Bulletin of the American Physical Society
2005 47th Annual Meeting of the Division of Plasma Physics
Monday–Friday, October 24–28, 2005; Denver, Colorado
Session KP1: Poster Session V |
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Room: Adam's Mark Hotel Grand Ballroom I & II 9:30am |
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KP1.00001: C-MOD, JET, AND FUTURE DEVICES |
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KP1.00002: Plasma Performance Study on an All-metal Tokamak -- Alcator C-Mod Yijun Lin, B. Lipschultz, E. Marmar, M. Greenwald, A. Hubbard, I. Hutchinson, J. Irby, B. LaBombard, M. Reinke, J. Rice, S. Scott, J. Terry, D. Whyte, S. Wolfe, S. Wukitch High-Z plasma facing components (PFCs) are being considered by ITER owing to their advantages such as low tritium retention and high heat flux handling capability. After replacing all boron nitride (BN) protection tiles on the ICRF antennas with molybdenum tiles and removing boron residues on the in-vessel Mo tiles, we transformed Alcator C-Mod back to a genuine all-metal tokamak prior to the FY2005 experimental campaign. The ICRF antennas were found to have the same power and voltage handling capabilities as previously with BN tiles. The RF heated H-mode performance with plain Mo wall was rather poor with H89 $\sim $ 1.0 along with high radiated power. Boronization was shown to be necessary in obtaining the best performance plasmas, by reducing the Mo level and radiated power in the plasma. We have carried out experiments to study the effect of boronization at different boron deposition locations. A variety of boronization techniques, including electron cyclotron discharge, glow discharge, and between-shot boronization, has been compared. A new world tokamak record of volume average pressure $<$P$>$ = 1.8 atmosphere, at ITER B field and ITER beta normal, was achieved in Alcator C-Mod with a boronized all-metal wall. [Preview Abstract] |
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KP1.00003: A Statistical Analysis of Momentum Transport Scaling in Alcator C-Mod Plasmas with No Momentum Input Yuri Podpaly, Charles Bocchino, John Rice, Alexander Ince-Cushman It has been observed that in L- to EDA H-mode transitions with no momentum input and in L-mode plasmas with auxiliary ICRF hearing in Alcator C-Mod tokamak plasmas there exists an anomalous momentum transport. A one dimensional, source free, momentum transport equation at the central chord of the plasma, ignoring convection and treating boundary conditions as a step function, was used to model the core velocity obtained by a high resolution x-ray spectrometer. It was found that the momentum diffusivity varied between D$_{\phi ,H}\sim $ 0.1 m$^{2}$/s and D$_{\phi ,L} \quad \sim $ 0.3 m$^{2}$/s which corresponded to a characteristic momentum confinement time ($\tau _{\phi ,L} \quad \sim $ 0.02 s, $\tau _{\phi ,H} \quad \sim $ 0.08 s). In order to find a plasma scaling law $\tau _{\phi }$ was compared to plasma parameters initially focusing on H-factor, energy confinement time, density, and current. Initial results suggest a positive correlation between H-factor and momentum confinement time. [Preview Abstract] |
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KP1.00004: The H-mode Power Threshold and Plasma Rotation in Alcator C-Mod John Rice, Martin Greenwald, Jerry Hughes, Amanda Hubbard, Brian LaBombard, Yijun Lin, Earl Marmar, Steve Wolfe, Steve Wukitch It has long been known that the H-mode power threshold is higher with the X-point located away from the gradB drift direction. Recently, the role of rotation in the H-mode transition has been indicated in C-Mod plasmas. L-mode discharges in the USN configuration (away from gradB) exhibit strong (50 km/s) rotation in the counter-current direction, both in the core and at the edge. LSN discharges have relatively modest counter rotation. Application of ICRF power, which increases the plasma stored energy, increments the rotation in the co-current direction, proportionately. The transition to H-mode occurs when the core rotation switches from counter- to co-current, hence higher power is required to induce the transition in USN. Recent results with varying plasma current will be presented. [Preview Abstract] |
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KP1.00005: High Performance ITB Plasmas in Alcator C-Mod C.L. Fiore, N.P. Basse, P.T. Bonoli, D.R. Ernst, A.E. Hubbard, M.J. Greenwald, E.S. Marmar, J.E. Rice, S.M. Wolfe, S.J. Wukitch, K. Zhurovich, P.E. Phillips Internal transport barrier plasmas with average pressure greater than 1 atmosphere have been obtained in Alcator C-Mod using two techniques. In one method, high magnetic field (6.3T) and high plasma current (1.3 MA) are combined with 3 MW off-axis ICRF power to optimize the performance. In the other, high off-axis power ($>$ 2.3 MW) is used to create an ITB plasma which is then heated with central ICRF power. To form an ITB in the pressure channel, particle and thermal flux is reduced in the barrier region which then allows the Ware pinch to peak the central density while maintaining the central temperature. Gyrokinetic code simulation suggests that steepening of the density profile destabilizes TEM modes inside the barrier, ultimately driving sufficient outgoing particle flux to balance the inward pinch and halt further density rise. Experimentally, increasing levels of density fluctuations are observed as the central density peaks, although the location of these fluctuations is not resolved. This report will examine the recent high power operation and explore the implications of increased turbulent transport on high power operation. [Preview Abstract] |
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KP1.00006: Investigation of the triggering mechanism for internal transport barriers in Alcator C-Mod. K. Zhurovich, C.L. Fiore, D.R. Ernst, A.E. Hubbard, M.J. Greenwald, E.S. Marmar, J.E. Rice Internal transport barriers (ITBs) can be routinely produced in C-Mod steady enhanced D$_{\alpha }$ (EDA) H-mode plasmas by applying ICRF at $\vert $r/a$\vert \quad \ge $ 0.5 (off-axis heating). The triggering mechanism of these ITBs is under consideration. The importance of the magnetic shear and the critical scale length a/L$_{T}$ are being explored. Preliminary results from TRANSP analysis suggest that the ITB triggering could depend on the magnetic shear. At the same time a/L$_{T}$, which has been seen to decrease as the ICRF resonance position is moved outward by raising the magnetic field, is likely to play a role in suppressing ITG turbulence. These effects are studied using a kinetically constrained EFIT model as well as the gyrokinetic code GS2. Recent experimental results as well as the results from the analysis will be presented. [Preview Abstract] |
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KP1.00007: Density and Temperature Fluctuations in on Alcator C-Mod Plasmas with Peaked Density Profiles P.E. Phillips, W.L. Rowan, M.B. Sampsell, R.B. Bravenec, A.G. Lynn, N. Basse, B. Bose, E.M. Edlund, C. Fiore, A. Hubbard, L. Lin, M. Porkolab, E.S. Marmar, S.J. Wukitch Core density and temperature fluctuations in plasmas with peaked density profiles are observed with a heterodyne electron-cyclotron-emission (ECE) system in the Alcator C-Mod tokamak. ECE systems typically measure electron temperature only; this ECE system is also able to detect density fluctuations in certain cases due to its oblique viewing angle and refractive effects as the densities near cut-off. The diagnostic is unique in that the signal fluctuations are an amplified version of the density fluctuations. The peaked density profiles are a result of internal transport barriers (ITB's) generated by two different methods: off-axis ion cyclotron resonance heating (ICRH) and lithium pellet injection. The principle results described here are the first measurements of localized core fluctuations in the Alcator C-Mod ITB and of fluctuations associated with the quench of the density rise due to the ITB. [Preview Abstract] |
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KP1.00008: Simulations of disruption mitigation by high-pressure gas jet on Alcator C-Mod V.A. Izzo, R.S. Granetz, D.G. Whyte, M. Bakhtiari A high pressure gas-jet system has recently been tested as a means of disruption mitigation on Alcator C-Mod. Magnetohydrodynamic simulations are performed with NIMROD to investigate the mechanisms of thermal quench onset given various assumptions about impurity penetration depth and radiative cooling rate. Several simulations in which impurity penetration is varied between 1.5 and 3cm from the separatrix demonstrate the importance of proximity to the q = 2 surface for producing a rapid thermal quench. While the 2/1 mode is destabilized in all cases as the current profile contracts, radiative cooling at q = 2 greatly increases the growth rate of the mode over those cases where the impurities do not extend to q = 2. In the latter cases, the thermal quench begins once the width of the 2/1 island grows to overlap with the radiating edge, at which point stochastization of the flux surfaces begins. In another simulation, results from the radiative cooling code KPRAD are used as input for NIMROD, to produce more realistic radiation rates with the goal of performing a detailed comparison with experiment. Plans for running the two codes interactively are in development. [Preview Abstract] |
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KP1.00009: Molybdenum density profiles on C-Mod using FAC generated cooling curves M. Reinke, I. Hutchinson, B. Lipschultz, J. Rice, J. Terry For tokamaks with high-Z plasma facing components, maintaining a low impurity content is necessary to produce high quality, repeatable discharges. A GENeral Impurity Emissivity (GENIE) method is outlined for determining impurity profiles using experimental spectroscopy data, an impurity transport code, and the atomic physics package, Flexible Atomic Code (FAC). Modular programming is emphasized in order to make the method extendable to arbitrary impurities, diagnostic sets and tokamaks. Development of GENIE is ongoing, but a necessary first step is to verify FAC. A testing stage of GENIE that ignores transport is demonstrated and the results are validated against the published molybdenum cooling-curve generated using HULLAC. Bolometry and Thomson scattering data are used to determine molybdenum density profiles on Alcator C-Mod using the Mo cooling-curve. Instances where this method fails are shown as well to illustrate the need for a more advanced version of GENIE that generates and uses charge state distributions that assume transport. [Preview Abstract] |
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KP1.00010: Impurity poloidal rotation for 0.75 $<$ r/a $<$ 1.0 in Alcator C-Mod plasmas W.L. Rowan, I.O. Bespamyatnov, R.V. Bravenec, D.R. Ernst, D.F. Beals, R.S. Granetz, R.M. McDermott Measurements of poloidal rotation, temperature, and density gradient for boron impurity ions in Alcator C-Mod will be presented for 0.75 $<$ r/a $<$ 1.0 in L-mode, enhanced D-alpha (EDA), and ELMing H-Mode discharges. The emphasis here is on comparing poloidal rotation in different discharge regimes and on comparison with neoclassical predictions. The measurements are derived from CXRS and from spectroscopy of ambient impurity emission. For the CXRS data, the main analysis issues are proper accounting for the empirical uncertainties in the rotation measurement and the energy dependence of the charge exchange cross sections. For the ambient data, it is unfolding of the local rotation from chord-averaged measurements. Profile changes of the rotating impurity play a role in understanding the poloidal rotation changes in the L to H transition so impurity profiles will be included where possible. We will also present radial electric field estimates based on the measurements. [Preview Abstract] |
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KP1.00011: Ion temperature in Alcator C-Mod H-mode discharges with ELM's and with the quasi-coherent (QC) mode Igor O. Bespamyatnov, W.L. Rowan, R.V. Bravenec, D.F. Beals, R.S. Granetz, A.M. Hubbard, R.M. McDermott, J.L. Terry H-mode regimes with discrete ELM's may offer the advantage of steady state but possibly coupled with the disadvantage of enhanced divertor erosion. On C-Mod, the enhanced D-alpha (EDA) H-mode regime achieves steady state through increased particle transport due to a high m and n QC mode rather than via discrete ELM's. Recently, a robust H-mode with discrete ELM's (possibly type 1) was produced in C-Mod during JFT-2M similarity studies. This new C-Mod regime offers the possibility of comparing ion temperature near the pedestal in steady state H-mode discharges where particle transport is increased with the commonly observed QC mode or with ELM's. Thermal transport analysis (TRANSP) will be included in the comparison. The data presented is from analysis of ambient spectra and charge exchange recombination spectroscopy (CXRS). CXRS analysis using a DNB will be discussed in detail, including expected uncertainties and limits on ion temperature, rotation, and density. A long pulse, high current beam was recently installed and is now commissioning on C-Mod. Expected improvements in CXRS will be discussed. [Preview Abstract] |
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KP1.00012: Statistical Analysis of Charge Exchange Measurements of Ion Temperature and Velocity at the Edge of Alcator C-Mod Rachael McDermott, Bruce Lipschultz, Ian Hutchinson, William Rowan Charge exchange spectroscopy yields ion temperatures and velocities by measuring the Doppler width and shift of a spectral line emitted by the population of ions in question. There are uncertainties inherent in such measurements due to the photon statistics associated with the spectra and the presence of a distribution of background photons. These statistical uncertainties can be calculated without fitting the line shape provided that knowledge of the CXS signal and background distributions is available. These uncertainties represent the minimum uncertainties achievable through the line fitting process. Two such analyses have been performed at Alcator C-Mod to determine the constraints statistical uncertainties impose on the reliability of charge exchange measurements in the pedestal region of Alcator C-Mod. The uncertainty imposed by the fit to the spectrometer instrument function has also been examined. [Preview Abstract] |
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KP1.00013: Characterization of the New Diagnostic Neutral Beam on Alcator C-Mod R.V. Bravenec, W.L. Rowan, I. Bespamyatnov, R.S. Granetz, D.F. Beals, R. McDermott, J. Ko, S.D. Scott A new diagnostic neutral beam (DNB) manufactured by the Budker Institute of Nuclear Physics has been installed on Alcator C-Mod.~ The beam is capable of 7A extraction current at 50 kV for a continuous duration of 1.5 s, or up to 3.0 s with modulated duty cycle. This is in contrast to the previous DNB which was limited to a 50-ms pulse at $\sim $5A. Characteristics of the beam such as its density in the plasma and cross-sectional profile measured using beam-emission spectroscopy (BES) will be presented, as will component mix, beam divergence, and neutralization fraction measured spectroscopically in the drift duct. In addition, first results from BES measurements of plasma density fluctuations using the new beam will be presented and discussed. Likewise, we present first results from charge-exchange recombination spectroscopy and the expected uncertainties in boron temperature, rotation, and density as functions of beam brightness. [Preview Abstract] |
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KP1.00014: Study on the Characteristics of Wire Grid Polarizer for Alcator C-Mod Motional Stark Effect Diagnostic Jinseok Ko, Steve Scott A wire grid polarizer (WGP) has been installed on the in-vessel optics module of the Motional Stark Effect (MSE) diagnostic system in Alcator C-Mod tokamak. The polarized light produced by this WGP can be utilized to measure the change in polarization angle by Faraday rotation through the diagnostic system when the tokamak is operated in its normal condition. Intensive WGP tests on the off-site optical table have been done to investigate the effect of non-normal incidence on the WGP which is indeed the situation inside the tokamak. A model has been developed to understand and simulate various effects of the WGP structure such as changes in angle-of-incidence and reflection/transmission coefficients due to the anti-reflection coating layer and the glass substrate. These analytic predictions and test results are compared with the tests in the tokamak where the in-vessel WGP is used. [Preview Abstract] |
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KP1.00015: Visible Spectroscopy for Doppler Measurements on Alcator C-Mod using a Transmission Grating Spectrometer Alexander Graf, Mark May, Peter Beiersdorfer, William Rowan A high throughput (f/3) Doppler spectrometer has been installed on the Alcator C-Mod tokamak for the 2005 run campaign. This spectrometer will be used for ion rotation velocity and ion temperature measurements. The impurity rotation and temperature will be determined from the Doppler shifted and broadened spectral lines of ionized impurities in the plasma (e.g. B II, B V and Ar IX). We have measured first spectra using several fiber optic views both in the divertor and inside the separatrix at the midplane. We have been able to measure a spectral resolution ($\lambda/\Delta \lambda$) of 13000 (FWHM = 0.5 $\AA$). Comparisons with the existing visible spectrometers, Chromex and Kaiser, will be given. [Preview Abstract] |
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KP1.00016: Spatially resolved neon and fluorine soft X-ray spectra on Alcator C-MOD Alexander Ince-Cushman, John Rice, Manfred Bitter, Sang Gon Lee, Yuri Podpaly A new high resolution ($\lambda $/$\Delta \lambda \sim $2000) x-ray spectrometer has been installed on Alcator C-Mod. The spectrometer consists of a spherically bent mica crystal and an x-ray sensitive CCD camera arranged in the Johann configuration which allows for spatial resolution in one dimension. The system was designed to measure impurity temperature and rotational velocity based on emission line spectra from helium-like neon (1s$^{1}$2p$^{1}\to $1s$^{2})$ in a narrow spectral band centered on $\lambda $=13.5 {\AA}. The instrument was mounted with a radial view below the midplane (r/a$\sim $0.8). This view allows for impurity temperature profile measurements -- and potential measurements of the poloidal rotation velocity profile - in the pedestal region. The fact that the view is radial prevents the measurement of toroidal rotation. In addition to the neon emission lines, strong fluorine lines (1s$^{1}$4p$^{1}\to $1s$^{2})$ were also observed. The presence of these fluorine lines makes it possible to simultaneously make spatially resolved measurements of both the neon and fluorine impurities with a single diagnostic. [Preview Abstract] |
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KP1.00017: Toroidal Flow Measurements of the Pedestal Region of Alcator C-Mod Using a $D_2$ Puff to Stimulate Boron CXRS Kenneth Marr, Bruce Lipschultz, Brian Labombard, John Rice, James Terry Here we present the use of Charge-eXchange Recombination Spectroscopy (CXRS) to measure the toroidal velocity and temperature of fully-stripped boron in the inner-wall pedestal region (region around the last closed flux surface) of Alcator C-Mod. The $n = 7 \rightarrow 6$ emission at 494.467nm is stimulated by a puff of neutral $D_2$ gas at the inner-wall midplane. The puff localizes the emission and negates the need for line-of-sight integration. It is assumed that the boron has obtained equilibrium with the bulk plasma and therefore is also a good measure of bulk toroidal velocity and temperature. The measurement apparatus, analysis methodology, and some results are presented here. The results will also be compared to similar measurements of the same parameters. Though potentially able to provide continous measurement (depending on puff length) of these parameters in the pedestal region, this method provides only a limited radial profile due to the limited intersection of $B^{+5}$ with the injected neutrals. [Preview Abstract] |
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KP1.00018: Pellet Imaging Diagnostic Brock Bose, Earl Marmar Ultra high speed imaging (max frame rate = 500 kHz) of injected Li pellets into Alcator C-Mod during previous campaigns identified the presence of poloidally moving striations in the pellet's ablation cloud. The behavior of these striations is remarkably different in L-mode and H-mode plasmas. In L-mode plasmas, the velocity of the striations tend to change direction on a length scale of the order of tens of gyro-radii, ranging from $\pm$3000 m/s. In H-mode plasmas the striations currently have only been observed to move in the direction of the ion diamagnetic drift, with velocities that range up to 4000 m/s. During the 2005 campaign a stereoscopic imaging system was installed on Alcator C-mod to observe the ultra- short time scale (2 $\mu$s) ablation dynamics of injected lithium pellets in order to determine the cause for both the formation and evolution of these striations. Presented here are the experimental observation of the ablation process and explanation in terms of ablation dynamics and radial electric fields in the tokamak plasma. [Preview Abstract] |
