview Abstract] 

NP8.00087: Effects of nonlinear viscosity on plasma flow induced island healing in stellarators C.C. Hegna The theory of island healing by plasma flows in stellarators [1] is extended to include the effects of nonlinear neoclassical viscosity. The theory was developed in an effort to explain observations from LHD that showed spontaneous healing of vacuum islands when a critical $\beta$ is exceeded. The theory uses torque balance and island evolution equations to describe transitions between states with large nonrotating islands to states where rotation shielding suppresses island formation. The balance of neoclassical damping and crossfield viscosity produces a radial boundary layer for the plasma rotation profile outside the separatrix of a locked magnetic island. The boundary layer width is related to the strength of the healing viscous torque. This work is extended by accounting for the nonlinear dependence of the neoclassical flow damping coefficients on the plasma flow. In the small flow limit, the resulting viscous torque is linear with the plasma flow. However, in sufficiently collisionless plasmas, nonlinear viscosity effects are important and the resultant viscous torque is proportional to the squareroot of the plasma flow velocity. Implications for magnetic island/transport barrier interactions will be discussed. \\[4pt] [1] C. C. Hegna, Nucl. Fusion 51, 113017 (2011) [Preview Abstract] 

NP8.00088: Scaling Optimization of the SIESTA MHD Code Sudip Seal, Steven Hirshman, Kalyan Perumalla SIESTA is capable of computing threedimensional plasma equilibria with magnetic islands at high spatial resolutions for toroidally confined plasmas. Originally, it was developed to exploit the smallscale parallelism offered by sharedmemory machines. Algorithms designed for sharedmemory machines do not necessarily scale to large number of processors on large distributedmemory machines. Mainly, this is because communication overheads in distributedmemory architectures can easily and very quickly dominate the gain in computation time as the number of processors is increased. Here, we report the results of a scaling effort that increases both the speed and resolution of the SIESTA magnetohydrodynamic equilibrium code on largescale tightly coupled distributedmemory computing platforms. We investigate the performance profile of the original SIESTA code to identify scaledependent bottlenecks and develop scalable alternative functionality. This improves both its runtime speed (on the same number of processors) as well as its scalability (across larger number of processors) by an order of magnitude. The net outcome allows SIESTA to utilize a few thousand processors and to simulate high spatialresolution scenarios in under an hour for the first time. [Preview Abstract] 

NP8.00089: Modifications to the shear Alfv\'{e}n continua due to the presence of a magnetic island C.R. Cook, S.P. Hirshman, D.A. Spong, C.C. Hegna, D.T. Anderson, R. Sanchez Most studies of the shear Alfv\'{e}n spectrum of toroidal confinement devices assume the existence of topologically toroidal magnetic surfaces. In this work, we will address how the presence of a magnetic island alters these calculations. In particular, the analytic theory of gaps induced by an island in the Alfv\'{e}n continua of a cylindrical plasma will be presented. This calculation will be compared to the wellknown results for the toroidicityinduced Alfv\'{e}n eigenmode gap. This theory utilizes island straight fieldline coordinates, which will be detailed. Early and planned work will be discussed regarding the use of SIESTA along with STELLGAP to analyze the effects of islands and quasisinglehelicity states on the Alfv\'{e}n continua in RFPs. SIESTA is a 3D MHD equilibrium code capable of resolving islands. The Hessian matrix computed in SIESTA can be used to solve the MHD eigenmode equations, allowing the Alfv\'{e}n continua to be determined in the presence of islands. STELLGAP is a code that computes the Alfv\'{e}n spectrum from a toroidal VMEC equilibrium converted to Boozer coordinates through the BoozXform code. Comparing the continua from the STELLGAP case without islands to the SIESTA case with islands will allow us to verify the presented theory in the future. [Preview Abstract] 

NP8.00090: 3D DIIID Equilibrium Calculations with Magnetic Islands Allan Reiman, Don Monticello, Sam Lazerson We discuss 3D equilibrium calculations for the DIIID tokamak that have been performed using the PIES code, focusing particularly on a single shot that has been studied by a number of different codes in the context of the FY 2012 FES Theory Milestone. The shot was part of an experimental campaign to study the suppression of edge localized modes (ELMs) using an externally imposed nonaxisymmetric magnetic perturbation. [Preview Abstract] 

