Particle confinement and transport coefficients in ac plasmas on the HT-7 superconducting tokamak

A quasi-steady-state alternating current (ac) plasma operation was achieved successfully on the HT-7 superconducting tokamak. It is found in ac plasmas that the particle confinement time of positive current plasma (τp ∼ 17 ms) is lower than that of negative current (τp ∼ 31 ms) plasma. Therefore, the particle transport coefficients are investigated in ac plasmas by the gas puff modulation method on the HT-7 tokamak. It is observed that the particle diffusion coefficient (D) for the positive plasma current case is almost the same as for the negative one, but the absolute value of inward pinch velocity (V) of positive current plasma is much lower than that of the negative one. The evolution of density profile is studied in detail in ac plasmas