Session CP9: Poster Session II: Waves, Turbulence and Flow; Non-Neutral & Dusty Plasma I; Field Reversed Configuration and Spheromaks

Room: Hall A


   [Preview Abstract]


CP9.00002: Overview of studies of turbulence, transport and flows in the Large Plasma Device
T.A. Carter , D. Schaffner , G. Rossi , B. Friedman , J.E. Maggs , D. Guice , S. Vincena , M.V. Umansky

The Large Plasma Device (LAPD) at UCLA is a 17m long, 0.6m diameter linear magnetized plasma in which broadband edge turbulence driven by pressure and flow gradients is observed. Particle transport barriers are observed with bias-driven cross-field flows in LAPD.\footnote{J. E. Maggs, et al. Phys. Plasmas 14, 052507 (2007); T. A. Carter and J. E. Maggs, Phys. Plasmas 16, 012304 (2009)} New biasable limiters have been installed, allowing for a continuous variation in the edge flow and flow shear. Initial experiments using this new capability have shown confinement degradation at low flow/shear and improved confinement with both positive and negative azimuthal flow and flow shear. The 3D Braginskii fluid turbulence code BOUT (and now BOUT++) has been modified for and verified in cylindrical geometry for application to LAPD.\footnote{P. Popovich, et al. Phys. Plasmas 17, 102107 (2010)}. Nonlinear simulations yield good qualitative and semi-quantitative agreement with LAPD data\footnote{P. Popovich, et al., Phys. Plasmas 17, 122312 (2010)} Finally, a new fast-framing camera has been applied to imaging visible light fluctuations in LAPD as a turbulence diagnostic and initial results will be discussed.    [Preview Abstract]


CP9.00003: Observation of improved and degraded confinement through driven flow on the Large Plasma Device
D.A. Schaffner , T.A. Carter , G.D. Rossi , D.S. Guice , J. Maggs , S. Vincena , B. Friedman

Density confinement improvement and degradation is observed in the edge plasma of the Large Plasma Device (LAPD) at UCLA through conditions of spontaneous, biased-driven and minimal azimuthal flow states. A floating, biasable, annulus-like limiter plate is placed between the cathode and the plasma chamber to provide a known edge boundary potential and a means of inducing a radial electric field to drive azimuthal flow in the direction opposite the natural flow state. With this configuration, a range of flow states can be achieved from the clockwise spontaneous flow to a minimal flow state to a large counter-clockwise driven flow. In both the clockwise and counter-clockwise flow states a steepened density gradient is observed at the cathode edge while in the low flow state, a ``confinement degradation'' or broad density gradient is seen. A plot of shearing rate versus gradient scale length for each flow state lies on a single curve suggesting that only shearing is correlated to confinement and not flow direction. The relationship between particle flux, Reynolds Stress, and flow/confinement state are also explored as well as the instabilities observed---i.e. drift-wave, Kelvin-Helmholtz and rotational interchange modes.    [Preview Abstract]


CP9.00004: Stable Eigenmodes and Energy Dynamics in a Model of LAPD Turbulence
Brett Friedman , T.A. Carter , M.V. Umansky

A three field Braginskii fluid model that semi-quantitatively predicts turbulent statistics in the Large Plasma Device (LAPD) at UCLA is analyzed. A 3D simulation of turbulence in LAPD using the BOUT++ fluid code is shown to reproduce experimental turbulent properties such as the frequency spectrum and correlation length with semi-qualitative and semi-quantitative accuracy. In an attempt to explain turbulent saturation in the simulation, equations for the energy dynamics are derived and applied to the results. The degree to which stable linear drift wave eigenmodes draw energy from the system and the affect that zonal flows have on transferring energy to stable eigenmode branches is explored. It is also shown that zonal flows drive Kelvin-Helmholtz flute modes, which come to dominate the energy dynamics in the quasi steady state regime.    [Preview Abstract]


CP9.00005: Progress in turbulence studies in the TORPEX Simple Magnetized Torus
Ivo Furno , Ambrogio Fasoli , Alexandre Bovet , Mark Gilmore , Kyle Gustafson , Davoud Iraji , Benoit Labit , Diane Lancon , Joaquim Loizu , Paolo Ricci , Christian Theiler

We report on advances in understanding ideal interchange electrostatic turbulence, related turbulent structures and their effect on particle, heat, current, and toroidal momentum transport in TORPEX magnetized plasmas. These advances are obtained using high-resolution electrostatic and magnetic probes, fast visible imaging, scan of the control parameters, linear fluid models and nonlinear global 3D numerical simulations. We describe methods to influence the dynamics of turbulent structures, such as varying the connection length or using biased electrodes. The effect of turbulence on fast ion phase space dynamics is studied using movable fast ion source and detector. Results are compared with simulations of tracer fast ions injected into simulated TORPEX turbulent fields, which are part of an extensive validation and verification project. Finally, we describe future developments, which include a helicon antenna to decouple plasma production from the magnetic field and a new internal toroidal conductor to close magnetic field lines.    [Preview Abstract]


CP9.00006: Development of an Internal Helicon Source for the TORPEX Simple Magnetized Torus
M. Gilmore , I. Furno , P. Marmillod

A new helicon plasma source is being developed for the TORPEX device in order to expand the range of accessible plasma parameters. TORPEX (\underline {Tor}oidal Plasma \underline {Ex}periment) is a Simple Magnetized Torus with major radius 1 m, and minor radius 20 cm, well-suited to basic plasma physics studies such as on intermittent turbulence and transport, and fast ion-turbulence interaction dynamics. Currently, TORPEX operates with a 2.45 GHz microwave source, which produces plasmas with average n $\sim $ 10$^{15}$ - 10$^{17}$ m$^{-3}$ and T$_{e} \quad \sim $ 10 eV, at B$_{tor} \quad \sim $ 775 G on axis, via electron cyclotron and upper hybrid resonance absorption. The new helicon source, which will be internal to the vacuum chamber, is expected to produce plasmas with average n $\sim $ 10$^{18}$ - 10$^{19}$ m$^{-3}$ and T$_{e} \quad \sim $ 5 eV over a wide range of B$_{tor}$. Initial results from an m = 0 antenna in TORPEX, as well as results from a parallel internal antenna development in the linear HelCat device at the University of New Mexico are presented.    [Preview Abstract]


CP9.00007: Drift wave turbulence in the Texas Helimak
Dmitry Meyerson , Wendell Horton , Francois Waelbroeck , Kenneth Gentle

The BOUT++ framework is used to study resistive drift-wave turbulence in the Texas Helimak. Experimental electrostatic fluctuation data is compared with results from a three dimensional axysymmetic simulation as well as analytic predictions. The physical basis for the simulation is a nonlinear 3 field, cold ion, drift-ordered fluid model. In the linear limit eigenmodes of the system are examined analytically. The helimak is a low temperature experimental plasma device that allows convenient comparisons between theoretical models and experimental evidence. The most important geometric effects founds in a tokamak's SOL, magnetic shear and toroidicity, are present in this device. BOUT++ is an open source, C/C++ based, framework developed to quickly prototype physical models by decoupling the physics of a given model and the particular numerical methods used to evolve the desired set of equations. The original motivation was the study of the relatively low temperature scape-off-layer (SOL) in high temperature plasma devices. Two motivations are (1) to validate models of the scrape-off- layer (SOL) and (2) to investigate the role of $E_r$ shear in forming transport barriers. A 3D axisymmetric configuration is assumed with a finite difference equations along the helical magnetic field line and in the bi-normal direction.    [Preview Abstract]


CP9.00008: Potential and Flow Profiles and Fluctuation Dynamics in a Large Scale Helicon Plasma With Electrode Biasing
Alan Lynn , Shuangwei Xie , Tiffany Hayes , Mark Gilmore , Lincan Yan , Andrew Sanchez

Experiments utilizing two sets of biased electrodes to affect the velocity flow shear in the linear HelCat device are described. HelCat (Helicon-Cathode) is a 4 m long, 50 cm diameter experiment. A grid electrode was placed at the source end of the experiment ($\sim $ 7 cm in front of the helicon antenna) and biased with respect to the vacuum chamber wall, while a set of concentric ring electrodes terminated the plasma column at the far end and was biased in various ways. Flow profiles exhibit complicated changes with bias in both the azimuthal and parallel directions. Drift fluctuations can be partially or fully suppressed by biasing. During the onset of suppression, the fluctuations exhibit complicated dynamics, which can be chaotic or more dynamically complex, and involve turbulent transport, density gradients, azimuthal flows and neutral collisionality. Additionally, an axial return flow toward the source is observed which appears to be driven by neutral damping and a stress tensor coupling.    [Preview Abstract]


CP9.00009: Optimal Azimuthal Velocity Profile Control by E$\times $B Actuation in HELCAT
Zeki Ilhan , Eugenio Schuster , Shuangwei Xie , Mark Gilmore , Andrew Ware

Turbulence, and turbulence-driven transport are ubiquitous in magnetically confined plasmas, where there is an intimate relationship between turbulence, transport, destabilizing mechanisms like gradients and currents, and stabilizing mechanisms like shear. We investigate active control of fluctuations via manipulation of flow profiles in a magnetized laboratory plasma device (HELCAT). Measurements of the azimuthal velocity are assumed available at several radial points within the plasma and E$\times $B flow profiles are controlled via biased ring electrodes. An optimal control algorithm is designed to regulate the radial azimuthal velocity profile around a prescribed desired profile. The effectiveness of the controller and the effect of the shape of the radial azimuthal velocity profile on RMS fluctuations are analyzed via numerical simulations.    [Preview Abstract]


CP9.00010: Nonlinear Saturation Physics of the ETG Modes
Vladimir Sokolov , E Tokluoglu , A.K. Sen

Production and identification of electron temperature gradient (ETG) mode and the measurement of electron thermal conductivity due to it have been successfully done in a basic experiment in Columbia Linear Machine CLM [1,2]. Now we report the nonlinear saturation mechanism of the ETG modes. The bi-coherence experimental data shows coupling between two high frequency $(\sim 2MHz)$ and one low frequency $(\sim 40kHz)$ modes. The 3-wave coupling model (two radial harmonics ETG and one ion acoustic mode) yielded a theoretical saturation level of ETG mode $\sim 5 \%$, which roughly agrees with experiments. The role of ion acoustic mode in the saturation of ETG mode has also been experimentally demonstrated by using unique feedback techniques. This research was supported by U.S. Department of Energy Grant No. DE-FG02-98ER-54464. \\[4pt] [1] X.Wei, V.Sokolov, and A.K. Sen, Phys. Plasmas 17, 042108 (2010) \\[0pt] [2] V. Sokolov, A.K. Sen, APS DPP10, TP9.00022    [Preview Abstract]


CP9.00011: Velocity shear stabilization of Rayleigh-Taylor instabilities
Ching Pui Hung , Adil Hassam

Rayleigh-Taylor modes in magnetized fluids can be stabilized by flow shear. A detailed numerical study of this effect is revisited in linear and nonlinear regimes, with various cross-field velocity profiles. A 2D dissipative MHD code is employed to simulate the instabilities. It is found that for fixed flow shear V', the linear growth rates increase with the wave-number kL transverse to the density gradient and the B-field, but become small for large kL. In addition, the unstable regime in k-space shrinks for higher V', which is consistent with the fact that higher k modes would be more susceptible to flow shear and the well recognized result of significant stabilization at V'$^{2}>$gn'/n. In the nonlinearly saturated regime, the density fluctuation and the degree of flattening of the initial inverted density profile are found to decrease as V' increases; unstable modes are almost completely stabilized when V' is a few times the RT growth rate. The mode cascades to longer wavelengths and other results will be compared with observations of magnetic fluctuations from the Maryland Centrifugal Experiment, MCX. Finally, Kelvin-Helmholtz instabilities are also observed in the simulation; the stability criterion for the onset of the KH, similar to the Rayleigh inflexion theorem, will also be examined.    [Preview Abstract]


CP9.00012: Catalytic Alpha-Channeling of Wave Energy in Mirror Devices
Andrey Zhmoginov , Nathaniel Fisch

The possibilities for alpha-channeling in mirror reactors are significantly broadened if the alpha particle energy is channeled to minority ions rather than fuel ions. The minority ions then collide preferentially with the fuel ions, thereby completing the channeling of the alpha energy to the fuel ions. This technique, which relaxes the wave requirements since the wave need not now resonate both with the fuel ions and alpha particles, may be thought of as ``catalytic alpha channeling.'' It may be particularly important in mirror fusion, as opposed to tokamak fusion, since the channeling effect in mirror machines exploits very different wave modes in very different ways.    [Preview Abstract]


CP9.00013: Propagation of helicon waves with magnetic boundaries
V.P. Anitha , Devendra Sharma , Shyama Prasad Banerjee , S.K. Mattoo , Predhiman Kaw

Propagation of bounded whistlers is analyzed in presence of a radially sheared magnetic field (Bo) where the boundary effects are assumed to be provided purely by sharp magnetic field gradients. The propagation of a plane polarized wave requires the constituent left and right circularly polarized waves with single k value to have different radial extents, a condition which is inaccessible in cases of conventional, conducting or dielectric, physical boundaries. The possibility of achieving such a plane polarized bounded mode is explored in an alternate set up with magnetic field boundaries. The results are correlated with experimental observations in the Large Volume Plasma Device (LVPD) where a transition from a right handed to a left handed polarized helicons wave was detected in addition to the presence of a plane polarized wave. When contribution of a nonuniform B$_{o}$ was taken in to account in finding numerical solutions for the wave magnetic field component B$_{z}$(r)a good agreement was recovered with the measured B$_{z}$(r). The numerically obtained k values were used to find a dispersion relation that provided an improved agreement with the measure dispersion data as compared to the conventional Helicon dispersion relation applicable to physical boundaries.    [Preview Abstract]


CP9.00014: The Physics of Ion Decoupling in Magnetized Plasma Expansions
Dennis Hewett , Stephen Brecht , David Larson

The coupling of a super-Alfv\'enic plasma expansion within a magnetized background plasma is examined. Such coupling plays an important role in several high-energy, quasi-neutral, plasma configurations; the focus here is on High Altitude Nuclear Explosions (HANEs). Fully 3-D Kinetic Ion Simulation Modeling reveals, for some initial conditions, strong coupling of the debris to the magnetized background ionosphere even though all collision processes between the ions have been neglected. The interaction dynamics are found to be sensitive to initial conditions. A slight increase in the ion charge density of the background plasma allows the debris ions to decouple and slip through the magnetized background. These decoupled ions in the expanding plasma then follow trajectories typical of single particle motion. The salient features of this process, guided by 1-D simulations, lead to two thresholds for the onset of decoupling. The first threshold depends on the ratio of the charge density of the expanding plasma to that of the background plasma. The second threshold is evident when the expanding plasma has a finite pulse length comparable to the gyro-radius of the energized background ions.    [Preview Abstract]


CP9.00015: Scattering of Magnetic Mirror-trapped fast Electrons by an Alfv\'{e}n Wave
Yuhou Wang , Walter Gekelman , Patrick Pribyl , Dennis Papadopoulos

Highly energetic electrons produced naturally or artificially can be trapped in the earth's radiation belts for months, posing a danger to satellites. A technique for artificially de-trapping these electrons is under investigation at the Large Plasma Device (LaPD) at UCLA. The experiment is performed in a quiescent afterglow plasma ($n_e =0.1-1\times 10^{18}/m^3$, $T_e \approx 0.5eV$, $B_0 =400-1600G$, $L=18m$, and $diameter=0.6m)$. A population of runaway electrons is generated by 2$^{nd}$ harmonic ECRH (P=25kW, $\tau $=10-50ms, f=2.45GHz), as evidenced by production of X-rays with energy up to 5MeV. The fast electrons are trapped in a magnetic mirror field (R$_{m}$=1.1-4). A shear Alfv\'{e}n wave ($f$=110-230 kHz, $B_{wave}$=2G) is launched with a rotating magnetic field antenna. The Alfv\'{e}n wave is observed to dramatically affect the trapped fast electrons and scatter them out of the mirror.    [Preview Abstract]


CP9.00016: Conversion of lower hybrid waves to whistler waves in the presence of a density striation
Bart Van Compernolle , Walter Gekelman , Patrick Pribyl

