Lower hybrid current drive efficiency affected by effective charge number and electron temperature in HT-7 tokamak

The lower hybrid current drive experiment has been performed on the HT-7 tokamak. The wave power varied from 100 kW to 700 kW with a frequency of 2.45 GHz. The relation between the power of lower hybrid wave and the average effective charge number and electron temperature was studied. It is shown that the current drive efficiency is proportional to the electron temperature, and inversely proportional to the effective charge number. The dynamic control of the impurity of plasma is a key to improve the current drive efficiency.