Session CP9: Poster Session II: Basic Plasma Physics: Non-Neutral, Dusty, Complex, and Low Temperature Plasmas; General Spherical Torus; Pinch Physics; Basic Plasma Physics: Magnetic Reconnection

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Room: Riverside West





CP9.00001: BASIC PLASMA PHYSICS: NON-NEUTRAL, DUSTY, COMPLEX, AND LOW TEMPERATURE PLASMAS

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CP9.00002: Chaotic Neoclassical Ripple Transport in Nearly Axisymmetric Penning-Malmberg Trap
A.A. Kabantsev , C.F. Driscoll

Neoclassical transport (NCT) due to axial asymmetries is ubiquitous in magnetic fusion plasma confinement. Collisional scattering (at rate $\nu$) is often regarded as the main mechanism during the crossing of ripple-caused separatrices. However, in certain cases {\it collisionless} particle orbits can cross the separatrices. Recent experiments\footnote{A.A. Kabantsev, Phys.~Rev.~Lett. (submitted, 2010).} have now characterized a novel {\it collisionless} form of NCT, where {\it chaotic} separatrix crossing occurs due to plasma rotation across $\theta$-ruffled separatrices, or due to wave-induced separatrix fluctuations. This mechanism has previously been taken to be ineffective because of presumed symmetries of such crossings.\footnote{H. Mynick, Phys. Fluids {\bf 26}, 2609 (1983).} Experiments with controlled separatrix ruffles or temporal variations now unambiguously distinguish the chaotic and collisional contributions. The chaotic NCT dominates when ruffles or waves spread the separatrix energy more than collisional spreading; then, the effects of the ruffled separatrix on both the transport magnitude nad its distinctive $\sin^2 \theta$ dependence become clearly dominant in the data, enabling close quantitative comparison to the theory.\footnote{D.H.E. Dubin, Phys.~Rev.~Lett. (submitted, 2010).}    [Preview Abstract]

 



CP9.00003: Damping Measurements of Plasma Modes
F. Anderegg , M. Affolter , C.F. Driscoll

For azimuthally symmetric plasma modes in a magnesium ion plasma, confined in a 3 Tesla Penning-Malmberg trap with a density of $n \sim 10^7$cm$^{-3}$, we measure a damping rate of $2$s$^{-1}$$< \gamma < 10^4$s$^{-1}$ over a wide range in temperature ($5 \times 10^{-6} \mathrm{eV} < T < 5$eV) and aspect ratio ($0.25 < \alpha < 25$), with a wave amplitude of $\delta n / n \simeq 5$\%. Changing the aspect ratio, $ \alpha = L_p / 2r_p$, of the plasma column, alters the frequency of the mode from 16 KHz to 192 KHz. The oscillatory fluid displacement is small compared to the wavelength of the mode; in contrast, the fluid velocity, $\delta \mathrm{v}_f$, can be large compared to $\overline{\mathrm{v}}$. The real part of the frequency satisfies a linear dispersion relation. In long thin plasmas ($\alpha > 10$) these modes are Trivelpiece-Gould (TG) modes, and for smaller values of $\alpha$ they are Dubin spheroidal modes. However the damping appears to be non-linear; initially large waves have weaker exponential damping, which is not yet understood. Recent theory\footnote{M.W. Anderson and T.M. O'Neil, Phys. Plasmas {\bf 14}, 112110 (2007).} calculates the damping of TG modes expected from viscosity due to ion-ion collisions; but the measured damping, while having a similar temperature and density dependence, is about 40 times larger than calculated. This discrepancy might be due to an external damping mechanism.    [Preview Abstract]

 



CP9.00004: Degenerate Mixing of Trivelpiece-Gould Waves on a Cold, Finite-Length Plasma Cylinder
M.W. Anderson , T.M. O'Neil , R.W. Gould

In the cold-fluid dispersion relation $\omega = \omega_p / [1 + ( k_\perp / k_z)^2]^{1/2}$ for Trivelpiece-Gould waves on an infinitely-long magnetized plasma cylinder, the transverse and axial wavenumbers appear only in the combination $k_\perp / k_z$. As a result, for any frequency $\omega < \omega_p$, there are infinitely many degenerate waves, all having the same ratio $k_\perp / k_z$. On a cold finite-length plasma cylinder, each longitudinal normal mode is a mixed superposition of these degenerate waves. Here several such modes are calculated for a single-species plasma cylinder with rounded ends. A striking feature of these modes is that the short-wavelength waves add constructively along cones\footnote{R.K. Fisher and R.W. Gould, Phys. Rev. Lett. {\bf 22}, 1093 (1969).} given by $dz / dr = \pm (\omega_p^2 / \omega^2 - 1)^{1/2}$. Thus, the mode structure of even a low order mode is substantially more complicated than the single sine wave approximation typically assumed. Also, the admixture of short wave lengths substantially enhances the viscous damping of the mode.    [Preview Abstract]

 



CP9.00005: Waves and Instabilities in Multispecies Nonneutral Plasmas
D.H.E. Dubin

This poster describes how several plasma waves and instabilities that have previously been studied only in neutral plasmas can also occur in multi-species nonneutral plasmas. Among these are ion sound waves, drift waves and ion temperature gradient (ITG) waves. The occurrence of these waves does not rely on the neutrality of the plasma, but rather on the coexistence of at least two species, at least one of which responds to the waves in a nearly adiabatic fashion; the others well-approximated by fluid theory. This typically (but not necessarily) requires a large mass ratio between species, but has nothing to do with the sign of the charge. The dispersion relations for these waves are similar to those in neutral plasmas, but there are some important differences. For example, weakly damped ion sound waves may propagate in a nonneutral plasma even when $T_e = T_i$, provided $n_i / n_e \geq15$. Furthermore, drift and ITG waves are not necessarily unstable, the instabilities do not necessarily cause plasma loss, and they can be controlled (turned on and off) by manipulation of the density and temperature profiles using standard experimental techniques such as centrifugal separation and laser cooling/heating.    [Preview Abstract]

 



CP9.00006: Construction of 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. We describe the construction (in progress) of a novel multicell Penning-Malmberg (PM) trap designed 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 device will use 1 kV confinement potentials and consists of 21 PM cells in three banks of 7 cells. It is contained in a UHV vacuum system in a warm-bore magnet operating at 5 tesla. Each cell will have the capability to apply rotating electric fields to the plasma for increased radial confinement. A 40 cm long master cell will be used to move plasmas, received from a buffer-gas positron accumulator, across the magnetic field into off-axis cells using auto-resonant excitation of the diocotron instability.$^{2}$ Details of the design will be discussed and related to previous baseline experiments. Additional experiments with a test electrode structure will be conducted to minimize the diameter of the PM cells and to optimize confinement in off-axis cells in the less uniform portions of the magnetic field near the ends of the magnet. Anticipated uses of this device will be discussed.    [Preview Abstract]

 



CP9.00007: Tailored Electrostatic Beams From Single-Component Plasmas
Tobin Weber

A non-destructive technique was recently developed to create high quality, magnetized electron (or positron) beams in a high magnetic field Penning-Malmberg (PM) trap.\footnote{T. R. Weber, J. R. Danielson and C. M. Surko, Phys. Plasmas {\bf 15}, 012106 (2008).} Expanding upon this technique, a class of electrostatic beams has been produced by extracting these beams from their guiding magnetic field. This procedure involves 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 is focused with an Einzel lens to small transverse dimensions ($r = 0.12$ cm). Experimental results are presented for beams from a $4.8$ T field PM trap. Details of the extraction physics, including the unavoidable velocity kick that the particles suffer upon extraction, are discussed. A generalized beam emittance is introduced to characterize beam quality. Applications and prospects for the future are discussed, including use of a magnetic spoke arrangement to further improve beam quality.    [Preview Abstract]

 



CP9.00008: Two sources of asymmetry-induced transport
D.L. Eggleston

We have added collisional effects to our single-particle code\footnote{D.~L. Eggleston, Phys. Plasmas {\bf 14}, 012302 (2007).} by applying random velocity steps along with a drag force in the particle equation of motion. By following the time variation of the mean square change in radial position we can obtain a diffusion coefficient $D$ which can be compared with analytical theory and experiment. For asymmetries of the form $\phi_1(r)\cos{(kz)}\cos{(\omega t - l\theta)}$ and low collision frequency, there are two contributions to the transport. The first is that given by resonant particle transport theory\footnote{D.~L. Eggleston and T.~M. O'Neil, Phys. Plasmas {\bf 6}, 2699 (1999).} and is produced by particles with velocity near $\pm(l\omega_R - \omega)/k$, where $\omega_R$ is the azimuthal rotation frequency. The second is produced by the low velocity particles identified in Ref.~2 that are axially trapped in the asymmetry potential. These produce a stronger variation of $D$ with $\omega$ with a peak near $\omega=l\omega_R$. The width of the peak $\Delta\omega$ increases with center wire bias and decreases with radius, while the height shows the opposite behavior. Diffusion due to axially trapped particles is typically comparable to or larger than that from resonant particles. This may explain the discrepancies between experiments and resonant particle theory.\footnote{D.~L. Eggleston and B.~Carrillo, Phys. Plasmas {\bf 10}, 1308 (2003).}    [Preview Abstract]

 



CP9.00009: Understanding and improving confinement in CNT
Paul Brenner , Thomas Pedersen , Xabier Sarasola , Benoit Durand de Gevigney , Peter Traverso

Confinement studies in the Columbia Non-neutral Torus (CNT) are providing new insights into the physics of pure electron plasmas confined on magnetic surfaces. The confinement of pure electron plasmas has now been measured in the absence of internal objects . These transient plasmas exhibit confinement times that are shorter than expected and have a strong dependence on neutral pressure. Plasmas created by electron emission in one direction have been compared to those created by emission in two directions. The confinement is significantly longer when emitting in only one direction, suggesting that a two-stream instability is present and affects the radial transport rate. Progress on verifying the existence of a two-stream instability will be presented. Experimental results from previously unexplored stellarator configurations, with low shear and large islands will also be shown.    [Preview Abstract]

 



CP9.00010: Overview of recent results from CNT
Thomas Sunn Pedersen , Allen H. Boozer , Paul W. Brenner , Benoit Durand de Gevigney , Xabier Sarasola , Peter Traverso

This poster will give an overview of recent results from The Columbia Non-neutral Torus (CNT). CNT was recently reconfigured by repositioning the internal coils, creating magnetic surfaces substantially different from those previously used. Field line mapping, confinement, and stability results will be summarized; they are covered in more detail in adjacent posters. Numerical studies of drift orbits will be presented. Toroidal resonances and electrostatic perturbations can create complicated unconfined orbits in CNT, which can affect confinement negatively but also provides ways of injecting electrons, or positrons. The issue of Debye shielding in a non-neutral plasma is discussed. Debye screening is very different compared to the textbook calculation for a quasineutral plasma. The ability to affect drift orbits with external electrostatic perturbations may be used to inject electrons or positrons across the magnetic surfaces. An update on the plans for an electron-positron plasma experiment will also be given.    [Preview Abstract]

 



CP9.00011: Field line mapping and equilibrium reconstructions in new CNT Configuration
Peter Traverso , Thomas Pedersen , Paul Brenner , Xabier Sarasola , Benoit Durand de Gevigney

The Columbia Non-neutral Torus (CNT) has the useful feature of having adjustable coil geometry, creating up to three different stellarators each having a completely new shape to its magnetic surfaces and a different Iota profile. Recently the tilt angle between the two interlocking coils has been changed for the first time on CNT, allowing a study of the new magnetic geometry. In the new configuration field line mapping has been accomplished for multiple current ratios and magnetic fields to confirm the existence of good nested magnetic surfaces. At a specific current ratio a large one-three island chain is created. Plasma parameters have been measured with the new coil configuration, both in cases of a large internal island chain, and in cases without. Full 3D equilibrium reconstructions of potential and density are being performed using a modified version of the existing Poisson-Boltzmann solver. Field line mapping in this configuration will be presented, and a progress report on the equilibrium reconstructions will also be given.    [Preview Abstract]

 



CP9.00012: Observation of Trivelpiece-Gould modes in toroidal pure electron plasma
F. Choudhury , M.R. Stoneking , A.R. Knoedler

Non-neutral (electron) plasma are confined in the Lawrence Non-neutral Torus II (major radius = 17.4 cm, minor radius = 1.27 cm, B $\sim $ 550 G) with a purely toroidal magnetic field. The plasma is diagnosed by measuring the flow of image charge to and from isolated sectors of the fully segmented conducting boundary. Long confinement times ($>$300 ms) in both partial (270$^{\circ}$ arc) and fully toroidal traps indicate the production of nearly steady-state conditions and permit study of intrinsic toroidal effects on dynamics and transport. We report the first observations of Trivelpiece-Gould modes (space-charge waves) [A.W. Trivelpiece and R.W. Gould, J. Appl. Phys. \textbf{30}, 1784 (1959)] with poloidal mode number $m$=0 in toroidal non-neutral plasma. The fundamental mode at 1.3 MHz and the first few harmonics are excited with a tone burst in partially toroidal conditions. We also report on attempts to observe Trivelpiece-Gould modes in plasma confined in a fully toroidal trap, and on attempts to use numerical modeling to identify toroidal effects on these modes. This work is supported by the National Science Foundation Grant PHY-0812893.    [Preview Abstract]

 



CP9.00013: Axisymmetric Eigenmodes of Spheroidal Pure Electron Plasmas
Yosuke Kawai , Haruhiko Saitoh , Zensho Yoshida , Yasuhito Kiwamoto

The axisymmetric electrostatic eigenmodes of spheroidal pure electron plasmas have been studied experimentally. It is confirmed that the observed spheroidal plasma attains a theoretically expected equilibrium density distribution, with the exception of a low-density halo distribution surrounding the plasma. When the eigenmode frequency observed for the plasma is compared with the frequency predicted by the dispersion relation derived under ideal conditions wherein the temperature is zero and the boundary is located at an infinite distance from the plasma, it is observed that the absolute value of the observed frequency is systematically higher than the theoretical prediction. Experimental examinations and numerical calculations indicate that the upward shift of the eigenmode frequency cannot be accounted for solely by the finite temperature effect, but is significantly affected by image charges induced on the conducting boundary and the resulting distortion of the density profile from the theoretical expectation.    [Preview Abstract]

 



CP9.00014: Centrifugal separation in electron-antiproton plasmas
Joel Fajans

In thermal equilibrium, the antiprotons in an electron/antiproton plasma will be concentrated on the plasma's outer radial edge. We here report the first observation of such centrifugal separation in this system, as well as the first report of separation in a system in which the required cooling is provided by cyclotron radiation rather than by laser cooling. We will also present measurements of the timescale on which thermal equilibrium is attained, and discuss the relaxation mechanisms.    [Preview Abstract]

 



CP9.00015: The Effect of Multipole-Enhanced Diffusion on the Joule Heating of a Cold Non-Neutral Plasma
Steven Chapman , Alex Povilus , Joel Fajans

One proposed technique for trapping anti-atoms is to superimpose a Ioffe-Pritchard style magnetic-minimum neutral trap on a standard Penning trap used to trap the charged atomic constituents. Adding a magnetic multipole field in this way removes the azimuthal symmetry of the ideal Penning trap and introduces a new avenue for radial diffusion. Enhanced diffusion will lead to increased Joule heating of a nonneutral plasma, potentially adversely affecting the formation rate of anti-atoms and increasing the required trap depth. We present a model of this effect with comparison to measurements from an intended anti-atom trap.    [Preview Abstract]

 



CP9.00016: Autoresonant-spectrometric determination of the residual gas composition in the ALPHA experiment apparatus
Marcelo Baquero-Ruiz

The ALPHA antihydrogen trapping apparatus uses a cryogenic vacuum system that allows us to work at very low pressures and neutral particle densities. Nevertheless, it has been seen that the few neutral gas particles remaining in the trap have a small but noticeable effect on some of our experiments. This makes it interesting for us to know the density and composition of the neutral particles. Here we report the implementation of a system for measuring the composition of the residual gas inside the apparatus based on autoresonant ion extraction from an electrostatic potential well. The system uses the setup already in place for the experiment and offers an effective and non-invasive way of measuring the substances present inside our apparatus.    [Preview Abstract]

 



CP9.00017: Search for Trapped Antihydrogen in ALPHA
Niels Madsen

Antihydrogen ($\bar{H}$) spectroscopy promises the most precise tests of the symmetry of matter and antimatter and can possibly offer new insights into the baryon asymmetry of the universe. $\bar{H}$ is however produced only in small quantities. The ALPHA collaboration therefore plans to trap $\bar{H}$ to permit the use of precision atomic physics tools for comparisons of antihydrogen and hydrogen. Trapping of $\bar{H}$ is challenging as neutral atom traps are shallow ($\sim$0.6~K for ground state atoms) compared to typical recorded $\bar{H}$ temperatures. The $\bar{H}$ is formed at the temperature of the $\bar{p}$ used for the synthesis. As no atom cooling is readily available the constituent $\bar{p}$ and positrons ($e^+$) must be cold for the creation of $\bar{H}$. We show how ALPHA has addressed this challenge and we discuss the first systematic attempt at identifying trapped $\bar{H}$ in our system. This includes special techniques for fast release of the trapped anti-atoms, as well as a silicon vertex detector to identify $\bar{p}$ annihilations. The silicon detector is crucial to efforts to reduce the background. We further discuss the background from mirror-trapped $\bar{p}$, and how we can differentiate these from trapped $\bar{H}$ atoms.    [Preview Abstract]

 



CP9.00018: Autoresonant Excitation of Antiproton Plasmas
William Bertsche

We will present results of the first longitudinal autoresonant excitation of a thermal antiproton plasma. We apply a swept-frequency drive field to an antiproton plasma in an anharmonic potential to resonantly control the longitudinal energy of the particles in the potential. We observe autoresonant excitation of the plasma as a macroparticle in the regime of cold, dense plasmas, while warmer, tenuous plasmas are not excited completely (as predicted by theory [1]). This technique has been used for initiating the formation of antihydrogen, as it provides a flexible method for injecting antiprotons into a positron plasma of fluctuating space-charge while minimizing the kinetic energy of the antiprotons possessed by the antiprotons just after injection. As efforts to trap and conduct spectroscopy on antihydrogen require the formation of cold antihydrogen, minimizing energy mismatches in formation is key to successful trapping. \textbf{References} [1] Barth, I., \textit{et al,} Phys. Rev. Lett. \textbf{103}, 155001 (2009)    [Preview Abstract]

 



CP9.00019: Evaporative Cooling of Antiprotons to Cyrogenic Temperatures in a Penning Trap
Eoin Butler

Evaporative cooling has proven to be an invaluable technique in atomic physics, allowing for the study of effects such as Bose-Einstein condensation. We present the first application of evaporative cooling to charged particles stored in a Penning Trap. We have achieved cooling of a cloud of antiprotons to a temperature as low as 9~K, two orders of magnitude lower than ever directly measured previously [1]. Our measurements are well-described by appropriate rate equations for the temperature and number of particles. The technique has direct application to the ongoing attempts to produce a trapped sample of antihydrogen, where the trap depths are extremely shallow ($\sim 0.6~\mathrm{K}$ for ground state atoms). \newline [1] Andresen, G. B., \textit{et al} (ALPHA), Phys. Rev. Lett. \textbf{105}, 013003 (2010)    [Preview Abstract]

 



CP9.00020: Characterization of a non-neutral ion trap for the determination of the half-life of ionized $^7$Be
Bryan G. Peterson , Daniel Erickson , Chad Williams , Grant W. Hart

We have constructed a non-neutral ion trap in order to measure the rate of decay of singly-ionized $^7$Be. $^7$Be is the lightest isotope that decays exclusively by electron capture. Because any of the electrons can be captured in the decay, the removal of any of the four electrons can measurably affect the rate. In addition, the decay of this isotope is generally measured with the atom embedded in some other material so the actual electron configuration is not well known whereas the ions in the plasma will have a well-defined configuration. We are using a boron carbide plasma to characterize the operation of the trap. This provides a plasma with ion masses that are comparable to that of $^7$Be as well as providing three different masses (78\% $^{10}$B, 20\% $^{12}$C, 2\% $^{11}$B). This will allow us to evaluate the resolution and sensitivity of the Fourier Transform Ion Cyclotron Resonance Mass Spectrometry technique that will be used to monitor the rate of conversion of $^7$Be to $^7$Li. The status and results of this characterization will be presented.    [Preview Abstract]

 



CP9.00021: Axisymmetric Bernstein modes in a non-neutral plasma: Boundary conditions and 6/7 of the Brillouin limit
Grant W. Hart , Ross L. Spencer