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KP1.00019: Electromechanical Tests of a New Scanning Probe for Alcator C-Mod Noah Smick, Brian Labombard The success of a recently installed magnetically-driven swing probe on the high-field side scrape-off layer in Alcator C-Mod$^{1}$ has prompted us to proceed with a second, more capable electromechanical probe. The new probe will plunge linearly into the plasma and will use four electrodes to provide temperature and density profiles and potential fluctuations as well as parallel and perpendicular Mach number with high spatial resolution up to the separatrix. This probe will be used to investigate in more detail the ballooning-like transport asymmetry and resultant strong plasma flows observed by the original probe. The electromechanical response of the new probe is presently being evaluated in a 4.5 tesla magnetic field. These tests will allow us to develop a model for the eddy currents and back-EMF that the device will experience in C-Mod. This work also allows us to evaluate the mechanical action and durability of the design. $^{1}$N. Smick et al., J. Nucl. Materials \textbf{337-339} (2005) 281, N. Smick et al., Bull. Amer. Phys. Soc. \textbf{49} (2004) 74. [Preview Abstract] |
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KP1.00020: Initial Results from the C-Mod Prototype Polarimeter-Interferometer K.R. Smith, J. Irby, R. Leccacorvi, E. Marmar, R. Murray, R. Vieira An FIR interferometer-polarimeter system is being developed to measure density and poloidal field profiles and fluctuations in C-Mod. During the last run campaign a CO$_{2}$ and HeNe prototype system using a set of retro-reflectors on the inner wall was made operational to determine the level of vibration compensation required, and the noise levels to expect in the experimental environment.~ Scrape-off layer plasma effects were also evaluated as well as the survivablity of the invessel components.~ A standard two-color system was used for density measurements while two different techniques were used to assess polarization measurement noise levels. Results from these measurements will be discussed as well as the design of the prototype system. [Preview Abstract] |
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KP1.00021: A Laser Scattering Diagnostic for Real-Time Measurements of Dust in Alcator C-Mod Aaron Bader, Robert Granetz We assembled a prototype diagnostic for future installation inside Alcator C-Mod to detect large particles (dust) in the scrape off layer. The diagnostic will use a photomultiplier tube to detect scattered laser light from particles in the beam path. The laser beam will be introduced into the vessel using fiber optics and similarly the scattered light will exit the vessel through fiber optics and an optical filter. We present the design for the diagnostic and initial lab results indicating limits on particle size detection. Additionally, we present issues dealing with the installation including background bremsstrahlung noise and places in the vessel that the diagnostic may be installed. [Preview Abstract] |
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KP1.00022: An upgraded PCI diagnostic to detect and localize high-k waves and fluctuations in Alcator C-Mod* L. Lin, M. Porkolab, N.P. Basse, E.M. Edlund, D.R. Ernst, Y. Lin, S.J. Wukitch Phase Contrast Imaging (PCI) diagnostic has been used previously to study mode conversion of ICRF waves$^{1}$ and plasma fluctuations in the ITG/TEM regime$^{2}$. Recent modifications to the imaging optics have increased the maximum k$_{R}$ from 8 cm$^{-1}$ to 25 cm$^{-1}$. New digitizers extend the frequency response to 5MHz (sampling rate of 10MHz). This makes it possible to study microscale turbulence in the ETG regime (k$_{\bot } \rho _{e}\sim $0.1, f$\le $5MHz). Furthermore, mode converted waves in the ICRF regime will be studied where k$_{\bot }\sim $10-25 cm$^{-1} $ correspond to ICW/IBW waves$^{1}$. A system consisting of a partially masked phase plate on a rotatable stage has been installed, which provides localized measurements for large k$_{\bot }$ fluctuations along the vertical 32 channel viewing chords$^{3}$. Initial results of high-k and vertical localization measurements will be presented. \\ \\$^{*}$Work supported by U. S. DOE under DE-FG02-94-ER54235 and DE-FC02-99-ER54512. \\ \\$^{1}$E. Nelson-Melby et al, Phys. Rev. Letts. \textbf{90}, 155004 (2003). \\$^{2}$N. Basse et al, Phys. Plasmas \textbf{12}, 052512 (2005). \\$^{3 }$S. Kado et al, Jpn. J. Appl. Phys. \textbf{34}, 6492 (1995). [Preview Abstract] |
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KP1.00023: Reflectometry Upgrade on Alcator C-Mod Arturo Dominguez, N.P. Basse, J. Irby, Y. Lin, E.S. Marmar, G.J. Kramer We present results from the baseband upgrade conducted on the reflectometry diagnostic system in the Alcator C-Mod tokamak and outline plans for additional upgrades to be implemented in the near future. Until now, the reflectometry apparatus has used the amplitude modulation (AM) technique to study the density profile and density fluctuations in C-Mod. Despite being appropriate for profile measurements, the AM technique has a reduced turbulence sensitivity as compared to the baseband technique. An initial upgrade \footnote{Y. Lin, PhD Thesis} preformed by Y. Lin {\it {et al}} on the 88GHz channel (corresponding to $n_e=$9.58 $10^{19} m^{-3}$) is explained and its characteristic measurements are shown as compared with the AM results. Two higher frequency channels (132GHz and 140GHz) using the baseband technique have been installed in collaboration with PPPL and initial results will also be presented. Based on the improved performance of the apparatus due to its initial upgrade, a full baseband upgrade is proposed for all remaining channels (50GHz, 60GHz, 75GHz and 110GHz) in the reflectometry system. [Preview Abstract] |
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KP1.00024: Observation of reverse shear Alfv\'{e}n eigenmodes in Alcator C-Mod and their modeling with NOVA* E.M. Edlund, M. Porkolab, N.P. Basse, L. Lin, S.J. Wukitch, G.J. Kramer The phase contrast imaging (PCI) system on Alcator C-Mod has observed reverse shear Alfv\'{e}n eigenmodes (RSAE) during the current ramp with early ICRF heating. Using the ideal MHD code NOVA$^{1}$, the frequency chirping characteristics of these modes can be modeled with good accuracy. It is noted that the minimum frequency may be interpreted as the geodesic deformation of Alfv\'{e}n continuum at low frequency$^{2}$. RSAEs observed with PCI show intermittent behavior that suggests a significant continuum interaction. Ignoring fast particle effects, the MHD eigenmode solutions from NOVA are compared to the experimental data. The central shear and q$_ {min}$ are adjusted until a good fit is achieved. Possible q profiles based on this analysis will be presented. \\ \\$^{*} $Work supported by USDOE Contract DE-AC02-76-CH0-3073 and Coop. Agree. No. DE-FC02-99-ER54512\\ \\$^{1}$C.Z. Cheng and M.S. Chance, J. Comp. Phys. \textbf {71}, 124 (1987).\\ $^{2}$M.S. Chu et al., Phys. Fluids B \textbf{4}, 3713 (1992). [Preview Abstract] |
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KP1.00025: A Comparison of Measured and Calculated TAE Damping Rates in Alcator C-Mod J. Snipes, J. Sears, N. Gorelenkov The damping rates of stable moderate toroidal mode number (3 $\le $ n $\le $ 14) toroidal Alfv\'{e}n eigenmodes (TAEs) have been measured in C-Mod Ohmic plasmas through synchronous detection of magnetic pick-up coil signals with actively driven antenna current signals in a number of discharge conditions. The measured damping rates are in the range 0.5{\%} $< \quad \gamma $/$\omega $ $<$ 4{\%}, which are similar to those measured in JET for n=1. In contrast to JET, however, the damping rates are lower for diverted plasmas with relatively high elongation and larger for inner wall limited plasmas with low elongation. Several of these discharges have been modeled with the Nova-K code to calculate the expected damping including continuum, radiative, collisional, and Landau damping. The modeling is found to be very sensitive to the assumed safety factor profile with a $\pm $10{\%} change in q resulting in up to an order of magnitude change in the calculated damping rate. Given this sensitivity, it is possible to get good agreement between the experiment and the modeling for reasonable q profiles. An accurate benchmarking of the code with experiment would require very accurate measurements of the q profile that are presently not available. [Preview Abstract] |
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KP1.00026: Results from Real-time Open-loop Alfv\'{e}n Eigenmode excitation in Alcator C-Mod J. Sears, W. Burke, R.R. Parker, J. Snipes, V. Tang, S. Wolfe, A. Fasoli The Active MHD diagnostic system excites Alfv\'{e}n eigenmodes in Alcator C-Mod and measures their damping rates, or margin to instability. Resonant modes are stimulated with two moderate-n antennas positioned above and below the outboard midplane. The antennas are fed by power amplifiers equipped with automatically tuned capacitive networks capable of matching in the range of 30 kHz to 1 MHz. The driving frequency follows in real-time the center of the Toroidal Alfv\'{e}n Eigenmode gap, $f_{TAE}=v_A/4\pi qR$, making small excursions away from the gap to observe the modes' damping characteristics. The effect of shear on mode damping rate was studied during an elongation scan of inner wall limited plasmas. The destabilizing effect of ICRF-heated fast ions with energies above 1/3 the Alfven speed, $v_A=B/ \sqrt{ \mu_0 \rho}$, was also studied. Finally the diagnostic regularly records mode damping rates in plasmas tailored to other experiments. Results are presented. [Preview Abstract] |
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KP1.00027: First Results From the Alcator C-Mod Lower Hybrid Experiment Ronald Parker, Nils Basse, Stefano Bernabei, Nevell Greenough, Montgomery Grimes, David Gwinn, Joel Hosea, David Johnson, Atma Kanojia, Brian LaBombard, John Liptac, David Terry, James Terry, Gregory Wallace, Randy Wilson A lower hybrid system operating at 4.6 GHz and capable of 3 MW source power has been installed on Alcator C-Mod. The grill facing the plasma consists of 4 rows of 24 waveguides. Electronic control of the amplitude and phase of the 12 klystrons supplying the RF power enables the launcher's n$_{\vert \vert }$ spectrum to be dynamically controlled over a wide range with a time response of 1 ms. Since the deposition of current depends on n$_{\vert \vert }$ as well as the temperature profile, the spatial distribution of the driven current can be varied with the same time response. Detection of fast electron Bremsstrahlung is the primary means of monitoring the driven current profile. Initial measurements at the 100 kW power level show that reflection coefficients as low as 7{\%} are obtained at optimal phasing and density at the grill mouth. Comparison of these results with modeling predictions will be presented in a companion paper. [Preview Abstract] |
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KP1.00028: Modeling of Lower Hybrid Experiments on Alcator C-Mod J. Liptac, P. Bonoli, R. Parker, B. LaBombard, V. Tang, Y. Peysson, J. Decker, R. Harvey Correct interpretation of lower hybrid current drive experiments requires detailed modeling of coupling, power deposition, and hard x-ray emission. Results from a LH coupling code[1] are compared to measurements of the reflection coefficients using local plasma parameters at the grill. Simulation of current drive experiments and the resulting hard x-ray spectra are performed using the Fokker-Planck codes CQL3D[2] and DKE[3] coupled to ray tracing. Results from CQL3D and DKE are compared for different antenna phasings in which the forward parallel refractive index is varied from 2 to 3. Simulations are also used to investigate the use of ``compound'' launcher spectra to control the location of LH current generation. [1] M. Brambilla, Nuclear Fusion(16) 1, 1976 p47 [2] R. Harvey and M. McCoy, GA-A20978, 1992 [3] J. Decker and Y. Peysson, EUR-CEA-FC-1736, 2004 [Preview Abstract] |
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KP1.00029: Modeling of Nonthermal Electron Cyclotron Emission due to Lower Hybrid Current Drive on Alcator C-Mod A.E. Schmidt, P.T. Bonoli, A.E. Hubbard, R.W. Harvey, A.P. Smirnov Lower Hybrid Current Drive (LHCD) has been installed on Alcator C-Mod and will soon be increased in power for current profile control. The lower hybrid waves will generate non-thermal electrons, which will affect the electron cyclotron emission (ECE) spectrum. C-Mod has several outboard midplane ECE diagnostics, normally used to measure electron temperature in Maxwellian plasmas. CQL3D/GENRAY [1] is a modeling package that employs a 3-D Fokker-Planck solver and performs a self-consistent nonthermal ECE calculation. It receives an input of thermal temperature and density profiles as well as injected LH N$_{\vert \vert }$ spectrum, and returns perturbed distribution functions and the ECE spectra associated with these distributions. GENRAY's output of ECE spectra with varied LH powers and plasma parameters can be compared to thermal spectra. These will be used to determine the conditions under which the ECE temperature measurements are reliable. Simulations also provide information about how the ECE spectra can be used to determine properties of the nonthermals, including spatial and energetic distribution. [1] R. W. Harvey and M. G. McCoy, General Atomics Report GA-A20978 (1992). [Preview Abstract] |
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KP1.00030: Experimental studies of C-Mod ICRF minority tails via a multi-channel compact neutral particle analyzer V. Tang, R. Parker, P. Bonoli, C. Fiore, R. Granetz, A. Hubbard, J. Irby, Y. Lin, J. Liptac, E. Marmar, S. Wukitch, K. Zhurovich, R. Harvey, R. Andre Recent experimental results from the upgraded multi-channel Compact Neutral Particle Analyzer (CNPA) system are presented and compared with numerical simulations. The CNPA system consists of Si diode detectors and measures charge exchange (CX) induced energetic ($>$40 keV) neutral particles for ICRF hydrogen minority tail temperature diagnosis. A new long-pulse diagnostic neutral beam (DNB) provides the neutrals for active CX. The discussed data involve measurements of the Hydrogen-minority energy spectrum during low to moderate (n$_{e}$l$\sim $2x10$^{20}$/m$^{2})$ density ICRF plasmas with up to $\sim $3 MW of ICRF power and B$_{T }$from 4.4 to 6.2T. During these discharges, evidence of fast ion resonance localization and tail temperatures greater than 100keV is observed. The energy distributions are compared with a synthetic diagnostic based on CQL3D Fokker-Planck simulations. ICRF power deposition densities and efficiencies are also inferred. [Preview Abstract] |
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KP1.00031: Initial results from mode conversion current drive experiments on Alcator C-Mod A. Parisot, S.J. Wukitch, P. Bonoli, Y. Lin, R. Parker, M. Porkolab, A.K. Ram, J.C. Wright Current drive experiments using mode converted waves in the ion cyclotron range of frequencies are being conducted in the Alcator C-Mod tokamak. While the strong and localized electron damping of Ion Cyclotron Waves (ICWs) suggests possible current drive, the efficiency may be lowered by poloidal field and propagation effects, interaction with thermal electrons and magnetic trapping. Using predictions from the full wave code TORIC [M. Brambilla, \textit{Plasma. Phys. Cont. Fusion} 41 (1999)], optimal scenarios have been defined for C-Mod and will be studied experimentally based on loop voltage analysis and changes in the sawtooth period. Initial results will be presented and compared with latest developments in the TORIC modeling. This includes current drive efficiency calculations for ICWs using quasilinear diffusion coefficients from TORIC [Bilato et al., \textit{Nucl. Fusion}, 42 (2002)] imported in the Fokker-Planck codes RELAX [Westerhof et al., Rijnhuizen Report 92-211] and CQL3D [Harvey et al, \textit{Phys. Plasmas}, 12 (2005)]. [Preview Abstract] |
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KP1.00032: Comparison of H and 3He Minority Heated Discharges in Alcator C-Mod ICRF Experiments S.J. Wukitch, Y. Lin, A. Parisot, P.T. Bonoli, M. Porkolab In Alcator C-Mod, minority ion cyclotron heating is the primary auxiliary heating scenario and we have depended upon H minority and 3He minority scenarios for given frequency and magnetic fields, ie H minority at 80 MHz and 5.4 T. Previous 3He minority heating experiments on C-Mod have shown a lower heating efficiency compared with H minority heated discharges and stronger than expected dependence on 3He minority concentration. A qualitative explanation for these results may be the lower single pass absorption for 3He than H minority. The weak absorption allows parasitic absorption mechanisms to compete more effectively than in the case of strong absorption. Previous experiments were limited in scope by the combination of available frequencies and magnetic fields. Recent experiments focused upon a direct comparison of H and 3He heated discharges at $\sim $5 T. Initial results indicate that the heating effectiveness can be optimized and confirm a strong sensitivity to 3He concentration. Results from additional experiments comparing the heating effectiveness and impurity production with H minority heated discharges will be presented. [Preview Abstract] |
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KP1.00033: Alcator C-Mod Digital Plasma Control System S.M. Wolfe, J.A. Stillerman, M. Ferrara, T.W. Fredian, I.H. Hutchinson A new digital plasma control system (DPCS) has been implemented for Alcator C-Mod. The new system was put into service at the start of the 2005 run campaign and has been in routine operation since. The system consists of two 64-input, 16-output cPCI digitizers attached to a rack-mounted single-CPU Linux server, which performs both the I/O and the computation. During initial operation, the system was set up to directly emulate the original C-Mod ``Hybrid'' MIMO linear control system. Compatibility with the previous control system allows the existing user interface software and data structures to be used with the new hardware. The control program is written in IDL and runs under standard Linux. Interrupts are disabled during the plasma pulses to achieve real-time operation. A synchronous loop is executed with a nominal cycle rate of 10 kHz. Emulation of the original linear control algorithms requires 50 $\mu $sec per iteration, with the time evenly split between I/O and computation, so rates of about 20 KHz are achievable. Reliable vertical position control has been demonstrated with cycle rates as low as 5 KHz. Additional computations, including non-linear algorithms and adaptive response, are implemented as optional procedure calls within the main real-time loop. [Preview Abstract] |
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KP1.00034: The role of kinetic electron effects in gyrokinetic turbulence simulations at high and low collisionality David Mikkelsen, William Dorland The influence of kinetic electrons is studied in gyrokinetic turbulence simulations of a C-Mod EDA H-mode plasma. Higher resolution simulations that employ larger domains and extend the range of $k_{\theta}$ qualitatively confirm previous conclusions. First, simulations including realistic geometry, collisions, and kinetic electron effects exhibit a clear Dimits shift in spite of the high collisionality. Second, lowering the collisionality to values more typical of other tokamaks raises the transport and lowers the critical value of $R/L_T$. Linear stability calculations of primary and secondary modes are used to elucidate the role of collisionality in changing the drive of the primary instability and the damping due to secondary instabilities. The stability calculations are also compared to the different requirements for convergence at low and high collisionality. A new method for estimating the uncertainty of time averaged fluxes is presented, and its robustness is demonstrated by application to many long turbulence simulations. [Preview Abstract] |
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KP1.00035: Modelling of Multiple Impurity Effects in Tokamak Boundary Plasmas Paula Belo, Vassili Parail, Gerard Corrigan, John Hogan, David Heading, James Spence, Carine Giroud Recent simulations using the EDGE2D code with \textit{single} impurity species (either C or Ne) indicate that impurity compression and enrichment increase with the electron density until the onset of divertor plasma detachment. However, in ITER the boundary plasma (SOL) may contain \textit{several} impurity species: the fusion ash (He), the wall materials (C, Be, W) and possibly seeded impurities (Ar, Ne). The aim of the present study is to determine if the presence of multiple impurity species in the SOL gives rise to synergistic effects on their compression and enrichment, specifically the effect of C on the screening of a seeded impurity (Ne). EDGE2D simulations for H-mode JET plasmas indicate little effect of C on compression and enrichment of Ne when N$_{C}$/N$_{Ne}$ $<$ 0.3, and a factor of two increase when N$_{C}$/N$_{Ne} \quad >$ 3 (N$_{C}$ and N$_{Ne}$ denote the total impurity content in the computational grid). [Preview Abstract] |
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KP1.00036: Modeling wall/divertor effects on transport in JET trace tritium experiments D.L. Hillis, J. Hogan, K-D. Zastrow, D. Coster, D. Reiter, JET-EFDA Contributors To study SOL effects on particle transport scaling, using available edge data, we analyze three JET T puffing cases with NBI heating, covering a range in n$_{e}$ and with varying ELM behavior. Self- consistent near-inlet wall fluxes and transient ELM effects on wall saturation are calculated with the solps (b2-Eirene) code, while wall recycling is modeled with the WDIFFUSE code. As the measured fueling efficiency for T puffing pulses is $<$10{\%}, near-inlet wall or divertor strike point recycling dominates. The plausible assumption for core T recycling, that 0$<$R$_{Tcore}<$1, may not be valid. Even trace T puffing is found to produces a local high density, T enriched region near the gas inlet. Variations in ELM activity lead to transient particle flux affecting saturation properties. Progress in clarifying the roles of these processes could be achieved through dedicated experiments on edge/pedestal trace T transport, to complement previous core studies. [Preview Abstract] |
