Stabilization of energetic-ion-driven MHD modes by ECCD in Heliotron J

Nagasaki, K.; Yamamoto, Satoshi; Kobayashi, S.; Sakamoto, K.; Nagae, Y.; Sugimoto, Yuki; Nakamura, Yuji; Weir, G.; Marushchenko, N. B.; Mizuuchi, T.; Okada, H.; Minami, Takashi; Masuda, Kai; Ohshima, S.; Konoshima, S.; Shi, Nan; Lee, H. Y.; Zang, L.; Arai, S.; Watada, H.; Fukushima, Hideyuki; Hashimoto, Katsushi; Kinoshita, Naoki; Motojima, G.; Yoshimura, Y.; Mukai, K.; Volpe, F.; Estrada, T.; Sano, F.

doi:10.1088/0029-5515/53/11/113041

Cited by 20 publications

(26 citation statements)

References 28 publications

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“…Figure 1 (a) shows the radial profile of EC-driven plasma current density j EC calculated by ray tracing code TRAVIS [25] under experimental conditions. The N || scan of ECCD indicates that TRAVIS predictions are consistent with measured plasma current by Rogowski coil within a factor of 2 in Heliotron J plasmas [16,26].…”

Section: Methodssupporting

confidence: 55%

Suppression of fast-ion-driven MHD instabilities by ECH/ECCD on Heliotron J

et al. 2017

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Experiments of suppressing fast-ion-driven MHD instabilities such as energetic particle modes (EPMs) and global Alfvén eigenmodes (GAEs) have been made by using a second harmonic X-mode electron cyclotron heating (ECH) and current drive (ECCD) in the helical-axis heliotron device, Heliotron J. ECCD experiments show that the GAE destabilized by fast ions of neutral beam injection (NBI) with the observed frequency around 140 kHz are fully stabilized, and the EPMs with the observed frequency around 90 kHz are suppressed when the EC-driven plasma current flowing in the counter direction reaches approximately 0.7 kA. The low magnetic shear under the vacuum condition is modified into positive magnetic shear when counter-ECCD is applied, and the amplitude of GAEs and EPMs decreases with an increase of the EC-driven plasma current. These results indicate that magnetic shear is a key role in controlling GAEs as well as EPMs. The comparison of the calculation of shear Alfvén spectra with experimental results shows that the increasing continuum damping rate with an increase in local magnetic shear by EC-driven current is important for both EPMs and GAEs. Moreover, the increase in plasma current lead to the inward movement of GAEs. This effect would also contribute to suppression of GAEs because the continuum damping rate increases more and more toward core. Steady ECH is also found experimentally to be effective to control the amplitude of both GAEs and EPMs. The amplitude of EPMs, and especially for GAEs decreases with an increase in the ECH power under fixed density conditions.

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Section: Methodssupporting

confidence: 55%

Suppression of fast-ion-driven MHD instabilities by ECH/ECCD on Heliotron J

et al. 2017

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“…This prediction is consistent with the experimental results, and GAE and the EPM are often observed in the neutral beam injection (NBI) heating plasma of Heliotron J [8]. Recently, controlling an energetic-particle-driven mode was attempted using a current drive induced by electron cyclotron resonance heating (ECRH) and was successfully achieved through the mechanism of magnetic shear formation and/or a change in the rotational transform [9].…”

Section: Introductionsupporting

confidence: 86%

Edge plasma responses to energetic-particle-driven MHD instability in Heliotron J

et al. 2015

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Two different responses to an energetic-particle-driven magnetohydrodynamic (MHD) instability, modulation of the turbulence amplitude associated with the MHD instability and dynamical changes in the radial electric field (E r) synchronized with bursting MHD activities, are found around the edge plasma in neutral beam injection (NBI) heated plasmas of the Heliotron J device using multiple Langmuir probes. The nonlinear phase relationship between the MHD activity and broadband fluctuation is found from bicoherence and envelope analysis applied to the probe signals. The structural changes of the E r profile appear in perfect synchronization with the periodic MHD activities, and radial transport of fast ions are observed around the last closed flux surface as a radial delay of the ion saturation current signals. Moreover, distortion of the MHD mode structure is clarified in each cycle of the MHD activities using beam emission spectroscopy diagnostics, suggesting that the fast ion distribution in real and/or velocity spaces is distorted in the core plasma, which can modify the radial electric field structure through a redistribution process of the fast ions. These observations suggest that such effects as a nonlinear coupling with turbulence and/or the modification of radial electric field profiles are important and should be incorporated into the study of energetic particle driven instabilities in burning plasma physics.

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“…Experiments carried out on DIII-D also show that localized electron cyclotron heating (ECH) can drastically alter beam driven AE activity including, in some cases, the stabilization of RSAEs and improve fast ion confinement [64,141,142]. Similar experiments have been carried out on several devices, altering AE activity in Heliotron J [143] the TJ-II stellarators [144] and on ASDEX Upgrade [145]. The suppression occurs when ECH is deposited near q min in DIII-D experiments (Fig.…”

Section: Potential For Control or Avoidance Of Aes To Improve At Scenmentioning

confidence: 86%

DIII-D Research to Prepare for Steady State Advanced Tokamak Power Plants

et al. 2018

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We review progress made on the advanced tokamak path to fusion energy by the DIII-D National Fusion Facility (Luxon et al. in Nucl Fusion 42:614, 2002). The advanced tokamak represents a highly attractive approach for a future steady state fusion power plant. In this concept, there is a natural alignment between high pressure operation, favorable stability and transport properties, and a highly self-driven ('bootstrap') plasma current to sustain operation efficiently and without disruptions. Research on DIII-D has identified several promising plasma configurations for fully non-inductive operation with potential applications to a range of future devices, from ITER to nuclear science facilities, to compact or large scale fusion power plants. Significant progress has been made toward realizing these scenarios, with the demonstration of high b access, off-axis current drive techniques, model based profile control, and stability and ELM control in reactor relevant physics regimes. Radiative techniques have also been pioneered to develop improved compatibility with divertor requirements, and simultaneous access to high performance pedestals. Research has also developed major advances in physics understanding, validating concepts of kinetic damping of ideal MHD instabilities that enable high b operation, identifying how current profile and b influence plasma turbulence in order to validate and improve turbulent transport models, and understanding the physics of energetic particle redistribution due to Alfvénic and other instabilities. These advances have been partnered with development of a rigorous integrated modeling framework used to interpret and validate individual physics models of the various aspects of plasma behavior, and to guide development of improved regimes and upgrades. These tools are also being used to develop and validate concepts for future reactors directly. Having established these foundations, DIII-D is now undergoing a substantial upgrade to raise power, current drive, electron heating and 3-D field capabilities in order to validate this physics and test conceptual solutions in reactor-relevant physics regimes, with a goal to resolve the key scientific and technology questions to enable a decision on a future steady state fusion power plant.

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Stabilization of energetic-ion-driven MHD modes by ECCD in Heliotron J

Cited by 20 publications

References 28 publications

Suppression of fast-ion-driven MHD instabilities by ECH/ECCD on Heliotron J

Suppression of fast-ion-driven MHD instabilities by ECH/ECCD on Heliotron J

Edge plasma responses to energetic-particle-driven MHD instability in Heliotron J

DIII-D Research to Prepare for Steady State Advanced Tokamak Power Plants

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