Axisymmetric Bernstein modes exist in a cylindrical non-neutral plasma in the vicinity of the cyclotron frequency. Using a kinetic-theory model we have analyzed the theory of these modes in a rigid-rotor thermal equilibrium. We find that in the central region of the plasma (where the density is constant) the perturbed velocity is proportional to the Bessel function J$_{1}(k r)$, with $k$ having a distinct value for each mode. There are two distinct modes with separate $\omega$s for each $k$. We have improved our simulation of these modes in our $r-\theta$ PIC code by finding a set of parameters where we can both resolve the Debye length and avoid Landau damping of the modes. We find that in a thermal equilibrium plasma the perturbed velocity closely matches this J$_{1}(k r)$ in the interior of the plasma. The dispersion relation derived from the theory also matches the values of $\omega$ and $k$ seen in the simulation. We also see the two families of modes in the simulation at different frequencies for the same initial velocity perturbation in the plasma. The boundary conditions that need to be applied to constrain $k$ at the free boundary of the plasma are unclear from the physics and appear to be different for the two modes. The theory also breaks down in a region surrounding 6/7 of the Brillouin limit. Progress in understanding these issues will be discussed.    [Preview Abstract]

 



CP9.00022: Fluid Modes of a Spherically Confined Yukawa Plasma
Hanno Kaehlert , Michael Bonitz

The normal modes of a three-dimensional Yukawa plasma in an isotropic, harmonic confinement are investigated by solving the linearized cold fluid equations. The eigenmodes are found analytically in terms of hypergeometric functions. The mode frequencies solely depend on the dimensionless plasma parameter $\xi=\kappa R$, where $R$ is the plasma radius and $\kappa$ the inverse screening length. The eigenfrequencies increase monotonically with $\xi$ and saturate in the limit $\xi\to\infty$. Compared with the results in the Coulomb limit [D. H. E. Dubin, Phys. Rev. Lett. \textbf{66}, 2076 (1991)], we find a new class of modes characterized by the number $n$ which determines the number of radial nodes in the perturbed potential. We compare the fluid modes with molecular dynamics simulations and find good agreement for low order modes and weak to moderate screening.    [Preview Abstract]

 



CP9.00023: Experiments and simulation of dust motion in toroidal dust clouds in a weakly magnetized plasma
Alexander Piel , Torben Reichstein , Iris Pilch

In the presence of a magnetic field, dust clouds of micrometer sized particles can attain a toroidal shape with a dust-free region in the center. We had shown before [1] that the formation of such toroidal clouds can be described by a hierarchical model. In first order, the radial dust confinement is governed by a balance of the electric field force and the radial component of the ion drag force. In second order, the azimuthal component of ion drag that arises from the ion Hall effect is in competition with the weight force and gas friction. Above a threshold, the dust performs an azimuthal motion. Here, we present a refined model for dust confinement and rotation that also accounts for collective forces and inertial effects. The model is presented in two versions, by integrating the equations of motion or by molecular dynamics simulation. The model calculations are compared with experimental results for the inhomogeneous velocity field of the streaming particles.\\[4pt] [1] I. Pilch et al, Phys. Plasmas 15, 103706 (2008)    [Preview Abstract]

 



CP9.00024: Frequency clusters in self-excited dust density waves
Kristoffer O. Menzel , Oliver Arp , Alexander Piel

Self-excited dust density waves were studied under microgravity conditions. Their non-sinusoidal shape and high degrees of modulation suggests that nonlinear effects play an important role in their spatio-temporal dynamics. The resulting complex wave pattern is analyzed in great detail by means of the Hilbert transform, which provides instantaneous wave attributes, such as the phase and the frequency. Our analysis showed that the spatial frequency distribution of the DDWs is usually not constant over the dust cloud. In contrast, the wave field is divided into regions of different but almost constant frequencies [1]. The boundaries of these so-called frequency clusters coincide with the locations of phase defects in the wave field. It is found that the size of the clusters depends on the strength of spatial gradients in the plasma parameters. We attribute the formation of frequency clusters to synchronization phenomena as a consequence of the nonlinear character of the wave.\\ $\left[1\right]$ K. O. Menzel, O. Arp, A.Piel, Phys. Rev. Lett. {\bf 104}, 235002 (2010)    [Preview Abstract]

 



CP9.00025: Nonlinear magnetoplasmons in strongly coupled Yukawa and Coulomb plasmas
Torben Ott , Michael Bonitz , Zoltan Donk\'{o} , Peter Hartmann

The wave spectra of magnetized and strongly coupled 2D-Yukawa plasmas have recently been computed numerically~[1]. Good agreement between existing theories and the simulation was found. The magnetized Yukawa plasma sustains two modes, the magnetoplasmon and the magnetophonon, the frequencies of which are of the order of the Einstein or cyclotron frequency. In this contribution, we report on the existence of additional high-frequency plasma oscillations at multiples of the magnetoplasmon, based on extensive molecular dynamics simulations. The emergent modes are reminiscent of the well-known Bernstein modes but are renormalized by the strong interparticle correlations. We present detailed numerical results and an analytical explanation of the observed features~ [2].\\[4pt] [1] Hou \textit{et al.}, Phys. Plas., {\bf 16}, 73704 (2009)\\[0pt] [2] Bonitz \textit{et al.}, Phys. Rev. Lett., in print (2010)    [Preview Abstract]

 



CP9.00026: Bi-Dust Solitary Waves
Julio Puerta , Pablo Martin

Propagations of non-linear solitary waves in bi-dust plasma system is analyzed. In the present treatment one of the dust particles is assumed to be much smaller than other one, in such a way that there are enough time for these particles to reach quasi thermal equilibrium. Maxwell-Boltzmann factors are therefore applied for the density distribution of electrons, ions and light dust grains. The treatment of the problem can now be made by the method of the pseudo-potential taking in to account temperature effects in function of the density of the first grains. A density threshold can be found. In the limit where the light grain density tends to zero recovering the effects found by other authors are founded, where one kind of grains is only present [1,2]. Several numerical calculations for different values of the characteristic parameters will be shown. \\[4pt] [1] Rao N. N., Shukla P. K. and Tu M. Y. (1990), Planet Space Science \underline {\textbf{38}}, 543 \\[0pt] [2] Mendoza-Brice\~{n}o C. A., Russel S. M. and Mamun A. A., (2000) Planet Space Science \underline {\textbf{48}}, 599    [Preview Abstract]

 



CP9.00027: Non-Gaussian Velocity Distribution of Microparticles in Plasma under Microgravity Conditions
Amit K. Mukhopadhyay , J. Goree , Bin Liu , V.E. Fortov , A.M. Lipaev , V.I. Molotkov , O.F. Petrov , G.E. Morfill , H.M. Thomas , A.V. Ivlev

In an experiment performed on the International Space Station using the PK-3 Plus instrument, 3.4-micron plastic microparticles were introduced in a neon glow-discharge plasma. The microparticles became negatively charged and were confined by ambipolar electric fields. Using laser illumination and video cameras, microparticles were imaged and their motions tracked using image analysis software. We calculate the velocity distribution function f(v) for the random motion. We find that f(v) is non-Maxwellian with an elongated high-energy tail for this non-equilibrium system and f(v) is fit well by the Tsallis distribution. This distribution is popular in the field of statistical physics for non-equilibrium systems. Work in Iowa was supported by NASA grant~NNX07AD22G. Work in Germany was supported by DLR/BMWi grant no 50WP0203 and by RFBR grant no. 06 02 08100.    [Preview Abstract]

 



CP9.00028: Tiling analysis of melting in strongly-coupled dusty plasma*
W.D. Suranga Ruhunusiri , Yan Feng , Bin Liu , John Goree

A dusty plasma is an ionized gas containing micron-size particles of solid matter, which collect electrons and ions and become negatively charged. Due to large Coulomb interparticle potential energies, the microparticles represent a strongly-coupled plasma. In the absence of an external disturbance, the microparticles self-organize, arranging themselves in a crystalline lattice, due to their Coulomb interaction. If kinetic energy is added, the arrangement of microparticles becomes disordered, like atoms in a liquid. This melting process can be characterized by a proliferation of defects, which previous experimenters measured using Voronoi analysis. Here we use another method, tiling [1] to quantify defects. We demonstrate this method, which until now has been used only in simulations, in a dusty plasma experiment. A single layer of 4.83 $\mu $m polymer microparticles was electrically levitated in a glow discharge argon plasma. The lattice was melted by applying random kicks to the micoparticles from rastered laser beams. We imaged the particle positions and computed the corresponding tiling for both the crystalline lattice and liquid states. [1] Matthew A. Glaser, Phys. Rev A 41, 4585 (1990) $^{*}$Work supported by NSF and NASA.    [Preview Abstract]

 



CP9.00029: Probe Induced Low Density Dust Regions in Complex Plasma
Brandon Harris , Natalie Walker , Jorge Carmona Reyes , Jimmy Schmoke , Mike Cook , Lorin Matthews , Truell Hyde

Spherical, micrometer particles within a Coulomb crystal levitated in the sheath above the powered lower electrode in a GEC reference cell are examined using a Zyvex S100 nanomanipulator. Using the S100, a vertical probe was positioned within the cell at various locations with respect to the crystal formed within the sheath. As the probe was lowered toward the horizontal plane of the dust layer, a low density, circular dust region was formed. In this case, a horizontal force balance exists between the confining potential, the interparticle Coulomb repulsion and the probe, which acquires a negative charge (if unpowered) in the same manner as the dust. Treating the probe analytically as a line charge while adjusting its height and dc bias, the dust charge and Debye length were determined. These analytical and experimental results will be compared to Samsonov's previous experiment employing a charged wire.    [Preview Abstract]

 



CP9.00030: A Simple Method to Measure the Interaction Potential between Dielectric Grains in a Dusty Plasma
Zhuanhao Zhang , Ke Qiao , Jie Kong , Lorin Matthews , Truell Hyde

A simple, minimally perturbative method is introduced to experimentally measure the interaction potential between two individual dust particles, levitated in the sheath of a radio-frequency (RF) argon discharge. In this technique, a single dust particle is dropped into the plasma sheath to interact with a second individual dust particle already situated at the system's equilibrium point, without introducing any external perturbation. The resulting data is analyzed using a method employing a polynomial fit to the particle displacement, X(t), to reduce uncertainty in subsequent calculations. Employing this technique, the interaction potential is measured and shown to be well-described by a screened Coulomb potential and to decrease with increasing pressure. The charge on the particle and the effective dust screening distance are both calculated. It will be shown for the first time experimentally that the charge on a particle in the sheath of an RF plasma decreases with increasing pressure, in agreement with theoretical predictions. The screening distance also decreases with increasing pressure as expected. This technique can be used for rapid determination of particle parameters in dusty plasma.    [Preview Abstract]

 



CP9.00031: Conducting Particles Within a Dusty Plasma
Jorge Carmona Reyes , Lorin Matthews , Truell Hyde

The Yukawa interaction between charged grains within the two-dimensional horizontal layer formed in the sheath above the powered lower electrode in a GEC rf reference cell leads to the formation of disordered or ordered structures depending on whether short or long range ordering dominates as determined by the ratio of the particle's inter-particle potential energy to its average kinetic energy. Although this process has been examined in detail for melamine resin particles, conducting particles have not yet been fully investigated. In this work AU coated MF particles were observed, illuminated by a 80 mW diode laser. Observed behaviors will be discussed.    [Preview Abstract]

 



CP9.00032: The Dust Accelerator Facility at CCLDAS
Anthony Shu , A. Collette , R. Cosentino , K. Drake , N. Duncan , M. Horanyi , S. LeBlan , T. Munsat , P. Northway , S. Robertson , Z. Sternovsky , E. Thomas , M. Wagner , T. Wingfield , E. Grun , R. Srama

The lunar surface is continually bombarded with micrometeorites, primarily within the 0.1-1 $\mu$m and $<$ 100 km/s range. The impacts of such particles at the lunar surface introduce significant potential hazards to humans and instruments, but also create a scientifically rich complex system. Upon impact into the lunar regolith, cratering and micro-plasma creation can lead to liberation of many types of materials into the charged lunar dusty plasma. To address the many scientific and technical questions surrounding micrometeorites at the lunar surface, we describe an accelerator facility under construction at the Colorado Center for Lunar Dust and Atmospheric Studies at the University of Colorado. Key technical features of the 3 MV Pelletron-based accelerator include high achievable charge and mass, up to realistic micrometeorite parameters, precise selection of particle size and velocity, high repetition and data acquisition rates. Recent technical work has focused on a SIMION-based study to improve beam focusing and steering, and an FPGA-based filtering and selection unit for detection and selection of individual charged particles during flight. The implementation and design of these advancements will be presented.    [Preview Abstract]

 



CP9.00033: Characterization of single-file diffusion in one-dimensional dusty plasma
W.L. Theisen , T.E. Sheridan

Single-file diffusion occurs in one-dimensional systems when particles cannot pass each other and the mean-squared displacement (msd) of these particles increases with time t. Diffusive processes that follow Ficks law predict that the msd increases as t, however, single-file diffusion is sub-Fickean meaning that the msd is predicted to increase as t$^{1/2}$. One-dimensional dusty plasma rings have been created under strongly coupled, over-damped conditions. Particle position data from these rings will be analyzed to determine the scaling of the msd with time. Results will be compared with predictions of single-file diffusion theory.    [Preview Abstract]

 



CP9.00034: Acoustic pulses in dusty plasma 1-ring
T.E. Sheridan , James C. Gallagher

Properties of acoustic pulses in a one-dimensional dusty plasma are studied experimentally. Waves are launched by compressing one end of an incomplete 1-ring having $n=65$ particles using a laser for laser pulse durations $\Delta t_{\rm laser} = 0.10$--2.0 s. This procedure excites a large-amplitude compressive pulse which propagates for a significant distance. The wave amplitude increases with $\Delta t_{\rm laser}$ for $\Delta t_{\rm laser}\le0.5$ s and then becomes constant. Velocity perturbations up to $\approx10\%$ of the measured acoustic speed $c = 15.5\pm0.2$ mm/s are observed. However, the acoustic speed is independent of wave amplitude, indicating that nonlinear effects are not significant.    [Preview Abstract]

 



CP9.00035: Observation of dust jets due to a dust-discharge instability
Su-Hyun Kim , Jonathon R. Heinrich , Robert L. Merlino

We have observed an instability that occurs in a DC anodic glow discharge dusty plasma when a floating plate with a 5 mm aperture was placed in front of the 4 cm diameter anode disk. The instability is characterized by a periodic quenching and re-ignition of the discharge at frequencies in the range of 2 to 6 Hz. When the discharge is quenched, the dust cloud is ejected from the aperture in the form of a jet at speeds on the order of the dust acoustic speed. The jet retracts back toward the aperture when the discharge is re-ignited. The phenomena was studied using video imaging of laser light scattered from the dust.    [Preview Abstract]

 



CP9.00036: Dust structurization observed in a dc glow discharge dusty plasma
Jonathon R. Heinrich , Su-Hyun Kim , Robert L. Merlino

Dusty plasmas, which are inherently open systems which require an ionization source to replenish the plasma absorbed on the grains, tend to exhibit self-organization. Various structures have been observed in dusty plasmas such as dust crystals, voids, and vortices. Due to the presence of drifting ions in dc discharge plasmas, spontaneously excited dust acoustic waves are also a common occurrence. By adjusting the discharge parameters we have observed a new phenomenon in dusty plasmas -- the spontaneous formation of three-dimensional stationary dust density structures. These structures appear as an ordered pattern consisting of alternating regions of high and low dust density arranged in a nested bowl-type configuration The stationary structure evolves from dust density waves that slow down as their wavelength decreases and eventually stop moving when the wavelength reaches some minimum size.    [Preview Abstract]

 



CP9.00037: Measurement of Spatially Resolved Velocity Distributions in a Dusty Plasma
Ross Fisher , Edward Thomas

The three dimensional velocity space distribution of charged microparticles in a weakly-coupled (fluid-like) dusty plasma was measured using stereoscopic particle image velocimetry (stereo-PIV). In previous studies a single, spatially averaged, velocity space distribution was obtained over the entire microparticle cloud in the plasma [J. Williams and E. Thomas, Phys. Plasmas, 13, 063509 (2006)]. The data analysis techniques have been refined such that spatially resolved measurements of the velocity space distribution can be now be obtained. This poster will present measurements from dust clouds with and without the presence of dust density waves.    [Preview Abstract]

 



CP9.00038: Analysis of waves at a dust cloud - plasma interface
E. Thomas , J. Shaw , M. Chaudhuri , U. Konopka , H. Thomas

For the last two decades, detailed measurements have been made of a wide variety of complex plasma waves - from compressional dust density waves to transverse dust lattice waves. However, the dynamics of these waves as they interact with the dust - plasma boundary layer is complex and many questions related to the dissipation of waves at the surface remain. This presentation reports on an analysis of microgravity and ground-based studies of waves at the dust cloud boundary layer. Particle image velocimetry measurement techniques are used to construct velocity and frequency maps of particle~motion throughout the cloud and at the surface. The analysis suggests that the source of the waves is near the center of the cloud -- most likely, the void boundary.    [Preview Abstract]

 



CP9.00039: Application of PIV techniques to phase transition and wave experiments in complex (dusty) plasmas
L. Couedel , E. Thomas , J. Williams , V. Nosenko , S. Zhdanov , A. Ivlev , H. Thomas , G. Morfill

Over the last decade, particle image velocimetry (PIV) techniques have been applied in the study of complex (dusty) plasmas to study a wide range of wave and transport activity. While much of this work has involved the use of hardware configured specifically for PIV, the increased availability of higher speed imaging ($i.e. >$100 fps) over the last few years has allowed this diagnostic technique to be applied directly to video data without the need for specialized hardware. This poster will present the results of recent studies applying the PIV technique to phase transition measurements during the melting of a two-dimensional plasma crystal, as well as limitations that arise from the use of non-specialized hardware. In particular, we will show that this use of the PIV technique can identify compressional and transverse waves excited by the melting front.    [Preview Abstract]

 



CP9.00040: Initial application of tomographic particle image velocimetry to complex (dusty) plasmas
J. Williams

Over the last decade, two-dimensional and stereoscopic particle image velocimetry (PIV) techniques have been applied in the study of wave, transport and thermal properties of complex (dusty) plasma. While a great deal of insight has been gained from these studies, these studies have also indicated that volumetric three-dimensional information is needed. To address this need, the Wittenberg University Plasma Laboratory (WUPL) has recently acquired and installed a tomographic PIV (tomo-PIV) diagnostic system for dusty plasma investigations. It employs a synchronized dual YAG laser, four camera system for measuring the particle transport in three dimensions over an extended volume. This poster will present information on this diagnostic technique and preliminary results.    [Preview Abstract]

 



CP9.00041: Electrostatic dust cyclotron instability in a plasma with warm dust
Marlene Rosenberg

The excitation of electrostatic dust cyclotron (EDC) waves is a possible signature of the presence of magnetized charged dust in a plasma. The EDC instability is driven by ions drifting along the external magnetic field. Using kinetic theory, this instability is examined in a collisional, magnetized plasma containing submicron sized dust grains that have large thermal speeds. Neutral-charged particle collisions and dust-dust collisions are included in the analysis. The critical ion drift for exciting EDC waves is compared with that for exciting dust acoustic waves. Conditions for the excitation of higher harmonic EDC waves are also explored. Application to possible laboratory dusty plasmas immersed in large magnetic fields is discussed.    [Preview Abstract]

 



CP9.00042: A Comparative study of Eletromagnetic instabilities in a Lorentzian dusty plasma
Nazish Rubab , Nikolai Erkaev , Daniel Langmayr , Helfried Biernat

This study presents a theoretical approach to analyze the infuence of kappa distributed streaming ions and magnetized electrons on the plasma wave propagation in a dusty plasma. In particular, analytical expressions under certain conditions are derived for various fundamental instabilities and modes of propagations. A dispersion relation for kinetic Alfv\'{e}n wave (KAW)-like streaming instability has been derived. The effects of dust particles, plasma beta $\beta _i $, Lorentzian index on the growth rates and the threshold streaming velocity for the excitation of the KAW instability are examined. It has been observed that a sufficient amount of dust grains introduce two instabilities; one near cut-off frequency and the other below electron cyclotron frequency. Further, a comparative study of electromagnetic waves propagating along and across the external magnetic field has been made. Possible applications to various space and astrophysical situations are discussed.    [Preview Abstract]

 



CP9.00043: Improved Inertial Electrostatic Confinement Device for $^3$He-$^3$He Fusion
Gabriel Becerra , John Santarius , Gerald Kulcinski

Ions in inertial electrostatic confinement (IEC) systems are accelerated radially by an electrostatic field between two spherical grids, a configuration in which $^3$He-$^3$He fusion has previously been demonstrated as part of the advanced fuels program at the University of Wisconsin\ [1]. A campaign is underway to enhance the experimental setup, in order to sustain cathode voltages beyond 200\ kV. Additionally, the helicon plasma source and its ion extraction system are being upgraded to deliver ion currents of $\sim$60\ mA. These improvements will help achieve the goal of significantly raising the $^3$He-$^3$He fusion rates, to allow for a detailed diagnostic study of IEC physics with helium-3 fuel, as well as a direct comparison with a theoretical model\ [2]. Initial results will be presented. \\[4pt] [1] G.R. Piefer, ``Performance of a Low-Pressure, Helicon Driven IEC 3He Fusion Device,'' Ph.D. thesis, University of Wisconsin-Madison (2006). \newline[2] G.A. Emmert and J.F. Santarius, ``Atomic and molecular effects on spherically convergent ion flow. I. Single atomic species,'' {\it Physics of Plasmas} {\bf17}, 013502 (2010).    [Preview Abstract]