NP8.00091: Enhancement of neoclassical toroidal viscosity by bounce harmonic resonance in perturbed tokamaks Kimin Kim, JongKyu Park, Gerrit J. Kramer, Allen H. Boozer, Jonathan E. Menard Demonstration of bounce harmonic resonance is reported using a newly developed deltaf code, POCA (Particle Orbit Code for Anisotropic pressures). POCA is a driftkinetic deltaf guidingcenter orbit code to calculate neoclassical transport in perturbed tokamaks. Basic features of POCA are presented with successful benchmarking tests in the axisymmetric and nonaxisymmetic configurations. Bounce harmonic resonances were clearly found by POCA, which has been predicted to significantly enhance the NTV transport by the resonances between bounce motions and electric precessions. Simulation results indicate strong NTV peaks at the electric precession frequency resonating with bounce frequencies, consistently with the theory prediction. A new type of closed orbits formed by the combinations of bounce motions with precessions is observed, which prevents phase mixing of bounce orbit thus enhances the NTV transport. This work was supported by the US DOE Contract \#DEAC0209CH11466. [Preview Abstract] 

NP8.00092: Effects of nonaxisymmetric magnetic fields on tokamak equilibria with finite beta and rotation Francois Louis Waelbroeck, Linjin Zheng, Ilon Joseph Resonant Magnetic Perturbations (RMP) are used in tokamaks for suppressing the edge localized modes (ELMs). In this work, we combine the AEGIS code with twofluid resistivelayer theory to compute the plasma response to RMPs, including the particle pumpout and the accelerating torque in the edge. The AEGIS code is a linear ideal MHD code that uses an adaptive integration scheme. For the purpose of the present RMP calculation, AEGIS is functionally similar to the IPEC code but accounts additionally for the effects of plasma rotation. We use AEGIS to calculate the amplitude of the singular currents in the resonant layers, which we combine with the numerical integration of the resistive layer equations to calculate the quasilinear transport fluxes. [Preview Abstract] 

NP8.00093: Safetyfactor profile dependence of the diamagnetic effect on fusion alpha particle losses in a rippled tokamak Michinao Bunno, Yuji Nakamura, Yasuhiro Suzuki, Koji Shinohara, Go Matsunaga, Keiji Tani The finite number of the toroidal field coils (TFCs) breaks the symmetry of tokamak plasmas. The nonaxisymmetric field from TFCs is called toroidal field (TF) ripple. Because of TF ripples, energetic ion losses are increased in tokamak plasmas. With increasing the beta value, the plasma changes the magnetic field structures and energetic ion losses. The diamagnetic effect due to the poloidal plasma current is one of the most important finite beta effects. In this study, we clarified how the diamagnetic effect and the fusion alpha particle losses are changed by the safetyfactorprofile. Keeping the plasmapressure profile and the shape of plasma boundary, the MHD equilibrium was solved by the VMEC code for different safetyfactor profiles. To investigate the diamagnetic effect, we created the two kinds of field structures: the MHD equilibrium fields with and without the toroidal field due to the plasma current. Trajectories of 10,000 fusion alpha particles were followed in each MHD equilibrium field with different safetyfactor profile. By comparing the loss rates, the safetyfactor dependence of the diamagnetic effect on the fusion alpha particle losses was clarified in this study. [Preview Abstract] 

NP8.00094: A new look at the origin of tokamak density limit scalings D.A. Gates, L. DelgadoAparicio The empirical scaling law of the density limit in tokamaks and reversedfield pinches has long been known and is a surprisingly robust experimental result [1]. Whereas the form of the empirical scaling evolved over decades of experimental activities, the physics mechanism for the onset of the density limit has remained elusive. A novel theoretical approach [2] has been recently proposed, in which the onset criterion for radiation driven islands in combination with a simple cylindrical model of tokamak current channel behavior is consistent with the empirical scaling of the Greenwald density limit [1]. This quantitative model is derived from a power balance condition between Ohmic heating and radiative losses in the island interior, and sheds light at the phenomenon that may underlie the density limit and which is common to all reactor schemes. The development of this analytical model also provides  for the first time  a predictive capability that identifies critical local variables and is capable of relating these to global engineering parameters. \\[4pt] [1] M. Greenwald, \textit{et al.}, Plasma Phys. Controlled Fusion, \textbf{44}, R27, (2002). \\[0pt] [2] D. A. Gates and L. DelgadoAparicio, Phys. Rev. Lett., \textbf{108}, 165004, (2012). [Preview Abstract] 

