Session GP1 - Poster Session IV.
POSTER session, Tuesday afternoon, October 30
Exhibit Hall B,
We have started to study the EC assisted start-up in JT-60U, where the plasma volumes at the breakdown is much smaller than the volume of the vacuum vessel. The breakdown voltage is successfully reduced by EC injection of 160\,\mathrmkW on center resonance from 30\,\mathrmV to 4\,\mathrmV which corresponds to the electric field of 0.26\,\mathrmV/m. This result satisfies the ITER requirement of 0.3\,\mathrmV/m. The study of the parameter scan, such as EC power, prefill pressure and resonance position, were done under the condition of low electric field of 0.26\,\mathrmV/m. The Ip-ramp up rate was not changed by increasing EC power up to \sim1\,\mathrmMW. The Ip ramp-up rate decreases with the prefilling pressure, while the plasma start-up at the low electric field was succeeded in the experimental pressure range of 2.7\times10^-3\,\mathrmPa to 1.7\times10^-2\,\mathrmPa. When the resonance position was shifted 71\,\mathrmcm(\sim0.7a) inward from center, the Ip ramp-up rate clearly decreases. Moreover, the Ip ramp-up was obtained only at the center resonance in the case of 2nd harmonic resonance condition. These results may indicate that the optimize of EC plasma formation is key to obtain the robust Ip ramp-up at low electric field. In conclusion, the experiments describes demonstrate that low voltage startup (E<0.3\,\mathrmV/m) is feasible in large tokamak.