The conversion of electrostatic waves to electromagnetic waves is a fundamental process in plasma physics. Electrostatic waves in the outer magnetosphere produced by the solar wind are believed to be partially converted into electromagnetic waves which can propagate into the inner magnetosphere, and influence the lifetime of trapped particles in the radiation belts. A new series of experiments in the Large Plasma Device (LAPD) at UCLA focuses on the conversion of lower hybrid waves to whistler waves through the interaction with a density striation. Both the linear regime and the non-linear regime will be studied. In the linear regime the density striation is created by introducing an obstacle in the machine, while in the non-linear regime the density striation will be created by the lower hybrid wave itself through the ponderomotive force. A 16 element slow wave antenna (length 2 m, f $<$ 150 MHz) has installed, and is fed by 16 arbitrary waveform generators allowing for arbitrary amplitude and phase on the antenna elements. Electric dipole probes and magnetic loop probes are used to map out the wave patterns inside and outside the striation. Preliminary results in the linear regime showed the presence of both lower hybrid and whistler waves, and showed evidence of a trapped mode within the density striation. Work funded by DOE and performed at the Basic Plasma Science Facility funded by DOE/NSF.    [Preview Abstract]


CP9.00017: Whistler propagation in nonuniform magnetic fields
J.M. Urrutia , R.L. Stenzel

The propagation of whistler waves when the magnetic field presents gradients comparable or smaller to the plane wavelength has been studied. Such a magnetic field occurs when a Helmholtz coil is immersed in a uniform background magnetic field, leading to magnetic null regions and islands as well as closed field lines. Whistler wavepackets have been launched in three distinct regions of this magnetic configuration and detailed maps of their propagation been obtained in situ. The packets are observed to be trapped on closed field lines where they propagate as Gendrin modes. In contrast, when the packets are launched against the null regions, they are observed to propagate around the nulls. Hence, the oblique nature of whistlers is very evident as they travel in non-uniform field regions.    [Preview Abstract]


CP9.00018: Ion Sound Turbulence
Reiner Stenzel , J. Manuel Urrutia

The turbulence created by streaming ions through a stationary plasma is studied. The velocity of the streaming ions is selected via a biasing voltage. In situ probes are used to measure the local and time-varying plasma parameters, ion distribution functions, and the turbulence itself. Density fluctuations are recorded in time and space, Fourier transformed into frequency space, and cross-correlated in space. The fluctuations are identified as ion sound modes and their growth rate is shown to depend on the beam energy. The interaction of density fluctuations with electromagnetic waves is investigated. Strong scattering of electromagnetic signals is observed when the wave is guided by a transmission line through a turbulent plasma. The effect is enhanced by forming a transmission line resonator and applying frequencies on the slope of the resonance curve. This suggests a possible method to eliminate the modulation of a high frequency signal by plasma turbulence.    [Preview Abstract]


CP9.00019: Gradient instabilities in Hall thruster plasmas
Winston Frias , Andrei Smolyakov

There exist a number of fluctuations observed in Hall thruster plasmas. In this work, by using two-fluid theory, we study instabilities induced by the equilibrium electron plasma flow, gradients of the equilibrium density and temperature in combination with an inhomogeneous magnetic field. Effect of electron collisions and electron inertia are studied and characteristic plasma parameters for each excitation mechanisms are determined. Transitions between different regimes and connections with instabilities in other Hall plasmas, e.g. such as Earth ionosphere plasmas, are investigated.    [Preview Abstract]


CP9.00020: Simulating dynamics modulation in a neon glow discharge plasma
P.M. Miller , H. Gunell , M.E. Koepke

Dynamics modulation occurs when two ionization wave modes in a glow discharge plasma alternate as the dominant mode in response to a periodic driving force. This phenomenon has been observed experimentally in a neon discharge using a chopped beam from a narrow-band ring dye laser tuned to a wavelength near the metastable neon transition at 588.35 nm. In addition, an analytical periodic-pulling model has been described which includes a mode-amplitude normalization of the driving term which is consistent with the experimental data and provides a mechanism for the observed modulation. In this poster, we show that the experimentally-observed time series of luminosity oscillations can be reproduced by solving two coupled van der Pol equations using a Runge-Kutta routine with a driving term than can be renormalized when a mode change is detected. With appropriate parameter selections, the output is quantitatively comparable to the experimental result.    [Preview Abstract]


CP9.00021: Ion flow shear measurements using LIF at the NRL SPSC
Christopher Cothran , Erik Tejero , William Amatucci

Ion cyclotron instabilities due to strongly sheared plasma flow have been studied experimentally at the Naval Research Laboratory Space Physics Simulation Chamber (SPSC). These experiments have characterized both electrostatic and, for the first time, electromagnetic instabilities as described in Tejero {\it et al}, Phys. Rev. Lett. {\bf 106}, 185001 (2011). A two-axis laser induced fluorescence (LIF) diagnostic has now been used to directly measure the flow profile generated in the plasma; previously, this profile could only be inferred from emissive probe electric field measurements. The 2mm spatial resolution of the LIF measurements is sufficient to observe the ion gyroscale flow shear required for the instability.    [Preview Abstract]


CP9.00022: Spontaneous Electromagnetic Emission from a Strongly Localized Plasma Flow
Erik Tejero , William Amatucci , Gurudas Ganguli , Christopher Crabtree , Christopher Cothran , Edward Thomas

The laboratory experiments to be presented establish that strongly localized DC electric fields perpendicular to the ambient magnetic field can behave as a radiation source for electromagnetic ion cyclotron waves, transporting energy away from the region of wave generation. \textit{In situ} observations of sheared plasma flows collocated with electromagnetic wave activity have led to this laboratory effort to investigate the impact of electromagnetic, velocity shear-driven instabilities on the near-Earth space plasma dynamics. The transition from electrostatic to electromagnetic ion cyclotron (EMIC) wave propagation has been investigated under scaled ionospheric conditions. The general wave characteristics and wave dispersion experimentally observed are in agreement with the current theoretical models. In addition, the electromagnetic component of these waves increased by two orders of magnitude as the plasma $\beta $ was increased. The observed EMIC waves are predominantly azimuthally propagating m=1 cylindrical waves, which propagate in the direction of the \textbf{E}$\times $\textbf{B} drift. Experimental observations and comparison to theory will be presented.    [Preview Abstract]


CP9.00023: Construction of an electron-ion hybrid experiment in a magnetized plasma column
Ami DuBois , James Creel , Edward Thomas, Jr.

Localized radial electric fields in a magnetized plasma column can lead to many plasma instabilities. Previous work in the Auburn Linear Experiment for Instability Studies (ALEXIS) has focused on instabilities in the ion cyclotron regime where the scale length of the radial electric field is of the same order as the ion gyroradius. A new dual plasma source experiment in ALEXIS, a 170 cm long and 10 cm diameter magnetized plasma column, has been designed to study a new regime of instabilities that occur when a sharp, localized, radial electric field scale length is much less than the ion gyroradius but greater than the electron gyroradius. Under these conditions, this electric field is then expected to have little effect on the ions, but the electron trajectories will be modified. This can give rise to an electron-ion hybrid (EIH) instability, which produces a broadband wave spectrum in the lower hybrid frequency range. Both fusion and space plasma studies have made observations of lower hybrid instabilities. This work seeks to understand how regions of sheared electron flows generate may contribute to localized ion heating via wave-particle interactions. This presentation will focus on the setup of this new experiment, as well as initial measurements of radial electric field and electron densities.    [Preview Abstract]


CP9.00024: Measurements and spectral modeling of neutral Argon as a diagnostic in the ALEXIS plasma
Andrew Kiene , Stuart Loch , Ami DuBois , Ashley Eadon , Edward Thomas

We present spectral measurements and theoretical results for an argon plasma experiment on the ALEXIS (Auburn Linear~Experiment for Instability Studies) device. Langmuir probe measurements for the electron temperature and density profiles along the line of sight were taken for a wide range of plasma B-field settings. Comparisons with theoretical models show that the plasma is not in ionization equilibrium. A theoretical spectrum is constructed using the line of sight profiles and recently calculated R-matrix atomic data. We also investigate the role of a non-equilibrium population in the neutral Ar metastable and how that affects the spectrum.    [Preview Abstract]


CP9.00025: Magnetic field effect on cylindrical impedance probe diagnostics
David Walker , Richard Fernsler , David Blackwell , William Amatucci

To test geometry independence predicted theoretically in earlier work with spherical impedance probes,\footnote{D.N. Walker, R.F. Fernsler, D.D. Blackwell, W.E. Amatucci, \textit{Phys. Plasmas }\textbf{17}, 113503 (2010)} we used a 100-1 (length -- radius) aspect ratio cylindrical probe. In the impedance measurements, a network analyzer supplies a millivolt driving rf signal and plasma diagnostics are based on the real and imaginary parts of the complex plasma impedance returned by the analyzer for a given probe bias. The theoretical basis of the work indicates that in the thin sheath limit the results should be independent of probe geometry. With probe alignment along a small magnetic field $\sim $ 2 gauss, we compared the cylinder's impedance-based plasma measurements to those for which we swept the same cylinder as a Langmuir probe.\footnote{\textit{NRL Memorandum Report 6750-11-9331 }(2011)} In both cases the impedance probe format showed a higher density, the same plasma potential, and a comparable electron temperature to the Langmuir sweep. We will present recent data showing the effect of varying the orientation and magnitude of the applied field.    [Preview Abstract]


CP9.00026: Communication through a plasma sheet around a fast moving vehicle
V.I. Sotnikov , S. Mudaliar , T. Genoni , D. Rose , B.V. Oliver , T.A. Mehlhorn

Investigation of the complicated problem of scattering of electromagnetic waves on turbulent pulsations induced by a sheared flow inside a plasma sheath is important for many applications including communication with hypersonic and re-entry vehicles. Theoretical and computational work aimed at improving the understanding of electromagnetic wave scattering processes in such turbulent plasmas is presented. We analyze excitation of low frequency ion-acoustic type oscillations in a compressible plasma flow with flow velocity shear and influence of such turbulent pulsations on scattering of high frequency electromagnetic waves used for communication purposes. We have appropriately included in our analysis the presence of electron and ion collisions with neutrals as well as electron - ion collisions. Results of numerical solutions for plasma density and electric field perturbations for different velocity profiles have been used in the derived expressions for scattered wave energy and scattering cross section.    [Preview Abstract]


CP9.00027: Ion Heating in Pulsed Helicon Sources
Earl Scime , Richard Magee , Jerry Carr Jr. , Matthew Galante , Greg Lusk , Dustin McCarren , Eric Reynolds , Stephanie Sears , Robert Vandervort , Robert Hardin

Previous measurements demonstrated a strong correlation between ion temperature and the ratio of the antenna frequency to the local lower hybrid frequency. When strong ion heating occurs, the ion temperature profile in steady-state helicon sources is flat or peaked at the edge; suggesting an edge localized ion heating mechanism. The same parameters that yield the largest ion temperatures are also predicted to have the strongest damping of slow waves in the edge. Here we present observations that further support the conclusion that short wavelength slow waves parametrically decay into electrostatic modes and also directly heat ions. Collective Thomson scattering measurements indicate significant wave power at frequencies of $f \sim $ 100 kHz and perpendicular wave numbers of $\sim $ 89 rad/cm. The waves are localized to the same region as lower frequency ion acoustic waves are observed with probes. By pulsing the helicon source and observing the time evolution of the ion temperature profile, we find that the ion temperature profile flattens out and then becomes hollow at the same time the parametrically driven ion acoustic waves appear.    [Preview Abstract]


CP9.00028: Laser Induced Fluorescence Measurements of Argon Neutrals in Two Helicon Sources
Amy Keesee , Dustin McCarren , Earl Scime

A laser induced fluorescence (LIF) scheme to measure velocity distribution functions (VDFs) of argon neutrals was previously developed by the West Virginia University helicon source group [\textit{Keesee et al}., 2004]. The original measurements were performed with a low power, $<$ 15 mWatt, diode laser with a limited tuning range centered on the 667.9125 nm (vacuum wavelength) pump wavelength. To obtain a sufficient population in the initial, non-metastable state, the helicon source had to be operated at fill pressures greater than 10.5 mTorr. Here we present new neutral VDF measurements with an amplified tunable diode laser (up to 350 mWatts) capable of scanning over 25 GHz. With this new laser, we have been able to obtain neutral VDF measurements over a broader range of pressures in our large helicon plasma source as well as obtain measurements in the recently upgraded and much smaller CHEWIE helicon source. In addition to measurements of the neutral temperature, we will present measurements of the bulk neutral flow for plasma conditions that result in the formation of an electric double layer which produces an ion beam in an expanding helicon plasma.    [Preview Abstract]


CP9.00029: Ion Flow and Temperature Measurements in Turbulent CSDX Plasmas
Dustin McCarren , Earl Scime , Saikat Thakur , Ty Lee , George Tynan

Experiments in the Controlled Shear Decorrelation Experiment device have shown that an azimuthally symmetric, radially sheared plasma fluid flow arises spontaneously when the primarily axial magnetic field lines terminate on insulating boundaries. Theory suggests that the shear flow is sustained by the Reynolds stress generated by collisional drift turbulence. The measurements were based on Time Delay Estimation, which cannot distinguish between ion fluid velocities and wave phase velocities, and Mach probes, which are perturbative. We present measurements of the radial profiles of ion flows and temperatures as measured with laser induced florescence in argon. The measurements were obtained with a portable, high power ($>$ 350 W), tunable diode laser-based system operating at 668.614 nm. Mode hop free tuning of the laser over 30 GHz permitted the measurement of the entire ion velocity distribution function in a single laser frequency scan. The absolute wavelength was simultaneously recorded for each laser frequency. We will report radial profiles of ion temperature and bulk flow for both turbulent and quiescent flow regimes.    [Preview Abstract]


CP9.00030: Characterization of Electrostatic Fluctuations During Electric Double Layer Formation
Jerry Carr , Saikat Chakraborty-Thakur , Matthew Galante , Dustin McCarren , Stephanie Sears , Richard Magee , Eric Reynolds , Robert Vandervort , Greg Lusk , Earl Scime

Electrostatic probe measurements in pulsed, expanding helicon plasmas indicate the presence of a coherent $\sim$16 kHz wave when a double layer appears in the expansion region. Time- resolved measurements of the instabilities and the beam component of the ion velocity distribution demonstrate significant correlations throughout the duration of the pulse, approaching unity at times, between the downstream ion beam (the ion beam is a signature of an upstream double layer) and the electrostatic wave amplitudes. The ion velocity distribution is measured with laser induced fluorescence and the waves with a two-tip floating probe. As the helicon source pulse evolves, the double layer appears and then fades away as the amplitude of electrostatic fluctuations increases. The wave measurements yield a parallel wave number of -2.4 cm$\ ^{-1}$ and perpendicular wave number of 1.7 cm$\ ^{-1}$, relative to the background magnetic field. The wave phase speeds are consistent expectations for ion acoustic waves and are observed when the ion beam velocity is approximately twice the ion sound velocity.    [Preview Abstract]


CP9.00031: Resonant Wave Heating of Argon Ions in the Hot hELicon eXperiment (HELIX)
Stephanie Sears , Jerry Carr Jr. , Justin Elfritz , Matthew Galante , Richard Magee , Dustin McCarren , Robert VanDervort , Eric Reynolds , Earl Scime

Alfv\'{e}n wave damping is the dominant physical process invoked in leading theoretical models of ion heating in the solar corona.~ The construction of a new external antenna by the West Virginia University helicon source group to launch large-amplitude (B$_{1}$~ $\sim $ 10{\%} of B$_{0})$ shear Alfv\'{e}n waves in argon plasma provides a new experimental tool to investigate possible ion heating due to the damping of these waves.~ The ion temperatures are measured with time-resolved Laser Induced Fluorescence while magnetic sense coils are used to measure the phase velocity and amplitudes of the propagating waves. A new, small-scale magnetic sense coil provides sub ion gyroradius spatial resolution and new differential amplifiers block the ambient rf noise at high frequencies. Here we present both the antenna and the new b-dot probe designs, measurements of the plasma perturbations and spatially-localized field measurements, as well as comparisons of these experimental results with 3 dimensional PIC simulations of Alfv\'{e}n wave propagation in plasmas with strong density gradients.    [Preview Abstract]


CP9.00032: Experimental Study of Double Layer in Helicon Plasma with Diverging Magnetic Field
P.K. Chattopadhyay , Kshitish Barada , J. Ghosh , S. Kumar , Y.C. Saxena

Existence of double layer in helicon plasma with diverging magnetic field was first reported by Boswell (Appl. Phys. Lett., 1356, 82, 2003). Later many other researchers have also observed DL with the simultaneous presence of ion beam only. Though there are some speculations about the existence of the DL but the issue is far from resolved. In the present study, double layer in helicon plasma with diverging magnetic field has been investigated. Double layers with both electron and ion beams are observed for the first time. The experiment is performed in a glass tube of inner diameter 10 cm and length 70 cm connected to a stainless steel chamber of inner diameter 21 cm and length 50 cm. A 13.56 MHz RF (Radio Frequency) source $(Prf < 1.2$ KW) with a capacitive L matching network is used to power the m = +1 helicon antenna. Diagnostics used are Langmuir probe, B-dot probe and an emissive probe for the present study. Characterization of double layer under different operational parameters such as magnetic field, pressure, and RF power will be presented. Detailed observations along with a model to explain the existence of DL will be presented.    [Preview Abstract]


