External kink modes in a Large Helical Device (LHD) equilibrium with self-consistent bootstrap current

Magnetohydrodynamic (MHD) stability studies of low- mode-number free-bounda ry kink modes in a finite-beta Large Helical Device (LHD) [A. Ilyoshi, et a l. Fusion Technology 17, 169 (1990)] equilibrium series with self-consisten t bootstrap current find some serious free-boundary modes. They indicate th at care must be taken in the design of high-beta experiments. Since the LHD configuration is flexible, with the possibility of introducing or modifyin g dipole and quadrapole fields, unbalancing the currents in the helical coi ls, operating with a high-temperature divertor, and changing the collisiona lity regime by working with different values of temperature and density, pa ths to high-beta operation should exist. Comparison of the experimental res ults with these theoretical predictions for the studied equilibrium sequenc e will provide understanding of the MHD stability properties of LHD. (C) 19 99 American Institute of Physics. [S1070-664X(99)03206-1].