Stellarator turbulence at electron gyroradius scales

Abstract

Electromagnetic gyrokinetic simulations of electron-temperature-gradient- driven modes on electron gyroradius scales are performed in the geometry of an advanced stellarator fusion experiment, Wendelstein 7-AS. Based on linear simulations, a critical electron-temperature-gradient formula is established which happens to agree quite well with a previously derived formula for tokamaks in the appropriate limit. Nonlinear simulations are used to study the turbulence and transport characteristics which are dominated by the presence of high-amplitude radially elongated vortices or 'streamers'. The role of Debye shielding effects is also examined.