Resistive stability of a plasma with runaway electrons

Helander, P.; Grasso, D.; Hastie, R. J.; Perona, A.

doi:10.1063/1.2817016

Cited by 32 publications

(81 citation statements)

References 17 publications

(41 reference statements)

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“…Whilst the ideal MHD modes are insensitive to the nature of plasma current (Ohmic or RE), the resistive MHD instability in runaway plasmas was investigated in [11]. It was shown that the linear growth rate of the resistive modes in a runaway-dominated plasma is approximately the same as in a plasma without runaways, but with the same current profile.…”

Section: Tokamaksmentioning

confidence: 99%

Linear MHD stability analysis of post-disruption plasmas in ITER

Aleynikova

Huijsmans²,

Aleynikov

2016

Plasma Phys. Rep.

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Most of the plasma current can be replaced by a runaway electron (RE) current during plasma disruptions in ITER. In this case the post-disruption plasma current profile is likely to be more peaked than the pre-disruption profile. The MHD activity of such plasma will affect the runaway electron generation and confinement and the dynamics of the plasma position evolution (Vertical Displacement Event), limiting the timeframe for runaway electrons and disruption mitigation. In the present paper, we evaluate the influence of the possible RE seed current parameters on the onset of the MHD instabilities. By varying the RE seed current profile, we search for subsequent plasma evolutions with the highest and the lowest MHD activity. This information can be applied to a development of desirable ITER disruption scenario.

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Section: Tokamaksmentioning

confidence: 99%

Linear MHD stability analysis of post-disruption plasmas in ITER

Aleynikova

Huijsmans²,

Aleynikov

2016

Plasma Phys. Rep.

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“…31 Previous work found that the linear properties of the classical tearing mode are essentially determined by the thermal plasma, and linear stability is approximately the same as in a plasma without REs but with the same current profile. 32 Unfortunately, internal measurements of the current profile are not possible in these conditions, as the heating beam used for motional stark effect (MSE) measurements fuels the discharge, overwhelms the ohmic heating power, and compromises RE emission measurements. However, no measurable change in internal inductance ( i ) is observed in these plasmas -both on the long time scale of the gradual HXR growth and the prompt time scale of the ECE rise.…”

Section: B Classical Instabilitymentioning

confidence: 99%

The non-thermal origin of the tokamak low-density stability limit

Paz-Soldan¹,

Haye²,

Shiraki³

et al. 2016

Nucl. Fusion

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DIII-D plasmas at very low density exhibit onset of n=1 error field (EF) penetration (the 'low-density locked mode') not at a critical density or EF, but instead at a critical level of runaway electron (RE) intensity. Raising the density during a discharge does not avoid EF penetration, so long as RE growth proceeds to the critical level. Penetration is preceded by non-thermalization of the electron cyclotron emission, anisotropization of the total pressure, synchrotron emission shape changes, as well as decreases in the loop voltage and bulk thermal electron temperature. The same phenomena occur despite various types of optimal EF correction, and in some cases modes are born rotating. Similar phenomena are also found at the low-density limit in JET. These results stand in contrast to the conventional interpretation of the low-density stability limit as being due to residual EFs and demonstrate a new pathway to EF penetration instability due to REs. Existing scaling laws for penetration project to increasing EF sensitivity as bulk temperatures decrease, though other possible mechanisms include classical tearing instability, thermo-resistive instability, and pressure-anisotropy driven instability. Regardless of first-principles mechanism, known scaling laws for Ohmic energy confinement combined with theoretical RE production rates allow rough extrapolation of the RE criticality condition, and thus the low-density limit, to other tokamaks. The extrapolated low-density limit by this pathway decreases with increasing machine size and is considerably below expected operating conditions for ITER. While likely unimportant for ITER, this mechanism can explain the low-density limit of existing tokamaks operating with small residual EFs.

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“…Here, we introduce a simple modification of the resistive MHD equations, similar to the one used in Ref. [3], to investigate the potential impact of fast electrons on turbulence. In this model, both thermal and fast electrons contribute to the total current.…”

Section: Mhd Modelmentioning

confidence: 99%

Effect of fast electrons on the stability of resistive interchange modes in the TJ-II stellarator

Garcia

Ochando

Carreras³

et al. 2016

Physics of Plasmas

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In this paper, we report on electromagnetic phenomena in low-β plasmas at the TJ-II stellarator, controlled by external heating. To understand the observations qualitatively, we introduce a simple modification of the standard resistive MHD equations, to include the potential impact of fast electrons on instabilities. The dominant instabilities of the modeling regime are resistive interchange modes, and calculations are performed in a configuration with similar characteristics as the TJ-II stellarator. The main effect of the trapping of fast electrons by magnetic islands induced by MHD instabilities is to increase the magnetic component of the fluctuations, changing the character of the instability to tearing-like and modifying the frequency of the modes. These effects seem to be consistent with some of the experimental observations.

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Resistive stability of a plasma with runaway electrons

Cited by 32 publications

References 17 publications

Linear MHD stability analysis of post-disruption plasmas in ITER

Linear MHD stability analysis of post-disruption plasmas in ITER

The non-thermal origin of the tokamak low-density stability limit

Effect of fast electrons on the stability of resistive interchange modes in the TJ-II stellarator

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