NP8.00095: Generalized resistive wall boundary conditions for cylindrical and toroidal geometry in Nimrod A.L. Montgomery, C.C. Hegna, C.R. Sovinec, S.E. Kruger, S.A. Sabbagh A generalized resistive wall boundary condition is implemented in Nimrod, making it possible to study both cylindrical and toroidal geometries with arbitrary toroidal shaping. The magnetic fields inside the computational domain are matched at the wall with external fields found using a vacuumfield solver. Results using the generalized boundary condition for a periodic cylinder with an analytically simple equilibrium are compared with theory and previous numerical work. The new boundary condition is tested for toroidal geometry in the large aspect ratio, circular crosssection limit. With a toroidal resistive wall condition, Nimrod can be used with a reconstructed National Spherical Torus Experiment (NSTX) equilibrium to study passive resistive wall mode stabilization with rotation [1,2]. Methods for including external resonant magnetic perturbations in the generalized boundary condition will also be discussed.\\[4pt] [1] S.A. Sabbagh et al., Nucl. Fusion, \textbf{46} 635 (2006).\\[0pt] [2] S.A. Sabbagh et al., Nucl. Fusion, \textbf{50} 025020 (2010) [Preview Abstract] 

NP8.00096: ExtendedMHD Studies of FlowProfile Effects on Edge Harmonic Oscillations in QHmode Discharges J.R. King, K.H. Burrell, A.M. Garofalo, T.G. Jenkins, S.E. Kruger, P.B. Snyder It is desirable to have an ITER Hmode regime that is quiescent to edgelocalized modes (ELMs). ELMs deposit large, localized, impulsive, surface heat loads that can damage the divertor. One such quiescent regime with edge harmonic oscillations (EHO) is observed on DIIID, JET, JT60U, and ASDEXU [1]. The physical mechanisms of EHO are not fully understood, but linear MHD calculations suggest EHO may be a saturated kinkpeeling mode partially driven by flowprofile shear [2]. We present preliminary EHO computations using the extendedMHD NIMROD code. The model incorporates firstorder FLR effects and parallel heat flows. Using reconstructed DIIID profiles from discharges with EHO, we scan the $E\times B$ and polodial flow profiles and compute linear stability. The aim is to ascertain the role of the $E\times B$ flow shear, as motivated by experimental results [3], and to compare with theoretical predictions where the growth rate is enhanced at intermediate wavenumbers and cutoff at large wavenumbers by diamagnetic effects [4]. Initial nonlinear computations exploring the EHO saturation mechanism are presented.\\[4pt] [1] Phys. Plasmas, v19, p056117, 2012 (and refs. within).\\[0pt] [2] Nucl. Fusion, v47, p961, 2007.\\[0pt] [3] Nucl. Fusion, v51, p083018, 2011.\\[0pt] [4] Phys. Plasmas v10, p4405, 2003. [Preview Abstract] 

NP8.00097: Fully Parallel MHD Stability Analysis Tool Vladimir Svidzinski, Sergei Galkin, JinSoo Kim, Yueqiang Liu Feasibility study of fully parallelizing plasma stability code MARS is made. MARS calculates eigenmodes in 2D axisymmetric toroidal equilibria in MHDkinetic plasma models. It is a powerful tool for studying MHD and MHDkinetic instabilities and it is widely used by fusion community. Parallel version of MARS is intended for simulations on local parallel clusters. It will be an efficient tool for simulation of MHD instabilities with low, intermediate and high toroidal mode numbers within both fluid and kinetic plasma models, already implemented in MARS. Parallelization of the code includes parallelization of the construction of the matrix for the eigenvalue problem and parallelization of the inverse iterations algorithm, implemented in MARS for the solution of the formulated eigenvalue problem. Construction of the matrix is parallelized by distributing the load among processors assigned to different magnetic surfaces. Two approaches of parallelization of the solution of the eigenvalue problem are evaluated: 1) repeat steps of the present MARS algorithm using parallel libraries and procedures; 2) solve linear blockdiagonal sets of equations, formulated in the inverse iteration algorithm in MARS, by parallel libraries and procedures. The results of these studies will be reported. [Preview Abstract] 

NP8.00098: Toroidal energy principle covering both ideal MHD and perturbed equilibria in tokamaks Leonid Zakharov, Luca Guazzotto A special representation of the MHD energy principle, based on vector potential perturbations is derived. For the ideal MHD model it is equivalent to the conventional representation where the plasma displacement is used as the test function. At the same time, the new representation has significant advantages in being: (a) applicable for calculations of perturbed equilibria (which have island at the resonant surfaces), and (b) consistent with the coordinate system used in generating an equilibrium. In particular, this form makes obvious the plasma edge stability in the LiWF regimes, what in 2005 was used for predicting the ELMs stabilization by Li conditioning. The perturbed equilibrium code, written with this approach, is suitable for Wall Touching Kink Mode studies and investigations of the thermal quench and runaway production/losses during disruptions in tokamaks. The code is a section in a more general Cbstbcode, which is under development. It will utilize all advantages of the psiform of MHD, which is unique also in providing opportunities to investigate the plasma edge, where the resonant surfaces are densely packed and the conventional stability models are inapplicable. [Preview Abstract] 