CP9.00033: Experimental Study of Low Magnetic Field Density Peaking in Helicon Plasma
Kshitish Barada , P.K. Chattopadhyay , J. Ghosh , S. Kumar , Y.C. Saxena

In addition to the dense plasma performances at high magnetic field $(B > 200$ Gauss), the local density peak at $B < 50$ Gauss was observed previously in various helicon plasma sources. This is a resonance phenomenon unlike density change during capacitive to inductive to wave mode transitions. In the present experiment, however, multiple density peaks are observed for the first time when magnetic field is varied upto 100 Gauss. Detail characterization of the density peak phenomenon with respect to different operational parameters such as magnetic field, pressure and RF (radio frequency) power has been done. Initial analysis suggests the density peaks are due to coupling of Trivelpiece-Gould (TG) mode with Helicon mode. The experiment is performed in a glass tube of inner diameter 10 cm and length 70 cm connected to a stainless steel chamber of inner diameter 21 cm and length 50 cm. A 13.56 MHz RF source $(Prf < 1.2 $KW) with a capacitive L matching network is used to power the m = +1 Helicon antenna. Diagnostics used are Langmuir probe, B-dot probe and an emissive probe for the present study.    [Preview Abstract]


CP9.00034: Magnetic Effects in a Moderate-Temperature, High-Beta, Toroidal Plasma Device
W.F. Edwards , A.K. Singh , E.D. Held

A small toroidal machine (STOR-1M; minor radius 4.5 cm), on loan from the University of Saskatchewan, has been modified to operate at hydrogen ionization levels $\sim$0.1\%, beta values between 0.1 and 1, electron number density $\sim$5x1016/m3, temperature $\sim$5 eV, and applied toroidal magnetic field $\sim$20 gauss. Plasma is generated using magnetron-produced microwaves. Langmuir and Hall probes determine radial profiles of electron number density, temperature, and magnetic field. For most values of the externally-applied magnetic field, the internal field is the same with or without plasma, however, in a narrow window of B, diamagnetism and other effects are present. The effect is observed with no externally induced current; plasma currents are self generated through some sort of relaxation process. Beta and radius conditions correlate well with similar magnetic structures in the laboratory (eg., plasma focus, Z pinch) and in space (eg., Venus flux ropes, solar coronal loops).    [Preview Abstract]


CP9.00035: Plasma Properties of Microwave Produced Plasma in a Toroidal Device
Ajay Singh , W.F. Edwards , Eric Held

We have modified a small tokamak, STOR-1M, on loan from University of Saskatchewan, to operate as a low-temperature ($\sim$5 eV) toroidal plasma machine with externally induced toroidal magnetic fields ranging from zero to $\sim$50 G. The plasma is produced using microwave discharges at relatively high pressures. Microwaves are produced by a kitchen microwave-oven magnetron operating at 2.45 GHz in continuous operating mode, resulting in pulses $\sim$0.5 s in duration. Initial measurements of plasma formation in this device with and without applied magnetic fields are presented. Plasma density and temperature profiles have been measured using Langmuir probes and the magnetic field profile inside the plasma has been obtained using Hall probes. When the discharge is created with no applied toroidal magnetic field, the plasma does not fill the entire torus due to high background pressure. However, when a toroidal magnetic field is applied, the plasma flows along the applied field, filling the torus. Increasing the applied magnetic field seems to aid plasma formation - the peak density increases and the density gradient becomes steeper. Above a threshold magnetic field, the plasma develops low-frequency density oscillations due to probable excitation of flute modes in the plasma.    [Preview Abstract]


CP9.00036: Existence of Fluctuation Depletion Layer in Simple Magnetized Torus
Rajwinder Kaur , A.K. Singh , A. Sarada Sree , S.K. Mattoo

This paper presents an experimental finding of the existence of Fluctuation Depleted Layer (FDL) in the plasma center of BETA, a simple magnetized toroidal device. It is observed that the plasma center is deficient of both coherent and turbulent components of the excited fluctuations. The fluctuations seem to be consistent with the transport characteristics of fluxes of energy, matter and entropy. Consistency check is given by the comparison of predicted FDL from profile of time-averaged plasma parameters with the experimentally determined FDL. This gives an experimental proof that FDL is a consequence of operation of principle of self-consistency in BETA. Self consistency forces spatial profiles of plasma parameters to adjust themselves to profile of fluctuations such that fluxes of energy and matter injected by the source is transported out at the boundaries.    [Preview Abstract]


CP9.00037: Supersonic ExB Rotation in a Highly Ionized, Low Temperature Plasma
Martin E. Griswold , Yevgeny Raitses , Nathaniel J. Fisch

We have built an apparatus to study electron rotation in low temperature plasmas with magnetized electrons and unmagnetized ions. We use a magnetic coil and an electrode to induce electron ExB rotation in a highly ionized low temperature plasma which is supplied by a Hall thruster that we are using as a plasma source. We are interested in studying effects that occur in the plasma when the electron rotation speed approaches the thermal speed of the electrons.    [Preview Abstract]


CP9.00038: A novel experiment to measure ion self-helicity conservation
Setthivoine You , Jens von der Linden , Lenny Paritsky , James Geier , Stewart Jacobs

A novel experiment is designed to test ion self-helicity conservation during plasma relaxation [1] with unique diagnostics for observing plasma jet collisions with compact toroids. A pair of conical theta pinches merge two compact toroids while another pair of planar coaxial guns shoot smaller plasma jets tangentially on to the compact torus to induce net bulk angular rotation. A large vacuum chamber, flexible gas injection arrangements and power supplies are designed to allow for a range of $S*;\beta$ values and ion flow velocities to explore regimes with two-fluid effects on compact toroid configurations. Two sequential ion flow maps in each shot can be reconstructed from 3D vector tomography of multichannel bulk ion Doppler spectroscopy [2]. With an insertable 3D array of B-dot probes, the ion self-helicity can be measured in the entire 3D volume twice in each discharge. A fast ion gauge measures time-resolved neutral gas profiles to optimize gas injection. A novel two-fluid plasma lattice Boltzmann numerical model [3] is being developed to support the interpretation of experimental measurements. [1] L.C. Steinhauer, A. Ishida, Phys. Plasmas, 5, 7, (1998) [2] S. You, H. Tanabe, Y. Ono, A.L. Balandin, J. Fusion Energy, 29 (2010) [3] J. von der Linden, S. You, Two-fluid Plasma Lattice Boltzmann model, this meeting.    [Preview Abstract]


CP9.00039: Development and Performance Tuning of the Dusty Plasma Simulation Code DEMON
Robert Jefferson , Mark Cianciosa , Edward Thomas

Dusty (complex) plasmas are found in a broad range of environments ranging from the largest nebula to the manufacturing of the smallest microchips. In these systems, charged micro particles are suspended in a background plasma. The mutual interaction between the microparticles and the plasmas, in particular, the exchange of charge and energy, leads to the emergence of new plasma behaviors. Numerical tools that complement experimental investigations can provide new insights into the complex behaviors of dusty plasmas. The newly developed DEMON (Dynamic Exploration of Microparticle clouds Optimized Numerically) code is a tool to simulate dusty plasmas using experimentally relevant parameters. DEMON is an adaptive time step 2D N-body simulation of a dusty plasma using the $4^{th}$ order Runge-Kutta method to solve the equations of motion. A main feature of DEMON is use of a modular force model made possible though the use of Object- Oriented programming techniques. A careful choice of physical constraints, allows the simulation of realistic plasma parameters. This presentation is discuss the capabilities, performance and results of the DEMON code.    [Preview Abstract]


CP9.00040: Measurement of an ellipsoidally symmetric velocity space distribution within a weakly-coupled dusty plasma
Ross Fisher , Edward Thomas

The spatially resolved phase space distribution (PSD) was measured for a weakly coupled (fluid-like) dusty plasma using stereoscopic particle image velocimetry (stereo-PIV). It was found that the velocity space component of the PSD could not be modeled with the standard, spherically symmetric, tri-Maxwellian distribution function model. Instead, these data were modeled with the more general, ellipsoidally symmetric, tri-variant normal (tri-normal) distribution function. This presentation will discuss the two distribution models (the tri-Maxwellian and the tri-normal) as applied to experimentally measured PSDs for the dust component of the plasma.    [Preview Abstract]


CP9.00041: Overview of dusty plasma research in the Auburn Plasma Sciences Laboratory
E. Thomas , R. Fisher , J. Shaw , M. Cianciosa , R. Jefferson , P. Price , K. Wood

Over the last fifteen years, the Auburn Plasma Sciences Laboratory (PSL) has pursued experimental and computational investigations of dusty (complex) plasmas. Much of this work has centered on the measurement of transport, collective behavior, and thermal properties of the charged microparticle component of a dusty plasma using particle image velocimetry (PIV) techniques. This presentation will give an overview of recent and upcoming dusty plasma studies in the PSL with a particular emphasis on ground-based studies of microgravity phenomena, simulations of the dust particle velocity space distribution function, and the development of new experimental hardware.    [Preview Abstract]


CP9.00042: Measurement of the three-dimensional wave process in the dust acoustic wave
Jeremiah Williams

A complex (dusty) plasma is a four-component system composed of ions, electrons, neutral particles and charged microparticles. The presence of the microparticles gives rise to new plasma phenomena, including collective modes such as the dust acoustic wave. The dust acoustic wave mode has been the subject of intense experimental and theoretical study since being predicted in 1990 and identified experimentally in 1994. Previous experimental studies of this wave mode have been restricted to measurements in a single thin sheet of the dusty plasma system. In this work, we use tomographic image velocimetry techniques to examine the three-dimensional wave process over extended volume.    [Preview Abstract]


CP9.00043: Force on a small grain in the plasma wake of another
I.H. Hutchinson

A solid, negatively charged, grain lying in the plasma wake of another experiences a transverse force that often aligns or misaligns the two grains. The force arises in part from the oscillatory plasma wake potential, but hitherto the importance of the additional ion-drag perturbation has been controversial. The ion-drag perturbation is intrinsically one order smaller than the wake-potential force in the ratio of grain size ($r_p$) to Debye length ($\lambda_{De}$). So ion-drag perturbation is important only in nonlinear wakes and can't be evaluated by linear analytic approximations. Fluid treatments are likewise unsatisfactory. Therefore, rigorous kinetic-ion 3D PIC simulations of the force in the nonlinear regime are here performed, providing for the first time a quantitative calculation of the wake force between two interacting grains. It is found that even for quite large grains, $r_p/\lambda_{De}=0.1$, whose wake amplitude is already partially limited by nonlinearity, the force is dominated by the wake-potential-gradient. The ion-drag perturbation is a small effect at relevant grain separations. The wake potential structure can then on its own help explain the preferred alignment of floating dust grains.    [Preview Abstract]


CP9.00044: Ion Collection by a Sphere in a Magnetized Collisional Plasma
Christian Bernt Haakonsen , Ian H. Hutchinson

Ion collection by a dust grain in a plasma is important in determining its charging and dynamics. In particular, the (local) floating potential on the grain's surface tends to that which balances the electron and ion currents, thus determining the grain's equilibrium surface charge (distribution). In tenuous plasmas with background magnetic fields the electron currents are affected by the magnetic field if the electron Larmor radius is comparable to or smaller than the size of the grain. This alters the floating potential, and thus ion collection. Strong magnetic fields may even give ion Larmor radii comparable to the grain size, further affecting collection. Examples of dust grains in such tenuous magnetized plasmas may include areas (e.g.) behind tokamak divertor plates, or dedicated dusty-plasma experiments with strong magnetic fields. The hybrid particle-in-cell (PIC) code SCEPTIC3D is used to study ion collection by a sphere in a magnetized collisional plasma. The collection by conducting and insulating spheres is examined, especially the effects of magnetization and charge-exchange collisions on the electron and ion currents to the sphere.    [Preview Abstract]


CP9.00045: Instabilities in strongly coupled Yukawa liquids
M. Rosenberg , G.J. Kalman , P. Hartmann

Yukawa systems are systems of charged particles that interact via a screened Coulomb (Yukawa) interaction. If the electrostatic potential energy between neighboring charged particles is much larger than their thermal (kinetic) energy but smaller than that required for crystallization the system is in the strongly coupled liquid phase. Various plasmas such as dusty plasmas or ultracold neutral plasmas can exist in this liquid phase. Here, we investigate several streaming instabilities in the strongly coupled liquid phase of dusty plasmas, including (1) a dust-dust instability and (2) a dust acoustic instability. Applications to possible experimental parameters are discussed.    [Preview Abstract]


CP9.00046: Alignment of dust particles in subsonic flows
Alexander Piel

The role of ion drag forces for the alignment of dust particles is studied for subsonic flows. While alignment by wake-field attraction is a well known mechanism for supersonic flows, it is argued here that ion-scattering forces become more important in subsonic ion flows. A model of non-overlapping collisions is introduced and numerical results are discussed. For typical conditions of dusty plasma experiments, alignment by drag forces is found strong enough to overcome the destabilizing force from Coulomb repulsion between dust particles. It turns out that the major contribution to the horizontal restoring force originates from the transverse momentum transfer, which is usually neglected in ion drag force calculations because of an assumed rotational symmetry of the flow.    [Preview Abstract]


CP9.00047: The origin of the roton minimum
G.J. Kalman , S. Kyrkos , K.I. Golden , P. Hartmann , Z. Donko

The roton minimum is a deep minimum in the collective excitation spectrum of the liquid, forming around fairly high k-values. We have discovered, through MD simulations, that this appears to be a general feature of strongly coupled liquids and is ubiquitous in 2D and 3D Yukawa liquids. We suggest that the physical origin of the roton minimum has to be sought in the quasi-localization of particles in a strongly correlated liquid and in the ensuing formation of local microcrystals whose averaged frequency dispersion would show roton minimum-like feature. Focusing on the phonon dispersion in a 2D crystal lattice, the position of the roton minimum is coincident with that of the closest point on the Brillouin zone boundary. To show how this leads to the development of the roton minimum, we have constructed a model for the dynamical structure function $S({\rm {\bf k}},\omega )$ of a 2D lattice system. By using the classical fluctuation dissipation theorem we obtain $S({\rm {\bf k}},\omega )$ through a lattice model for the density response function $\chi ({\rm {\bf k}},\omega )$, where the liquid behavior is emulated by a phenomenological collision frequency. The liquid dispersion relation is calculated through angular averaging. We examine its behavior in the vicinity of the Brillouin zone boundaries, and compare the results with MD simulations.    [Preview Abstract]


CP9.00048: High Resolution Density Sculpting of Ultracold Neutral Plasmas to Excite Collective Modes
Patrick McQuillen , Jose Castro , Thomas Killian

Ultracold Neutral Plasmas (UNPs) are created by photoionizing laser cooled atoms near the ionization threshold. They provide extremely clean and controllable experimental conditions and a means of studying strongly coupled plasmas in the laboratory. By virtue of their extremely cold temperatures ($\sim$1K), the Coulombic potential energy can dominate thermal kinetic energies and lead to interesting collective effects. A recent advance in creation techniques allows the production of UNPs with controllable initial density distributions. This technique has allowed us to excite and measure dispersion of the low frequency Ion Acoustic Wave (IAW) as well as produce streaming plasmas with tunable velocities. With recent upgrades to our ionizing and imaging system we will continue these studies at much shorter length scales, those comparable to Debye shielding lengths and approaching average interatomic spacing. In this regime, where concepts of Debye shielding break down along with many fundamental plasma approximations, we can test predictions of deviations from classical plasma behavior.    [Preview Abstract]


CP9.00049: Vortex electron current and fundamental non-ambipolarity of charged particles fluxes in 2D unmagnetized plasmas
Anatoly Kudryavtsev , Eugene Bogdanov , Alexander Chirtsov

It is shown that even for non-magnetic single-component plasma bounded by dielectric walls, in case of any 2D geometry, the condition of ambipolarity of fluxes (that is equality of electron and ion fluxes) is violated and vortex electric current arises. Since any complications (such as conductive walls, non-uniformity of mobilities, multicomponent consist of plasma, presence of magnetic field etc.) will only make worse the ambipolarity of fluxes, it may to declare that classical conception of ambipolar diffusion is not valid already for general 2D case. It is rather exclusive case and cannot be a paradigm for description of transport of charged particles in plasma. Thus, the ambipolarity of fluxes is rather exclusive case which is true only for simple idealized 1D models like length-uniform positive column of glow DC discharge. The presence of vortex component of current leads necessarily to additional Joule heating of electron gas. Also, the inequality of electron and ion fluxes can lead to such nontrivial phenomenon as arise of friction forces which are capable to enforce on neutral gas.    [Preview Abstract]