 



CP9.00044: Inertial Electrostatic Confinement Modeling and Comparison to Experiments
Gilbert Emmert , John Santarius , Eric Alderson , David Donovan

In inertial-electrostatic confinement (IEC), a high voltage accelerates ions between concentric, nearly transparent grids, usually in spherical geometry. For typical parameters ($\sim $0.3 Pa $\approx $ 2 mTorr, $\sim $100 kV, $\sim $30 mA, $\sim $0.5 m anode diameter), atomic and molecular processes dominate operation. A numerically solved integral equation[1,2] approach to modeling D$^{+}$, D$_{2}^{+}$, D$_{3}^{+}$, and D$^{-}$ ions passing through D$_{2}$ background gas will be summarized. The approach yields the energy spectra of ions and neutrals and the radial profile of the neutron production. Comparisons with experimental data for a University of Wisconsin IEC device will be presented.\newline[1] G.A. Emmert and J.F. Santarius, ``Atomic and Molecular Effects on Spherically Convergent Ion Flow I: Single Atomic Species'', Phys. Plasmas 17, 013502 (2010) \newline[2] G.A. Emmert and J.F. Santarius, ``Atomic and Molecular Effects on Spherically Convergent Ion Flow II: Multiple Molecular Species'', Phys. Plasmas 17, 013503 (2010).    [Preview Abstract]

 



CP9.00045: Using an Inertial Electrostatic Confinement (IEC) Nuclear Fusion Device as a Pulsed Neutron Source: Optimizing the Pulse Shape
Richard Bonomo

Pulsed neutron sources may prove to be valuable for detecting illicit nuclear materials in items being smuggled across borders or checkpoints. Work already accomplished by Sorebo et al.\ [1] at the U. of Wisconsin demonstrated the basic detection concept by successfully detecting \underline{delayed} $^{235}$U fission neutrons using neutron pulses generated by an IEC fusion device. \underline{Numerical} studies imply the detection of the much more copious \underline{prompt} induced-fission neutrons would be preferable; the \underline{experimental} detection of prompt neutrons represents a challenge: the prompt, fission-produced neutron and interrogating neutron pulses may overlap. After IEC device operation and past work by Sorebo et al.\ are reviewed, efforts to produce a properly shaped interrogating neutron pulse are described. Efforts drawing, in part, on techniques used in hard-switched power inverters are highlighted.\\[4pt] [1] J.H. Sorebo, G.L. Kulcinski, R.F. Radel, and J.F. Santarius, ``Special Nuclear Materials Detection Using IEC Fusion Pulsed Neutron Source,'' \it{Fusion Science and Technology} \bf{56}, 540 (2009).    [Preview Abstract]

 



CP9.00046: Studies of Negative Ion Generation in an Inertial Electrostatic Confinement Fusion Device
Eric Alderson , John Santarius , Gil Emmert , David Donovan , Gerald Kulcinski

The discovery of negative ion generation in Inertial Electrostatic Confinement (IEC) devices [1] has prompted a campaign to extend understanding of negative ion phenomena in IEC devices. Theoretical studies include modeling negative ion physics in IEC devices by adding negative ion generation and propagation to a 1-D computational model of ion and fast neutral currents in IEC devices [2], to produce negative ion spectra that can be compared with experiment. Experimental studies of negative ions in an IEC device focus on examining negative ion current spatial profiles, generated by a mobile Faraday Cup in the IEC device source region. This study explores the relationship between negative ion production and cathode geometry, and looks for evidence of negative ion focusing. The improved understanding of IEC physics from this work will be presented and the viability of the IEC as a negative ion source will be evaluated.\\[4pt] [1] D.R. Boris, et al., Phys. Rev. E. 80, 036408 (2009).\\[0pt] [2] G.A. Emmert and J.F. Santarius, Phys. Plasmas 17, 013503 (2010).    [Preview Abstract]

 



CP9.00047: Spatial and Energy Profiling of D-D Fusion Reactions in an Inertial Electrostatic Confinement Fusion Device
David Donovan , Gerald Kulcinski , John Santarius

The University of Wisconsin-Madison Inertial Electrostatic Confinement (IEC) Group utilizes highly transparent, concentric spherical electrodes to create a potential well that is used to accelerate charged particles towards the center of the well. The cathode is placed at a high voltage (10-100 kV) to accelerate deuterium ions to speeds that allow fusion to occur with background gas (2 mTorr), ions embedded in the cathode wires, and other fast particles. A new diagnostic has been developed that uses the time of flight (TOF) of the resulting fusion products to determine where the fusion event occurred along a radial line through the electrodes. The diagnostic is also capable of collecting the energy of the fusion reactants using the magnitude of the Doppler shift of the fusion products. The TOF diagnostic has been used with levels of accuracy never before achieved on an IEC device to collect spatial and energy profiles of the fusion reactions occurring along a radial line through a spherical IEC device while varying parameters such as background pressure, cathode voltage, and cathode design.    [Preview Abstract]

 



CP9.00048: Spectral line emission from helicon heated plasmas
T.M. Biewer , R.H. Goulding , D.L. Hillis , R. Isler , S. Meitner

There has been a resurgence of interest in linear plasma devices as a method to study plasma-material interfaces under high power and particle flux. As the size and power of the linear machines is increased they yield important results for fusion-grade toroidal devices such as ITER and DEMO. A 5 cm diameter helicon plasma source developed at ORNL routinely provides high density (n$_{e }\ge $ 10$^{19}$ m$^{-3})$ hydrogen plasmas for ion source development and other work. Recently, a 15 cm diameter, 1.5 m long linear machine has been built at ORNL using a new helicon antenna designed for input powers up to 100 kW, producing a plasma that will be used to bombard material targets. Visible spectroscopy has been used to measure emission line spectra of the helicon heated plasma from 200 nm to 1100 nm in real time at low resolution. Moreover, a separate diagnostic has been used to measure the intrinsic spectra of He II light from 10 sightlines to estimate the ion temperature and flow velocities (radial, axial, and azimuthal) at multiple axial locations in the device. Data from these diagnostics will be shown and their interpretation discussed.    [Preview Abstract]

 



CP9.00049: Microwave produced plasma in a Toroidal Device
A.K. Singh , W.F. Edwards , E.D. Held

A currentless toroidal plasma device exhibits a large range of interesting basic plasma physics phenomena. Such a device is not in equilibrium in a strict magneto hydrodynamic sense. There are many sources of free energy in the form of gradients in plasma density, temperature, the background magnetic field and the curvature of the magnetic field. These free energy sources excite waves and instabilities which have been the focus of studies in several devices in last two decades. A full understanding of these simple plasmas is far from complete. At Utah State University we have recently designed and installed a microwave plasma generation system on a small tokamak borrowed from the University of Saskatchewan, Saskatoon, Canada. Microwaves are generated at 2.45 GHz in a pulsed dc mode using a magnetron from a commercial kitchen microwave oven. The device is equipped with horizontal and vertical magnetic fields and a transformer to impose a toroidal electric field for current drive. Plasmas can be obtained over a wide range of pressure with and without magnetic fields. We present some preliminary measurements of plasma density and potential profiles. Measurements of plasma temperature at different operating conditions are also presented.    [Preview Abstract]

 



CP9.00050: Characteristics of Low Frequency Electrostatic Fluctuations in a Magnetized Toroidal Plasma
R. Kaur , A.K. Singh , R. Singh , A. Sarada Sree , S.K. Mattoo

This paper deals with the experimental investigation of fluctuations in a simple magnetized toroidal device BETA at the Institute for Plasma Research, Bhat, Gandhinagar, India. The BETA plasma shows territorially different characteristics tagged by varying signatures of fluctuations. The presence of limiter and differing sign of density gradient with respect to the magnetic field curvature determine these signatures in different region. As a result the simple magnetized tori are not very simple devices. This paper presents an experimental investigation of turbulence in the device. It is argued that pure Rayleigh-Taylor mode can not explain all features of the instabilities observed experimentally. A sheared poloidal plasma flow has been measured and the effect of this on plasma instabilities will be presented in the paper.    [Preview Abstract]

 



CP9.00051: Dynamics of Strongly Correlated Ions in a Partially Ionized Quantum Plasma
Patrick Ludwig , Michael Bonitz , Hanno K\"ahlert , James W. Dufty

A scheme which allows to compute the dynamics of strongly correlated classical ions embedded into a partially ionized quantum plasma by first principles molecular dynamics is presented. The dynamically screened dust approach of Joyce and Lampe [Phys. Rev. Lett. 88, 095006 (2002)] is generalized to quantum systems.[1] The electrons are treated fully quantum-mechanically taking into account their dynamical screening of the ion-ion interaction in linear response on the basis of an extended Mermin formula. The scheme allows to include the effect of the electron dynamics, electron streaming, wake effects and electron magnetization. \\[4pt] [1] P. Ludwig, M. Bonitz, H. Kählert, and J. W. Dufty, J. Phys. Conf. Series 220, 012003 (2010)    [Preview Abstract]

 



CP9.00052: Non-linear Plasma Wakes
I.H. Hutchinson

Objects moving through plasmas give rise to strong plasma perturbations which are vital for understanding space-craft or dusty plasma interactions, for example. If the object is smaller than the Debye length, $\lambda_{De}$, and if ion Landau damping is small because $T_i \ll T_e$, then linearized response theory predicts an oscillatory wake extending over many wavelengths. However, these linearized predictions' accuracy is doubtful, since the floating potential is several times $-T_e/e$. A non-linear computational kinetic-ion treatment of the unmagnetized problem has therefore been undertaken using a 3-D hybrid PIC code, for a spherical object. It shows that while the wavelength of the wake oscillations agrees with the linear approximation ($2\pi v_p /\omega_{pi}$), their amplitude is nonlinearly limited. The wake potential does not exceed typically $\sim 0.2 T_e/e$, no matter how strong the perturbation by the object [i.e.\ its normalized charge $\bar{Q}\equiv Q/(4\pi\epsilon_0 \lambda_{De} T_e/e)$]. Linear response is accurate only for approximately $\bar{Q}<0.02$, which means the wake of a floating sphere is linear only if it has a small radius $<0.01 \lambda_{De}$. Larger objects require non-linear calculations in which greater wake damping occurs. The detailed shape of wakes will be presented.    [Preview Abstract]

 



CP9.00053: GENERAL SPHERICAL TORUS

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CP9.00054: Electron-ion collision frequency in very cold plasma
Shannon Dickson , Devin Konecny , Scott Robertson

We have generated very cold plasma in carbon monoxide gas in a large-diameter cooled copper microwave cavity supported within a larger vacuum chamber. The cylindrical cavity is 57 cm in diameter and 61 cm tall and has a microwave resonance at 872 MHz. The cavity wall and the interior CO gas are cooled to 90 K by liquid nitrogen. Earlier experiments showed that CO is an effective electron cooling agent as a consequence of its dipole moment [Phys. Plasmas 17, 033508 (2010)]. With hot-filament discharge currents in the range 1 - 16 mA, densities are in the range 10$^{8}$ - 10$^{9}$ cm$^{-3}$ and electron temperatures are as low as 0.019 eV ($\sim $200 K). At room temperature, the Q of the cavity is reduced from 396 without plasma to 320 with plasma, which provides a measure of the electron-ion collision frequency. Experiments are continuing with cooled plasma to make the first measurements of the electron-ion collision frequency at these low temperatures.    [Preview Abstract]

 



CP9.00055: Status of the the Lithium Tokamak eXperiment (LTX)
R. Majeski , L. Berzak , S. Gershman , E. Granstedt , C.M. Jacobson , R. Kaita , T. Kozub , B. LeBlanc , N. Logan , D.P. Lundberg , M. Lucia , K. Snieckus , D. Sobers , J. Timberlake , L. Zakharov , T. Gray , R. Maingi , K. Tritz , L.R. Baylor , C.E. Thomas , V. Soukhanovskii , M. Nieto

LTX is a modest spherical tokamak with R=0.4 m, a=0.26 m, and $\kappa $=1.5. Design targets are a toroidal field of 3.2 kG, plasma current up to 400 kA, and a discharge duration of 100 msec. LTX is the first tokamak designed to investigate modifications to equilibrium and transport when global recycling is reduced to 10 -- 20{\%}. LTX is fitted with a heated (up to 500 C) shell, conformal to the last closed flux surface, over 85{\%} of the plasma surface area. The plasma-facing surface of the shell will be evaporatively coated with a thin ($<$ 100 micron) layer of molten lithium, retained by surface tension. A second shell has been constructed, and plasma-sprayed with molybdenum as a high-Z substrate for the lithium. LTX is thus the first tokamak designed to operate with a full hot high-Z wall. First operation with a liquid lithium film wall is scheduled for Summer 2010; results will be presented.    [Preview Abstract]

 



CP9.00056: Quantification of Eddy Currents and Their Effects on Plasma Start-up in a Conducting, Double-walled Spherical Tokamak
L. Berzak , R. Kaita , T. Kozub , N. Logan , R. Majeski , J. Menard , L. Zakharov

The Lithium Tokamak eXperiment (LTX) is designed to investigate the novel, low-recycling lithium wall operating regime for magnetically confined plasmas. LTX reaches this regime through a heated shell coated with liquid lithium internal to the vacuum vessel and conformal to the plasma last-closed-flux surface. This structure is closely coupled to the plasma, highly conductive, and not axisymmetric. The three-dimensional nature of the shell causes the eddy currents and resultant magnetic fields to be three-dimensional as well. An extensive array of magnetic diagnostics has been designed with three-dimensional capabilities and implemented to quantify the temporal history and magnitude of error fields due to the large eddy currents. Primary sources and paths of eddy currents have been elucidated. To further quantify eddy currents and to develop a means of mitigating their effect during the low density, low temperature plasma start-up phase, two- and three-dimensional electromagnetic codes have been developed. Data analysis coupled with simulations has led to a successful approach to plasma start-up in the presence of these non-axisymmetric eddy currents.    [Preview Abstract]

 



CP9.00057: 3-D Modeling of Magnetic Fields for the Lithium Tokamak eXperiment
N. Logan , L. Berzak , R. Kaita , R. Majeski , J. Menard , L. Zakharov

The Lithium Tokamak eXperiment (LTX) is designed to investigate low-recycling operating regimes by surrounding 85{\%} of the last closed flux surface with liquid lithium evaporated onto a copper and stainless steel shell conformal to the plasma. Fields generated by currents in this conducting shell have significant effects on magnetic configurations. To understand these effects, the commercially available code Aether [http://www.fieldp.com] is used to simulate time varying magnetic fields in a 3-D model of LTX. The model is built using LTX CAD files and divided into a regular mesh for computing the evolution of coupled electromagnetic vector quantities through time and space. Applicable boundary conditions and symmetries are analyzed. Comparisons with measured data, results from a 2-D code, and results from a 3-D code designed specifically for LTX demonstrate the possible benefits and limitations of using this commercial code.    [Preview Abstract]

 



CP9.00058: Molecular Cluster Injection for High-Density Fueling on the Lithium Tokamak eXperiment (LTX)
D.P. Lundberg , R. Kaita , R. Majeski , D.P. Stotler

LTX is designed to reduce global recycling, by reducing the neutral hydrogen density in the plasma edge with a liquid lithium wall. Gas-based fueling systems, such as wall-mounted gas puffers or supersonic gas injectors, are ill-suited for use in a low-recycling plasma, as they source a significant amount of gas into the plasma edge. Following experiments on the HL-2A tokamak by Yao, et al. (Nucl. Fusion 47(2007) 1399), a Molecular Cluster Injector (MCI) was designed to supply a high-density, collimated fueling source for LTX. When operated with H$_{2}$ backing pressures of 50-150psia, a 4ms MCI pulse produces molecular densities of 1-4x10$^{16}$ cm$^{-3}$ at distances over 20cm from the nozzle, and supplies a particle flux of 340-775 torr-lit/s, sufficient to replace the predicted LTX particle inventory. The H$_{2}$ density profiles are consistent with flows that produce molecular clusters of a few hundred molecules each, which is expected to improve neutral penetration into the plasma core, relative to pure gas-phase injection. The neutral penetration into LTX plasmas will be diagnosed by a fast visible camera with an H$_{\alpha}$ filter, as well as microwave interferometry.    [Preview Abstract]

 



CP9.00059: Spectroscopic Measurements on the Lithium Tokamak eXperiment
Erik Granstedt , Robert Kaita , Richard Majeski , Travis Gray , Rajesh Maingi , Kevin Tritz , Vlad Soukhanovskii

The Lithium Tokamak eXperiment (LTX) is a spherical torus designed to investigate the very low-recycling, liquid lithium wall regime for magnetically confined plasmas. Visible spectroscopic measurements made using two filterscopes (one viewing the center-stack, one the shell edge and molybdenum limiter) give (D$_\alpha$) a qualitative idea of the particle fueling/recycling, (CIII and OII) an indication of progress in LTX wall conditioning, and (LiI) an indication of the lithium-plasma interaction. The reflectivity of the plasma-facing-components hinders accurate quantitative measurements of recycling using D$_\alpha$ emission; the negligible VUV reflectivity of lithium motivates use of Lyman-$\alpha$ emission instead. Three instruments measure Lyman-$\alpha$ emission around most of the poloidal cross-section: two arrays viewing the center stack/inboard shell and outboard shell, and a single diode viewing a molybdenum limiter. The effects of fueling and wall conditioning on Lyman-$\alpha$ emission will be discussed. Lyman-$\alpha$ measurements will be used with a neutral transport code to calculate calculate recycling and the neutral particle deposition profile.    [Preview Abstract]

 



CP9.00060: First Results from the LTX High-Speed Digital Holography System
C.E. (Tommy) Thomas Jr. , L.R. Baylor , S.K. Combs , S.J. Meitner , D.A. Rasmussen , E.M. Granstedt , R. Majeski , R. Kaita

The LTX CO$_{2}$ laser (9.1 microns) digital holography system has been operational in the lab for several months and preparations are underway for installation on LTX. The system uses a nominal 20 Watt CO2 laser and a high-speed infra-red (IR) camera to record holograms in real time with an exposure of 4 $\mu $s or less. A 92{\%} efficient acousto-optic modulator (AOM) with pulse width control down to less than 1 $\mu $s and asynchronously pulsable at rates up to about 1 MHz provides exposure control. The FLIR SC4000 digital IR camera can acquire data at 420 fps at 320 x 256 pixels varying up to 43,000 fps at 4 x 64 pixels. Noise levels as low as 3 nm (3 x 10$^{-4}$ fringes, or an electron density of 8x10$^{11}$ cm$^{-3}$ over a 10 cm path) have been observed in the laboratory, although noise levels are likely to be higher when mounted on an actual fusion experiment. First laboratory measurement results will be presented, along with any first results from operation on LTX, if available.    [Preview Abstract]

 



CP9.00061: The Lithium Tokamak Experiment Thomson Scattering Diagnostic
C.M. Jacobson , R. Kaita , B.P. LeBlanc , R. Majeski , T. Strickler

The Lithium Tokamak Experiment (LTX) is a spherical tokamak designed to study the low-recycling regime though the use of a liquid-lithium coated shell conformal to the last closed flux surface. A low recycling rate is expected to flatten core electron temperature profiles, raise edge temperatures, and strongly affect electron density profiles. A Thomson scattering diagnostic is used to measure radial $T_{e}$ and $n_{e}$ profiles. The system uses a 15 J, 30 ns pulsed ruby laser and measures profiles of up to 16 radial points on the horizontal midplane at a single temporal point for each discharge. Scattered light is imaged though a spectrometer into an intensified CCD. Two transmission gratings are available for the spectrometer to increase temperature range. In order to protect optical windows from becoming coated with lithium, the system uses automated shutters and gate valves. Preliminary measurements will be presented.    [Preview Abstract]

 



CP9.00062: Langmuir probe diagnostics on the Lithium Tokamak Experiment (LTX)
M. Lucia , S. Gershman , D. Sobers , R. Kaita , R. Majeski , L. Berzak , C.M. Jacobson , T. Kozub , D.P. Lundberg , R. Marsala , K. Snieckus , J. Taylor

Experiments on LTX will provide the first data from a tokamak with liquid lithium as the main ($\sim $90{\%} surface coverage) plasma-facing component (PFC). Previous work on the Current Drive Experiment Upgrade has suggested that a low-recycling lithium wall would dramatically alter edge plasma temperature and density. A Langmuir probe diagnostic has been constructed to measure these plasma parameters in the scrape-off layer on the midplane of LTX. The probe assembly has four cylindrical tips, constituting a floating probe, a swept single probe, and a swept double probe. Analysis of probe characteristics will be presented to compare the edge plasma parameters with and without lithium PFC operation. Langmuir probe tips were designed to limit and tolerate build-up of lithium and lithium oxide surface coatings, as they affect probe results in poorly understood ways. The effects of any coatings that form will be discussed.    [Preview Abstract]

