SUMMARYIon kinetic effect on the low-n toroidal modes in compact torus (CT) plasmas such as spherical tokamak (ST), spheromak, field reversed configuration (FRC), and compact reversed field pinch (RFP) was investigated by using different ion species. The experimental results indicate that ion kinetic stabilization of the low-n modes was obtained in the low-q 95 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-q 95 (~4) ST regime, all low-n (1 to 4) toroidal modes were stable for both high S * and low S * .

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