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KP1.00037: Edge stability analysis of JET Quiescent H-mode experiments. M.F.F. Nave, G. Huysmans , J-S. Lonnroth, V. Parail, M. Marascheck, W. Suttrop The edge stability of JET QH-mode plasmas has been studied using the transport code JETTO coupled to a quasi-linear model for ballooning and peeling modes. Attempts on JET to access the Quiescent H-mode (QM-mode) regime with counter-NBI heating, produced plasmas with extended ELM-free phases up to 1.5 s duration. These were characterised by continuous edge n=1 MHD modes similar to the DIII-D ``edge harmonic oscillation.'' Some of the edge parameters, such as high edge pedestal temperatures (T$_{i,e }\sim $ 2-3 keV) and high current densities are similar to the ELM-free hot-ion H-mode regime previously studied at JET. The latter was also characterised by an n=1 mode, the outer mode, observed in co- and counter- NBI when the edge was kink unstable, but still below the unstable ballooning threshold. Here we explore the possibility that the edge n=1 mode observed in the QH-mode plasmas may be a saturated peeling/ external kink mode. Continuous peeling modes can be obtained at high edge temperature, because slow current redistribution maintains the edge current unstable for long periods$.$ Modelling assumptions have been verified using the MHD stability code MISHKA. Predictive simulations with current ramp-up and ramp-down will be presented. [Preview Abstract] |
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KP1.00038: Testing the Porcelli Sawtooth Trigger Module G. Bateman, A.H. Kritz, M.F.F. Nave, V. Parail The Porcelli sawtooth trigger model [1] is implemented as a module for the National Transport Code Collaboration Module Library [2] and is tested using BALDUR and JETTO integrated modeling simulations of JET and other tokamak discharges. Statistical techniques are used to compute the average sawtooth period and the random scatter in sawtooth periods obtained during selected time intervals in the simulations compared with the corresponding statistical measures obtained from experimental data. It is found that the results are affected systematically by the fraction of magnetic reconnection during each sawtooth crash and by the model that is used for transport within the sawtooth mixing region. The physical processes that affect the sawtooth cycle in the simulations are found to involve an interaction among magnetic diffusion, reheating within the sawtooth mixing region, the instabilities that trigger a sawtooth crash in the Porcelli model, and the magnetic reconnection produced by each sawtooth crash. [1] F. Porcelli, \textit{et al.,} Plasma Phys. Contol. Fusion \textbf{38} (1996) 2163. [2] A.H. Kritz, \textit{et al.,} Comput. Phys. Commun. \textbf{164 }(2004) 108; http://w3.pppl.gov/NTCC. Supported by DOE DE-FG02-92-ER-54141. [Preview Abstract] |
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KP1.00039: Damping Rate of $n=1$ EAEs as a Function of Plasma Elongation C.J. Boswell, J.A. Snipes, A. Fasoli, D. Testa, JET EFDA Contributors Fast particles can resonate with Alfv\'{e}n eigenmodes (AEs) and drive them unstable up to amplitudes at which they cause rapid radial transport of the fast particles. Knowing the mechanisms that damp the AEs may allow the ability to control the impact they have on the radial transport of the fast particles. Detailed studies of the damping rate of the $n=1$ toroidally-induced Alfv\'{e}n eigenmodes (TAEs) on JET have shown that in limiter discharges as the elongation and triangularity of the plasma shape is increased the damping rate of the TAEs also increases. New studies, presented here, of the damping rate of the $n=1$ elliptically-induced Alfv\'{e}n eigenmodes (EAEs) localized at the edge of the plasma, show that as the plasma elongation, $\kappa$, increases the damping rate decreases to $\gamma/\omega = 0.7$\% at $\kappa = 1.55$, less than 1/4 the TAE damping rate at the same elongation. This may be due to the widening of the EAE gap as elongation increases and therefore less interaction with the shear Alfv\'{e}n continuum, an effect that does not occur for the TAE gap. This difference in behavior between the $n=1$ TAEs and the $n=1$ EAEs may help in the understanding of the processes that lead to the total damping rate of AEs in general. [Preview Abstract] |
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KP1.00040: Recent progress in understanding runaway generation trends during disruptions in JET Vladislav Plyusnin, Jan Mlynar, Barry Alper Runaway electrons (REs) generated during disruptions in large tokamaks can cause high heat loads, melting and sputtering of the materials used for plasma facing components and the vacuum chamber. A comprehensive understanding of the trends of runaway generation is needed to avoid possible detrimental consequences of REs in ITER. Analysis of recent experiments on disruption generated REs in JET [V.V. Plyusnin et al. Fusion Energy 2004, EX/P2-27] requires further advances in the modelling of the runaway process. This paper summarizes recent developments in understanding runaway generation trends achieved on the basis of numerical modelling. The model simulates RE generation from the very beginning of the current quench phase, focussing on the influence of the dynamics of the runaway current-carrying channel in time and space on the evolution of the RE parameters. The experimental trends and numerical simulations show that runaway electrons might be an issue for ITER and therefore it remains prudent to develop mitigation methods that suppress runaway generation. [Preview Abstract] |
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KP1.00041: The Columbus device Matteo Salvetti, Bruno Coppi The Columbus device [1] is proposed as one component of a spectrum of experiments needed to explore the physics of fusion burning plasmas. Columbus has a larger volume than Ignitor by about 50{\%}, lower current densities in the magnet systems and capability to sustain longer plasma pulses. The machine preserves the ability to confine, under macroscopically stable conditions, plasmas with peak pressures exceeding 3 MPa, corresponding to ignition at central plasma densities around 10$^{21}$ nuclei/m$^{3}$ and to reach this regime by ohmic heating alone. The presence of an ICRH system will expand the capabilities of the device. In our opinion, a spectrum of ``Science First'' devices is the only viable path to an efficient fusion program development and plasma ignition is an important milestone to be achieved before undertaking the construction of a Demo reactor requiring minimization of the external heating power. The Iter design envisages that about one third of its heating power be supplied from the outside in order to maintain its plasma pressure at the desired values. The Columbus program is proposed as a U.S. counterpart to the Ignitor project conducted in Italy and to be complementary to it. The machine costs can be minimized by incorporating the main engineering solutions devised for Ignitor. [1] Coppi,B. and Salvetti,M.,``\textit{Highlights of the Columbus Concept}'', M.I.T. Report, PTP02/06 (2002). [Preview Abstract] |
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KP1.00042: Context of the Ignitor Experiment$^*$ G. Cenacchi, F. Bombarda, P. Detragiache, M. Romanelli, B. Coppi, A. Airoldi The Ignitor machine\footnote{B. Coppi, A. Airoldi, et al., \textit{Nucl. Fusion} \textbf{41(9)}, 1253 (2001)} has been designed to produce toroidal plasma currents up to 11 MA within relatively small dimensions with reasonable safety factors against macroscopic plasma instabilities. Ignition is achieved mainly with Ohmic heating, thanks to the high poloidal field obtainable, but an ICRH system is included to add flexibility. Particle fuelling is through both gas and high speed pellet injection. Demonstration of ignition, the study of the physics of the ignition process, and the heating and control methods for a magnetically confined burning plasma are the most pressing issues at present and they are specifically addressed by Ignitor. High magnetic field experiments can overlap with the envisioned operational regimes of large-scale devices in terms of the relevant dimensionless plasma parameters but they are unique in their abilities to approach ignition and thus open the way for better types of fusion reactors. Notice that even with H, He, and D Ignitor will provide results that can justify, by themselves, the construction of the machine. The experimental life of the Ignitor device will follow three stages, characterized mainly by different plasma components: phase I in H and $^4$He, phase II in D and phase III in D-T, where the most ambitious part of the program will be carried out.\\ $^*$Supported in part by ENEA and CNR of Italy and the US DOE. [Preview Abstract] |
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KP1.00043: The Ignitor Experiment: Deuterium-Tritium Phase A. Airoldi, D. Farina, B. Coppi, F. Bombarda, G. Cenacchi, P. Detragiache, M. Romanelli The most ambitious phase of the scientific program of the Ignitor experiment involves Deuterium-Tritium plasmas with magnetic fields up 13 T and plasma current up 11 MA. In the burning plasma regimes envisaged, the control of the plasma evolution and the transition from ignited to sub-ignited discharges are of particular interest. Steady state, sub- ignited conditions are presented where the amount of injected heating, in the presence of sawtooth oscillations, is adjusted so as to compensate for different hypotheses on the thermal ion transport. The results point out that, by properly adjusting the RF injection, similar performances assessed by the ignition critical factor $I_f= P_{\alpha} /P_{loss}$ can be obtained. The confinement time is about 1.5 higher than that of the ITER97L scaling, during the steady state phase, in line with the results obtained by the FTU machine in the presence of ECRH, a heating process like that to be produced by the $\alpha$--particles. Since the physics of transport and stability of fusion plasmas is not yet fully understood and Ignitor is expected to require short times to become productive, its construction will be highly beneficial to future large-scale experiments. Notice that $Q>10$ ($Q=P_ {fus}/P_{input}$) can easily be obtained in Ignitor on the basis of its design. [Preview Abstract] |
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KP1.00044: The ICRH Physics of the Ignitor Experiment A. Cardinali, F. Bombarda, G. Cenacchi, A. Coletti, M. Sassi, B. Coppi, A. Airoldi, R. Maggiora In Ignitor (high field and high plasma current experiment) the ignition phase can be reached by Ohmic heating only. Nevertheless an ICRH system has been included in the design to control the plasma temperature in the sub-ignited phase. To assist the approach to ignition, the ICRH heating can be applied during the ramp of the magnetic field and plasma current, in a Deuterium-Tritium plasma mixture. Taking into account these conditions, an interval of frequencies (80-120 MHz) and powers (5-18 MW, distributed over 4+2 port of the machine by means of double strap antennas), have been selected. A modest amount of power (5-6 MW), at the frequency of 115 MHz, is sufficient to accelerate considerably the attainment of ignition by increasing the plasma temperature near ``ideal ignition'' conditions, where bremsstrahlung emission is compensated by $\alpha$-particle heating. Full wave code simulations (D-T 50\%-50\%, $B_T(0)$ from 9 to 13 Tesla, and $I_p$ from 7 to 11 MA) have shown a direct ion heating at the second harmonic of Tritium, with a power transfer of 80\% on the bulk ion species and the remainder on the electrons. The resulting deposition profiles are used to study of the temperature profiles evolution and the $\alpha$-particle production by appropriate transport codes. [Preview Abstract] |
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KP1.00045: Magnetic Diagnostics for Ignitor F. Alladio, G. Pizzicaroli, F. Bombarda All the electromagnetic diagnostics commonly used in present experiments to measure plasma parameters such as current, loop voltage, horizontal and vertical position, plasma beta, toroidal and poloidal modes, etc., are adopted for Ignitor. The moderate neutron fluence and very intense neutron flux expected in Ignitor demand the use of fully inorganic insulating materials, for which permanent radiation damage should be limited, but transient, reversible effects cannot be excluded. More data is needed to verify the sensitivity of the chosen materials to the radiation background, but in the meantime, an R\&D program has started with the purpose of selecting insulator materials, testing impregnation techniques, verification of installation feasibility for all types of magnetic diagnostic coils. Full size prototypes are being manufactured. The magnetic coils system must be closely integrated with the plasma chamber as it requires early installation. While the initial positioning of the in-vessel components should be possible with relative ease (before the welding of the individual sectors of the plasma chamber), their replacement and maintenance in the course of the experimental life of the machine can be problematic. Therefore, an adequate level of redundancy is being considered. [Preview Abstract] |
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KP1.00046: Plasma Position Diagnostics for Ignitor G. Pizzicaroli, G. Maddaluno, F. Bombarda The new Gas Electron Multiplier (GEM) detectors, developed at CERN, have demonstrated the possibility of their use for fusion plasma diagnostics in recent measurements obtained by the NSTX and FTU devices. Their application to burning plasma experiments, specifically Ignitor, is being considered for measurements of plasma radiation in the UV and X-ray spectral range. In particular, the high counting rate capability of these detectors can be used for real-time control of the plasma vertical and horizontal positions. At the same time, alternative imaging methods employing fast IR thermography are also being considered for the same purpose. In order to verify the viability of GEM detectors as a diagnostics suitable for Ignitor, a basic version of the instrument, featuring a small diameter (30 mm) and only few pixels read-out, is being assembled for easy installation on any presently available device, in a location close to the plasma. The positioning of the detector relatively far from the plasma is also a possible solution to avoid neutron and $\gamma$-radiation induced noise. The compact front-end electronics and gas system are ready, while the actual GEM, the associated mechanical support and the data acquisition system are being procured. [Preview Abstract] |
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KP1.00047: Plasma Radiation Cooling in the Ignitor Experiments$^*$ E. Gamboa, F. Bombarda The Ignitor experiment is designed to reach ignition at relatively low temperatures ($T_e \cong T_i \cong 11$ keV) and high densities ($n_0 \cong 10^{21}$ m$^{-3}$). Under these conditions the plasma parameters at the edge are such that the estimated thermal loads on the molybdenum first wall are everywhere relatively modest, thanks to the high fraction of power radiated by the plasma main species and by the small amounts of impurities trapped in the edge region. In the reference ohmic ignition scenario this fraction is expected to amount to more than 70\% of the total power. The respective roles of the radiation emitted by the core and by the edge of the plasma column is analyzed as a function of plasma parameters, impurity fraction, impurity spatial distribution, and atomic species. The present analysis supports the original results\footnote{C. Ferro et al., ENEA Report RT/ERG/FUS/94/14, Italy (1994)} that led to choose a ``limiter configuration'' for Ignitor instead of a ``divertor'' one, with all the consequent benefits deriving from a more efficient use of the volume available inside the magnet's bore, and by using a high Z material for the first wall tiles. The non-functionality of divertors in high density plasma regimes has been highlighted also by experiments carried out on the Alcator C-Mod machine\footnote{B. LaBombard et al., \textit{Nucl. Fusion} \textbf{40}, 2041 (2000)} \\ $^*$Supported in part by ENEA of Italy and by the US DOE. [Preview Abstract] |
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KP1.00048: Simulation of Deuterium Pellet Ablation in Ignitor and Other Fusion Experiments$^*$ J. Thomas, L.R. Baylor, P.B. Parks, F. Bombarda An advanced high speed ($\leq 4$ km/sec), two-stage pellet injector is being developed by ENEA of Italy, in collaboration with Oak Ridge National Laboratory, for fueling and density profile control in the Ignitor experiment. Using the Neutral Gas Shielding (NGS) ablation model\footnote{P.B. Parks, R.J. Turnbull,\textit{Phys. Fluids} \textbf{21}, 1735 (1978)}, an analysis of deuterium pellet penetration in Ignitor was conducted for various pellet sizes and speeds in order to assess the range of operational scenarios in which pellets can reach significant penetration. Until Ignitor is completed, the injector could be tested on a currently operating device to test its capabilities and usefulness in different plasma regimes. In order to match the versatility of such an injector to each experiment, the NGS model was used to simulate penetration data for four candidate machines (JET, DIII-D, Alcator C-Mod, and FTU), assuming a standard low field side injection at midplane, while varying the most relevant plasma parameters. [Preview Abstract] |
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KP1.00049: The New High Speed Pellet Injector for the Ignitor Experiment$^*$ S. Migliori, A. Frattolillo, F. Bombarda, L.R. Baylor, S.K. Combs, D. Fehling, C. Foust, G. Roveta A four barrel, two-stage pellet injector for the Ignitor experiment is under construction in collaboration between the ENEA Laboratory at Frascati and Oak Ridge National Laboratory. The goal is to reach pellet velocities of about 4 km/s, capable of penetrating near the center of the plasma column when injected from the low field side, in order to control the density profile, especially during the crucial phase of the initial current ramp, and as a possible method to fuel the discharge or to provide fast burn control during the ignited phase. The innovative concepts at the basis of the injector design are the proper shaping of the propulsion gas pressure front and the use of fast valves to considerably reduce the requirements on the expansion volumes necessary to prevent the propulsion gas to reach the plasma chamber. The complete propelling and gas removal systems have been built and tested at CRIOTEC. ORNL is responsible for the design, construction, and testing of the pellet injector vacuum chamber, the cryogenic systems, the gun barrels, and pellet diagnostics. Integrated testing at high pellet speeds with a wide range of operating parameters explored is also going to be carried out at ORNL. [Preview Abstract] |
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KP1.00050: Structural Analysis of the Ignitor Load Assembly A. Bianchi, B. Parodi, A. Cucchiaro, G. Celentano, G. Cenacchi, C. Crescenzi, P. Frosi, G. Mazzone, A. Pizzuto, G. Ramogida, M. Roccella, B. Coppi The structural analysis of all components of the Ignitor machine, and of their mechanical interactions, has been performed by using the Finite Element Method and ANSYS program for the most advanced plasma scenarios. Friction coefficients have been taken into account at the interfaces between relevant components. The results show that the stresses produced are within the allowable limits at the considered temperatures of the magnet. The out-of-plane loads were carefully evaluated by means of a dedicated code developed in ENEA, both for the reference operating scenario and for the worst plasma disruption. The disruption scenario chosen as representive of the most dangerous plasma conditions in Ignitor is a Vertical Displacement Event followed by a fast thermal and current quench, simulated by the MAXFEA code. The resulting loads were also confirmed by the ANSYS code. The average shear stress at the toroidal field coil interfaces due to these out-of-plane loads is lower than the friction coefficient and do not increase significantly the in-plane maximum equivalent stresses. [Preview Abstract] |
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KP1.00051: Construction of Plates of the Toroidal Field Magnet of Ignitor and Relevant Advances G. Celentano, A. Cucchiaro, C. Crescenzi, P. Frosi, G. Mazzone, F. Boert, H.G. Wobker, B. Coppi A new material, OFHC copper, has been adopted for the Toroidal Field Coils plates, in place of ETP copper. The new material is consistent with a machined and welded cooling channel on each individual turn (each coil consists of 10 turns and the toroidal magnet is composed of 24 coils). Two full size TFC turns have been manufactured by Kabel Metal to identify the technical difficulties concerning the fabrication and the hardening of the OFHC material. Several samples of the cooling channel are machined and ready for validation of the Electron Beam (EB)welding process. [Preview Abstract] |