 



CP9.00063: Characterization of lithium evaporators for LTX
M. Nieto-Perez , R. Majeski , J. Timberlake , D. Lundberg , R. Kaita , B. Arevalo-Torres

The presence of lithium on the internal components of fusion devices has proven to be beneficial for reactor performance. The Lithium Tokamak Experiment (LTX) will be the first experimental fusion device operating with a significant portion of its internal surface coated with lithium. One of the key capabilities in the device is the reliable production of lithium films inside the reactor. This task is accomplished with the use of lithium evaporators, specially designed for LTX using resistively heated yttria crucibles. In the present work, results from the operation of one of these evaporators on a separate test stand are presented. Deposition measurements at different power levels were performed using a quartz crystal deposition monitor, and temperature distributions in the evaporator crucible and its content were obtained using an infrared camera and a dip-in thermocouple probe. Modeling of the evaporation cloud was done with the raytracing software OptiCAD, and comparisons between the computations and the temperature and flux measurements were performed, in order to accurately predict spatial lithium deposition rates in different locations of the LTX device.    [Preview Abstract]

 



CP9.00064: Performance of 200~kW Diagnostic Neutral Beam
E. Schartman , E.L. Foley , F. Levinton , J. Kwan , K.N. Leung , R. Wells , Y. Wu , H. Vainionpaa

The interaction of neutral beam atoms with a magnetized plasma provides diagnostic access to the interiors of fusion experiments. Measurable parameters include ion temperature and velocity, density fluctuations and also local magnetic field direction. Nova Photonics, Inc and Lawrence Berkeley National Laboratory are developing a diagnostic neutral beam for use in fusion experiments which lack neutral heating beams, or on which a heating beam is not suitable for diagnostics. Our beam was designed to produce a 1~s duration, 5~x~8~cm elliptical cross section hydrogen beam at energies up to 40~kV and up to 5~A current. Details of the beam performance at 40~kV operation will be presented. The accelerator grids will be re-gapped to operate at 15-20~kV for deployment on the Lithium Tokamak Experiment. Simulations of the re-gapped grids and initial performance will be presented. This work is supported by the U.S. DOE under grant DE-FG02-05ER86256.    [Preview Abstract]

 



CP9.00065: The {\sc Pegasus} Toroidal Experiment program
A.J. Redd , J. Barr , M.W. Bongard , M.G. Burke , R.J. Fonck , E.T. Hinson , D.J. Schlossberg , K.E. Thome

The {\sc Pegasus} program is developing nonsolenoidal startup and growth techniques for tokamaks, and exploring plasma stability at near-unity aspect ratio. Helicity injection from localized current sources (plasma guns) in the plasma periphery have produced $I_p \ge$ 0.17MA to date, consistent with helicity balance and Taylor relaxation constraints. Compact passive electrodes can also be used for helicity injection and $I_p$ growth, given a tokamak discharge already formed by the plasma guns. During helicity injection, the plasma edge exhibits bursty low-n MHD activity and ion spectroscopy shows strong ion heating, consistent with turbulent magnetic relaxation processes. After gun shutoff, the plasmas are MHD quiescent, and $I_p$ can be grown and sustained above 0.20 MA, due to formation of sheared magnetic profiles in the core region. Efficient handoff from helicity injection to inductive drive requires relatively slow $I_p$ rampup during helicity injection, to build up significant core current density. Plasma stability is dominated by peeling-like modes at large jedge/B, and large-scale low-m/n=1 core activity. Probe-measured edge profiles constrain equilibrium fits, and allow direct tests of peeling-ballooning theory.    [Preview Abstract]

 



CP9.00066: Equilibrium and Stability Properties of \textsc{Pegasus} Edge Plasmas
M.W. Bongard , J.L. Barr , R.J. Fonck , E.T. Hinson , A.J. Redd

ELM-like filamentary edge instabilities are observed under conditions of high ${j_\parallel } \mathord{\left/ {\vphantom {{j_\parallel } B}} \right. \kern-\nulldelimiterspace} B$ ($\ge $ 1 MA/m$^{2}$T) in \textsc{Pegasus}. Their properties include: a high-$m$, low-$n$ (1--5) electromagnetic signature, consistent with $m \mathord{\left/ {\vphantom {m n}} \right. \kern-\nulldelimiterspace} n\simeq q_a $; characteristic frequencies $<$ 100 kHz; high poloidal coherence; rotation; and, explosive filament detachment followed by accelerating outboard radial propagation. Presently, these modes' dependence on the peeling instability parameter ${j_\parallel } \mathord{\left/ {\vphantom {{j_\parallel } B}} \right. \kern-\nulldelimiterspace} B$ is being systematically studied through variation of ${\partial I_p } \mathord{\left/ {\vphantom {{\partial I_p } {\partial t}}} \right. \kern-\nulldelimiterspace} {\partial t}$ and I$_{TF}$. To date, all data indicate these instabilities lie in the peeling regime. The modest edge $T_e $ and short pulse lengths of \textsc{Pegasus} afford direct diagnostic access to the edge via internal magnetic and Langmuir probe measurements. A novel edge probe utilizing a radial array of Hall-effect sensors\footnote{ M.W. Bongard \textit{et al.,} accepted for pub. in Rev. Sci. Instrum. (2010)} measures $B_z (R,t)$ with high spatial and $\sim $50 $\mu s$ temporal resolution, and provides strong experimental constraint on $j(\psi )$ in equilibrium reconstructions on ELM-relevant timescales. Initial magnetic equilibrium reconstructions and ideal stability analysis with DCON imply instability when edge filamentation occurs.    [Preview Abstract]

 



CP9.00067: Plasma Properties in the \textsc{Pegasus} Edge Region
E.T. Hinson , M.W. Bongard , R.J. Fonck , B.A. Kujak-Ford , G.R. Winz

The plasma edge region in the \textsc{Pegasus} ST exhibits: peeling modes at high ${j_\parallel } \mathord{\left/ {\vphantom {{j_\parallel } B}} \right. \kern-\nulldelimiterspace} B$; broadband electrostatic turbulence; and strong deformation due to large-scale internal tearing modes. In addition, local helicity injection sources in the edge give rise to large current densities in the plasma scrapeoff, and potentially to a large non-axisymmetric edge current distribution. To address these issues, electrostatic and magnetic probes are deployed to measure the edge characteristics. A pair of scanning Langmuir probes measure edge $n_e $, $T_e $, and $p_e $ in ohmic discharges. For an ohmically driven plasma with $I_p =125$ kA, $B_T =0.15$ T, time-average profiles indicate $n_e =9$ eV, $T_e =$ 7x10$^{18}$ m$^{-3}$ at the radial location of the plasma limiter. A new 3-axis magnetic probe array is under consideration to measure ${j_\parallel } \mathord{\left/ {\vphantom {{j_\parallel } B}} \right. \kern-\nulldelimiterspace} B$ in the edge of ohmic and helicity-driven discharges. This $j_\parallel (R,t)$ is of special interest for quantifying helicity-driven Taylor relaxation states.    [Preview Abstract]

 



CP9.00068: Ion Temperature Measurements in the \textsc{Pegasus} Toroidal~Experiment
M.G. Burke , M.W. Bongard , R.J. Fonck , D.J. Schlossberg

Ion temperature measurements are being made on the \textsc{Pegasus}~Toroidal~Experiment in OH and helicity-injection driven plasmas using thermal Doppler broadening of emission spectra. The system consists of a 0.75 meter~monochromator~with UV sensitive optics, an image intensifier, and a high speed imaging system that can achieve a 5 kHz frame rate.~Presently the system achieves a spectral resolution of 0.21 {\AA}, and collects light over a single radial chord. Of particular interest is the ion temperature evolution during non-solenoidal startup using point source helicity injection. Turbulent magnetic reconnection during helicity injection is expected to provide strong ion heating, as seen in lab and astrophysical plasmas. Indeed, $\left\langle {T_i } \right\rangle $ is measured to be $\sim $ 0.5 keV while $\left\langle {T_e } \right\rangle $ is estimated to be $\le 0.1$ keV from passive impurity spectroscopy. Presently the system is used to compare the $T_i $ evolution of plasmas produced through helicity injection, OH drive, and hybrid current drive scenarios. Future upgrades will provide plasma rotation measurements using multiple tangential views in \textsc{Pegasus}.    [Preview Abstract]

 



CP9.00069: Study of Impurities in the \textsc{Pegasus} Toroidal~Experiment
K.E. Thome , A.S. Dowd , R.J. Fonck , D.J. Schlossberg

In the \textsc{Pegasus} experiment, three distinct operating regimes are currently under study: 1) ohmic heating; 2) helicity injection from local arc guns in the plasma edge; 3) and helicity-driven startup followed by ohmic drive. The levels and roles of impurities are significant for each regime. They are of particular importance in helicity-driven plasmas due to the presence of local plasma gun injectors in the scrape-off region. Plasma impurities are monitored by: a 32 channel AXUV bolometer diode array to determine $P_{RAD} $; a visible bremsstrahlung spectrometer to determine $\left\langle {Z_{eff} } \right\rangle $; and a SPRED VUV spectrometer to identify the impurity species. Ohmic plasmas show very low radiated power, with VUV spectra dominated by O emission. Helicity driven plasmas show strong N and O emissions, which presumably arise from interaction with the guns' BN shields. Determination of absolute impurity concentration is in progress. Qualitatively, it is noted that plasmas with handoff from helicity to ohmic drive do not show radiative collapse, despite $P_{RAD} $ levels comparable to that of a purely helicity-driven plasma.    [Preview Abstract]

 



CP9.00070: Low-m Tearing Mode Studies on \textsc{Pegasus}
J.L. Barr , M.W. Bongard , R.J. Fonck , B.T. Lewicki , A.J. Redd

Large scale, low-m/n=1 tearing activity is commonly observed in ohmic discharges on \textsc{Pegasus}. Accentuated by broad regions of low magnetic shear, this tearing activity can limit performance in high TF utilization regimes (${I_p } \mathord{\left/ {\vphantom {{I_p } {I_{TF} }}} \right. \kern-\nulldelimiterspace} {I_{TF} }\approx$ 1) where $q_0$ is a low-order rational. In addition to increasing TF to raise $q_0 $, tearing activity can be mitigated by: TF ramp-downs; electrostatic preioniziation to obtain OH breakdown at lower TF; and, DC helicity injection to provide strong edge current drive. Systematic scans of TF, $I_p$, and ${\partial I_p } \mathord{\left/ {\vphantom {{\partial I_p } {\partial t}}} \right. \kern-\nulldelimiterspace} {\partial t}$ are presently being conducted to characterize these modes under a range of operational conditions. Measurements of magnetic activity via internal Mirnov probes are complicated by electrostatic noise arising from \textsc{Pegasus'} high-frequency switching power supplies. This noise can be mitigated somewhat by shielding and signal processing, but can be eliminated altogether by freewheeling all power supplies for a brief period.    [Preview Abstract]

 



CP9.00071: Design of the Thomson Scattering Diagnostic on the \textsc{Pegasus} Toroidal Experiment
D.J. Schlossberg , R.J. Fonck , B.A. Kujak-Ford , B.T. Lewicki , J.I. Moritz

A critical question concerning use of point-source helicity injection for non-inductive startup is whether, as $I_p $ increases, energy confinement is dominated by cross-field transport or by parallel losses due to field line stochasticity. Furthermore, resistively-driven helicity dissipation during plasma formation must be characterized. Both of these topics are important for predictive scaling to larger tokamaks. In addition, $T_e $ and $n_e $ profiles are needed for accurate magnetic equilibrium reconstructions at high $\beta _T $ and $I_N $. To resolve these issues, a Thomson scattering diagnostic is being developed for the \textsc{Pegasus} Toroidal experiment. The design is guided by systems on MST\footnote{ J.A. Reusch, et al. RSI \textbf{79}, 10E733 (2008)} and HSX.\footnote{ K. Zhai, et al. RSI \textbf{75}, 10 (2004)} Scattered light from an incident Nd-YAG laser ($\lambda =1064$ nm) will be detected by a polychromator system. Implementation on \textsc{Pegasus} will measure $n_e $ and $T_e $ at $\ge $ 10 radial locations for plasmas with $n_e \ge $ 10$^{19}$ m$^{-3}$ and $T_e \quad \sim $ 10 eV -- 1 keV, with radial resolutions of $\sim $1.75 cm and 5 cm for fine and coarse configurations, respectively.    [Preview Abstract]

 



CP9.00072: Numerical Simulation of Non-inductive Startup in the Pegasus Toroidal Experiment
J.B. O'Bryan , C.R. Sovinec , T.M. Bird

Nonlinear numerical computation is used to investigate DC helicity injection from washer-gun plasma sources in the Pegasus Toroidal Experiment (Univ. of Wisconsin). Resistive MHD simulations with the NIMROD code (nimrodteam.org) are used to model non-inductive startup, with emphasis on the relaxation of the non-axisymmetric current channels into a ``tokamak-like'' plasma. Simulations utilize fully three-dimensional, anisotropic, temperature-dependent thermal conductivity corrected for regions of low-magnetization [Braginskii, Reviews of Plasma Physics, 1965], temperature-dependent resistivity, and Ohmic heating. Off-diagonal Fourier-component coupling is investigated as a means of improving preconditioning of the temperature advance.    [Preview Abstract]

 



CP9.00073: Full-wave Modeling of EBWs in Pegasus
Sara Gallian , Michael Bongard , Francesco Volpe , Jonathan Jacquot , Alf K\"ohn

We model the injection of ordinary(O) and extraordinary(X) waves at 2.45GHz, their conversion in Electron Bernstein Waves(EBWs) and the initial propagation of EBWs in the Pegasus spherical torus, by means of the recently improved IPF-FDMC finite-difference-time-domain Maxwell-fluid solver. Simulations are performed in 2D in cylindrical and Cartesian coordinates, in a poloidal, horizontal or ``oblique'' cut (at the magnetic pitch inclination, where the OXB conversion is most efficient). The OXB and XB conversion efficiencies are evaluated for various antenna designs and launch geometries. Reflections from the wall and collisions at the upper hybrid are included. The motivation for the full-wave approach is that the O and X vacuum wavelength (12cm) is comparable with the plasma radius(30-45cm). EBWs, however, develop a short wavelength fulfilling the ray tracing approximation. For this reason, EBW wavefronts are separated from the long-wavelength O and X-mode by means of high-pass spatial filtering of the full-wave results. Then, local wave-vectors are defined, that might serve as initial conditions for future ray tracings including absorption.    [Preview Abstract]

 



CP9.00074: Double null merging start-up experiments on UTST
Takuma Yamada , Shuji Kamio , Keita Abe , Morio Sakumura , Qinghong Cao , Naoto Suzuki , Takenori Watanabe , Michiaki Inomoto , Yuichi Takase , Yasushi Ono , Ryota Imazawa , Koji Ishiguchi

The University of Tokyo Spherical Tokamak (UTST, Univ. Tokyo) is a unique device in the world that demonstrates merging start-up of spherical tokamak (ST) by using double null merging (DNM) method. Unlike the other plasma merging devices, such as MAST (UKAEA) and TS-3/4 (Univ. Tokyo), the poloidal field coils of UTST are located outside the vacuum vessel, for the purpose of more reactor-relevant merging startup. The goals for the UTST experiment are to generate a high-beta ST through magnetic reconnection, and to sustain it by external heating such as neutral beam injection. Using the present power supply under construction, we successfully demonstrated the DNM start-up whose plasma current and the duration time are 40 kA and 0.6 ms. We increased them to 120 kA and 1.2 ms, respectively, by using a central solenoid coil in addition to the DNM discharge. Our 2D magnetic probe array composed of 290-channel pickup coils directly measured field line reconnection of two merging ST plasmas and its heating power of 1.7 MW using jxB plasma pressure.    [Preview Abstract]

 



CP9.00075: Multipoint spectroscopy measurement of spherical tokamak heating by plasma merging method in UTST
Shuji Kamio , Qinghong Cao , Keita Abe , Morio Sakumura , Naoto Suzuki , Takenori Watanabe , Koji Ishiguchi , Ryota Imazawa , Takuma Yamada , Michiaki Inomoto , Yuichi Takase , Yasushi Ono

Temporal evolutions of ion temperature/flow were observed to investigate the heating effect of the plasma merging in the UTST device by using a multipoint Doppler spectroscopy measurement system. The bulk plasma ion temperature measured by carbon impurity line was about 15-25 eV after the plasma merging, indicating that the ion heating was not significant in the present experimental condition. However, anomalous rise in the carbon line width was observed in the early phase of the plasma merging. Since the carbon impurity emission comes from the X point and also from the vicinity of the center stack, we assumed that the broadened spectrum contains the radially bi-directional outflow component near the X point and the stationary component near the center stack. The estimated outflow velocity from the spectroscopy was about 24 km/s, which showed good agreement with the Alfven velocity of 22 km/s and the velocity of the reconnected field line motion of 35 km/s.    [Preview Abstract]

 



CP9.00076: Application of electric double layer capacitor to sec-order DC power supply for plasma confinement experiments TS-3 and UTST
K. Abe , M. Inomoto , T. Yamada , A. Kuwahata , S. Kamio , M. Sakumura , Q.H. Cao , T. Watanabe , N. Suzuki , R. Imazawa , Y. Ono

Electric double layer capacitor (EDLC) is an electrochemical capacitor which has much higher energy density and larger capacity compared with conventional capacitors and applied as energy-storage devices in electric vehicles and so on. In this research, we developed a new application of the EDLC to a sec-order quasi-DC power supply like flying-wheel motor-generators. We employed an EDLC with capacity of 29.4 F and the voltage and current ratings of 100 V and 100 A, respectively and constructed an EDLC power supply for equilibrium coils of magnetically confined plasma experiments. This EDLC-type DC power supply is about one-order cheaper than the conventional flying-wheel motor-generators. We demonstrated its initial operation with peak current of 100 A and duration time of 3 s. We applied the EDLC power supply for the TS-3 device and confirmed the plasma discharge operation. The EF coil current waveform has flat top duration of about 1 s, which is much longer than TS-3 and other fusion plasma experiments.    [Preview Abstract]

 



CP9.00077: Physical Design and Transport Simulation of the STOR-U Tokamak
Dazhi Liu , Chijin Xiao , Akira Hirose

The Saskatchewan TORus Upgraded (STOR-U) tokamak is a new spherical tokamak (ST) with tight aspect ratio = 1.7, plasma major/minor radius = 55/32 cm, plasma current 2 MA and 1.5 T toroidal field. The research scope of the STOR-U project covers ST engineering, high $\beta$ plasma confinement and transport, advanced plasma fueling by compact torus injection, helicity injection for plasma start-up and development of advanced plasma diagnostics. In this presentation, design and numerical studies on STOR-U toroidal/poloidal field systems are described. Various plasma equilibria have been obtained to meet the discharge requirements through variation in elongation, ($k \leq 3$), triangularity ($\Delta \leq 0.5$) and divertor configurations. The poloidal coil current waveforms have been determined for plasma breakdown and start-up. In addition, STOR-U plasma transport simulations have been carried out using the ASTRA code. The results reveal that, compared with purely ohmic heating, 3MW NBI heating significantly increases both $T_i$ and $T_e$ by $46\%$ and $15\%$, achieving 2.4 and 2.2 $keV$ (at center), respectively. Bootstrap current ratio, $f_{bs}$, is larger than $50\%$. Results of simulation with different transport models are also presented.    [Preview Abstract]

 



CP9.00078: An atmospheric pressure air plasma source for polymer surface modification
Shujun Yang , Jiansheng Tang

An atmospheric pressure air plasma source was generated through dielectric barrier discharge (DBD). The plasma source was characterized on electron density, emission spectrum, and ozone density. The modification of polyethyleneterephthalate (PET) surfaces by this plasma was investigated. PET strips were exposed to the plasma at the exit of the plasma source. Water contact angles were measured for surfaces modified with different processing parameters. The contact angle could drop from 70 to 37 degrees within less than one second of modification. The change in contact angles was monitored as a function of time. The surface modification was found to be mainly a chemical and photochemical process.    [Preview Abstract]

 



CP9.00079: PINCH PHYSICS

   [Preview Abstract]

 



CP9.00080: Beryllium liner z-pinches for Magneto-Rayleigh-Taylor studies on Z
R. McBride , S. Slutz , C. Jennings , D. Sinars , R. Lemke , M. Martin , R. Vesey , M. Cuneo , M. Herrmann

