Development of a KSTAR ICRF antenna for long pulse operation

Abstract

A prototype ion cyclotron range of frequency (ICRF) antenna with RF power of 6 MW has been developed for the long pulse (300 s), high power operation in the Korea superconducting tokamak advanced research (KSTAR) tokamak. Cooling paths in the antenna were carefully designed to remove the dissipated RF power loss. An RF power test has been performed to estimate the standoff capability of the antenna. A high power RF test at a frequency of 30 MHz gives a standoff voltage of 30.5 kVp for 60 s and 23.2 kVp for 300 s (without cooling). During the RF pulse, the peak voltage, forward/reflected powers, temperature of the antenna, and gas pressure are measured. A vacuum feedthrough of 1 MW RF power has been developed, which has two alumina ceramic cylinders and an O-ring seal. For cooling of the ceramic parts, dry air is injected into the ceramic surface through two outer nozzles. Independent cooling water channels are installed to cool the inner conductor of the feedthrough. RF high voltage tests show that stable operation is possible, with a peak voltage of 28.9 kVp for 300 s, without any severe damage.

The RF conditioning of vacuum feedthrough for high power ICRF heating in KSTAR

“…The frequency range of the system is 25-60 MHz. The long pulse and high power capability of the antenna [8] and transmitter [9] for 300 s of operation was tested individually at the test stand or dummy load.…”

“…The shot number 10603 is H-mode shots with 3 MW of NBI and 0.63 MW of ICRF with frequency of 30. 8 MHz. An axial toroidal magnetic field is 2 T and plasma current is 0.6 MA.…”

Initial phase wall conditioning in KSTAR

“…The KSTAR ICRF antenna consists of four current straps covered with a Faraday shield as shown in figure 3(b)). It is powered by a 2 MW RF transmitter through a vacuum transmission line, pressurized resonant loop and double liquid stub tuner [33]. Two poloidal limiters are attached on both sides of the ICRH antenna.…”

Development of a compact ICRF antenna for high-power and long-pulse plasma heating in the KSTAR

“…Ion Cyclotron Range of Frequencies (ICRF) heating has been conducted in the Korea Superconducting Tokamak Advanced Research (KSTAR) [1] using the ICRF antenna with four center-grounded current straps [2]. However, this antenna suffered frequent damage by arcing on the ceramic feedthroughs [3].…”