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KP1.00052: Plasma Chamber and First Wall of the Ignitor Experiment$^*$ A. Cucchiaro, G. Celentano, C. Crescenzi, P. Frosi, G. Maddaluno, G. Mazzone, A. Pizzuto, G. Ramogida, M. Roccella, B. Coppi, A. Bianchi, B. Parodi, F. Lucca, A. Marin The new designs of the Plasma Chamber (PC) and of the First Wall (FW) system are based on updated scenarios for vertical plasma disruption (VDE) as well as estimates for the maximum thermal wall loadings at ignition. The PC wall thickness has been optimized to reduce the deformation during the worst disruption event without sacrificing the dimensions of the plasma column. A non linear dynamic analysis of the PC has been performed on a 360$^\circ$ model of it, taking into account possible toroidal asymmetries of the halo current. Radial EM loads obtained by scaling JET measurements have been also considered. The low-cycle fatigue analysis confirms that the PC is able to meet a lifetime of few thousand cycles for the most extreme combinations of magnetic fields and plasma currents. The FW, made of Molybdenum (TZM) tiles covering the entire inner surface of the PC, has been designed to withstand thermal and EM loads, both under normal operating conditions and in case of disruption. Detailed elasto-plastic structural analyses of the most (EM) loaded tile-carriers show that these are compatible with the adopted fabrication requirements. \\ $^*$Sponsored in part by ENEA of Italy and by the U.S. DOE. [Preview Abstract] |
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KP1.00053: Remote Handling System for Ignitor$^*$ L. Galbiati, A. Cucchiaro, G. Celentano, C. Crescenzi, P. Frosi, G. Mazzone, A. Pizzuto, G. Ramogida, M. Roccella, A. Bianchi, B. Parodi, F. Lucca, A. Marin, B. Coppi Since access in Ignitor is through the limited width of the equatorial ports, the use of remote handling (RH) technology for any in-vessel intervention is required, even before the vessel becomes activated. In particular, the first wall of Ignitor, which is made of TZM (Molybdenum) tiles mounted on Inconel tile-carriers covering the entire plasma chamber, has been designed to be installed and replaced entirely by the RH system. The presence of radiation screens inside the cryostat and around the ports ensure a sufficiently low level of activation around the machine to avoid the need of ex-vessel RH techniques. The in-vessel RH system is based on two transporters carrying an articulated boom with end-effectors, supported by a movable structure over a transport system that can be lifted and set in position adjacent to two opposite horizontal ports. The design of the in-vessel RH system, of the boom and its enclosure, and of the most significant end-effectors (welding and cutting tools, and tools for the removal and handling of tile carriers) has been completed. A series of other dedicated tools for installation and maintainances of diagnostics components, of the RF antennas, vacuum cleaners, tools for general inspection and metrology are included in the design. \\ $^*$Sponsored in part by ENEA of Italy and by the U.S. DOE. [Preview Abstract] |
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KP1.00054: Preliminary Analysis of Position and Shape Control of Ignitor Plasmas$^*$ F. Villone, R. Albanese, G. Rubinacci, V. Cocilovo, A. Coletti, A. Cucchiaro, A. Pizzuto, G. Ramogida, M. Roccella, M. Santinelli, B. Coppi The CREATE\_L linearized MHD deformable plasma response model\footnote{R. Albanese, F. Villone, \textit{Nucl. Fusion} \textbf{38}, 723 (1998).} has been applied to the plasma configurations that Ignitor can produce. This model assumes an axisymmetric plasma described by few global parameters ($\beta_ {pol}, l_i, I_p$ and an effective resistance. The growth rate of the vertical stability and the power required by active stabilization systems have been estimated, confirming the possibility of achieving an effective stabilization by the Poloidal Field Coil (PFC) system as presently designed. The position control involves two sets of coils with up-down anti-symmetric currents, while all the other coils have up-down symmetric currents. The two pairs of coils that provide the most efficient vertical control are P6 and P12. The required power and voltage match the present power supply system. In addition, a preliminary assessment of the requirements for the control of the plasma cross section shape has been carried out. The results show that by using the PFC system it is possible in principle to reject undesired shape modifications due to plasma perturbations. [Preview Abstract] |
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KP1.00055: The Pulsed Power Supply System for Ignitor A. Coletti, G. Candela, R. Coletti, P. Costa, G. Maffia, M. Santinelli, F. Starace, M. Sforna, G. Allegra, L. Trevisan, A. Florio, A. Monne, R. Novaro Thyristor amplifiers are adopted to drive the Ignitor poloidal and toroidal field coils generating the magnetic field necessary to confine the plasma column. A distributed Poloidal Field Coil (PFC) system, made of 13 up and down symmetric coils, regulates the plasma current and controls both plasma position and shaping. An iterative optimization process of the whole power supply system, carried out in collaboration with Ansaldo Ricerche and ASI Robicon, has identified the most appropriate current distribution within each PFC and led to modify the coil geometry, easing the requirements on the power supplies and on the adopted materials relative to previous analyses. As a result, the total installed power (defined as $V_ {max} \times I_{max}$) has been reduced from about 3300 MVA to 2400 MVA. The appropriate government authority, GRTN, has carried out an in-depth analysis of the connection of the Ignitor power supply to the Italian 400 kV Grid at the node of Rondissone (near Turin), a possible site for the experiment. The power requirements were found to be consistent with the European 400 kV grid operational requirements. [Preview Abstract] |
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KP1.00056: Ignitor Edge Plasma Modeling$^*$ F. Subba, R. Zanino, A. Airoldi, F. Bombarda, G. Cenacchi, G. Maddaluno, B. Coppi A realistic evaluation of the thermal loads to be expected on the Ignitor first wall is crucial for the machine design optimization. Moreover, it is important to estimate the wall loads under a range of different operating conditions, because the LCFS of the plasma is nearly conformal to the physical wall shape, so that the thermal loads are more uniformly distributed over a large surface, but are also very sensitive to small changes in the plasma configuration. The original estimates of the thermal loads on the first wall, carried out with a cosine model and a parametrized plasma equilibrium, have recently been extended with the inclusion of the actual equilibrium configuration in the reference operating scenario and a number of off-normal conditions, including poor relative positioning of the plasma column with respect to the solid walls, effects of manufacturing tolerances in the wall assembly and start-up transients. A more accurate evaluation than that offered by the simplistic cosine model would require the full 2D modeling of the plasma in the SOL. In principle this could be done by an edge plasma code such as, for example, SOLPS. However, the particular limiter geometry of Ignitor represents a very challenging task for the application of traditional edge modeling tools. The formulation of a new computational tool flexible enough to be applied to Ignitor is being undertaken. \\ $^*$Supported in part by ENEA of Italy and by the US DOE. [Preview Abstract] |
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KP1.00057: Implications of Recent Physics Advances for the Design and Operation of Burning Plasma Experiments such as ITER and FIRE Dale Meade, Charles Kessel New operating modes have been developed for tokamaks including improved H-modes, modes for long duration inductive operation and advanced tokamak(AT) modes aimed at high-$\beta $ steady-state operation. The new H-mode scaling with reduced beta degradation developed by the ITPA projects to significantly higher fusion gains in FIRE and ITER. The hybrid inductive mode developed on ASDEX-U and DIII-D leads to improved confinement at moderate $\beta $ that would be suitable for burning plasma studies (Q = 10 to 20) on ITER and FIRE, and increased duration for neutron production on ITER. Using the Tokamak Simulation Code (TSC), an AT scenario has been developed for FIRE with $\beta _{N}$= 4, f$_{bs}$ $\approx $ 80{\%} and Q = 5 -- 10 that would provide DT fusion power densities of 5 MWm$^{-3}$ and a neutron wall loading of $\approx $ 2 MWm$^{-2 }$for durations of 3-5 plasma current redistribution times. Recent experiments on DIII-D with $\beta _{N} \quad \approx $ 4 sustained for 2 sec provide confidence that this regime can be attained. Studies are underway to develop similar AT modes for ITER. For both ITER and FIRE the exploitation of AT modes is limited by power handling capability of the present first wall designs. Work supported by DOE Contract No. DE-AC02-76CH03073. [Preview Abstract] |
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KP1.00058: The energy Park Wallace Manheimer If world development is to continue, per capita energy use in the developing world must increase to levels in the developed world. Restrictions on how much CO2 mankind can responsibly put into the atmosphere complicate the task further. Studies show that by 2050 the world will require an additional 10-30 terawatts (TW) of carbon free power, at least as much additional, as the 10 TW generated today with fossil fuel. Neither mined uranium nor renewable energy is capable of sustained power production at this level. This paper proposes, an ‘energy park’, a self contained unit a square mile or two in area which supplies about 7 GW of electrical power or hydrogen, emits no CO2, has little or no proliferation problem, and cleans up its own waste. Most of the energy is supplied by conventional nuclear power plants. However the nuclear fuel is bred by a fusion reactor, which is the key to the energy park. The waste cleanup is done by a combination of fission, fusion, and patience. There is neither long time storage nor long distance travel for materials with proliferation risk or long lived radio nuclides. Thus only thorium comes into the park, and only electricity and hydrogen go out. [Preview Abstract] |
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KP1.00059: MAGNETIC PLASMA AND ICF TARGET FABRICATION TECHNOLOGY |
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KP1.00060: Observation of the Effect of Fast Ions on Fueling Pellet Ablation Mitsuyasu Hoshino, Ryuichi Sakamoto, Hiroshi Yamada, Tokihiko Tokuzawa, Kazumichi Narihara, Masaki Osakabe, Ryuhei Kumazawa, Tetsuo Watari Ablation of fueling pellets has been investigated for intensive neutral beam injection (NBI) heated plasmas in Large Helical Device (LHD). When measured penetration depth of injected pellets in the experiment is compared with a theoretical model employing ablation only due to the heat flux of thermal electrons, systematic deviation from this model is observed in plasmas containing highly energetic (up to 180 keV) fast ions due to NBI heating. The effect of fast ions on pellet ablation has been quantified by using the stored energy of fast ions in a plasma as an index. The effect has also been confirmed by means of calculations of the ablation model including contributions of not only thermal electrons but also fast ions to the ablation. [Preview Abstract] |
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KP1.00061: A Gyrotron-Powered Pellet Accelerator F.W. Perkins, P.B. Parks Plans for fuelling ITER call for accelerated pellets which propagate in guide-tubes. The tubes undergo 90 \r{ } bends so that the pellets can enter the plasma along the high field-side of the separatrix. Both theory and experiment find that for V$\ge $ 500m/s, centrifugal force in the bends will fracture the pellets and elongate the cloud of debris. This contribution outlines the design of a plasma accelerator sufficiently flexible so that 90\r{ } bends can be avoided for the high-speed portions of the trajectory. The key element is to recognize that the guide tubes can also serve as a waveguide for millimeter waves. Operation proceeds as follows: A pellet is introduced into a guide tube of diameter 5mm at low velocity $\sim $10m/s and propagates until the remaining trajectory is straight and normal to separatrix. At this point, a 1 MW gyrotron is energized and power propagates until it encounters the pellet. The pellet has a 4-region structure and acts as a gun. The rear region (5mm) is diamond which passes the millimeter waves and provides inertia. Next is a 2mm region of frozen D doped with lithium which adsorbs the millimeter waves and vaporizes. The third region is a thin lithium layer which is several skin depths in extent and reflects millimeter waves. The 5 mm front region is a frozen DT bullet accelerated by the vaporized absorbing layer. The bullet now has a straight trajectory. 1D simulations of the gun will be presented. [Preview Abstract] |
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KP1.00062: Pellet Fueling R{\&}D for ITER L.R. Baylor, S.K. Combs, T.C. Jernigan, W.A. Houlberg, D.A. Rasmussen, P.B. Parks Pellet injection is the primary fueling technique planned for fueling of ITER burning plasmas. Efficient fueling with D-T is a requirement for achieving high fusion gain and it cannot be achieved with gas fueling alone. Injection of pellets from the inner wall has been shown on present day tokamaks to provide efficient fueling and is planned for use on ITER. Modeling of the fueling deposition from inner wall pellet injection using the Parks ExB drift model [1] indicates that reasonably sized pellets have the capability to fuel well inside the separatrix. Scaling of mass deposition from this model shows a strong edge temperature pedestal and pellet size dependence.~ Isotopically mixed D-T pellets can provide efficient tritium fueling that will minimize tritium wall loading when compared to gas puffing. Currently the performance of the ITER inner wall guide tube design is under test. The results of these tests and their implication for ITER fueling will be discussed. The ITER pellet injection technology requirements and remaining development issues will be presented along with a conceptual design for implementation on ITER. [1] Parks, P.B., Baylor, L.R.., Phys. Rev. Lett. \textbf{94} (2005) 125002. [Preview Abstract] |
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KP1.00063: Experimental study of compact toroid acceleration and transportation with the SPICA and HIT-CTI2 injectors N. Fukumoto, M. Nagata, J. Miyazawa, H. Yamada, T. Asai, T. Takahashi, A. Sanpei, S. Masamune, M. Irie The acceleration and transportation of a compact toroid (CT) have been studied for Tokamak and Helical refueling purposes. The SPICA injector has been developed as a fueller for LHD at NIFS. We conducted various systematic scan of the operation parameters. The following CT parameters were obtained: v $\sim $ 300 km/s, n $\sim $ 6 x 10$^{21}$ m$^{-3}$ and B $\sim $ 0.2 T. However, in the experimental demonstration of CT injection into the 3.6 m long test chamber, the performance was not high enough to realize the core CT penetration into LHD. Therefore, CT injection into a flux conserver has been performed to optimize the operation parameters. In addition, we recently proposed vertical CT injection with forked drift tubes so that the CT can be injected in any radial position in the target plasma. The injection port can be flexibly switched shot-by-shot by applying an external magnetic field, which acts as a magnetic wall to obstruct one exit in the forked tube, guiding the CT to another exit. In order to study this unique control method of CT transportation, experimental switching of the CT traveling direction in the forked tube has been carried out using the HIT-CTI2 at the University of Hyogo. Results from these experiments will be presented. [Preview Abstract] |
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KP1.00064: Dynamics of Hydrogenic Retention, Diffusion, and Trapping in Molybdenum G.M. Wright, D.G. Whyte, J.G. Kulpin, R. Doerner, A.J. Nosek, J.M. Shea Hydrogenic retention, diffusion and trapping in plasma-facing components (PFC) are of great importance when examining wall fuelling and tritium retention issues for ITER. The Alcator C-Mod tokamak uses molybdenum for their PFC material, covered with boron films from regular boronizations. After cleaning the interior of the machine, Alcator C-Mod had purely Mo tiles. In the following shots, over 50{\%} of the injected deuterium was not recovered and thought to be lost in the walls. Repeated shots showed no signs of this ``wall pumping'' becoming saturated. This unexpected behaviour could have severe consequences for tritium retention in ITER, which is considering refractory metal tungsten PFC. The dynamics of D retention and diffusion must be resolved to understand these issues in pulsed tokamaks. The C-Mod tiles, deuterium-implanted Mo samples provided by the PISCES experiment at University of California-San Diego, and pure Mo samples will be studied using the DIONISOS experiment at the University of Wisconsin-Madison. Ion beam analysis will be used to investigate the dynamics of plasma-driven implantation and diffusion of deuterium in molybdenum as a function of plasma density, sample bias, surface temperature, and time. [Preview Abstract] |
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KP1.00065: Be-W alloy formation on W targets exposed to Be seeded deuterium plasma in PISCES M. Baldwin, R. Doerner, D. Nishijima, K. Ertl, J. Roth, Ch. Linsmeier, K. Schmid, A. Wiltner In ITER, cross field transport to the Be first wall will lead to an eroded Be impurity flux in the scrape-off plasma flow into the divertor that is expected to be in the concentration range of 1-10{\%}. The W armor plating in the divertor will therefore be subject to both intense plasma and Be impurity ion bombardment. W is known to alloy with Be forming the stable phases Be$_{2}$W, Be$_{12}$W and Be$_{22}$W, which have melting points significantly lower than that of pure W. The formation of such alloys could have serious implications for ITER divertor operation. A collaborative effort between UCSD PISCES and IPP has been established to investigate Be-W alloy formation in both static (IPP) and divertor plasma simulator (UCSD) experiments. Results will be presented at the meeting. [Preview Abstract] |
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KP1.00066: Molybdenum and Carbon Cluster Angular Sputtering Distributions Under Low Energy Xenon Ion Bombardment Eider Oyarzabal, Jonathan Yu, Russ Doerner, Jeremy Hanna, George Tynan, Kurt Taylor, Klaus Schmid Molybdenum and carbon cluster (C$_{2}$ and C$_{3})$ angular sputtering distributions are measured during xenon ion bombardment from a plasma, with incident ion energy from $E_{Xe}$=50 to 225 eV. A quadrupole mass spectrometer (QMS) is used to detect the fraction of sputtered neutrals that is ionized in the plasma, and to obtain the angular distribution by changing the angle between the target and the QMS aperture. The angular sputtering distribution for molybdenum presents a maximum at 60\r{ } with respect to the target normal. The dependence of the total sputtering yield on incident ion energy is in good agreement with previous experiments. Interestingly, for carbon, the angular distribution of the sputtered C$_{2}$ and C$_{3}$ clusters depends on the energy with which they are ejected. The low energy population of sputtered particles has a broad maximum at 45\r{ }, while the high energy population has a sharp maximum at 60\r{ }. The maximum for the entire population of sputtered clusters occurs at about 45-60\r{ }. [Preview Abstract] |
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KP1.00067: Plasma Interactions with Mixed Beryllium-Carbon Surfaces R. Doerner, M. Baldwin, D. Nishijima, R. Seraydarian, J. Roth, K. Schmid, A. Wiltner Mixed material investigations of the Be-C system, using the PISCES-B facility, are described. A beryllium atom beam is used to `seed' beryllium impurities into deuterium plasma, simulating ITER first wall erosion and subsequent flow in the SOL to the divertor. The interaction of this beryllium containing plasma with C substrates is investigated. Small ($\sim $0.1{\%}) Be concentrations result in Be-rich surface layers formation on plasma-exposed samples and lead to suppression of both chemical erosion and physical sputtering of the carbon substrate. Eroded material codeposited away from the plasma interaction region is composed almost entirely of Be and D. The level of codeposition of Be and D at room temperature is on the same order as that expected from codeposition of C with D, however the retained D is released thermally from Be codeposits at much lower temperature when compared to C codeposits. Also the amount of D retained in Be codeposits formed at higher temperature is much smaller than the amount of D in similar C codeposits. [Preview Abstract] |
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KP1.00068: Behavior of beryllium atoms eroded from beryllium targets exposed to deuterium plasmas in PISCES-B Daisuke Nishijima, Russ Doerner, Matthew Baldwin, Ray Seraydarian, George Tynan, Jeff Brooks, J.P. Allain, M. Nieto Understanding the characteristics of beryllium (Be) as both a material and an impurity in plasmas is important for the successful operation of ITER since the current design of ITER has Be as the first wall material. The angular distribution of Be atoms eroded and transported from Be targets exposed to steady-state deuterium plasmas with low incident ion energy, up to 140 eV, has been investigated in the linear divertor simulator PISCES-B. The two-dimensional profile of ground state Be atom density near the target has been derived with spectroscopic methods. A comparison between the measurement and WBC Monte Carlo simulation indicates a deviation from a cosine angular distribution. The angular distribution is found to be insensitive to the incident ion energy between 40 and 140 eV. The angular distribution was measured at two Be surface temperatures (450 and 700 $^{o}$C). At the lower surface temperature, the angular distribution seems to be more peaked. Experiments at both lower, down to 50 $^{o}$C, and higher surface temperatures are planned. [Preview Abstract] |
