抄録
The ion kinetic or skin depth effect on the relaxation of merging spheromaks to a field-reversed configuration (FRC) was investigated experimentally using varied S* (the average number of the ion skin depth) from 0.5 to 10.The merging spheromaks relax either to an FRC (λp˜0) or to another spheromak (λp˜λTaylor), depending on whether their initial poloidal eigen value λpwas smaller or larger than the threshold value λ0. The up-scaled TS-4 experiment under varied skin depths with several ion species revealed that the threshold value λ0 for the relaxation to an FRC increased inversely with the S* value. The decrease in S* promoted the relaxation to an FRC, annihilating the magnetic helicity, in sharp contrast with the conventional Taylor relaxation. The low S* relaxation to an FRC was observed to suppress the all low-n modes with the fast rotation of those modes.
