Global gyrokinetic simulation of turbulence driven by kinetic ballooning mode

Abstract

Nonlinear evolution of the kinetic ballooning mode (KBM) is investigated by extending the global toroidal gyrokinetic simulation code (GKNET) to an electromagnetic regime. It is found that the saturation process of KBM, which is unstable at high normalized pressure b, is significantly different from the ion temperature gradient (ITG) mode, which is unstable at low b. The KBMs get saturated by producing zonal flows and zonal magnetic fields. The production of zonal flow is weak in the initial saturation phase of KBM, which is in contrast to the ITG mode which produces strong zonal flows in the initial saturation phase. However, strong zonal flows are produced in the subsequent evolution of KBM, and a quasisteady state of KBM turbulence is established. In addition to the zonal flows, some low toroidal number modes, which are linearly stable against the KBM, dominate the KBM turbulence. The strong zonal magnetic field is also produced by the KBM. These zonal modes regulate the KBM turbulence.

Numerics and computation in gyrokinetic simulations of electromagnetic turbulence with global particle-in-cell codes

“…One can see how the growth rate decreases with beta until a certain threshold is reached beyond which the growth rate begins to strongly increase. This is a typical ITG-to-KBM transition pattern [7,5]. Here, the growth rate is computed from the linear phase of the perturbed energy flux evolution, see below for more details.…”

“…There are a number of gyrokinetic codes which develop capabilities for global simulations in electromagnetic regimes, for example GEM [2], GTC [3,4], XGC [5], GENE [6], GKNET [7], GKW [8]. In this paper, we employ the well-established gyrokinetic particle-in-cell (PIC) codes ORB5 [9] and EUTERPE [10].…”

“…There are only two examples of global gyrokinetic KBM turbulence simulations, reported so far: Ref. [7] using the Eulerian code GKNET and Ref. [4] where the gyrokinetic PIC code GTC has been used.…”

Linear gyrokinetics of electron–positron plasmas in closed field-line systems

“…In the KBM case this spectral feature leads to issues of saturation and resolution in turbulence studies. Recently, it was shown (Ishizawa et al 2019) that the use of a global code can overcome these issues and it is our hope that this is also the case for studies of electron-positron plasmas.…”

Verification of a Fully Implicit Particle-in-Cell Method for the $v_\parallel$ Formalism of Electromagnetic Gyrokinetics in the XGC Code

“…There are important physics effects in magnetically confined fusion devices that, in addition to kinetic electrons, require the inclusion of electromagnetic perturbations. Electromagnetic capabilities have been implemented in a number of particle and continuum gyrokinetic codes including GEM [9,10,11], GTC [4,13,14,15], EUTERPE [16,17], ORB5 [18,19,20], GENE [21,22,23], Gkeyll [24,25], GYRO [26,27], GKV [28,29], and GKNET [30,31]. However, application to long-wavelength MHD-type modes is often limited due to numerical difficulties.…”