Status of electron cyclotron wave technology

A review of the two key technologies for the electron cyclotron wave (ECW) system, the gyrotron source and the window, is presented. In both fields, significant progress has been made to meet the requirements of the heating and current drive systems planned for devices such as W7-X or ITER, namely 1 MW-CW (continuous wave) in the frequency range 140-170 GHz. Gyrotrons in this performance range have been tested in long pulse operation (many seconds). With the use of a diamond window, extremely long pulse (much greater than 10 s) or true CW operation is possible. Tests presently underway confirm such a promising behaviour of the window, paving the way towards the development of megawatt CW tubes.