Upgrade of ECRH launcher for NTM real-time control on HL-2A tokamak

Highlights: • Upgrade of ECRH launcher on HL-2A for real-time control of NTMs. • First RT control experiments by ECH on HL-2A with CTM island as target. • Time constant of changing power deposition point is ∼150 ms. • Half width of EC power deposition profile is ∼5 cm at the 2/1 island position. - Abstract: Electron cyclotron resonance heating and current drive (ECRH/ECCD) are deemed to be one of the best option to control the neoclassical tearing modes (NTMs), which are potential danger for steady state operation in fusion reactors. Recently, one of the two ECRH equatorial launchers on HL-2A tokamak has been upgraded to satisfy the real-time control requirements. The upgrade of the rotation and driving mechanism accelerates the tuning speed of poloidal injection angle of EC beam significantly, which permits the modification of the EC power deposition position in real time. Analyses on the beam injection angles and wave power losses, together with calibration results on test bed indicate that the new launcher has a good launching performance. The upgraded No. 2 ECRH launcher was successfully applied in the first proof-of-principle experiment for NTM real-time control, in which within 250 ms suppression of the classical tearing modes (CTMs) by ECRH/ECCD was realized for the first time on HL-2A.