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

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

doi:10.1063/1.4867066

Cited by 11 publications

(8 citation statements)

References 39 publications

(29 reference statements)

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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%

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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%

“…The present model was already used to study the stability of PM during sawtooth-like events and internal collapses [85][86][87][88], TAE [65] and EIC [89] activity in LHD, indicating reasonable agreement with the observations.…”

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

Self Cite

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show abstract

“…The present model was already used to study the linear stability of LHD plasma, particularly the AE destabilization by EP [22], AE stability of plasma with multiple EP populations [23], the effect of the tangential NBI current drive on the stability of pressure and EP driven MHD modes [24] as well as EIC stabilization strategies [25], showing a reasonable agreement with the observations. In addition, nonlinear studies were performed reproducing the sawtooth-like and internal collapse events observed in LHD plasma [26][27][28][29].…”

Section: T I (Kev)mentioning

confidence: 99%

Theoretical analysis of the saturation phase of the 1/1 energetic-ion-driven resistive interchange mode

et al. 2021

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The aim of the present study is to analyze the saturation regime of the energetic-ion-driven resistive interchange mode (EIC) in the LHD plasma. A set of non linear simulations are performed 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 hellically trapped EP component is introduced through a modification of the averaged drift velocity operator to include their precessional drift. The non linear simulation results show similar 1/1 EIC saturation phases with respect to the experimental observations, reproducing the enhancement of the n/m = 1/1 resistive interchange modes (RIC) amplitude and width as the EP β increases, the EP β threshold for the 1/1 EIC excitation, the further destabilization of the 1/1 EIC as the population of the helically trapped EP increases and the triggering of burst events. The frequency of the 1/1 EIC calculated during the burst event is 9.4 kHz and the 2/2 and 3/3 overtones are destabilized, consistent with the frequency range and the complex mode structure measured in the experiment. In addition, the simulation shows the inward propagation of the 1/1 EIC due to the non linear destabilization of the 3/4 and 2/3 EPMs, leading to the partial overlapping between resonances during the burst event. Finally, the analysis of the 1/1 EIC stabilization phase shows the excitation of the 1/1 RIC as soon as the flattening induced by the 1/1 EIC in the pressure profile vanishes, leading to the retrieval of the pressure gradient at the plasma periphery and the overcoming of the RIC stability limit.

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“…In the case of the hard MHD limit, the instability spreads on modes with different helicities along the plasma and the events driven are global relaxations. The events studied in the soft MHD limit are the non resonant 1/3 and 1/2 sawtooth like events, and the internal disruptions and resonant 1/3 sawtooth like events in the hard MHD limit 9,11,12 . There is experimental evidence of these events in LHD, expect in the case of the internal disruption 13 .…”

Section: Introductionmentioning

confidence: 99%

Magnetic turbulence and pressure gradient feedback effect of the 1/2 mode soft-hard magnetohydrodynamic limit in large helical device

et al. 2014

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The aim of this study is to analyze the feedback process between the magnetic turbulence and the pressure gradients in LHD inward-shifted configurations as well as its role in the transition between the soft-hard MHD regimes for instabilities driven by the mode 1/2 in the middle plasma. In the present paper we summarize the results of two simulations with different Lundquist numbers, S = 2.5 × 10 5 and 10 6 , assuming a plasma in the slow reconnection regime. The results for the high Lundquist number simulation shows that the magnetic turbulence and the pressure gradient in the middle plasma region of LHD are below the critical value to drive the transition to the hard MHD regime, therefore only relaxations in the soft MHD limit are triggered (1/2 sawtooth like events) [Phys. Plasmas 19, 082512 (2012)]. In the case of the simulation with low Lundquist number, the system reaches the hard MHD limit and a plasma collapse is observed.

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

Cited by 11 publications

References 39 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

Theoretical analysis of the saturation phase of the 1/1 energetic-ion-driven resistive interchange mode

Magnetic turbulence and pressure gradient feedback effect of the 1/2 mode soft-hard magnetohydrodynamic limit in large helical device

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