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KP1.00069: A Compact X-pinch X-ray source for Characterization of Inertial Confinement Fusion Capsules Farhat Beg, Rich Stephens, Brian DeBono, David Haas, Sam Eddinger, Haibo Haung, Greg Andreev We present initial results from experiments performed to characterize Beryllium coated plastic capsules using a compact x-pinch pulser, which produces 80 kA current with a rise time of 40 ns. Various wire materials including tungsten, molybdenum and aluminum were used. X-pinch length and angle were varied to obtain maximum x-ray yield and photon energies. X-rays in 5-9 keV energy range were used for phase contrast radiography of ICF capsules. Results with plastic capsules (1 mm diameter, 20 micron thick wall) show a phase contrast effect at the edges of the capsule wall. The sharpness of the image reveals source size of less than 3 micron. [Preview Abstract] |
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KP1.00070: Understanding the Fabrication Process of Multi-layered Cocktail Coatings H. Wilkens, A. Nikroo, D.R. Wall, J. Gunther, J.S. Harper, N.E. Teslich, R.J. Wallace Sputtered multi-layered depleted uranium (DU) and gold cocktail coatings created at General Atomics are being characterized in collaboration with Lawrence Livermore National Laboratory to elucidate how different process conditions affect the quality and composition of the sputtered films. Calculations have shown that adding a high Z material like DU to a gold hohlraum will improve the conversion efficiency to x-rays of the incoming laser energy incident on the hohlraum wall [1]. Transmission electron microscopy (TEM) images of coatings made on a variety of different materials are presented, including flat substrates such as cellulose acetate and silicon, as well as coatings on rotating cylindrical acrylic and aluminum mandrels which are used to fabricate hohlraums. TEM images typically show clear intermixing of the DU and Au layers, and depth-profiling Auger electron spectroscopy and energy dispersive x-ray analysis done in cross-section accurately measure the material composition profile.\par \vspace{0.5em} \noindent [1]~ T.J.\ Orzechowski, et al., Phys.\ Rev.\ Lett.\ ${\bf 77}$, 3545 (1996). [Preview Abstract] |
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KP1.00071: Dual Theta Assembly and Characterization System Justin Stolp, Chris Russell, Eric Breden, Randy Holt, Wyotek Krych, Suzi Grine-Jones, Diana Schroen, Gary Smith, John Streit Target designs can contain specifications for precisely angled components and characterization of these targets can require multiple views at precise alignments. To meet these needs Target Fab has built a workstation capable of both assembly and characterization of these targets. Recent advances in motion controllers, optics, video CCDs, computer assisted metrology systems, and software format exchange are the building blocks we used in the development of the Dual Theta Assembly and Characterization System. This system has a working envelope of approximately 50mm$^{3}$, with a field of view that ranges from 25mm$^{2}$ to less than 1mm$^{2}$, and a spherical coordinate system that makes accurate target assembly and characterization of just about any design. This presentation will explore how the technologies are merged to help assist the research community with micro-component fabrication. I will discuss how commercially available systems can be configured to solve some of the more interesting challenges faced by a target fabricator when in the process of building a four or more axis assembly. I will show how video metrology can make the characterization of a target part of the assembly process instead of being a post-assembly step. This ability is extremely useful reducing time by allowing the builder to ensure quality during each step of assembly. [Preview Abstract] |
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KP1.00072: Proposal for a Combined Time History and Time-Dependent Temperature Diagnostic for the NIF C.R. Christensen The time history of nuclear burn in an ICF implosion can be inferred from either the fusion product neutrons, or from fusion gamma rays. However, velocity spreading of the neutrons due to the high temperature of the reacting ions (tens of keV) limits the resolution achievable by a diagnostic based on neutrons. Gamma-based diagnostics suffer from the small branching ratio ($\sim $10$^{-5})$, and so would probably not have enough dynamic range to see all the features of interest for ICF ignition studies on the NIF. An analytic solution has been obtained that will allow individual determination of burn history and time-dependent temperature, using an array of neutron detectors at a wide range of distances from the implosion. Time resolution achievable depends on the number of detectors used, their response characteristics, their spacing, and nuclear yield and background. Simulations will be presented that demonstrate the utility of this diagnostic for NIF ignition studies. [Preview Abstract] |
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KP1.00073: Compact Helicon Plasma Source for III-N Semiconductor Growth Reactive Nitrogen Species Production Costel Biloiu, Xuan Sun, Zane Harvey, Ryan Murphy, Earl Scime High plasma density and high ion exit flow speed make the helicon discharge potentially attractive for plasma assisted molecular beam epitaxy of III-N semiconductors. By a proper selection of the helicon wave phase velocity and input power it is possible to modify the electron velocity distribution function - thereby increasing the production of molecular excited species, which are favorable to the growth process, and decreasing the production of ionic species, which are detrimental for the epilayer. Further, the expansion of the helicon plasma into the diffusion chamber permits, through spontaneous radiative relaxation, the different N$_{2}$ triplet excited states to cascade down to the metastable $A{ }^3\Sigma _u^+ $ state. With a sufficiently long transit time to the expansion chamber, the long lived $A{ }^3\Sigma _u^+ $ state becomes the dominant reactive nitrogen specie in the plasma. Optical emission spectroscopy investigations in the diffusion chamber show that under certain working conditions, the N$_{2}$ first positive system ($B{ }^3\Pi _g \to A{ }^3\Sigma _u^+ $, $\Delta $v = 0 at 1051 nm, $\Delta $v = 1 at 872.23 nm, $\Delta $v = 2 at 775.32 nm, and $\Delta $v = 3 at 654.48 nm) bands, are the dominant transitions in expanded, nitrogen, helicon-generated, plasma. [Preview Abstract] |
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KP1.00074: Mass Separation of Nuclear Waste Surrogates in the Archimedes Demonstration Unit D.L. Winslow, F. Anderegg, B.P. Cluggish, R.L. Freeman, J. Gilleland, T.J. Hilsabeck, W.D. Lee, A.A. Litvak, R.L. Miller, T. Ohkawa, A.P. Poloski, S. Putvinski, S. Taunier, K.R. Umstadter, J. Zhang The Archimedes Demonstration Unit (ADU) has successfully separated a nuclear waste surrogate into light and heavy waste streams. ADU is a large scale (L = 3.9 m, a=0.37 m) cylindrical Plasma Mass Filter$^{1}$ that utilizes perpendicular electric and magnetic fields to generate a low-pass filter on atomic mass. This technology could reduce the volume of high level nuclear waste at the Hanford site in Richland, Washington. Over the last year, several techniques have been used to evaporate and inject waste surrogates into a rotating sodium metal plasma in ADU. Both spectroscopic and material collection techniques show that the Filter reduces the amount of heavy material in the light waste stream by a factor of 20 or more, with mass collection rates of about 0.25 g/s. Results of the experimental mass separation tests, parameter scaling of the mass separation, and supporting modeling will be presented. $^{1}$T. Ohkawa, ``Plasma Mass Filter'', U.S. Patent 6 096 220, August 1, 2000. [Preview Abstract] |
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KP1.00075: Rotating, Sodium Plasmas in the Archimedes Demonstration Unit B.P. Cluggish, S.F. Agnew, F. Anderegg, R.L. Freeman, J. Gilleland, T.J. Hilsabeck, R.C. Isler, W.D. Lee, A.A. Litvak, R.L. Miller, T. Ohkawa, S. Putvinski, K.R. Umstadter, D.L. Winslow, J. Zhang Rotating, sodium plasma columns have been created for separation experiments with nuclear waste surrogates in the Archimedes Demonstration Unit (ADU). The ADU is a 0.37 m radius, 3.9 m long, Plasma Mass Filter that uses a radial electric field and an axial magnetic field to separate ions by mass at high throughput. This technology could reduce the volume of high level nuclear tank waste at the Hanford site in Richland, Washington. Sodium is used as a working gas because it is the primary metallic element in the tank waste. An 1100K boiler feeds up to 1 g/s of sodium vapor into the Filter, where 300-500 kW of rf power ionizes it into a plasma of density of $3-4 \times 10^{18}$ m$^{-3}$ and T$_e \approx 1-3$ eV. Measurements indicate that sodium plasmas ExB rotate faster than argon plasmas, presumably because sodium atoms stick to the walls and do not recycle back into the plasma. Profiles of density, velocity, and temperature will be presented and compared to similar measurements in argon plasmas. [Preview Abstract] |
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KP1.00076: Neutral density profiles in a helicon source Amy Keesee, Earl Scime, Annemie Bogaerts Ion-neutral and electron-neutral collisions can be important mechanisms for Alfv\'{e}n wave damping [Hanna and Watts, 2001], ion cyclotron wave damping, and flow thermalization in helicon sources [Kline et al., 1999, 2003, Scime et al., 1998]. Neutral pumping, which leads to reduced neutral pressures on axis, has been suggested to play an important role in the physics of cylindrically symmetric helicon sources [Gilland et al., 1998, Degeling et al., 1999]. The spatial distribution, temperature, and flow of neutral atoms in helicon sources are poorly understood quantities. The presence of an electron beam at the center of a helicon source has been debated [Chen and Hershkowitz, 1998, Chen and Blackwell, 1999]. We have measured radial profiles of argon neutral density using laser-induced fluorescence (LIF) and passive emission spectroscopy. These diagnostics only measure the relative densities of the probed atomic states. To find the overall neutral density, a collisional-radiative (CR) model is used. The EEDF and a test neutral density profile are inputs to the CR model code. The output profiles of argon excited states are compared to the respective states measured via LIF and spectroscopy. If the spectroscopic data are inconsistent with a purely Maxwellian electron energy distribution, an electron beam at the center of the discharge can be included in the EEDF to test for its presence. [Preview Abstract] |
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KP1.00077: Spectroscopy Study of the ASTRAL helicon plasma source David Branscomb, Robert Boivin, Stuart Loch, Mitch Pindzola A spectroscopy study of the ASTRAL (\textbf{A}uburn \textbf{S}teady s\textbf{T}ate \textbf{R}esearch f\textbf{A}ci\textbf{L}ity) helicon plasma source is presented. A spectrometer which features a 0.33 m Criss-Cross Scanning monochromator and a CCD camera is used for this study. ASTRAL produces Ar plasmas with the following parameters: n$_{e}$ = 10$^{12}$ to 10$^{13}$ cm$^{-3}$ and T$_{e}$ = 2 to 15 eV. Ar I , Ar II and Ar III species are monitored as a function of rf power. In the 250 to 450 nm range, Ar II transitions dominate the spectrum and very few Ar I transitions are present. In the 300 to 400 nm range Ar III transitions are barely visible at low power and become intense at high power. In the 700-1000 nm range, Ar I transitions dominate the spectrum while very few Ar II transitions are observed. Ar II and Ar III intensity increases with rf power while Ar I intensity are independent of power. This constant Ar I intensity strongly suggests that neutral depletion occurs within the core as the power is raised. A discussion relative to the different observations is presented with links to theoretical excitation rate coefficients. [Preview Abstract] |
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KP1.00078: Development of high efficient plasma gun for MgO evaporation process Yong-Sup Choi, Kangil Lee, Jinpil Kim, SeongHo Jeong, Young-Wook Choi MgO evaporation process is a critical process in PDP(Plasma Display Panel) manufacturing. Plasma-beam evaporation method (or ion plating method) is widely used for MgO film deposition because the plasmas activate particles in evaporation process to make MgO films dense and high quality. However, difficulty of control and deterioration of gun components by plasma make the MgO process as a neck one. To resolve the neck process, high rate and robust plasma gun is requested. The high rate could be achieved by two ways, one is to increase the gun power and the other is to improve the gun efficiency. However, gun power increase is restricted by life and breakage of PDP glass, which could be caused by heat load from the plasma. To improve gun efficiency, energy transfer mechanism of plasma gun to MgO is researched and the high efficient plasma gun is developed based on the energy transfer mechanism. Plasmas transfer their energy to MgO by mostly plasma ions, which are accelerated in sheath region in front of MgO surface. To make the gun efficient, the plasma parameters should be controlled to increase the sheath voltage. The developed high efficient gun shows higher rate and life than the existed plasma gun. [Preview Abstract] |
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KP1.00079: Two-Dimensional Fluid Simulation of a Radio-Frequency Oxygen Plasma: Comparison of Inductively coupled plasma and Capacitively coupled plasma S.H. Lee, S.M. Choi, J.K. Lee Oxygen plasma is used for various material processes, including the removal of photoresist patterns and the deposition of thin SiO$_{2}$ layers. Negative ion plays an important role in an electronegative discharge. Dissociative attachment of metastable molecules and detachment of metastable atoms are the main reaction for the production and loss of negative ion(O$^{-})$. So, we consider eight species in the oxygen simulation, the positive ions O$^{+}$ and O2$^{+}$ and the negative ion O$^{-}$, electron, molecular oxygen, metastable molecular oxygen, atomic oxygen, metastable atomic oxygen. In our simulation, we assume that the temperature of neutral gas is 350K and the density of molecular oxygen is constant. We simulated in various model geometries, including conventional ICP source and VHF(Very High Frequency){\_}ICP source that consists of the parallel resonance antenna to overcome the problem of non-uniformity and CCP source. From simulation data in above model geometries, we observed the characteristics of pure oxygen plasma with power and pressure and frequency and finally the results from our simulation are compared with experimental data and other group's simulation data.\newline * Jusung Engineering Co, Gwangju-Gun, Gyeonggi, S.Korea [Preview Abstract] |
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KP1.00080: Charge-up effects with respect to flux ratios of electrons to ions in 3D charge-up simulations Sung Jin Kim, Hae June Lee, Jae Koo Lee Charge-up damage is one of plasma process induced damages and comes from different motions of ions (anisotropic motion) and electrons (isotropic motion). We have performed a three-dimensional charge-up simulation [1] to examine charge-up effects. Kinetic results of particles obtained from 1D particle-in-cell Monte Carlo collision (PIC-MCC) simulations [2] are used as input parameters of the 3D charge-up simulation. Charge-up potentials and etching rates are calculated in trenches hundreds of nanometers wide. The role of charge-up effects in etching profile evolution is investigated. In 3D charge-up simulation, reflection between sidewall and ions is considered using reflection coefficients calculated by a TRIM code. Since ion reflection creates undesirable etching profiles such as bowing, trenching, and notching, the gradient of etching profile created by reflected particle is studied. Charge-up effects by inequality of ion and electron fluxes injected in electrode are investigated with respect to an electron temperature and a trench width. We optimize flux rates of electrons to ions to produce good anisotropic etching profiles. *This work is supported by Tera-level nanodevices in Korea Ministry of Science and Technology. [1] H.S. Park, S.J. Kim, J.K. Lee, IEEE Trans. Plasma Science, 31 (2003) 703 [2] H.C. Kim, J.K. Lee, Phys. Rev. Lett., 93 (2004) 085003 [Preview Abstract] |
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KP1.00081: Motion of an Arc through a Long Coaxial Channel with an Applied Magnetic Field Brian Bures, Jason Wright, Andrew Gerhan, Mahadevan Krishnan Cathodic arc plasma deposition is a well established process for the production of decorative coatings. To expand the applications of cathodic arc deposition techniques, Alameda Applied Sciences Corporation has developed a method of depositing thin films on the insides of tubes using our Coaxial Energetic Deposition (CED) process. The CED process uses a cathodic arc from a central cathode to transfer cathode material to the coaxial substrate. The anode is either the coaxial substrate or a mesh anode depending on the application. For example, polymer or ceramic tubes could not serve as anodes. An external solenoid produces a magnetic field so that the arc spirals along the cathode. The axial velocity determines the time spent in the tube while the angular velocity affects the uniformity of the coating within the tube. This paper discusses the effect of variations in both the angular and axial velocity of the arc at different applied magnetic fields, using electric probes. [Preview Abstract] |
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KP1.00082: RF Power Coupling and Plasma Transport In Magnetized Capacitive Discharges Philip Ryan, Mark Carter, Daniel Hoffman Static magnetic fields have been used to expand the operational envelope, increase power efficiency, and control processing parameters in capacitively-coupled radio frequency plasma discharges. A simple physical model has been developed to investigate the roles of the plasma dielectric tensor and plasma transport in determining the ion flux spatial profile along a wafer surface over a range of plasma density, neutral pressure and magnetic field strength and orientation. The model has been incorporated into the MORRFIC code and calculations have been made for a capacitively-coupled 300-mm etch tool operating at frequencies greater than 100 MHz. A two-dimensional transport model accounts for magnetized cross-field diffusion. Results isolate magnetic field effects that are caused by modification of the plasma dielectric from transport effects that are caused by the reduced electron mobility perpendicular to the magnetic field. Various sheath models have been evaluated for numerical stability and self consistent properties and will be discussed. [Preview Abstract] |
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KP1.00083: Effect of the Magnetic Field on the Plasma Discharge in a Miniaturized Cylindrical Hall Thruster Yevgeny Raitses, Artem Smirnov, Nathaniel Fisch Hall thrusters of the conventional annular design become inefficient when scaled to low power. Their lifetime decreases significantly due to the channel wall erosion. Cylindrical geometry Hall thrusters have lower surface-to-volume ratio than conventional annular thrusters and, thus, seem to be more promising for scaling down. A miniaturized cylindrical Hall thruster (50 -- 300 W power range) exhibits performance comparable with conventional annular Hall thrusters of the similar size [1,2]. Kinetic modeling of electron dynamics in the thruster channel [3] allows one to optimize the electron confinement over a family of realizable magnetic field and plasma potential distributions. In the present work, the effect of the magnetic filed on the thruster efficiency, as well as on the distributions of the plasma potential, plasma density, and electron temperature is studied experimentally. The results of the experiments suggest the ways for further optimization of the electron transport in the thruster.\newline 1. Y. Raitses and N.J. Fisch, Phys. Plasmas \textbf{8}, 2579 (2001). \newline 2. A. Smirnov, Y. Raitses, and N.J. Fisch, J. Appl. Phys. \textbf{92}, 5673 (2002). \newline 3. A. Smirnov, Y. Raitses, and N.J. Fisch, Phys. Plasmas \textbf{11}, 4922 (2004). [Preview Abstract] |
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KP1.00084: Plasma-Wall Interaction and Electron Temperature Saturation in Hall Thrusters Artem Smirnov, Yevgeny Raitses, David Staack, Nathaniel Fisch Existing Hall thruster models predict that secondary electron emission from the channel walls is significant and that the near-wall sheaths are space charge saturated. The plasma-wall interaction and its dependence on the discharge voltage and channel width were studied through the measurements of the electron temperature, plasma potential, and plasma density in a 2 kW Hall thruster [1,2]. The experimental electron-wall collision frequency is computed using the measured plasma parameters. For high discharge voltages, the deduced electron-wall collision frequency is much lower than the theoretical value obtained for the space charge saturated sheath regime, but larger than the wall recombination frequency. The observed electron temperature saturation appears to be directly associated with a decrease of the Joule heating, rather than with the enhancement of the electron energy loss at the walls due to a strong secondary electron emission. The channel width is shown to have a more significant effect on the axial distribution of the plasma potential than the discharge voltage. 1. Y. Raitses, D. Staack, M. Keidar, and N.J. Fisch, Phys. Plasmas \textbf{12}, 057104 (2005). 2. Y. Raitses, D. Staack, A. Smirnov, and N.J. Fisch, Phys. Plasmas \textbf{12}, 073507 (2005). [Preview Abstract] |