Magnetic Liner Inertial Fusion (MagLIF) [S. A. Slutz, \textit{et al.}, Phys. Plasmas \textbf{17} 056303 (2010)] is a promising new concept for achieving $>$100 kJ of fusion yield on Z. The greatest threat to this concept is the Magneto-Rayleigh-Taylor (MRT) instability. Thus an experimental campaign has been initiated to study MRT growth in fast-imploding ($<$100 ns) cylindrical liners. The first sets of experiments studied aluminum liner implosions with prescribed sinusoidal perturbations (see talk by D. Sinars). By contrast, this poster presents results from the latest sets of experiments that used unperturbed beryllium (Be) liners. The purpose for using Be is that we are able to radiograph ``through'' the liner using the 6-keV photons produced by the Z-Beamlet backlighting system. This has enabled us to obtain time-resolved measurements of the imploding liner's density as a function of both axial and radial location throughout the field of view. This data is allowing us to evaluate the integrity of the inside (fuel-confining) surface of the imploding liner as it approaches stagnation.    [Preview Abstract]

 



CP9.00081: Results from magneto-Rayleigh-Taylor Instability Experiments on Thin Foils Driven by a 1-MA LTD
J.C. Zier , S.G. Patel , A.M. Steiner , R.M. Gilgenbach , D.M. French , M.R. Gomez , Y.Y. Lau , M.G. Mazarakis , M.E. Cuneo , M.R. Lopez

Foils are under investigation as imploding liners for magnetized target fusion. We report our latest design and experimental progress on the magneto-Rayleigh-Taylor instability. Planar foils driven by the 1-MA LTD, MAIZE, are the dynamic loads for this investigation. Initial experiments utilized 400 nm Al foils accelerated by asymmetric placement between return current plates. Diagnostic deployment, transmission line and load hardware, and experimental progress will be presented.    [Preview Abstract]

 



CP9.00082: A Theoretical Study of Anisotropy in the magneto-Rayleigh-Taylor Instability (MRT) on a Thin Foil
Y.Y. Lau , J.C. Zier , I.M. Rittersdorf , R.M. Gilgenbach , S.G. Patel , A.M. Steiner , M.R. Gomez , M.E. Cuneo , S. Slutz , A.L. Velikovich , D. Colombant

MRT on foils is expected to be different from the conventional Rayleigh-Taylor instability by the presence of the unidirectional current that drives MRT. In one configuration, two return-current plates on opposite sides of the foil are used to accelerate the foil. The MRT growth can then be controlled by the foil's initial position. However, the effects of the magnetic field on either side of the foil will be different, and time-varying. We have used a simple MHD model to analyze this configuration. Issues such as anisotropy and feedthrough are studied, thus illustrating the differences and similarities on Rayleigh-Taylor growth driven by magnetic pressure and by gas pressure.    [Preview Abstract]

 



CP9.00083: Plasma Spectroscopy of the Double Post-Hole Convolute on Sandia's Z-Machine*
Matthew Gomez , Ron Gilgenbach , Mike Cuneo , Mike Lopez , Greg Rochau , Ryan McBride , Jim Bailey , Pat Lake , Yitzhak Maron

In large-scale pulsed power systems, post-hole convolutes combine current from several magnetically insulated transmission lines just before the load. Current losses in the convolute and the final feed gap on the Z-Machine have been measured in some cases to be as high as 10-20{\%}. The goal of these experiments is to characterize plasma conditions in the convolute in an attempt to correlate the plasma formation with current losses. Preliminary data show sharp onset of strong continuum emission and a number of spectral-line absorption features. LiF was deposited onto convolute components as a localized dopant to confirm the origin of the these emissions. Experimental results as well as simulated spectra from PrismSpect will be presented. *MRG sponsored by SSGF through NNSA. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the US DOE's NNSA under contract DE-AC04-94AL85000.    [Preview Abstract]

 



CP9.00084: Incident Wire Array Z-pinch Plasma Radiation Fluence Effects on the Filter Material Property {\&} Implications on the Observed Radiation Parameters
Y.K. Chong , J. Thornhill , A. Velikovich , J. Giuliani , J. Davis , R. Clark , D. Ampleford , C. Coverdale , B. Jones

The wire array Z-pinches on the refurb. Z are marked by an intense bright emission of high energy non-LTE photons. In order to diagnose the radiation in such a hostile environment, a number of materials w/ varying composition are used to provide select optimized radiation filtering. Traditionally, the various radiation parameters are determined from the deconvolution of the actual observed values using an appropriate time invariant filter response function (FRF). Under exposure to the radiation, however, the materials may undergo significant changes. We examine the response of various filters to an intense radiation from the plasmas. A MHD+multifreq. rad. x-port code is employed to establish the time varying non-LTE radiation {\&} to investigate the evolution of the materials subject to the field. A characterization of the material EOS/FRF is made {\&} their effect on the radiation characteristics are quantified w/ a goal of optimized filter design/deployment.    [Preview Abstract]

 



CP9.00085: Spectroscopic study of z-pinch stagnation
B. Jones , C.A. Jennings , E.P. Yu , S.B. Hansen , G.A. Rochau , J.E. Bailey , C.A. Coverdale , D.J. Ampleford , M.E. Cuneo , Y. Maron , V. Fisher , V. Bernshtam , A. Starobinets , L. Weingarten

Fast z-pinches provide intense 1-10 keV photon energy radiation sources. Here, we analyze time-, space-, and spectrally- resolved $\sim$2 keV K-shell emissions from Al (5$\%$ Mg) wire array implosions on Sandia$'$s Z machine pulsed power driver. The stagnating plasma is modeled as three separate radial zones, and collisional-radiative modeling with radiation transport calculations are used to constrain the temperatures and densities in these regions, accounting for K-shell line opacity and Doppler effects. We discuss plasma conditions and dynamics at the onset of stagnation, and compare inferences from the atomic modeling to three-dimensional magneto-hydrodynamic simulations.    [Preview Abstract]

 



CP9.00086: Three-dimensional simulations of wire-array Z pinch stagnation
Edmund Yu , Yitzhak Maron , Brent Jones , Mike Cuneo , Chris Jennings , Dawn Flicker

Detailed understanding of the stagnation process of an imploding wire-array Z pinch has been hampered by its complicated 3D nature, which would seem to preclude use of the usual 1D models of stagnation. However, the 3D connected nature of the Z pinch's trailing mass network also endows the wire array with certain properties which might allow a 1D description. In this work we explore the applicability of simple 1D pictures of stagnation, such as the Noh shock stagnation and isentropic compression, to 3D wire array simulations. We also discuss the role of the magnetic field, ram pressure, and angular momentum during the stagnation process. Finally, we comment on implications for measuring the ion temperature.    [Preview Abstract]

 



CP9.00087: Kelvin-Helmholtz instability in magnetized high-energy density plasma
Radu Presura , Sandra Stein , David Martinez , Showera Haque , Leela O'Brien

Sheared flows perpendicular to a magnetic field often produce the Kelvin-Helmholtz instability (KHI) which mediates mixing across the magnetic field. This was observed, for example, at the interaction of the solar wind with the earth's magnetotail. An experiment was performed on the NTF Zebra z-pinch generator to investigate the KHI development in magnetized high energy density plasma. In an initially planar configuration, plasma flows were generated with sets of parallel wires inclined with respect to the median plane of the pinch. The flow was directed towards an ohmically heated and ablated metallic foil placed in the median plane. Due to the interaction with the plasma formed on the foil surface, the flow was redirected along the foil and acquired a transverse velocity gradient. Vortices characteristic to the KHI were observed.    [Preview Abstract]

 



CP9.00088: Plasma Temperature Estimates from EUV Spectroscopy of an Aluminum Rod pulsed with MA Current
Stephan Fuelling , Tom J. Awe , Bruno S. Bauer , Irvin R. Lindemuth , Richard E. Siemon , Kevin C. Yates

Plasma formation on the surface of aluminum rods driven by Zebra, a 1 MA, 100 ns rise time driver, resulting in a magnetic field between 1.5 - 4 MG has been studied. Plasma forms when the surface magnetic field reaches about 2.2 MG. This threshold is important for applications in magneto inertial fusion and magnetic insulated transmission lines of pulsed power systems. In particular, we want to understand the behavior of the inner liner surface in liner compression experiments of a field-reversed-configuration plasma performed at Shiva Star, AFRL, Albuquerque, New Mexico. Extreme ultraviolet (EUV) emission spectra from the aluminum surface were compared to PrismSPECT modeled spectra to determine the plasma temperature. In addition, EUV photodiodes with directly deposited filters were used to measure radiated power. For 1 mm diameter aluminum rods the temperature was estimated as $\ge $15 eV which is in agreement with temperature estimates from measurements in the visible and with radiation-MHD modeling.    [Preview Abstract]

 



CP9.00089: Development of absorption spectroscopy for wire-array Z-pinches
A. Anderson , V.V. Ivanov , P. Hakel , R.C. Mancini , P. Wiewior , T. Durmaz , A.L. Astanovitskiy , O. Chalyy , S.D. Altemara , D. Papp , E. McKee , J.P. Chittenden , N. Niasse , A.P. Shevelko

The 50 TW Leopard laser was coupled with the 1 MA Zebra generator for the x-ray backlighting of wire arrays. The Leopard laser is based on the chirped pulse amplification and can operate in subpicosecond or subnanosecond regimes. Several materials were tested in both regimes and samarium was selected for subnanosecond backlighting in the range of 7-9 {\AA}. One ray of Al wire-arrays was investigated at the ablation and implosion stages. Two focusing conical spectrometers with mica crystals recorded reference and main spectra on x-ray film. Collimators protected spectrometers against the x-ray burst from the main Z-pinch. Comparison of spectra of backlighting radiation with reference spectra indicates absorption lines in the range of 8.2-8.4 {\AA}. The electron temperature of wire-array plasma was estimated from simulations with atomic kinetics models.    [Preview Abstract]

 



CP9.00090: Analysis of Implosion and Radiative Properties of Ag Single Planar Wire Array Z-pinches on Zebra at UNR*
S.F. Keim , A.S. Safronova , V.L. Kantsyrev , A.A. Esaulov , I. Shrestha , M.E. Weller , K.M. Williamson , N.D. Ouart , V. Shlyaptseva , G.C. Osborne

Silver is the highest atomic number element (z = 47) to be investigated for L-shell radiative characteristics at 1.0MA on the Zebra pulsed-power generator at UNR and has been shown to produce radiation yields up to 29kJ in planar wire arrays (PWAs). Silver is also expected to reach the highest electron temperature for PWAs. In order to investigate this more thoroughly, the results of experiments with two Ag single PWA implosions are explored using a full diagnostic suite. In particular, implosion and radiative characteristics of the two single PWA loads, one consisting of eight 15$\mu $m Ag wires (M $\sim $ 296 $\mu $g) and another of nearly identical mass consisting of seven 15$\mu $m Ag wires and one 30$\mu $m Al wire, are analyzed over a broad spectral range, from 15eV to 10keV. Synthetic spectra produced by a new non-LTE kinetic model of Ag are compared to the results of spatially resolved time-integrated x-ray spectroscopy to assess L-shell Ag plasma parameters and their axial gradients. The importance of the continued study of Ag PWAs is also discussed. *This work was supported by NNSA under DOE Cooperative Agreements DE-FC52-06NA27588, DE-FC52-06NA27586, and in part by DE-FC52-06NA27616.    [Preview Abstract]

 



CP9.00091: Comprehensive Analysis of Radiative Properties of Brass and Al Arranged in Nested Cylindrical Wire Arrays*
M.E. Weller , N.D. Ouart , A.S. Safronova , V.L. Kantsyrev , A.A. Esaulov , K.M. Williamson , I. Shrestha , G.C. Osborne , V. Shlyaptseva , S.F. Keim , A. Stafford , C.A. Coverdale

Experimental results of nested cylindrical wire arrays (NCWA) consisting of brass (70{\%} Cu and 30{\%} Zn) wires on one array and Al (5056, 5{\%} Mg) wires on the other array performed on the UNR Zebra generator at 1.0 MA current are compared and analyzed. Specifically, radiative properties of K-shell Al and Mg ions and L-shell Cu and Zn ions are compared as functions of the placements of the brass and Al wires on the inner and outer arrays. A full diagnostic set which included more than ten different beam-lines was implemented. Identical loads were fielded to allow the timing of time-gated pinhole and x-ray spectrometers to be shifted to get a more complete understanding of the evolution of plasma parameters over the x-ray pulse. The importance of the study of NCWAs with different wire materials is discussed. *This work was supported by NNSA under DOE Cooperative Agreements DE-FC52-06NA27588, DE-FC52-06NA27586, and in part by DE-FC52-06NA27616. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.    [Preview Abstract]

 



CP9.00092: Analysis of results of recent implosions of palladium wire loads arranged in single planar wire arrays on Zebra at UNR
A.M. Covington , T. Darling , A.S. Safranova , V.L. Kantsyrev , A.A. Esaulov , I. Shrestha , K.M. Williamson , S. Keim , V. Shylaptseva , G.C. Osborne , M.E. Weller , N.D. Ouart

Experiments with palladium wire loads were performed on Zebra at UNR to understand the implosion and radiative properties of this unique wire material. The loads were planar wire arrays (PWA) arranged in a single row for a uniform load with twelve palladium 10 $\mu $m wires (total mass M $\sim $ 227 $\mu $g) and a combined load with five palladium 25 $\mu $m wires and one aluminum 40 $\mu $m wire (M$\sim $656 $\mu $g). A full diagnostic set which included more than ten different beam-lines was implemented. The implosion of these Pd loads produced a high radiation yield (27 kJ for a heavier load) which is comparable to recently tested Ag PWA loads. The main focus was put on comparison of implosion and radiative characteristics of these two shots and with results for the identical Ag PWA load. Future experiments with modified palladium wires and their applications are discussed.    [Preview Abstract]

 



CP9.00093: Assessment of Proton Deflectometry for Exploding Wire Experiments
S. Bott , M. Wei , D. Mariscal , K. Gunasekera , G. Collins , F. Beg , J. Kindel , A. Covington , R. Presura , N. LeGalloudec , P. Wiewior , C. Plechaty , T. Burris-mog , Y. Paudel , S. Stein , O. Chalyy , A. Astanovitskiy

Determination of B-field structures in pulsed power driven exploding wire experiments is vital to the benchmarking of 3D simulations, but is complicated by the presence of large volumes of hot, dense plasma. Optical and electrical probe diagnostics typically fail early in the experiment. We present progress on a new project which examines the use of proton deflectometry to measure magnetic fields in pulsed power plasmas. Experimental work is carried out at the Nevada Test Facility (NTF) using both 10J 0.3ps Leopard laser and the 1.6MA ZEBRA pulsed power driver. Leopard provided focussed intensities of $\sim$5x10$^{19}$ W cm$^{-2}$, and generated up to 8 MeV protons from thin metallic targets with good reproducibility and low divergence. The first tests of proton beam deflection in pulsed power experiments, along with comparison to initial simulation work will be presented.    [Preview Abstract]

 



CP9.00094: Absorption Spectroscopy of Pulsed Power Driven Metal Plasmas
Patrick Knapp , Sergei Pikuz , Tania Shelkovenko , Adam Cahill , John Greenly , David Hammer

We present here the use of the continuum radiation from X-pinch-produced point x-ray sources for absorption spectroscopy as a new diagnostic to investigate the properties of aluminum plasmas created by pulsed power machines at 500 kA and 1 MA. This technique is being developed to provide a path towards determining time and space resolved plasma parameters (charge state, temperature and density) under conditions that are inaccessible to traditional x-ray spectroscopic diagnostics. The diagnostic apparatus, setup and characterization will be described, including estimates of spatial and spectral resolution. Preliminary results from exploding wires and wire array z-pinches are shown and compared with synthetic spectra. The technique is also applied to the dense core of exploding wires, which is known to exist in a multiphase state and has previously eluded quantitative study. This research is supported by the NNSA SSAA program under DOE Cooperative Agreement DE-FC03-02NA00057.    [Preview Abstract]

 



CP9.00095: Time Resolved Single Wire Aluminum Optical Spectroscopy Experiments
Kate Blesener , Sergey Pikuz , Tatiana Shelkovenko , Isaac Blesener , David Chalenski , David Hammer , Yitzhak Maron , Vladimir Bernshtam

We are exploring the conditions of plasmas generated by current-driven explosions of single fine aluminum wires, including temperatures, electron density, ionization state, and potentially magnetic field, using time-resolved emission spectroscopy at visible wavelengths. The experiments are being carried out with 15$\mu $m to 75$\mu $m Al wires driven by the 10kA, 500ns rise time LCP3 pulser. To determine the magnetic field, a new diagnostic method is being developed which makes use of Zeeman-effect-produced differences in the line shapes of two fine structure components of a multiplet that are equally broadened by Stark and Doppler effects. This method has been demonstrated at the Weizmann Institute of Science in laser-produced plasmas with lower energy densities [1]. \\[4pt] [1] E. Stambulchik, \textit{et al.} Phys. Rev. Lett. \textbf{98}, 225001 (2007).    [Preview Abstract]

 



CP9.00096: Radial Foil Experiments on Cobra with Imposed B-Field
Peter Schrafel , Pierre Gourdain , John Greenly , Bruce Kusse

Previous investigations of exploding radial foils have shown the formation of an axial plasma jet in the early stages of the foil explosion. In this case a thin load foil is pressed at an outer annulus held at ground, and contacted in the center by a small straight rod cathode driven by the 1MA COBRA accelerator. Present experiments focus on the jet development when an externally produced B-field is applied. Some involve a field created by permanent magnets which runs perpendicular to the direction of jet propagation. Here we focus on experiments in which the B-field is created by a Helmholtz-coil configuration with field lines running parallel to the direction of jet propagation in the region of interest. Applied fields range from 0.5-2.0T.    [Preview Abstract]

 



CP9.00097: Double cathode experiments using radial foil configurations on the COBRA generator
B.H. Pang , A.Y. Gorenstein , J.E. Kim , P.-A. Gourdain , D.A. Hammer , B.R. Kusse

As part of the Laboratory of Plasma Studies at Cornell University, our research group has been investigating the dynamics and the collision of plasma bubbles formed by the explosion of metallic foils. A 100-ns rise time 1MA current runs through an aluminum foil, five micron thick, stretched horizontally onto the anode of the COBRA pulsed power generator. Cathode contacts consist of two hollow stainless pins equally spaced about the center of the foil. The parameters of this experiment include the spacing (3 mm) and inclination of the cathode pins (parallel or at a 45 degree angle). During the explosion, plasma bubbles are formed around each pin. As the bubbles grow and collide, interesting features appear in both experiments. For the parallel cathode configuration, a plasma plume forms above the center between the two bubbles before collision occurs. The plume resembles a twisted helix. For the slanted cathode configuration a plasma sheet forms when the two bubbles collide, and possibly a shock front is formed after the collision. The sheet extends inside a vertical plane just above the foil geometrical center. The electron density of this plasma sheet is approximately 5x10$^{18}$ cm$^{-3}$, and its velocity is below 150 km/s.    [Preview Abstract]

 



CP9.00098: Axial Instability Growth in Tungsten Wire Array Z-Pinches
Adam Cahill , Patrick Knapp , John Greenly , Sergei Pikuz , Tania Shelkovenko , David Hammer

The individual exploding wires in wire array z-pinches have been shown to suffer from axially non-uniformity beginning from the moment of plasma formation. This non-uniformity grows in amplitude and wavelength until it reaches what appears to be a material dependent wavelength at the time array implosion begins. Previous work by Knapp et al. [1] studied the temporal evolution of this instability in aluminum wire arrays. We have extended that work to include the evolution of tungsten wire array instabilities. Time gated laser shadowgraphy is used to track wavelength and amplitude over a series of shots to develop a record of the instability's growth. We attempt to identify array parameters which significantly contribute to the growth of this instability. \\[4pt] [1] Knapp, P. F., J. B. Greenly, P. A. Gourdain, C. L. Hoyt, M. R. Martin, S. A. Pikuz, C. E. Seyler, T. A. Shelkovenko, and D. A. Hammer. ``Growth and Saturation of the Axial Instability in Low Wire Number Wire Array Z Pinches.''~\textit{Physics of Plasmas}~17 (2010). Web.    [Preview Abstract]

 



CP9.00099: Experimental r-$\theta $ density profiles of wire-array and cylindrical foil Z-pinches on COBRA
Isaac Blesener , John Greenly , Sergey Pikuz , Tatiana Shelkovenko , Bruce Kusse , Charles Seyler

Calibrated r-$\theta $ ion density profiles from wire-array and cylindrical foil experiments on the 1-MA COBRA machine will be presented. Profiles are axially averaged over the 1-cm height of the array. The data was gathered using an axial X pinch backlighter.\footnote{I.C. Blesener et al., ``Axial x-ray backlighting of wire-array Z-pinches using X pinches'', Rev. Sci. Instrum. 80, 123505 (2009).} Images have better than 5-micron resolution with calibrated ion densities from 10$^{18}$ to 10$^{20}$ cm$^{-3}$. The latest data will be presented, comparing the timing and development of ablation streams and precursor formation between wire-arrays and cylindrical foils. Experimental data will also be compared to simulation results.    [Preview Abstract]

