HEXAPOLE FIELD EFFECTS ON CURRENTLESS MHD EQUILIBRIUM AND STABILITY OF L=2 HELIOTRON TORSATRON

Averaged flux surfaces with respect to the toroidal angle in l=2 helio tron/torsatrons are deformed in D-shape or inverse D-shape by the hexa pole field. D-shape deformation of vacuum flux surfaces enhances magne tic well or reduces magnetic hill in Heliotron-E and Large Helical Dev ice (LHD) configuration. However, complete elimination of the magnetic hill region is not obtained by the D-shape deformation without substa ntial reduction of plasma radius. The inverse D-shape deformation degr ades MHD stability against ideal interchange modes in the central regi on of both devices for fairly peaked pressure profiles. In the LHD con figuration, a broad pressure profile proportional to (1 - psi2)2 degra des the MHD stability and the hexapole effect is almost irrelevant, wh ere psi is a poloidal flux function; however, second stability appears against both the local and non-local interchange modes.