The anomalous Doppler instability during lower-hybrid current drive

Luckhardt, S.C.; Bers, A.; Fuchs, V.; Shoucri, M.

doi:10.1063/1.866146

Cited by 15 publications

(10 citation statements)

References 6 publications

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“…The low-density discharge regime is characterized by a large energetic-electron population. When the ratio of the electron plasma frequency to electron cyclotron frequency ω pe /ω ce < 0.3, according to the empirical values in a number of devices, an anomalous Doppler instability (ADI) can be excited [21][22][23][24]. For discharge #10580 with toroidal field B t = 1.3 T, the ADI is excited when the density is less than the critical density n ec ≈ 0.14 × 10 19 m −3 .…”

Section: Baes Excited By Energetic Electronsmentioning

confidence: 99%

Destabilization of beta-induced Alfvén eigenmodes in the HL-2A tokamak

Chen

Ding²,

Liu

et al. 2011

Nucl. Fusion

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Beta-induced Alfvén eigenmode (BAE) during a strong tearing mode activity (termed as m-BAE) has been observed and investigated in HL-2A. BAE excited by energetic electrons (termed as e-BAE) has been identified both in the Ohmic and ECRH plasma. The hard x-ray spectrum detected by cadmium telluride and the non-thermal radiation measured by electron cyclotron emission are used to analyse the behaviour of the energetic electrons. Experimental results show that the e-BAE is related not only to the populations of the energetic electrons, but also their energy distribution. An interesting result about the BAEs modulated by a supersonic molecular beam and gas puffing is presented. In addition, BAEs during a sawtooth cycle are described in this paper. To assess the identification of the e-BAE and m-BAE, the generalized fishbone-like dispersion relation and magnetic-island-induced BAE dispersion relation are solved near marginal stability, respectively. Compared with experimental results, the calculation analysis shows that the observed frequencies are all close to the theoretical results.

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Section: Baes Excited By Energetic Electronsmentioning

confidence: 99%

Destabilization of beta-induced Alfvén eigenmodes in the HL-2A tokamak

Chen

Ding²,

Liu

et al. 2011

Nucl. Fusion

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“…pe =! ce < 0:3 according to the empirical values in several machines, the anomalous Doppler instability (ADI) can be excited [16][17][18][19]. For no.…”

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confidence: 99%

β-Induced Alfvén Eigenmodes Destabilized by Energetic Electrons in a Tokamak Plasma

et al. 2010

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The β-induced Alfvén eigenmode (BAE) excited by energetic electrons has been identified for the first time both in the Ohmic and electron cyclotron resonance heating plasma in HL-2A. The features of the instability, including its frequency, mode number, and propagation direction, can be observed by magnetic pickup probes. The mode frequency is comparable to that of the continuum accumulation point of the lowest frequency gap induced by the shear Alfvén continuous spectrum due to finite β effect, and it is proportional to Alfvén velocity at thermal ion β held constant. The experimental results show that the BAE is related not only with the population of the energetic electrons, but also their energy and pitch angles. The results indicate that the barely circulating and deeply trapped electrons play an important role in the mode excitation.

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“…Many studies report observational signatures of this plateau-like electron distribution in Alcator tokamak 3,4 as well as use it extensively to explain radiation patterns and heating observed in experiments. 5,6 The agreement between the predicted and measured profiles is usually good, but on the other hand, even some recent works report discrepancies between the measured and simulated hard x-ray spectra that may be explained by neglected or underestimated electron diffusion physics. 4 In the type III radio burst problem, the solar burst electrons are accelerated and eventually the-bump-on-tail distribution is formed on the electron distribution function.…”

Section: Introductionmentioning

confidence: 95%

“…8 and 9 that the electron distribution with a tail of energetic electrons that have a plateau-like or even decreasing power-like distribution function is unstable with respect to excitation of waves at anomalous Doppler resonance (ADR). 6 x ð2Þ k À k ð2Þ z v z þ x ce ¼ 0; where x ð2Þ k and k ð2Þ z are the frequency and parallel wave number for excited waves. This is so-called fan instability that is an effective mechanism of pitch angle diffusion of the tail electrons.…”

Section: Introductionmentioning

confidence: 99%

A stochastic mechanism of electron heating

Galinsky

Shevchenko

2012

Physics of Plasmas

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Due to Landau resonant interaction with lower hybrid waves in the lower hybrid current drive scheme part of electrons are accelerated and, as a result of this, a tail of energetic electrons is formed on the electron distribution function. The same situation takes place in the problem of type III radio bursts when the suprathermal burst electrons acquire a plateau distribution due to excitation of plasma waves in the solar wind plasma. These distributions are unstable with respect to the cyclotron excitation of waves at anomalous Doppler resonance ("fan" instability). In this case, the tail electrons interact simultaneously with both (i) waves that accelerate or decelerate them ( Cerenkov resonance) and (ii) waves excited in the process of the fan instability that led to their pitch angle diffusion. Because velocity diffusion lines of electrons formed due to heir interaction with each type of waves intersect, this interaction can lead not only to pitch angle diffusion but also to heating of electrons mainly in perpendicular direction. We investigated this mechanism of electron heating and studied the temporal evolution of the electron temperature and the energy of excited waves. Our results show significant enhancement of the electron perpendicular temperature T ? due to this stochastic heating mechanism. V C 2012 American Institute of Physics. [http://dx.

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The anomalous Doppler instability during lower-hybrid current drive

Cited by 15 publications

References 6 publications

Destabilization of beta-induced Alfvén eigenmodes in the HL-2A tokamak

Destabilization of beta-induced Alfvén eigenmodes in the HL-2A tokamak

β-Induced Alfvén Eigenmodes Destabilized by Energetic Electrons in a Tokamak Plasma

A stochastic mechanism of electron heating

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