Bulletin of the American Physical Society
53rd Annual Meeting of the APS Division of Plasma Physics
Volume 56, Number 16
Monday–Friday, November 14–18, 2011; Salt Lake City, Utah
Session UP9: Poster Session VIII: C-Mod Tokamak; DIII-D II; Solar, Interplanetary, and Magnetospheric Plasma Physics; Plasma Technology; |
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Room: Hall A |
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UP9.00001: C-MOD TOKAMAK AND DIII-D II |
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UP9.00002: GYRO Simulations of Turbulently Driven Density Peaking in C-Mod Plasmas D.R. Mikkelsen, M. Bitter, L. Delgado-Aparicio, K.W. Hill, M. Greenwald, J.W. Hughes, Y. Ma, Y. Podpaly, J.E. Rice, J. Candy, R.E. Waltz In turbulence simulations with H \& D mixtures the deuterium density profile is slightly more peaked than hydrogen, while electron density peaking is insensitive to H/D. Adding a low-Z impurity has no effect on density peaking. Density peaking is weakly affected when the Ti profile is varied to align the predicted heat flux to the experimental transport analysis. Robust predictions of peaking are obtained with a novel simulation procedure: each hydrogenic species is represented by two ions in the simulations (e.g. two D and two H); they differ only by having different density gradients, but these offset each other so the total R/Lni for each species matches the electron R/Lne. Linear interpolation of the predicted particle fluxes determines the individual R/Lni that meet the null-flux condition required for each hydrogenic species; integrating the R/Lni profiles gives the predicted density peaking. Studies of the density peaking of low-, medium-, and high-Z impurities are planned. [Preview Abstract] |
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UP9.00003: Controlling fluctuations in an ITB and comparison with gyrokinetic simulations D.R. Ernst, C.L. Fiore, A. Dominguez, Y. Podpaly, M.L. Reinke, J.L. Terry, N. Tsujii, I. Bespamyatnov, M. Churchill, M. Greenwald, A. Hubbard, J.W. Hughes, J. Lee, Y. Ma, S. Wolfe, S. Wukitch We have modulated on-axis ICRF minority heating to trigger fluctuations and core electron transport in Alcator C-Mod Internal Transport Barriers (ITB's). Temperature swings of 50\% produced strong bursts of density fluctuations, measured by phase contrast imaging (PCI), while edge fluctuations from reflectometry, Mirnov coils, and gas puff imaging (GPI) simultaneously diminished. The PCI fluctuations are in phase with sawteeth, further evidence that they originate within the ITB foot. Linear gyrokinetic analysis with GS2 shows TEMs are driven unstable in the ITB by the on-axis heating, as in Refs. [1,2]. Nonlinear gyrokinetic simulations of turbulence in the ITB are compared with fluctuation data using a synthetic diagnostic [1]. Strong ITB's were produced with high quality ion and electron profile data. \\[4pt] [1] D. R. Ernst et al., 20th IAEA Fusion Energy Conference (2006), Chengdu, China, paper IAEA-CN-149/TH/1-3. \newline [2] D. R. Ernst et al., Phys. Plasmas 11 (2004) 2637. [Preview Abstract] |
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UP9.00004: Study of Plasma Rotation by Modulating ICRF Power on Alcator C-Mod Chi Gao, John Rice, Matthew Reinke, Yuri Podpaly, Luis Delgado-Aparicio, Yijun Lin X-ray emission intensity and toroidal rotation velocity profiles are studied with modulated ICRF heating using high resolution X- ray spectometers and analysis tools that provide spatially- resolved intensity, ion-temperature, and rotation profiles. These profiles respond to the power modulation with different behaviors under plasma current and magnetic field scans. Preliminary analysis shows that modulated intrinsic rotation scales with modulated stored energy ($\sim$1 km/s$\cdot$kJ). Fourier analysis indicates the rotation propagates from the edge to the core. Further analysis will be done on the relation between local plasma energy and intrinsic rotation to separate local and non-local effects of stored energy on intrinsic rotation. A linear acceleration term associated with the toroidal rotation velocity is observed in ICRF-modulated L mode discharges, which we will try to relate to the diffusion and convection terms of momentum flux. [Preview Abstract] |
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UP9.00005: Plasma impurity composition in the Alcator C-Mod tokamak Igor Bespamyatnov, William Rowan, Kenneth Liao, Matthew Reinke, Michael Churchill Accurate characterization of the impurities in tokamak plasmas is an important task. Impurities can lead to fuel dilution, enhanced radiative losses and can affect main-ion and electron transport through Z$_{eff}$. The task of quantifying the impurities in Alcator C-Mod tokamak is critical. C-Mod's plasma contains a variety of intrinsic (B, F, Fe, Mo, W), seeded (He, N, Ne, Ar) and purposefully injected (Al, Ca, Ni) impurities during regular operations. Z$_{eff}$ of well-confined C-Mod plasma may reach values greater than 5. In order to properly characterize these impurity effects, density of each impurity should be accurately quantified. C-Mod employs several spectroscopic diagnostics to diagnose impurities. Here we attempt to perform a constrained analysis of the impurity content for a variety of the C-Mod plasma discharges. The goal is to develop a technique to combine results from multiple diagnostics into a joint analysis. Reliable estimates of impurity content and Z$_{eff}$ are sought as the result. The initial focus here is on the measurement of the absolute boron density by means of CXRS. Boron is usually the major low-Z impurity in C-Mod. The accuracy of the boron density measurements and main sources of uncertainties will be discussed in detail. [Preview Abstract] |
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UP9.00006: Empirical scaling of ELMy H-mode pedestals on Alcator C-Mod and comparisons with the EPED model J.R. Walk, J.W. Hughes, A.E. Hubbard, J. Terry, P.B. Snyder H-mode discharges on the Alcator C-Mod tokamak featuring edge- localized modes (ELMs) are used to find empirical scalings of the plasma pedestal with bulk plasma and engineering parameters. Pedestals in ELMy discharges typically reach densities of $5 \times 10^{19}$--$2.5 \times 10^{20}$ m$^{-3}$ and temperatures of 400--1000 eV (corresponding to 20--50 kPa in the pressure pedestal), over a width of 3--5\% of poloidal flux. We present the results of a wide range of C-Mod ELMy H- mode discharges, including plasma current scans over 700kA--1MA, as well as shaping variation both in elongation (1.45--1.6) and upper/lower triangularity (0.15--0.3 and 0.7--0.8), in continuation of previous ELMy pedestal studies on C-Mod. Observed pedestal scalings are compared with the results of the most recent iteration of the EPED class of models, which uniquely predict the pedestal width and height for a set of scalar input parameters by a combination of stability calculations for coupled edge kink/peeling and ballooning MHD modes, and the localized kinetic analogue to the MHD ballooning mode. [Preview Abstract] |
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UP9.00007: PCI measurements of Turbulence and Transport in Alcator C-Mod P. Ennever, M. Porkolab, J. Dorris, N. Tsujii, E. Davis Measurements of turbulent density fluctuations on C-Mod using Phase Contrast Imaging (PCI) are reported. PCI is an interferometric technique that measures line-integrated density fluctuations at frequencies up to 2 MHz in the wave number range 0.5-30 cm$^{-1}$ [1]. The PCI system on C-Mod consists of a beam that passes vertically through the plasma core and images onto a 1-D array of 32 HgCdTe detectors. Owing to lack of localization along the beam path, the signal includes contributions from the plasma edge as well as the core. To distinguish edge turbulence from that emanating from the core, we compare the spectrum to other edge localized turbulence measurements (ie, GPI, reflectometry). The core turbulence spectrum is modeled by a synthetic PCI diagnostic and nonlinear global GYRO analysis [2]. Fluctuation spectra predicted by GYRO will be compared with those measured with PCI in different modes of plasma operation. Supported by US DoE awards DE-FG02-94-ER54235 and DE-FC02-99-ER54512. \\[4pt] [1] M. Porkolab, et al, IEEE Transactions on Plasma Science, \textbf{34}, 229 (2006). \\[0pt] [2] C. Rost et al, Phys. Plasmas \textbf{17}, 062506 (2010). [Preview Abstract] |
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UP9.00008: Edge Turbulence Studies in Alcator C-Mod with Phase Contrast Imaging and BOUT++ E.M. Davis, M. Porkolab, P. Ennever, N. Tsujii, J.W. Hughes, X.Q. Xu Energy confinement in tokamaks is believed to be strongly controlled by plasma transport in the edge region just inside the last closed magnetic flux surface. A first principles understanding of these edge processes requires effective coupling between experiment and theory. Phase Contrast Imaging (PCI) is a mature Alcator C-Mod diagnostic using a type of internal interferometry to measure $\int \tilde{n}_{e} dl$. C-Mod's thirty-two chord PCI beam collects data from both the plasma core and edge, making it well-suited for edge turbulence studies. The Boundary-plasma Turbulence (BOUT++) code is capable of nonlinear fluid boundary turbulence analysis in a general geometry. Using experimentally measured profiles as input, BOUT++ calculations show that typical C-Mod EDA H-modes are ideal MHD stable, but become linearly unstable when the pedestal resistivity is included ($S < 10^{9}$). The computed resistive ballooning mode growth rate in such shots is shown to scale approximately as $\eta^{1/3}$, consistent with theory. Inclusion of nonlinear effects allows comparison of the calculated turbulence spectrum with PCI measurements. The results and implications of these comparisons will be discussed. [Preview Abstract] |
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UP9.00009: A study of poloidal asymmetries in the pedestal region R.M. Churchill, B. Lipschultz, S. Lisgo, F. Reimold, J. Goldstein Simultaneous CXRS measurements of boron density, velocity, and temperature in the pedestal region ($0.8< r/a < 1.05$) at the low- and high-field sides (LFS and HFS) of Alcator C-Mod allow studies of variations in boron density and total velocity on a flux surface. While previous studies used different neutral sources (a 50keV hydrogen neutral beam at the LFS and a thermal D2 gas puff at the HFS) to localize CXRS measurements we have recently expanded our diagnostic set to allow thermal gas CXRS at both locations, thus removing uncertainties due to different measurement techniques and cross-section. We have also upgraded our modelling capability to utilize the DIVIMP code, which uses the plasma-neutral code combination of OSM-EIRENE to determine the local neutral density. Comparisons between CXRS methods using different neutral sources will be shown as well as an exploration of whether the constants $K(\psi)$ and $\omega(\psi)$ in the description of $\bf{V}=\frac{K(\psi)}{n}\bf{B}+\omega(\psi){R^2}\nabla\phi$ are constant on a flux surface as typically assumed. The above comparisons will be shown for a variety of H-mode and I-mode plasmas. Supported by USDoE award DE-FC02-99ER54512. [Preview Abstract] |
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UP9.00010: Proposed Heuristic Model for Fuzz Growth on Metal Surfaces Roman Ochoukov, Dennis Whyte The growth of nano-scale rods, or fuzz, is observed experimentally on tungsten and molybdenum surfaces exposed to an incident He flux with ion energies $>$10 eV. It is experimentally determined that the growth of fuzz follows a diffusion-like equation as a function of the He exposure time $t$: \textit{x $\sim $ (2Dt)}$^{1/2}$, where $x$ is the fuzz thickness and $D$ is the effective diffusion coefficient. This growth is consistent with the incident He flux \textit{$\Gamma $}$_{o}$ being reduced at a rate of \textit{d$\Gamma $(x)/dx = -$\alpha \Gamma $(x)}$^{3/2}$ as the He ions traverse the fuzz. \textit{$\alpha $} is an integration constant. Based on the above assumption, we derived a relation between $x$, \textit{$\Gamma $}$_{o}$, and $t$: \textit{x + 2$\alpha $ }$^{-1}$\textit{$\Gamma $}$_{o}^{-1/2}$\textit{ = (2Dt)}$^{1/2}$. The notable features of this equation, for a fixed exposure time, are: 1) the saturation of the fuzz thickness as \textit{$\Gamma $}$_{o}$ approaches\textit{ $\infty $} and 2) the minimum threshold value of the incident He flux \textit{$\Gamma $}$_{o}$ required to initiate fuzz growth. Both of these features are experimentally observed. Another notable feature is that it requires a minimum He fluence \textit{$\Gamma $}$_{o}t_{min}$ at the metal surface to initiate fuzz growth. [Preview Abstract] |
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UP9.00011: Retarding Field Analyzer and Ion Sensitive Probe for Boundary Plasma Profile Measurements in Alcator C-Mod: Design and Initial Results Dan Brunner, Brian LaBombard, Roman Ochoukov, Dennis Whyte We are developing two new scanning probe heads to measure the ion and electron distribution functions and plasma potential. The Ion Sensitive Probe (ISP) is a Katsumata style probe: the difference in gyro-radii of electrons and ions is used to scrape off the electrons such that the ion distribution function perpendicular to the magnetic field and plasma potential may be deduced. A domed Langmuir probe is included in the head to measure electron temperature and density. The Retarding Field Analyzer (RFA) measures electron (EEDF) and ion energy distribution functions (IEDF) parallel to the magnetic field (in both directions) as well as plasma potential and density. Of particular interest is the response of the boundary layer (EEDF and plasma potential) to Lower Hybrid (LH) waves. For this purpose, an additional stationary RFA has been placed on a limiter that connects magnetically to a LH launcher. Design considerations for handling the large heat flux (100's MW/m$^2$), space charge effects and small signal levels ($\sim\mu$A) along with initial measurements will be presented. [Preview Abstract] |
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UP9.00012: An accelerator-based in-situ surface diagnostic for plasma-wall interactions science on Alcator C-Mod Zach Hartwig, Dennis Whyte, Harold Barnard, Brandon Sorbom, Pete Stahle Boundary science in magnetic fusion devices is severely hindered by a dearth of in-situ diagnosis of plasma facing component (PFC) surfaces. The ideal in-situ PFC diagnostic would perform surface composition measurements on a plasma shot-to-shot time scale with 1~$\mu$m depth and 1~cm spatial resolution over large PFC areas. To this end, the customary laboratory surface diagnostic - nuclear scattering of MeV ions - is being adapted to the Alcator C-Mod tokamak. A compact ($\sim$1~m), high-current ($\sim$mA) radio-frequency quadrupole accelerator injects 0.9 MeV deuterons into the vacuum vessel. The deuterons are steered to PFC surfaces with tokamak magnetic fields in between plasma shots, where they induce high-Q nuclear reactions with low-Z isotopes in the first $\sim$10~$\mu$m of material. The induced gammas and neutrons are detected with scintillators, where energy spectroscopy provides quantitative surface analyses. Techniques to measure the thickness of low-Z PFC film coatings and profiles of retained hydrogenic fuel are presented along with simulated measurements by ACRONYM, a comprehensive Geant4 synthetic diagnostic. [Preview Abstract] |
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UP9.00013: Simulation of disruptions on C-Mod in support of the new outer divertor project F. Poli, C. Kessel, P. Titus, H. Zhang, J. Doody, R. Granetz, B. Lipschultz Disruptions in C-Mod lead to large forces on structures inside the vacuum vessel and can be grouped in two classes depending on whether they begin with a thermal quench (midplane disruptions) or not (VDEs). VDEs induce the largest currents in the lower divertor, which is being re-designed to be toroidally continuous and allow operation at high temperatures ($<$600C). Both types of disruptions have been simulated with TSC and the vector potential has been integrated in the ANSYS code (ANSYS$\textregistered$ Multiphysics, Release 12.1) to calculate magnetic fields, induced currents in the structures of interest and forces. These forces are then used to calculate stress and deformation in the part. The TSC simulations are adjusted (thermal quench time, halo temperature and width, etc) to match the plasma characteristics as close as possible to experiments. The results of these simulations will be shown and the dependence of disruption time scales and characteristics on these plasma parameters and the new outer divertor structures will be discussed. [Preview Abstract] |
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UP9.00014: Radiation asymmetry in gas jet mitigated disruptions on Alcator C-Mod G.M. Olynyk, R.S. Granetz, M.L. Reinke, D.G. Whyte, I.H. Hutchinson The radiated energy during the thermal quench (TQ) of gas jet mitigated disruptions on Alcator C-Mod is toroidally asymmetric, and the degree of asymmetry correlates with the growth rate of low-$n$ MHD modes during the pre-TQ phase of the disruption [Olynyk et al., \emph{Bull. Am. Phys. Soc.} {\bf 55}(15), TP9.00071]. In order to investigate the spatial and temporal structure of the asymmetry, a toroidal array of ultraviolet photodiodes (serving as solid-state bolometers) has been designed and installed. Details of the design and implementation of the diagnostic are presented. The new diagnostic system is used in concert with existing poloidal magnetic field pickup coils to investigate in more detail the role of MHD activity in triggering the TQ. Results from gas jet disruption mitigation experiments are presented. The implications for the ITER disruption mitigation system are discussed. [Preview Abstract] |
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UP9.00015: Effectiveness of Disruption Mitigation and Toroidal Asymmetry with Two Gas Jets R.S. Granetz, G.M. Olynyk, M.L. Reinke, D.G. Whyte, S. Coombs, M. Sugihara Alcator C-Mod has done extensive disruption mitigation studies in the past using a high-pressure gas jet at a single toroidal location. Measurements with a pair of AXUV diode arrays (de facto solid-state bolometers) show that there can be a large toroidal asymmetry of the radiated power during mitigated disruptions. This is problematic for the ITER first wall, so ITER is planning to use multiple gas jets at a number of toroidal locations to reduce the asymmetric wall loading. To test the effectiveness of this concept, a 2nd gas jet is being added to Alcator C-Mod at a location around the torus from the existing jet. In addition, a toroidally distributed set of 5 AXUV diodes is being installed to provide enhanced toroidal resolution of radiated power. Experiments to measure the effect on toroidal asymmetry with the two gas jets will be performed early in the next campaign (fall 2011). Additional studies of other issues with two gas jets, such as mitigation of halo currrents and thermal loads, non-synchronous timing, different gas combinations, etc are also being planned. [Preview Abstract] |
