RF heated wall conditioning discharges in JT-60U

In series of experiments in 2000 and 2008, helium wall conditioning discharges by ECRF heating (ECH) were extensively studied in JT-60U with BT = 3.6 T and PECRF ⩽ 2.5 MW. Homogeneous ECH conditioning discharges were reproducibly obtained by applying the horizontal field as large as 0.2% of BT. It was found that the horizontal field is effective to extend He plasma toward high field side from the fundamental resonant surfaces of ECH. The ECH wall conditioning discharge with PECRF = 2.5 MW and tpulse = 1.5 s was applied after the plasma disruption with W = 3.3 MJ and the successful recovery of the current ramp-up with 0.5 V/m of ohmic electric field was obtained.