Exceeding the beta limit in a tokamak SOL, and initial mirror equilibria studies – some Gkeyll results

We show full-F electromagnetic gyrokinetic simulations for a tokamak Scrape-Off Layer (SOL) in a sheath-connected regime that find that the normalized pressure gradient can reach 4 times the ideal ballooning limit without a significant increase in the turbulent flux to broaden the SOL width, extending our earlier results [https://doi.org/10.1063/5.0082486]. A model helical geometry for the SOL is used, and parameters roughly approximate the National Spherical Torus Experiment (NSTX). Linear analysis of interchange-ballooning modes including sheath and diamagnetic effects indicate that high α may be explainable by radially non-local and ExB shear effects, etc. Part 2: as an initial step towards studying drift-interchange/ballooning-driven turbulence in mirrors, we did 1x-2v simulations of mirror evolution starting from an isotropic initial condition, as a loss-cone is evacuated and repopulated by scattering of particles and an ambipolar potential starts to build up, consistent with Pastukhov's picture. We describe computational challenges of high mirror ratios and offer a force softening method to mitigate small time steps needed with colossal magnetic field gradients produced by HTS coils, providing a 19X speedup [https://arxiv.org/abs/2305.06372].