High power RF test of liquid phase shifter for KSTAR tokamak

Abstract

Summary form only given, as follows. Summary form only given. A liquid phase shifter is developed for long pulse and high power operation of the KSTAR ICRF heating system. A conventional phase shifter (trombone type) uses sliding contact and it often causes some problem due to local temperature increase and insulation breakdown for long pulse operation under high power. To solve such problems, a phase shifter using liquid instead of gas for the insulating dielectric medium is developed. The liquid phase shifter contains a liquid between the inner conductor and outer conductor of the coaxial transmission line. By changing the liquid level instead of shifting the electric short-end, the electrical length of the line can be changed based on the difference between RF wavelength in liquid and in gas due to the difference in relative dielectric constant. A liquid phase shifter using the silicon oil as a dielectric insulator is constructed. It is mainly composed of 9-3/16 coaxial transmission line and a liquid level controller. The transmission phase length can be changeable from 0 to 130 at 30MHz by varying the liquid level. A high power RF test is performed to study the standoff capability of the liquid phase shifter. During the RF pulse, line voltage, reflected power and liquid temperature were measured. A RF test shows that the liquid phase shifter has a high standoff voltage and pulse length of 40kV for 60sec, 35kV for 300sec.