NP8.00099: A fast highorder solver for the GradShafranov equation Andras Pataki, Antoine Cerfon, Jeffrey Freidberg, Leslie Greengard We present a new fast solver to calculate highly accurate fixedboundary plasma equilibria in toroidally axisymmetric geometries. By combining conformal mapping methods with Fourier and integral equation methods in the unit disk, we show that highorder accuracy can be achieved for the solution of the GradShafranov equation and its first and second derivatives. Smooth arbitrary plasma crosssections as well as arbitrary pressure and poloidal current profiles can be given as inputs to the solver. Equilibria with large Shafranov shifts and steep pressure pedestals are computed without difficulty. Spectral convergence is demonstrated by comparing the numerical solution with a known exact analytic solution. For ITERlike and NSTXlike equilibria, we typically achieve 10+ digit accuracy for the solution and its derivatives in under a minute on a single CPU core on a 512 by 512 grid. [Preview Abstract] 

NP8.00100: Computational Study of the GradShafranov Equation with Flow in Helical Symmetry Lorenzo Siddi, Luca Guazzotto, Giovanni Lapenta, Roberto Paccagnella We present a numerical solution of the modified GradShafranov equation in cylinder geometry and in the presence of macroscopic rotation. The main challenge is the full inclusion of helical symmetry, a problem relevant in a variety of scenarios. Cylindrical symmetry is often used as lowestorder approximation of the GradShafranov equation in Tokamaks. However, in many other situations in astrophysical and laboratory plasmas, helical symmetry is a better assumption, in particular in Reversed Field Pinch (RFP) configurations in SingleHelicity states. The ``GradShafranov'' equation is written in helical symmetry with a convective term expressed by toroidal and poloidal velocities. Two equations are obtained: a nonlinear PDE for the magnetic flux $\Psi(r,u)$ and an algebraic equation for the density $\rho(r,u,\Psi)$ ($u$ is the variable along the helix). Here, we report on our progress in the development of a numerical method and computational code to solve the coupled nonlinear system. Examples of applications are described. [Preview Abstract] 

NP8.00101: Gyrokinetic Simulation of Internal Kink Mode in Toroidal Geometry Joseph McClenaghan, Zhihong Lin Magnetohydrodynamic (MHD) instabilities excited by equilibrium current in toroidal fusion devices play important roles in plasma stability and confinement. Kinetic effects are important in the excitation and saturation of the MHD modes, as well as resulting transport. In this work, we have applied Gyrokinetic Toroidal Code (GTC) to study kinetic effects in currentdriven MHD modes. As the first step, we have performed GTC simulation of the n=m=1 internal kink mode, which has been studied extensively in tokamak experiments, theory and MHD simulations. We will compare the dispersion relation and mode structure from the simulation to the ideal MHD theory in a low beta, large aspect ratio limit to verify the gyrokinetic simulation of currentdriven MHD modes. [Preview Abstract] 

NP8.00102: Macroscopic MHD instabilities during current rampup phase under the operational constraints of superconducting coils Yongkyoon In, J.G. Bak, Y.M. Jeon, J. Kim, W.C. Kim, W.H. Ko, K.D. Lee, S.G. Lee, S.W. Yoon Inductive current rampup rates in the superconducting devices are quite constrained to remain much lower primarily due to the operational safety of the superconducting coils than in conventional tokamaks. A systematic study in KSTAR showed that higher current rampup rates tended to destabilize global MHDs more easily. On the other hand, high current rampup rates are also thought to have been accompanied by hollowed pressure (or temperature) profiles, in that the current diffusion time, which is proportional to T$_{e}^{3/2}$, at high current ramp up rates becomes much longer than at other low current ramp up rates. Considering that the hollowness, rather than current rampup rates, was highly correlated with the macroscopic MHDs at a similar study in CMod [1], both current rampup rates and hollowness are being investigated to address the causality of these MHDs. The understanding of the destabilization mechanism of MHDs in the current rampup phase of superconducting devices, in comparison with other conventional devices, will reinforce the physics basis for the technical constraints that would be imposed on the startup scenario of ITER and future reactors to be equipped with superconducting coils. \\[4pt] [1] Y. In, PhD thesis, MIT (2000). [Preview Abstract] 