CP9.00050: Optimizing Electrostatic Beams Formed from Single-Component Plasmas
C.S. Schallhorn , J.R. Danielson , T.R. Weber , C.M. Surko

A non-destructive technique has been developed to create high quality, magnetized electron (or positron) beams using a high magnetic field Penning-Malmberg (PM) trap.\footnote{T. R. Weber, et al., {\it Phys. Plasmas} {\bf 15}, 012106 (2008) and {\it Phys. Plasmas} {\bf 16}, 057105 (2009).} Building on this technique, a class of electrostatic beams was produced by extracting these beams from the guiding magnetic field.\footnote{T. R. Weber, et al., {\it Phys. Plasmas} {\bf 17}, 123507 (2010).} This procedure involved adiabatic transport of the beam to lower magnetic field, followed by a fast, nonadiabatic extraction to zero field. Once in the zero-field region, the beam was focused with an Einzel lens to small transverse dimensions (r = 0.12 cm). We describe further development of this technique using an iron-alloy ``spider''\footnote{W. Stoeffl, P.Asoka-Kumar, R. Howell, {\it Appl. Surf. Sci.}, {\bf 149}, 1 (2009).} at the field-extraction point to minimize the transverse momentum imparted to the beam particles. Potential uses of the novel electrostatically guided positron beams that can be produced using this technique will be discussed.    [Preview Abstract]


CP9.00051: A Multicell Trap for Positron Storage
J.R. Danielson , C.M. Surko

There are many potential applications of high-capacity and/or portable antimatter traps, including multiplexing the output of high-flux positron beams, study of electron-positron plasmas, and eventually the construction of an annihilation gamma-ray laser at 0.51 MeV. We describe recent progress in the design and construction of a novel multicell Penning-Malmberg (PM) trap to store in excess of $5 \times 10^{11}$ positrons.\footnote{J. R. Danielson, T. R. Weber, and C. M. Surko, {\it Phys. Plasmas} {\bf 13}, 123502 (2006).} The construction and planned objectives of a test electrode structure will be discussed. A key issue to be determined is the quality of confinement in off-axis cells in the less uniform portions of the magnetic field near the ends of the magnet. Protocols for filling off-axis cells and handling plasmas with kiloelectron volt levels of space charge will be described. A new scenario to rapidly dump the contents of the multicell trap will be discussed.    [Preview Abstract]


CP9.00052: Identification and Manipulations of Impurity Ions in Magnesium Ion Plasma
F. Anderegg , M. Affolter , C.F. Driscoll , D.H.E. Dubin

A nominally ``pure'' Mg24$^+$ ion plasma accumulates impurity ions over periods of hours to days by charge exchange with residual background gas ($P \sim 10^{-10}$ Torr) in a Penning-Malmberg trap. We use thermal cyclotron spectroscopy (TCS) to identify ion impurities, and observe spatial separation at low temperatures. TCS consists of applying rf bursts at the impurity cyclotron frequencies, with LIF measurement of the majority species heating due to collisions with the heated impurites. We find that for short bursts the heating is proportional to the burst amplitude squared, and to the square of the burst duration, as predicted by a simple single particle model. We spatially separate the impurities from the Magnesium ions by two different techniques: a) With laser cooling to $T < 10^{-3}$ eV, the $E \times B$ rotation causes centrifugal separation, with heavier ions at larger radii. We typically observe a 5--20\% ``hole'' in the center of the Mg plasma where the ``dark'' lower-mass impurities reside; and we directly observe the Mg25 and Mg26 at the outer edge of the Mg24 column. b)~Resonant laser pressure in the $z$-direction pushes on the Mg24, and the species separates longitudinally when this laser force is greater than the mass-dependent centrifugal force.    [Preview Abstract]


CP9.00053: Damping of Plasma Modes in Ion Plasmas
M. Affolter , F. Anderegg , C.F. Driscoll , M. Anderson , T.M. O'Neil

We observe damping of Langmuir modes in Mg$^+$ ion plasmas with different-mass ion impurities, and compare to nascent theory treating inter-species drag and bulk viscosity. The cylindrical ion plasmas have density $n \sim 10^7$cm$^{-3}$, length $L_p \sim 10$cm, and radius $R_p \sim 0.5$cm in a field of $B = 3$Tesla, with plasma temperatures controlled over the range $10^{-5} < T < 1$eV. For $T \geq 0.1$eV, damping rates agree closely with Landau theory for the standing $m_\theta = 0$, $k_z = 1$ Langmuir mode at frequency $f \sim 20$kHz. The damping from $10^{-2}$eV $< T < 0.1$eV is not yet understood. For $T \leq 10^{-2}$eV, damping rates $10 < \gamma < 10^3$ increase with (controlled) impurity fraction, and increase with decreasing temperature as expected for collisional drag, as $\gamma \propto T^{-3/2}$. For $T < 10^{-3}$eV, a {\it decrease} in $\gamma$ is observed; and theory must include effects of strong magnetization, ion-ion correlations, spatial isotope separation, and bulk viscosity. Additionally, the wave damping is generally dependent on {\it initial} amplitude at the lowest temperatures, where the wave-induced ion velocity exceeds the ion thermal velocity.    [Preview Abstract]


CP9.00054: Collisional Relaxation of a Strongly Magnetized, Two Isotope, 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 26, 2128 (1983).} that is composed of two species with slightly different mass is discussed. We have in mind two isotopes of the same singly ionized atom. Parameters are assumed to be ordered as $\Omega_{c1}$, $\Omega_{c2} \gg | \Omega_{c1} - \Omega_{c2} | \gg \overline{v} / b$, where $\Omega_{c1}$ and $\Omega_{c2}$ are the two cyclotron frequencies, $\overline{v}$ is the thermal velocity, and $b$ is the classical distance of closest approach. For this ordering, the total cyclotron action for the two species, $J_1 = \sum_{ j \epsilon 1} m_1 v_{{\perp}_1}^2 / 2 \Omega_{c1}$ and $J_2 = \sum_{ j \epsilon 2} m_2 v_{{\perp}_j}^2 / 2 \Omega_{c2}$, are adiabatic invariants that constrain the collisional dynamics. On the time scale of a few collisions, entropy is maximized subject to the constancy of the total Hamiltonian $H$ and the two actions $J_1$ and $J_2$, yielding a Gibbs distribution of the form $\exp [ - H/T - \alpha_1 J_1 - \alpha_2 J_2 ]$. Collisional relaxation to the usual Gibbs distribution, $\exp [ - H/T ]$, takes place on two time scales, each of which is exponentially longer than the usual collisional time scale. First, the two species share action so that $\alpha_1$ and $\alpha_2$ relax to a common value $\alpha$. On an even longer time scale, the total action ceases to be a good constant of the motion and $\alpha$ relaxes to zero.    [Preview Abstract]


CP9.00055: Algebraic Diocotron Mode Damping due to Radial Particle Losses
A.A. Kabantsev , T.M. O'Neil , C.F. Driscoll

Algebraic damping of the $m=1$ diocotron mode amplitude, $D (t) = D(0) - \Gamma t$, is observed in pure electron plasmas which are losing particles radially to the cylindrical wall. Experimentally, this effect is observed at high magnetic fields and low plasma temperatures, where 2D electrostatic effects presumably dominate over 3D dissipative effects. In this regime, the algebraic damping rate $\Gamma$ is observed to be approximately equal to the particle loss rate, i.e. $\Gamma \sim (d/dt) \ln N$ over more than an order of magnitude in $\Gamma$. A simple 2D model of wave and plasma angular momentum exchange at the wall predicts the observed algebraic damping, and, based on the experiments, suggests that it may co-exist with exponential growth from other 2D processes such as plasma drag from collisions with neutrals. This algebraic damping will also be contrasted to the exponential growth (or damping) observed from resistive (or feed-back) wall voltages, and from near-center ejection (or injection) of electrons.    [Preview Abstract]


CP9.00056: Squeeze Effects on Plasma Wave Damping
A. Ashourvan , D.H.E. Dubin

Theory is presented for the damping of cylindrically-symmetric plasma modes in a nonneutral plasma column due to a squeeze potential applied to the center of the column. Squeeze divides the plasma into passing and trapped particles; the latter cannot pass over the squeeze. In collisionless theory, mode damping is caused by Landau resonances at energies $E_n$ for which the bounce frequency $\omega_b (E_n )$ and the wave frequency $\omega$ satisfy $\omega = n \omega_b ( E_n )$. A squeeze induces bounce harmonics in the perturbed trapped particle distribution with $n \gg 1$ because such particles see a substantially non-sinusoidal time variation in the perturbed potential as they bounce off the squeeze. This allows resonances at energies $E_n \sim T$ and therefore causes substantial damping, even when $\omega$ is large compared to the thermal bounce frequency $\omega_b (T)$. Adding collisions to the theory broadens these resonances and also creates a boundary layer at the separatrix between trapped and passing particles that further enhances the damping. Theory will be compared to experiments and simulations that observe enhanced damping due to applied squeeze.    [Preview Abstract]


CP9.00057: Distinguishing Bounce-Resonant from Bounce-Averaged Neo-Classical Transport
C.F. Driscoll , A.A. Kabantsev , D.H.E. Dubin

Experiments, theory, and simulation for single-species plasmas now show quantitative agreement for both Bounce-Resonant (BR) and Bounce-Averaged (BA) Neo-Classical Transport, with distinct magnetic field scalings over $0.5 < B < 12.$kG. Here, we consider cylindrical pure electron plasmas, with particle orbit excursions caused by a global ``field error'' such as magnetic tilt (analogous to global toroidal curvature); and with controlled electrostatic separatrices producing populations of trapped and un-trapped particles. With distinct trapped-particle populations, BA theory correctly describes both {\it collisional} NCT scaling as $\nu^{1/2} B^{-1/2}$, and the novel {\it chaotic} NCT scaling as $\nu^0 B^{-1}$ which occurs when the separatrix is ``ruffled'' in the $E \times B$ drift direction.\footnote{A.A. Kabantsev {\it et al.}, Phys. Rev. Lett. {\bf 105}, 205001 (2010); D.H.E. Dubin and Yu.A. Tsidulko, Phys. Plasmas {\bf 18}, 062114 (2011).} For weak magnetic fields, BR transport dominates, typically scaling as $B^{-2}$ to $B^{-3}$, with different scalings observed for $z$-extended and $z$-localized field errors. Also, we are able to observe the transition from banana regime to plateau regime, with dependence on applied error field strength $\epsilon$ changing from $\epsilon^2$ to $\epsilon^{1/2}$.    [Preview Abstract]



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CP9.00059: Turbulent Stresses in LAPD and CSDX
A.D. Light , Y. Sechrest , D.A. Schaffner , S.H. Muller , G.D. Rossi , D. Guice , T.A. Carter , G.R. Tynan , S. Vincena , T. Munsat

Turbulent momentum transport can affect phenomena as diverse as intrinsic rotation in self-organized systems, stellar dynamo, astrophysical accretion, and the mechanism of internal transport barriers in fusion devices. Contributions from turbulent fluctuations, in the form of Reynolds and Maxwell stress terms, have been predicted theoretically and observed in toroidal devices. In an effort to gain general insight into the physics, we present new results from turbulent stress measurements on two linear devices: the LArge Plasma Device (LAPD) at the University of California, Los Angeles, and the Controlled Shear De-correlation eXperiment (CSDX) at the University of California, San Diego. Both experiments are well-characterized linear machines in which the plasma beta can be varied. Electrostatic and magnetic fluctuations are measured over a range of plasma parameters in concert with fast imaging. Maxwell and Reynolds stresses are calculated from probe data and fluctuations are compared with fast camera images using velocimetry techniques.    [Preview Abstract]


CP9.00060: Effect of boundary conditions on drift turbulence and zonal flows in a linear plasma device
Saikat Chakraborty Thakur , Min Xu , Peter Manz , Nicolas Fedorczak , George Tynan

\textbf{C}ontrolled \textbf{S}hear \textbf{D}e-correlation e\textbf{X}periment (CSDX) is a linear magnetized plasma device dedicated to the studies of drift wave turbulence-zonal flow (DWT-ZF) interaction and the generation of intrinsic rotation in a simple plasma configuration. Previous experimental studies which demonstrated the existence of an azimuthally symmetric radially sheared plasma fluid flow (zonal flow) were carried out in the configuration where all the magnetic field lines exiting the two ends of the device terminate on insulating surfaces. To study the effect of parallel currents flowing through the end plates, the experimental set up is modified such that the magnetic field lines now end in conductors. Preliminary results from the conducting boundary condition experiments show the absence of drift wave turbulence and zonal flows. Results will be shown from a series of controlled experiments comparing the effects of the insulating and the conducting boundary conditions on the plasma behavior.    [Preview Abstract]


CP9.00061: Scrape-off layer transport as boundary conditions for edge rotation
Nicolas Fedorczak , George Tynan , Pascale Hennequin

Recently, experimental studies of SOL flows phenomena have revealed the influence of such flows in the dynamics of intrinsic rotation in L-mode and the threshold of L-H transition[1][2]. Since the phenomena in question occurs in L-mode, the explanation must take into account turbulence and turbulent transport to figure out the interaction of SOL flows on core rotation and electric field shear prior to the transition. Here we explore the possibility that SOL flows (parallel and transversal) exert a turbulent stress on the confined plasma near the last closed flux surface. Namely we focus on the inward turbulent transfer of SOL parallel momentum driven by ballooning particle flux [3], and the effect of magnetically sheared ballooning structures on the establishment of a net radial flux of poloidal momentum across the LCFS. A preliminary model is derived and compared to measurements of edge velocity increments when the SOL topology is changed from LSN to USN (or equivalent with limiters) in Tore Supra and DIII-D.\\[4pt] [1] B. LaBombard et al. Nucl. Fusion 44,(2004) \newline [2] P. Hennequin et al. EPS 2010\newline [3] N. Fedorczak et al. J. Nucl. Mater. 2011    [Preview Abstract]


CP9.00062: Turbulence and Turbulence Suppression in the Helimak
Kenneth Gentle , William Rowan , Ken Liao , Bo Li

The Helimak is an approximation to the infinite cylindrical slab, but with open field lines of finite length. Radially-segmented isolated end plates allow application of radial electric fields that drive radial currents. Above a threshold in applied voltage (driven current), the fractional turbulent amplitude is greatly reduced. Reductions are observed for both positive and negative bias. Concurrent measurements of the ion flow velocity profile are made by Doppler spectroscopy. The turbulence -- density, potential, and temperature fluctuations, will be compared with simulations from a fluid model for this geometry, which also shows reduced turbulence with bias. Comparisons of turbulence reduction with changes in radial correlation length and flow shear will be given. Although the radial correlation length is much smaller than the plasma, turbulent structures of large spatial scale but short lifetime are seen. The amplitude reduction is associated with shrinkage in size of the structures. No evidence of zonal flows has been found. Work supported by the Department of Energy OFES DE-FG02-04ER54766.    [Preview Abstract]


CP9.00063: Magnetic Structure of the Maryland Centrifugal Experiment
William Young , C.A. Romero-Talam\'as , R. Reid , R.F. Ellis , A.B. Hassam

The Maryland Centrifugal Experiment (MCX) plasma confinement concept combines a magnetic mirror geometry with a radial electric field generated by a biased, axial electrode. The resulting ExB force drives a sheared rotation with a centrifugal force component along open field lines providing axial confinement. Several magnetic loop arrangements measure axial and azimuthal profiles of magnetic fields generated by the MCX plasma. Internal magnetic probes make local 3-axis magnetic measurements on a microsecond to millisecond timescale over a typical 5 ms discharge, providing insight into the coarse structure of currents within the MCX plasma. External loops measure the averaged magnetic fields on a millisecond timescale, limited by the time response of the vacuum vessel. Along with interferometric average density measurements, these axial profiles yield a 2D density profile, peak rotation velocity, and peak temperature, via ideal MHD equilibrium theory using a numeric, perturbative solution of the Grad-Shafranov equation including supersonic rotation. There is remarkable agreement between this solution and multichord impurity Doppler spectroscopy measurements. This comparison demonstrates the efficacy of centrifugal confinement.    [Preview Abstract]


CP9.00064: Electron Cyclotron Measurements on the Maryland Centrifugal Experiment
Remington Reid , William Young , Christina Allen , Richard Ellis , Carlos Romero-Talamas , Adil Hassam

