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

Ohshima, S.; Kobayashi, S.; Yamamoto, Satoshi; Nagasaki, K.; Mizuuchi, T.; Okada, H.; Minami, Takashi; Hashimoto, K.; Shi, Nan; Zang, L.; Kasajima, K.; Kinoshita, Naoki; Ohtani, Y.; Nagae, Y.; Mukai, K.; Lee, H.Y.; Matsuura, Hiroto; Takeuchi, Masaki; Konoshima, S.; Sano, F.

doi:10.1088/0029-5515/56/1/016009

Cited by 10 publications

(9 citation statements)

References 27 publications

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“…For example, two-dimensional electron cyclotron emission (ECE) imaging data from DIII-D showed a radially twisted reversed shear Alfvén eigenmode (RSAE) that could not be reproduced in ideal MHD but was reproduced when a fast-ion gradient was included in the gyrofluid model [17]. Other experimental examples of radial phase variation in 1D and 2D measurements include [18][19][20][21][22][23][24]. Simulations have noted 'croissant' [5] and 'boomerang' [10] 2D structures for beta-induced Alfvén eigenmodes (BAE).…”

Section: Introductionmentioning

confidence: 99%

The radial phase variation of reversed-shear and toroidicity-induced Alfvén eigenmodes in DIII-D

Heidbrink¹,

Hansen²,

Austin³

et al. 2022

Nucl. Fusion

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The eigenfunction of an instability contains information about energy flow in the wave. In this study, the amplitude and phase of electron cyclotron emission (ECE) radiometer data from hundreds of DIII-D reversed shear Alfven eigenmodes (RSAE) and toroidicity-induced Alfven eigenmodes (TAE) are analyzed along the outboard horizontal midplane. The radial phase profile can be flat, linearly rising or falling, convex or concave; in other words, a wide variety of shapes is observed. For a particular mode, often the radial phase profile remains approximately constant as the mode evolves in time but sometimes it changes rapidly. Many TAEs and some RSAEs have phase profiles that are rather flat where the mode amplitude is largest but rise steadily by ~2pi at large major radius. Rapid phase changes are observed when the frequencies of an RSAE and TAE overlap and the modes couple. The phase profile depends weakly on the fast-ion gradient that would appear in the absence of wave-induced transport. Linear and quadratic fits to the phase profiles, together with many plasma parameters, are assembled into RSAE and TAE databases. In both cases, large variability is observed. For RSAEs, the strongest phase dependencies are on electron temperature Te, RSAE mode frequency, and the density of carbon impurities. For TAEs, the strongest dependencies are on beam power and major radius of the mode. In general, the average RSAE radial phase profile is essentially flat but the TAE profile has non-zero slope and curvature.

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Section: Introductionmentioning

confidence: 99%

The radial phase variation of reversed-shear and toroidicity-induced Alfvén eigenmodes in DIII-D

Heidbrink¹,

Hansen²,

Austin³

et al. 2022

Nucl. Fusion

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“…7,8 The impact of the energetic particle driven MHD bursts on bulk plasmas has also been studied. 9,10 However, there are few experimental results reported on the impact of these MHD instabilities on ion velocity distribution of bulk ions.…”

Section: Introductionmentioning

confidence: 99%

Observation of distorted Maxwell-Boltzmann distribution of epithermal ions in LHD

et al. 2017

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A distorted Maxwell-Boltzmann distribution of epithermal ions is observed associated with the collapse of energetic ions triggered by the tongue shaped deformation. The tongue shaped deformation is characterized by the plasma displacement localized in the toroidal, poloidal, and radial directions at the non-rational magnetic flux surface in toroidal plasma. Moment analysis of the ion velocity distribution measured with charge exchange spectroscopy is studied in order to investigate the impact of tongue event on ion distribution. A clear non-zero skewness (3rd moment) and kurtosis (4th moment -3) of ion velocity distribution in the epithermal region (within three times of thermal velocity) is observed after the tongue event. This observation indicates the clear evidence of the distortion of ion velocity distribution from Maxwell-Boltzmann distribution. This distortion from Maxwell-Boltzmann distribution is observed in one-third of plasma minor radius region near the plasma edge and disappears in the ion-ion collision time scale.

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“…The upper limit of the detectable frequency for density oscillations is 200 kHz, which is determined by the cut-off frequency of the current amplifier. The BES is routinely used to identify the radial location of MHD modes in Heliotron J [37,38,44]. A perpendicularly viewed gas-puffing imaging (GPI) system is installed at the #14.5 section to observe the edge density fluctuation [45,46].…”

Section: Diagnostics and Analysis Techniquesmentioning

confidence: 99%

Observation of a beam-driven low-frequency mode in Heliotron J

et al. 2019

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A low-frequency electromagnetic mode (LF-mode) has been observed in a stellarator/heliotron device, Heliotron J. The LF-mode is observed only in neutral beam heated plasmas with a co-current, which increases the rotational transform. The observed LF-mode peaks at rho = 0.86–0.91, where rho = r/a is the normalized minor radius. The LF-mode propagates in the ion diamagnetic drift direction, and the poloidal mode number is m ~ 6–8, determined with a combination of Mirnov coil arrays and 2D fast camera measurement. A high m number induces significant Doppler shift from the background ion flow. The frequency is corrected with both E × B rotation and the ion diamagnetic flow. The corrected frequency is almost consistent with the beta-induced Alfvén eigenmode gap evaluated with the STELLGAP code, although very close to the accumulation point. The mode could also be a global Alfvén eigenmode.

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

Cited by 10 publications

References 27 publications

The radial phase variation of reversed-shear and toroidicity-induced Alfvén eigenmodes in DIII-D

The radial phase variation of reversed-shear and toroidicity-induced Alfvén eigenmodes in DIII-D

Observation of distorted Maxwell-Boltzmann distribution of epithermal ions in LHD

Observation of a beam-driven low-frequency mode in Heliotron J

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