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UP9.00016: A `shoelace' antenna system for direct excitation of C-Mod's quasi-coherent mode and boundary layer turbulence B. LaBombard, T. Golfinopoulos, R. Parker, W. Burke, R. Leccacorvi, R. Vieira, J. Zaks, R. Granetz, M. Greenwald, E. Marmar, M. Porkolab, S. Wolfe, P. Woskov, S. Wuktich Experiments indicate that short wavelength, drift-Alfvenic turbulence largely sets the transport levels in the plasma edge: pressure gradients in L and H-mode are `clamped' at canonical values of the MHD parameter ($\alpha _{MHD})$; broadband and coherent fluctuations have strong magnetic signatures, with k$_{\bot }\rho _{s}\sim $ 0.1 being prominent. A quasi-coherent mode (50 kHz $<$ f $<$ 150 kHz, 1 $<$ k$_{\bot }<$ 2 cm$^{-1})$ drives particle transport in C-Mod's EDA H-modes, making them steady-state without ELMs. With the idea of exciting, controlling or otherwise exploiting this transport behavior, we are developing a novel, high k$_{\bot }$ antenna system to drive drift-Alfvenic modes at the outer midplane with k$_{\bot }\sim $ 1.5 cm$^{-1}$. A `shoelace' style winding is placed in close proximity to the last-closed flux surface. In principle, this scheme inductively drives parallel current fluctuations that mimic intrinsic plasma fluctuations but at larger amplitude. Details of the antenna system design, its planned modes of operation and initial results will be presented. [Preview Abstract] |
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UP9.00017: Electrical Characteristics and Performance of the Alcator C-Mod Quasi-Coherent Mode Antenna System T. Golfinopoulos, B. LaBombard, R.R. Parker, W. Burke, R. Leccacorvi, R. Vieira, J. Zaks, E.M. Davis, R. Granetz, M. Greenwald, E. Marmar, M. Porkolab, S.M. Wolfe, P.P. Woskov, S.J. Wukitch, X. Xu We have designed a new antenna for the purpose of coupling to the Quasi-Coherent Mode (QCM) and other edge fluctuations in Alcator C-Mod [see poster by B. LaBombard et al.]. A guiding principle of the design was to create a magnetic field perturbation matched in frequency ($\sim100$ kHz) and wave vector ($k_{\perp}\approx1.5$ cm$^{-1}$) to the spontaneously-occurring QCM, and with amplitude several times larger at the mode flux surface. The basic electrical and electromagnetic properties of the antenna built to meet this goal are discussed. In addition, an engineering review of the power system is provided, with a description of a discretely-variable L-style impedance matching network which provides very fine resolution in the range from 50 to 300 kHz, reflecting $<10$ \% power in initial bench tests. Preliminary results of the first experimental campaign are compared with supporting calculations from BOUT++ simulations. [Preview Abstract] |
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UP9.00018: Formation and stability of impurity-induced snakes in Alcator C-Mod Luis F. Delgado-Aparicio, R. Grantez, J. Rice, Y. Podpaly, W.A. Cooper, M.L. Reinke, L. Sugiyama, S. Wolfe, M. Bitter, D. Gates, E. Fredrickson, M. Greenwald, K. Hill, E. Marmar, N.A. Pablant, S. Scott, R. Wilson Impurity-induced $m=1$ snakes are observed in Alcator C-Mod, caused by the release of molybdenum impurities from the tiles covering the vacuum vessel. Using AXUV bolometers, the SXR tomographic arrays and a High-Resolution X-ray imaging spectrometer it was possible to determine that $(n_{Mo}/n_{e})_{max}\sim0.1\%$ before the snake formation, which is responsible for a factor of two increase in resistivity from its impurity-free case. The saturated island width can depend on a stabilizing $\Delta$' term and the local changes of $dZ_{eff}$ and $dP_{rad}$, while its stability criteria are satisfied by the measured enhanced plasma pressure and resistivity on the center of the island, in agreement with compressible resistive MHD models. The possibility that the snake is due to an MHD equilibrium with a 3D helical core with axisymmetric boundary conditions will also be discussed. Supported by USDoE DE-FC02-99ER54512 at C-Mod and DE-AC02-09CH11466 at PPPL. [Preview Abstract] |
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UP9.00019: New correlation electron cyclotron emission temperature fluctuation diagnositc for Alcator C-mod C. Sung, A.E. White, J. Irby, W.A. Peebles, X. Nguyen A new Correlation Electron Cyclotron Emission (CECE) system for the measurement of electron temperature fluctuation is planned for Alcator C-mod. The multi-channel CECE radiometer will use the spectral decorrelation technique [1] to measure turbulent fluctuations that are below thermal noise levels. The design of the optics and Intermediate Frequency (IF) section was constrained using predictions from nonlinear gyrokinetic turbulence simulations using the GYRO code. A Gaussian optical system will provide high poloidal spatial resolution ($\omega_0 < 0.5$ cm) needed to measure long-wavelength core turbulence at C-Mod, $k_{\theta}\rho_s < 0.5 $. The IF section will employ tunable band-pass filters to optimize turbulence measurements. We will present details of the new CECE system design and laboratory tests of the optics and IF section.\\[4pt] [1] G. Cima et al, \emph{Phys. Plasmas}, {\bf 2}, 720 (1995) [Preview Abstract] |
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UP9.00020: Investigation of the Thomson Scattering/ECE discrepancy at high temperature on Alcator C-Mod and DIII-D A.E. White, P. Bonoli, A.E. Hubbard, J.W. Hughes, Y. Lin, Y. Ma, S.J. Wukitch, M.E. Austin, B.D. Bray, C.C. Petty, R.I. Pinsker, R. Prater, R.W. Harvey High temperature plasmas [$T_e\, (0) > 7$ keV] have been produced with ion cyclotron resonance heating at Alcator C-Mod and with neutral beam and fast wave heating at DIII-D. In optically thick tokamak plasmas, $T_e$ measurements made with Thomson Scattering (TS) and Electron Cyclotron Emission (ECE) diagnostics are typically in excellent agreement. However, past experiments at TFTR and JET have shown the existence of a disagreement between $T_e$ measured by TS and ECE when $T_e\geq 7$ keV, as well as evidence of distortions in the bulk of the electron distribution function. Preliminary results from the DIII-D and C-Mod experiments indicate no such discrepancy between TS and ECE when $T_e\, (0) > 7$ keV. Comparisons between TS and ECE measurements in high temperature DIII-D and C-Mod plasmas, and comparisons of measured ECE spectra with simulations, will be presented. [Preview Abstract] |
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UP9.00021: C-Mod Polarimeter Development and Application to Magnetic Fluctuation Measurements W.F. Bergerson, P. Xu, D.L. Brower, W.X. Ding, J.H. Irby The single chord polarimeter has been expanded to three chords with extensive engineering upgrades to address measurement phase errors associated with stray magnetic fields, vibrations, path length variations, and polarization sensitive beam splitters. Simultaneous multichord measurements allow for internal measurements of the equilibrium poloidal magnetic field which serve to constrain EFIT and identify current profile dynamics associated with lower hybrid current drive. With reduced system noise, fluctuations have been observed in the polarimetry signal that are associated with core tearing modes. Fluctuations due to the edge localized quasi-coherent mode are also seen. Efforts are underway to differentiate between density and magnetic fluctuations in the polarimetry measurement via cross correlation techniques and combined density measurements. Expanding the system bandwidth to $>$1 MHz will make it feasible to directly measure fluctuations related to fast particle instabilities driven by ICRH. This work supported by the DOE. [Preview Abstract] |
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UP9.00022: Internal Magnetic Field Measurements using the New Three Chord Polarimeter on C-Mod P. Xu, W.F. Bergerson, D.L. Brower, W.X. Ding, J.H. Irby, E.S. Marmar A single-chord poloidally viewing FIR polarimetry diagnostic was successfully operated on C-Mod during the FY10 C-Mod campaign. Observation of significant changes in the measured Faraday rotation during lower hybrid current drive (LHCD) experiments and during sawtooth crashes confirms that the C-Mod polarimetry measurement is sensitive to plasma current profile changes. Reduction of vibration induced noise during toroidal field ramp up and ramp down, and the calibration of the wire mesh beamsplitters, was necessary to ensure reliable rotation measurements. Tests employing changes in $\vert $B$_{T}\vert $ and plasma current direction were performed to ensure no contamination from the toroidal magnetic field. The measured signal agrees well with a synthetic Faraday rotation signal derived from EFIT. Optical design and layout of the new three-chord polarimeter will be discussed. High-sensitivity planar-diode Schottky detectors provide fast time response and low system noise. Observation of plasma current profile changes during LHCD experiments using the multichord system will be presented, as well as upgrade plans for up to 10 chords . [Preview Abstract] |
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UP9.00023: Performance evaluation of MSE on Alcator C-Mod S. Scott, R. Mumgaard, R. Granetz, R. Shugayev, M. Chung Performance of the Motional Stark Effect (MSE) diagnostic has been compared to first-principle numerical simulations by moving the Stark-split beam spectrum past MSE's narrow bandpass filters. The relative position of the Stark spectrum to the filters was varied by ramping the toroidal field at fixed q; changing the filter temperature; and swapping one filter for another. We compare the signal strength and polarization fraction of beam emission to simulations that model the MSE emission using a modified version of the PERF code (NC Hawkes et al., Rev. Sci. Instrum. \textbf{70}, 894 (1999)). The simulation includes models for beam attenuation, beam excitation, Stark emission, aperture broadening, the measured filter response function, and background visible Bremsstrahlung emission. This work confirms analytic comparisons of the expected MSE signal strength between C-Mod and other tokamaks which suggest that the polarized signal intensity on C-Mod is unexpectedly low by a factor of several. Measurements of the beam performance using calorimeters, beam-target neutron production during deuterium beam injection, and IR measurements of a stainless steel target heated by the beam will be discussed. [Preview Abstract] |
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UP9.00024: Inter-shot calibration of the MSE diagnostic on Alcator C-Mod Robert Mumgaard, Steven Scott Extensive efforts to eliminate thermal stress-induced birefringence within in-vessel lenses have reduced but not eliminated spurious drift in the calibration of the MSE diagnostic on Alcator C-Mod. In previous campaigns, the diagnostic utilized a quiescent Ohmic portion of each plasma discharge to calibrate it against magnetic equilibrium reconstructions (EFIT). This method introduces additional sources of error and places constraints on discharges for which MSE q-profile measurements can be obtained. Therefore, a system has been designed and installed to calibrate the diagnostic before and after each discharge. Light with four known linear polarizations is sequentially and reproducibly input into the diagnostic objective lens using wire-grid polarizers and a fiber-optic-based illumination system. The system also allows for experiments to identify the cause of the spurious drift to be conducted independent of plasma, fields or vacuum. The accuracy and reproducibility of the calibration system will be presented, along with results of experiments to identify the cause of the spurious drift. Supported by USDoE awards DE-FC02-99ER54512 and DE-AC02-09CH11466. [Preview Abstract] |
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UP9.00025: Upgraded SXR/EUV Spectroscopy Capabilities for Alcator C-Mod M.A. Chilenski, T. Christensen, M. Greenwald, M.L. Reinke, J. Terry, A.E. White, P. Beiersdorfer, E. Magee Alcator C-Mod is equipped with several spectrometers for the SXR/EUV range. These instruments provide a survey of the impurity content of the plasma, particularly K-shell emission from low-Z elements (B to Ne), L-shell emission from mid-Z elements (Ar to Fe) and M-shell emission from intrinsic Mo. Diagnosis of these lines is important for understanding impurity transport and main ion dilution in C-Mod. The X-ray and Extreme Ultraviolet Spectrometer (1-7nm, 2400l/mm grating) has been calibrated using an electron impact x-ray source with a variety of anodes to give lines from 6.76nm (B K$\alpha$) to 1.19nm (Na K$\alpha$). The Long Wavelength and Extreme Ultraviolet Spectrometer (2-40nm, 1200l/mm grating) is being commissioned for use on C-Mod, with the intent of replacing an aging 2.2m Rowland circle spectrometer presently used to survey the longer EUV wavelengths ($\lambda<100$nm) and monitor M-shell Mo emission. The new instrument is both more compact and should provide significantly better spectroscopic data. [Preview Abstract] |
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UP9.00026: Energetic Ion Losses in the Alcator C-Mod Tokamak D.C. Pace, R.S. Granetz, A. Bader, R.R. Parker, R. Vieira, S.J. Wukitch, D.S. Darrow, S.J. Zweben A scintillator-based fast ion loss detector (FILD) is presently being commissioned on the Alcator C-Mod tokamak to resolve the energy and pitch angle of energetic ions that are lost from the plasma due to interactions with MHD modes, edge localized modes, and ion cyclotron resonance heating (ICRH) injection. Energetic ion populations are generated by applying ICRH in the minority heating regime, producing tail energies up to 2 MeV and driving a variety of Alfv\'en eigenmodes. The 2 MHz sampling rate of the detector allows for the identification of convective losses across the range of encountered Alfv\'enic frequencies. A comprehensive design study optimized the FILD to overlap its observed ion phase space with that of the compact neutral particle analyzer array that measures radial energy and density profiles of confined ICRH tail ions. Initial results from this diagnostic system will be presented in the context of the extensive C-Mod ICRH experiment and simulation/modeling effort. [Preview Abstract] |
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UP9.00027: New instrumentation and analysis for particle transport and fast ion measurements in Alcator C-Mod William Rowan, I.O. Bespamyatnov, M.W. Brookman, K.T. Liao, R.T. Mumgaard, R.S. Granetz Measurement of ion temperature and rotation in the core of a high density plasma with CXRS is challenging, but experience with the challenges and recent experiments facilitated developments that will lead to progress in particle transport and fast ion transport. Particle measurements require detailed beam profiles and maintenance of calibrations through a campaign. To improve beam profiles, direct measurement of beam width and beam simulation are now supplemented by beam emission measurements that are simultaneous in space and time with the CXRS measurements. Pre campaign radiometric calibrations are maintained by in situ bremsstrahlung measurements. Accurate spatial localization was found to require a detailed analysis of the emission distribution along the intersection of viewchord and beam. Measurement of fast ions generated by minority heating required attenuation of interfering radiation and surprisingly required calibration of polarization sensitivity of optics to assist in removing background. [Preview Abstract] |
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UP9.00028: Fast ion charge exchange measurements during minority heating in Alcator C-Mod Ken Liao, William Rowan, Igor Bespamyatnov, Steve Wukitch, Yijun Lin, Aaron Bader, David Pace, Naoto Tsujii Ion cyclotron range of frequencies (ICRF) power is the primary auxiliary heating method in Alcator C-Mod and we utilize D(H) and D($^{3}$He) minority heating scenarios (minority in parentheses). Measuring the energetic ion distribution provides a direct means to validate simulations used to calculate ICRF power deposition. The fast and thermal minority ion distributions are measured by observing line emission using active charge exchange where the H I (656.3 nm) or He II (468.6 nm) lines are monitored for the H$^{ }$or $^{3}$He minority heating scenarios, respectively. The $^{3}$He measurements have developed more quickly than H measurement due to improved S/N (ambient D emission interferes with H line). Initial results from energetic ion detection, minority ion density, temperature, and velocity profiles will be reported for D($^{3}$He) discharges. Diagnostic design for H minority measurements will also be presented. [Preview Abstract] |
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UP9.00029: Simulation study of toroidal flow generation by ICRF minority heating in Alcator C-Mod plasma S. Murakami, K. Itoh, L.J. Zheng, J.W. Van Dam, P. Bonoli, J.E. Rice, C.L. Fiore, A. Fukuyama The toroidal flow generation by the ICRF minority heating is investigated in the Alcator C-Mod plasma applying GNET code [1], in which the drift kinetic equation is solved in 5D phase-space. We obtain a steady state distribution of energetic minority ions and the flux surface averaged toroidal flow is evaluated. It is found that a co-directional toroidal flow is generated outside of the RF wave power absorption region and that the dominant part of toroidal flow does not depend on the sign of $k_{\parallel}$. The averaged toroidal flow velocity reaches about 30\% of central ion thermal velocity ($P_{ICRF} \sim 1.7$MW)[2]. When we change the sign of the toroidal current we obtain a reversal of the toroidal flow velocity, which is consistent with the experimental observations. We show that the toroidal precession motion of energetic tail ions accelerated by the ICRF heating plays an important role in generating the averaged troidal flow. We also compare with the experimental results about the RF resonance location and plasma parameter dependencies [3].\\[0pt] [1] S. Murakami, {\it et al.}, Nucl. Fusion {\bf 46}, S425 (2006). [2] S. Murakami, {\it et al.}, Proc. 23rd IAEAFusion Energy Conference, {\bf THW/P4-03} (2010). [3] J.E. Rice, {\it et al.}, Nucl. Fusion {\bf 42}, 510 (2002). [Preview Abstract] |
