Overview of the Alcator C-Mod Research Program

Scott, Steve; Bader, A.; Bakhtiari, M.; Basse, N.; Beck, W.; Biewer, T. M.; Bernabei, S.; Bonoli, P.; Böse, B.; Bravenec, R. V.; Bespamyatnov, I.O.; Childs, R.; Cziegler, I.; Doerner, R.; Edlund, E.; Ernst, D. R.; Fasoli, A.; Ferrara, Marco; Fiore, C. L.; Fredian, T.; Graf, Alexander; Graves, T. P.; Granetz, R.; Greenough, N.; Greenwald, M.; Grimes, M.; Grulke, O.; Gwinn, D.; Harvey, R. W.; Harrison, Soren; Hender, T. C.; Hosea, J.; Howell, D. F.; Hubbard, A.E.; Hughes, J. W.; Hutchinson, I. H.; Ince‐Cushman, A.; Irby, J.; Jernigan, T. C.; Johnson, D.; Ko, Jinseok; Koert, P.; LaBombard, B.; Kanojia, A.; Lin, L.; Lin, Y.; Lipschultz, B.; Liptac, J.; Lynn, A. G.; MacGibbon, P.; Marmar, E.; Marr, Kenneth D.; May, Mark; Mikkelsen, D. R.; McDermott, R. M.; Parisot, A.; Parker, R.; Phillips, C. K.; Phillips, P. E.; Porkoláb, M.; Reinke, M.L.; Rice, J.E.; Rowan, W. L.; Sampsell, M.; Schilling, G.; Schmidt, Andréa; Smick, N.; Смирнов, А. П.; Snipes, J. A.; Stotler, D.P.; Stillerman, J.; Tang, V.; Terry, D.R.; Terry, J. L.; Ulrickson, M.; Vieira, R.; Wallace, G. M.; Whyte, D.G.; Wilson, J. R.; Wright, G.M.; Wright, J. C.; Wolfe, S.; Wukitch, S.J.; Wurden, G. A.; Yuh, H.; Zhurovich, K.; Zaks, J.; Zweben, S. J.

doi:10.1088/0029-5515/49/10/104014

Cited by 32 publications

(33 citation statements)

References 42 publications

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“…In general, at Alcator C-Mod, 62 the heat transport in Ohmic L-mode discharges has proven to be very challenging to model with nonlinear gyrokinetic simulations. 9,10 In addition, there are several interesting transport observations in Alcator C-Mod Ohmic discharges that appear to occur together, highlighting the complex nature of coupled transport channels.…”

Section: Introductionmentioning

confidence: 99%

Quantitative comparison of electron temperature fluctuations to nonlinear gyrokinetic simulations in C-Mod Ohmic L-mode discharges

et al. 2016

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Long wavelength turbulent electron temperature fluctuations (kyρs < 0.3) are measured in the outer core region (r/a > 0.8) of Ohmic L-mode plasmas at Alcator C-Mod [E. S. Marmar et al., Nucl. Fusion 49, 104014 (2009)] with a correlation electron cyclotron emission diagnostic. The relative amplitude and frequency spectrum of the fluctuations are compared quantitatively with nonlinear gyrokinetic simulations using the GYRO code [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)] in two different confinement regimes: linear Ohmic confinement (LOC) regime and saturated Ohmic confinement (SOC) regime. When comparing experiment with nonlinear simulations, it is found that local, electrostatic ion-scale simulations (kyρs ≲ 1.7) performed at r/a ∼ 0.85 reproduce the experimental ion heat flux levels, electron temperature fluctuation levels, and frequency spectra within experimental error bars. In contrast, the electron heat flux is robustly under-predicted and cannot be recovered by using scans of the simulation inputs within error bars or by using global simulations. If both the ion heat flux and the measured temperature fluctuations are attributed predominantly to long-wavelength turbulence, then under-prediction of electron heat flux strongly suggests that electron scale turbulence is important for transport in C-Mod Ohmic L-mode discharges. In addition, no evidence is found from linear or nonlinear simulations for a clear transition from trapped electron mode to ion temperature gradient turbulence across the LOC/SOC transition, and also there is no evidence in these Ohmic L-mode plasmas of the “Transport Shortfall” [C. Holland et al., Phys. Plasmas 16, 052301 (2009)].

