Multichannel heterodyne radiometers with fast-scanning backward-wave oscillators for ECE measurement on HT-7 tokamak

Two sets of fast-scanning heterodyne radiometer receiver systems employing backward-wave oscillators (BWOs) in 78-118 and 118-178 GHz were developed a nd installed for electron cyclotron emission (ECE) measurements on HT-7 sup erconducting tokamak. The double sideband (DSB) radiometer in 78-115 GHz me asures 16 ECE frequency points with a scanning time period of 0.65 ms. The other radiometer in 118-178 GHz consists of one independent channel of DSB heterodyne receiver with intermediate frequency (IF) of 100-500 MHz and two channels of single sideband (SSB) heterodyne receiver that are sensitive t o upper sideband and lower sideband individually; the IF frequency of the S SB channels are 1.5 GHz around the local oscillator frequencies with 1 GHz bandwidth. By employing a novel design, this unique radiometer measures 3 E CE frequency points at each of the 16 local oscillator frequency points in 118-178 GHz, and the full band can be swept in 0.65 ms period, thus the rad iometer measures 48 ECE frequency points in 0.65 ms in principle. Each of t he local oscillators' frequency points can be preset by program to meet spe cific physics interests. Horizontal view of ECE was installed to measure el ectron temperature profiles; vertically viewing optics along a perpendicula r chord was also installed to study nonthermal ECE spectra. Preliminary mea surement results were presented during ohmic and pellet injection plasmas. (C) 2001 Elsevier Science B.V. All rights reserved.