NP8.00103: Sideways Force Produced During Disruptions H.R. Strauss, R. Paccagnella, J. Breslau, S. Jardin, L. Sugiyama We extend previous studies [1] of vertical displacement events (VDE) which can produce disruptions. The emphasis is on the non axisymmetric ``sideways'' wall force $F_x.$ Simulations are performed using the M3D [2] code. A VDE expels magnetic flux through the resistive wall until the last closed flux surface has $q < 3.$ At this point the plasma is unstable to an $(m,n) = (2,1)$ mode. A theory of sideways force produced by this mode in the presence of a VDE is presented. The wall force depends strongly on $\gamma\tau_w,$ where $\gamma$ is the mode growth rate and $\tau_w$ is the wall resistive penetration time. The force $F_x$ is largest when $\gamma\tau_w $ is a constant of order unity, which depends on the initial conditions. For large values of $\gamma \tau_w,$ the wall force asymptotes to a relatively smaller value, well below the critical value ITER is designed to withstand. The principle of disruption mitigation by massive gas injection is to cause a disruption with large $\gamma\tau_w$. \\[4pt] [1] H. R. Strauss, R. Paccagnella, and J. Breslau,Phys. Plasmas \textbf{17}, 082505 (2010) \par\noindent [2] W. Park, E.V. Belova, G.Y. Fu, X. Tang, H.R. Strauss, L.E. Sugiyama, Phys. Plasmas \textbf{6}, 1796 (1999). [Preview Abstract] 

NP8.00104: ABSTRACT WITHDRAWN 

NP8.00105: Nonlinear dynamics of plasma with surface current in tokamak disruption events S.A. Galkin, V.A. Svidzinski, J.E. Grubert, L.E. Zakharov The Disruption Simulation Code (DSC), which was initially implemented in 2D (single helicity) geometry, has recently been developed in a fully 3D toroidal geometry with adaptation to the moving plasma boundary. DSC3D simulates freeboundary ideal onefluid MHD nonlinear dynamics of plasma separated from conducting invessel structures by a vacuum region. The vacuum magnetic field is calculated using both Green's functions and Poisson equation methods. Different regimes of plasmatouchingwall scenarios, leading to the formation of a Hiro current,\footnote{L.E. Zakharov. Phys. Plasmas, v.15, 062507 (2008)}$^,$\footnote{L.E. Zakharov, S.A. Galkin, S.N. Gerasimov, Phys. Plasmas 19, 055703 (2012)} will be discussed. Corresponding sideways forces applied to the plasmafacing components and to the vacuum vessel will be calculated. Progress on the DSC3D development, including both ideal and resistive onefluid MHD models, will be presented. Implementation of the resistive MHD model, together with a realistic wall model, will enable DSC3D to address the MHD issues of the entire disruption problem. This will also be an important step toward the prediction of disruptions in ITER and understanding opportunities for mitigation schemes. [Preview Abstract] 

NP8.00106: Pressure driven tearing modes in the Reverse Field Pinch Roberto Paccagnella In a recent paper [1] experimental measurements of magnetic field perturbations in the RFXmod Reverse Field Pinch device has been compared with stability calculations and interpreted as resistive g modes. In this paper a deeper analysis reveals that the modes discussed in [1] although as correctly stated in the paper are effectively mainly driven by the pressure gradient, they have a clear tearing parity. We analyze the dependence of the growth rate of these modes on several physical parameters including the Lundquist number, S, the plasma beta and also the changes in the equilibrium current and pressure profiles. The work confirms a previously published result [2] showing that these modes are converted to ideal interchange instabilities at very high beta. \\[4pt] [1] Zuin M. et.al. , Nucl. Fusion 50 (2010) 052001.\\[0pt] [2] Merlin D. et.al., Nucl. Fusion 29 (1989) 1153. [Preview Abstract] 

NP8.00107: On the stability of a particle driven Alfven mode localized within the minimum q in reversed shear D.P. Brennan, C.C. Kim, J.M. Finn Recent simulations have indicated the nonresonant m/n=1/1 mode is easily driven by particles in toroidal configurations with reversed shear and the minimum in the safety factor q just above 1. Experimental data from DIIID also indicates a similar structure is observed in Hybrid discharges, which includes a low amplitude n=1 mode in a nonlinearly saturated state. Here we investigate the analytic properties of this 1/1 nonresonant mode driven unstable by particles, and the nonlinear evolution of the system, including resonant modes, with the deltaf kineticMHD model in the 3D extended MHD code NIMROD. The mode is localized within the minimum in q$\ga$1 in reversed shear configurations. It is a stable continuum mode without particles, and has a tophat structure with finite displacement only inside of the location of the minimum in q. The physics of this delimitation of the displacement and the mode destabilization are reviewed as the minimum in q crosses 1 and the resonant q=1 mode becomes unstable. [Preview Abstract] 

