Effect of the RF wall conditioning on the high performance plasmas in the Large Helical Device

The wall conditioning using radio frequency (RF) plasma was carried out using Ion Cyclotron Range of Frequency (ICRF) heating and/or Electron Cyclotron Resonance Heating (ECRH) with the working gas of helium under the established confinement magnetic field. After sufficient numbers of repetitive wall discharge conditioning (DC, ICDC for ICRF and ECDC for ECRH), the formation of the parabolic electron density profile and the increase of the central ion temperature T_i were observed. There was no difference in the attained central T_i of the NBI discharge just after the conditioning using a similar value of input energy regardless of the applied RF source. Thus, it is concluded that both ICDC and the ECDC are effective for the higher T_i plasma production under the established magnetic field in the Large Helical Device. The effective RF wall conditioning scenarios are also investigated for high T_i plasma production