Global gyrokinetic nonlinear simulations of kinetic infernal modes in reversed shear tokamaks

Ishida, Yuichi; Ishizawa, A.; Imadera, Kenji; Kishimoto, Y.; Nakamura, Yuji

doi:10.1063/5.0013349

Cited by 6 publications

(5 citation statements)

References 50 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It is found that the stable local maximum of E r is formed near the q min surface only in the kinetic electron cases (b) and (c). This is because the kinetic electron dynamics provide a finite phase difference between density perturbation and electrostatic potential, leading to a more unstable infernal type of linear ITG instability near the q min and resultant stronger zonal flow generation [28]. From some linear and nonlinear benchmark tests, it is confirmed that the linear growth rate in the hybrid electron case is roughly 1.7 times larger than that in the adiabatic electron case and the established zonal flow is corrugated, leading to the nonlinear upshift of critical ITG (∼ 10%).…”

Section: Spontaneous Itb Formation In Reversed Magnetic Shear Plasmamentioning

confidence: 99%

ITB formation in gyrokinetic flux-driven ITG/TEM turbulence

Imadera¹,

Kishimoto²

2022

Plasma Phys. Control. Fusion

View full text Add to dashboard Cite

The formation mechanism of Internal Transport Barriers (ITBs) in flux-driven turbulence is studied by means of the full-f gyrokinetic code GKNET. In the adiabatic electron case with a weak magnetic shear configuration, toroidal momentum injection can change the radial mean electric field E_r through the radial force balance, leading to a kind of driven ITB formation in which the ion thermal diffusivity by Ion Temperature Gradient (ITG) turbulence decreases to the neoclassical transport level. Only co-current toroidal rotation in the outer region can benefit the ITB formation, which mechanism is identified to originate from a positive feedback loop between the radial E_r shear and resultant momentum flux. On the other hand, in the kinetic electron case with a reversed magnetic shear configuration, robust co-intrinsic rotation is driven near the q_min surface in ITG turbulence and sustain the E_r shear through the radial force balance, leading to the spontaneous reduction of ion turbulent thermal diffusivity, while it is not observed in the adiabatic electron case. In the presence of electron heating, counter-intrinsic rotation by Trapped Electron Mode (TEM) turbulence is selectively driven in the negative magnetic shear region, which provides steeper E_r shear formation and resultant larger reduction of ion turbulent thermal diffusivity. It indicates that the co-existence of different modes can trigger the discontinuity near q_min and then spontaneous ITB formation.

show abstract

Section: Spontaneous Itb Formation In Reversed Magnetic Shear Plasmamentioning

confidence: 99%

ITB formation in gyrokinetic flux-driven ITG/TEM turbulence

Imadera¹,

Kishimoto²

2022

Plasma Phys. Control. Fusion

View full text Add to dashboard Cite

show abstract

“…The global effect is found to be a key to resolve the problem, and leads to a quasi-steady turbulent state [37][38][39][40][41][42]. In addition, global simulations enable us to evaluate turbulent transport in zero magnetic shear region which can appear in plasmas with weak or reversed magnetic shear [43,44], from which internal transport barrier is initiated in higher input power regime [45].…”

Section: Introductionmentioning

confidence: 99%

Plasma beta dependence of turbulent transport suggesting an advantage of weak magnetic shear from local and global gyrokinetic simulations

Ishizawa,

Kishimoto,

Imadera

et al. 2024

Nucl. Fusion

Self Cite

View full text Add to dashboard Cite

A higher plasma $\beta$ is desirable for realizing high performance fusion reactor, in fact, one of the three goals of JT-60SA project is to achieve a high-$\beta$ regime. We investigate key physical processes that regulate the $\beta$ dependence of turbulent transport in L-mode plasmas by means of both local and global gyrokinetic simulations. From local simulations, we found that the turbulent transport does not decrease as $\beta$ increases, because the electromagnetic stabilizing effect is canceled out by the increase of the Shafranov shift. This influence of the Shafranov shift is suppressed when the magnetic shear is weak, and thus the electromagnetic stabilization is prominent in weak shear plasmas, suggesting an advantage of weak magnetic shear plasmas for achieving a high-$\beta$ regime. In high $\beta$ regime, local gyrokinetic simulations are suffered from the non-saturation of turbulence level. In global simulations, by contrast, the electromagnetic turbulence gets saturated by the entropy advection in the radial direction to avoid the zonal flow erosion due to magnetic fluctuations. This breakthrough enables us to explore turbulent transport at a higher $\beta$ regime by gyrokinetic simulations.

show abstract

“…In addition to the fluid models, kinetic models have also been used for the analysis of the infernal modes. The linear stability analysis [15] and the nonlinear simulation analysis [16] of kinetic infernal modes in circular cross-section tokamaks have been performed using a gyrokinetic model.…”

Section: Introductionmentioning

confidence: 99%

“…Figure16. The radial profile of the (m, n) = (0, 0) component of the pressure at the initial state (the black curve) and at the saturated state (the green and red curves) corresponding to figure 14.…”

mentioning

confidence: 99%

Kinetic-magnetohydrodynamic hybrid simulation of infernal modes in circular tokamak plasmas with effects of kinetic thermal ions

Sato,

Todo,

Aiba

et al. 2024

Nucl. Fusion

View full text Add to dashboard Cite

Effects of the kinetic thermal ions on ideal infernal modes and resistive infernal modes have been investigated by using magnetohydrodynamic (MHD) simulation without kinetic thermal ions and kinetic-MHD hybrid simulation with kinetic thermal ions. For the ideal infernal modes, the pressure profile is significantly flattened at the saturated state for both the models with and without the kinetic thermal ions. As the beta value decreases, the ideal infernal modes are stabilized while the resistive infernal modes are still unstable. For the resistive infernal modes, while the saturated pressure profile is significantly flattened in the MHD simulation without kinetic thermal ions, the pressure profile is not flattened at the saturated state in the kinetic-MHD hybrid simulation with kinetic thermal ions. The suppression of the saturation level by the effects of the kinetic thermal ions results from the phase mismatch between the radial velocity and perturbed pressure mode structures. This indicates that kinetic thermal ions play an essential role for the suppression of pressure profile flattening due to slowly growing resistive MHD instabilities.

show abstract

Global gyrokinetic nonlinear simulations of kinetic infernal modes in reversed shear tokamaks

Cited by 6 publications

References 50 publications

ITB formation in gyrokinetic flux-driven ITG/TEM turbulence

ITB formation in gyrokinetic flux-driven ITG/TEM turbulence

Plasma beta dependence of turbulent transport suggesting an advantage of weak magnetic shear from local and global gyrokinetic simulations

Kinetic-magnetohydrodynamic hybrid simulation of infernal modes in circular tokamak plasmas with effects of kinetic thermal ions

Contact Info

Product

Resources

About