2021/06/01 by I. J. McKinney, I.J. McKinney, M. J. Pueschel +8 · 4 citations
Physics and Astronomy · #Magnetic confinement fusion research #Ionosphere and magnetosphere dynamics #Solar and Space Plasma Dynamics
paper · doi:10.1017/s0022377821000581
Kinetic-ballooning-mode (KBM) turbulence is studied via gyrokinetic flux-tube simulations in three magnetic equilibria that exhibit small average magnetic shear: the Helically Symmetric eXperiment (HSX), the helical-axis Heliotron-J and a circular tokamak geometry. For HSX, the onset of KBM being the dominant instability at low wavenumber occurs at a critical value of normalized plasma pressure β \rm KBM\rm crit that is an order of magnitude smaller than the magnetohydrodynamic (MHD) ballooning limit β \rm MHD\rm crit when a strong ion temperature gradient (ITG) is present. However, β \rm KBM\rm crit increases and approaches the MHD ballooning limit as the ITG tends to zero. For these configurations, β \rm KBM\rm crit also increases as the magnitude of the average magnetic shear increases, regardless of the sign of the normalized magnetic shear. Simulations of Heliotron-J and a circular axisymmetric geometry display behaviour similar to HSX with respect to β \rm KBM\rm crit . Despite large KBM growth rates at long wavelengths in HSX, saturation of KBM turbulence with β > β \rm crit\rm KBM is achievable in HSX and results in lower heat transport relative to the electrostatic limit by a factor of roughly five. Nonlinear simulations also show that KBM transport dominates the dynamics when KBMs are destabilized linearly, even if KBM growth rates are subdominant to ITG growth rates.