The Maryland Centrifugal Experiment (MCX) uses supersonic rotation to stabilize dense plasmas (n$\sim $10$^{14}$/cc) confined in an axisymmetric magnetic mirror. This rotation is generated using an axial electrode to drive large radial currents though the plasma. The MCX plasma delivers a sufficient heat flux to make the vast majority of the plasma inaccessible to electrostatic probes, making direct measurements of the electron temperature unworkable. Electron cyclotron radiation, propagating in the whistler mode has been used in past experiments to measure the axial electron temperature distribution in mirror type machines and has the advantage of working in very dense plasmas. A radiometer has been installed on MCX to measure this radiation and the axial electron temperature is being measured. Abrupt changes in the intensity of the ECE radiation are correlated with bulk plasma instabilities provide information to further diagnose these instabilities.    [Preview Abstract]


CP9.00065: The Role of Geodesic Acoustic Mode on Regulating the Particle Transport in the Edge of HL-2A Tokamak
T. Lan , D.F. Kong , C.X. Yu , A.D. Liu , H.L. Zhao , J.L. Xie , W.D. Liu , L.W. Yan , W.Y. Hong , J.Q. Dong , K.J. Zhao , J. Qian , J. Chen , X.R. Duan , Y. Liu

Three sets of Langmuir triple probe arrays separated poloidally are applied to study the transport properties in the edge of HL-2A tokamak. The Geodesic Acoustic Mode (GAM) zonal flow clearly exhibits the intermittent characteristics. The radial particle flux has been studied under different GAMs amplitude levels. The experiment results reveal that the radial particle flux has been suppressed by 13\% during the strong GAM bursts case contrasting to weak GAM cases in the frequency range of ambient turbulence. Moreover, the higher of GAM power causes more reducing of radial particle flux. The powers of density fluctuations and coherence between density and potential fluctuations domain most flux reducing, while the cross phase between density and potential fluctuations and power of potential fluctuations contribute few. It indicates that the GAMs may regulate the transport mainly by changing the amplitude of ambient turbulence.    [Preview Abstract]


CP9.00066: Correlation Study of Fluctuation and Coherent Structure of $T_e$ with the 2-D ECEI System on KSTAR
M.J. Choi , G.S. Yun , W. Lee , H.K. Park , N.C. Luhmann, Jr. , C.W. Domier , A.J.H. Donn\'e

Correlation study of the electron cyclotron emission (ECE) has been routinely used to measure a low level mesoscale electron temperature fluctuation ($\le 1$\%) in tokamak plasmas [1, 2]. Application of the correlation technique to the 2-D ECEI system which has $\sim 400$ independent channels in 2-D space is ideal for the simultaneous measurement of poloidal and radial correlations of the coherent structure as well as the mesoscale fluctuations. The KSTAR dual ECEI system, composed of two independent sets of detectors, is capable of decorrelating the thermal and electric noises between two detector sets, and therefore 2-D correlation analysis is possible. Correlated fluctuation level spectra over 2-D/3-D poloidal/radial space will be addressed and their spatial structures will be assessed in this study. In addition, effects of the plasma rotation (poloidal and toroidal) in determination of the correlation spectra are studied in conjunction with the required long integration time.\\[4pt] [1] S. Sattler and H. J. Hartfuss, Phys. Rev. Lett. 72, 5 (1994).\\[0pt] [2] A. E. White et. al., Phys. Plasmas 15, 056116 (2008).    [Preview Abstract]


CP9.00067: Scaling of Intrinsic Rotation in tokamaks with ion temperature and plasma current
M.F.F. Nave , F.I. Parra , A.A. Schekochihin , C. Giroud , J. de Grassie , J.H.F. Severo , P. de Vries

Studies of spontaneous plasma rotation are relevant for ITER where momentum sources will be small. Here we study toroidal velocity profiles with rotation monotonically increasing from the core to the outside. This type of profile with either counter or a small co current rotation in the core are often observed in tokamaks. We compare data from devices with a large size range (DIII-D, JET, TCABR and TCV [1]) and different heating mechanisms. The maximum difference in velocity correlates linearly with the change in ion temperature divided by plasma current with a proportionality constant of order 10 km/s MA /keV. This scaling can be recovered from simple theoretical arguments based on the symmetry properties of the turbulent transport of toroidal angular momentum. \\[4pt] [1] A.Scarabosio et al. PPCF 48, 663 2006.    [Preview Abstract]


CP9.00068: Modeling of two-dimensional transport in tokamak plasmas for integrated analysis of core and peripheral plasmas
H. Seto , A. Fukuyama

In order to describe the behavior of tokamak plasmas in both core and peripheral regions self-consistently, two-dimensional transport simulation is desirable and becoming feasible. We have formulated transport equations with poloidal-angle dependence from Braginskii equations for two-dimensional transport analysis. Following assumptions have been made to derive these equations; axisymmetry, MHD equilibrium, transport process much slower than the Alfv\'en velocity, and weak time dependence of basis vectors. The set of transport equations is composed of continuity equation, equation for velocity including the neoclassical viscosity, and equation of energy transport for each species. These equations are coupled with equations for electromagnetic field; Grad-Shaftranov equation, magnetic diffusion equation, and Poisson equation for electrostatic potential. Preliminary numerical results of two-dimensional transport analysis will be presented.    [Preview Abstract]


CP9.00069: Two dimensional non-local transport across zonal shear flows
A. Kullberg , D. Del-Castillo-Negrete , G.J. Morales , J.E. Maggs

The standard diffusive model assumes that the fluxes are entirely determined by the local value of the gradient. Although this paradigm has had considerable success, there are situations in which this prescription (i.e. Fick's law) does not hold; instead, the flux at a point may depend on the gradients throughout the entire spatial domain. Examples of this type of transport include perturbative experiments in tokamaks, numerical simulations of turbulent plasmas, and generalized random walk theoretical models. This presentation describes recent results on non-local transport in the presence of zonal shear flows. The study is based on a 2-dimensional equation that has a poloidal zonal flow coupled to a radial non-local transport channel. This work extends upon previous research by incorporating a cylindrical, 2-dimensional (albeit azimuthally averaged), non-local radial transport operator. Numerical results relating to several aspects of transport across the zonal shear flow are presented, including a numerical study of the creation of resonant traveling thermal waves inside the flow by an oscillating heat source, and the propagation of cold pulses across the zonal flow. In the case of thermal waves, resonance occurs when the source frequency matches the rotational angular frequency of the flow.    [Preview Abstract]


CP9.00070: Lattice Boltzmann Representation of Electrostatic Drift Wave Turbulence
Bo Zhang , George Vahala , Linda Vahala

Zonal flows are low frequency coherent structures that are generated by small scale drift wave turbulence, and in turn these flows can lead to a suppression in the turbulence and in anomalous transport. Recent work by Dewar et. al. on the Hasegawa-Wakatani model has found that density gradients build up the turbulent kinetic energy to a critical level which then leads to the onset of zonal flows and turbulence suppression. The Hasegawa-Wakatani mode extends the one-field Hasegawa-Mima theory to include the effects of electron motion along the toroidal magnetic field. Dewar et. al. note that zonal fluctuations do not contribute to the parallel current. There are 3 extensions need to standard Lattice Boltzmann (LB) methods to solve the Dewar model: Poisson brackets, Poisson equation, and hyperdiffusive operators. We have tested these three LB elements separately and benchmarked them against exact solutions. We discuss progress on the actual implementation of LB to electrostatic drift wave turbulence.    [Preview Abstract]


CP9.00071: Effects of ion-temperature-gradient driven turbulence on magnetic islands
Akihiro Ishizazwa , F. Waelbroeck , R. Fitzpatrick , W. Horton , N. Nakajima

Effects of ion-temperature-gradient driven turbulence on magnetic islands are investigated by means of numerical simulations of a reduced set of two-fluid equations which include not only electron diamagnetism but the ion diamagnetism in slab geometry. Simulations are carried out in the island fixed frame, where the width and poloidal location of magnetic island do not change. Uniform ExB flow is applied to the island, and the drive as well as the drag force acting on the island are calculated as a function of the externally applied flow velocity. The turbulent fluctuations enhance the momentum exchange across the sepratrix of island and thus enhance the drag force acting on the island. The zonal flow produced by the turbulence makes the island propagation velocity deviate strongly from the one without the turbulence.    [Preview Abstract]


CP9.00072: Effects of Particle Deposition Profile on LH Transition and Hysteresis Dynamics
Mikhail Malkov , Patrick Diamond , Weiwen Xiao

The necessary ingredients in minimal model of the LH transition are: i) heat and particle transport ii) electric field shear suppression iii) heating and fueling sources. Of these, the most sensitive element seems to be the spatial structure of the fueling profile. It is known that deeper fueling (shallow pellet injection) can lower the transition threshold, and that SMBI (Supersonic Molecular Beam Injection) can maintain an H-mode reduced firing repetition rate, once the transition is achieved. This suggests hysteresis occurs in fueling, as well as heating. Given these observations, we generalize earlier work on transition modeling to treat two component fueling. In particular, we model fueling as occurring both by edge neutral penetration, and internal deposition (SMBI) at a finite depth within the separatrix. We also consider a periodic repetitive internal deposition by SMBI firing. Then we explore the sensitivity of the transition criterion. A further extension of previous analyzes is to replace the constant transport coefficients by gradient dependent. As an initial step, we determine the LH phase co-existence criterion for a two component fueling model. In particular, we explore the dependence of co-existence on the depth, relative strength and frequency of SMBI fueling.    [Preview Abstract]


CP9.00073: Theory of Turbulent Impurity Transport in ITER based Experiments in Alcator C-Mod
Xiangrong Fu , W. Horton , S. Benkadda , I.O. Bespamyatnov , C.L. Fiore , W.L. Rowan

Impurity transport is modeled for C-Mod's I-mode discharges using quasilinear theory. I-mode is one of the new high confinement modes produced on Alcator C-Mod. It is characterized by L-mode like density profile but strong temperature peaking. For typical discharges, we calculate the dimensionless parameters required to obtain the eigenvalues and eigenvectors for several sets of gyro-fluid equations which model ordinary drift waves, impurity drift waves and trapped electron modes. Based on analysis of eigenvalues and eigenvectors, the relative phase shift of the density fluctuation-to-electric potential fluctuation is obtained for each $k$-vector. The fluctuation spectrum is determined by a combination of nonlinear simulations, empirical formulas and experimental results. Impurity transport coefficients for the particle diffusivity $D_z$ and pinch velocity $v_z$ are computed and compared with the experiments. We identify several sources for pinch velocity: the curvature effect, the temperature gradient, and the viscosity. The degree to which the results do and do not agree with the experiments is quantified. Based on these results, we extrapolate the analysis to predict impurity transport in ITER.    [Preview Abstract]


CP9.00074: Generalized Weight-Based PIC Simulation Schemes for Tokamak Plasmas
W.W. Lee , S. Ethier , R. Ganesh

A generalized weight-based particle simulation schemes suitable for simulating microturbulence in magnetic fusion plasmas, where the zeroth-order inhomogeneity is important, has recently been developed [1]. The schemes is a generalization of the perturbative simulation schemes developed earlier for PIC simulations [2]. The new two-weight scheme, which can simulate both the perturbed distribution ($\delta f $) and the full distribution (total-F) within the same code, has now been extended to simulate tokamak plasmas using the GTC code [3]. Its development is based on the concept of multiscale expansion, which separates the scale lengths of the background inhomogeneity from those associated with the perturbed distributions. In this paper, we will demonstrate the correctness and the usefulness of such a code, which starts out as a $\delta f$ code and gradually evolves into a full-F code. The $\delta f$ part would help us with the noise issue in the linear stage and the full-F part of the code could be useful when the particle weights become too large or it becomes necessary to simulate the realistic situation where the sinks and sources for the simulation become important. [1] W. W. Lee, T. G. Jenkins and S. Ethier, Comp. Phys. Comm. {\bf 182}, 564 (2011). [2] S. E. Parker and W. W. Lee, Phys. Fluids B {\bf 5}, 77 (1993). [3] Z. Lin, T. S. Hahm, W. W. Lee, W. M. Tang and R. White, Science {\bf 281}, 1835 (1998).    [Preview Abstract]


CP9.00075: Full Linearized Fokker-Planck Collisions in Neoclassical and Gyrokinetic Transport Simulations
E.A. Belli , J. Candy

The full linearized Fokker-Planck collision operator has been implemented in the drift-kinetic code NEO and the effects on multi-species neoclassical transport are studied. Fast numerical algorithms for treatment of the field particle operator that can accurately treat the disparate velocity scales that arise for multi-species plasmas are presented and compared. The method is Eulerian-based and uses a Legendre series expansion in pitch angle and a novel Laguerre spectral method in energy, which is introduced to ameliorate the rapid numerical precision loss that occurs for traditional Laguerre spectral methods. With NEO, the physical accuracy and limitations of commonly-used model collision operators, such as the Connor and Hirshman-Sigmar operators, as well as models with ad hoc momentum restoring terms, are studied, and the effects on neoclassical impurity poloidal flows and neoclassical transport for experimental parameters are explored. Extension of the method for use in linear gyrokinetic stability calculations of the highly-collisional plasma edge is also explored.    [Preview Abstract]


CP9.00076: Numerical implementation of a local, $\delta f$ gyrokinetic model for intrinsic rotation
Michael Barnes , Felix Parra

Sheared plasma rotation has been shown to reduce turbulent transport and improve plasma stability. Many fusion experiments induce strong rotation via direct external momentum injection, but large, dense devices such as ITER are not expected to have large external momentum input. However, Experiments on a range of fusion devices have demonstrated significant rotation in the absence of external momentum input. The details of this ``intrinsic'' rotation need to be understood so that we can determine if ITER and next generation fusion devices will benefit from rotational shear. Here we describe implementation of a local, $\delta f$ gyrokinetic model for intrinsic rotation in \texttt{GS2}. This model self-consistently treats the finite $\rho_*$ terms that are required to determine turbulent momentum fluxes in the absence of large mean plasma flows, flow shear, or up-down asymmetry. We present results from nonlinear gyrokinetic simulations demonstrating the fundamental symmetry of the gyrokinetic-Maxwell system that necessitates inclusion of finite $\rho_*$ terms when studying intrinsic rotation. We also show how the amplitudes and wavelengths of turbulent fluctuations scale with important parameters such as the safety factor and temperature gradient, which validates the ordering used in our analytic model. Finally, we present preliminary momentum transport results from nonlinear simulations with the finite $\rho_*$ terms included.    [Preview Abstract]


CP9.00077: Development of delta-f particle code for 3D neoclassical transport calculations in tokamaks
Kimin Kim , Jong-Kyu Park , Gerrit J. Kramer , Allen H. Boozer

A new delta-f particle code has been developed in order to calculate neoclassical transport precisely and efficiently in 3D tokamak configurations. Neoclassical transport becomes not only highly complex in 3D tokamaks, but also important in establishing a self-consistent 3D equilibrium. The new code calculates guiding-center orbits on flux coordinates, to efficiently provide viable information to a 3D equilibrium solver, as well as to obtain fundamental properties of 3D neoclassical transport such as Neoclassical Toroidal Viscosity (NTV). Also in the new code, collisions are modeled with modified Lorentz operator to study the essence of pitch-angle scattering while preserving momentum conservation, which is critical to separate 3D effects from 2D effects in transport. The code will be able to test complex parametric dependency that is predicted by analytic NTV theories, and also will be able to improve the predictability by including more precise orbits for both passing and trapped particles. Detailed progress will be presented, and preliminary simulation and benchmark results will be discussed. This work was supported by the US DOE Contract \#DE-AC02-09CH11466.    [Preview Abstract]


CP9.00078: Micro-turbulence driven parallel plasma current in tokamaks
W.X. Wang , S. Ethier

Global gyrokinetic simulations show that ion temperature gradient (ITG) and trapped electron mode (TEM) turbulence can drive a significant parallel current in meso-scale (zonal current). The underlying dynamics is closely related to nonlinear plasma flow generation [1] by turbulent residual stress [2]. However, unlike toroidal momentum which is mostly carried by ions, the turbulent current is mainly carried by electrons in the laboratory frame, and shows finer radial scale in comparison with poloidal and toroidal zonal flows. In both collisonless TEM and ITG turbulence, substantial electron current is first generated in the positive direction of magnetic field and remains quasi-stationary in post-saturation phase. The current generation by turbulence exhibits the similar characteristic dependence on plasma parameters as that of plasma flow generation [3]. Specifically, it increases with pressure gradient, decreases with equilibrium current Ip and increases with the radial variation of safety factor. Also discussed are interesting phase space structures between TEM and ITG turbulence driven current to elucidate the roles of resonant and non-resonant electrons. In collaboration with T. S. Hahm, P. H. Diamond (UCSD), F. L. Hinton (UCSD), A. H. Boozer (Columbia U.), G. Rewoldt, W. M. Tang and W. W. Lee. [1] W. X. Wang et al., Phys. Plasmas \textbf{17}, 072511 (2010). [2] P. H. Diamond \textit{et al., }Phys. Plasmas \textbf{15}, 012303 (2008). [3] W. X. Wang \textit{et al., }Phys. Rev. Lett. \textbf{106,} 085001 (2011).    [Preview Abstract]