NP8.00108: Modeling TAE Response To Nonlinear Drives Bo Zhang, Herbert Berk, Boris Breizman, Linjin Zheng Experiment has detected the Toroidal Alfven Eigenmodes (TAE) with signals at twice the eigenfrequency.These harmonic modes arise from the second order perturbation in amplitude of the MHD equation for the linear modes that are driven the energetic particle free energy. The structure of TAE in realistic geometry can be calculated by generalizing the linear numerical solver (AEGIS package). We have have inserted all the nonlinear MHD source terms, where are quadratic in the linear amplitudes, into AEGIS code. We then invert the linear MHD equation at the second harmonic frequency. The ratio of amplitudes of the first and second harmonic terms are used to determine the internal field amplitude. The spatial structure of energy and density distribution are investigated. The results can be directly employed to compare with experiments and determine the Alfven wave amplitude in the plasma region. [Preview Abstract] 

NP8.00109: LBQ2D, Extending the Line Broadened Quasilinear Model to TAEEP Interaction Katy Ghantous, Nikolai Gorelenkov, Herbert Berk The line broadened quasilinear model was proposed and tested on the one dimensional electrostatic case of the bump on tail\footnote{H.L Berk, B. Breizman and J. Fitzpatrick, Nucl. Fusion, 35:1661, 1995} to study the wave particle interaction. In conventional quasilinear theory, the sea of overlapping modes evolve with time as the particle distribution function self consistently undergo diffusion in phase space. The line broadened quasilinear model is an extension to the conventional theory in a way that allows treatment of isolated modes as well as overlapping modes by broadening the resonant line in phase space. This makes it possible to treat the evolution of modes self consistently from onset to saturation in either case. We describe here the model denoted by LBQ2D which is an extension of the proposed one dimensional line broadened quasilinear model to the case of TAEs interacting with energetic particles in two dimensional phase space, energy as well as canonical angular momentum. We study the saturation of isolated modes in various regimes and present the analytical derivation and numerical results. Finally, we present, using ITER parameters, the case where multiple modes overlap and describe the techniques used for the numerical treatment. [Preview Abstract] 

NP8.00110: Theory and simulation of the fishbone burst cycle Fulvio Zonca, Sergio Briguglio, Liu Chen, Claudio Di Troia, Giuliana Fogaccia, Valeria Fusco, Gregorio Vlad, Xin Wang Numerical simulation results show that both ion [1] and electron [2] fishbones are characterized by nonlinear dynamic evolutions that are strongly interlinked with suprathermal particle transport, which occurs because of secular particle loss from the region inside the $q=1$ surface. We present a theoretical model of the nonlinear burst cycle, revisiting that originally proposed in [3] and comparing the predicted behavior of nonlinear mode dynamics and energetic particle redistributions with numerical simulation results. In particular, we derive the renormalized solution of the nonlinear particle distribution function and show that frequency sweeping is dictated by phaselocking in the waveparticle resonance condition and show that secular particle losses are consistent with the modeparticle pumping process, originally described by [4].\\[4pt] [1] G. Y. Fu et al., Phys. Plasmas {\bf 13}, 052517 (2006).\newline [2] G. Vlad, S. Briguglio, G. Fogaccia, F. Zonca, C. Di Troia, V. Fusco, X. Wang, {\sl Electron fishbone simulations in FTUlike equilibria using XHMGC}, TH/P603 presented at the IAEA FEC 2012, San Diego.\newline [3] F. Zonca et al., arXiv:0707.2852v1 [physics.plasmaph] (2007).\newline [4] R. B. White et al., Phys. Fluids {\bf 26}, 2958 (1983). [Preview Abstract] 

NP8.00111: Analysis of energetic particle induced longlived modes in HL2A tokamak Xiaogang Wang, Xianqu Wang The effect of energetic particle on longlived modes observed in HL2A plasmas is investigated. The marginal stable pressuredriven ideal MHD mode on the $q=1$ rational surface is found driven by energetic particles generated during NBI. The dispersion relation of the mode is then derived for different magnetic shear. By analyzing the dispersion relation, we find that the ion diamagnetic drift play a major destabilizing role on the longlived mode. The numerical analysis is also compared with observation on HL2A. [Preview Abstract] 

