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 thepositive current plasma is lower than that of the negative current plasma. The particle transportcoefficients are investigated in AC plasmas by a gas puff modulation method. It is observed thatthe particle diffusion coefficient for the positive plasma current case is almost the same as that forthe negative one, but the absolute value of inward pinch velocity for the positive current plasmais much lower than that of the negative one. The result of the particle transport model study is inagreement with the experimental confinement study. The intensity of Ha emission and impuritiesemission of CIII, OII and OV for the negative current plasma are much lower than that for thepositive current plasma. The radiation from Ha, O11, CIII and ECE signals from the negativeto the positive current phase showed less ionization and lower parameters than those from thepositive to the negative one. The difference of particle transport and confinement in AC plasmasis not predicted by the current theory.
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