Fast ion driven drift instability in reversed shear plasmas

Abstract

It is shown that electron drift waves can be destabilized by trapped fast ions produced by a fusion reaction because a significant fraction of those particles reverses their precession direction in reversed shear plasmas toward the electron diamagnetic direction and can resonate with the electron drift wave. We perform a local stability analysis and calculate the consequent quasi-linear transport caused by this new instability using bounce-averaged gyrokinetic equations in toroidal geometry and under fusion reactor conditions. We consider the equilibrium distribution function of fast ions as the slowing down distribution and compare with the equivalent Maxwellian case for illustration. The instability occurs when the temperature profile of fast ions peaks sufficiently compared to the density profile, and the magnetic shear is strongly negative. The resulting particle flux of fast ions is outward, while the particle flux of main hydrogenic ions can be inward. Published under license by AIP Publishing.