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UP9.00030: Magnetic field-aligned ICRF antenna to minimize RF sheaths* M.L. Garrett, S.J. Wukitch, P. Koert, D.G. Whyte One of the primary challenges of ICRF heating is the minimization of impurities associated with ICRF operation. A new magnetic field-aligned antenna was optimized for magnetic flux coupling, power handling, and minimized integrated E-parallel. Initial simulations performed using both slab and cylindrical geometry suggested nearly complete cancellation of E-parallel. Using 3-D toroidal models, the cancellation of E-parallel is more modest, suggesting 3-D geometrical effects are important. Using FEM with a 3-D toroidal cold plasma model, four antenna phases were analyzed for the field-aligned antenna: [0,$\pi $,0,$\pi $], [0,0,$\pi $,$\pi $], [0,$\pi $,$\pi $,0], [0,0,0,0]. In each case, the field-aligned antenna had reduced integrated E-parallel relative to the existing non-aligned antenna geometry, with the greatest reduction for monopole [0,0,0,0] phasing. The new field-aligned ICRF antenna has been installed on Alcator C-mod. Results will be presented characterizing operational sensitivity to both field line pitch and toroidal phasing. EM analysis will be compared with current and voltage data from eight pairs of I-V probes installed in the antenna box. *Supported by USDoE award DE-FC02-99ER54512 [Preview Abstract] |
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UP9.00031: Rotated 4-strap ICRF antenna: design and initial results S.J. Wukitch, W. Beck, J. Doody, M. Garret, P. Koert, Y. Lin, R. Vieira, J. Terry Previously, we have utilized low Z thin films to mitigate impurities related to ion cyclotron range of frequency (ICRF) antenna operation. A new rotated antenna is has been designed and installed to minimize impurity production by imposing symmetry along the total magnetic field line. The antenna is aligned to a 10\r{ } field pitch where the typical discharge range is 7-13\r{ } in C-Mod. Compared to our standard antennas (0\r{ } pitch), the power density (MW/m$^{2})$ for the rotated antenna is $\sim $50{\%} higher for a given injected power for the rotated antenna due a decrease in available surface area. Due to geometric limitations, two locations have the RF electric field aligned with the total magnetic field and have potential to limit the antenna voltage handling. Initial results from experiments characterizing the power and voltage limits of the antenna will be presented. Using the standard antennas as reference, we will also present results from comparison of antenna impurity characteristics and their impact on the scrape off layer transport. [Preview Abstract] |
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UP9.00032: I-mode Plasmas with Combined ICRF Mode Conversion Flow Drive and Minority Heating on Alcator C-Mod Y. Lin, M.L. Reinke, J.E. Rice, S.J. Wukitch, R. Granetz, M. Greenwald, A.E. Hubbard, E.S. Marmar, Y.A. Podpaly, M. Porkolab, N. Tsujii, S. Wolfe High performance I-mode plasmas have been obtained via ICRF mode conversion heating and flow drive, plus ICRF minority heating. The plasmas have reversed magnetic field (B$_{t0}\sim $5.1 T) and lower-single-null shape. External $^{3}$He is puffed to have n$_{He3}$/n$_{e}\sim $0.1 and the residual H level n$_{H}$/n$_{e}$ is about 0.05. We use 50 MHz RF power ($\le $2.5 MW) for D($^{3}$He) mode conversion flow drive and heating, and 80 MHz RF power ($\le $2.5 MW) for D(H) minority heating. The obtained I-mode plasmas have high T$_{e}$ ($\le $8 keV) and large rotation ($\le $100 km/s). The rotation profile has a large shear at r/a $\sim $ 0.9, which may help further enhance the plasma confinement. Because of the long slowdown time at high T$_{e}$ and relatively low density, a high energy H tail is generated. The tail also affects the sawtooth oscillation and produces large sawtooth crashes, which also trigger neoclassical tearing modes. The appearance of the NTMs often coincides with a slowdown of plasma rotation. The onset condition of these NTMs is at the low collisionality regime within the criterion established by studies on other tokamaks. [Preview Abstract] |
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UP9.00033: Progress in modeling and experiment to approach AT regime on Alcator C-Mod S. Shiraiwa, P.T. Bonoli, I. Faust, O. Meneghini, A. Hubbard, R.R. Parker, G.M. Wallace, J.R. Wilson Key issues in approaching an advanced tokamak (AT) regime where the majority of plasma current is sustained by bootstrap (BS) current on Alcator C-Mod are to improve confinement via current profile modification and to drive the rest of current at high density using LHCD. As for the first issue, fully non-inductive operation has been demonstrated at a current of $\sim0.5$ MA and at a density close to what is expected on ITER steady state operations. MSE pitch angle measurement showed that these plasmas had a flat or weak reversed shear profile, and TRANSP modeling of the current profile evolution is in good agreement with experiment. Some of these discharges exhibited the formation of an ITB on the electron temperature profile. This barrier formation was always observed about 200-300ms (longer than a current penetration time) after the turn-on of LHCD, suggesting an improved confinement mode due to shear reversal. As for driving current at high density with a high BS fraction, modeling suggests that a key is to maintain good single pass power absorption. [Preview Abstract] |
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UP9.00034: Effects of ICRF and/or LHCD on SOL density profiles and fluctuations in Alcator C-Mod Cornwall Lau, Greg Hanson, Yijun Lin, Steve Wukitch, Ian Faust, Jerry Hughes, Brian Labombard, Yunxing Ma, Orso Meneghini, Ron Parker, Syun'ichi Shiraiwa, Jim Terry, Greg Wallace, John Wilgen Antenna operation and antenna-plasma interactions during RF heating and current drive are greatly influenced by the scrape-off-layer (SOL) densities. A swept-frequency X-mode reflectometer installed on Alcator C-Mod measures the SOL density profiles and fluctuations at three poloidal locations adjacent to the Lower Hybrid (LH) launcher. The application of LH power consistently decreases the density in front of the LH launcher, consistent with a ponderomotive force; the application of ICRF power also decreases the density in front of the LH launcher, which may be consistent with ICRF sheath induced convective cells. LH power also seems to strongly modify the density profile shape in the near and far SOL, especially at high line averaged densities. The reflectometer measured density profiles and preliminary results on phase fluctuation behavior will be presented and compared with measurements from other diagnostics, such as Thomson scattering and gas puff imaging diagnostic. This work is supported by U.S. DoE under awards DE-AC05-00OR22725 and DE-FC02-99ER54512. [Preview Abstract] |
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UP9.00035: The detection of lower hybrid (LH) waves using reflectometry in Alcator C-Mod S.G. Baek, R.R. Parker, S. Shiraiwa, G. Wallace, A. Dominguez, P.T. Bonoli, E.S. Marmar, G.J. Kramer The development of a scattering diagnostic using an O-mode reflectometer system at 60 and 75 GHz to study LH waves in the scrape off layer of Alcator C-Mod is presented. The direct measurement of LH wave fields can help us to better understand their propagation and absorption of LH waves, especially in high density plasma where the penetration is limited. To assess the use of the scattering interaction as a diagnostic tool, coupling coefficients in a 1D plasma model are calculated. Based on this model, the high frequency stage of both O-mode reflectometry channels have been modified and new power detection stages have been added. The width and the amplitude of the scattered waves can be extracted from these measurements. The initial measurement of scattered signals suggests that the ray paths of lower hybrid waves may be different from the ray paths predicted by the ray tracing code, GENRAY. The possible role of scattering of lower hybrid waves from low frequency density fluctuations in modifying the ray paths is studied using GENRAY/CQL3D. [Preview Abstract] |
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UP9.00036: Lower Hybrid Wave Neutral Excitation, Ionization and SOL Power Loss of the Alcator C-Mod Tokamak I. Faust, J.L. Terry, M.L. Reinke, O. Menegini, R.R. Parker, S. Shiraiwa, G.M. Wallace, J.R. Wilson High density (n$_e>10^{20} $ m$^{-3}$), moderate T$_e$, diverted Lower Hybrid Current Drive (LHCD) discharges on Alcator C-Mod exhibit little or no current drive, as indicated by low levels of hard X-ray emission. High temperature (T$_e$=4 keV), high- field (B$_t$=8 T) helium plasmas have shown decreased SOL modification and increased X-ray emission from the core plasma. Previous work has shown LH induced changes to the scrape-off-layer (SOL), suggesting SOL-localized LH power deposition occurs, possibly through collisional absorption. However, electron-ion collisional absorption was found to be weak in full-wave simulations. In order to characterize collisional absorption as a loss mechanism, initial experiments were conducted to measure emission from neutrals in LHCD discharges. Results are presented on the modification of the SOL as measured using radially-resolved VUV and visible emission from regions in which field lines are connected or unconnected to the LH launching structure. Implications of the presented data will be discussed with respect to the LHCD density limit. [Preview Abstract] |
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UP9.00037: Lower hybrid current drive in a high density diverted tokamak G.M. Wallace, I.C. Faust, A.E. Hubbard, O. Meneghini, R.R. Parker, S. Shiraiwa, P.T. Bonoli, B.L. LaBombard, B. Lipschultz, C. Lau, J.L. Terry, D.G. Whyte, J.C. Wright, S.J. Wukitch, A.E. Schmidt, J.R. Wilson, R.W. Harvey, A.P. Smirnov LHCD is the primary non-inductive current drive mechanism on Alcator C-Mod, a compact tokamak with parameters (plasma density, $B_\phi$, magnetic topology, and LH wave frequency) similar to ITER. Efficient current drive has been demonstrated on C-Mod at moderate densities ($\bar{n}_e \sim 0.5 \times 10^{20}$~m$^{-3}$). However, as density increases fast electron bremsstrahlung and non-thermal ECE, which are used as proxies for fast electrons generated by LHCD, drop faster than expected based on data from limited tokamaks. The steep decline of fast electron emission at high density is attributed to collisional damping of the LH waves in the SOL combined with weak Landau damping of the LH waves inside the confined plasma. Experiments have identified several methods to mitigate the impact of parasitic absorption in the SOL. Higher non-thermal emission is observed in discharges with elevated off-axis $T_e$ as well as in limited discharges. Ray tracing/Fokker-Planck simulations of these discharges predict the observed dependencies when the effects of collisional absorption in the SOL are included in the model. Supported by USDoE awards DE-FC02-99ER54512 and DE-AC02-09CH11466. [Preview Abstract] |
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UP9.00038: Off-Axis neutral beam current drive on DIII-D C.C. Petty, J.R. Ferron, P.A. Politzer, R. Prater, M.A. Van Zeeland, J.M. Park, M. Murakami, W.W. Heidbrink, C.M. Muscatello, C.T. Holcomb, B.A. Grierson Experiments on the DIII-D tokamak have studied neutral beam current drive (NBCD) during off-axis deposition in greater detail than previously possible. Full radial profiles of the beam ion density and driven current density have been obtained for beams steered 16.5 deg downwards. Novel experiments compare the NBCD profile for on-axis and off-axis injection by modulating between these choices at 5 Hz. The sinusoidal response of the motional Stark effect (MSE) signals can be either compared to numerical simulations or utilized to directly determine the NBCD profile. More standard studies compare the change in the non-inductive current profile, determined from the poloidal flux evolution, for steady (un-modulated) on-axis and off-axis beam injection. The NBCD profiles are crosschecked with the beam ion density profiles measured by Fast Ion D-alpha (FIDA) spectroscopy. The effect of transport from microturbulence on the NBCD profile is also investigated. [Preview Abstract] |
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UP9.00039: Off-axis Neutral Beam Injection as a Tool for Expanding the Operating Space of DIII-D High $f_{NI}$ Discharges J.R. Ferron, T.C. Luce, P.A. Politzer, J.C. DeBoo, R.J. La Haye, C.T. Holcomb, M.J. Lanctot, F. Turco, J.M. Park, Y. In, M. Okabayashi The newly installed capability for 5~MW off-axis neutral beam injection is being utilized to broaden the pressure and current density profiles and raise the minimum $q$ value in DIII-D discharges with noninductive current fraction $f_{NI}$ near 1. Broader pressure is expected to allow stable access to increased $\beta_N$ and increase the bootstrap current density $J_{BS}$ off-axis. Reducing the on-axis current drive allows access to higher $q_{min}$, increasing the on-axis $J_{BS}$ and improving tearing mode stability. This is a path toward DIII-D (and a steady-state powerplant) $f_{NI}=1$ discharges at $q_{95} = 5$, which require $\beta_N \geq 4$. Initial experiments have demonstrated $q_{min}$ maintained above 2 with broader pressure profiles than previously observed. Analysis of the noninductive current profiles and high $\beta_N$ stability of discharges with off-axis beam injection will be presented [Preview Abstract] |
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UP9.00040: Scaling of Energy Confinement with Rotation for Advanced Inductive Plasmas in DIII-D P.A. Politzer We report the scaling of the energy confinement time in moderately high beta ($2.2\leq\beta_N\leq3.3$) advanced inductive plasmas in DIII-D, based on an analysis of a database of 630 discharges that have stationary conditions for $\geq 1$ s ($\sim\tau_R$). In dedicated experiments it was found that $\tau_E$ decreases by $\sim$40\% from the highest to the lowest accessible rotation, prompting this study. Both power-law and offset-linear models are fit to the data, with the rotation represented by either $M_A$ or $M_S$, the Mach number based on the Alfv\'en or the sound speed. A power-law ($\tau = C\, B^{a_B}\, n^{a_n}...\, M^{a_M}$) is the most commonly used model, but there are strong physical arguments for a model that does not yield zero confinement for zero rotation, e.g., offset-linear ($\tau = C_a\, B^{a_B}\, n^{a_n}...+C_b\, B^{b_B}\, n^{b_n}...\, M$). As there are values in the dataset that fall outside the general trend, the fitting is done by minimizing the mean absolute deviation, a method more robust than the common $\chi^2$ minimization. There is no significant statistical difference between fits using $M_A$ or $M_S$. Also no significant difference is found between the power-law and offset-linear models. [Preview Abstract] |
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UP9.00041: Access conditions for advanced inductive scenarios G.L. Jackson, T.C. Luce, P.A. Politzer, E. Joffrin Employing advanced inductive (AI) regimes in ITER requires knowledge of suitable startup trajectories to achieve stationary AI performance. As part of the International Tokamak Physics Activity (ITPA), a database of DIII-D discharges has been assembled to quantify access conditions for stable AI discharges. The ITPA goals are (1) to assemble a database of a jointly defined set of variables from several tokamaks and (2) perform similarity experiments based on analysis of that database to demonstrate AI access conditions for ITER. The DIII-D AI database now contains 77 variables from 1294 discharges. The most important parameter to predict access to stable DIII-D AI discharges is the level of auxiliary heating in the ramp-up phase, but there is little correlation with internal inductance ($\ell_i$). While the current profile is important, $\ell_i$ is not sufficiently sensitive to show the correlation in the presence of a current ramp. A complementary database has been assembled for JET AI discharges. Similarities and differences in the two machines will be reported as well as plans to merge the two databases. [Preview Abstract] |
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UP9.00042: ITER demonstration discharges in DIII-D with dominant electron heating T.C. Luce, G.L. Jackson, J.R. Ferron, R.J. La Haye, P.A. Politzer, E.J. Doyle, J.M. Park DIII-D has investigated experimentally the ITER baseline H-mode scenario with a series of scaled demonstration discharges using the ITER shape and matching key dimensionless fusion performance parameters such as normalized beta, confinement factor and collisionality [1]. This work was recently extended to discharges with dominant electron heating, as ITER will have. In DIII-D, six gyrotrons inject up to 3.5 MW of heating power, allowing access to these ITER baseline scenario discharges with only small additions of neutral beam power. For neutral beam (NB) heated discharges it was found that the current profile is critical in obtaining reproducible discharges without tearing modes [2] and we will discuss the parameter range for EC discharges. Plans to extend this investigation by further lowering the net NB torque will also be presented. \vskip6pt \noindent [1] E.J. Doyle, et al., Nucl. Fusion {\bf 50} (2010) 075005. \par\noindent [2] F. Turco and T.C. Luce, Nucl. Fusion {\bf 50} (2010) 095010. [Preview Abstract] |
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UP9.00043: Pellet ELM Pacing Developments on DIII-D L.R. Baylor, T.C. Jernigan, N. Commaux, S.J. Meitner, S.K. Combs, T.H. Osborne, P.B. Parks, E.J. Strait, M.E. Fenstermacher, C.J. Lasnier, R.A. Moyer, J.H. Yu D$_2$ pellets injected into DIII-D H-mode plasmas from the low field side have been shown to increase the ELM frequency above the pellet frequency and reduce their size. The pellet injector on DIII-D is being modified to increase the pellet repetition rate for ELM pacing from 14 to $>$30~Hz and reduce the pellet size from 1.8 to 1.3~mm. An injection line has been added to inject pellets from the low field side near the divertor to test the proposed injection geometry on ITER. Experiments will inject the smaller pellets from three different low field side locations and from the inner wall to compare the physics of the pellet ELM triggering. Fast cameras will provide images of the pellet events to compare the ELM triggering process at all the low field side injection points. Results from the higher repetition rate ELM pacing experiments and implications for controlled ELM triggering on ITER will be discussed. [Preview Abstract] |
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UP9.00044: Study of the Heat Flux Induced by Pellet Triggered ELMs on the Divertor During Pacing Experiments on \mbox{DIII-D} N. Commaux, L.R. Baylor, T.C. Jernigan, T.H. Osborne, P.B. Parks, M.E. Fenstermacher, C.J. Lasnier, R.A. Moyer, J.H. Yu The purpose of the pellet ELM pacing on ITER is to reduce significantly the heat flux on the divertor thus increasing its lifespan. D$_2$ pellets injected into \mbox{DIII-D} H-mode ITER-like plasmas at 14~Hz have been shown to decrease the maximum heat flux on the divertor during each individual ELM. The relation between the pellet injection frequency, the ELM frequency and the heat load, which is critical to scale this technique to ITER, is studied in detail. The evolution of the heat footprint on the plasma facing components will be compared to a natural ELM case using fast framing IR camera data. One of the possible challenges of the pellet pacing technique is the possible toroidal asymmetries of the wall interaction of the first filament triggered by a pellet injection. This issue will be evaluated using vacuum field line tracing calculation and visible fast framing camera data. The implications of this study on the efficiency of pellet ELM pacing on ITER will be discussed. [Preview Abstract] |