CP9.00079: Progress of Parallel Validation Tools for Fusion Simulations as Applied to Synthetic Diagnostic Efforts
Srinath Vadlamani , Sveta Shasharina , Scott Kruger , Mark Durant , Dimitre Dimitrov , Chris Holland , Jeff Candy , Scott Parker , Yang Chen , Weigang Wan , Allen Sanderson

The verification and validation (V\&V) of fusion simulation codes is necessary to ensure proper support of ever-increasingly expensive experiments such as ITER. Synthetic diagnostics are an important and useful tool for these V\&V efforts, and is the focus of the Parallel Validation Tools for Fusion Simulations project. We will present our effort to develop standards, called schemas, for the data exchange between codes and synthetic diagnostics. We have developed a formal schema (expressed with XML Schema syntax) for specification of data for visualization and for data exchange. We have also developed a python tool for verification of HDF5 data against the formal schema. We will present the API for writing and reading HDF5 data complaint with the standards above in Fortran90, IDL, python, C and the VisIt visualization tool, enabling the user to decide the tool that works best to accomplish their goals. We will present the development of synthetic diagnostics based on this capability. These tools will be applied to the GYRO and the GEM codes for synthetic diagnostics using DIII-D experimental profiles.    [Preview Abstract]


CP9.00080: Validation of Tokamak Equilibria: Reconciling Theory and Observation Using BEAST
Gregory von Nessi , Matthew Hole , Jakob Svensson

We present a new technique for reconciling force-balance models with diagnostic observations via the statistical theory of Bayesian analysis. This method forms the backbone of a new data analysis code called BEAST (Bayesian Equilibrium Analysis and Simulation Technique) and is based on refactoring the force-balance relation into two different forward models, each associated with a 'fractional' observation, which are subsequently used in the Bayesian inference of the plasma equilibrium. By using a variant of the nested sampling algorithm, the evidence of the inferred posterior distribution is calculated and provides a relative quantification of how much the inferred equilibrium differs from a force-balance solution. Results are presented for discharges on the Mega-Ampere Spherical Tokamak (MAST), which are calculated using pickup coil, flux loop and Motional-Stark Effect (MSE) diagnostic data.    [Preview Abstract]


CP9.00081: Three-Dimensional Magnetic Field Line Analysis of Two Merging Spheromaks with Counterhelicity
Keii Gi , Toru Ii , Toshiyuki Umezawa , Michiaki Inomoto , Yasushi Ono

The TS-3 and TS-4 experiments at the University of Tokyo have demonstrated the counterhelicity merging of two spheromaks to form an oblate Field-Reversed Configuration (FRC). Significant ion heating of magnetic reconnection was experimentally observed and explained by the slingshot effect [1], but its detailed mechanism is left unsolved. We analyzed for the first time three-dimensional structures of magnetic field lines to trace the shape of them. After the two-dimensional magnetic probe array measures the magnetic field vector, its numerical integration for tracing the magnetic field lines is made by the Dormand-Prince method in a cylindrical coordinate system. The sharp bending of the magnetic field lines is identified near the X point, suggesting that the Hall effect in process of magnetic reconnection affects the slingshot. The shape of the reconnecting magnetic field lines is affected by the current sheet dissipation. We will present two cases of counterhelicity merging [2] with the Hall effect.\\[4pt] [1] Y. Ono et al., Phys. Rev. Lett. 76, 3328 (1996).\\[0pt] [2] M. Inomoto et al., Phys. Rev. Lett. 97, 135002 (2006).    [Preview Abstract]


CP9.00082: Active Stabilization of FRCs by Intermittent Merging of Counter-Helicity Spheromaks in TS-3 and TS-4 Merging Experiments
Shizuo Inoue , Yasushi Ono , Shingo Ito , Michiaki Inomoto , Ritoku Horiuchi

Since 1990, an efficient formation method of a field-reversed configuration (FRC) has been developed in the TS-3. The slingshot and spontaneous formation of toroidal flow was measured during the FRC merging formation in TS-3 and TS-4 experiments. We found this shear-flow produced by the sling-shot motion suppresses the n=1 tilt instability of FRCs by transforming the n = 1 mode into the n = 2 and higher mode. A new method for continuous sheared-flow generation is proposed for stabilization and heating of the FRCs using intermittent merging of a pair of spheromaks with opposing toroidal field. We studied about this concept by comparing our simulations with our TS-4 experiments. We simulated for the first time the FRC plasma with the intermittent merging of a pair of counterhelicity spheromaks using the MHD code. We will present how the intermittent merging maintains the flow shear as well as the stability of FRCs and then will show initial results in TS-4 intermittent merging experiment in comparison with the simulation results.    [Preview Abstract]


CP9.00083: Oblate Field-Reversed Configuration Experiments with Neutral Beam Injection
T. Ii , K. Gi , T. Umezawa , M. Inomoto , Y. Ono

The effect of energetic beam ions on oblate Field-Reversed Configurations (FRCs) has been studied experimentally in the TS-4 plasma merging device. In order to examine its kinetic effects, we developed an economical pulsed Neutral Beam Injection (NBI) system by using a washer gun plasma source and finally attained the beam power of 0.6 MW (15 kV, 40 A) for its pulse length of 0.5 ms, longer than the FRC lifetime in TS-4. The Monte Carlo simulation indicates that the tangential NB ions of 15 keV are trapped between the magnetic axis and the separatrix. We found that two merging high-$s$ ($s$ is plasma size normalized by ion gyroradius) hydrogen spheromaks with opposite helicities relaxed into the large scale FRC with poloidal flux as high as 15 mWb under the assistance of the NBI. Without the assistance of NBI, however, they did not relax to an FRC but to another spheromak. These facts suggest some ion kinetic effects such as toroidal ion flow are essential to FRC stability. Recently, two new NB sources with acceleration voltage and current of 15 kV and 20 A were installed on the TS-4 device on the midplane for tangential injection, increasing the beam power over 1 MW. We will start the upgraded FRC experiments using the 1 MW NBI for ion flow control.    [Preview Abstract]


CP9.00084: FRC Lifetime Studies for the Field Reversed Configuration Heating Experiment
Chris Grabowski , James Degnan , David Amdahl , Rachel Delaney , Matthew Domonkos , Mark Lehr , Ricardo Magallanes , Randy Robinson , Edward Ruden , William White , Don Gale , Mark Kostora , John McCullough , Wayne Sommars , Michael Frese , Sherry Frese , Frank Camacho , Sean Coffey , Thomas Intrator , Glen Wurden , Richard Siemon , Stephan Fuelling , Bruno Bauer , Alan Lynn , Norman Roderick

The goal of the Field-Reversed Configuration Heating Experiment (FRCHX) is to demonstrate magnetized plasma compression. A requirement is that the trapped flux inside the FRC must persist long enough for the compression process to be completed, which is approximately 20 microseconds. Lifetime measurements of the FRCs formed for FRCHX show lifetimes of only 7 $\sim $ 9 microseconds once the FRC has entered the capture region. Results from recent FRCHX experiments will be presented, and possible reasons for the lifetime limitations will be discussed along with several approaches for overcoming these limitations. This work is supported by DOE-OFES.    [Preview Abstract]


CP9.00085: Magnetic Reconnection and Electron Energization from Whistlers in the Laboratory and in Simulations
C. Correa , W. Horton , G. Moreno , H.V. Wong

Theory and simulations are developed to interpret laboratory experiments for nonlinear whistlers by Stenzel {\it} [R. Stenzel, J. M. Urritia, and K. D. Strohmaier, Plasma Phys. and Control. Fusion {\bf 50}, 074009 (2008)]. In that experiment, an alternating current induces large-amplitude magnetic fluctuations $\widetilde B_z$ that launch whistler waves in an Argon plasma with dimensionless electron pressure $\beta_e \approx 1$, electron skin depth of 50 mm and field- aligned scale length $L_z=1.5m$. A field-reversed configuration that leads to 'spheromak' vortex configuration and X and O points. Magnetic reconnection accelerates electrons from the thermal energy of 3 to 5 eV up to 30 eV. The electron Hall dynamics of whistlers, including two Poisson bracket nonlinearities that give rise to vortex structes and pondermotive forces from the nonlinear magnetic pressure forces, are simulated using a two-fluid MHD nonlinear code. Structures of nonlinear whistlers similar to those observed in the experiment, and self-ducting are observed.    [Preview Abstract]


CP9.00086: Improvements in CTIX Plasma Formation and Acceleration
Robert D. Horton , David Q. Hwang , Dean A. Buchenauer

The advantage of fast-moving compact toroids for fueling and disruption mitigation is the ability to deposit fuel or high-Z material into the central region of a magnetized plasma at higher speed than neutral gas. An important objective for CT application is to maximize plasma density while minimizing the neutral gas fraction. The combination of active switching in a formation region, together with snowplow plasma buildup in an acceleration region, is a promising approach to achieving these goals. The Compact Toroid Injection Experiment (CTIX) has recently been modified to permit formation-region active switching, using multiple spark-gap switches operated in parallel. Parallel spark-gap operation is straightforwardly scaled to high power, but requires timing accuracy of tens of nanoseconds to achieve equal current division between switches. The techniques used to achieve this timing on CTIX will be discussed. Operating comparison between passive and active formation-region switching will be made, including gas utilization efficiency, achievable density, and total compact-toroid kinetic energy. Accelerator-region density buildup will be demonstrated with multiple gas species, suitable for either hydrogen fueling or non-hydrogenic disruption control.    [Preview Abstract]


CP9.00087: Impurity Generation and Transport in CTIX
D. Buchenauer , R.D. Horton , R. Klauser , B.E. Mills , S.B. Van Deusen , D.Q. Hwang

The Compact Toroid Injection Experiment (CTIX) produces a high density, high velocity hydrogen plasma which maintains its configuration in free space on a MHD resistive time scale. Earlier studies have shown that impurities generated through plasma surface interactions within CTIX can be observed exiting the accelerator, although depth profile analysis of silicon collector probe data indicated they are not traveling at the full velocity of the compact toroid plasma. To improve gas utilization in the formation region, CTIX has converted to active switching from the passive technique used in past studies. Here we present results extending our impurity studies to compare passive and active switching using several new diagnostics: (1) Rutherford Backscattering Spectrometry and Auger Depth Profiling of silicon collector probes, (2) spectroscopy at several axial locations, and (3) residual gas analysis following plasma discharges. Designs for improved electrode surfaces will also be discussed.    [Preview Abstract]


CP9.00088: Overview of FRC experiments in the C-2 device
Michel Tuszewski

Large-size hot FRCs are produced in the C-2 device by merging two dynamically-formed, high-beta, Compact Toroids [1]. Typical plasma parameters after merging are separatrix radius : 0.5 m, separatrix length: 3 m, density: 5$\times $10$^{19}$ m$^{-3}$, deuterium ion temperature: 0.5 keV, and electron temperature: 0.2 keV. The main goal of the FRC experiments in the C-2 device is to achieve FRC sustainment, with heating and current drive from perpendicular (to B) neutral beam injection, and with pellet fuelling. Maximizing the FRC lifetime is important before attempting sustainment. Hence, the focus of present C-2 experiments is to improve the FRC target as much as possible. Techniques are being developed to improve plasma stability and confinement by controlling open-field-line conditions. Recently, enhanced confinement and longer FRC lifetimes have been achieved. In addition, the n = 2 rotational mode has been eliminated without using multipole magnetic fields. Some details of these exciting results will be presented.\\[4pt] [1] M.W. Binderbauer et al., Phys. Rev. Lett., 105, 045003 (2010).    [Preview Abstract]


CP9.00089: Formation performance and upgrade paths for the C-2 System [1]
E. Trask , E. Garate , R. Mendoza

Tri Alpha Energy's C-2 experimental system is a linear device consisting of two separate multi-coil theta-pinch formation sections and a central confinement vessel. Two high-beta compact toroids (CTs) are formed by sequential firing of the main reversal coils in the formation sections. Field-reversed configurations (FRCs) are formed by the dynamic collision of the two CTs. The performance of the machine formation sections has been well quantified, with observed flux trapping efficiencies up to 60{\%} and energy conversion efficiencies up to 10{\%}. Strong correlations between formation efficiencies and global FRC performance are observed. Data will be presented showing the correlations between the various formation efficiencies and FRC parameters such as confinement times. Due to the flexibility of control for each formation section, several different formation methods that may increase the efficiency of energy delivery to the plasma will also be discussed. [1] M. W. Binderbauer \textit{et al}, Phys.Rev.Lett. \textbf{105,} 045003 (2010).    [Preview Abstract]


CP9.00090: NIMROD Simulations of FRC Formation, Translation, Merging and Stability
Ales Necas , Richard Milroy

We report on progress made in using the NIMROD code to simulate formation, translation and merging of FRCs in the C-2 experiment [1]. This sequence is simulated in 2D and 3D, with and without inclusion of the Hall term. As will be shown, the Hall term is responsible for transient toroidal magnetic fields, which annihilate fast after merging, consistent with experiments. Rotational and tilt instabilities are also being investigated via NIMROD in the context of different possible experimental configurations (such as in-situ vs dynamic formation or single vs double sided injection). For example, one-sided translation with an initial tilt perturbation shows that growth of the tilt mode is suppressed with inclusion of Hall MHD. This and other select results will be examined more closely. \\[4pt] [1] M. W. Binderbauer \textit{et al}, Phys.Rev.Lett. \textbf{105,} 045003 (2010).    [Preview Abstract]



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CP9.00092: Rotation Studies on the C-2 FRC Experiment
Deepak Gupta , Bihe Deng , Sean Dettrick , Jon Douglass , Eusebio Garate , Houyang Guo , John Kinley , Emil Ruskov , Xuan Sun , Matthew Thompson , Lothar Schmitz

Although high rotation velocity in a FRC may lead to rotational instabilities, it is also believe that shear flow helps in improving FRC stability and transport. In the C-2 experiment [1], diagnostics such as multi-chords and fast-response ion Doppler spectroscopy, multi-chords CO$_2$ interferometry, bolometer tomography, Doppler backscattering, Mirnov probe arrays and mach probes are available to measure the rotation, its profile and associated instabilities. In past, suppression of n=2 rotational mode and associated reduction in the rotation velocity have been reported on C-2 via the use of quadrupole magnetic field [2]. Recently, biased electrodes are used on C-2 to control the rotation profile of the edge plasma layer. Local velocity, rotation profile and macroscopic rotation measurements as well as mode analysis were performed. Results on FRC rotation and effects of electrode biasing will be presented.\\[4pt] [1] M.W. Binderbauer {\em et al}, Phys.Rev.Lett. {\bf 105}, 045003 (2010)\\[0pt] [2] H.Y. Guo {\em et al}, Phys.Plasmas {\bf 18}, 056110 (2011)    [Preview Abstract]


CP9.00093: Direct Measurement of Impurity Transport in a Field Reversed Configuration
T. Roche , N. Bolte , W.W. Heidbrink , R. McWilliams , F. Wessel

An optical tomography system has been developed and implemented in the Flux Coil Generated Field Reversed Configuration (FCG-FRC) at Tri Alpha Energy. Sixteen chords view $\sim35\%$ of the FRC at the mid-plane. The chords are arranged in two identical fans of eight chords each. To measure transport of an impurity species, argon, an FRC is generated using either Nitrogen or Deuterium as the primary species. A puff valve is activated prior to the shot such that the argon begins to bleed in to the vacuum chamber as the FRC is formed. The gas is puffed at the optimal location for tomographic reconstruction. Each chord is collimated to illuminate a fiber optic cable which is fed to an array of photomultiplier tubes which are fitted with neutral density and band pass filters to allow the appropriate amount of light from the emitting, singly ionized, argon at $434.8 nm$ to be measured. Using a preliminary assumption that density of argon is proportional to light intensity gathered data have been used to reconstruct density profiles. These profiles often peak near the field null. The data are being analyzed to determine diffusive and convective transport coefficients.    [Preview Abstract]


CP9.00094: Plasma transport Simulation in Field Reversal Configuration
Sangeeta Gupta , Sean Dettrick , D.C. Barnes

A Quasi-1D (Q1D) transport code was developed at Tri Alpha for predicting and interpreting the macroscopic time evolution of FRC plasmas in the C-2 field-reversed configuration experiment [1]. Q1D solves the time dependent radial transport equations for multiple ions species with rotation, representing the mid-plane of an experimental device. In the closed field region, important 2-D effects are incorporated in the Q1D code by transfer of particles, angular momentum and energy from inside to outside flux surfaces as well as axial length change in response to axial force balance. The closed field region is coupled with the SOL (Scrape Off layer) region by using the one-point parallel loss model. Parallel heat conduction is used as the dominant mechanism for electron heat transport in the SOL region while convective loss is used for parallel particle transport. Numerical results with C-2 relevant parameters will be presented and shown to be in reasonable agreement with experiments. \\[4pt] [1] M. W. Binderbauer \textit{et al}, Phys.Rev.Lett. \textbf{105,} 045003 (2010).    [Preview Abstract]