NP8.00112: Simulation study of Alfven eigenmode induced energeticion transport in LHD Seiya Nishimura, Yasushi Todo, Noriyoshi Nakajima, Masaki Osakabe, Satoshi Yamamoto, Donald A. Spong, Yasuhiro Suzuki For the achievement of magnetic confinement fusion, the interaction between Alfven eigenmodes (AEs) and energetic ions is an important issue to be resolved. In the Large Helical Device(LHD), the AE bursts and the energeticion transport and losses have been observed during the neutral beam injection. However, it has not been clarified yet how the 3dimensional magnetic field affects the AE induced energeticion transport. It is worth investigating this problem since the particle dynamics in the 3dimensional configuration such as the helical trapping might enhance the transport. In this study, we perform the reduced simulation, where the AE spatial profile calculated with AE3D code is assumed to be constant in time and the evolution of the amplitude and the frequency is computed in a way consistent with the interaction between the energetic ions and AE. The energeticion dynamics is followed in the electromagnetic field that is the sum of the equilibrium field by HINT code and the AE perturbation. It is found that the AE amplitude continues to increase gradually after the exponential growth for the isotropic energeticion velocity distribution, whereas the saturation takes place for the beamtype distribution. We will report on the detailed analysis of the energeticion dynamics. [Preview Abstract] 

NP8.00113: Transonic Flow in a Tokamak Eliezer Hameiri, Luca Guazzotto Observed poloidal velocity $V_p$ in tokamaks is of the order of the poloidal sound speed ($c_{sp} \equiv c_s B_p/B$). At this range, the governing GradShafranov (GS) equation changes type twice: From elliptic near the center (low velocity) to hyperbolic where $V_p \simeq C_{sp}$ and back to elliptic when the velocity is higher still. Previous work established the existence of a contact discontinuity across which density falls and the Mach Number increases. The GS equation is solved as if it is elliptic and a hyperbolic region never appears, presumably because it is very narrow. Here we consider this matter analytically. First, we approximate the nonlinear GS equation such that it can be solved analytically. Second, we construct a linear model problem having similar transitions of type as the transonic plasma equation. The model problem is solved analytically and shows the expected hyperbolic region. We treat the equation asymptotically, expanding in the ratio of sound to Alfv\'en speed, corresponding to the width of the hyperbolic region. As this becomes very small, the hyperbolic region shrinks to naught, leaving no trace left over, so that solving the GS equation as an elliptic problem with a contact discontinuity yields the correct asymptotic approximation to the solution. [Preview Abstract] 

NP8.00114: Model Improvement for Transonic Flows Luca Guazzotto, Riccardo Betti, Steve Jardin Finite toroidal and poloidal flows are routinely observed in the edge plasma region of tokamaks. MHD theory predicts that when the poloidal velocity becomes transonic with respect to the poloidal sound speed ($c_{sp} \equiv c_s B_p/B$, where $B_p$ is the poloidal field) transient shocks will develop in the transonic region. The shocks will move in the poloidal direction and disappear once they reach the location of the minimum transverse flow cross section. After the transient, a steadystate pedestal in plasma density and pressure is left, with the height of the pedestal depending on the poloidal location. Timedependent and equilibrium calculations confirm the theoretical picture. Here we present several improvements to the existing numerical and theoretical results. Derivation and implementation of an equilibrium numerical solution explicitly enforcing the correct jump condition across the transonic discontinuity are shown. This has an effect on equilibrium profiles only if the discontinuity is located in a highbeta region. We also show that the transonic discontinuity is removed and replaced by a boundary layer through a twofluid treatment of the plasma. The implementation of an expression for neoclassical poloidal viscosity in timedependent simulations is also discussed. [Preview Abstract] 

NP8.00115: Snakes and sawteeth in nonlinear MHD Linda Sugiyama, Luis DelgadoAparicio The ``snake,'' a helical $m/n=1/1$ concentration of ion density near the $q=1$ magnetic surface in a toroidal confined plasma, is shown to arise naturally in nonlinear resistive MHD when the plasma density evolves. The results help to resolve the theoretical problems posed by long snake lifetimes and their coexistence with periodic sawtooth crashes. Numerical simulations with the M3D code show that a helical density perturbation imposed around $q=1$ can form a quasisteady helical state over $q\ge 1$. Within $q<1$, two principal outcomes depend on the magnitude of $\tilde{n}/n$ and the 1/1 internal kink stability and correspond to the two main types of snake formation observed in experiments. For a small $q<1$ region, the applied density drives a new type of slowly growing mode with some features of the nonlinear internal kink. It resembles the early broad kink seen in heavyimpurityion snakes in ohmic discharges, including recent observations on Alcator CMod. For a larger, more unstable $q<1$ region, the helical density perturbation drives a conventional kink, leading to a rapid sawtooth crash. The crash redistributes the density to a localized helical concentration over $q\le 1$, consistent with the formation of sawtoothinduced snakes. [Preview Abstract] 