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UP9.00045: Physics Modeling of ARIES-AT H.E. St. John, A.D. Turnbull, M. Choi, S.P. Smith, R.J. Buttery, L.L. Lao, P.B. Snyder We describe the theoretical modeling of predicted steady state ARIES advanced tokamak discharges from the perspective of MHD, energy transport, rf current drive, and core/edge stability simulations. The modeling requires the interaction of codes from each of these categories and a significant challenge has been the creation of a framework that minimizes the expert knowledge and tedium involved in performing the necessary calculations. Our solution to this problem was the creation of a state file driven integrated modeling framework, IMFIT, that contains, in part, the required expert system and generates the necessary state, file driven interfaces. The general techniques developed are applied to indicate what the performance limits of steady state ARIES discharges are expected to be with turbulent transport, lower hybrid current drive, and edge pedestal stability limits enforced. [Preview Abstract] |
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UP9.00046: Effect of hydrogen minority on the power balance for fast wave heating in DIII-D R. Prater, R.I. Pinsker, M. Choi, R.W. Harvey, Yu. Petrov, M. Porkolab Experiments on L-mode discharges in DIII-D using high harmonic fast waves to heat the beam ions have shown moderately high heating efficiency at the 4th harmonic of deuterium (60 MHz) but much poorer efficiency at the 8th harmonic (116 MHz) [1]. Linear theory [1] suggests that the difference in absorption should be much smaller, but calculations with ORBIT-RF show little heating at 116 MHz [2]. An alternative suggestion for where the fast wave power goes in the 116 MHz case is to a small hydrogen minority which might develop a strong energetic tail [3] without affecting the neutron rate. The Fokker-Planck code CQL3D has recently been augmented by CompX to support the calculation of the distribution functions of two ion species simultaneously. This model will be applied to explore the effects of a range of hydrogen concentrations for comparison to the experiment. \vskip6pt \noindent [1] R.I. Pinsker, et al., Nucl. Fusion {\bf 46}, S416 (2006). \par\noindent [2] M. Choi, et al., Nucl. Fusion {\bf 46}, S409 (2006). \par\noindent [3] E.F. Jaeger, private communication. [Preview Abstract] |
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UP9.00047: Modeling of Simultaneous Interaction of Fast Ions with Multiple Fast Waves (FWs) in Tokamaks M. Choi, R.I. Pinsker, V.S. Chan, C.M. Muscatello In recent moderate to high harmonic FW heating and current drive experiments in DIII-D, a synergy effect was observed when the 6th harmonic 90 MHz FW is applied to the plasma being heated by neutral beams and the 4th harmonic 60 MHz FW. Measured neutron rate and stored plasma energy from the two combined FWs were much stronger than the sum of those from separate 4th and 6th harmonic FWs. Theoretically, this can occur at the presence of a large population of fast ions satisfying $k_\perp\,\rho\geq 1$ ($k_\perp$ is the perpendicular wave number, and $\rho$ is the fast ion Larmor radius). Preliminary investigation using a 5-D finite-orbit Monte-Carlo code ORBIT-RF coupled with 2-D full wave code AORSA suggests that preheating beam ions with the 60 MHz FW produces a large fast ion population above beam injection energy, which may allow significant damping of 90 MHz FW on beams tails. For quantitative comparison of theory with experiments, ORBIT-RF is upgraded to model simultaneous interaction of fast ions with multiple FWs. Computed synthetic FIDA signals and neutron reaction rates will be compared with measured quantities. [Preview Abstract] |
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UP9.00048: Upgrade Plans and Performance of the DIII-D ECH System J. Lohr, M. Cengher, Y.A. Gorelov, H.J. Grunloh, A.G. Kellman, C.J. Pawley, W. McDaniel, R.C. O'Neill, D. Ponce, R. Prater, J.F. Tooker, R.A. Ellis, M. Blanck, P. Borchard, K. Felch, S. Cauffman An upgrade is in progress on the DIII-D gyrotron complex, to increase the number of gyrotrons from 6 to 8 and raise the injected rf power from 3.5 to 5.5~MW. The 1st step in this upgrade is the production of a depressed collector diode gyrotron planned for initial operation in early 2012 operating at 110~GHz and generating 1.2~MW, the same frequency as the existing gyrotrons. The 8th gyrotron for the complex is planned for completion in 2013. This gyrotron will operate at 117.5~GHz and generate 1.5~MW for a pulse length of 10~s. The upgrade includes a 4th dual launcher and new high voltage power supply. The present installation has been upgraded by rerouting the waveguide transmission lines to reduce the number of miter bends, increasing the scanning speed and pointing accuracy of the articulating launcher mirrors and providing for aiming scans, with feedback, during a plasma shot. [Preview Abstract] |
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UP9.00049: ECH Launchers on DIII-D Y.A. Gorelov, J. Lohr, M. Cengher, D. Ponce, R.A. Ellis Three fully articulating dual launchers, which can steer the rf beams poloidally and toroidally through $\pm$20$^\circ$ in each direction, are installed on DIII-D. All are designed and built by PPPL. Each launcher has a fixed focusing mirror followed by a flat steering mirror. Two of the six focusing mirrors were damaged during the past 2 experimental campaigns on DIII-D. The focusing mirrors were made from stainless steel (SS) with a thin layer of copper (Cu) on the surface. Thermal calculation predicts that these mirrors should withstand pulse lengths up to 10~s with incident rf power of 850~kW from the existing gyrotrons. In 2008 local stress cracking of the Cu surface was found on some focusing mirrors. In some cases, the Cu was melted exposing the SS to the rf beam. Rapid thermal runaway and extensive melting resulted. All focusing mirrors were replaced with ones made from solid Al-15 Glidcop construction in 2011. The new design of steerable mirrors was also installed on all launchers. The steering mirrors are moved by dc electric motors, providing full poloidal scans in $\approx$2~s and improved positioning accuracy compared with the air motors previously installed. [Preview Abstract] |
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UP9.00050: Performance Measurements for the ECH Transmission Lines on DIII-D M. Cengher, J. Lohr, Y.A. Gorelov, D. Ponce, C.P. Moeller The power measurements in the waveguide transmission lines of the ECH system in DIII-D for the six 110~GHz gyrotrons showed higher transmission coefficient after eliminating 14~miter bends, rerouting the lines, and improving the angular alignment of the rf beam at the waveguide input. The transmission in the waveguide lines increased by between 2\% and 7\% per line, translating into more than 120~kW power gain when the gyrotrons are tuned up for high power. The linearity of the power injected in the tokamak with the gyrotron cavity loading was verified for all 6 systems. After the realignment of the rf beam at the waveguide input, the measured HE$_{11}$ mode content was between 85\% and 94\%, contributing to the increase in the transmission coefficient. A higher HE$_{11}$ mode content is expected to improve transmission in future conversion miter bends. A 4-port rf monitor was used with a directional coupler to measure the HE$_{11}$, HE$_{21}$, and TE$_{01}$ mode amplitudes. The 4-port monitor and dummy load measurements for one gyrotron show that a maximum in the HE$_{11}$ mode corresponds to the best angular alignment. [Preview Abstract] |
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UP9.00051: Progress in GYRO Validation Studies of DIII-D \mbox{H-mode} Plasmas C. Holland, K.H. Burrell, C.C. Petty, J. Candy, C.T. Holcomb The need for a validated predictive capability of turbulent transport in ITER is now widely recognized. However, to date most validation studies of nonlinear codes such as GYRO have focused upon low power L-mode discharges, which have significant differences in key dimensionless parameters such as $\beta$ and $\rho^* = \rho_s/a$ from more ITER-relevant H-mode discharges. In order to address this gap, the results of nonlinear GYRO simulations of a range of DIII-D H-mode discharges (including quiescent H-mode, hybrid, and steady state discharges) are presented. These H-mode studies focus upon three physics effects, motivated by key differences between L- and H-mode plasmas. The first is the linear and nonlinear effects of finite $\beta$ in plasmas where $\beta_N = \beta/(I/aB)$ varies from 1.5-2.5, 3-5 times higher than typical L-mode values. Second is the impact of nonlocality at typical DIII-D H-mode $\rho^*$ values, which in contrast to typical L-modes can be non-negligible. Third is the stabilizing effect of a significant density of energetic particles. [Preview Abstract] |
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UP9.00052: Electron Profile Stiffness and Critical Gradient Studies in an L-mode Discharge in DIII-D J.C. DeBoo, K.H. Burrell, C.C. Petty, S.P. Smith, A.E. White, C. Holland, E.J. Doyle, J.C. Hillesheim, T.L. Rhodes, L. Schmitz, G. Wang, L. Zeng, G.R. McKee Several heat flux scans have been performed in an L-mode discharge in DIII-D with the goal of investigating the stiffness and critical gradient in the electron channel at $\rho=0.6$, 0.4 and 0.3. The heat flux scans employed 6 gyrotrons operating for 3.5~s with a shot-by-shot variation in heat flux achieved by moving 1 gyrotron/shot from just outside to just inside the region of interest. The stiffness was studied as a function of 4 different toroidal rotation conditions, low rotation with ECH only, higher rotation with co-NBI and counter-NBI, and lower rotation with balanced-NBI. Preliminary results indicate that toroidal rotation does not appear to play a strong role in determining the stiffness of the electron profile. For the ECH only condition at $\rho=0.6$ very low values of temperature gradient were obtained, well below the critical gradient estimated by the gradient where the heat flux projects to zero. [Preview Abstract] |
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UP9.00053: The geodesic acoustic mode and zonal flows in DIII-D J.C. Hillesheim, W.A. Peebles, T.A. Carter, T.L. Rhodes, L. Schmitz Turbulence model validation experiments have generally shown more disagreement towards the edge, $r/a>0.75$, than in the core; this motivates more detailed comparisons of measured turbulence and zonal flow characteristics to models and simulations. Measurements have been made in DIII-D with two multichannel Doppler backscattering systems at toroidal locations separated by 180 deg. Observations show that the GAM in L mode DIII-D plasmas can occur as a radially coherent eigenmode, consistent with theory when finite $k\,\rho_i$ effects are included. The intermittency of the GAM has been quantified; its autocorrelation time is fairly short, ranging from $\sim 3$ to $\sim 15$ GAM periods in cases examined. Conditionally averaged bispectral analysis shows the strength of the nonlinear interaction of the GAM with broadband turbulence varies with the magnitude of the GAM. In otherwise similar discharges, the GAM's amplitude is significantly smaller with counter-injected neutral beams than with co-injection. Initial comparisons to simulations will be presented. [Preview Abstract] |
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UP9.00054: Dependence of Electron and Ion Transport on $T_e/T_i$ in Low Collisionality QH-mode Plasmas L. Schmitz, T.L. Rhodes, J.C. Hillesheim, W.A. Peebles, G. Wang, L. Zeng, C. Holland, K.H. Burrell, J.C. DeBoo, S.P. Smith, R. Prater, J.S. deGrassie, G.M. Staebler, G.R. McKee, W.M. Solomon Core electron/ion thermal transport and its dependence on ITG/TEM/ETG-scale turbulence are examined in high temperature, strongly rotating QH-mode plasmas, at ITER-relevant collisionality ($\nu_e^* \sim 0.05$). To simulate central electron heating by $\alpha$-particles, ECH has been used to achieve $0.6 \leq T_e/T_i \leq 1.1$. ITG/TEM-scale density fluctuations remain virtually unchanged, while electron temperature fluctuations, and gyroBohm-normalized electron and ion diffusivities increase with $T_e/T_i$. Linear stability calculations support a transition to a TEM-dominated regime due to increased $T_e/T_i$ and a reduced ion temperature gradient $R/L_{Ti}$ with ECH. Initial GYRO nonlinear calculations will be shown. At reduced toroidal rotation, ITG-dominated QH-mode plasmas [$T_e(0)/T_i(0)\sim 0.6$] exhibit 20\% increased global energy confinement time and $\beta_N$, [Preview Abstract] |
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UP9.00055: Particle transport measurements on DIII-D using perturbative techniques E.J. Doyle, L. Zeng, T.L. Rhodes, L. Schmitz, W.A. Peebles, T.E. Evans, S. Mordijck Perturbative particle transport measurements have been initiated on DIII-D and data obtained under a wide variety of operating conditions, including: L-mode, ELMing and ELM-free H-mode, QH-mode, and L- and H-mode plasmas with resonant magnetic perturbations (RMPs). Particle diffusivities (D) and pinch velocities (V) are determined from high resolution profile reflectometry data using perturbative techniques (e.g. modulated gas puffing), employing a simple analytic model [1]. Results show a considerable variation in D and V with operating regime, e.g. D is in general higher in L-mode than in H-mode, while V is more negative (inward) in H-mode than L-mode. Using these techniques we have obtained the first direct measurements to confirm that D increases and the magnitude of V is reduced but still inward during $n=3$ RMP application, in both L- and H-mode plasmas. \vskip6pt \noindent [1] H. Takenaga, et al., Plasma Phys. Control Fusion {\bf 40}, 183 (1998). [Preview Abstract] |
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UP9.00056: Neoclassical Theory for Toroidal and Poloidal Rotation C. Bae, W.M. Stacey, W.M. Solomon Rotation of tokamak plasmas is of intrinsic interest and also important for stabilization of MHD modes. Neoclassical rotation theory and gyroviscosity both depend on the poloidal dependence of the magnetic flux surface geometry. The circular [$R = R_\theta (1+\epsilon cos\theta)$, $B = B_\theta cos\theta$] flux surface formulation [1] was found to overpredict toroidal rotation velocities in DIII-D by a factor of about 2. We now represent neoclassical plasma rotation theory in the more accurate ``Miller equilibrium" flux surface geometry [2] for comparison with a pair of co- and ctr-injection DIII-D discharges. The Miller model takes into account Shafranov shift, elongation, and triangularity. Development of the neoclassical plasma rotation theory for either the circular or Miller equilibrium models is complete. Comparison of the new neoclassical calculation with experiment for the circular model shows the same factor of 2 over-prediction of the toroidal velocities found for previous shots [1]. Calculations based on the Miller equilibrium are in progress.\par \vskip6pt \noindent [1] H.~Matsuura and Y.~Nakao, Phys.\ Plasmas {\bf 13}, 062508 (2006).\par \noindent [2] R.L.\ Miller et al., Phys.\ Plasmas {\bf 5}, 973 (1998). [Preview Abstract] |
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UP9.00057: Modeling of Toroidal Rotation in Low Torque DIII-D Discharges with TGLF+NEO G.M. Staebler, J.E. Kinsey, R.E. Waltz, E.A. Belli Momentum transport due to gyrokinetic turbulence is now included in the Trapped Gyro-Landau Fluid (TGLF) quasi-linear transport model. The TGLF model includes the following causes of momentum transport: Parallel velocity shear, parallel velocity, $E\times B$ Doppler shift shear, up/down asymmetry of flux surfaces, and diamagnetic velocity shear. For discharges with significant unbalanced neutral beam torque the diamagnetic level flows can be neglected compared to the $E\times B$ toroidal velocity. The predicted toroidal rotation in these cases agrees well with data for the limited survey completed so far. For low-torque balance NBI injection cases, the $E\times B$ velocity is of the same size as the diamagnetic velocity. Even for zero external torque, there can be a toroidal rotation generated by the Reynolds stresses due to all of the contributions other than the parallel velocity shear. Results for a low-torque DIII-D discharge will be presented using TGLF combined with neoclassical transport and poloidal flows computed using the high-accuracy NEO code. Density, temperature, and rotation are predicted. [Preview Abstract] |
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UP9.00058: Documentation and Search for Missing Near Edge \mbox{L-mode} Transport R.E. Waltz, C. Holland While GYRO simulations of the core ($0 < r/a < 0.7$) in typical DIII-D L-modes seems to be in good agreement with experiment, local GYRO simulated low-$k$ ($k_\theta\rho_s<1$) transport and turbulence intensity is about 5-fold lower than experimentally inferred levels in the near edge L-mode ($r/a=0.7-0.95$) DIII-D shot 128913 [1]. Global slice GYRO simulations of this and other well-studied discharges [2] are presented here to further document the shortfall. TGLF transport simulations over a large L-mode database indicate this short fall is not atypical and L-modes easily transit to H-like profiles. High edge e-i collisionality stabilizes the TEM modes so that $\chi_\epsilon$ decreases like T$^{7/2}/n$ to the cold edge. The very high magnetic shear stabilizes the ITG despite the very high temperature gradient drive and high $q$. High-$k$ ETG can make up for the shortfall in the electron but not the ion channel. Near edge L-mode transport is highly local. Artificially large edge damping of the zonal flows/GAMs helps only somewhat.\par \vskip6pt \noindent [1] C.~Holland, A.E.\ White, et~al., Phys.\ Plasmas {\bf 16}, 052301 (2009).\par \noindent [2] R.E.~Waltz, et al., Phys.\ Plasmas {\bf 13}, 072304 (2006). [Preview Abstract] |