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KP1.00085: Ultraviolet tomography of kink dynamics in a magnetoplasmadynamic thruster F. Bonomo, P. Franz, G. Spizzo, L. Marrelli, P. Martin, F. Paganucci, P. Rossetti, M. Signori, M. Andrenucci, N. Pomaro We present the results of a project concerning the ultraviolet (UV) imaging of a plasma for space applications, produced in a magneto-plasmadynamic (MPD) thruster. MPD are a class of high power electric space propulsion devices that accelerate a plasma to high velocities ($>$10 km/s), by exploiting the Lorentz force between the discharge electrical current and a self induced and externally applied magnetic field. The imaging system has been realized by inserting 3 arrays of UV-enhanced photodiodes (with built-in amplifiers) directly into the plastic structure of the anode. This advanced diagnostic design allows for a detailed tomographic reconstruction of the emissivity spatial structure, both in the axial direction z (corresponding to a wavenumber n) and azimuthal direction (wavenumber m) with high time resolution. A magneto-hydrodynamic (MHD) instability, with mode numbers m=1 and n=1 has been observed, which might affect the performances of the thruster. [Preview Abstract] |
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KP1.00086: Experiments and PIC Simulations on the UM Large Area, ECR Electric Propulsion Neutralizer Y. Hidaka, R.M. Gilgenbach, W.D. Getty, M.C. Jones, V.B. Neculaes, Y.Y. Lau We report experimental and simulation results of the Getty ECR plasma source [1, 2], as a plasma neutralizer for electric propulsion. This device generates a uniform plasma over a large ECR area created by rows of permanent magnets placed between a large, S-band microwave horn and a chamber. The metal magnet bars are cross-polarized to minimize microwave reflection. Electron densities are overdense (up to 6E11 /cc) with 2.45 GHz at 100's W. Currents were extracted by biasing a collector positively with both pulsed and DC power supplies. For low DC voltages, electron currents were measured (rather than discharge currents). Experimental parameters: gas pressure, extraction voltage, microwave power, and the position and size of the collector were varied and compared. 2D MAGIC simulations of this source confirmed that most energy transfer from the microwaves into particles occurs near the ECR region, and cross-field diffusion is under investigation with MAGIC. \newline [1] W.D. Getty and J.B. Geddes, J. Vac. Sci. Tech. B, v.12, pp. 408-415 (1994). \newline [2] W.D. Getty, US Patent {\#} 5,466,295 (1995). [Preview Abstract] |
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KP1.00087: Carbon Film Deposition and Flaking Studies in Ion Thruster Environments Jeremy Hanna, Rusell Doerner, Tynan George, Johnathan Yu, Eider Oyarzabal, Kurt Taylor Sputtering of carbon atoms from carbon-composite acceleration grids in ion thrusters is a well known issue. Less is known of the effects of this sputtered material within the thruster. As this sputtered carbon is deposited on the thruster walls, this carbon layer grows in thickness, and will eventually begin to flake. If these carbon flakes are of substantial size, they could then cause serious problems with the plasma flow through the grid, as well as shorting issues for the high voltage ion optics. A series of studies of carbon deposition has been carried out at UCSD. Carbon is sputtered into a vacuum chamber using a magnetron sputtering source, and allowed to accumulate on a substrate. Deposition rates are measured in the chamber using a crystal microbalance. The substrate is temperature cycled from 200\r{ } C to -185\r{ } C to simulate thruster shutdown in deep space. After a given deposition time, this substrate is removed from the vacuum chamber and film quality and flaking is investigated by scratching the film with a razor and directly imaging the surface using an electron microscope. Results of relative film thickness versus film `quality', or flaking potential and flake size, will be presented for various processed substrate surfaces. [Preview Abstract] |
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KP1.00088: Rapid Pneumatic Transport of Radioactive Samples - RaPToRS S. Padalino, S. Lynch, M. Barrios, C. Sangster, V. Glebov Some ICF neutron activation diagnostics require quick retrieval of the activated sample. Minimizing retrieval times is particularly important when the half-life of the activated material is on the order of the transport time or the degree of radioactivity is close to the background counting level. These restrictions exist in current experiments performed at the Laboratory for Laser Energetics, thus motivating the development of the RaPToRS system. The system has been designed to minimize transportation time while requiring no human intervention during transport or counting. These factors will be important if the system is to be used at the NIF where radiological hazards will be present during post activation. The sample carrier is pneumatically transported via a 4 inch ID PVC pipe to a remote location in excess of 100 meters from the activation site at a speed of approximately 7 m/s. It arrives at an end station where it is dismounted robotically from the carrier and removed from its hermetic package. The sample is then placed by the robot in a counting station. This system is currently being developed to measure back-to-back gamma rays produced by positron annihilation which were emitted by activated graphite. Funded in part by the U.S. DOE under sub contract with LLE at the University of Rochester. [Preview Abstract] |
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KP1.00089: Broadband Calibration of Radio-Frequency Magnetic Probes S. Messer, W.E. Amatucci, D.D. Blackwell, D.N. Walker We present a calibration method for radio-frequency magnetic probes operating between 30 kHz and 100 MHz. We examine the limits of basic formulas for estimating probe sensitivity, discuss improved models, and examine the frequency-dependence of the magnetic field source. The resulting calibration procedure gives both the phase and amplitude of the probe's response. We confirm the validity of the calibration by comparing theoretical and experimental models of probe behavior and by examining deconvolution of probe data showing sharp features in the raw signals. [Preview Abstract] |
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KP1.00090: A 300 GHz Collective Scattering System for Low Temperature Plasmas Robert Hardin, John Heard, Earl Scime, Mike Spencer, Ryan Murphy, Zane Harvey A compact, portable 300 GHz homodyne collective scattering system is being installed on the WVU helicon plasma source. Collective scattering is a non-perturbative method capable of directly measuring the short wavelength, high frequency, fluctuations in plasmas. The initial focus of the experiments at WVU will be to measure the so called ``Trivelpiece-Gould'' wave, or slow wave, which is believed to be responsible for the high RF absorption efficiency of helicon sources. The system, once primary testing and initial experiments are complete, will be transported to the Reconnection Scaling Experiment (RSX) at Los Alamos National Laboratory (LANL), and will be used to detect and identify fluctuations due to Lower-Hybrid Drift Instabilities (LHDI) generated during magnetic reconnection. We will present initial beam profiles of the source and lenses, comparison to the predictions of the optical design program ZEMAX, beam splitter performance, and overall performance benchmark measurements. [Preview Abstract] |
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KP1.00091: Performance Envelope of Flow Velocity Induced by a Single OAUGDP$^{\mbox{{\textregistered}}}$ Electrohydrodynamic (EHD) Plasma Actuator J. Reece Roth, Xin Dai Electrohydrodynamic (EHD) plasma actuators using the One Atmosphere Uniform Glow Discharge Plasma (OAUGDP$^{\mbox{{\textregistered}}})$ are emerging as a promising aerodynamic flow control technology.$^{1}$ It has been found that a single plasma actuator on the leading edge of a NACA-0015 airfoil increased its stall angle from 15$^{\circ}$ to 21$^{\circ}$ at free-steam flow velocities up to 75 m/s,$^{2}$ promising flow control applications at aircraft take-off and landing speeds. We are conducting a research program to maximize the induced flow velocity and minimize the power consumption of plasma actuators by adjusting the electrode width, width ratio, gap distance, dielectric thickness, and dielectric material.$^{3}$ In this paper, we report the induced flow velocity and input power to the actuator as functions of the dielectric material, and RF voltage and frequency. We find that quartz and Teflon are superior dielectric materials. $^{1}$J. R. Roth: {\it Physics of Plasmas}, Vol. 10, No. 5 (2003). $^{2}$D.F.Opaits et al., 43rd AIAA Aerospace Sciences Meeting Reno, NV, January 10-14, 2005. $^{3}$J. R. Roth, Xin Dai, Jozef Rahel, and D. M. Sherman, 43rd AIAA Aerospace Sciences Meeting Reno, NV, January 10-14, 2005 [Preview Abstract] |
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KP1.00092: SPACE AND ASTROPHYSICAL PLASMAS |
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KP1.00093: Transverse Acceleration of Ionospheric Ions by Localized Fields A.K. Ram Rocket observations in the auroral ionosphere show the existence of spatially localized intense electric fields in density depleted regions [1]. The spatial extent of the localized fields is small compared to the thermal Larmor radii of the ambient ions. It is also found that an energized population of ions emanates from these regions. The ions are accelerated transverse to the geomagnetic field and the gain in energy is sufficiently large to allow the ions to escape the ionosphere and populate the magnetosphere. The linear model of wave-particle interactions cannot explain the observed gains in energy. I have been studying, theoretically and computationally, the characteristic features of localized fields in density cavities, and the nonlinear interaction of ions with such fields. Details of these calculations and comparisons with observations will be discussed. The interaction of low energy ions with localized electrostatic field structures is found to be significantly different from the interaction with a set of plane waves [2]. The acceleration occurs over a shorter time scale and the phase space of the energized ions is chaotic. For long-time interactions the ions can undergo large energy gains akin to L\'evy flights. [1] K.A.\ Lynch et al., {\it J.\ Geophys.\ Res.} {\bf 104}, 28,515 (1999). [2] A.K. Ram, A. Bers, and D. Benisti, {\it J.\ Geophys.\ Res.} {\bf 103}, 9431 (1998). [Preview Abstract] |
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KP1.00094: Initial Results from UHF and HF Radar Studies of Ionospheric Interaction Experiments at HAARP J.P. Sheerin, R. Ilie, E.L. Roesler, W.A. Bristow, B. Watkins High power HF radiowave-ionosphere interaction experiments have begun at the HAARP Ionospheric Research Observatory in Gakona, AK. Recent upgrades to this facility permit a new generation of experiments at unprecedented intensities. The SuperDARN radar station in Kodiak, AK is now routinely employed to measure HF backcatter from irregularities and upper hybrid modes induced the interaction volume. Construction has now begun on a new UHF radar facility, AMISR, currently located at HAARP. We use AMISR to probe strong Langmuir turbulence (SLT) induced in the interaction region. Complementary to these radar probes are new stimulated electromagnetic emissions (SEE) receivers (SIERRA) which record the emissions that propagate to the ground. We report on a series of experiments using the coordinated observations of the new radar and SEE diagnostics at the increased HF powers available. Using short HF pump pulses, we are able to discriminate, characterize, and compare prompt SEE spectra with plasma line signatures now detectable by the AMISR radar. Experimental results are compared to predictions from recent modeling efforts. [Preview Abstract] |
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KP1.00095: Reduced Vlasov Simulations of Auroral Transition Layers Naresh Sen, David L. Newman, Martin V. Goldman The existence of \textit{transition layers} (including \textit{laminar double layers}) in the auroral downward current region is now observationally well established by satellites such as FAST. Understanding the structure of such transition layers perpendicular to the geomagnetic field $\mathbf{B}$ requires simulations in at least two spatial dimensions. While the phase-space dynamics parallel to $\mathbf{B}$ is typically very complex and requires solution of the full Vlasov equations, the perpendicular dynamics can often be modeled using \textit{reduced} algorithms, thereby relaxing computational demands. Here, we assume the electrons are strongly magnetized and the ions are weakly magnetized. The perpendicular ion dynamics are modeled using a ring of modes in the transverse velocity plane. The radius $v_{\perp}$ of the ring is the nominal perpendicular thermal velocity. Preliminary results show agreement with the results of kinetic linear theory. Nevertheless, the method precludes transverse heating due to $v_{\perp}$ being a constant. Electrostatic ion Bernstein waves propagating perpendicular to the magnetic field at the ion cyclotron frequency and its harmonics are observed, consistent with observations. The effects of varying perpendicular ion temperature and ion magnetization on the structure of the double layers are considered. [Preview Abstract] |
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KP1.00096: Nonlinear Evolution of Current-Driven Instabilities in Weakly Magnetized Magnetospheric Plasmas David L. Newman, Martin V. Goldman, Naresh Sen In many regions of Earth's magnetosphere, including magnetic reconnection sites, the electrons are weakly magnetized according to the criterion $\Omega_e< \omega_e$. These regions often contain strong currents with gradients perpendicular to $\mathbf{B}$ (i.e., shear). Reduced Vlasov simulations (N. Sen et al., this meeting), which permit computationally fast evaluation of phase-space dynamics of magnetized plasma species, are employed to simulate the nonlinear evolution of sheared current-driven instabilities in magnetospheric plasmas with weakly magnetized electrons and (effectively) unmagnetized ions. For sufficiently large currents, the plasma will be Buneman unstable. For currents near the Buneman threshold, double layers can form and accelerate electron beams, resulting in secondary two-stream instabilities. Both cases can lead to the formation of electron phase-space holes with bipolar electric field signatures such as those recently observed by \textit{Cluster} near a reconnection site in Earth's magnetotail.\footnote{C. A. Cattell et al., \textit{JGR}, 110, A01211 (2005).} In certain regimes, electron holes appear to form in regions of maximum current but later localize near the edge of the current-carrying region. The generation of low- and high-frequency waves and the evolution of the currents will also be discussed. [Preview Abstract] |
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KP1.00097: Experimental Investigation of Solitary structures using high frequency microprobes Walter Gekelman, Pat Pribyl, Eric Lawrence, Paul Kintner High frequency $(f\simeq f_{pe} \mbox{ )}$phenomena are routinely observed by spacecraft and have been studied in laboratory plasmas. One example is electron solitary structures,which are believed to be vorticies in electron velocity space. These structures are estimated to move at approximately half the electron thermal velocity and are several Debye lengths in diameter. This poses a challenge in a dense magnetoplasma where the Debye length is tens of microns, and the electron thermal speed is of order 10$^{8}$ cm/s. The probes under development are described by Pribyl et al., `` Microprobe Development at the Basic Plasma Science Facility,'' in poster session 5.7.0. The exisitng probe bandwidth is 100 MHz-2GHz. This limited the density for these experiments to 5X10$^{10}$ cm$^{-3}$. The probe was placed in a 3 mm diameter field aligned electron beam. Negative going spiky structures were observed in the beam. They are observed to move at half v$_{the} $ and conditional averaging yields a temporal half width of 10 ns. Skewness, kurtosis and other properties of these structures will also be presented. Results with a new probe with smaller tips (2.5 microns) spaced 20 microns apart will be presented as well. [Preview Abstract] |
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KP1.00098: Effect of Magnetic Clouds and IP Shocks on AL and D$_{st}$ Indices M.L. Mays, J. Pratt, E. Spencer, W. Horton, I. Doxas We construct analytic solar wind signals using data from ACE for the Wang et al. Oct. 3-6 2000 event in which a fast forward shock advanced into a preceding magnetic cloud. We examine the response of the WINDMI model, an eight dimensional model of the solar wind driven magnetosphere-ionosphere system, to our analytic signals for this event. The auroral magnetometer AL signal result from the model driven by the analytic solar wind dynamo voltage captures the 8 substorms in the main phase of the storm. The model mid-latitude magnetometer D$_{st}$ signal used to quantify magnetospheric storms has the correct qualitative feature of a sharp rise for the expansion phase and a slower decay for the recovery phase. The role of the shock can be examined by using analytic signals in which the shock feature in the density, solar wind velocity, and magnetic field are tested individually. The shock near the end of the 42 hr magnetic cloud is shown to be largely responsible for the very large region 1 field aligned current surges associated with the $-AL > 1300 $nT peaks at the end of the main phase of the storm. [Preview Abstract] |
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KP1.00099: Analysis of the October 3-7 2000 Geomagnetic Storm E. Spencer, W. Horton, I. Doxas, J. Kozyra The 8 dimensional plasma physics model WINDMI is used to analyze the October 3-7, 2000 geomagnetic storm using solar wind input data from the ACE satellite. This period contains an extended interval of well-defined and quasi-periodic auroral activations called sawtooth oscillations, a phenomena whose relationship to substorm processes and to upstream solar wind drivers is still under debate. The model predicts both the occurrence of 8 auroral activations identified as sawtooth events during the 24 hour period on the 4th of October, and also an earlier multiple sawtooth interval on the 3rd of October, in agreement with the measured AL index. These intervals occur during steady but moderate solar wind IMF Bz values and the periodicity of the sawtooth events was not directly related to any periodic features in the upstream solar wind. The model also predicts the geomagnetic Dst index through the main and recovery phase of the storm. A genetic algorithm optimization routine was used to tune the parameters of the model to obtain a solution that has low ARV with respect to the AL index and also captures the eight substorms. Preliminary results of the analysis of the April 15-24 2002 storm are also presented. [Preview Abstract] |
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KP1.00100: Undulations at the Equatorward Edge of the Aurora Associated with Instabilities in the Dusk/Afternoon Sector Plasma Sheet W.S. Lewis, J.L. Burch, W. Horton, J.C. Perez, H.U. Frey, P.C. Anderson On February 6, 2002 a series of large-scale undulations along the equatorward edge of the auroral oval were observed with the Far-Ultraviolet Wideband Imaging Camera on NASA's IMAGE satellite during the recovery phase of a moderate magnetic storm. The undulations occurred in the 18.5-14.5 magnetic local time sector between 63$^{\mathrm o}$ and 71$^{\mathrm o}$ magnetic latitude. Their wavelength and crest-to-base length averaged 292~km and 224~km, respectively; and they propagated westward with an average speed of $0.90\pm0.06$~km/s. Such undulations are a relatively uncommon auroral phenomenon, and the mechanism that produce them and the magnetospheric conditions under which they occur are not well understood. Simulations and theory are presented to interpret the undulations as the nonlinear stage of the balloning-interchange mode in the presence of a sheared $\mathbf E\times\mathbf B$ flow. Comparison of the simulations and the data suggest that the Richardson's number is about ten. [Preview Abstract] |
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KP1.00101: Possibility of an Alfvenic Wave Resonator in the Magnetosphere Manish Mithaiwala, Gurudas Ganguli, Leonid Rudakov There has been recent activity in understanding the origin of high energy ($>$1 MeV) ``killer electrons'' in the Earth's magnetosphere. Previous work has identified the energization mechanism to be quasilinear diffusion involving whistler and ion-cyclotron waves\footnote{Mithaiwala, M.J. and W. Horton. JGR \textbf{110}. July 2005.}, which are generated by temperature anisotropy. It is known that whistler waves, through reflection at the lower-hybrid resonance, can form a resonator. We find that in a multi-ion species environment, such as the Earth's magnetosphere, the bi-ion rotation\footnote{Ganguli, G. and L. Rudakov. Phys. Plasmas \textbf{12}. April 2005.} (cutoff) frequency and Buchsbaum (resonance) frequency are important for the propagation and evolution of Alfvenic waves near the ion-cyclotron frequency. Here we show that Alfvenic waves with (k$_{\bot }>>$ k$_{z})$ can be captured by a magnetic cavity to form a strongly localized Magnetospheric Resonator which can interact with the electrons over a long time period and can lead to both energization and loss of the electrons. The Alfvenic waves can be generated by a ring distribution of one of the ion species. Ring ion distributions are known to form when the solar wind interacts with the magnetosphere or a comet interacts with the solar wind, and by the release of chemicals in the magnetosphere. [Preview Abstract] |