CP9.00095: Edge Biasing Experiment in C2 FRC (Field Reversed Configuration)
Xuan Sun , E. Garate , B. Deng , D. Gupta , S. Dettrick , E. Ruskov , L. Schmitz , H. Guo , M. Tuszewski

Edge biasing has long been used in various fusion devices to actively control the plasma potential profile in order to suppress radial transport by decorrelating density and potential fluctuations through flow shear. However, it has mostly not been employed in FRC plasmas except in one recent effort in the Colorado FRC. Owing to their near 2ms lifetime with adequately long quiescent phase, the FRCs in C2 offer a competent testbed for such experiments. Two types of electrodes have been deployed in C2, i.e, a ring electrode and a point electrode. The stationary ring electrode ensures biasing of the whole magnetic surface in the scrape off layer while the movable point electrode can make contact with the FRC separatrix or further inside. Both negative and positive biases, up to 800 Volts, have been applied on C2 FRCs. The influence on the plasma potential, density and edge rotation profiles, fluctuation levels, as well as the global FRC performance, will be reported.    [Preview Abstract]


CP9.00096: Equilibrium profiles and correlation with instabilities in the C-2 FRC experiment
Bihe Deng , Hiroshi Gota , John Kinley , Xuan Sun , Matt Thompson , Michel Tuszewski

Plasma equilibrium profiles and fluctuations in the C-2 field reversed configuration (FRC) experiment [1] are measured by an array of diagnostic systems, including interferometers, bolometer arrays, Thomson scattering, internal electrostatic and magnetic probes. Plasma electron density and temperature profiles and evolutions under various operation conditions will be presented. The profile dependence of the dominant n=2 instability (frequency, growth rate, threshold, etc.) will be explored. The effects of the instability on the profile changes will also be examined. \\[4pt] [1] M. W. Binderbauer \textit{et al}, Phys.Rev.Lett. \textbf{105,} 045003 (2010).    [Preview Abstract]


CP9.00097: Density Fluctuation and Edge Profile Measurements at the TAE Field Reversed Configuration Machine
Emil Ruskov , Lothar Schmitz , Lei Zeng , Tony Peebles , Bihe Deng

Microwave reflectometry/Doppler Backscattering (DBS) is used for the first time to probe density fluctuations in a FRC plasma. A six channel tunable heterodyne system coupled to monostatic beam optics and a steerable parabolic mirror launches~ X/O-mode waves (26-90 GHz) towards the C-2 FRC plasma [1]. At oblique incidence, DBS is used to measure density turbulence with k$_{\theta }\rho _{i} \quad <$ 4. Turbulence levels increase with radius and are correlated with the density gradient: they are large in the SOL, and small near the field null. Recently, a dedicated, fast swept profile reflectometer was developed for measurement of the edge density profile in the 0.3-2.2x10$^{13}$ cm$^{-3}$ range, with 2.5 $\mu $s maximum time resolution. The challenging requirements were solved with a bistatic two-band design, a specialized fast varactor-tuned source, and very fast data acquisition using a 1 Gs/s LeCroy oscilloscope. Sample edge density profiles, their comparison with the wings of CO2 interferometer profiles, and some physics implications will be discussed. \\[4pt] [1] M. W. Binderbauer \textit{et al}, Phys.Rev.Lett. \textbf{105,} 045003 (2010).    [Preview Abstract]


CP9.00098: Fast-ion Characteristics in Colliding FRCs with Neutral Beam Injection
Ryan Clary , Artem Smirnov , Sergey Korepanov , Sean Dettrick

Tri Alpha Energy's C-2 device [1] aims to explore confinement properties of colliding Field-Reversed Configuration (FRC) plasmas, augmented with neutral beam injection. Naturally, it is desirable to understand the general characteristics of the resulting fast- ion population. For this purpose, several 16 channel silicone-based Neutral Particle Bolometers (NPB) have been designed and installed on the C-2 device, measuring charge-exchanged fast-neutrals originating from the fast-ion population. We present results illustrating the effects on fast-ions from wall recycling and from the $\mathrm{n}=2$ rotation instability. In addition we find good agreement between NPB measurements and Monte Carlo simulations. The NPB diagnostics are a spatially resolved complement to the energy resolved Neutral Particle Analyzers installed on the C-2 device. \\[4pt] [1] M. W. Binderbauer {\it et al}, Phys. Rev. Lett., {\bf 105}, 045003 (2010)    [Preview Abstract]


CP9.00099: Fast ion diagnostics for the C-2 experiment
Sergey Korepanov , Ryan Clary , Artem Smirnov , Sean Dettrick , Sergey Murakhtin , Sergey Polosatkin

One of the goals of the C-2 experiment [1] is to explore FRC sustainment and current drive from neutral beam injection. Studies of the relaxation and confinement of hot anisotropic ions created by the neutral beams are considered to be key elements of the experimental research program. To realize this approach a set of diagnostics for the measurement of local parameters of fast ions has been developed. In particular, this set includes diagnostics to measure the local energy (neutral particle analyzer, LiNb3-based pyro-bolometers) and the angular distribution function (silicone-based neutral particle bolometers). For numerical studies of fast ion dynamics a Monte Carlo code has been elaborated. \\[4pt] [1] M. W. Binderbauer \textit{et al}, Phys. Rev. Lett., 105 \textbf{,} 045003 (2010).    [Preview Abstract]


CP9.00100: Impact of vessel-wall-coatings on the edge neutral density of a field-reversed configuration plasma
Matthew Thompson , Bihe Deng , Jon Douglass , Deepak Gupta , John Kinley , Ales Necas , Xuan Sun , Alan Van Drie , Max Wyman

In any magnetic plasma confinement device, it is advantageous to limit hot-ion loss through charge-exchange with cold neutral gas by minimizing the gas density near the plasma. A system of titanium and lithium evaporators has been used extensively in the C-2 field-reversed configure experiment [1] to coat the vessel walls with neutral-gas-absorbing film. The effectiveness of these coatings at reducing the recycling of neutrals from the wall, and hence the neutral particle density near the plasma, is evaluated using multiple diagnostic systems and analyses. Chief among these is the reconstruction of time-resolved neutral particle density profiles from measurements of D$_{\alpha}$ radiation, which show a significant reduction in gas densities when a fresh coating is applied. Simulations of neutral gas behavior with the Monte Carlo code DEGAS2 agree well with the measured neutral particle density profiles. \\[4pt] [1] M. W. Binderbauer \textit{et al.}, Phys. Rev. Lett. \textbf{105}, 045003 (2010)    [Preview Abstract]


CP9.00101: Finite Larmor Radius approximation for waves propagation in cylindrical plasma configurations
Laura Galeotti , Francesco Ceccherini , Marco Brambilla , Daniel C. Barnes , Francesco Pegoraro

We present an analytical derivation in cylindrical geometry of the Finite Larmor Radius approximation for the wave equations in the cyclotron frequency range and show a set of numerical results obtained with a new extended version of the code FELICE [1,2] which allows for arbitrary profiles of field, densities and temperatures. Obtaining a cylindrical FLR approximation is of great relevance for studying the wave propagation in plasma configurations like FRC's and theta-pinches in particular. The generic configuration we consider can be divided in the radial direction in two regions, i.e, a ``plasma region'' and a ``vacuum region''. In the former the wave propagation is computed numerically from the FRL approximation found, in the latter instead a general analytical solution has been calculated and implemented in the code. A detailed description on how to ensure both the overall causality of the propagation process and the correct matching conditions for the antenna surface and the vacuum/plasma surface is shown as well. \\ $[{\rm 1}]$ M.\,Brambilla, Plasma. Phys. and Contr. Fus. {\bf 31}, 723 (1989) \\ $[{\rm 2}]$ M.\,Brambilla, Plasma. Phys. and Contr. Fus. {\bf 35}, 41 (1993)    [Preview Abstract]


CP9.00102: Including electron kinetic effects in FRC simulations
Elena Belova , R.C. Davidson

A kinetic description for the electrons has been implemented in the 3D nonlinear hybrid HYM code, where the electrons are described as delta-f drift kinetic particles. Initial conditions are generated assuming that electron distribution function is a function of the three integrals of motion, and the electron temperature is fraction of the ion temperature. Numerical benchmarks have been performed in order to verify conservation laws, and study the accuracy of electron orbit integration depending on the electron time step. A new version of the HYM code with drift-kinetic electron description has been used to study the effects of kinetic electrons on FRC equilibrium and relaxation. It is shown that both parallel and perpendicular electron pressure evolves from the initial peaked profile towards hollow profiles with local minimum near the FRC magnetic null point. Comparisons of the two-fluid simulation results and the drift-kinetic electrons simulation results demonstrate that the ions spin up faster, when the drift-kinetic electron model is used. Initial results of 3D simulations studying the effects of kinetic electrons on the FRC stability will be presented.    [Preview Abstract]


CP9.00103: Hybrid equilibria of divertor tori with application to field-reversed configurations
Loren Steinhauer

High-beta plasmas of interest to fusion energy are poorly captured by fluid or even extended-fluid models. In local regions of low magnetic field (O-point, X-points) as well as regions with steep gradients [separatrix, scrape-off-layer (SOL)] even the gyroviscous model is questionable. An adequate treatment of the ion species calls for a fully kinetic treatment. The electrons can still be treated as a warm massless fluid. The label ``hybrid equilibrium'' describes this combination of fully-kinetic ions and fluid electrons. A flexible analytic solution to the steady Vlasov equation for the ions is found. Since it allows for loss of unconfined ions, it is called an ``end-loss'' distribution. Analytic forms of the important moments of the distribution are also found. While the fluid description of the electron fluid is straightforward, the paradigm for the electrostatic potential requires some care, especially to account for electrical shorting. Hybrid equilibria (kinetic ions + electron fluid + potential) require modest computations. Computed equilibria of field-reversed configurations yield insight into the SOL thickness, naturally sheared ion flows, and global confinement properites.    [Preview Abstract]


CP9.00104: Construction of the PFRC-2 Device
S.A. Cohen , B. Berlinger , A. Brooks , C. Brunkhorst , M. Edwards , J. Gumbas , C. Myers

Upgrades to the PFRC device are being made, under an ARRA grant, to enable exploration of FRC plasmas heated by odd-parity rotating magnetic fields (RMF) to keV electron and ion temperatures. The new 84-cm-long, 22.7-cm-ID vacuum vessel is made of polycarbonate, with 87 penetrations for diagnostics, feedthroughs, and pumps. Eight internal high-temperature-superconductor flux conservers with BN shields are installed to allow extension of the plasma duration to over 0.1 s. The RMF power capability has been increased from 20 to 200 kW of 0.1 s duration. PFRC-2 operations are scheduled to begin in December 2011.    [Preview Abstract]


CP9.00105: Characteristics of Muti-pulsing CHI driven ST plasmas on HIST
M. Ishihara , T. Hanao , K. Ito , K. Matsumoto , T. Higashi , Y. Kikuchi , N. Fukumoto , M. Nagata

The flux amplification and sustainment of the ST configurations by operating in Multi-pulsing Coaxial Helicity Injection (M-CHI) method have been demonstrated on HIST. The multi-pulsing experiment was demonstrated in the SSPX spheromak device at LLNL. In the double pulsing discharges, we have observed that the plasma current has been sustained much longer against the resistive decay as compared to the single CHI. We have measured the radial profiles of the flow velocities by using Ion Doppler Spectrometer and Mach probes. The result shows that poloidal shear flow exists between the open flux column and the most outer closed flux surface. The poloidal velocity shear at the interface may be caused by the ion diamagnetic drift, because of a steep density gradient there. The radial electric field is determined by the flow velocities and the ion pressure gradient through the radial momentum balance equation. We have investigated the contribution of ExB or the ion pressure gradient on the poloidal velocity shear by comparing the impurity ion flow obtained from the IDS with the bulk ion flow from the Mach probe. It should be noted that the diamagnetic drift velocity of the impurity is much smaller than ExB drift velocity. We will discuss characteristics of M-CHI-driven ST plasmas by varying TF coil current and the line averaged electron density.    [Preview Abstract]


CP9.00106: Equilibrium fitting analysis and propagation of magnetic fluctuations in the Multi-pulsing HIST plasmas
K. Matsumoto , T. Hanano , K. Ito , M. Ishihara , T. Higashi , Y. Kikuchi , N. Fukumoto , M. Nagata

The current drive by Multi-pulsing Coaxial Helicity Injection (M-CHI) has been performed on HIST in a wide range of configurations from high-q ST to low-q ST and spheromak generated by the utilization of the toroidal field. It is a key issue to investigate the dynamo mechanism required to maintain each configuration. To identify the detail mechanisms regarding a helicity transport from the edge to the core region, we have investigated the characteristics of magnetic field fluctuations observed in M- CHI experiments. We have fitted internal magnetic field data to a ST configuration calculated by the equilibrium code with a hollow pressure profile in order to find the sustained configurations. Fluctuation frequency is identified as about 80 kHz and it has been found to propagate from the open flux column region toward the core region. The toroidal mode n=0 is dominant in the high TF coil current operation. Alfven wave generation has been identified by evaluating its velocity as a function of plasma density or magnetic field strength. We will discuss the relationship between the Alfven wave and helicity propagation.    [Preview Abstract]


CP9.00107: Measurements of dynamo effect on double-CHI pulse ST plasmas on HIST
K. Ito , T. Hanao , M. Ishihara , K. Matsumoto , T. Higashi , Y. Kikuchi , N. Fukumoto , M. Nagata

Coaxial Helicity injection (CHI) is an efficient current-drive method used in spheromak and spherical torus (ST) experiments. An anticipated issue for CHI is achieving good energy confinement, since it relies on the magnetic relaxation and dynamo. This is essentially because CHI cannot drive a dynamo directly inside a closed magnetic flux surface. Thus, it is an important issue to investigate dynamo effect to explore CHI current drive mechanisms in a new approach such as Multi-pulsing CHI method. To study the dynamo model with two-fluid Hall effects, we have started from the generalized Ohm law. We have measured each MHD dynamo term and Hall dynamo term separately by using Mach probe and Hall probe involving 3-axis magnetic pick-up coils. The result shows that the induced electric field due to MHD dynamo is large enough to sustain the mean toroidal current against resistive decay in the core region. In the other hand, the anti-dynamo effect in the MHD dynamo term is observed in the central open flux column (OFC) region. From the viewpoint of two-fluid theory, ion diamagnetic drift is opposite to the electron diamagnetic drift, maybe resulting in the anti-dynamo effect. Hall dynamo may arise from the fluctuating electron diamagnetic current due to high electron density gradient which is large in the OFC region.    [Preview Abstract]


CP9.00108: Nonlinear MHD simulation of current drive by multi-pulsed coaxial helicity injection in spherical torus
Takashi Kanki , Masayoshi Nagata , Yasuhiro Kagei

The dynamics of structures of magnetic field, current density, and plasma flow generated during multi-pulsed coaxial helicity injection in spherical torus is investigated by 3-D nonlinear MHD simulations. During the driven phase, the flux and current amplifications occur due to the merging and magnetic reconnection between the preexisting plasma in the confinement region and the ejected plasma from the gun region involving the $n$=1 helical kink distortion of the central open flux column (COFC). Interestingly, the diamagnetic poloidal flow which tends toward the gun region is then observed due to the steep pressure gradients of the COFC generated by ohmic heating through an injection current winding around the inboard field lines, resulting in the formation of the strong poloidal flow shear at the interface between the COFC and the core region. This result is consistent with the flow shear observed in the HIST. During the decay phase, the configuration approaches the axisymmetric MHD equilibrium state without flow because of the dissipation of magnetic fluctuation energy to increase the closed flux surfaces, suggesting the generation of ordered magnetic field structure. The parallel current density \textit{$\lambda $} concentrated in the COFC then diffuses to the core region so as to reduce the gradient in \textit{$\lambda $}, relaxing in the direction of the Taylor state.    [Preview Abstract]


CP9.00109: Fast Ion Doppler Spectroscopy Measurements During Magnetic Reconnection in a Compact Torus
Saeid Houshmandyar , Xiaokang Yang , Tian-sen Huang