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UP9.00059: Coherent Beam-Ion Losses During Instabilities in \mbox{DIII-D} X. Chen, W.W. Heidbrink, R.K. Fisher, M.A. Van Zeeland, D.C. Pace, M. Garcia-Munoz A scintillator-based fast-ion loss detector (FILD) was installed on DIII D in 2010 [1] and successfully measured coherent losses produced by fast-ion driven instabilities. Loss signals at mode frequencies were observed for off-axis fishbones [2], toroidal Alfv\'en eigenmodes (TAEs) [3], reversed-shear AEs (RSAEs) [3], and energetic-particle driven geodesic acoustic modes. Modeling of the TAE and RSAE experiments indicate that the observed losses are predominately counter-passing ions that are scattered onto lost trapped-ion orbits by the AEs [4]. The original FILD detector is $\sim$45$^\circ$ below the midplane. For the 2011 campaign, a second FILD detector is installed at $\theta \approx 0^\circ$ and has already observed prompt losses. Observations of coherent losses from the pair of FILD detectors will be reported.\par \vskip6pt \noindent [1] R.K.~Fisher, et al., Rev.\ Sci.\ Instrum.\ {\bf 81} (2010) 10D307.\par \noindent [2] W.W.~Heidbrink, et al., Plasma Phys.\ Control.\ Fusion {\bf 53} (2011) 085028.\par \noindent [3] D.C.~Pace, et al., Plasma Phys.\ Control.\ Fusion {\bf 53} (2011) 062001.\par \noindent [4] M.A.~Van~Zeeland, et al., Phys.\ Plasmas {\bf 18} (2011) in press. [Preview Abstract] |
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UP9.00060: Measurements of Fast-Ion Transport by Resonant Interaction at a Sawtooth Crash C.M. Muscatello, W.W. Heidbrink Tokamak sawteeth consist of a reorganization of the plasma magnetic field and various plasma parameters. Observations indicate that distributions of superthermal ions can also be affected at the crash event. The bulk of energetic ions experiencing redistribution have passing orbits and low to moderate energies ($\leq$100~keV) where transport due to flux-attachment is valid. Sawtooth experiments at DIII-D employing the fast-ion deuterium-alpha (FIDA) diagnostic suite indicate that even high-energy ions ($>$100~keV) can experience appreciable redistribution. The transport mechanism, in this case, is different; a class of trapped particles with near zero toroidal precession velocity and narrow orbit width can satisfy the nonlinear wave-particle resonance condition. Trapped within the magnetic well of the helical perturbation, the particle transforms to a ``superbanana" orbit through the resonant interaction. The effect manifests as a plateau in the trapped fast-ion profile at the resonance layer. [Preview Abstract] |
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UP9.00061: ABSTRACT WITHDRAWN |
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UP9.00062: Alfv\'en Eigenmodes in a DIII-D Discharge Simulated in GYRO E.M. Bass Alfv\'en eigenmodes (AEs) are excited by, and cause transport of, beam or fusion energetic particles (EPs). We examine a beam-heated, shear-reversed DIII-D discharge (142111) where toroidal Alfv\'en eigenmodes (TAEs) and reverse shear Alfv\'en eigenmodes (RSAEs) flattened the beam EP density profile. With the gyrokinetic code GYRO [1], we follow low-$n$ unstable TAEs and RSAEs in this discharge. TAEs and RSAEs are tracked (with GYRO's parallel eigenvalue solver) as the minimum safety factor $q_{min}$ evolves in time. RSAE frequency sweeping and RSAE-TAE mode-mode interaction (where the mode distinction is blurred) are observed. In this full gyrokinetic treatment, all eigenfunctions are perturbed from the canonical MHD form. Poloidal twisting [2] and on-surface peaking of poloidal harmonics (EPM-like) [3] are examples. The global transport ``footprint'' corresponds to regions of strong local drive for dominant modes, generally less so for subdominant modes.\par \vskip6pt \noindent [1] J.~Candy and R.E.~Waltz, Phys.\ Rev.\ Lett.\ {\bf 91}, 045001 (2003).\par \noindent [2] B.J.~Tobias et al., Phys.\ Rev.\ Lett.\ {\bf 106}, 075003 (2011).\par \noindent [3] E.M.~Bass and R.E.~Waltz, Phys.\ Plasmas {\bf 17}, 112319 (2010). [Preview Abstract] |
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UP9.00063: Improvements to the Motional Stark Effect Diagnostic on DIII-D M.J. Lanctot, C.T. Holcomb, S.L. Allen, M.E. Fenstermacher, J.D. King, J.R. Ferron, T.C. Luce Recent modifications to the motional Stark effect diagnostic on DIII D have improved detection of the Stark-split beam emission and reduced uncertainty in the inferred magnetic field line pitch angles. The core system's signal-to-noise ratio was increased and systematic errors reduced following the installation of redesigned monochrometers and by refining the in-vessel calibration procedure. Modeling of the neutral beam emission and MSE optics motivated the installation of narrowband optical filters for edge channels leading to reduced channel-to-channel offsets. The measurements are used to validate the modeling results, and constrain the edge magnetic field in equilibrium reconstructions of high confinement mode plasma scenarios. Modeling is used to assess the ability of the edge system to constrain the edge plasma current and the effect of mixed polarization states on the MSE pitch angles. Finally we investigate the specifications for future upgrades aimed at informing tearing mode stability studies. [Preview Abstract] |
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UP9.00064: Ion Temperature and Toroidal Velocity Fluctuation Measurements Using Two-Point Ultra-Fast CHarge Exchange Recombination Spectrometer (UF-CHERS) I.U. Uzun-Kaymak, R.J. Fonck, G.R. McKee, Z. Yan An upgraded version of the UF-CHERS high efficiency, high throughput, customized spectrometer, has been deployed at DIII-D to observe CVI charge exchange emission at 529 nm using an array of cooled avalanche photodiode detectors (APDs) with 1~$\mu$s time resolution. The new spectrometer achieves 80\% transmission efficiency at the wavelength of interest with 0.27~nm resolution. Accompanied with low noise preamplifiers APDs can achieve high-frequency response up to 400~kHz. Fast time scale ion-temperature fluctuation measurements are crucial to characterizing turbulence and potentially identifying the underlying instabilities driving low-k turbulence. Initial results will evaluate the diagnostic capabilities with observations of thermal fluctuations. Measurements of the collisionality dependence of turbulence and transport, obtained from an upcoming experiment, will be investigated in detail. [Preview Abstract] |
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UP9.00065: Applications of Collisional Radiative Modeling of Helium and Deuterium for Image Tomography Diagnostic of $T_e$, $N_e$, and $N_D$ in the DIII-D Tokamak J.M. Munoz Burgos, N.H. Brooks, M.E. Fenstermacher, W.H. Meyer, E.A. Unterberg, O. Schmitz, S.D. Loch, C.P. Balance We apply new atomic modeling techniques to helium and deuterium for diagnostics in the divertor and scrape-off layer regions. Analysis of tomographically inverted images is useful for validating detachment prediction models and power balances in the divertor. We apply tomographic image inversion from fast tangential cameras of helium and D$_\alpha$ emission at the divertor in order to obtain 2D profiles of $T_e$, $N_e$, and $N_D$ (neutral ion density profiles). The accuracy of the atomic models for He~I will be cross-checked against Thomson scattering measurements of $T_e$ and $N_e$. This work summarizes several current developments and applications of atomic modeling into diagnostic at the DIII-D tokamak. [Preview Abstract] |
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UP9.00066: Restoring Transmission of Irradiated Image Fiber Bundles C. Chrobak, R.A. Moyer, J.H. Yu, M.A. Van Zeeland Image fiber bundles are employed in fusion experiments and other high radiation environments where they are used to transmit an image from an unprotected objective lens to a radiation shielded camera. Due to their exposure to neutron and gamma radiation the transmission of these expensive image fiber bundles can rapidly degrade, especially at the shorter visible wavelengths, and require costly replacement. A cost-effective, non-destructive heat treatment process can recover the spectral transmission lost due to the radiation damage of the fiber bundle. The results and the apparatus used for the first successful restoration of the transmission of an image fiber bundle across its entire wavelength band will be presented. [Preview Abstract] |
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UP9.00067: Measurement of Neutral Hydrogen Density in a Helicon Plasma M.E. Galante, R.M. Magee, D.W. McCarren, E.E. Scime, N.H. Brooks, R.L. Boivin A new diagnostic system based on two-photon absorption laser-induced fluorescence (TALIF) has been developed to measure neutral hydrogen density in the edge of fusion plasmas. 205~nm photons from a frequency tripled dye laser are injected co-propagating into the plasma chamber where they excite the 1s-3D transition in neutral hydrogen. The 3D state then decays emitting light at 656~nm. The emission intensity is directly proportional to the ground state hydrogen density. With the tabulated atomic absorption rates for hydrogen and krypton, TALIF measurements of krypton gas provide an absolute calibration. Here we present the technical details and measured performance of the TALIF system (laser line width, pulse length, pulse energy, RMS stability) and TALIF measurements of room temperature krypton gas. The krypton measurements are compared to expectations and the measured line widths are analyzed in terms of Doppler and saturation broadening. We also present TALIF measurements of the radial profiles of the absolute neutral hydrogen and neutral temperature in a helicon plasma source as a function of source parameters. [Preview Abstract] |
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UP9.00068: A TALIF Diagnostic for the DIII-D Tokamak R.M. Magee, M.E. Galante, D.W. McCarren, E.E. Scime, R.L. Boivin, N.H. Brooks The density profile of hydrogenic neutrals in the edge of DIII-D plays an important role in the problems of momentum transport, pedestal formation, and plasma-wall interaction, but an accurate measurement has proven difficult. A two-photon absorption laser induced fluorescence (TALIF) diagnostic is under construction and is intended to provide temporally and spatially resolved neutral density measurements in the pedestal region. This three-level TALIF scheme offers the advantages of direct excitation of ground state atoms, emission in the visible portion of the spectrum, a high degree of spatial localization, and the potential for a Doppler-free measurement. The large background of D$_\alpha$ emission, the principal challenge of the measurement, can be overcome by the focusing of a high power (1~MW) UV laser. Calculations of the SNR show that densities of 10$^{15}$~m$^{-3}$ or lower can be measured with a spatial resolution of 0.3~mm. We present design details of the proposed laser system, calculations of the expected performance in DIII-D and in a helicon source plasma, and measurements of the HI profile in the helicon plasma. [Preview Abstract] |
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UP9.00069: Edge Resolution and Laser Upgrades for the Thomson Scattering System at DIII-D B.D. Bray, M. Watkins, C. Liu, T.M. Deterly, D.M. Ponce, D. Eldon The DIII-D Thomson scattering system has been significant upgraded over the last year. Four new 1~Joule/pulse, 50~Hz ND:YAG lasers have been installed. These new lasers significantly increase the measurement frequency, and are run in addition to the previous set of eight, 20~Hz lasers. Installation of the lasers required an expansion of the Thomson laser room and a replacement of the laser control system. Concurrently, twenty smaller fiber bundles were installed to image the plasma edge and ten new polychromators added to the system. These new fibers double the spatial resolution of the Thomson system and improve the ability of the system to measure the steep edge gradients. The results from the upgrade as well as planned upgrades for the upcoming run campaign will be presented. [Preview Abstract] |
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UP9.00070: Imaging and modeling DIII-D core turbulence by means of the Phase Contrast diagnostic A. Marinoni, J.C. Rost, M. Porkolab, J.R. Dorris, K.H. Burrell The Phase Contrast Imaging (PCI) diagnostic on the DIII-D tokamak has recently been modified to image density fluctuations near the plasma mid-radius. Although the PCI measures line integrals, an optical filter provides a certain degree of spatial localization thus restricting the measurements to the plasma core or edge. The DIII-D NBI system has also been recently upgraded by extending its vertical tilting, allowing new heating and rotating scenarios. The present work exploits these two upgrades and shows preliminary analysis of core-heated plasmas in various scenarios, evaluating the contributions to the signal from the core and the edge. Emphasis is placed on the analysis of transitions between different turbulent regimes, and how these compare to theoretical predictions. Time-space frequency spectra and correlation lengths are evaluated and compared to gyrokinetic modeling via a recently developed Synthetic Diagnostic tool that simulates micro-instabilities as seen by the PCI through line integrals. [Preview Abstract] |
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UP9.00071: Kinetic effects of energetic particles on a 2/1 resistive MHD instability in a DIII-D discharge D.P. Brennan, C.C. Kim, R.J. La Haye The kinetic effects energetic particles have on the stability of the m/n=2/1 tearing mode in a DIII-D discharge are investigated as a function of q$_{min}$, $\beta $, S=$\tau _{R}$/$\tau _{A}$ and $\beta _{frac}=\beta _{h}$/$\beta $ ($\beta _{h}$ is energetic particle $\beta )$.~ Using experimental equilibrium reconstructions as a basis we generate a series of equilibria varying q$_{min}$ and $\beta $. The non-ideal MHD stability of the n=1 mode is then calculated including the $\delta $f kinetic-MHD model in the 3-D extended MHD code NIMROD. The particle distribution models the slowing-down distribution from neutral beams in experiment. The interaction between the particles and the mode drives a real frequency and changes the linear stability. For the range of ideal unstable, resistive unstable and MHD stable modes, this drive is~analyzed in phase space with particle diagnostics. In the ideal unstable regime at low q$_{min}$, the particles damp the mode. However, it is observed that in the MHD-only stable regime, the interaction is strong near the axis, and can cause destabilization of the n=1 mode. These results are compared with experimental data, which includes low amplitude n=1 and 2 in a nonlinearly saturated state. [Preview Abstract] |
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UP9.00072: SOLAR, INTERPLANETARY, AND MAGNETOSPHERIC PLASMA PHYSICS |
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UP9.00073: The Effects of Kinetic Alfven and Whistler Wave Turbulence and the Evolution of Electron Distribution in Solar Wind Plasma Manish Mithaiwala, Leonid Rudakov, Gurudas Ganguli, Chris Crabtree The high beta solar wind plasma turbulence is dominated by the kinetic Alfven waves (KAW) [1]. Though the measured high-energy tail on the electron distribution function can be a signature of the presence of whistler waves (WW) as well [2]. In Maxwellian plasma both KAW and WW are Landau damped at high beta, and only for the specific case of WW with $k_\bot =0$ is there no Landau damping. Due to the inhomogeneous solar wind plasma these parallel propagating WW should quickly develop large perpendicular wavenumbers $\left\langle {k_\bot } \right\rangle >\left\langle {k_{\vert \vert } } \right\rangle $. However, as we have shown recently using measured KAW spectra, Landau damping establishes a plateau in the parallel electron distribution function and damping is strongly diminished [3]. The theory of WW in high beta inhomogeneous plasma will be presented and the impact of the electron cyclotron resonance with WW on the evolution of the electrons high energy tail will be discussed. Supported by ONR. \\[0pt] [1] O. Alexandrova\textit{ et. al.}, PRL (2009)~; F. Sahraoui \textit{et. al.}, PRL (2010). \\[0pt] [2] T. Nieves-Chinchilla and A. F. Vin\~{ }as, JGR (2008). \\[0pt] [3] L. Rudakov \textit{et. al.}, Phys. Plasma, \textbf{18}, 012307 (2011). [Preview Abstract] |
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UP9.00074: Quasilinear Evolution and Perpendicular Ion Heating in the Turbulent Solar Wind Leonid Rudakov, Chris Crabtree, Gurudas Ganguli, Manish Mithaiwala The measured spectrum of kinetic Alfven wave (KAW) fluctuations in the turbulent solar wind plasma is used to calculate the electron and ion distribution functions resulting from quasi-linear diffusion. Quasi-linear diffusion establishes a step-like profile on the distribution function over parallel velocity [1]. The size of ``plateau'' $v_m $, which can be created within the time of travel of solar wind plasma to the Earth $\sim $ 10$^{5}$ s, is estimated for electrons as $v_{me} /v_{te} \sim (10^{-7}t)^{1/6}\sim 0.5$, while for ions $v_{mi} /v_{ti} \sim (10^{-2}t)^{1/7}\sim 3$. In this case the evolution of the ion tail distribution function can be approximated as $f_{tail} \sim t^{-1/7}\exp (-\vert v_z \vert ^7/v_{mi}^7 )$. As a result, the Landau damping of KAW and whistlers in the high beta solar wind plasma is strongly\underline { }diminished. Also the ion tail distribution function is found to be unstable to electromagnetic ion cyclotron (EMIC) waves [2]. These waves pitch angle scatter the parallel component of the ion velocity into the perpendicular velocity. With less than 1{\%} of turbulent magnetic field energy in EMIC waves the perpendicular ion heating can be possible. Supported by ONR. \\[0pt] [1] L. Rudakov \textit{et. al.}, Phys. Plasma, \textbf{18}, 012307 (2011).\\[0pt] [2] L. Rudakov \textit{et. al.}, arxiv.org:physics.plasm-ph:1012.2398v2, (2011b). [Preview Abstract] |
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UP9.00075: An Improved Radioastronomical Method of Detecting Propagating Coronal Alfven Waves Steven Spangler Several observational techniques indicate the presence of plasma turbulence in the solar corona. It is of interest to show that the turbulence propagates outward. The propagation speed constrains the dispersion relation of the turbulence. Faraday rotation fluctuations due to coronal turbulence diagnose turbulent magnetic field fluctuations. I discuss a new method for measuring propagating Faraday rotation fluctuations in the corona. The technique uses double radio sources in which the line of sight to one component passes through the corona at a greater radial distance than the other. The time series of Faraday rotation of the two components are analyzed in terms of correlation functions. A cross correlation function with significant value at non-zero lag indicates propagating fluctuations and gives the speed of propagation. The technique works directly with the measured Stokes parameters Q and U, not the polarization position angle $\chi$. The technique is illustrated with a set of measurements made with the Very Large Array (VLA) radio telescope. [Preview Abstract] |