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KP1.00102: Global Hybrid Simulation of the Interaction Between Foreshock Waves and the Dayside Magnetosphere Yu Lin, Xueyi Wang A 3-D global-scale hybrid simulation is carried out for dynamics of the dayside bow shock-magnetosphere system associated with the quasi-parallel bow shock. First, the foreshock waves and the associated shock reformation process are investigated. In particular, the generation and structure of diamagnetic cavities, with a decrease in the magnetic field and density, in the foreshock of the quasi- parallel shock are discussed. Second, the interaction of the foreshock-originated pressure pulses with the dayside magnetosphere is simulated. The diamagnetic cavities that are generated in the turbulent foreshock due to the ion beam plasma interaction are found to lead to strong surface perturbations at the magnetopause. Third, the coupling between the pressure pulses and the magnetosphere is studied. The compressional waves are found to mode convert to shear Alfv\'en waves and kinetic Alfv\'en waves (KAWs) through the Alfv\'en resonance process in nonuniform plasmas. The shear Alfv\'en waves lead to the field line resonance and produce field-aligned currents in the dipole magnetospheric field. [Preview Abstract] |
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KP1.00103: Alfven-cyclotron scattering of solar wind ions: Hybrid simulations S. Peter Gary, Lin Yin, Dan Winske Alfv\'en-cyclotron fluctuations at sufficiently short wavelengths and at propagation approximately parallel or antiparallel to a background magnetic field ${\bf B}_o$ in a relatively uniform, collisionless plasma can interact with protons and heavy ions. A cyclotron resonance between such fluctuations and the thermal velocity distribution of an ion species enables strong pitch-angle scattering, typically leading to an increase in the perpendicular (to ${\bf B}_o$) energies of that species. If alpha particles are a minority species, as in the solar wind, the proton and alpha resonance conditions are sensitive functions of the alpha/proton relative speed $v_{\alpha p}$ parallel or antiparallel to ${\bf B}_o$. This presentation describes hybrid simulations in which damped Alfv\'en-cyclotron fluctuations are imposed upon a homogeneous plasma bearing both protons and alpha particles. The results show the ion species responses to cyclotron resonant fluctuations as functions of several parameters, including the alpha/proton relative speed and the magnitude of the fluctuating magnetic field energy density. Simulation results are compared against spacecraft measurements in the solar wind near 1 AU to test the hypothesis that solar wind alphas display signatures of Alfv\'en-cyclotron scattering. [Preview Abstract] |
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KP1.00104: Hybrid simulations of coronal mass ejection shock structures Luis Gargate, Ricardo Fonseca, Luis Silva, Robert Bingham Coronal mass ejections (CME's) are large scale solar events consisting of massive quantities of over-dense hot plasma that is ejected from the sun's streamer belt in a region known as the corona. CME's can travel at speeds up to 1000 km/s interacting with the slower solar wind and causing the formation of highly energetic ions due to wave particle interactions in the shock front. The actual acceleration mechanisms of the energetic ions are still under strong debate. The acceleration processes of solar energetic particle events due to CMEs are investigated. A 3D hybrid particle code, called dHybrid, is used to simulate the corona environment. Initial conditions are set in accordance with MHD models of the corona widely described in the literature. The simulation reveals the presence of shock like structures, being the source of SEPs. The acceleration mechanism of ions in the shocks is examined; the simulations indicate that surfatron acceleration is the mechanism responsible for the most energetic ions. [Preview Abstract] |
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KP1.00105: Radial profile of large scale velocity and magnetic field fluctuations in the solar wind J.J. Podesta Solar wind measurements obtained by several different spacecraft in the ecliptic plane are used to determine the radial profile of the variance of the velocity and magnetic field fluctuations between 0.3 and 30 astronomical units (AU). The radial decay law is a fundamental physical property of the turbulence and is important because of its suspected connection to the heating of the solar wind plasma. For each spacecraft, one hour averages of the velocity vector, density, and magnetic field vector are sorted into radial bins (subintervals) and the variance in each bin is computed. Most of the power in the fluctuations is contained in the largest scales, with periods in excess of one hour in the spacecraft frame, so that one hour average data is sufficient to estimate the total power (total variance) in the fluctuations. The measurement is difficult primarily because of the limited amount of data outside of 1 AU. The speed of the spacecraft limits the dwell time in each bin and, therefore, the number of data points available in each bin. The measurements are also significantly affected by solar wind transients and solar cycle variations. Theoretical models are also discussed. [Preview Abstract] |
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KP1.00106: New Limits on Small-Scale Turbulence in the Solar Corona Steven Spangler, Laura Spitler Many observed characteristics of the solar corona are interpreted as heating by ion cyclotron waves. Intense electromagnetic plasma waves, with wavelengths of the order of the ion inertial length or smaller, can be detected via a phenomenon called Faraday screen depolarization (Spangler and Mancuso, ApJ 530,491,2000). The fine scale turbulent magnetic field randomizes the Faraday rotation within the beam of a radio telescope, causing a decrease in the degree of linear polarization. We present new observations specifically intended to measure this effect. Observations were made with the Very Large Array radiotelescope on August 16 and 18, 2003, of the extended radio source 3C228 when it was occulted by the corona. The line of sight to the source passed at a heliocentric distance of $6.2 R_{\odot}$ on August 16, and $4.7 R_{\odot}$ on August 18. No indication is seen of depolarization by the corona. On August 16, the most conservative limit is that the degree of polarization is $\ge 0.75$ of its intrinsic value. A more likely limit is that the degree of polarization with the corona interposed is $\ge 0.85$ that in the absence of the corona. Even stronger limits are obtained on August 18. We discuss the implications of these measurements for the amplitude and outer scale of Alfv\'{e}n-Ion Cyclotron turbulence in the corona. [Preview Abstract] |
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KP1.00107: A Theory of Weak Magnetohydrodynamic Turbulence in the Solar Tachocline Shane Keating, Patrick Diamond It has been argued [1] that any self-consistent model of the solar tachocline must incorporate some large-scale primordial magnetic field in the interior to maintain solid rotation there against the ``burrowing'' action of the convection zone. Here, we seek to develop a theory of weak MHD turbulence in the presence of intense stable stratification, and to calculate the radial transport of magnetic flux from the interior into the tachocline. Quasilinear analysis of the 2D resistive MHD equations coupled to a bouyancy force suggests that such transport is strongly quenched. A more sophisticated approach, based on multiple time- scale seperation, leads to a wave-kinetic formalism. Analysis is under way for certain special triad classes, in the presence of a ``sea'' of internal waves. Finally, it is hoped that a calculation of the turbulent resistivity will lead to an estimate of the thickness of the solar tachocline. \newline \newline [1] D. Gough and M.E.McIntyre, Nature 394, 755-757. [Preview Abstract] |
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KP1.00108: Nonlinear Simulations of the kinetic MRI Prateek Sharma, Gregory W. Hammett, Eliot Quataert, James M. Stone We present results of local shearing box simulations of turbulence driven by the magnetorotational instability (MRI) in the collisionless regime. MHD equations have been generalized to include anisotropic pressure and heat conduction along the field lines. We use an approximate form of a fluid closure that was chosen to model Landau damping (Snyder et al, Phys. Plasmas, 4, 3974 (1997)). The motivation is to study MRI turbulence and transport in radiatively inefficient accretion flows (one striking example is accretion on to the $\sim 3 \times 10^{6} M_0$ black hole in the center of our galaxy), where the mean free path is believed to be much larger than the system size. Invariance of $\mu=v_\perp^2/2B$ implies that as the field is amplified, the plasma becomes more anisotropic ($p_\perp>p_\parallel$). This gives rise to anisotropic stress which has been shown to be an important component of the total stress. Upper limits on pressure anisotropy due to mirror and cyclotron microinstabilities are used that are motivated by linear theory and particle simulations. [Preview Abstract] |
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KP1.00109: Magnetoinductive Particle-In-Cell Simulations of Ion Shell Instabilities Maha Ashour-Abdalla, Jean-Noel Leboeuf, David Schriver, Jean-Michel Bosqued, Nicole Cornilleau-Wehrlin, Vladimir Sotnikov Ion shell distributions have been observed in space by the Cluster satellites within the Earth's plasma sheet boundary layer in a background of thermal electrons and cold ions. The ion shell distributions are isotropically distributed in velocity space on a sphere with drift velocity of the order of the Alfven speed. The ion shells are observed to be associated with intense electrostatic and electromagnetic wave emissions. To examine the properties of the ion shell distributions, electromagnetic PIC simulations have been performed in the magnetoinductive approximation with full dynamics for ions and guiding center electrons. The PIC simulations show that the ion shells are unstable to electrostatic and electromagnetic waves with common frequencies at harmonics of the ion cyclotron frequency in agreement with Cluster observations. Details of phase space, distribution function, and wave mode evolution will be presented. [Preview Abstract] |
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KP1.00110: Kinetic Aspects of Solar Coronal Heating Padma Shukla, Robert Bingham The solar corona plasma is maintained at temperatures of millions of degrees much hotter than the photosphere, at a temperature of just 6000K. In this paper plasma heating based on kinetic theory of wave particle interactions including kinetic Alfven waves and lower-hybrid drift modes are presented. The corona plasma is collision-less and so must rely on turbulent wave heating models such as lower-hybrid drift models at reconnection sites or kinetic Alfven waves. The transition region at altitudes of about 2000km is an important boundary chromosphere since it separates the collision dominated photosphere/chromosphere and the collisionless corona. The collisionless plasma of the corona is ideal for supporting kinetic wave plasma interactions. Wave particle interactions lead to anisotropic non-maxwellian plasma distribution functions which may be investigated using spectral analysis procedures being developed at the present time. [Preview Abstract] |
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KP1.00111: Neutrino Landau Damping in Dense Stellar Plasmas Robert Bingham, Luis Silva, J.T. Mendonca, P.K. Shukla, A. Serbeto In high energy density stellar interiors neutrinos play a significant role in cooling the dense fusion plasma. A number of processes involving neutrinos are invoked to explain energy transport by neutrino emission stellar interiors. Processes that are considered important are the plasma process in which transverse or longitudinal photons decay in to neutrino pairs, the photo neutrino process a variation of Chevenkov emission and the URCA process. We consider another collective process based on the Landau damping or growth of plasma waves by neutrinos. In this case neutrinos Landau damp on plasma waves carrying away the energy. This mechanism can reduce the cooling time of neutron stars by orders of magnitude. The effect of magnetic fields will also be considered. [Preview Abstract] |
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KP1.00112: Modified Jeans Instability for Dust Grains in a Plasma Gian Luca Delzanno, Giovanni Lapenta In two recent papers, Delzanno et al. [1, 2] have pointed out that an electron emitting (for instance due to photoemission) dust grain immersed in a plasma can sustain profiles of the shielding potential having an attractive potential well (reminiscent of the Lennard-Jones potential for the attraction among atoms). The presence of a potential well in the shielding potential has important consequences as it can lead to attractive forces on other grains even if they have the sign of charge and can be particularly important for astrophysical systems. In this study, we will present the kinetic theory of the modified Jeans instability [3], where a system of dust particles interacts through the gravitational and electrostatic forces. The latter, however, is not modeled with the Coulomb potential but with the potential well discovered in Refs. [1, 2]. We show that the well acts broadening the spectrum of gravitationally unstable modes and enhance their growth rates, even with respect to the pure gravitational case [3]. On the other hand, a pure Debye-Huckel potential always acts as to stabilize the system. [1] G. L. Delzanno, A. Bruno, G. Sorasio, G. Lapenta, Phys. Plasmas 12, 062102 (2005). [2] G. L. Delzanno, G. Lapenta, M. Rosenberg, Phys. Rev. Lett. 92 (3), 035002 (2004). [3] G. L. Delzanno, G. Lapenta, Phys. Rev. Lett. 94, 175005 (2005). [Preview Abstract] |
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KP1.00113: New insights into extragalactic jets: A combination of simulations and observations Giovanni Lapenta, P. Kronberg Jets in active galactic nuclei (AGN) are very interdisciplinary laboratories, and still as enigmatic as they are remarkable plasma systems. Recent analyses of observations, and simulations by us are providing some important constraints on their physical parameters, and on computational models. This is leading to a better understanding of the physical constraints, and of the systems in which they are immersed. Expertise in plasma physics is required to understand their inner workings and to design a model of the physics behind them. In an attempt to bridge the gap between the fundamental plasma physics processes and these astrophysical ``laboratories,'' we have pooled astrophysics and plasma physics expertise in an attempt to gain insight into two well-imaged kiloparsec-scale astrophysical jets in the radio galaxies 3C303 and 3C274. Our approach is intended to provide the two communities with a common language and common understanding of the range of numbers and physical properties typically involved [1]. We present the results of our investigation, listing specific numbers (or ranges) for all the quantities of interest to plasma physics. The new insights are used to constrain specific plasma physics models of jets. \newline [1] G. Lapenta, P. Kronberg, Astrophys. J., 625, 37, 2005. [Preview Abstract] |
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KP1.00114: 3D MHD Simulations of Large-Scale Structures of Magnetic Jets Hui Li, Gianni Lapenta, John Finn, Shengtai Li Extragalactic radio jets represent a significant amount of magnetic energy (and perhaps magnetic flux) flow from supermassive black holes inside massive galaxies to the intergalactic medium (IGM). Magnetic fields are believed to play an important role in determining the overall structure of astrophysical jets, though many fundamental questions remain, such as what collimation mechanisms are, what determines the lobe formation, etc. We will present 3D MHD simulations of the formation of large scale magnetic jets/``towers,'' evolved from an isolated and idealized initial state where magnetic fields are injected in a small volume. We will present a detailed analysis of the ``tower'' structure, collimation mechanisms, instabilities, and flux conversion processes. We will also compare our simulation results with astrophysical jet observations. [Preview Abstract] |
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KP1.00115: Kink Stability of MHD Equilibria with Line Tying Evstati Evstatiev, Gian Luca Delzanno, John M. Finn, Giovanni Lapenta We have studied the line-tied kink stability of cylindrical equilibria for applications to solar loops and flux core spheromak formation. Our semi-analytic formulation allows in principle for plasmas or arbitrary length and arbitrary current density profiles; it involves expansion in a series of basis function which are radial eigenfunctions, some with real $k_z$ and some for which $k_z$ is complex. The boundary conditions are applied on a set of radial grid points at the ends, or alternatively integrating over selected distributed basis functions. The dispersion relation is found from the determinant of the resulting matrix. For most cases, the matrix becomes prohibitively stiff for even a moderate number of basis functions. We have modified the process so that the boundary conditions at the ends overdetermine the basis function coefficients, and we therefore satisfy the boundary conditions in a least squares sense. The effectiveness of this approach will be discussed. We also show nonlinear simulations, leading to a nonlinearly saturated kink with topological changes due to magnetic reconnection. Results with stabilization due to hollow pressure profile, possibly related to collimation of astrophysical jets, will be shown. [Preview Abstract] |
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KP1.00116: A New Cyclotron Radiation Mechanism in Astrophysics, Space and the Laboratory Barry Kellett, Robert Bingham, Kevin Ronald, David C. Speirs, Alan D.R. Phelps, Adrian Cross, Irene Vorgul, R.A. Cairns, C.G. Whyte, Craig Robertson, John Tonge From the study of the radio and X-ray emission from stars, we discovered a new radiation emission mechanism produced by energetic electrons entering a region of increasing magnetic field. This cyclotron maser process was found to be extremely efficient at converting electron energy into radio frequency emission. When a beam of electrons enters a region of increasing magnetic field strength, conservation of magnetic moment leads to the electron beam forming a crescent or horse-shoe shaped distribution in velocity space. Such a distribution is unstable and leads to the generation of cyclotron maser type radiation. [Preview Abstract] |
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KP1.00117: Theory of a new cyclotron maser instability with application to space and laboratory plasmas Irene Vorgul, Robert Bingham, R.A. Cairns, Kevin Roland, David Speirs, Alan Phelps, Barry J. Kellett Conservation of the magnetic moment results in the formation of a crescent, or horseshoe shaped velocity distribution when a beam of electrons moves into an increasing magnetic field. The resultant horseshoe shaped velocity distribution has been shown to be unstable with respect to a cyclotron-maser type instability. This instability has been postulated as the mechanism responsible for auroral kilometric radiation and also non-thermal radiation from other astrophysical bodies. In this paper the previous theory, that assumed an infinite uniform plasma, is extended to apply to a bounded cylindrical geometry. This more exact theory in bounded cylindrical geometry is also directly relevant to a laboratory experiment currently being carried out. [Preview Abstract] |
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KP1.00118: Controlled Laboratory Experiments on expanding magnetic flux ropes Mio Nakamoto, Walter Gekelman, James Chen, Patrick Pribyl, Kevin Connolly A laboratory experiment which was designed to study the expansion of a magnetic flux rope in a geometry similar to that of Coronal Mass Ejections (CME) is underway at UCLA. A 10 cm cathode and adjacent, movable anode are placed at the lower edge of a plasma column in a three meter long, one meter diameter plasma column. The cathode and anode, which constitute the stationary footprints of the flux rope during each run, are housed within solenoidal magnets (oriented at right angles to the device axis) are pulsed at the same (1 Hz) repetition rate as the background plasma ( n = 10$^{12}$ cm$^{-3}$, Dia = 30 cm , 200 G $<$ B$_{z} <$ 700 G). The arched and magnetized flux rope rises into the background plasma. The experiment is diagnosed with magnetic probes, Langmuir probes and Mach probes. The issues to be addressed are the relationship between the flux rope and ambient magnetic field. The experiment will examine the scaling of the acceleration and expansion of the flux rope and the separation of the anode/cathode (flux rope footprints) as well as heating and coupling of the flux rope and ambient plasma. [Preview Abstract] |
