MHD Characteristics in High-beta Regime of the Large Helical Device

The highest volume averaged beta value beta_t of 2.2% at B_t = 0.75 T (gas puff) and 2.4 % at B_t = 1.3 T (pellet) in all of helical devices have been achieved in the Large Helical Device (LHD). The beta_t dependence of MHD activities has been investigated in NBI plasmas. The n/m = l/2 mode excited in the core region and / = l resonant modes in peripheral region have been observed. Both of the fluctuation amplitudes increase with beta_t and the pressure gradient. The strong n/m = l/2 mode which affects plasma profile have been observed in high-beta_t discharges and the abrupt disappearance of the mode leads to the restoration of T_e profile. Violent instabilities which terminate the plasma and degradation of global energy confmement have not been observed so far