The internal disruption as hard Magnetohydrodynamic limit of 1/2 sawtooth like activity in large helical device

Varela, J.; Watanabe, K. Y.; Ohdachi, S.

doi:10.1063/1.4747534

Cited by 14 publications

(14 citation statements)

References 22 publications

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“…The present model was already used to study the stability of PM during sawtooth-like events and internal collapses [88,89,90,91], TAE [68] and EIC [92] activity in LHD, indicating reasonable agreement with the observations. T th,0 n th,0 < β tot > V A0 (keV) (10 20 m −3 ) (%) (10 6 m/s) 4 0.3 1.8 3.98 Table 1.…”

Section: Equations and Numerical Schemesupporting

confidence: 80%

Effect of the tangential NBI current drive on the stability of pressure and energetic particle driven MHD modes in LHD plasma

Varela¹,

Cooper²,

Nagaoka³

et al. 2020

Nucl. Fusion

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The aim of the present study is to analyze the stability of the pressure gradient driven modes (PM) and Alfvén eigenmodes (AE) in the Large Helical Device (LHD) plasma if the rotational transform profile is modified by the current drive of the tangential neutral beam injectors (NBI). This study forms a basic search for optimized operation scenarios with reduced mode activity. The analysis is performed using the code FAR3d which solves the reduced MHD equations describing the linear evolution of the poloidal flux and the toroidal component of NBI current drive 2 the vorticity in a full 3D system, coupled with equations for density and parallel velocity moments of the energetic particle (EP) species, including the effect of the acoustic modes. The Landau damping and resonant destabilization effects are added via the closure relation. On-axis and off-axis NBI current drive modifies the rotational transform which becomes strongly distorted as the intensity of the neutral beam current drive (NBCD) increases, leading to wider continuum gaps and modifying the magnetic shear. The simulations with on-axis NBI injection show that a counter (ctr-) NBCD in inward shifted and default configurations leads to a lower growth rate of the PM, although strong n = 1 and 2 AEs can be destabilized. For the outward shifted configurations, a co-NBCD improves the AEs stability but the PM are further destabilized if the co-NBCD intensity is 30 kA/T. If the NBI injection is off-axis, the plasma stability is not significantly improved due to the further destabilization of the AE and energetic particle modes (EPM) in the middle and outer plasma region.

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Section: Equations and Numerical Schemesupporting

confidence: 80%

Effect of the tangential NBI current drive on the stability of pressure and energetic particle driven MHD modes in LHD plasma

Varela¹,

Cooper²,

Nagaoka³

et al. 2020

Nucl. Fusion

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“…Previous investigations pointed out that this LHD configuration remains in the soft MHD limit for the instabilities driven in the middle plasma region 25 . Only the 1/2 sawtooth like events are driven, not its version in the hard MHD limit called internal disruption 26,27 .…”

Section: Introductionmentioning

confidence: 71%

Hard magnetohydrodynamic limit in 1/3 sawtooth like activity in LHD

et al. 2014

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The optimization of LHD discharges in inward-shifted configurations with 1/3 sawtooth like activity is an open issue. These relaxation events limit the LHD performance driving a periodic plasma deconfinement. The aim of this study is to analyze the 1/3 sawtooth like activity in plasmas with different stability properties to foreseen the best operation conditions and minimize its undesired effects. We summarize the results of several MHD simulations for plasmas with Lundquist numbers between 10 5 and 10 6 in the slow reconnection regime, studying the equilibria properties during the onset of a chain of 1/3 sawtooth like events. The research conclusions point out that the hard MHD limit can be reached in the inner plasma region after the onset of a strong 1/3 resonant sawtooth like event and trigger a plasma collapse. The collapse can be avoided if the system remains in the soft MHD limit, namely in a regime with a pressure gradient and a magnetic turbulence below the critical values to drive the soft-hard MHD transition. In the soft MHD limit the system relaxations are the non resonant 1/3 sawtooth like events or a weak version of the 1/3 resonant sawtooth like events. A system relaxation in the soft MHD regime drives a minor plasma deconfinement that doesn't limit the LHD performance if the event periodicity is not very high.

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“…6 There are also many simulation studies about the effect of the resistive interchange instability in the nonlinear saturation phase on the plasma confinement property. [7][8][9][10][11] The characteristics of the perturbed current due to the resistive interchange instability and the consequent magnetic island have been reported, although the reports are for the limited range of the b value and the S number. However, it is increasing for the demand of the systematical prediction of the characteristics of the resistive interchange instability, e.g., the magnetic island formation property, to interpret the LHD experiments results.…”

Section: Introductionmentioning

confidence: 99%

Characteristics of magnetic island formation due to resistive interchange instability in helical plasma

et al. 2014

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Focusing attention on the magnetic island formation, we investigate the characteristics of the resistive interchange magnetohydrodynamics instabilities, which would limit a high beta operational regime in helical type fusion reactors. An introduction of a new index, i.e., the ratio of the magnetic fluctuation level to the radial displacement, enables us to make a systematic analysis on the magnetic island formation in the large helical device-like plasmas during the linear growth phase; (i) the interchange instability with the second largest growth rate makes the magnetic island larger than that with the largest growth rate when the amplitude of the radial displacement in both cases is almost the same as each other; (ii) applied to a typical tearing instability, the index is smaller than that for the interchange instability with the second largest growth rate

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The internal disruption as hard Magnetohydrodynamic limit of 1/2 sawtooth like activity in large helical device

Cited by 14 publications

References 22 publications

Effect of the tangential NBI current drive on the stability of pressure and energetic particle driven MHD modes in LHD plasma

Effect of the tangential NBI current drive on the stability of pressure and energetic particle driven MHD modes in LHD plasma

Hard magnetohydrodynamic limit in 1/3 sawtooth like activity in LHD

Characteristics of magnetic island formation due to resistive interchange instability in helical plasma

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