Evaluation of transmission efficiency of the ECH/CD transmission lines in integrated commissioning phase on JT-60SA

Abstract

An electron cyclotron heating and current drive (ECH/CD) system with two transmission lines (TLs), TL#1 (waveguide inner diameter ⌀=31.75 mm) and TL#2 (⌀=60.3 mm), has been installed and operated on JT-60SA for the integrated commissioning phase. In order to evaluate the transmission efficiency of the TLs, the theoretical loss of each TL component is calculated assuming pure HE11 mode. In addition, the millimeter wave power at the beginning and end of two TLs was measured experimentally by calorimetric dummy loads (DLs) at high-power of ∼ 400 kW for ∼ 0.3 s. The output power of the gyrotron is estimated by using the measured power at the beginning of each TL with the theoretical loss between the DL and the gyrotron. The injection power to the tokamak from a launcher is also estimated by using the measured power at the end of each TL with the theoretical loss between the DL and the launcher. Using these values, the transmission efficiencies, defined as the ratio of the gyrotron output power to the tokamak injection power, are evaluated for both TLs, which are ∼70% for TL#1 at 110 GHz, and 80 % (82 GHz), 82 % (110 GHz), and 84 % (138 GHz) for TL#2. The total power injected into the tokamak by the combination of TL#1 and TL#2 is expected to be 1.5 MW. It is found that the measured transmission efficiency of TL#2 shows a good agreement with the theory, while the measured transmission efficiency of TL#1 was slightly lower than the theoretical value. To investigate this result, power measurements are also performed at additional locations on the TL#1 with additional DLs.