Ion Kinetic Effect on the Low-n Toroidal Modes in Compact Torus Plasmas

Ion kinetic effect on the low-n toroidal modes in Compact Torus (CT) plasmas such as Spherical Tokamak (ST), spheromak, Field-Reversed-Configuration and compact Reversed-Field-Pinch (RFP), was investigated by using different ion species. The experimental result that indicates ion kinetic stabilization of the low-n modes was obtained in the low q₉₅ regime. It was clearly shown that the n=1 mode was stabilized in the FRC under the low S regime (S: averaged number of ion skin depth). The suppression of the n=2 mode activity in the low S RFP plasma was also observed. In the high q₉₅(~ 4) ST regime, all low-n (1~4) toroidal modes were stable in the both cases of the high S and low S.