A Lower Hybrid Current Drive System on the Superconductive Tokamak HT-7

A lower hybrid current drive system has been built for the HT-7 superconductive tokamak to deliver a 1.2-MW microwave at a frequency of 2.45 GHz for a pulse length of up to 5 s. Twelve klystron amplifiers are used as wave generators, each generating a 100-kW (130 kW at maximum) microwave. A grill coupler composed of 2 x 12 waveguides is used to launch the waves from the 12 klystrons. The wave phase difference between the adjacent waveguides in either row of the grill can be set at any desired value by feedback controlling the digital phase shifters in the low-power microwave circuits in front of the klystrons. The 12 klystrons are fed by two equal high-voltage power supplies. The technical reliability of the system is shown by experimental results.