RF Power Dissipation on the KSTAR ICRF Antenna

Abstract

The KSTAR (Korea Superconducting Tokamak Advanced Research) ICRF (ion cyclotron range of frequency) antenna system has Faraday shield tubes to protect it from direct exposure to the plasma environment. The RF heating profiles on the Faraday shield and on the current strap of the KSTAR ICRF antenna were theoretically studied and compared with experimental results. The poloidal configuration of the magnetic field was calculated by using a commercial 2-D FEM (finite element method) code, from which the heat load profile along the circumference of the Faraday shield surface was deduced. The heat loads on the top and the bottom surfaces facing the adjacent Faraday shield were found to be relatively high. The toroidal configuration of the magnetic field was calculated, and the toroidal profiles of the heat loads on the Faraday shield and the strap were deduced. The heat load has a maximum value at the joining position of the Faraday shield with the cavity wall. The heat loads on both the rounded edges of the current strap were found to be relatively high. For a strap current of 677 A (peak), which corresponds to a maximum voltage of 30.0 kVp, the maximum heat loads on the Faraday shield and on the current strap were 381 and 57 kW/m 2 , respectively, at a frequency of 30 MHz. A RF test was performed to investigate the standoff capability of the antenna without any cooling. In that test, we measured the temperature profiles on the Faraday shield and on the current strap by using an IR camera and then compared the results with the calculated heat loads. The maximum temperature of the Faraday shield was 374 • C for a maximum voltage of 30.0 kVp and a pulse length of 66 s. The temperature profiles agreed well with the calculated heat load profiles.