Particle confinement and coherence of turbulence with lower hybrid current drive on HT-7 tokamak

A improved particle confinement plasma produced by using lower hybrid current drive (LHCD) has been obtained on the HT-7 superconducting tokamak. It is found that the particle confinement time increases with the LHW power, but saturates at a critical power (PLHW∼300kW). Therefore, the fluctuation level and coherence of turbulences are investigated by a CO2 collective scattering system. It is observed that the power spectrum for OH discharge is almost the same as for the LHCD plasma, but the value of cross-spectrum between kθ=12cm−1 and kθ=20cm−1 is reduced with increasing LHW power. The possible mechanisms responsible for improved particle confinement and the evolution of density profile are studied in detail in LHCD plasma.