ECRH system, microwave diagnostics and experimental results in the EAST tokamak

Electron cyclotron resonance heating (ECRH), as a highly efficient and controllable heating tool, has been widely used in tokamak magnetic confinement devices [1]. Usually, the EC power can be injected as narrow Gaussian beams, which gives rise to highly localized power deposition. Consequently, ECRH and electron cyclotron current drive (ECCD) have been expolied to an ideal candidate for local transport studies and for the control of various magnetohydrodynamics (MHD) instabilities occurring in tokamak plasmas. Unlike other RF heating techniques, EC wave can propagate in vacuum and the coupling is insentitive to the parameters at plasma edge, which suggests that the antenna can be located far away from the plasma. This advantage makes ECRH an attractive scheme for a thermonuclear device like ITER, in which, the launcher cannot be close to the plasma in order to avoid the material erosion and thermal damage. EAST is a fully superconducting tokamak with a major radius of R0 = 1.90 m and a minor radius of a = = 0.45 m. The EC system will consist of a 4 MW continuous wave (CW) at 140 GHz (second harmonic of the extraordinary mode) for heating and current drive applications [2, 3]. In line with the long pulse operational capability of EAST, it was designed for a pulse length up to 1000 s. Benefitting from a pulse step modulator (PSM) type of power supply system it has a capability of fast modulation frequency up to 1 kHz. There are four gyrotrons produced by two different venders, namely, No1.and No.3 are provided by Russian company GYCOM, and the other two by CPI, USA. The specific parameters are shown in