Development of a direct mirror angle detector for ITER EC launchers

Abstract The new mirror angle detector applying a variable capacitor and several hundreds MHz RF wave has been developed. It is composed of a rotary capacitor consisting of a rotary and stationary electrode, a RF feeder and RF circuits. Reflected RF wave at the rotary capacitor supposed to connect the rotation axis of the mirror comes back to the RF feeder and the phase change of reflected RF due to the overlap condition between the two electrodes tells us the rotation angle of the mirror. Application of a co-axial choke stub to the support of the stationary electrode has been utilized. As a result, cooling water can be supplied to the stationary electrode through the center conductor of the choke stub that can solve the cooling issue of the electrodes since it acts as a notch filter to isolate the electrode, electrically. In order to verify the design principle of the new mirror angle detector for the EC launchers, the mock-up of the detector and RF circuits were fabricated and tested. It was obtained that phase difference of the reflected RF wave at the rotation angle change of 14° was 26°, which was well agreed with the design value of 25.7°. It is concluded that the new angle detector is applicable to the ITER EC launcher steering mirror.