Observation of Low Frequency MHD Mode Driven by Energetic Particles in Large Helical Device Plasmas with Strong Interchange Mode Activities

Chen, Wei; Isobe, M.; Toi, K.; Ogawa, K.; Du, Xiaodi; Osakabe, M.; Ohdachi, S.

doi:10.1585/pfr.7.2402079

Cited by 7 publications

(4 citation statements)

References 17 publications

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“…A similar experimental result was also reported in Large Helical Device (LHD) low density plasmas [29], and it suggested the BAEs and EGAM were all excited during the strong interchange (IC) mode with neutral beam injection + electron cyclotron resonance heating, and the frequencies of BAEs and EGAM are constant. But after the ECRH was switched-off, the BAEs and IC modes disappeared, and the EGAM frequency was upwardsweeping.…”

Section: Experimental Conditions and Mode-number Analysissupporting

confidence: 77%

Observation of energetic-particle-induced GAM and nonlinear interactions between EGAM, BAEs and tearing modes on the HL-2A tokamak

Chen

Ding

et al. 2013

Nucl. Fusion

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In our previous letter, the geodesic acoustic mode (GAM) induced by energetic particles (EGAMs) was reported in low density ohmic plasma on HL-2A (Chen et al 2013 Phys. Lett. A 377 387). We extend the experimental results of the EGAM mode in this paper. During strong tearing modes (TMs), the beta-induced Alfvén eigenmodes (BAEs) and EGAM-induced density fluctuations are firstly measured by microwave Doppler reflectometers with different work frequencies. As predicted by theory, the measurements of magnetic probes and Doppler reflectometers suggest the EGAM magnetic oscillations have poloidal/toroidal mode numbers of m/n = 2/0, and are localized in the core with a broad radial structure. The mode frequency is less than that of the conventional GAM (i.e. fEGAM/fGAM < 1), and is constant in the radial direction. Our experimental results suggest that a density limit exists for the excitation of the EGAM in the ohmic plasma, and the density limit is improved with electron cyclotron resonance heating + neutral beam injection heating on HL-2A. The auto and cross squared bicoherences of magnetic and density fluctuations indicate that intense nonlinear interactions exist among EGAM, BAEs and strong TMs. These new observations will help us to understand the underlying physics mechanism for the excitation of fluctuations in the sub-Alfvén frequency range.

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Section: Experimental Conditions and Mode-number Analysissupporting

confidence: 77%

Observation of energetic-particle-induced GAM and nonlinear interactions between EGAM, BAEs and tearing modes on the HL-2A tokamak

Chen

Ding

et al. 2013

Nucl. Fusion

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“…Recently, BAEs have also been observed during strong tearing mode activities in FTU (Ohmic plasmas), TEXTOR (low-density plasmas) and HL-2A (electron cyclotron resonance heating (ECRH) or low-density plasmas) without fast ions [11][12][13][14]. BAEs are also reported in HL-2A ECRH plasmas with fast electrons [15], during a sawtooth cycle in ASDEX-U and Tore Supra plasmas with fast ions [16,17] and LHD [18] plasmas during strong interchange modes. BAEs during strong tearing modes are characterized by mode numbers (m, n) and (−m, −n) propagating at exactly the opposite velocity in the island rest frame and they appear when the island has reached a certain amplitude.…”

Section: Introductionmentioning

confidence: 99%

Experimental observation of beta-induced Alfvén eigenmodes during strong tearing modes on the EAST tokamak in fast-electron plasmas

Chen

et al. 2013

Plasma Phys. Control. Fusion

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Beta-induced Alfvén eigenmodes (BAEs) during strong tearing modes are investigated on the EAST tokamak systematically, and the relation between the BAE frequencies and plasma parameters such as electron density ne , ion temperature T i , the profile of safety factor q(ρ) or the intensity of Ḃθ (the width of the magnetic island w) is given in detail during the injection of the power of lower hybrid wave (LHW) (or is also accompanied by the injection of ion cyclotron resonance frequency) comprehensively. All the conditions show that the values of BAE frequencies f BAE ∝ (T e + 7 4 T i ) 1/2 are in agreement with the generalized fishbone-like dispersion relation, and the activities of the BAEs have a strong interaction with the process of magnetic reconnection.The BAEs are formed during the injection of the power of LHW, and disappear immediately when the power of LHW is turned off on the EAST tokamak. The LHW plasmas or the runaway discharge in Ohmic plasmas can increase the population of fast electrons, which plays a role in the activities of BAEs and a possible excitation mechanism for the BAEs during the strong tearing mode activities.

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“…Plasma destabilization by energetic particles (EP) injected via neutral beam injectors (NBI) is routinely observed in Large Helical Device (LHD) discharges [1][2][3][4][5][6][7][8][9]. EP-driven instabilities enhance the EP transport leading to EP losses before thermalization, reducing the LHD performance due to inefficient plasma heating [10][11][12][13][14][15][16][17][18][19].…”

Section: Introductionmentioning

confidence: 99%

Simulation of the TAEs’ saturation phase in the Large Helical Device: MHD burst

Varela¹,

Spong²,

Todo³

et al. 2022

Nucl. Fusion

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The aim of the present study is to analyze the saturation regime of the Toroidal Alfven Eigenmodes (TAE) in the LHD plasma, particularly the MHD burst. The linear and non linear evolution of the TAEs are simulated by the FAR3d code that uses a reduced MHD model for the thermal plasma coupled with a gyrofluid model for the energetic particles (EP) species. The linear simulations indicate the overlapping of $1/2-1/1$, $2/3-2/4$ and $3/5-3/6$ TAEs in the inner-middle plasma region and frequency range of $45-75$ kHz, triggered by EPs with an energy of $T_{f} = 45$ keV and EP $\beta = 0.022 $. The non linear simulations show that $2/3-2/4$ and $3/4-3/5$ TAEs are further destabilized due to the energy transfer from $1/1-1/2$ TAE, leading to a broad TAEs radial overlapping and the MHD burst triggering. The energy of $1/1-1/2$ TAE is also non linearly transferred to the thermal plasma destabilizing the $0/0$ and $0/1$ modes, inducing the generation of shear flows and zonal currents as well as large deformations in the thermal pressure and EP density radial profiles. The non linear simulation reproduces the same succession of instabilities and the same frequency range with respect to the experiment. The instability propagates outward during the bursting phase, showing a large decrease of the EP density profile between the middle-outer plasma, pointing out the loss of part of the EP population that explains the decrease of the plasma heating efficiency observed during the MHD burst.

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Observation of Low Frequency MHD Mode Driven by Energetic Particles in Large Helical Device Plasmas with Strong Interchange Mode Activities

Cited by 7 publications

References 17 publications

Observation of energetic-particle-induced GAM and nonlinear interactions between EGAM, BAEs and tearing modes on the HL-2A tokamak

Observation of energetic-particle-induced GAM and nonlinear interactions between EGAM, BAEs and tearing modes on the HL-2A tokamak

Experimental observation of beta-induced Alfvén eigenmodes during strong tearing modes on the EAST tokamak in fast-electron plasmas

Simulation of the TAEs’ saturation phase in the Large Helical Device: MHD burst

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