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KP1.00119: An experimental investigation of the emission mechanisms of the auroral kilometric radiation Alan D.R. Phelps, Kevin Roland, David C. Speirs, Adrian Cross, Robert Bingham, Irene Vogul, R.A. Cairns, Barry J. Kellett, Colin G. Whyte, Craig Robertson When a beam of electrons encounters an increasing magnetic field along its vector of motion, conservation of the magnetic moment results in the formation of a crescent or horseshoe shaped velocity distribution. A scenario analogous to this occurs in the terrestrial auroral zone where particles are accelerated into the polar regions of the Earth's magnetic dipole and expand adiabatically in velocity space. The resultant horseshoe shaped velocity distribution has been shown to be unstable with respect to a cyclotron-maser type instability [1-3]. This instability has been postulated as the mechanism responsible for auroral kilometric radiation and thermal radiation from other astrophysical bodies [4]. In this paper we describe both theory and a laboratory experiment to investigate the generation of microwave radiation when an electron beam is magnetically compressed. [Preview Abstract] |
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KP1.00120: Electron energization at the mantle of non-magnetic planets as the source of planetary X-ray emission Vitali Shapiro, Kevin Quest, Robert Bingham In this paper it is argued that recently observed X-ray emission from planet Venus [1] can be explained as a combination of bremsstrahlung and line K-shell radiation produced by the interaction of energetic electrons with the neutral atmosphere. Electrons are energized due to interaction with lower hybrid waves excited at the ionospheric boundary (planetary mantle) by the so called modified two stream instability. This mechanism is similar to the mechanism previously proposed for the explanation of X-ray emission from comets [2,3]. Arguments are discussed why this mechanism presents more plausible explanation of Venus emission than fluorescent model (fluorescent scattering of the solar X-ray by planetary atmosphere) originally proposed by Dennerel et.al. \newline \newline [1] Dennerel et al, Astronomy and Astrophysics, 386, 319, 2002 \newline [2] Bingham et al., Science, v. 275. 49. 1997. \newline [3] Shapiro et al., J Geophys. Res., v. 104, 2537, 1999 [Preview Abstract] |
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KP1.00121: On the Radiation Spectrum of Hot Quasi-Spherical Accretion Flow onto a Neutron Star Juthika Khargharia, Mikhail Medvedev We study the observational properties of a hot, geometrically thick, optically thin accretion flow onto an unmagnetized (and weakly magnetized) spinning neutron star. We numerically compute the photon emission spectrum, assuming the flow is steady-state and the dominant emission mechanism is free-free emission. The key parameters are the flow (and the star) rotational velocity, $\Omega$, the radial infall velocity $v$, as well as the electron temperature and density, $T_e$ and $n_e$. The relativistic effects, important for rapidly rotating stars, are included. Various viewing angles with respect to the rotation axis are considered. We compare our results with available observational data. [Preview Abstract] |
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KP1.00122: Landau Quantization in Laser Plasma Interactions and Magnetic White Dwarf Stars Vithal L. Patel, Jaechul Oh Recently ultrahigh magnetic fields up to 0.7 Giga Gauss have been measured in high intensity laser interactions with matter [1]. The laser induced GG magnetic fields in the laboratory are possible and even larger ultrahigh fields naturally occur in neutron stars. Existence of such large magnetic fields significantly affects EOS through strong Landau quantization effect [2]. However weak Landau quantization may occur in high density plasmas with magnetic fields in MG range. We consider degenerate (T $<$ T$_{B})$ and high density ($\rho >\rho _B )$ plasmas with 100-500 MG in the laboratory as well as naturally occurring in the outer layers of hydrogen-helium of magnetic white dwarfs. Electrons populate several higher Landau levels in this regime. If the weak quantization effect manifests then quantities determined by thermal electrons near the Fermi level such as entropy and transport properties of plasmas are affected. This research was performed in Laser Plasma Branch, Plasma Physics Division, Naval Research Laboratory and was supported by DOE/NNSA. [1] U. Wagner, et. al., Phys. Rev. E 70, 026401 (2004). [2] S. Eliezer, et. al., Phys. Plasmas 12, 052115 (2005). [Preview Abstract] |
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KP1.00123: Study of Magnetorotational Instability and Free-Surface MHD Flow H. Ji, L. Berzak, M. Burin, E. Fredrickson, J. Goodman, N. Katz, W. Liu, X. Ma, K. McMurtry, E. Schartman, J. Stone, J. Waksman, R. Woolley, F. Cattaneo, A. Obabko, R. Rosner, P. Fischer, A. Kageyama, B.-F. Feng, N. Morley An overview is given on two laboratory experiments using liquid gallium to study basic physics problems with astrophysical importance. The first one concerns magnetorotational instability (MRI), which is regarded as a dominant mechanism for rapid angular momentum transport in magnetized accretion disks. Based on theoretical analyses, computer simulations, and prototype experiments, a short Couette flow apparatus has been constructed including two differentially rotating rings at both ends to minimize the Ekman effect. Current focus is to clearly demonstrate MRI and to study its nonlinear saturation. The second experiment is to study stability and turbulence in free-surface MHD flow, which is important in understanding X-ray bursts observed from neutron star surfaces, and also in implementing free-surface liquid metal flow across the magnetic field in fusion devices. Based on the results from a prototype experiment, a larger open- channel flow is built to achieve higher flow speeds and magnetic fields. Comparisons with state-of-art 3D MHD simulations are also planned. Work supported by DoE (DE-AC02-76-CH03073), NSF(AST-0205903, PHY-0215581), and NASA(ATP03-0084-0106, APRA04-0000-0152). [Preview Abstract] |
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KP1.00124: Hydrodynamics of the Princeton Magnetorotational Instability Experiment M.J. Burin, E. Schartman , H. Ji, W. Liu, J. Goodman Astrophysical accretion disks are thought to be turbulent, a state that promotes significant outward transport of angular momentum. The magnetorotational instability (MRI) is thought to provide the mechanism for turbulence in disks of sufficient ionization. For cooler (e.g. protostellar) disks however magnetic effects are possibly negligible, and purely hydrodynamic turbulence may be essential. It is claimed that turbulence may occur in these centrifugally-stable flows at a sufficiently high Reynolds number (\textit{Re}) via \textit{nonlinear} instabilities. However, with \textit{Re}-limited simulations and only a handful of relevant experiments, there is current uncertainty about this claim. A laboratory apparatus has recently been constructed that generates rapidly rotating, centrifugally-stable sheared flows with \textit{Re} $\le $ 10$^{7}$. Experiments include two primary diagnostics: Laser Doppler Velocimetry, providing turbulent intensity, and driving torque, providing a measure of angular momentum transport. Issues also discussed include the reduction of secondary flows driven by boundary layers (Ekman circulation) by a novel split end-cap design, as well as the effect of shear discontinuities (Stewartson layers) within the fluid. This work is funded by the U.S. DOE, NSF, and NASA. [Preview Abstract] |
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KP1.00125: Princeton MagnetoRotational Instability (MRI) Experiment: Recent Progress in the Search for the MRI E. Schartman, H. Ji, M. Burin, R. Cutler, P. Heitzenroeder, W. Liu, X. Ma, S. Raftopoulos, J. Waksman, J. Goodman, J. Stone, A. Kageyama The Princeton MRI Experiment investigates the MRI in a magnetized cylindrical liquid Gallium Couette flow with inner and outer radii of 7cm and 21cm, and height 28cm. At Reynolds Number of $10^7$ we expect to destabilize several modes of the MRI in the presence of a 0.5T axial magnetic field. Ekman effects are reduced via a pair of differentially rotating rings at the end caps. After flow characterization with water, the apparatus was filled with Gallium to search for signatures of the MRI: an amplified radial magnetic field, and enhanced turbulent viscosity coupling the cylinders. Initial diagnostics measure torque and external radial B fields. In the future internal magnetic field and flow diagnostics will be added. Our main objectives are to (1) clearly demonstrate MRI; (2) study its nonlinear behavior and angular momentum transport; (3) compare with simulations similar to those used in astrophysical disks. This work is supported by the US DOE, NSF, and NASA. [Preview Abstract] |
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KP1.00126: Two-dimensional Simulations of Magnetorotational Instability in a Magnetized Couette Flow Wei Liu, Jeremy Goodman, Hantao Ji In preparation for an experimental study of magnetorotational instability (MRI) in liquid metal, we present non-ideal two-dimensional magnetohydrodynamic simulations of the nonlinear evolution of MRI in the experimental geometry. The simulations adopt initially uniform vertical magnetic fields, conducting or insulating radial boundaries, and periodic vertical boundary conditions. No-slip conditions are imposed at the cylinders. We focus on the dependence of the MRI growth rate and angular momentum transport rates on Reynolds number and magnetic Reynolds number. Our growth rates compare well with existing local and global linear analysis. The nonlinear final state is steady and almost independent of resistivity for magnetic Reynolds numbers in the range $200\leq \leq 800$, although resistivity does influence the rate of evolution. A possible mechanism of nonlinear saturation is discussed. In addition, we study boundary conditions closer to those of the planned experiment such as radially conducting, vertically insulating boundary condition and full insulating boundary condition. Initial results on magnetic Ekman circulation and magnetic Stewartson layer as well as those on MRI, will be reported. This work is supported by the US Department of Energy, NASA under grant ATP03-0084-0106 and APRA04-0000-0152 and also by the National Science Foundation under grant AST-0205903. [Preview Abstract] |
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KP1.00127: The Madison Dynamo Experiment R.D. Kendrick, C.B. Forest, C.M. Jacobson, M.D. Nornberg, C.A. Parada, E.J. Spence A spherical dynamo experiment has been constructed at the University of Wisconsin-Madison's liquid-sodium facility. The experiment is designed to self-generate magnetic fields from flows of conducting metal. The apparatus consists of a 1 m diameter, spherical stainless steel vessel filled with liquid sodium. Two 100 Hp motors drive impellers which generate the flow. The motors have been operated up to 1200 RPM (60\% of design specification), achieving a magnetic Reynolds number of 130, based on impeller tip speed. Various polarizations of external magnetic fields have been applied to the sodium, and the induced magnetic field has been measured by both internal and external Hall probe arrays. Cavitation of the sodium is monitored using an ultrasonic transducer and suppressed through pressurization. Operating parameters and performance of the experiment are presented. Future plans for the experiment are discussed. [Preview Abstract] |
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KP1.00128: Approach to Magnetic Self-excitation in the Madison Dynamo Experiment E.J. Spence, R.A. Bayliss, C.B. Forest, C.M. Jacobson, R.D. Kendrick, M.D. Nornberg The Madison Dynamo Experiment is a 1 m diameter spherical vessel filled with flowing liquid sodium, used to study magnetic field generation and magnetohydrodynamic (MHD) turbulence. The approach to magnetic self-excitation is studied by applying magnetic fields of different polarizations and frequencies to the flowing fluid; internal and external probes measure the induced magnetic field. The induced field is used to determine the profiles of the fluid's mean velocity field through an inversion process. The resulting electromagnetic model of the system provides both the magnetic Reynolds number, $R_m$, and the magnetic growth rate. Variation in the geometry and speed of the fluid as a function of $R_m$ (for $0 < R_m < 110$) is presented, as well as an estimate of the critical $R_m$ required for self-excitation as computed from an eigenmode analysis. [Preview Abstract] |
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KP1.00129: MHD Turbulence in the Madison Dynamo Experiment M.D. Nornberg, R.A. Bayliss, C.B. Forest, C.M. Jacobson, R.D. Kendrick, E.J. Spence The inductive response of flowing liquid sodium in the Madison Dynamo Experiment is used to study properties of MHD turbulence. External coils generate a field which is advected by the flow. The turbulence and mean flow are investigated by measuring the induced magnetic field. The $\Omega$-effect is demonstrated by measuring the mean toroidal magnetic field. The power spectrum of magnetic field fluctuations is consistent with Kolmogorov-type turbulence with an apparent resistive dissipation scale within the inertial range. Fluctuations of the magnetic field corresponding to eddies passing the probe are used to measure the mean local velocity. Measurements of the internal toroidal field exhibit occasional bursts due to structures that are correlated over large regions within the flow. Conditional averaging is used to determine the characteristic size and speed of the structures. This technique is used to search for the filamentary structures responsible for dissipation in MHD turbulence. [Preview Abstract] |
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KP1.00130: Driven and Spontaneous Reconnection in the Lab and in Astrophysics D. Craig, A.F. Almagri, S.H. Choi, D.J. Den Hartog, G. Fiksel, S.C. Prager, J.S. Sarff, D.L. Brower, B.H. Deng, W.X. Ding Spontaneous reconnection (associated with plasma instabilities) and driven reconnection (associated with imposed plasma flows) exist in both laboratory and astrophysical plasmas. In the MST Reversed Field Pinch, both types of reconnection appear simultaneously during a sawtooth crash giving an opportunity to compare the two types. Measurements of the current sheet width in both cases are similar and consistent with the width of magnetic islands associated with the reconnection. The temporal behavior of both types of reconnection is also similar and exhibits an explosive character. The simultaneous presence of both types of reconnection enhances the overall release of magnetic energy in the system and also seems to be important for the production of strong ion heating, momentum redistribution, and MHD dynamo effects. Other naturally occurring examples of plasmas undergoing both types of reconnection (e.g. possibly solar flares) will be discussed and compared. Work Supported by U.S.D.O.E. and N.S.F. [Preview Abstract] |
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KP1.00131: Ion Heating During Reconnection Events in the MST Reversed Field Pinch G. Fiksel, D. Craig, D.J. Den Hartog, D.A. Ennis, S. Gangadhara, V.V. Mirnov, S.C. Prager, V.A. Svidzinski Sudden ion heating occurs during reconnection events in the Madison Symmetric Torus (MST) reversed field pinch. This phenomenon shares some common underlying features with a number of astrophysical and other laboratory plasmas. The reconnection events are characterized by quasi-periodic bursts of magnetic fluctuations accompanied by self-generation and redistribution of magnetic flux. The ion temperature typically doubles a very powerful source of energy deposition and a very efficient thermalization mechanism. The spatial profile of the rise in the ion temperature suggests that the heating mechanism is broad and active throughout the plasma volume. We observe that the impurity ions are heated more strongly than the bulk plasma ions. In addition, the impurities ion distribution function stays Maxwellian throughout the sawtooth cycle while the bulk ion distribution function exhibits deviation from the Maxwellian distribution. A number of theories are being examined to explain the full set of results. These include viscous damping of fluctuation induced ion flows and ion acceleration in the electric field induced by the reconnections. [Preview Abstract] |
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KP1.00132: Measurements of transport in a stochastic magnetic field J.S. Sarff, A.F. Almagri, J.K. Anderson, D. Craig, D.J. Den Hartog, G. Fiksel, C.B. Forest, B. Hudson, R. O'Connell, S.C. Prager Transport from stochastic magnetic turbulence could be important in astrophysical settings, such as thermal conduction in galaxy-cluster plasmas and cosmic ray propagation. The MST reversed field pinch provides an ideal laboratory for investigating transport resulting from magnetic field braiding. For example, the standard theoretical expectation for stochastic heat conduction is the product of the test-particle thermal velocity and the magnetic diffusivity. In MST, conditions can be controlled to vary the magnetic diffusivity, and the predicted transport then compared with power balance measurements. These agree, but only where the magnetic field is sufficiently stochastic, and only the portion of the fluctuations responsible for local field line tearing must be used to evaluate the magnetic diffusivity. The largest components of the fluctuations do not necessarily enhance transport. High energy particles can transport at a reduced rate if their drift orbits are not aligned with the magnetic field, observed for neutral beam-injected ions in MST. We will also describe the spectral features of the observed broadband spectrum of magnetic fluctuations, which exhibit power decay suggestive of MHD cascade physics. This may be relevant, for example, to magnetic fluctuations in the solar wind. Work supported by USDoE and NSF. [Preview Abstract] |
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KP1.00133: Formation of Intense Plasma Outflows from Laboratory Prominences S.K.P. Tripathi, P.M. Bellan Solar prominences have been simulated in a laboratory experiment using a four-electrode magnetized plasma source [1]. An ultra-high speed intensified CCD camera records visual images of the laboratory prominence evolution and a magnetic probe array measures internal magnetic fields. Laboratory prominences produced using low pressure argon and krypton form localized outflow from the main structure. These outflows appear immediately after Ar and Kr prominences become unstable and contact surrounding metal structures. Within a few microseconds after this event, the main structure disappears and the outflow becomes extremely intense and elongated. An analytic model based on Hamiltonian formalism predicts the existence of a critical parameter below which ions lose confinement in a force-free magnetic field and subsequently form intense outflows. This escape of ions from force-free magnetic fields has been verified in numerical computations of ion trajectories.\newline \newline [1] J. F. Hansen, S. K. P. Tripathi, and P. M. Bellan, Phys. Plasmas $\mathbf{11(6)}$, 3177 (2004) [Preview Abstract] |
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KP1.00134: Electromagnetic Radiation from Beam Driven Electrostatic Instabilities: Investigation using Computer Simulation S.M. Finnegan, N. Brenning, M.E. Koepke, I. Axnas, M.A. Raadu Two-dimensional, electromagnetic particle-in-cell simulations [J.P. Verboncoeur \textit{et al.}, Comp. Phys. Comm. \textbf{87}, 199 (1995)] were used to show, that the interaction of an electron beam, formed from electrons accelerated in a cathode sheath, with the background plasma as it travels into a plasma density gradient produces large-amplitude, high-frequency (HF) electric-field oscillations (close to local plasma frequency) spatially localized in the plasma-density-gradient region. The HF oscillations propagate away from the cathode with phase velocity 5x10$^{6}$ m/s. Half-wavelength, HF standing waves have previously been reported in 1-Dim. simulations [H. Gunell \textit{et al}., Phys. Rev. Lett. \textbf{77}, 5059 (1996)]. We plan to use 2-Dim. simulations to investigate lab-observed correlations between spatially localized, HF standing waves and electromagnetic radiation. We are interested in possible space applications. [Preview Abstract] |
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KP1.00135: Rayleigh-Taylor Modal Interactions in Supernova-Relevant Experiments C.C. Kuranz, R.P. Drake, K.L. Killebrew, D.J. Kremer, M.J. Grosskopf, T. Donajkowski, M.R. Taylor, C. Krauland, D.C. Marion, H.F. Robey, B. Blue, H.F. Hansen, A.R. Miles, J.F. Knauer, D. Arnett We report the results of new experiments to observe, using the high-resolution of a backlit pinhole diagnostic, interactions among modes unstable to the Rayleigh-Taylor instability at an interface that is shocked and then decelerated by a planar blast wave. We will report observations of the interactions among a 3D ``eggcrate'' mode and an imposed, longer-wavelength, sinusoidal mode. The experiment is relevant to the degree of penetration of interior stellar material into the outer layers of an exploding star. This research was sponsored by the National Nuclear Security Administration under the Stewardship Science Academic Alliances program through DOE Research Grant DE-FG52-03NA00064, and through DE FG53 2005 NA26014~ and other grants and contracts. [Preview Abstract] |
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