The preliminary results of ion temperature ($T_{i})$ and flow velocity measurements at the Prairie View (PV) Rotamak, which can operate in Field-Reversed Configuration (FRC) and Spherical Tokamak (ST) regimes, are presented. The measurements are performed through a fast (1 \textit{$\mu $}s time resolution) Ion Doppler Spectroscopy (IDS) diagnostics, which employs a Jarrell-Ash 50 monochromator with a ruled diffraction grating of 1180 G/mm line density, over 40 ms plasma discharge period. In order to identify the impurity emmision lines, a BWTek $i$-trometer spectrometer is used to record a time-integrated spectrum of each plasma shot. Furthermore, the measurements are extended to the magnetic reconnection experiments, where two FRCs are formed when magnetic shaping coils [\textit{Yang et al}, Phys. Rev. Lett \textbf{102}, 255004 (2009)] are energized, and later the two FRCs are merged when the DC current flowing through the shaping coils is shut off. Here, the variations in $T_{i}$ and flow velocity during the magnetic reconnection are investigated.    [Preview Abstract]


CP9.00110: Three-Axis Magnetic Field Measurements in the TCSU RMF Current Drive Experiment
K.M. Velas , R.D. Milroy

A 3-axis probe was installed on TCSU shortly before its shutdown. The probe has 90 windings that simultaneously measure B$_{r}$, B$_{\theta}$, and B$_{z}$ at 30 radial positions and is fully translatable. Positioning the probe at multiple axial positions and taking multiple repeatable shots allows for a full r-z map of the magnetic field. Initially, data has been processed with a 10 kHz low pass filter to capture the steady field. Higher frequency content has more shot-to-shot variability; it is difficult to map this axially. Plans include using a band pass filter to isolate the RMF frequency, which is consistent between shots. It is anticipated that the RMF field, in conjunction with the steady field, will yield a map of the full 3D rotating field structure. The 3- axis probe measurements are used to calculate the end-shorting torque, which opposes the RMF torque. Data from even- and odd-parity experiments will be compared. The NIMROD code has been adapted to simulate the TCSU experiment using boundary conditions adjusted to match both even- and odd-parity experimental conditions. A comparison of the n=0 components of the calculated fields to the 3- axis probe measurements shows agreement in the magnetic field structure of the FRC as well as in the jet region.    [Preview Abstract]


CP9.00111: Recent Development of Magnetic Field Measurements on Rotamak
Dhara Kalaria , Jermain Goss , Xiaokang Yang , Tian-Sen Huang

The new development of magnetic field measurements includes a series of Mirnov array for the study of magnetohydrodynamic (MHD) instability, and a magnetic probe array for the measurement of internal 3-Dimension magnetic field. The system of Mirnov array consists of four sets magnetic pick-up coils located at $Z=\pm $ 4 cm and $Z=\pm $ 30 cm along chamber axis; each array is made up of eight $B_{R}$-oriented coils mounted around the chamber surface at an equal interval of 45$^{\circ}$ toroidal angle. The 3-Dimentinal probe array was originally made at RPPL with University of Washington, Seattle; the probe array has a total of 90 windings that can be used to simultaneously measure $B_{r}, B_{\theta}$, and $B_{z}$ at 30 radial positions. The detailed system design which includes the data acquisition system and the primary experimental results will be presented.    [Preview Abstract]


CP9.00112: Overview of HIT-SI Results and Plans
D.A. Ennis , C. Akcay , C.J. Hansen , N.K. Hicks , A.C. Hossack , T.R. Jarboe , G.J. Marklin , B.A. Nelson , B.S. Victor

Experiments in the Helicity Injected Torus-Steady Inductive (HIT-SI) device have achieved record spheromak current amplification during operations in deuterium plasmas. HIT-SI investigates steady inductive helicity injection with the aim of forming and sustaining a high-beta equilibrium in a spheromak geometry using two semi-toroidal injectors. Recent operations in deuterium plasmas have produced toroidal plasma currents greater than 50 kA, with current amplifications (I$_{\mbox{\scriptsize tor}}/$I$_{\mbox{\scriptsize inj\_quad}}) > 3$, and poloidal flux amplifications ($\psi_{\mbox{\scriptsize pol}}/\psi_{\mbox{\scriptsize inj\_quad}}) > 10$. High performance deuterium discharges are achieved by initially conditioning the plasma-facing alumina surface of the HIT-SI confinement volume with helium plasmas. During subsequent deuterium operation the alumina surface strongly pumps deuterium, thereby limiting the density in the confinement volume. Additional measurements during high current deuterium discharges demonstrate reduced current and electron density fluctuations, impurity O {\small III} ion temperatures up to 50 eV and a toroidal current persistence for 0.6 ms after the injectors are shut off. Progress and plans for the HIT-SI3 configuration, with three injectors mounted on the same side of the confinement volume, will also be presented. Work supported by USDoE and ARRA.    [Preview Abstract]


CP9.00113: Evidence for Separatrix Formation and Sustainment with Steady Inductive Helicity Injection
B.S. Victor , T.R. Jarboe , A.C. Hossack , D.A. Ennis , B.A. Nelson , R.J. Smith , C. Akcay , C.J. Hansen , G.J. Marklin , N.K. Hicks

The Helicity Injected Torus with Steady Inductive Helicity Injection (HIT-SI) has achieved a breakthrough in the development of a new, more efficient current drive method for magnetic confinement fusion. Results include the first sustainment of toroidal plasma current of over 50 kA at 3 times the injected currents added in quadrature, the ratio of current density to electron density exceeding $10^{-14}$ A$\cdot$m, and toroidal current persistence of 0.6 ms after injector shut off. Separatrix toroidal currents--currents not linking the helicity injectors--are sustained at up to 40 kA. Results are achieved in HIT-SI during deuterium operations immediately after helium operations. Toroidal mode measurements for these high performance deuterium shots have a three stage evolution: initial growth of an n=1 eigenstate, rapid transition to a weak toroidal current and toroidal current growth coupled to a decrease in the n=1 activity with near constant helicity injection.    [Preview Abstract]


CP9.00114: Measurements of Energy and Helicity Cascades, Relaxation Rate, and Ion Temperature in HIT-SI
A.C. Hossack , J.S. Wrobel , T.R. Jarboe , D.A. Ennis , C.J. Hansen , G.J. Marklin , B.A. Nelson , R.J. Smith

Inverse cascades of magnetic helicity to lower toroidal modes and cascades of free energy to higher modes are observed in the HIT-SI device. Measurements from surface magnetic probes show that the helicity injectors initially couple to an $n $= 1 eigenmode of the confinement volume and the helicity in this mode subsequently decays to the $n$ = 0 minimum energy spheromak state. Thus helicity follows an inverse-cascade to lower $\lambda $ but magnetic energy released in the relaxation process follows a normal cascade to higher toroidal modes. The time delay between the predicted peaks in toroidal current assuming instantaneous relaxation and the actual toroidal current peaks as measured by the surface probes is a measure of the relaxation time. The relaxation time is measured to be 4.2 +/- 2.8 microseconds, much faster than the Sweet-Parker relaxation time of 60 to 100 microseconds. A Doppler spectrometer measures impurity ion temperatures in excess of 50 eV during recent deuterium operations, a significant increase from 20 eV with helium discharges. Work supported by USDoE.    [Preview Abstract]


CP9.00115: Commissioning of the Millimeter-Wave Polarimeter on the HIT-SI Spheromak
N.K. Hicks , R.J. Smith , D.A. Ennis , C.J. Hansen , T.R. Jarboe , B.S. Victor , J. Howard

The Helicity Injected Torus-Steady Inductive (HIT-SI) experiment investigates helicity injection current drive for magnetic confinement of fusion plasmas. A non- perturbative diagnostic of the internal magnetic field in HIT-SI discharges is needed to measure current-, q- and $\lambda$-profiles, and plasma polarimetry is the chosen diagnostic approach. The polarimeter diagnostic introduces a probe beam at millimeter wavelengths, and the beam's polarization is modified by the spheromak plasma as it propagates; measurement of this effect yields the density-weighted, line-integrated magnetic field strength parallel to the propagation. The diagnostic will also make an interferometric measurement of the electron density. A novel instrument design achieves relatively low cost and robustness to refraction by using a single radiation source (backward wave oscillator, swept-frequency centered on 300 GHz) and a single detector. The details of the design and implementation on HIT-SI are presented, as well as results from the commissioning of the instrument and initial magnetic field measurements. This research is supported in part by an appointment to the U.S. DOE Fusion Energy Postdoctoral Research Program administered by the Oak Ridge Institute for Science and Education.    [Preview Abstract]


CP9.00116: NIMROD simulations of HIT-SI plasmas
Cihan Akcay , Thomas Jarboe , Brian Nelson , Charlson Kim

HIT-SI (Steady Inductive Helicity Injected Torus) is a current drive experiment that uses two semi-toroidal helicity injectors driven at 5-15 kHz to generate steady inductive helicity injection (SIHI). All the plasma-facing walls of the experiment are coated with an insulating material to guarantee an inductive discharge. NIMROD is a 3-D extended MHD code that can only model toroidally-uniform geometries. The helicity injectors of the experiment are simulated as flux and voltage boundary conditions with odd toroidal symmetry. A highly resistive, thin edge-layer approximates the insulating walls. The simulations are initial-value calculations that use a zero $\beta$ resistive MHD (rMHD) model with uniform density. The Prandtl number ($Pr = 10$), and Lundquist number ($S = 5-50$) closely match the experimental values. rMHD calculations at $S\sim10$ show no growth of an $n=0$ mode and only a few kA of toroidal current whereas HIT-SI has demonstrated toroidal currents greater than 50~kA with a current amplification of 3. At higher $S (\ge20)$ the simulations exhibit significant $n=0$ magnetic energy growth and a current amplification exceeding unity: $\frac{I_{tor}}{I_{{\rm inj}}}\geq1$. While HIT-SI has shown evidence for separatrix formation, rMHD calculations indicate an entirely stochastic magnetic structure during sustainment. Results will also presented for Hall MHD, anticipated to play a crucial role in the physics of SIHI.    [Preview Abstract]


CP9.00117: Equilibrium and Stability Calculations in HIT-SI
Chris Hansen , George Marklin , Thomas Jarboe

The PSI-TET equilibrium code solves for solutions to the ideal MHD equilibrium equation mu0*j=lambda*B in arbitrary 3D geometry. A mimetic discretization on a tetrahedral mesh is employed. Geometric multigrid and a hybrid MPI/OpenMP parallelism model are used to provide solver scalability. Scalability has been shown to over 1 Billion degrees of freedom for the calculation of Taylor states. Lambda is allowed to vary across flux surfaces but must be constant in stochastic regions. Field line tracing is used to identify the location of stochastic regions and the magnetic axis. A fixed lambda profile, specified as a function of a flux surface variable, is used. Equilibria in HIT-SI have been computed for the homogenous (spheromak) and inhomogeneous (injector) fields separately for experimental comparison. Comparison of Taylor states with experimental data have shown good agreement during both the driven and decay phases for HIT- SI. Combined equilibria of interest with injector driving have also been computed for various lambda profiles. The code has recently been upgraded to include a linearized ideal MHD solver which has been used to compute the stability properties of HIT-SI equilibria. Equilibrium states and stability analysis will be presented for a range of lambda profiles with and without injector driving.    [Preview Abstract]


CP9.00118: Physical requirements and milestones for the HIT-PoP Experiment
Thomas Jarboe

Recent success with HIT-SI demonstrates the viability of steady inductive helicity injection (SIHI) as a spheromak formation and sustainment method. Results include the sustainment of toroidal current of over 50 kA, up to 40 kA of plasma current that is separate from the injectors, toroidal flux up to 6 times the peak injected flux, and j/n~$>$~10$^{{\-}14}$Am. All were achieved with 10MW or less applied power. This paper explores the requirements for a confinement test of the concept using a larger proof of principle experiment. The confinement experiment must not exceed the beta limit, the drift parameter limit, or the wall loading limit, where the drift parameter is (drift of electrons relative to ions to produce current)/(ion thermal speed). It must also exceed a minimum j/n, a minimum n$a$, and a minimum electron temperature, where $a$ is the minor radius. The drift parameter limit and beta limit appear to play defining roles in spheromak performance leading to a very favorable scaling of wall loading with size. The milestones sequence suggested is the following: 1. Startup at drift parameter and beta limit minimum density. 2. Raise current until j/n exceeds 10$^{-14}$Am. 3. Raise the current and temperature until T $\approx $ 50 eV for good ionization. 4. Raise the current and density until n$a \quad >$ 2x10$^{19}$ m$^{-2}$ for neutral screening. 5. Raise current and temperature until T $>$ 200eV so magnetic confinement can be studied.    [Preview Abstract]


CP9.00119: Extend MHD Simulations of Spheromaks
E.C. Howell , C.R. Sovinec

Nonlinear extended MHD simulations of decaying spheromaks are studied using the NIMROD code (JCP 195, 2004). Earlier work shows substantial agreement between resistive MHD simulations and experimental measurements of the Sustained Spheromak Physics Experiment (SSPX), except that simulations under-predict the peak observed electron temperature by as much as 40\%. This work investigates the confinement predicted by three extended models. The first model has a resistive MHD Ohm's law but evolves separate electron and ion temperatures. The second model has a single species temperature evolution but includes ion gyroviscosity and a 2-fluid Ohm's law. The third combined model has ion gyroviscosity, a 2-fluid Ohm's law, and separate temperature evolutions. The combined model predicts the hottest electron temperature of 84eV, but undergoes a large cyclical instability that cools the plasma below 50eV. The resistive MHD model that evolves separate temperatures peaks at 72eV. The model using the 2-fluid Ohm's law with single-temperature evolution undergoes a large instability early in the sustainment phase that transitions the q-profile from a standard spheromak profile to a monotonically decreasing profile, and temperature is limited to 65eV.    [Preview Abstract]


CP9.00120: Extended 3D MHD simulations of q-profile evolution spheromaks
Simon Woodruff , Nathan Mattor , Jennifer Baerny , James Stuber

The profile evolution of spheromaks from S$\sim $10$^{3}$ to S$\sim $107 is examined by use of the NIMROD code [1] for the PBX (minor radius, a$\sim $6cm, B$\mathbin{\lower.3ex\hbox{$\buildrel<\over {\smash{\scriptstyle\sim}\vphantom{_x}}$}} $0.1T) and ACE (a$\sim $10cm, B$\mathbin{\lower.3ex\hbox{$\buildrel<\over {\smash{\scriptstyle\sim}\vphantom{_x}}$}} $0.5T) experiments [2], and a next-step device that compresses a plasma from a0$\simeq $0.5m to af=0.15m (with a convergence ratio, C=a0/af of 3), and following usual adiabatic scaling relations to Te$\sim $5keV. q-profile evolution is determined mainly by resistive decay, observing the evolution of toroidal modes as mode-rational surfaces enter the plasma and grow islands (like [3][4]). However, at high S, resistive dissipation times are long, so dq/dr is compared with tilt growth rate for conformal walls to the no wall limit. Evidence of pressure-limiting behavior is presented. Dynamic simulations of spheromaks undergoing a compression are also presented, and predicted effects [5] of toroidal rotation are examined due to conservation of momentum during compression. \\[4pt][1] C. R. Sovinec, et al J. Comput. Phys. 195, 355 (2004)\\[0pt][2] S. Woodruff et al Proc. ICC 2010\\[0pt] [3] H. S. Mclean \textit{et al} Physics of Plasmas, v 13, n 5, p 56105-1-8 (2006)\\[0pt] [4] B. Cohen et al Phys. Plasmas 12, 056106 (2005)\\[0pt] [5] D. D. Ryutov UCRL-JRNL-227066 (2007)    [Preview Abstract]


CP9.00121: The Spheromak Turbulence Experiment: The Next Phase in Spheromak Physics
Ephrem Mezonlin , Kyron Williams , C.A. Weatherford , J.A. Johnson III , A.B. Alexander , Earl Scime , A. Keesee , G. Lusk , E. Reynolds , R. VanDervort , N.I. Arnold , K. Gilmore , E. Thomas Jr. , Simon Woodruff

The spheromak turbulence experiment (STPX) is a collaboration between FAMU, WVU, Auburn University, and Woodruff Scientific, Inc. The fundamental purpose of STPX is to advance Spheromak physics toward producing a burning plasma and new insights on astrophysical systems with magnetic reconnection. FAMU will employ microwave pulses to manipulate the stable state. In addition, closely coupled NIMROD modeling and experimentation will take place using the FAMU computational cluster. Auburn University is providing a pair of movable probe arrays consisting of a triple probe and a series of four saturation current/floating potential probes for making instantaneous measurements of plasma parameters. West Virginia University is providing an array of (N), X-MHz, B-dot coils for making measurements of magnetic fluctuations. West Virginia University is also providing an array of 25, 2 MHz bandwidth, B-dot coils and differential amplifiers for making high time-resolution measurements of magnetic fluctuations at the edge of the plasma. Woodruff Scientific designed and constructed the STPX vessel.    [Preview Abstract]