Electron temperature perturbations measured by electron cyclotron emissiondiagnostic systems in JT-60U

Electron cyclotron emission (ECE) diagnostic systems in JT-60U for the meas urement of electron temperature perturbations and the results of the measur ement are described. In 1999, the heterodyne radiometer system was upgraded , and the number of the channels was doubled to 24. It can now measure ECE ranging from 176 to 200 GHz. The heterodyne system enables the measurement of the location and structure of the magnetic island, which is observed in the steady state high beta (p) H-mode discharges. Behavior of an m/n = 1/1 mode and sawtooth oscillations during electron cyclotron heating and electr on cyclotron current drive is investigated by using the grating polychromat or. Here, m and n are poloidal and toroidal mode numbers, respectively. It is found that magnetic island width with m/n = 1/1 is decreased during elec tron cyclotron (EC) wave injection. It is also found that sawtooth period i s significantly expanded by EC wave injection near the q = 1 surface. The o btained maximum sawtooth-free period was about four times longer than the t heoretically predicted one. (C) 2000 Elsevier Science B.V. All rights reser ved.