Finite-gyroradius stabilization of diffuse high beta stellarators

A method is described for estimating the finite gyroradius stabilization of m⩾2 magnetohydrodynamic modes in diffuse high-β stellarators. The procedure combines both analysis and numerical computation. In particular, the difficult trajectory integrals which arise in the formulation are evaluated by plasma simulation techniques. The method is successfully applied to the m=2 modes in the high-β, l=1 stellarator configuration. It is found that the stability criterion for diffuse profiles is somewhat more optimistic than earlier estimates based on the sharp boundary model.