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UP9.00076: Identification of Compressive Fluctuations in the Solar Wind Inertial Range Kristopher Klein, Gregory Howes As a means of understanding the compressive components of turbulent large scale solar wind fluctuations, we have created sets of synthetic data based upon spectra of linear MHD or kinetic eigenmodes. At the scales of interest, these models are dependent on the plasma $\beta_i$, the relative fraction of energy in the fast and slow modes, and the angular power distributions of said modes. Using the correlation between density and parallel magnetic fluctuations as a measurement of the compressive behavior we can directly compare the synthetic data to in-situ satellite measurements. In doing so, we find results consistent with almost all of the compressive energy being in the kinetic slow mode. While there is good agreement between satellite data and the kinetic models, none of the fluid MHD models properly fit the satellite measurements. An examination of the angular power distribution indicates that the slow wave energy is strongly anisotropic in a preferentially perpendicular direction. These findings have implications for our understanding of the turbulent cascade as energy progresses to smaller scales, as a plasma devoid of fast mode energy would preferentially evolve to kinetic Alfven rather than whistler waves. Future work will entail creating similar synthetic data sets at these smaller scales to determine the characteristic wave modes. [Preview Abstract] |
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UP9.00077: Gyrokinetic Particle Simulation of Spectral Cascade and Collisionless Dissipation in Kinetic Alfven Wave Turbulence Xi Cheng The issue of spectral cascade and plasma heating in Alfvenic turbulence is a major unsolved problem in plasma physics. The possible heating mechanisms depend on direction of spectral cascade, i.e. perpendicular vs. parallel, and could be Landau damping of kinetic Alfven waves (KAW), ion cyclotron resonant heating and the stochastic heating by dispersive Alfven waves. Our work is focusing on perpendicular cascade to KAW. A massively parallel 3D gyro-kinetic particle-in-cell (PIC) code is developed to study spectral cascading and dissipation of Alfvenic turbulence with fully self-consistent nonlinear kinetic effects. From the gyrokinetic simulation we observed a magnetic energy spectrum with an index of ``-5/3'' in the inertial range, which recovers MHD model results. We also observed a break point at ion gyro-scale followed by a steepened spectra at $k_\perp\rho_s\sim 0.4$ and decouple of the electric and magnetic energy spectrum at $k_\perp\rho_i\sim 1.0$,which suggest that Landau damping of KAWs due to wave-particle resonance is a plausible mechanism of heating and collisionless dissipation complement with ion cyclotron resonance and nonlinear stochastic heating. [Preview Abstract] |
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UP9.00078: Gyrokinetic Particle Simulation of Kinetic Alfv\'en Wave Turbulence Onnie Luk, Xi Cheng, Peter Porazik, Zhihong Lin The previous studies of spectral cascade in Alfv\'enic turbulence clearly show signs of plasma heating, and there are several highly-debated explanations to this phenomenon. We have developed a nonlinear gyrokinetic particle simulation to study the perpendicular spectral cascade caused by Landau damping of kinetic Alfv\'en wave, which is one of those possible heating mechanisms. The nonlinear gyrokinetic code includes scalar potential, vector potential, and compressional magnetic perturbation to form a complete, self-consistent nonlinear simulation. We will discuss the simulation results in comparison with earlier simulation without the compressional magnetic perturbation. [Preview Abstract] |
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UP9.00079: Evolution of plasma parameters during impulsive eruption of a laboratory arched magnetic flux rope Shreekrishna Tripathi, Walter Gekelman Arched magnetic flux ropes (AMFRs) are arched-shaped current-carrying magnetized plasma structures that ubiquitously exist in the solar atmosphere. A laboratory plasma experiment has been built to produce AMFRs (n$\sim$10$^{19}$ m$^{-3}$, Te$\sim$10 eV, B$\sim$1 kG, L$\sim$0.5 m) using a LaB$_6$ plasma source. Two laser beams (1064 nm, $\sim$1 J/pulse) are used to produce controlled plasma flows from the foot-points of the AMFR that trigger the impulsive eruption of the AMFR. The erupting AMFR evolves in a large magnetized plasma produced by an additional LaB$_6$ source. Since the experiment is highly reproducible and runs continuously with a 0.5 Hz repletion rate, several thousands of identical loop eruptions can be generated and their spatiotemporal evolution can be recorded using computer-controlled movable probes. The AMFR images recorded using a high-speed CCD camera and measurement of plasma parameters using 3 axis magnetic loop and Langmuir probes demonstrate striking similarities between erupting laboratory AMFRs and solar flare loops. Results on the role of the ambient magnetic field in destabilizing the AMFR will also be presented. Reference: S. K. P. Tripathi and W. Gekelman, Phys. Rev. Lett. 105, 075005 (2010) [Preview Abstract] |
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UP9.00080: Whistler Anisotropy Instability in the Magnetosphere: Linear Theory and Particle-in-Cell Simulations S. Peter Gary, Kaijun Liu, Dan Winske Linear kinetic dispersion theory and two-dimensional particle-in-cell simulations have been carried out for the whistler anisotropy instability driven by the electron temperature anisotropy $T_{\perp e}/T_{\parallel e} >$ 1. If the ratio of the electron plasma frequency to the electron cyclotron frequency is greater than unity and $\beta_{\parallel e} \ge$ 0.025, the maximum growth rate of the whistler anisotropy instability is at propagation parallel to the background magnetic field ${\bf B}_o$ and the fluctuating fields are substantially electromagnetic. At smaller values of $\beta_{\parallel e}$, the maximum growth rate shifts to propagation oblique to ${\bf B}_o$, and the fluctuating electric fields become primarily electrostatic. If the electron velocity distribution can be described as the sum of two anisotropic components with different parallel temperatures, simulations show that each component drives the growth of a distinct, independent whistler instability. For typical magnetospheric parameters, this configuration gives rise to two distinct frequency bands of enhanced fluctuations, similar to the banded chorus often observed in the magnetosphere. [Preview Abstract] |
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UP9.00081: Gyrokinetic particle simulation of drift-compressional modes in dipole geometry Peter Porazik, Zhihong Lin Gyrokinetic particle simulation of low frequency compressional modes has been developed using flux coordinates in the global magnetic dipole geometry. The compressional component is formulated in a scalar form of the parallel magnetic perturbation and the gyro-averaging is performed explicitly in the configuration space. A reduced gyrokinetic model, in which the compressional perturbations are decoupled from the shear Alfv\'{e}n and electrostatic perturbations, has been implemented. Linear simulation results have been verified using a numerical Nyquist analysis of the dispersion relation in the slab limit. Global simulations of unstable drift-compressional modes in the dipole geometry with kinetic ions find that finite Larmor radius (FLR) effects reduce the linear growth rate significantly but change little the real frequency. Global eigenmode structures show that the modes are even along the equilibrium magnetic field and broadened by the FLR effects in the radial direction. Radial propagation away from the region of excitation is observed. [Preview Abstract] |
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UP9.00082: Preliminary Results of ICRH on the RT-1 Magnetospheric Device Yoshihisa Yano, Haruhiko Saitoh, Zensho Yoshida, Junji Morikawa, Atsushi Fukuyama The Ring Trap-1 device, which uses a levitating super-conducting magnet, has already achieved a stable confinement of high-beta plasma ($\beta_{local}>0.7$) by using ECRH(Electron Cyclotron Resonance Heating). Now we are aiming to heat ions by the use of ICRH(Ion Cyclotron Resonance Heating) as a next phase of the RT-1 experiment. In the dipole configuration, the magnetic field strength (0.01 - 0.5 T) and the plasma density ($n_e \sim 10^{17} m^{-3}$) are lower than in other plasma confinement devices. These features of the dipole plasma may generally result in low plasma loading impedance. Therefore we experimentally examined the loading impedance by the resonance method. In the experiment, a test antenna ($\phi$260 - 300, 3 turns) was installed around the RT-1 center-stack ($\phi$180). The RF frequency was 1 - 3 MHz and the RF input power was less than 200 mW. The observed loading impedance became higher when the RF frequency and the plasma density were increased. The maximum observed impedance was 17 $\Omega$ at 3 MHz and 0.6 $\Omega$ at 1 MHz. These dependences on the RF frequency and the plasma density agree with the preliminary calculation results. The detailed comparison between experiment and calculation will be presented. [Preview Abstract] |
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UP9.00083: Potential and current structures of auroral-like plasma terminating on neutral gas Christopher Cooper, Walter Gekelman The 3-D potential and current structures of a quiescent ($\delta $n/n $<$5{\%}), magnetized plasma terminating on a neutral gas have been measured and compared to theory. A thermally emissive LaB6 cathode biased $<$400 V ionizes a background helium gas. The 30 m plasma is not terminated by an electrode so there are no net currents in it. There are, however, complicated auroral-like closed-current structures. Hot electrons carry a field aligned currents and ions carry a cross field current to closure currents in the low density plasma halo around the plasma. Probes are used to measure the plasma's electric fields, currents, and basic plasma properties. A strong field-aligned neutral collision dominated double layer ($\Delta \phi $/kT$_{e} \quad \sim $ 1) terminates the auroral structure where the plasma pressure matches the neutral pressure. In this region, electric fields and neutral-collision dominated conductivities create comparable cross field and field aligned currents, closing the current loop. The experiment was carried out at the ETPD at UCLA, a large toroidal device (major radius = 5 m, 2 m wide, 3 m tall) with a pulsed (1 Hz) DC plasma discharge (t$_{d}\sim $20 ms, B$_{t}\sim $250 G, and B$_{v}<$6G, R$_{plasma}$=10cm, n$_{e}<$10$^{13}$cm$^{3}$, T$_{e}<$10eV, and T$_{i}\sim $T$_{e})$. [Preview Abstract] |
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UP9.00084: Ion acoustic solitons in the upward current region Clark Scholz, Daniel Main, David Newman, Robert Ergun The formation of ion acoustic solitons in the upward current region is demonstrated through one and two-dimensional Particle-in-Cell simulations. The simulations include cold ionospheric electrons, hot auroral cavity electrons and H$^+$ ions, and H$^+$ and O$^+$ beams. The interaction of the H$^+$ and O$^+$ beams in the auroral cavity leads to the formation of an earthward traveling H$^+$ population. In order to understand the mechanism which leads to the formation of the soliton, we then simplify the simulation so that it includes only a H$^+$ beam, hot electrons and an earthward traveling H$^+$ population (which mimics the population that forms in the more complicated simulation). Both the above plasmas are unstable to ion acoustic soliton formation. However, in order for the soliton to form, we show that it is necessary to trigger the formation of the soliton, which occurs at the interface of the earthward and the anti-earthward traveling H$^+$ population.After the initial soliton forms, ``baby'' solitons form from the initial soliton, consistent with previous studies (Kono, 1986). FAST data are presented which show the presence of earthward traveling ions and bipolar electric field structures in support of the above numerical results. [Preview Abstract] |
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UP9.00085: Induced Nonlinear Scattering of Magnetospherically Reflecting Whistlers C. Crabtree, L. Rudakov, G. Ganguli, M. Mithaiwala, V. Galinsky, V. Shevchenko Whistler waves play an important role in regulating the energetic electron population of the Earth's inner magnetosphere through pitch angle scattering of resonant electrons. There are many potential sources of whistlers in the lower magnetosphere ($L\sim2-3$), e.g., lightening discharges and unstable particle distributions. Once the whistler waves are generated, they are maintained in an effective cavity around the lower-hybrid resonant surface where they participate in pitch angle scattering of energetic resonant electrons before ultimately being dissipated. In this paper we demonstrate that when the energy density of whistler wave turbulence exceeds a threshold, which we estimate occurs at $\delta B\sim30-50$ pT, the process of nonlinear induced scattering by thermal electrons [1] dominates both electron-ion collisional damping and linear Landau damping. This has three important consequences: 1) the lifetime of whistler wave turbulence is increased from seconds to 10s of seconds, 2) the whistler wave packets spend more time away from the lower-hybrid surface and thus interact more efficiently with energetic electrons, 3) the lifetime of trapped electrons is reduced.\\[4pt] [1] Ganguli {\it et al.}, Phys Plasmas (2010). [Preview Abstract] |
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UP9.00086: Transitions in Ionospheric Turbulence from Farley-Buneman to Drift Gradient Regimes E. Hassan, W. Horton, S.K. Litt, A. Smolyakov, S. Benkadda A unified set of nonlinear partial differential equations for the Farley-Buneman and Drift-Gradient ionospheric turbulence are derived and solved numerically. The new model allows one to understand and compute the transition from the Type I regime, where the ion acoustic waves dominate, to the Type II regime where the EXB drift velocity is below the sound speed and the vertical electron density gradient drives the turbulence. In the unified systems of equations there is strong mode-coupling between the two types of dynamics. Simulations show both the large scale rising of the low density bubbles and the anomalous resistivity and electron heating from the driven ion acoustic fluctuations. [Preview Abstract] |
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UP9.00087: Kinetic simulations of meter-scale structures in Convective Equatorial Ionospheric Storms (Spread-F) Yakov Dimant, Yann Tambouret, Meers Oppenheim We present kinetic, particle-in-cell simulations of non-linear drift wave plasma instabilities and address their possible involvement in Convective Equatorial Ionospheric Storms (CEIS - also called Spread-F). These CEIS develop in the F-region ionosphere following sunset, as a large scale, vertical density gradient drives plasma flows across the geomagnetic field. A generalized Rayleigh-Taylor instability characterizes the basic physics of large scale (100 m - 100 km) instabilities, but this mechanism predicts that small scale waves (0.1 - 10 m) should remain stable. Yet, radars measure coherent echoes from small scale irregularities that exist simultaneously with the large scale turbulence. We explore the possibility that secondary gradients produced by the large scale instabilities lead to drift wave dynamics and small scale waves. The simulations involve collisionless plasma dynamics in both the 2-D plane perpendicular to B and 3-D. One direction is non-periodic, where a steep density gradient is maintained throughout. We present an analysis of the non-linear effects leading to the development of a stable ambipolar field that negates the ion diamagnetic drift and enhances the electron drift, ultimately leading to drift waves. [Preview Abstract] |
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UP9.00088: Light Recordings from Near-Earth Synchrotron Radiating Plasma Currents Anthony Peratt, Alfred Qoyawayma Synchrotron radiation in the visible is produced by an intense particle beam (currents) in the presence of a magnetic field in the direction of relativistic electron acceleration. Among the properties of synchrotron radiation are: high brightness and high intensity many orders of magnitude more than X-rays; a high level of polarization (linear or elliptical); high collimation, i.e. small angular divergence of the beam; and high brilliance, exceeding other natural and artificial light sources by many orders of magnitude. For example, a brilliance larger than 10$^{18}$ photons/s/mm$^2$/mrad$^2$ /0.1\%BW, where 0.1\%BW denotes a bandwidth 1$^{-3}\omega$ centered around frequency $\omega$. The properties of Birkeland currents from intense solar storms lasting decades but separated by millennia are: 56 pairs of currents (as in the penumbra of a dense plasma focus) enveloping the Earth on their passage through space. For the Earth, the electron flow is towards Antarctica. Both particle-in-cell simulations and man-made ground recordings indicate ground illumination of meter to decameter wide white lines fanning out at the poles [1,2]. \\[4pt] [1] A. L. Peratt and W. F. Yao, \textit{Physica Script} a \textbf{T131}, October 2008\\[0pt] [2] P. Devereux and N. Pennick, ``Lines on the Landscape,'' Robert Hale Ltd., London 1989. [Preview Abstract] |
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UP9.00089: PLASMA TECHNOLOGY |
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UP9.00090: Particle Simulations for Plasma-Plasma Intersecting Experiments Seigo Misaki, Toshinori Yabuuchi, Takuya Kono, Tatsuya Oishi, Kazuo A. Tanaka, Atsushi Sunahara Walls in a laser fusion reactor can be ablated by thermal load and become plasma. We have conducted experiments on the intersections of two plasma plumes created by laser ablations to study the behavior of the ablation plumes in the reactor. An ICCD camera was employed to measure time-resolved spatial distributions of emissions from the plumes using various types of target materials, such as Tungsten and Carbon. The results show a clear material dependence of the plume interactions. To understand the underlying physics of the plume intersections, we have developed a particle simulation code using Direct Simulation Monte Carlo (DSMC) techniques and coulomb collision model [1]. The simulation results are consistent with the experimental observation with the ICCD camera. The detailed comparison of the simulation and experimental results will be presented. \\[4pt] [1] T. TAKIZUKA and H. ABE, J. Comp. Phys., 25, 205(1977) [Preview Abstract] |
