Progress of Electron Cyclotron Heating/Current Drive Technology in JT-60U

Abstract

A key issue in attaining high plasma performance in the Tokamaks is the optimization of current profile, involving such functions as stabilizing the neo-classical tearing mode (NTM) and control of the internal transport barrier (ITB). In the JT-60U, a high power electron cyclotron heating (ECH) system at 110 GHz has been developed for local plasma heating and current drive. We have demonstrated the technical feasibility of an antenna which can scan EC beam in both the toroidal and poloidal directions. The toroidal scan enabled co- and counter- current drive and also pure plasma heating. Automatic stabilization of the NTM was demonstrated by means of current drive at the magnetic island employing feedback control of the poloidal beam angle. The total injected power has been extended to 2.8 MW for 3.6 sec and each gyrotron delivers ˜ 1 MW for 5 sec. This world record regarding the injection energy was attained by an upgrade of the gyrotron using an RF absorber in the beam tunnel to suppress the parasitic oscillation and to improve the transmission efficiency of the waveguide system.