NP8.00116: ABSTRACT WITHDRAWN 

NP8.00117: Transport timescale calculations of sawteeth and helical structures in noncircular tokamak plasmas Stephen Jardin, Nate Ferraro, Josh Breslau, Jin Chen We present results of using the implicit 3D MHD code M3D$C^{1}$ [1,2] to perform 3D nonlinear magnetohydrodynamics calculations of the internal dynamics of a shaped crosssection tokamak plasma that span the timescales associated with ideal and resistive stability as well as parallel and perpendicular transport. We specify the transport coefficients and apply a ``current controller'' that adjusts the boundary loopvoltage to keep the total plasma current fixed. The 3D 2fluid plasma model advances the magnetic field, velocities, electron and ion temperatures, and plasma density. We find that the plasma either reaches a stationary quasihelical state in which the central safety factor is approximately unity, or it periodically undergoes either simple or compound sawtooth oscillations [3] with a period that approaches a constant value. By comparing a deeshaped cross section with an elliptical shaped cross section, it is shown that the plasma shape has a large effect on determining the sawtooth behavior and the associated mode activity. Application to ITER shaped tokamak plasmas predict the magnitude of the 3D boundary deformation as a result of a stationary quasihelical state forming in the interior. \\[4pt] [1] J. Breslau, N. Ferraro, S.C. Jardin, \textit{Physics of Plasmas} \textbf{16} 092503 (2009) \\[0pt] [2] S. C. Jardin, N. Ferraro, J. Breslau, J. Chen, \textit{Computational Science and Discovery} \textbf{5} 014002 (2012) \\[0pt] [3] X. von Goeler, W. Stodiek, and N. Sauthoff, \textit{Phys. Rev. Lett}. \textbf{33}, 1201 (1974) [Preview Abstract] 

NP8.00118: MHD instabilities in JET Hybrid Scenario with the ITER Like Wall Matteo Baruzzo, Barry Alper, Tommaso Bolzonella, Antonio Botrugno, Clarisse Bourdelle, Paolo Buratti, Rui Coelho, Clive Challis, Ian Chapman, Peter de Vries, Carine Giroud, Michela Gelfusa, Emmanuel Joffrin, Nick Hawkes, Tim Hender, Jorg Hobirk, Joelle Mailloux, Francesco Orsitto, Gianluca Pucella, Onofrio Tudisco JET has been recently refurbished with an ITERlike Be first wall and W divertor, to study plasma wall interaction processes for ITER. In this work the new behaviour of the MHD instabilities will be characterized in the hybrid scenario, which with the Cwall in JET achieved high energy confinement, combined with good MHD stability to NTMs and ideal kinks. The same scenario developed for the ILW has produced good confinement, but interactions are observed between MHD phenomena and impurities coming from the wall. The q=1 MHD activity with the JET Cwall showed a negligible effect on plasma confinement, except NTM triggering. In some ILW hybrid pulses at the start of the heating phase a q=1 fishbone occurs, as with the Cwall, but it is often replaced by a continuous q=1 mode, with a significant reduction of confinement. ECE measurements also highlight a change from pure kink fluctuations to islands centered on q=1. NTMs have also been observed in these plasmas. Their appearance is coincident with a flattening of electron temperature profile within the island (the effect with the Cwall), but it is also correlated with enhanced radiation from the plasma core and a slow decrease of central electron temperature. [Preview Abstract] 

NP8.00119: Momentum transport due to overlapping tearing modes in tokamaks and reversed field pinches A.J. Cole, J.M. Finn, C.C. Hegna, P.W. Terry Quasilinear calculations related to momentum transport due to a spectrum of stable tearing modes in RFPs and tokamaks will be presented. In RFPs, the modes considered are stable high poroidal mode number modes with mode rational surfaces near the reversal layer, and driven by mode coupling originating by the linearly unstable modes with n $\sim$ 2 R/a. In tokamaks these are high poloidal mode number stable tearing modes near the edge that are driven by external field errors. In both cases the odes are weakly driven with closely packed rational surfaces, so that the tearing layers, but not the islands, overlap. We first present the total Maxwell and Reynolds forces found by integrating the Maxwell and Reynolds stresses across the layer of a single tearing mode. We also present a calculation of the total Maxwell and Reynolds torques about the layer center. The Reynolds torque is related to the effect which drives or damps zonal flows. The Maxwell and Reynolds torques are present because of terms which break the usual tearing mode symmetry, namely velocity shear across the layer and current density gradient in the layer. These results are shown in both the resistiveinertial and viscoresistive regimes. [Preview Abstract] 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit membership organization working to advance the knowledge of physics. 
© 2022 American Physical Society
 All rights reserved  Terms of Use
 Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 207403844
(301) 2093200
Editorial Office
1 Research Road, Ridge, NY 119612701
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700