Preliminary Design of O-mode Radiometer for ITER ECE Diagnostic

The ITER Electron Cyclotron Emission (ECE) diagnostic system will provide information about plasma electron temperature and its fluctuations and other important plasma parameters which are required for plasma control and physics studies. The temperature profile measurement in the first harmonic ECE frequency range from 122-230 GHz (for B-T = 5.3 T) is obtained by using an O-mode heterodyne radiometer. It is difficult to cover this wide frequency band by one radiometer, due to technological challenges in achieving wide bandwidth for the mixers. So, the present radiometer design has been optimized by considering four receivers, each of bandwidth similar to 30 GHz which can provide reliable temperature measurements. The splitting of frequency band into four receiver bands is efficiently achieved by considering a combination of quasi-optical and waveguide diplexers, optimizing power loss and cross-talk between the channels. The target spatial resolution of a/30, where "a" is the minor radius of the plasma cross section, is achieved by choosing Radiometer IF filter bandwidth of 1-2 GHz. Further, the radiometer is designed to achieve noise temperature < 10 eV. In this paper, the preliminary design and performance of O-mode Radiometer has been discussed.