Estimation of the loss in the ECH transmission lines for ITER

Full text: We present calculations of the loss in the ITER ECH transmission lines, including both the ohmic loss and the mode conversion loss of all of the components. Since the power generated by the gyrotron system is specified at 24 MW and the power delivered to the plasma should be at least 20 MW, the allowed loss in the lines must be held to a low value, no more than 17%. This value of loss, 17%, is also close to the theoretical loss value estimated by the ITER team, indicating that there is a challenge in achieving such a low loss value. Because some of the loss estimates are based on approximate theories, there is uncertainty in these estimates. Our estimate is a loss of about 11% for the transmission lines leading to the upper launcher. There is an additional 4% loss in the upper launcher itself. The total loss is thus 15% for the present estimate, slightly lower than the ITER Team estimate. For the transmission line to the equatorial plane launcher, the estimated total loss is 13% for the present calculation vs. 15% for the ITER Team. These estimates allow us to divide the loss budget between the two portions of the transmission line, since different parties are responsible for the different portions of the line. The transmission line losses are estimated here by approximate theories. Improved theories and measurement techniques are needed and are under development. We will present results on the estimation of the mode conversion in an oversized miter bend using the computer code HFSS. The results show the excitation of higher order modes at the bend. The results are compared with pyroelectric camera measurements of mode conversion at a miter bend in a demonstration transmission line at MIT. Experimental results on the measurement of low microwave loss using a vector network analyzer and a radiometer will be presented and the results compared with theory. The present results will also be compared, where possible, with results from high power testing at 170 GHz at JAEA in Japan. (author)