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UP9.00091: Experimental study on interactions of plasma plumes generated by laser ablation Toshinori Yabuuchi, Takuya Kono, Tatsuya Oishi, Kenshiro Kikuyama, Seigo Misaki, Kazuo A. Tanaka In fusion reactors, first walls will be exposed with heavy thermal loads and high energy particles. Once the wall is ablated, the dynamics of ablated plasma plumes is a key issue for sustaining the fusion reactions and maintaining the reactors. In our experiments, plasma plumes are created by UV laser ablation from concave targets. Two plumes moving in the perpendicular direction intersect each other in the center of the concave curvature[1]. Particle measurements have indicated that the two plumes collide with each other and the direction of their movement has been changed. Simultaneously, we have observed with the time-resolved 2D imaging system using ICCD camera that the dynamics of plasma plumes changes significantly due to the plume-plume interactions. In the conference, the detailed observation will be presented. \\[4pt] [1] Y. Hirooka et al 2010 J. Phys.: Conf. Ser. 244 032033 (2010) [Preview Abstract] |
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UP9.00092: Negative Ion Studies in an IEC Fusion Device E.C. Alderson, J.F. Santarius, G.A. Emmert, G.L. Kulcinski Understanding of negative ions in Inertial Electrostatic Confinement (IEC) fusion devices has made substantial progress since their discovery [1]. Modeling of negative ion formation and energy spectrum evolution has been undertaken by incorporating a negative ion physics module in a 1-D integral transport simulation of an IEC device [2]. Study of negative ion current focusing by the IEC device electrostatic potential structure has been undertaken by measuring the negative ion current azimuthal profile about the equator of the IEC device at various radii. This data set also allows for an extrapolation of total negative ion current produced in an IEC device at the studied parameters.\\[4pt] [1] D.R. Boris, et al., Phys. Rev. E. 80, 036408 (2009).\\[0pt] [2] G.A. Emmert and J.F. Santarius, Phys. Plasmas 17, 013503 (2010). [Preview Abstract] |
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UP9.00093: Integral Transport Analysis of Ions Flowing Through Neutral Gas Gilbert Emmert, John Santarius, Eric Alderson A computational model for the flow of energetic ions through a background neutral gas is being developed. Its essence is to consider reactions as creating a new source of ions or neutrals if the energy or charge state of the resulting particle is changed. For a given source boundary condition, the creation and annihilation of the various species is formulated as a 1-D Volterra integral equation[1] that can quickly be solved numerically by finite differences. The current work focuses on radially converging, multiple-pass, 1-D ion flow through neutral gas and a nearly transparent, concentric anode and cathode pair in spherical geometry. This has been implemented as a computer code for atomic (3He, 3He+) and molecular (D, D2, D-, D+, D2+, D3+) ion and neutral species, and applied to modeling inertial-electrostatic confinement (IEC) devices. The inclusion of negative ions is a recent development[2]. The code yields detailed energy spectra of the various ions and energetic neutral species. Comparisons with experimental data for a University of Wisconsin IEC device will be presented. \\[4pt] [1] G.A. Emmert and J.F. Santarius, Phys. Plasmas 17, 013502 [atomic] \& 13503 [molecular] (2010).\\[0pt] [2] E.C. Alderson, et al., this conference. [Preview Abstract] |
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UP9.00094: A Robust Modular IGBT Power Supply for Configurable Series/Parallel Operation at High Power and Frequency Timothy Ziemba, K.E. Miller, J.R. Prager, J.G. Carscadden Eagle Harbor Technologies (EHT) is developing a modular, solid-state power supply for pulsed high power ($>$ 10 MW) RF applications supported by a DOE SBIR Phase II. The prototype modules utilize a low-cost IGBT based system that can be assembled in multiple ways for a wide range of applications. Each module is capable of switching 2 kA at 1 kV up to megahertz frequencies with rise times of $\sim $40 ns. Experimental testing of the modules demonstrated both parallel (high current) and series (high voltage) configurations. The modules are designed for precise switching control, which reduces jitter ($<$ 5 ns) between modules, enabling robust series operation. Present work is focused on building individual modules with active overvoltage and overcurrent fault detection. Two prototype supplies will be demonstrated: one capable of switching 2 kA at 10 kV and the other capable of switching 20 kA at 1 kV. The prototype costs are estimated to be three times less than older generation IGBT based power supplies for similar high current pulsed applications and twenty times less for the pulsed high voltage and high power tube based RF applications. [Preview Abstract] |
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UP9.00095: Electrostatic Lithium Injection for Fusion Devices Peter Fiflis, Daniel Andruczyk, Vijay Surla, David Ruzic One of the most significant problems in fusion devices is controlling the recycling of hydrogen that is not used in the fusion process. A powerful getter of hydrogen, lithium, if injected into regions where it is needed, may getter hydrogen much more efficiently. Current lithium evaporation systems are inefficient in controlling where lithium deposits once injected, and a system that can control where it deposits would be invaluable. A solution may lie in a concept called electrospray, where charged lithium particles could be produced and controlled via electric and magnetic fields to target areas in need of getting impurities. While the electrospray concept has been used in other applications, the technique has yet to be applied to lithium injection. Preliminary research into the viability of an Electrostatic Lithium Injector (ELI) have shown that such a system may be capable of producing the lithium droplets and spray, and experiments are being performed to determine the optimal design. Modeling is also being done into using the ELI for repair of PFCs, and possibly even ELM control. Simulation has shown a lithium droplet can be made to follow an arbitrary path with application of a time varying voltage from 10 to -1700 V to the center stack of a tokamak. One run was able to calculate the voltage function required to make a lithium particle take a helical path. [Preview Abstract] |
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UP9.00096: Using a Balun Transformer Combiner for High Power RF Experiments M.C. Kaufman, P.V. Pesavento A novel coaxial power combiner design has been duplicated that has distinct advantages over other combiner geometries that can handle high power. This design is being applied to combine four 3 kW power supplies to obtain a 12 kW, 5 MHz system for an ICRF antenna on HSX. In the past, Wilkinson type combiners have had limited application to high power systems because of the lack of non-inductive, high power, 100$\Omega$ balance loads. With this new design, standard 50$\Omega$ dummy loads can be used instead for the balance load. The cost is considerably lower than lumped element combiner designs which are dominated by capacitor costs. At such a relatively low frequency, a 3-dB quarter-wave coupled-line coupler becomes impractically long, and a conventional branch-line hybrid requires 35$\Omega$-line, which is commercially unavailable. The balun combiner uses less transmission line than a ring hybrid and has good bandwidth characteristics even away from its best line impedance. Theoretical calculations and modeling were performed for line impedances from 65$\Omega$ to 75$\Omega$. Measurements from a low-power test device show excellent agreement with theory, and construction of the high power system is underway. [Preview Abstract] |
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UP9.00097: Non-linear modeling of RF in fusion grade plasmas Travis Austin, David Smithe, Ammar Hakim, Thomas Jenkins We are seeking to model nonlinear effects, particularly parametric decay instability in the vicinity of the edge plasma and RF launchers, which is thought to be a potential parasitic loss mechanism. We will use time-domain approaches which treat the full spectrum of modes. Two approaches are being tested for feasibility, a non-linear delta-f particle approach, and a higher order many-fluid closure approach. Our particle approach builds on extensive previous work demonstrating the ability to model IBW waves (one of the PDI daughter waves) with a linear delta-f particle model [1]. Here we report on the performance of such simulations when the linear constraint is relaxed, and in particular on the ability of the low-noise loading scheme, specially developed for RF and ion-time scale physics, to operate and maintain low noise in the non-linear regime. Similarly, a novel high-order closure of the fluid equations is necessary to model the IBW and higher harmonics. We will report on the benchmarking of the fluid closure, and its ability to model the anticipated pump and daughter waves in a PDI scenario.\\[4pt] [1] T.M. Austin, D.N. Smithe, ``Modeling ion cyclotron resonance heating using a hybrid $\delta$f particle-in-cell approach,'' in progress. [Preview Abstract] |
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UP9.00098: Density profile control using compact toroid injection in STOR-M Tokamak Takumi Onchi, Dazhi Liu, Chijin Xiao, Akira Hirose, Tomohiko Asai, Sean Wolfe The Saskatchewan TORus Modified (STOR-M) tokamak has a Compact Torus (CT) injector which allows tangential injection of high density plasmoid. The objectives of CT injection (CTI) into the core of plasma are to fuel tokamaks and also optimize the bootstrap current in the future reactors by control of the plasma pressure gradient. Measurement of soft X-ray bremsstrahlung emission profile have verified that CT particles are deposited in the core region from outside and steeper density gradient is generated via a balancing process after the asymmetric density profile is formed in STOR-M. The major radius of the core plasma is shifted outward and stays in equilibrium until the end of discharge. H alpha line-emission considerably decreases in the core region and the high emitting area with low temperature plasma exists in the edge region. A few milliseconds seconds after these altered profiles of the density and the emission by CTI are generated, stronger edge radial electric field as well as H-mode appears and the average electron density peaks. [Preview Abstract] |
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UP9.00099: 2D full wave analysis of EC wave structure in tokamak plasmas using FEM Yuichiro Maruyama, Atsushi Fukuyama Electron cyclotron (EC) wave propagation has been mostly analyzed by the ray tracing technique. For spherical tokamaks with high density, however, full wave analysis is necessary owing to the existence of evanescent layers and mode conversion to the Bernstein waves. Full wave analysis requires a lot of computational resources and finite element method (FEM) is expected to be suitable for parallel computing since it requires less computational resources compared with full or partial spectral method. We have already developed 3D full wave code using FEM, TASK/WF. In order to obtain better spatial resolution for the analysis of EC wave in tokamak plasmas, we have developed a 2D version with mixed base functions. The kinetic response of plasmas will be implemented as an integral representation of the dielectric tensor. Preliminary numerical results in small size tokamaks will be presented. [Preview Abstract] |
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UP9.00100: Visco-elastic model of the ``fuzz'' growth Sergei Krasheninnikov Recent experiments on the irradiation of Tungsten with helium-hydrogen plasma [1] have shown the formation of ``fuzz,'' filled with nano-bubbles, on the front surface of the sample. We present theoretical model describing ``fuzz'' growth. This model is based on plastic deformation of the ``skin'' of the ``fuzz'' fibers caused by newly growing nano-bubble on the tip of the fiber. Newly glowing bubble having high helium pressure inside creates an excessive force on surrounding tungsten ``skin'' of the fiber and forming pressure difference between base and nose of the fiber. As a result, tungsten ``flows'' through the ``skin'' from the base to the nose. This model predicts all main features observed in experiments: t to 1/2 growth of length of the fibers, strong temperature dependence of the growth rate, and the saturation of the growth with ion helium flux to the substrate.\\[4pt] [1] S. Takamura, et al., Plasma Fusion Res., 1, 051 (2006); M. J. Baldwin, and R. P. Doerner, Nucl. Fusion 48, 035001 (2008); R. S. Kajita et al., Nucl. Fusion 49, 095005 (2009) [Preview Abstract] |
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UP9.00101: Surface fluctuations in the Liquid Metal Experiment J. Rhoads, E. Spence, E. Edlund, J. Kubricht, P. Sloboda, H. Ji MHD fluids such as liquid metals become tied to magnetic field lines, which may have significant implications for thermal convection in proposed liquid-metal divertor concepts. Experiments have been conducted in the Liquid Metal Experiment (LMX) using a GaInSn eutectic alloy as a working fluid to investigate the anisotropization due to the magnetic field on turbulent structures in the flow. These experiments considered free-surface, wide aspect-ratio flow through a channel situated in a strong vertical magnetic field (up to $\textrm{Ha} \approx 50$). By tracking the deflection of the free surface in three locations of varying separation distance, correlation analysis in both the down-stream and cross-stream directions gave insight into how the fluctuations were affected by the application of the magnetic field. The cross-correlation of these signals as a function of separation distance showed the correlation-length, while the coherence of these signals indicated how the fluctuations were suppressed across the frequency spectrum. Experimental results and proposed explanations will be presented. [Preview Abstract] |
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UP9.00102: Study of Lithium on Molybdenum substrates in IIAX (Ion surface Inter Action Surface eXperiment) Priya Raman, Andrew Groll, Daniel Andruczyk, Vijay Surla, David Ruzic Plasma Facing Component(PFC) materials are critical to fusion reactor development. There is no one material that functions as an ideal PFC material. Coatings are applied to control the interaction between plasmas and the surrounding material. Boronization and lithiation are the most common methods of wall conditioning techniques that are currently used in tokamaks. In this work, we investigate lithium on molybdenum substrates for its wetting properties and erosion behavior. To understand the effect of boronization on wetting properties of lithium, a set of experiments have been conducted in the newly built facility, where liquid lithium is dropped on to a heated molybdenum substrate and the contact angle of lithium on substrate is measured. It is found that lithium wets both the molybdenum and the boronized molybdenum substrates. When lithium is sputtered, it has been observed that 55-65{\%} of the sputtered particles are ions [1] and the sheath returns them to the wall. Li on top of other layers may act differently. To examine this phenomenon and assess erosion measurements of lithium on mixed materials (Li/Mo, Li/B/Mo),a methodology to measure ionization fraction of the sputtered lithium in the IIAX facility is also presented. Work supported by DOE/ALPS contract: DEFG02- 99ER54515.\\[4pt] [1] J.P.Allain and D.N.Ruzic,\textit{Nucl.Fusion} \textbf{42} (2002), pp. 202--210. [Preview Abstract] |
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UP9.00103: ELM simulation experiments using transient heat and particle load produced by a magnetized coaxial plasma gun K. Shoda, I. Sakuma, D. Iwamoto, Y. Kikuchi, N. Fukumoto, M. Nagata It is considered that thermal transient events such as type I edge-localized modes (ELMs) and disruptions will limit the lifetime of plasma-facing components (PFCs) in ITER. It is predicted that the heat load onto the PFCs during type I ELMs in ITER is 0.2-2MJ/m2 with pulse length of $\sim $0.1-1ms. We have investigated interaction between transient heat and particle load and the PFCs by using a magnetized coaxial plasma gun (MCPG) at University of Hyogo. In the experiment, a pulsed plasma with duration of $\sim $0.5ms, incident ion energy of $\sim $30eV, and surface absorbed energy density of $\sim $0.3-0.7MJ/m2 was produced by the MCPG. However, no melting occurred on a tungsten surface exposed to a single plasma pulse of $\sim $0.7MJ/m2, while cracks clearly appeared at the edge part of the W surface. Thus, we have recently started to improve the performance of the MCPG in order to investigate melt layer dynamics of a tungsten surface such as vapor cloud formation. In the modified MCPG, the capacitor bank energy for the plasma discharge is increased from 24.5 kJ to 144 kJ. In the preliminary experiments, the plasmoid with duration of $\sim $0.6 ms, incident ion energy of $\sim $ 40 eV, and the surface absorbed energy density of $\sim $2 MJ/m2 was successfully produced at the gun voltage of 6 kV. [Preview Abstract] |
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UP9.00104: Performance of Lithium/Molybdenum Infused Trenches (LiMIT) concept under strong magnetic fields Wenyu Xu, Daniel Andruczyk, Vijay Surla, David Ruzic As fusion experimental devices progress, removing heat from the divertor region has become a challenging problem. An alternative is to use flowing liquid metal, especially lithium, as the plasma facing component with the advantage of providing a low-recycling surface which allows density control and higher confinement. The Lithium/Metal Infused Trenches (LiMIT) concept which utilizes the thermoelectric-magnetohydrodynamic (TEMHD) driven flowing liquid lithium to cool the divertor surface has been successfully demonstrated at the University of Illinois to withstand heatflux of 10MW/m2 under low magnetic field without significant evaporation. However, the major concern in using the flowing liquid lithium in real tokamak environment is the presence of strong magnetic field since the resulting MHD force will strongly damp the flow. In order to investigate the performance of LiMIT design under high magnetic field, the magnet coil is upgraded with a long time pulse to achieve a strong magnetic field comparable to the magnetic environment at divertor region. The results from this newly configured magnetic field environment will be presented and compared to theoretical estimates. This work was supported by DOE-DEFG02-99ER54515. [Preview Abstract] |