 



CP9.00100: Calibrated areal density measurements of cable-array Z-pinch plasmas at 1 MA
C.L. Hoyt , P.F. Knapp , S.A. Pikuz , T.A. Shelkovenko , P.-A. Gourdain , J.B. Greenly , D.A. Hammer

We present areal density measurements of multi-wire cable-array Z-pinch plasmas obtained using X-pinch x-ray backlighter radiographs. The elements of a cable array are made by twisting 2 - 4 wires into a cable with a twist wavelength ranging from 0.5mm to 4mm. In experiments on the 1 MA COBRA pulsed power generator, the radiographs of the cables displayed density structure not observed in standard wire-array z-pinches, including sharp density gradients in the form of spirals that follow the twisting wires and small scale striations that are the result of an undetermined mechanism. The X-ray radiographs were produced using the 3-5 keV spectral band of Mo X-pinches, which was obtained using 12.5 micron Ti filters. Ag, Ni, Cu and W cable-arrays have been tested, and film exposure was converted to plasma areal density using calibrated step wedges of the test material that were deposited on the Ti filter. X-pinch timing was monitored with 12.5 micron Ti filtered silicon diodes. Laser shadowgraphy and XUV self-emission diagnostics were also employed. This research is supported by the NNSA SSAA program under DOE Cooperative Agreement DE-FC03-02NA00057.    [Preview Abstract]

 



CP9.00101: Current Rise-Rate Scaling for Radial Wire Arrays
M. Mitchell , K. Chandler , S. Bland , F. Suzuki , G. Hall , A. Thomson , A. Lebedev , J. Chittenden , R. McBride , S. Pikuz , T. Shelkovenko , D. Hammer , B. Kusse

Radial wire arrays offer the potential for higher energy density of radiated x-rays compared to cylindrical arrays. Higher radiated energy density would allow for more compact hohlraums thus easing power requirements for ICF. In an effort to explore how radiated power scales with the rise-rate of the current we performed experiments on two 1 MA pulsed power generators with very different rise rates---MAGPIE at Imperial College with about 300 ns rise time and COBRA at Cornell with about 100 ns rise time. Comparisons of radiated power from 16-wire Al and Cu arrays over a range of masses are presented. Results from these initial experiments suggest that radiated power for a given material is similar when implosion times are matched to the current rise time. We also present comparisons of radiated power with modified array geometries such as wire length and cathode diameter. Some results from Ti/Ni and Fe/Ni arrays are also presented.    [Preview Abstract]

 



CP9.00102: Radial foil Z-pinch experiments on the MAGPIE generator
P. de Grouchy , F. Suzuki-Vidal , S.V. Lebedev , G. Swadling , G. Burdiak , S.N. Bland , G.N. Hall , A.J. Harvey-Thompson , E. Khoory , L. Pickworth , J. Skidmore , J.P. Chittenden , M. Bocchi , A. Ciardi , M. Krishnan

The dynamics of plasma formation in a radial foil Z-pinch are presented. The experimental setup consists of a $\mu $m-thick aluminum disc held between two concentric electrodes and subjected to a 1.4 MA, 250 ns current pulse from the MAGPIE generator. The JxB force acts on the ablated plasma from the foil forming a region of enhanced density on the axis. This precedes the pinching of plasma from current-driven magnetic ``bubbles''. The interaction of these features with an argon ambient (N$\sim $10$^{16-17}$ cm$^{-3})$ from a supersonic gas nozzle (Mach$\sim $9), particularly the formation of several shock structures will be presented and discussed.    [Preview Abstract]

 



CP9.00103: End-On Optical Interferometry of Precursor formation in Cylindrical Wire Array Z-Pinches
George Swadling , Sergey Lebedev , Simon Bland , Gareth Hall , Francisco Suzuki-Vidal , Adam Harvey-Thompson , Guy Burdiak , Nicolas Niasse , Louissa Pickworth , Essa Khoory , Philip de Grouchy , Jonathan Skidmore

A laser probing diagnostic system has been developed for applications on the MAGPIE pulsed power generator. This system is used to probe along the axis of wire arrays. This is a benefit as there is no requirement for Abel inversion in order to extract relevant information. This system has been used for both CW time resolved and pulsed spatially resolved Interferometry. Time resolve measurements were made using a Quadrature Interferometer system, using a CW 532nm Diode pump laser. The imaging system uses a sheared Mach-Zender scheme, powered by a pulse diode pumped laser of the same wavelength. Initial experiments were conducted using the well understood cylindrical wire array configuration. Initial data from these diagnostics will be presented along with comparisons to simple models and the results from 3D simulations using the GORGON MHD code.    [Preview Abstract]

 



CP9.00104: Development of a Non-LTE model for Z-pinch simulations
Nicolas Niasse , Jeremy Chittenden

Predicting the energetic and spectral characteristics of Z-pinch sources is a delicate task. It requires solving the Atomic Physics equations for plasmas in a wide range of conditions. In addition, the increasing optical depth of the plasma at stagnation can have a strong influence on its own dynamics, suggesting that simultaneous solution of both the magneto-hydrodynamic and radiative response is required. This constraint places a special emphasis on code optimization. We introduce a simple atomic model that can be run inline with the three dimensional resistive Eulerian MHD code GORGON developed at Imperial College. Based on a Screened-Hydrogenic Model (SHM) with nl splitting and making use of an inexpensive modification of the SAHA equation, this code has demonstrated a good ability to mimic Non-LTE plasma conditions. Preliminary results obtained with the standalone version of the model have shown good agreement with commercial packages (PrismSpect). Comparisons of predictions produced by the inline version with data from High Energy Density Plasma Physics (HEDP) experiments at Imperial College, Sandia National Laboratory and Centre d'Etudes de Gramat are presented. Synthetic Z-pinch XUV images and time dependant spectra are produced.    [Preview Abstract]

 



CP9.00105: Time and Space Resolved Synthetic Spectra of a Z-Pinch Stagnation
J. Giuliani , A.L. Velikovich , J.W. Thornhill , A. Dasgupta , J.P. Apruzese , R.W. Clark , S.T. Zalesak , B. Jones , C.A. Coverdale , C. Deeney

The stagnation phase of a Z pinch is examined for two alternative scenarios: (i) the reflection of a dense shell off of a hot but low density core, and (ii) the expansion of a shock wave from the axis as it accretes inflowing material. The former case is characteristic of 1D Lagrangian simulations and the latter is an extension of Noh's classic problem. This problem is first used to verify the hydrodynamics of the numerical code in the absence of radiation. Next the simulations for the assembly phase are performed in 1D for an argon pinch with collisional radiative equilibrium for the ionization kinetics and non-local probability-of-escape for the radiation transport. The results are used to produce time and space (radial) resolved synthetic spectra of the He-alpha and inter-combination lines. It is proposed that such spectroscopic observations could discriminate between these two opposing scenarios of a Z-pinch stagnation.    [Preview Abstract]

 



CP9.00106: Modeling and Spectroscopic Analysis of non-LTE Argon Plasmas
Arati Dasgupta , Ward Thornhill , John Giuliani , Jack Davis , Robert Clark , Brent Jones , Stephanie Hansen , Dave Ampleford , Chris Jennings , Christine Coverdale

We will present a detailed multilevel atomic model for all argon ions and its impact on the radiation hydrodynamics on a argon gas puff driven by the redesigned Sandia National Laboratory ZR accelerator. The atomic model employs an extensive atomic level structure to accurately model the pinch dynamics and the spectroscopic details of the emitted radiation. The atomic data are obtained using the state-of-the-art Flexible Atomic Code, and all relevant atomic processes are included in generating the model. The judiciously lumped atomic model of fine-structure levels is detailed but manageable. We analyze the behavior in the argon K- through M-shell ionization stages using temperature and density conditions predicted in 1-D and 2-D MHD calculations of implosions on ZR.    [Preview Abstract]

 



CP9.00107: Diagnosing Plasma Conditions in Copper Wire Array Shots on Z: Spatially-Averaged Analysis Compared to Inferred Properties of Individual Bright Spots
J.P. Apruzese , J.W. Thornhill , A.L. Velikovich , B. Jones , D.J. Ampleford , C.A. Coverdale

Recent copper wire array shots on Z, when spectroscopically analyzed on a spatially-averaged basis, appear to have achieved ion densities near 10$^{21}$ cm$^{-3}$, electron temperatures of 1.25 keV, and K-shell radiating participation of 70-85{\%} of the load mass. However, pinhole images of the shots reveal considerable structure, including several well-defined intensely radiating ``bright spots'', which may be due to enhanced density, temperature, or some combination of the two. We have analyzed these individual spots on selected shots, using line-outs of their spectrum and inferred powers based on their images. We compare the properties of these spots (are they dense, hot, or both?), and examine their effect on inferring the radiating mass.    [Preview Abstract]

 



CP9.00108: 2D Rad-MHD Model Assessment of Designs for Multiple-Shell Gas Nozzles for Z
J. Thornhill , J. Giuliani , A. Velikovich , J. Apruzese , Y. Chong , J. Davis , A. Dasgupta , R. Clark , B. Jones , C. Coverdale , D. Ampleford , C. Jennings , M. Cuneo , E. Waisman , M. Krishnan , P. Coleman

AASC is designing multiple-shell gas puff loads for Z. Here we assess the influence of the loads initial gas distribution on its K-shell yield performance. Emphasis is placed on designing an optimal central jet initial gas distribution, since it is believed to have a controlling effect on pinch stability, pinch conditions, and radiation physics [1]. We are looking at distributions that optimize total Ar K-shell emission and high energy ($>$10 KeV) continuum radiation. This investigation is performed with the Mach2 MHD code with non-LTE kinetics and ray trace based radiation transport. \\[4pt] [1] H. Sze, \textit{et al}., PRL, \textbf{95}, 105001 (2005).    [Preview Abstract]

 



CP9.00109: Structure and behavior of the imploding plasma in a laser triggered vacuum arc EUV source
Qiushi Zhu , Junzaburo Yamada , Nozomu Kishi , Masato Watanabe , Akitoshi Okino , Kazuhiko Horioka , Eiki Hotta

Dynamics of the imploding plasma and the relations with 13.5 nm EUV emissions in a laser assisted Sn based discharge produced plasma EUV source under moderate discharge current (17 kA amplitude, 120 ns risetime) have been experimentally investigated using time and spatially resolved laser shadowgraphy and Nomarski interferometry techniques. During compression, the imploding plasma shells and the zippering effect that the pinch collapses first from the anode side, and then along the remaining plasma column to the cathode side were observed. As soon as the plasma reaches the maximum compression, the sausage instability exists. The corresponding electron density map indicates that the radial density distribution displays an annular-shape at the crest of the plasma while a near-parabolic-shape at the neck, the maximum of the electron density is located at one peak of the annular distribution at the crest instead of the neck. It is also found that relatively strong EUV radiation is generated by the Z- pinch plasma with electron density larger than 1.5x10$^ {24}$ m$^{-3}$. However, shock waves due to the expansion of the plasma attaching on the anode can also cause weak EUV radiation.    [Preview Abstract]

 



CP9.00110: Multi-Kev X-Ray Emission from High-Z Gas Targets Fielded at Omega and NIF
Mark May , Kevin Fournier , Jeff Colvin , Jave Kane

We report on the measured X-ray flux from gas-filled targets shot at both the OMEGA and NIF laser facilities. The OMEGA targets were 1.8 mm long, 1.95 mm in diameter Be cans filled with either a 50:50 Ar:Xe mixture, pure Ar, pure Kr or pure Xe at $\sim $ 1 atm. The OMEGA experiments heated the gas with 20 kJ of 3$\omega $ ($\sim $350 nm) laser energy delivered in a 1 ns square pulse. The NIF targets were thin walled (25 $\mu $m), 4 mm long, 4 mm inner-diameter epoxy pipes filled with 1.2 atm of a 65:35 Ar:Xe mixture. The NIF experiments heated these targets with 350~kJ of 3$\omega $ ($\sim $350 nm) laser energy delivered in a 5 ns square pulse at up to 75~TW of laser power. The emitted X-ray flux was monitored with the X-ray diode based DANTE instruments in the sub-keV range. Two-dimensional X-ray images (for energies 3-5 keV) of the targets were recorded with gated X-ray detectors. The X-ray spectra were recorded with the HENWAY crystal spectrometer at OMEGA. The results from both experiments will be compared. This work performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.    [Preview Abstract]

 



CP9.00111: Multi-KeV X-Ray Yields From High-Z Gas Targets Fielded at the National Ignition Facility
K.B. Fournier , M.J. May , J.D. Colvin , J.O. Kane , C.A. Thomas , M. Schneider , R. Marrs , S. Compton , J. Moody , E. Bond , E. Dewald , J.F. Davis

We report on the measured X-ray flux from gas-filled targets shot with 112 -- 132 laser beams at the NIF. The targets were driven with up to 75~TW of laser power (350~kJ of 3$\omega $ laser energy delivered in a 5 ns modified-flat-top pulse). The targets were thin walled (25 $\mu $m), 4 mm long, 4 mm inner-diameter epoxy pipes designed to transmit X rays in the 1 -- 10 keV spectral band. The pipes were filled with 1.2 atm of an Ar:Xe mixture. The emitted X-ray flux was monitored with multiple channels of the NIF facility's two X-ray-diode based DANTE instruments in the sub-keV range, as well as around 3.2 keV (Ar K-shell emission) and in the 4.0 -- 6.5 keV band (Xe L-shell emission). Two-dimensional X-ray imaging (for energies $>$ 3 keV) of the targets was performed with a gated X-ray detector. The two dimensional images confirm supersonic, volumetric heating of the gas targets. Laser light scattered from the target plasma was monitored with the facility's full aperture backscatter system (FABS), and hard X rays produced by hot electrons from the target plasma were measured with the FFLEX diagnostic. We measure 15-20{\%} laser-to-X-ray conversion efficiency for X rays with energies greater than 3.0~keV. This work performed under the auspices of the U. S. DOE by LLNL under Contract DE-AC52-07NA27344.    [Preview Abstract]

 



CP9.00112: Pinch dynamics deduced from terminal current and voltage measurements in a Dense Plasma Focus
Mahadevan Krishnan , Brian Bures , Robert Madden

Terminal measurements of current and voltage in a dense plasma focus (DPF) are used with a circuit model to deduce the dynamical evolution of the plasma inductance. This inductance in turn gives the dynamical impedance and hence the peak voltage at the pinch, which is found to be $\sim $50kV or higher, for a $\sim $10kV bank voltage. Measurements are described of pinches in a 130kA and a 300kA DPF, with various gases. The dynamical inductance also measures the evolution of the radius of the current carrying region of the imploding pinch. The high pinch voltages and small pinch radii shed light on the neutron production mechanism in such DPFs.    [Preview Abstract]

 



CP9.00113: Hard X-ray Imaging of a 250 kA Plasma Focus in Inert Gases
Brian Bures , Mahadevan Krishnan , Robert Madden

The emission of hard x-rays from a plasma focus is well known. High atomic number gases like Ne and Ar produce bremsstrahlung photons at the anode rim and anode base, as well as from the pinch itself. The purpose of this work is to use the hard x-ray emission as a diagnostic for the pinch diameter and pinch length. Visible and soft x-ray images are commonly taken of inert gas pinches to look for pinch structure. The diameter of the pinches' hard x-ray emission is compared with deductions of the dynamical pinch radius from terminal voltage and current measurements, as well as a 1D numerical model that estimates both the pinch radius and pinch length. A step wedge spectrometer is used to examine the hard x-ray emission integrated over many shots.    [Preview Abstract]

 



CP9.00114: Gas-Puff Neutral Density Measurements Using PLIF
David Chalenski , Pierre Gourdain , Bruce Kusse

New experiments being considered for the 1 MA, 100-250 ns Cornell University COBRA pulser involve gas puff z-pinches. We are presently conducting proof-of-principle tests on diagnostics and hardware for these experiments. One of the requirements for these studies is the measurement of neutral density profiles of the injected gas puffs. For this we are considering a Planar Laser Induced Fluorescence (PLIF) method. PLIF is an ideal diagnostic for these measurements due to its non-invasive nature, good time (4ns) and spatial (100-300 $\mu$m) resolution. We present some initial results of PLIF measurements on our supersonic gas puff test stand using acetone as a fluorescent tracer and light from a 266 nm, frequency-quadrupled Nd:YAG as the excitation mechanism.    [Preview Abstract]

 



CP9.00115: Upgrade of a Theta Pinch Plasma Source for Energetic Plasma Flow Generation and Fusion-Related Material Interaction Study
Soonwook Jung , Vijay Surla , David Ruzic

In order to investigate material erosion by exposure to a burst of high density plasma in a laboratory setting, a theta pinch device called the Divertor Erosion and Vapor Shielding eXperiment facility was built at UIUC. It consists of a theta-pinch coil driven by pulse discharge from 32 $\mu $F capacitor bank to produce high density plasma. Recent measurements have shown that plasma sustains approximately for 100 $\mu $s at each pulse, with 1.0 $\pm $ 0.2(10)21 /m$^{3}$ plasma density and 12.5 $\pm $ 2.5 eV electron temperature. To simulate the extreme condition in magnetic fusion device a higher electron temperature is desired. For this reason, several upgrades have been implemented: (1) the main capacitor bank, for compression and heating was operated in conjunction with RF antenna and a preionization bank. (2) a guide magnetic field was installed to transport the flow minimizing losses in the radial direction and (3) a crow-bar circuit was added to prevent the pinch from ringing and therefore working against the imposed static magnetic field. The results from the upgrades will be presented.    [Preview Abstract]

 



CP9.00116: Kinetic effects of nuclear reactions in deuterium gas puffs
Brian Appelbe , Simon Vickers , Jeremy Chittenden

Deuterium gas puffs are the largest source of laboratory neutrons producing more than 10$^{13}$ neutrons on the Z machine at Sandia National Laboratories. However, the mechanisms producing these neutrons are poorly understood. In particular, the extent of non-thermal neutron production is an important issue for determining the scalability of the results to higher currents. In this work we present the results of a computational study of the nuclear reactions in a deuterium gas puff. We investigate this by simulating the gas puff implosion using the 3D MHD GORGON code. The data is post-processed with the addition of a kinetic species to model the non-thermal neutron production. Results show that non-thermal neutron production accounts for only a small fraction of total neutron production. The number of 14.1MeV neutrons produced by secondary DT reactions is also calculated. The ratio of secondary to primary neutrons is approximately 0.0001. Finally, the shape of the neutron spectra for both thermal and non-thermal plasmas are derived theoretically and compared with the composite neutron spectra produced by the code. The results show the sensitivity of the spectra to conditions of the deuterium plasma.    [Preview Abstract]

 



CP9.00117: Fusion Neutron Production in Deuterium and DT Z-Pinch Implosions with Seeded Axial Magnetic Field at Multi-MA Currents
A.L. Velikovich , J. Davis , J.L. Giuliani , Y.K. Chong , R.W. Clark , S.T. Zalesak , C.A. Coverdale , D.G. Flicker

We report 1D and 2D numerical and theoretical investigation of the thermal neutron production in deuterium and DT 100-300 ns Z-pinch implosions driven by the currents now accessible on refurbished Z and higher. On-axis plasma compression and thermal fusion neutron yield have been found to increase if D in the outer shell is replaced with a high-Z gas, whose radiative losses make the outer shell thin. With outer-to-inner-shell mass ratio greater than 2, the conventional density gradient/snowplow mechanism of RT instability mitigation becomes ineffective and extra efforts are needed for implosion stabilization. Seeded axial magnetic field $\sim $20-100 kG can stabilize Ar-on-D implosions at the expense of reducing the neutron yield. Our estimates indicate that thermal DD neutron yields approaching 10$^{15}$ are within the reach in deuterium gas-puff implosions on refurbished Z.    [Preview Abstract]

 



CP9.00118: BASIC PLASMA PHYSICS: MAGNETIC RECONNECTION

   [Preview Abstract]

 



CP9.00119: An effective resistivity model of collisionless driven reconnection in an ion-scale current sheet
Ritoku Horiuchi , Hiroaki Ohtani , Shunsuke Usami , Mitsue Den , Akira Kageyama

Many particle simulation studies [1,2] have revealed that frozen-in condition is broken due to particle kinetic effects and collisionless reconnection is triggered when current sheet is compressed as thin as ion kinetic scales under the influence of external driving flow. A reconnection system evolves into a quasi-steady state after an initial transient phase if the driving flow satisfies some condition [1]. In the steady state, reconnection electric field generated by microscopic physics evolves inside ion meandering scale so as to balance the flux inflow rate at the inflow boundary, which is controlled by macroscopic physics. That is, effective resistivity generated through this process can be expressed by balance equation between micro and macro physics. This effective resistivity model is applied to magnetic reconnection phenomena in the Earth magnetosphere. In case of southward solar wind magnetic field with an oblique component, intermittent plasmoid ejection was observed in the night-site region of the magnetosphere as a result of magnetic reconnection around 10-20 of the earth radius.\\[4pt] [1] W. Pei, R. Horiuchi, and T. Sato, Physics of Plasmas,Vol. \textbf{8} (2001), pp. 3251-3257.\\[0pt] [2] A. Ishizawa, and R. Horiuchi, Phys Rev Lett, Vol. \textbf{95}, 045003 (2005).    [Preview Abstract]

