Design of temperature compensating unit for the circulator in 6 MW 4.6 GHz LHCD system

The lower hybrid current drive (LHCD) system is an important part of the Experimental Advanced Superconducting Tokamak (EAST). As the main RF power amplifier, the klystron in the LHCD system is protected by a high power circulator. The temperature of the ferrites in the circulator drifts under high-power condition, which degrades the microwave performance of the circulator and even damages the klystron. In this paper, a design of Temperature Compensating Unit (TCU) is presented and eventually implemented to compensate for the high-power induced temperature drift. Experiments show that the TCU can lead to the high-power steady-state operation of the circulator.