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UP9.00105: Dust in the divertor sheath: a problem or a possible solution to a problem? Gian Luca Delzanno, Xianzhu Tang In this work, we will present results on dust transport in the magnetized sheath near the divertor plate of a tokamak. We consider conditions relevant to present short-pulse tokamak machines as well as conditions for long-pulse ITER/DEMO reactors. We solve the dust charging equation, the dust equation of motion and the equations for dust heating and mass loss in the magnetized sheath. We present parametric studies changing the divertor plasma conditions and the angle of the equilibrium magnetic field relative to the wall. Our main result is that, for conditions relavant to DEMO, the stronger heat flux to the wall severely limits the dust survivability and mobility. Consequently, a single dust grain tends to redeposit the material locally, in contrast to what happens in short-pulse machines. We will also discuss two fusion technology solutions to DEMO PFC based on externally introduced solid particulates.The dust patch represents a mitigation strategy where engineered solid dust particles are injected in the chamber to patch areas of net erosion at runtime. In the dust shield concept, tungsten dust particles are suspended above the divertor by the sheath electric field and are circulated poloidally by the sheath plasma flow. Thus, dust particles can be injected at one end of the divertor and be collected at the other end before they melt. During their transit across the divertor, they form a circulating shield that provides the primary heat exhaust. [Preview Abstract] |
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UP9.00106: Burn Control in Fusion Reactors via Isotopic Fuel Tailoring Mark D. Boyer, Eugenio Schuster The control of plasma density and temperature are among the most fundamental problems in fusion reactors and will be critical to the success of burning plasma experiments like ITER. Economic and technological constraints may require future commercial reactors to operate with low temperature, high-density plasma, for which the burn condition may be unstable. An active control system will be essential for stabilizing such operating points. In this work, a volume-averaged transport model for the energy and the densities of deuterium and tritium fuel ions, as well as the alpha particles, is used to synthesize a nonlinear feedback controller for stabilizing the burn condition. The controller makes use of ITER's planned isotopic fueling capability and controls the densities of these ions separately. The ability to modulate the DT fuel mix is exploited in order to reduce the fusion power during thermal excursions without the need for impurity injection. By moving the isotopic mix in the plasma away from the optimal 50:50 mix, the reaction rate is slowed and the alpha-particle heating is reduced to desired levels. [Preview Abstract] |
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UP9.00107: Development progress of plasma shaping controls in KSTAR Sang-hee Hahn, N.W. Eidietis, D. Mueller, Y.M. Jeon, S.W. Yoon, J.H. Kim, S.Y. Park, M.L. Walker An axisymmetric magnetic shape control system has been developed for creations and sustainment of double-null diverted shape of KSTAR, based on the real-time EFIT/isoflux algorithm. The real-time EFIT scheme is modified to deal with the influences of magnetic materials inside the magnet system. On the design of the isoflux algorithm, various techniques were used in order to decouple the coil responses by the shape changes from the plasma current feedback responses. In this work, we show experimental application results of the developed controls on the KSTAR at the 2011 plasma campaign, and analyze the effects of shaping on the plasma performances. [Preview Abstract] |
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UP9.00108: Construction of Control System for Floating High Energy Capacitors Zachary Tobin, Paul Bellan The circuitry for the Caltech magnetic reconnection experiment under construction requires two independent floating high energy capacitor power supplies to create linked plasma loops. This project requires the building of systems for controlling plasma generation, including timing circuitry to control the sequences of operation. Unlike with previous designs, timing functions are completely contained on a single printed circuit board. This allows the design to be easily replicated for use with the multiple independent capacitor involved. The timing circuitry first activates a high voltage power supply, then connects the power supply to the capacitor, and then disconnects the power supply so that the charged capacitor is floating. The circuitry then sends out a ``ready'' signal to a sequencer, which sequentially triggers the gas puff valves, bias magnetic field supply, and ignitron switch for the capacitor. The control circuit sequencing has been tested successfully with the capacitor discharging into a dummy load. [Preview Abstract] |
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UP9.00109: Magnetically Insulated Electron Flow in the 2.5-MeV URSA Minor LTD Joshua Leckbee, Timothy Pointon, Bryan Oliver The Linear Transformer Driver (LTD) is a compact type of inductive voltage adder (IVA) with the primary energy storage inside the IVA cells. The 2.5-MV URSA Minor LTD is designed to drive a magnetically insulated transmission line (MITL) and electron beam diode load. Because of its compact architecture, control of the electron power flow in the MITL (e.g. early time loss currents) is paramount to efficient operation. Results from experimental testing and 2-D particle-in-cell (PIC) simulations of magnetic insulation and electron loss in the MITL will be presented. The simulations compute the local energy deposition of electrons hitting the anode structures, including the dielectric insulator for each cavity. On URSA Minor, currents are measured in the cathode and anode conductors at four axial locations along the MITL. Measured currents and inferred voltages will be compared to the simulations. [Preview Abstract] |
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UP9.00110: Recent progress of cryogenic target fabrication technique for FIREX project Mitsuo Nakai, Takeshi Fujimura, Takayoshi Norimatsu, Yasushi Fujimoto, Takahisa Jitsuno, Shinji Machi, Hiroyuki Shiraga, Hiroshi Azechi, Akifumi Iwamoto, Hitoshi Sakagami Unique design of the cryogenic target with a gold conical guide and a fuel feeding capillary has been developed for the Fast Ignition Realization Experiment (FIREX) project at the Institute of Laser Engineering (ILE), Osaka University. In the scheme, the deuterium gas is to be fed in a foam layer of the shell and solidified. In the case of a foam shell filled with solid fuel, it is worried that bubble-like void may remain in the cell after the liquid-solid transition. We investigated the filling fraction of solid fuel in the Resolcinol-Formalehyde foam of a surrogate target. It was shown that the optimization of cooling speed and temperature gradient was quite promising to make a uniform solid layer with a low void fraction. In the presentation, interference measurement of the fuel- filled foam layer is focused and recent progress of the shell fabrication is also briefly reported. \\[0pt] [1] A. Iwamoto, et al., ``Study on possible fuel layering sequence for FIREX target,'' Journal of Physics: Conference Series, Vol. 244 (2010), 032039. [Preview Abstract] |
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UP9.00111: New Fusion Concept Using Coaxial Passing Through Each Other Self-focusing Colliding Beams (Invention) Ioseb Chikvashvili In proposed Concept it is offered to use two ion beams directed coaxially at the same direction but with different velocities (center-of-mass collision energy should be sufficient for fusion), to direct oppositely the relativistic electron beam for only partial compensation of positive space charge and for allowing the combined beam's pinch capability, to apply the longitudinal electric field for compensation of alignment of velocities of reacting particles and also for compensation of energy losses of electrons via Bremsstrahlung. On base of Concept different types of reactor designs can be realized: Linear and Cyclic designs. In the simplest embodiment the Cyclic Reactor (design) may include: betatron type device (circular store of externally injected particles -- induction accelerator), pulse high-current relativistic electron injector, pulse high-current slower ion injector, pulse high-current faster ion injector and reaction products extractor. Using present day technologies and materials (or a reasonable extrapolation of those) it is possible to reach: for induction linear injectors (ions{\&}electrons) -- currents of thousands A, repeatability -- up to 10Hz, the same for high-current betatrons (FFAG, Stellatron, etc.). And it is possible to build the fusion reactor using the proposed Method just today. [Preview Abstract] |
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UP9.00112: A multi-wavelength LIF detection system Fred Skiff, Dereth Drake, Tim Good We present preliminary results from a new pair of 16 channel photon-counting LIF detection systems designed for measurements of ion phase-space fluctuations using laser-induced fluorescence in an magnetized singly-ionized Argon plasma column. Conventional LIF detection systems use narrow-bandwidth interference filters to block background light. These filters have limitations in that they are normally limited to a single wavelength and must be of large diameter to work efficiently with light from a low f-number light-collection first-optic. Especially for experiments observing fluorescence on multiple transitions (or where fluorescence may be spread out over several decay paths) it is useful to be able to observe multiple transitions in the light from each light collection system. We describe a system consisting of two movable light-collecting periscopes where the collected light is expanded to 10 cm diameter beams which are analyzed by means of diffraction gratings and imaged onto 16 element photomuliplier tubes. In each of the channels the pulses are discriminated and counted with an adjustable dwell time. Because the light collection system is imaging, the multiple elements can be used to resolve multiple spatial points or multiple spectral lines. [Preview Abstract] |
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UP9.00113: New diagnostic facilities for Caltech plasma experiments Xiang Zhai, Paul Bellan An optically coupled high voltage probe (HV probe) and a visible and near infrared (VNIR) detector are being developed for Caltech solar coronal loop and astrophysical jet experiments. The HV probe uses a capacitive voltage divider coupled a fast LED to convert the electrical signal into an optical signal, which is then conveyed to a receiver via an optical fiber. A solar cell array powered by ambient laboratory lighting charges a capacitor that when triggered acts as a short-duration power supply for an onboard amplifier in the HV probe. The fast VNIR detector combined with specific atomic line filters measures the spectra with 10ns time resolution. Measurements show that before detachment, the gross VNIR emission power of the solar coronal plasma loop is a function of the axial electric current. H$\alpha$ and H$\beta$ line emission power is found to be $10^2\sim10^3$ greater than predicted by assuming local thermodynamic equilibrium. This indicates that the plasma is not in an ionization-recombination equilibrium state and can have a larger population of neutrals than predicted for an equilibrium state. [Preview Abstract] |
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UP9.00114: X-Ray Line-Shape Diagnostics and Novel Stigmatic Imaging Schemes for the National Ignition Facility M. Bitter, K.W. Hill, N.A. Pablant, L.F. Delgado-Aparicio, P. Beiersdorfer, E. Wang, M. Sanchez The concepts of a high-resolution x-ray imaging crystal spectrometer (XICS) and novel stigmatic imaging schemes for accurate measurements of x-ray line shapes and the x-ray emission profiles at the National Ignition Facility (NIF) will be presented. The XICS will allow measurements of the line shapes of x-ray lines from high-Z impurities, such as krypton or tungsten, which can be added as trace elements to the ICF target. The goal is to determine the ion temperature in the plasma by separating the Doppler broadening from the Stark broadening. In addition to line-shape measurements, it may also be possible to determine the electron temperature from a measurement of line intensity ratios. The novel stigmatic imaging systems consist of matched pairs of spherically bent crystals, whereby the astigmatism is fully eliminated, so that stigmatic images of an x-ray source can be obtained for almost arbitrary angles of incidence. These imaging schemes will have a much higher optical throughput than existing x-ray pinhole cameras. [Preview Abstract] |
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UP9.00115: The case for fission suppressed hybrid fusion (or: What is really a grand challenge?) Wallace Manheimer Fusion has been described (mistakenly in my view) as one of mankind's grand challenges. The real grand challenge is providing 10-30 terawatts (TW) of carbon free power by mid century. Pure fusion has no hope, fission suppressed hybrid fusion (FSHF) might. Do we go with conventional approaches, tokamaks and lasers, or study new concepts? Conventional approaches are so far ahead, they are the only hope. FSHF has the advantage of fitting in with current nuclear infrastructure. A single fusion reactor can power at least 5 light water reactors (LWR's) of equal power. As a fuel producer, fusion is an order of magnitude more prolific than fast neutron reactors like the integral fast reactor (IFR). But IFR's can burn all actinide wastes. This is a reasonably mature technology, at least compared to fusion. The combination of fuel production by fusion, power production mostly by LWR's and actinide waste treatment by IFR's has the potential of providing 30 TW of carbon free power, economically, environmentally soundly, and with no proliferation risk, at least as far into the future as the dawn of civilization was in the past. [Preview Abstract] |
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UP9.00116: Fission Fusion Hybrids: a nearer term application of Fusion M. Kotschenreuther, P. Valanju, S. Mahajan, B. Covele Fission-fusion hybrids enjoy unique advantages for addressing long standing societal acceptability issues of nuclear fission power at a much lower level of technical development than a competitive fusion power plant. For waste incineration, hybrids burn intransigent transuranic residues (with the long lived biohazard) from light water reactors (LWRs). The number of hybrids needed is 5-10 times less than the corresponding number of fast reactors (FRs). The highly sub-critical hybrids, with a thermal/epithermal spectrum, incinerate $>$ 95{\%} of the waste in decades rather than the centuries needed for FRs. For fuel production, hybrids can produce fuel for 3-4 times as many LWRs with no fuel reprocessing. Thorium fuel rods exposed to neutrons in the hybrid reach fissile concentrations that enable efficient burning in LWR without the proliferation risks of reprocessing. The proliferation risks of this method are far less than other fuel breeding approaches, including today's gas centrifuge. With this cycle, US Thorium reserves could supply the entire US electricity supply for centuries. The centerpiece of the fuel cycle is a high power density Compact Fusion Neutron Source (major+minor radius $\sim $ 2.5-3.5 m), which is made feasible by the super-X divertor. [Preview Abstract] |
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UP9.00117: Bulk and Thin Film Contact Resistance with Dissimilar Materials Y.Y. Lau, P. Zhang, W. Tang, M.R. Gomez, D.M. French, J.C. Zier, R.M. Gilgenbach Contact resistance is important to integrated circuits, thin film devices, carbon nanotube based cathodes, MEMS relays and interconnectors, wire-array z-pinches, metal-insulator-vacuum junctions, and high power microwave sources, etc. This paper summarizes the recent modeling efforts at U of M, addressing the effect of dissimilar materials and of finite dimensions on the contact resistance of both bulk contacts and thin film contacts. Accurate analytical scaling laws are constructed for the contact resistance of both bulk [1] and thin film [2] contacts over a large range of resistivity ratios and aspect ratios in Cartesian and cylindrical geometries. They were validated against known limiting cases; and spot-checks with numerical simulations and experiments. \\[4pt] [1] Lau~et al., \textit{J. Appl. Phys.}\textbf{105}, 124902 (2009); Gomez et al., \textit{Appl. Phys. Lett.} \textbf{95}, 072103 (2009); Zhang et al., \textit{J. Appl. Phys.} \textbf{108}, 044914 (2010). \\[0pt] [2] Zhang et al., \textit{Appl. Phys. Lett.} \textbf{97}, 204103 (2010);\textit{ J. Appl. Phys.} \textbf{109}, 124910 (2011); Proc. of the 57th IEEE Holm Conf. on Electrical Contacts (2011). [Preview Abstract] |
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UP9.00118: Isochoric Plasma Sources for Laser-Plasma Interaction Studies Michael J. Hay, Ernest J. Valeo, Nathaniel J. Fisch The resonant backward Raman compression of intense laser light in plasma requires a high-density plasma that is easily accessed by light. Gas jet technology is at its limit: either in density, so new technology is necessary to process shorter wavelength light; or in geometrical size, so new technology is necessary to process substantial powers at large aperture. However, aerogel or dense aerosol targets may overcome the limitations of gas jets. We present scaling relations that define the operating parameter space for compression using silica aerogels. Using \textsc{Ansys Fluent} we simulate dense aerosol formation under aerodynamic focusing. These simulations include momentum coupling between the carrier gas and the particles' virtual flow field. [Preview Abstract] |
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UP9.00119: Low-Impurity, Electrode-less Plasma Source for Fusion Applications James Prager, Timothy Ziemba, Kenneth Miller, Robert Winglee Eagle Harbor Technologies, in collaboration with the University of Washington, has developed a low-impurity, electrode-less plasma source (EPS) for start-up and source plasma injection for fusion science applications.~ In order to not interfere with the experiment, a pre-ionizer/plasma source must meet a few critical criteria including low impurity production, low electromagnetic interference (EMI), and minimal disruption to the magnetic geometry of the experiment.~ Two versions of the EPS have been created: a high particle flux device and a low magnetic flux device. ~Both versions were designed to be bakable and UHV compatable. Here we show the results from the Phase I program, including device construction and integration, plasma properties, and preliminary impurity studies.~ In addition, we discuss the Phase II work plan, which includes more extensive impurity studies. [Preview Abstract] |
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