 



CP9.00120: Studies on collisionless driven reconnection with a multi-hierarchy simulation model
Shunsuke Usami , Hiroaki Ohtani , Ritoku Horiuchi , Mitsue Den

Collisionless magnetic reconnection is believed to play an essential role in the rapid energy release such as solar flares and geomagnetic substorms. Also, reconnection process attracts considerable attention as coupling phenomenon between multiple spatial and temporal scales. A grand challenge in reconnection studies is to understand its multi-hierarchy structure. Then, a multi-hierarchy simulation model, which deals with both microscopic and macroscopic physics consistently and simultaneously, is developed. Our multi-hierarchy model is based on the domain decomposition method, which the domains differ in algorithm. Physics in the domain where microscopic kinetic effects are important is solved by PIC algorithm (PIC domain), while dynamics outside the PIC domain is expressed by MHD algorithm (MHD domain). Between the PIC and MHD domains, an interface domain with a finite width is inserted in order to interlock two domains smoothly. We first connect the PIC and MHD domains at the upstream boundary. We have successfully demonstrated that plasmas come from MHD to PIC domains and drive magnetic reconnection in the PIC domain [1]. Next, we would consider the connection at the downstream boundary. \\[4pt] [1] S. Usami, H. Ohtani, R. Horiuchi, and M. Den, Plasma Fusion Res. 4, 049 (2009).    [Preview Abstract]

 



CP9.00121: Fast Magnetic Reconnection and High Power Heating in TS-4 / UTST Spherical Tokamak Merging Experiments with Neutral Beam Injections
Yasushi Ono

The TS-4 and UTST spherical tokamak (ST) merging experiment revealed two types of fast magnetic reconnections: 3-D reconnection and plasmoid (current-sheet) ejection in addition to the anomalous resistivity of current sheet reported in 1995. The 3-D local deformation of current sheet was observed when two tokamak plasmas with low guide-field were over-compressed by external coils. Note that global mode amplitudes of merging toroids were maintained low during the reconnection. The toroidal asymmetry grew locally around the current sheet only during the reconnection and disappeared right after the reconnection. The intermittent reconnections by current sheet/ plasmoid ejection was observed when two tokamaks with high guide-field were over-compressed by the external coils. The reconnection (outflow) speed was slow during the flux pileup and was fast during the ejection. Due to the combination of pileup and ejection, the intermittent reconnection increased the averaged reconnection speed. These fast reconnections enable us to maximize the heating power of merging ST plasmas. High beta /high flow stability tests of ST plasmas are being made in TS-4 and UTST with the assistance of merging/ reconnection and 0.4MW and 0.7MW neutral beam injections (NBI). This work is supported by JSPS Core-to-Core Program 22001.    [Preview Abstract]

 



CP9.00122: Experimental Simulation of Magnetic Reconnection in the Sunspot Light Bridge
Yoshinori Hayashi , Hiroshi Tanabe , Michiaki Inomoto , Yasushi Ono , Toshifumi Shimizu , Shinsuke Imada , Naoto Nishizuka

Intermittent and recurrent chromospheric plasma ejections were discovered in the sunspot light bridge (LB) by the Solar Optical Telescope of the Hinode satellite (Shimizu et al. 2009, ApJ, 696, L66). Strong current was observed under the jet, suggesting existence of twisted flux tube in the vertical background field. The magnetic reconnection between the flux tube and the vertical field is considered to cause the plasma ejection. It is left unsolved why the intermittent reconnection continuing more than one day. Note that the magnetic configuration of LB is similar to the spheromak plasma maintained by vertical field in the laboratory. We formed spheromak in the TS-4 device and drove magnetic reconnection with center solenoid coil. We measured 2D magnetic profile of the reconnecting field lines between the spheromak and the solenoid coil by the magnetic probe array and local temperature, density and plasma flow at the reconnection point by the Langmuir probes and ion Doppler spectroscopy. We will discuss about the LB reconnection by comparing the laboratory experiment with the satellite observation.    [Preview Abstract]

 



CP9.00123: Plasma Pileup and Ejection during Impulsive Magnetic Reconnection in TS-4 Merging Experiment
Kensuke Suzuki , Atsushi Matsuda , Yoshinori Hayashi , Michiaki Inomoto , Yasushi Ono

Plasma pileup and ejection during magnetic reconnection have been investigated in the University of Tokyo Spherical Torus (TS-4) plasma merging experiment. We developed an eight-channel CO$_2$ laser interferometer to measure the time evolution of 1-D profile of electron density in the reconnection layer. Under the high guide field (B$_t$/B$_p\sim$5), the strong compression force(I$_{Acc}\sim$60kA) causes electron density to pileup in the current sheet. After the density reaches a certain critical value, the peaked density profile of the current sheet is transformed into hollow profile, indicating ejection of the accumulated plasma in the current sheet. The pileup and ejection are observed to cause large inflow and increase in the reconnection speed. After the ejection, both the inflow speed and the sheet size decrease. Under the weak compression force (I$_{Acc}\sim$0kA), the electron density in the current sheet and the reconnection rate stay constant right up until the end of reconnection. These results clearly indicate that the density pileup and ejection causes the fast reconnection. More detailed parameter dependence of reconnection speed will also be discussed.    [Preview Abstract]

 



CP9.00124: Investigation of Ion Heating Mechanism of Magnetic Reconnection by Use of Tomographic 2-D Ion Doppler Diagnostics
Hiroshi Tanabe , Akihiro Kuwahata , Setthivoine You , Hirotaka Oka , Patrick Copinger , Shingo Ito , Yoshinori Hayashi , Toru Ii , Alexandar Balandin , Michiaki Inomoto , Yasushi Ono

The TS-3 and TS-4 experiments at the University of Tokyo collides two tokamaks and spheromaks with co- and counter- helicities to form single high beta compact toroid. The ion temperature after the reconnection was found to increase with decreasing toroidal magnetic field, indicating strong dependence of ion heating effect on toroidal magnetic field. To investigate more detailed heating characteristics, we have developed 2-D local ion temperature measurement system by means of tomographic reconstruction for ion Doppler spectroscopy. We are now developing novel 2-D local ion toroidal flow diagnostics by use of the conversion technique of vector radon transform into scalar radon transform of flow vector potential [1]. After the quality of inversion results were tested by reconstruction simulation, the whole measurement system was installed on TS-3 and TS-4. The measured 2-D images of ion flow and temperature revealed the local ion acceleration and heating of magnetic reconnection - the ion heating by reconnection outflow.\\[0pt] [1] A. L. Balandin et al, Eur. Phys. J. D, 27, 125, 2003    [Preview Abstract]

 



CP9.00125: Reconnection experiments including 3D magnetic nulls
A. Le , J. Egedal , A. Vrublevskis

A rich collection of magnetic reconnection scenarios is possible in three dimensions depending on the topological and geometric structure of the magnetic field [1]. In recent experiments at the Versatile Toroidal Facility (VTF) three-dimensional effects were essential even in nearly axisymmetric plasmas with a non-vanishing toroidal field [2]. To explore reconnection in 3D geometries including magnetic null points, a new adjustable set of coils will be installed in the vacuum chamber of VTF. The range of vacuum magnetic field topologies attainable in VTF will be explored numerically. Plasma reconnection experiments will be run in these configurations, and measurements will be presented if available. \\[4pt] [1] CE Parnell, et al., (2009) ``Three-Dimensional Magnetic Reconnection, in Magnetic Coupling between the Interior and the Atmosphere of the Sun,'' eds. S.S. Hasan and R.J. Rutten, Springer-Verlag, Heidelberg, Berlin. \\[0ex] [2] Katz, N. et al., (2010) Phys. Rev. Lett. 104, 255004.    [Preview Abstract]

 



CP9.00126: Observations of formation and dynamics of plasma filaments in VTF
A. Vrublevskis , J. Egedal , A. Le

Plasma filaments, or ``blobs'', are propagating structures of increased plasma density relative to the background plasma. Blob dynamics are of importance in a variety of environments including fusion experiments and space. Previous investigations in the Versatile Toroidal Facility (VTF) studied the propagation of a single filament created using RF power [1]. Here we present observations made in a closed magnetic configuration including an X-line. We observed periodic density fluctuations along the plasma edge and filaments detaching and propagating away. Multiple probe arrays at different toroidal locations allowed us to investigate the 3D extent and evolution of the filaments focusing on the plasma edge. \\[4pt] [1] N. Katz et al., Phys. Rev. Lett. 101, 015003 (2008)    [Preview Abstract]

 



CP9.00127: New anisotropic electron pressure closure implemented in two fluid simulations of collisionless reconnection
O. Ohia , J. Egedal , A. Le , S.V. Lukin

Collisionless magnetic reconnection plays an important role in space and laboratory plasmas. The study of reconnection is aided by both fluid simulations and fully kinetic particle simulation. When comparing the various simulation schemes, it is found that the structure surrounding the electron diffusion region and the electron current layer differ vastly between kinetic and fluid simulations [1]. Recently, a new fluid closure has been obtained that relates parallel and perpendicular pressures to the density and magnetic field [2]. This closure is obtained using an adiabatic solution of the Vlasov equation which includes a field aligned electric potential that traps electrons and regulates their density. The closure agrees with fully kinetic simulations of guide-field reconnection and is likely to allow for new fluid simulations in better agreement with kinetic results. The new ``equations of state'' are now being implemented in two-fluid codes using the HiFi framework [3]. \\[0ex] [1] W. Daughton, et al., Phys. Plasmas 13, 072101 (2006).\\[0ex] [2] A. Le, et al., Phys. Rev. Lett. 102, 085001 (2009).\\[0ex] [3] V.S. Lukin, et al., J. Comput. Phys. Submitted (2009)    [Preview Abstract]

 



CP9.00128: The role of kinetic effects and parallel electric fields within the Hall current system of collisionless reconnection
J. Egedal , A. Le , W. Daughton

Aided by spacecraft observations in the Earth's geotail one of the main accomplishments in reconnection research is the identification of the Hall effect. While fluid models provide important insight into the Hall physics of the ion diffusion region, in-situ measurements of the electron distribution function reveal the presence of cold beams directed towards the X-line while energized electrons move away from the reconnection region. We present a new model that can account for these kinetic effects. The cornerstone of the model is a field aligned acceleration potential $\phi_{\parallel}$ introduced in Ref. [1]. This potential becomes large when the upstream electron beta is small [2]. Electrons accelerated in this potential can reach energies much larger than their ambient temperature. The combination of the direct parallel acceleration by $\phi_{\parallel}$ and pitch angle scattering in the exhaust region generates the characteristic signatures in the electron distribution function observed by spacecraft along the separatrix layers. Our studies are aided and supported by fully kinetic simulations of reconnecting current sheets. \\[1ex] [1] Egedal J, et al., (2009) Physics of Plasmas 16, 050701. \\[0ex] [2] Le A, et al., (2010) Geophys. Res. Lett. 37, L03106.    [Preview Abstract]

 



CP9.00129: Generalized Skilling Equation for Particle Acceleration in Reconnecting Magnetic Fields
Liang Wang , A. Bhattacharjee , M. Lee

While particle-in-cell simulations provide valuable information on particle acceleration in two-dimensional reconnection problems, such simulations are much rarer in three dimensions because of the limits of computing power. Hence, analytical approaches to calculating particle distribution functions need to be developed. In recent years, there have been attempts to use variants of Parker's transport equation to particle acceleration problems involving magnetic islands. In this paper, we present the derivation of a generalized Skilling equation (GSE) for guiding-center plasmas that is shown to reduce to Parker's transport equation under some strong assumptions, not generally valid for particle acceleration involving magnetic islands. The GSE assumes gyrotropy, but enables the treatment of anisotropy of the particle distribution function. The equation can be applied to relativistic as well as non-relativistic particles. We will present results on the application of this equation to hydrogen as well as pair plasmas.    [Preview Abstract]

 



CP9.00130: Reconnection rates and particle acceleration in electron-positron plasmas
Naoki Bessho , A. Bhattacharjee

We have performed 2D particle-in-cell simulations of magnetic reconnection and particle acceleration in electron-positron plasmas with no guide field, in relativistic as well as non-relativistic regimes. In the low-density regime, we demonstrate that the reconnection rate is systematically higher than in the high-density regime, attaining values of the order of unity in the impulsive growth phase. Under these conditions, the inertial term in the generalized Ohm's law is the most dominant term that supports the large reconnection electric field. An effective collisionless resistivity tracks the extension of the diffusion region in the late stage of the reconnection dynamics, and significant broadening of the diffusion region is observed. Because of the broadening of the diffusion region, no secondary islands, which limit the extension of the diffusion region, are produced. In the relativistic regime, we have observed ultrarelativistic particles accelerated by reconnection. We show analytically that the energy spectrum of accelerated particles near an X-line is proportional to a product of a power-law and an exponential function of energy. Simulations show that the energy spectra are consistent with the analytical predictions.    [Preview Abstract]

 



CP9.00131: Diamagnetic Effects on Asymmetric Reconnection: A Comparative PIC and Hall MHD Study
Stephen Abbott , Kai Germaschewski , Amitava Bhattacharjee

We present a comparative study of reconnection in a Harris current sheet with a guide field, modified by the addition of an equilibrium pressure gradient at the reconnection layer to introduce diamagnetic drifts, using Hall MHD and particle-in-cell (PIC) simulations. Previous kinetic studies of a similar configuration in magnetopause conditions showed significant decoupling of X-point and island drift speeds as the pressure gradient was suppressed across the growing island while steepening near the X-point, resulting in reduced reconnection rates. One goal of our comparative study is to investigate how much of the relevant kinetic physics is captured by two-fluid simulations, and differences that occur as the magnitude of the guide field is varied. We also extend the parameter space to stronger guide fields and higher $\beta$, relevant to fusion plasmas. Our Hall MHD simulations utilize the Magnetic Reconnection Code (MRC), which features a Generalized Ohm's Law including the Hall term and electron pressure gradient. It supports non-uniform grids and implicit time-stepping. PIC results are provided by the Particle Simulation Code (PSC). We focus on the nonlinear evolution of reconnection rates and the asymmetric structure of the X-point, and test the validity of recent expressions for the asymmetric reconnection rate recently proposed in the literature.    [Preview Abstract]

 



CP9.00132: On the question of hysteresis in Hall MHD Reconnection
Brian Sullivan , Amitava Bhattacharjee , Yi-Min Huang

Recently, questions have been raised regarding the cause of hysteresis, or bi-stability, of solutions to the equations that govern the geometry of the reconnection region in Hall magnetohydrodynamic (MHD) systems. This poster presents a comparison of the frameworks within which this controversy has arisen and illustrates that the Hall MHD hysteresis originally discovered numerically by Cassak {\it et al.}[Phys. Rev. Lett. 95, 235002 (2005)] is, in fact, a different phenomenon from that recently reported by Zocco {\it et al.} on the basis of analysis and simulations in electron MHD with finite electron inertia. [Phys. Plasmas 16, 110703 (2009)] We demonstrate that the analytic prediction of hysteresis in EMHD does not describe or explain the hysteresis originally reported in Hall MHD, which is shown to persist even in the absence of electron inertia.    [Preview Abstract]

 



CP9.00133: Current sheet formation and the plasmoid instability in large, hyperresistive Hall MHD systems
Amitava Bhattacharjee , Brian Sullivan , Yi-Min Huang

Recently, it has become clear that in high Lundquist number, resistive MHD simulations of magnetic reconnection, a super-Alfv\'enic plasmoid instability may significantly alter the dynamics of the reconnection process. Collisionless particle-in-cell simulations also exhibit copious plasmoid formation. Resistive Hall MHD simulations have been only recently shown to demonstrate similar behavior. Here it is found that not only resistive current sheets, but also current sheets in the presence of hyperresistivity or electron viscosity can exhibit violent plasmoid formation. We delineate the requirements for plasmoid formation in Hall MHD systems under such conditions. For sufficiently large Hall MHD systems, there exists a range of hyperresistivity for which plasmoids appear significant in generating sub-ion skin depth scale current sheets and in triggering Hall reconnection. In the plasmoid-unstable regime, previously obtained scaling laws for the dependence of the reconnection rate on hyperresistvity are altered, leading to regime where the reconnection rate becomes weakly dependent on hyperresistivity.    [Preview Abstract]

 



CP9.00134: Role  of the Plasmoid Instability in the Onset of Fast Reconnection
Yi-Min Huang , A. Bhattacharjee , Brian P. Sullivan

The problem of fast magnetic reconnection in high-Lundquist-number ($S$) plasmas has been an active research topic for several decades. The main challenge is to explain why reconnection in nature or laboratories, such as solar corona and fusion devices, can proceed so quickly from a relatively quiescent state when the plasma involved is highly conducting. The classic Sweet-Parker theory based on resistive MHD predicts a reconnection rate that scales as $S^{-1/2}$. For many systems of interest, the resulting Sweet-Parker reconnection rates are much slower than those observed. Recent work has demonstrated that there is a fundamental flaw in the Sweet-Parker argument. When the Lundquist number exceeds a critical value, the Sweet- Parker layer is unstable to the plasmoid instability. Moreover, the plasmoid instability becomes more unstable the higher the Lundquist number is. Within the framework nonlinear resistive MHD, the plasmoid instability realizes a recoonection rate that is insensitive to the value of $S$. We will present our recent progress in understanding the effects of this instability on resistive and Hall MHD reconnection. In particular, we will discuss the role of the plasmoid instability in triggering Hall reconnection. We will present scaling relations on the reconnection rate, current sheet thickness, and the numbers of plasmoids.    [Preview Abstract]

 



CP9.00135: Magnetic Field Reconnection and the quasi-seperatrix layer of three interacting flux ropes
Walter Gekelman , Bart Van Compernolle , Stephen Vincena

Three magnetic flux ropes are created in a background magnetoplasma (L = 16 m, $n_{backgnd} =2\times 10^{12}cm^{-3},n_{rope} =1\times 10^{13}cm^{-3},B_{0z} 330G$, He, plasma diameter = 60 cm). The ropes are made using a masked $LaB_6 $ , 8 cm diameter cathode and remote anode. Each rope carries 40 A of current. Magnetic field data is acquired in 16 perpendicular planes (size $l_x =l_y =15cm$, 3mm sampling) with axial spacing of 64 cm. The magnetic field lines generated from the data reveal that the flux ropes twist about themselves and each other in a complicated fashion in space and time and there are spatial locations at which transverse magnetic fields of opposite polarity are forced towards each other and reconnect. Fast photography of the light from a He II line shows similar structure. The magnetic field data is used to compute the quasi-seperatrix layer (QSL) much as it was in the case of two interacting flux ropes[1]. The QSL is a 3D region in which reconnection activity is likely to occur. This is shown in movies that illustrate the space-time evolution. \\[4pt] [1] E. Lawrence, W. Gekelman, Identification of a quasi-seperatrix layer in a reconnecting laboratory magnetoplasma, Phys. Rev. Lett., 103, 105002 (2009)    [Preview Abstract]

 



CP9.00136: 3D current, temperature and density profiles of three interacting flux ropes
Bart Van Compernolle , Walter Gekelman , Stephen Vincena

Three magnetic flux ropes are created in a background magnetoplasma (L = 16 m, n$_{background}$ = 2 10$^{12}$ cm$^{-3}$, n$_{rope}$ = 10$^{13}$ cm$^{-3}$, Helium, B$_{0z}$ = 330 G, plasma diameter = 60 cm). The ropes are made using a 8 cm diameter 'masked' Lanthanum Hexaboride (LaB$_6$) cathode and remote anode, 11 m away. The mask consists of a carbon plate with three one inch diameter holes cut out, center to center spacing is 1.5 inch. Each rope carries 40 amps of current and produces magnetic fields on the order of 4\% of $B_{0z}$. The 3D current structure is calculated from volumetric magnetic field data. The current channels are fixed to the cathode at one end, but are seen to twist about each other and merge away from the cathode. Return currents are observed and may be linked to reconnection events. Cross correlation analysis of ion saturation current measurements revealed large drift modes (m=1,2,3,4,...) surrounding the current channels. Swept Langmuir probe measurements, acquired at 2600 locations in a transverse plane show the spatial profile and temporal evolution of the density and temperature associated with the flux ropes.    [Preview Abstract]

 



CP9.00137: The Effect of Shear Flow on the Scaling of 2D Magnetic Reconnection
Paul Cassak

