Particles Behavior in Quasi-Steady-State AC Plasmas on HT-7 Tokamak

A quasi-stationary alternating current (AC) operation assisted by lower hybrid waves (LHW) was achieved recently in HT-7. It is found that the particle confinement time of the positive current plasma is lower than that of the negative current plasma. The particle transport coefficients are investigated in AC plasmas by a gas puff modulation method. It is observed that the particle diffusion coefficient for the positive plasma current case is almost the same as that for the negative one, but the absolute value of inward pinch velocity for the positive current plasma is much lower than that of the negative one. The result of the particle transport model study is in agreement with the experimental confinement study. The intensity of Hα emission and impurities emission of CIII, OII and OV for the negative current plasma are much lower than that for the positive current plasma. The radiation from Hα, OII, CIII and ECE signals from the negative to the positive current phase showed less ionization and lower parameters than those from the positive to the negative one. The difference of particle transport and confinement in AC plasmas is not predicted by the current theory.