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Section: Introductionmentioning

confidence: 99%

Quantitative comparison of electron temperature fluctuations to nonlinear gyrokinetic simulations in C-Mod Ohmic L-mode discharges

et al. 2016

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“…4,5 Discharges with reduced particle confinement have been maintained steady state, with no degradation in energy confinement. LHRF thus provides a potential tool for decoupling particle and thermal transport in the pedestal and reducing operating collisionality at a given normalized pressure β.…”

Section: Introductionmentioning

confidence: 99%

Modification of H-mode pedestal structure with lower hybrid waves on Alcator C-Mod

et al. 2010

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The application of lower hybrid waves (LH) in H-mode plasmas on Alcator C-Mod can result in significant reduction of core particle inventory, with no significant degradation of energy confinement. This phenomenon has been observed in steady enhanced D α (EDA) H-mode targets, which are sustained by ion cyclotron RF auxiliary heating, in which pedestal density n ped is usually tied firmly to plasma current I P and shows a strong resilience to changes in the edge neutral source. Upon application of up to 1MW LH power, n ped is reduced by up to 30%, while the temperature profile increases simultaneously such that the pressure pedestal remains constant or is slightly increased.Steady EDA H-mode operation with no edge-localized modes (ELMs) can be maintained while edge collisionality is reduced by factors of reductions of 2-4. Elevation of scrapeoff layer (SOL) density and electric currents accompany the application of LH (at levels as low as 400kW) with a fast time response (~10 -2 s), while full density pedestal relaxation and core density reduction occur on longer time scales (~10 -1 s). A similarly prompt counter-I P change in the edge toroidal velocity is also observed in response to LHRF, followed on longer time scales by a counter-I P change in the central rotation. The range of time scales of the plasma response may indicate that the radial locations of LH interactions (i.e., SOL vs. core), and power deposition mechanisms, are evolving in time.Understanding the responsible physical mechanisms and applying them to a broad range of H-mode discharges could provide a tool for improving density control, affecting edge MHD stability and applying modulation for transport studies.

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“…the temperature increased to compensate for the density pumpout. The rotation profile also was observed to go strongly in the counter-I p direction [173]. These studies were performed in Enhanced D α H-mode plasmas [21,118], and so the effect on ELMs and edge stability was not a focal point.…”

Section: Lhh/lwcdmentioning

confidence: 99%

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Eroshenko¹

2013

Phys.-Usp.

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Large edge localized modes (ELMs) typically accompany good H-mode confinement in fusion devices, but can present problems for plasma facing components because of high transient heat loads. Here the range of techniques for ELM control deployed in fusion devices is reviewed. Two strategies in the ITER baseline design are emphasized: rapid ELM triggering and peak heat flux control via pellet injection, and the use of magnetic perturbations to suppress or mitigate ELMs. While both of these techniques are moderately well developed, with reasonable physical bases for projecting to ITER, differing observations between multiple devices are also discussed to highlight the needed community R&D. In addition, recent progress in ELM-free regimes, namely quiescent H-mode, I-mode, and enhanced pedestal H-mode is reviewed, and open questions for extrapolability are discussed. Finally progress and outstanding issues in alternate ELM control techniques are reviewed: supersonic molecular beam injection, edge electron cyclotron heating, lower hybrid heating and/or current drive, controlled periodic jogs of the vertical centroid position, ELM pace-making via periodic magnetic perturbations, ELM elimination with lithium wall conditioning, and naturally occurring small ELM regimes.

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Overview of the Alcator C-Mod Research Program

Cited by 32 publications

References 42 publications

Quantitative comparison of electron temperature fluctuations to nonlinear gyrokinetic simulations in C-Mod Ohmic L-mode discharges

Quantitative comparison of electron temperature fluctuations to nonlinear gyrokinetic simulations in C-Mod Ohmic L-mode discharges

Modification of H-mode pedestal structure with lower hybrid waves on Alcator C-Mod

Physics news on the Internet (based on electronic preprints)

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