Magnetic reconnection experiences a shear flow when there is a net bulk plasma flow in the direction of the reconnecting component of the magnetic field. Such flow is expected to exist in usual conditions at the Earth's magnetosphere (caused by the solar wind at the polar cusps and at the dayside), in sawtooth events in tokamaks (due to poloidal bulk flow which can be set up by plasma drifts), and potentially in solar and astrophysical applications as well. The effect of shear flow on reconnection has been addressed in numerous studies, including a number in recent years, but a quantitative understanding of how shear flow affects the scaling of magnetic reconnection has not been obtained. We begin this effort with a careful study using large-scale Hall magnetohydrodynamics (Hall-MHD) and magnetohydrodynamic (MHD) numerical simulations. Specifically, we address the scaling of the reconnection rate and outflow speed with amplitude of the shear flow.    [Preview Abstract]

 



CP9.00138: Comparison of Secondary Islands in Collisional Reconnection to Hall Reconnection
Lucas Shepherd , Paul Cassak

Secondary islands (plasmoids) self-consistently occur during collisional (Sweet-Parker) reconnection at high Lundquist numbers, as in the solar corona and many tokamaks. Previous numerical studies of the effect of secondary islands on the transition to collisionless (Hall) reconnection considered systems with no separation of scales between the collisional and collisionless states. In this study [1], the first resistive Hall-magnetohydrodynamic (Hall-MHD) simulations to separate the two scales are presented. Three main results are found. There exists a regime in which secondary islands occur during resistive reconnection without collisionless effects entering, with a reconnection rate faster than Sweet-Parker but slower than Hall reconnection. The reconnection rate increases substantially when Hall reconnection begins, showing that secondary islands are not the cause of the fastest reconnection rates. The onset of Hall reconnection leads to the ejection of the secondary islands in the vicinity of the X-line, implying that energy is released more rapidly during Hall reconnection. \\[4pt] [1] Shepherd and Cassak, Phys. Rev. Lett., 105, 015004 (2010)    [Preview Abstract]

 



CP9.00139: Pressure anisotropy in two-fluid simulations of magnetic reconnection
Evan Johnson

Our goal is to replicate PIC simulations of magnetic reconnection using a parsimonious two-fluid plasma model. We compare two-fluid simulations of the GEM problem with published simulations of the GEM problem using kinetic models (Vlasov and PIC). We find that incorporating viscosity allows the two-fluid model to agree fairly well with kinetic models both in the rate of reconnection and in the structure of the electron and ion diffusion regions. We also study the effect of incorporating heat flux.    [Preview Abstract]

 



CP9.00140: Magnetic Reconnection Events in Weakly Collisional Regimes$*$
P. Buratti , B. Coppi

The known modes leading to macroscopic reconnection in weakly collisional plasmas, are: one related to the drift tearing mode [1] and another with the opposite phase velocity, in the ion diamagnetic velocity direction, requiring a high energy particle population [2]. Observation of islands, that suddenly appear at finite amplitude during a trigger event (like a sawtooth crash) led to the concept of metastable resistive tearing modes. But the observation of islands growing from very small amplitude without any trigger event [3] leads instead to considering the modes mentioned above requiring the prior excitation of other linearly unstable modes: a) for the drift-tearing mode, the micro-reconnecting mode, which is driven unstable by the electron temperature gradient [4]. b) for modes with the opposite phase velocity [5], pressure gradient driven macroscopic modes that have a similar phase velocity.\\[4pt] [1] B. Coppi, \textit{Phys. Fluids} {\bf8}, 2273(1965) [2] B. Coppi, \textit{Bull. Am. Phys. Soc}. {\bf45} (2000) 366. [3] P. Buratti \textit{et al}., 34h EPS Conf. on Pl. Phys. (July 2007) ECA {\bf31F} O-4.018 (2007) [4] B. Coppi, ``Collective phenomena...'' Publ. \textit{Word Scientific}, p. 59 (2007) [5] P. Buratti et al., 35th EPS Conf. Pl. Phys., (June 2008) ECA {\bf32D}, P-1.069 (2008)    [Preview Abstract]

 



CP9.00141: Progress on the MHD closure with kinetic ions and drift kinetic electrons
Jianhua Cheng , Yang Chen , Scott Parker , Dmitri Uzdensky

We have developed a Lorentz force ion, fluid electron kinetic MHD hybrid model [1]. Based on the GEM turbulence code, a second-order accurate implicit scheme that generalizes the previous implicit scheme for Lorentz force ion and drift kinetic electron [2] has been implemented. We have benchmarked the simulation on Alfv\'en waves, ion sound waves and whistler waves using analytical results for a uniform plasma. For the Harris sheet equilibrium with a guide field, we investigated the full evolution of the resistive tearing mode. The linear growth rate and mode structure agree well with the resistive MHD theory. In the nonlinear regime, several stages are identified including the secondary island formation, its coalescence with the main island and the nonlinear saturation. Also presented will be some preliminary results on magnetic reconnection with a finite guide field.\\[4pt] [1] D. Barnes, J. Cheng, and S. E. Parker, Phys. Plasmas {\bf{15}}, 055702 (2008).\\[0pt] [2] Yang Chen, Scott E. Parker, Phys. Plasmas {\bf{16}}, 052305 (2009).    [Preview Abstract]

 



CP9.00142: Building 3D data sets of flux tube dynamics
B. Loseth , T.P. Intrator , J. Sears

Magnetic Reconnection occurs when oppositely directed magnetic fields are advected towards each other as plasma flow. The magnetic fields diffuse through a small region where the frozen flux condition of ideal magnetohydrodynamics (MHD) breaks down and the field lines lose their identity and reconnect to other fields. The reconnection process is important in the confinement of fusion plasmas as well as long-standing solar-physics issues in solar flares, geomagnetic storms, and black hole accretion discs. The Reconnection Scaling Experiment (RSX) uses plasma guns to create one, two, or more parallel flux ropes in a cylindrical chamber with an axial magnetic guide field. The plasma channels twist helically and merge or bounce depending on the attractive force due to the parallel currents and the repulsive force associated with axial and azimuthal magnetic field line bending. The dynamics of merging and bouncing may lead to a new understanding of the statistical mechanics of magnetic fields and provide a means of visualizing three-dimensional MHD turbulence. An update of the RSX vessel including an adjustable magnetic probe array is currently under way and will allow for the building of 3D data sets of these dynamics.    [Preview Abstract]

 



CP9.00143: Generalized Kinetic Current-Sheet Equilibria
David L. Newman , Martin V. Goldman , Haihong Che , Giovanni Lapenta

The well-studied equilibrium distribution of the Harris current-sheet $[1]$ has long been a mainstay for the initialization of kinetic magnetic-reconnection simulations, typically with the addition of a uniform current-free background plasma. The Harris equilibrium was generalized by Yamada et al.~$[2]$ to include an electrostatic field. Here we present further generalizations of the Harris equilibrium that are exact stationary solution of the Vlasov-Maxwell equations for fields that vary in only one dimension: ${\bf B}=B_z(y)\hat z+B_x(y)\hat x$, and ${\bf E}=-(d\phi/dy)\hat y$. These generalizations allow for (1) Non-Maxwellian distributions, including distributions where the current is carried by velocity-space skew rather than drift; (2) Electrostatic fields that asymptotically vanish far from the current sheet; (3) Magnetic fields that rotate in the $x$--$z$ plane in association with a bifurcated current profile. Methods for implementing these new equilibria to initialize kinetic reconnection simulations will be addressed. \\[4pt] [1] E.~G.~Harris, \textit{Il Nuovo Cimento}, \textbf{23}, 115 (1962).\\[0pt] [2] M.~Yamada, H.~Ji, S.~Hsu, T. Carter, R.~Kulsrud, and F. Trintchouk, \textit{Phys.~Plasmas}, \textbf{7}, 1781 (2000).    [Preview Abstract]

 



CP9.00144: Influence of current-aligned instabilities on the 3D evolution of magnetic reconnection
V. Roytershteyn , W. Daughton , H. Karimabadi

Understanding of the interplay between collisionless magnetic reconnection and current-aligned instabilities represents a long-standing problem in reconnection research. Apart from its significance as a basic plasma physics issue, a better theoretical grasp on this problem is called for by an increasing availability of {\em in-situ} observations of the electron-scale structure of the diffusion region, both in space and in dedicated laboratory experiments. In this work we present the results of fully kinetic 3D particle-in-cell (PIC) simulations of collisionless magnetic reconnection in various geometries that have been recently made possible by the advent of petascale computing and highly scalable PIC codes. We demonstrate that while the reconnection layers are almost always unstable against a spectrum of electromagnetic instabilities in the lower-hybrid range $\omega_{ci} < \omega < \omega_{ce}$, the saturation amplitude and the role played by those instabilities varies greatly depending on the local parameters (electron beta, degree of asymmetry, etc). The implications of these results for space observations and laboratory experiments are discussed.    [Preview Abstract]

 



CP9.00145: Resistive MHD Simulations of X-Line Retreat and Competing Reconnection Sites
N.A. Murphy , A.K. Young

Most simulations and theories of magnetic reconnection assume that the diffusion region is symmetric and stationary. However, in many situations in nature and the laboratory, the reconnection layer moves with respect to the upstream plasma. To investigate the impact of current sheet motion on the reconnection process, we perform numerical simulations of multiple competing reconnection sites. In double perturbation simulations, the two X-lines retreat from each other as they develop. Early in time, the flow stagnation point is located closer to the obstructing magnetic island between the reconnection sites than the X-line so that the X-line is advected by the plasma flow. Late in time, the relative positions of the flow stagnation point and X-line switch so that the X-line retreats in the opposite direction of the local plasma flow. An expression for the rate of X-line retreat shows that the X-line position changes due to both advection and diffusion. In multiple perturbation simulations, isolated and large amplitude perturbations are most likely to survive. The number of X-lines changes due to diffusion of the normal component of the magnetic field in either the inflow and outflow directions. When the X-line is pulled towards one end of the current sheet, the flow stagnation point is generally located between the X-line and the current sheet center.    [Preview Abstract]

 



CP9.00146: Gyro-kinetic Electron and Fully-Kinetic Ion Particle Simulation of Tearing Mode Instability in a Harris Current Sheet
Xiang Lu , Xueyi Wang , Yu Lin , Kong Wei , Chen Liu

Two-dimensional simulations are carried out using our gyro-kinetic electron and fully-kinetic ion (GeFi, formerly GKe/FKi [1]) particle simulation model to investigate the collisionless tearing mode instability in a Harris current sheet in the presence of a finite guide field, under a realistic ion-to-electron mass ratio m$^{i}$/m$^{e}$. The simulation is performed in the plane that contains the anti-parallel magnetic field B$^{x}$ and the current sheet normal B$^{z}$. First, results based on the linearized delta-f scheme are compared with the eigenfunction and linear growth rate obtained from the drift kinetic eigenmode theory as well as the asymptotic matching results of Drake and Lee [2]. Effect of the electron-to-ion temperature ratio T$^{e}$/T$^{i}$, beta values, and the half-width of the current sheet are investigated. Second, the physics of saturation is studied using the nonlinear simulation scheme. \\[4pt] [1] Lin, Y., X. Y. Wang, Z. Lin, and L. Chen, Plasma Phys. Controlled Fusion, \textbf{47}, 657 ,2005. \\[0pt] [2] Drake, J.F, and Y.C.Lee, Phys.Fluids, \textbf{20}, 1341, 1977    [Preview Abstract]

 



CP9.00147: Nonlinear gyrofluid simulations of collisionless reconnection
Francois Waelbroeck , Daniela Grasso , Emanuele Tassi

The Hamiltonian gyrofluid model recently derived in Waelbroeck et al. [Phys. Plasmas 16, 032109 (2009)], is used to investigate nonlinear collisionless reconnection with a strong guide field by means of numerical simulations. Finite ion Larmor radius gives rise to a cascade of the electrostatic potential to scales below both the ion gyroradius and the electron skin depth. This cascade is similar to that observed previously for the density and current in models with cold ions. In addition to density cavities, the cascades create electron beams at scales below the ion gyroradius. The presence of finite ion temperature is seen to modify, inside the magnetic island, the distribution of the velocity fields that advect two Lagrangian invariants of the system. As a consequence, the fine structure in the electron density is confined to a layer surrounding the separatrix. Finite ion Larmor radius effects produce also a different partition between the electron thermal, potential, and kinetic energy, with respect to the cold ion case. Other aspects of the dynamics such as the reconnection rate and the stability against Kelvin-Helmholtz modes, are similar to simulations with finite electron compressibility but cold ions.    [Preview Abstract]

 



CP9.00148: Reconnection Effects in the Outer Heliosphere: Is the Magnetic Field in the Heliosheath Sector Region and in the Outer Heliosheath Laminar?
Merav Opher , James Drake , Marc Swisdak , Gabor Toth

All the current global models of the heliosphere are based on the assumption that the magnetic field in the outer heliosheath close to the heliopause is laminar. We argue that in the outer heliosheath the heliospheric magnetic field is not laminar but instead consists of nested magnetic islands. Recently, we proposed (Drake et al. 2009) that the annihilation of the ``sectored'' magnetic field within the heliosheath as it is compressed on its approach to the heliopause produces the anomalous cosmic rays and also energetic electrons. As a product of the annihilation of the sectored magnetic field, densly-packed magnetic islands are produced.These magnetic islands will be convected with the ambient flows as the sector boundary is carried to higher latitudes filling the outer heliosheath. We further argue that the magnetic islands will develop upstream where collisionless reconnection is unfavorable. Due to the high pressure of the interstellar magnetic field the sectored region is carried mostly to the northern hemisphere (Opher et al. 2007). We present a 3D MHD simulation with unprecedent numerical resolution that captures the sector boundary. We suggest that within our scenario we can explain significant anomalies in the observations of energetic electrons in the outer heliosphere.    [Preview Abstract]

 



CP9.00149: Acceleration of ions and electrons during magnetic reconnection in a multi-island environment
Kevin Schoeffler , James Drake , Marc Swisdak

Hard x-ray and gamma ray emission in flares, and energetic particles found by Wind in the magnetosphere imply an association between Magnetic reconnection and energetic ions and electrons. One explanation for the acceleration of these particles is by 1st order Fermi acceleration of particles bouncing in contracting magnetic islands. Using a particle-in-cell code, we investigate the effects of $\beta$ on the acceleration by simulating island growth in multiple interacting Harris current sheets. Many islands are generated, and particles are heated in this context. There is a striking difference between the heating of electrons vs. the heating of ions. There is a strong dependence on $\beta$ for electron heating, while the ion heating seems independent of $\beta$. Anisotropies are formed both with $T_\parallel > T_\perp$ and with $T_\parallel < T_\perp$. When the anisotropy reaches the marginal firehose condition or the marginal mirror mode condition, the anisotropy is constrained. The firehose instability and the dependence of the criteria for marginal firehose instability on $\beta$, may play an important role in the acceleration of ions and electrons. This study may shed light on particle acceleration mechanisms at sectored magnetic fields in the heliosheath, as well as other systems such as in the solar wind and the solar corona.    [Preview Abstract]

 



CP9.00150: Super-Alfv\'enic energy transport during magnetic reconnection
Michael Shay , James Drake , Jonathan Eastwood

The transport of energy away from a magnetic reconnection site is a critical problem for understanding many plasma systems. For example, the hard X-rays at magnetic field footpoints during a solar flare are believed to be due to energy propagated along magnetic field lines from the reconnection site. Similarly, the auroral signatures during substorms are related to energy transport away from reconnection in the magnetotail. In the substorm case, the time delay between reconnection onset and auroral brightening has in certain cases been found to be substantially shorter than the Alfven transit time, pointing to physics beyond MHD. Kinetic Alfven waves, however, can be much faster and could possibly explain the time lag. To test this possiblity, we simulate large scale reconnection events with the kinetic PIC code P3D and examine the disturbances on a magnetic field line as it propagates through a reconnection region. In the regions near the separatrices but relatively far from the x-line, the propagation physics is governed by the physics of kinetic Alfven waves and generates substantial Poynting flux sufficient to create aurora. Comparisons with Cluster magnetotail reconnection observations will be performed.    [Preview Abstract]

 



CP9.00151: The kinetic structure of slow shocks and reconnection exhausts
Y.H. Liu , J. Drake , M. Swisdak

Ion heating by Petschek reconnection associated slow shocks is one of the potential heating mechanisms for solar flares and the solar wind (ie., Tsuneta 1995). But, the structure of these shocks in a collisionless plasma is still an open question. Therefore a detail study of the kinetic structure of the reconnection exhaust and how ions/electrons are accelerated is necessary. Instead of performing a complete particle-in-cell reconnection simulation, whose simulation domain is strictly limited by the available computational power, a nearly 1-D Riemann problem is designed to study the nonlinear wave propagation of exhaust down to several hundreds ion inertial lengths from reconnection site, with an extension of nearly 500 ion inertial lengths. To our surprise, we find a critical temperature anisotropy (ie., $1-(P_\|-P_\perp)/\mu_0 B^2)$ )= 0.25 around the sharp front of downstream rotational waves of collisionless slow shocks at various oblique propagation angles. An explanation is proposed by looking into the anisotropic fluid theory, in particularly the anisotropic Derivative Nonlinear-Schrodinger-Burgers equation, with an intuitive model of an energy closure for a oblique shock with a fair amount of back-streaming ions that escape from the shock downstream region. The importance of the anisotropy value 0.25 (independent of plasma beta and propagation angle with respect to the magnetic field) is recognized as being the degeneracy point of slow and intermediate modes. At very oblique propagating angles (ie., $\theta_{BN} \ga 80^{\circ}$ ), a firehose-like instability develops in the downstream region, which might link to the proton temperature anisotropy distribution in the solar wind (ie., S. D. Bale et. al 2009).    [Preview Abstract]

 



CP9.00152: Current sheet break-up via fast plasmoid formation in the island coalescence problem the ultra-high Lundquist number regime ($ S \sim 10^9 $)
J.N. Shadid , R.P. Pawlowski , L. Chac\'on , D.A. Knoll

The break-up of Sweet-Parker current sheets into smaller plasmoids has been recently the subject of attention as a possible mechanism for fast reconnection in resistive MHD. Various studies, both theoretical\footnote{N. Loureiro et al., {\em Phys. Plasmas}, {\bf 14} (2007)} and numerical,\footnote{G. Lapenta, {\em Phys. Rev. Lett.}, {\bf 100} (2008)} have shown that the fast formation of small structures is not only possible, but in fact unavoidable for large enough Lundquist numbers. In this study, we have used state-of-the-art computational capabilities to perform simulations of the Fadeev island coalescence problem in the ultra-high Lundquist number regime ($ S \sim 10^9 $) to investigate if thin current sheets dynamically formed in this strongly driven problem are prone to break-up by fast plasmoid instabilities. Our computational capabilities are unique in that we employ massively parallel implicit solvers in combination with static spatial adaptivity to resolve evolving layers, thus guaranteeing numerical accuracy in such challenging regimes. The numerical simulations confirm that plasmoid break-up of dynamically formed current sheets occur for $ S > 10^6 $.    [Preview Abstract]

 



CP9.00153: Hyper-resistivity in 2D-MHD turbulence
Zhibin Guo , P.H. Diamond

Many simulations show when turbulence (or instability) develops in an ordinary Sweet- Parker configuration. The current sheet region will enlarge and then the magnetic reconnection rate will largely increase. This indicates that current diffusion, which can be described by a hyper-resistivity term in mean field's evolution equation, plays an important role in turbulence reconnection. Another reason to study hyper-resistivity is turbulence resistivity is constrained by equipartition tendency (such as in 2D-MHD, it is in the same order with collisional resistivity by Zeldovich relation). A method to deal with this fluctuation-mean field problem is through Two-Scale Direct Interaction Approximation (TSDIA), however with it's complex algebra, no calculation is carried. Here, based on a physical assumption, we used a new method to deal with an inhomogeneous mean field evolution in the existence of strong fluctuation. Since it's simple algebra, we can calculate both turbulence resistivity and hyper-resistivity explicitly. The result shows they share a similar structure with quasi-linear one. An estimation is also made which shows the reconnection rate scale.    [Preview Abstract]

 



CP9.00154: Fast 2D magnetic reconnection: relating anomalous resistivity and two-fluid MHD models
V.S. Lukin , M.G. Linton

It is well-known that the laminar 2D uniform resistivity MHD model of magnetic reconnection is too slow to reproduce reconnection rates inferred from astrophysical observations. Several alternative micro-physics models have been developed to address this problem. In particular, it has been shown that both the ion-electron two-fluid model and the anomalous resistivity singe-fluid MHD model are capable of altering the structure of the 2D reconnection region to allow for reconnection rates that are sufficiently fast to be consistent with the observations. Here, we attempt to relate the two models by conducting simulations using both in a large idealized domain. To do so, we take advantage of the freedom to choose a particular form of anomalous resistivity and the existing analytic descriptions of the reconnection region within both models. We use the analytical tools to choose a form of resistivity to reproduce the characteristics of a two-fluid reconnection region and validate it in self-consistent numerical simulations. Implications of the study for using anomalous resistivity to model two-fluid effects in macroscopic MHD simulations will be discussed.    [Preview Abstract]