Shear Alfvén continua in stellarators

Shear Alfvén continua have been calculated for stellarators over a range of shapes and aspect ratios as a first step toward understanding Alfvén instability induced fast ion losses in such systems and possible means for minimizing these losses. Stellarators introduce strong poloidal/toroidal couplings in both |B| and the gρρ metric coefficient that can induce new continuum gap structures not present in axisymmetric tokamaks. Low field period (Nfp=2–3), low aspect ratio devices result in strongly coupled toroidal mode families (n=±n0,±n0±Nfp,±n0±2Nfp, etc.) that lead to helically coupled Alfvén gaps at lower frequencies and with wider gap structures than are the case for larger aspect ratio, higher field period stellarator devices.