Experimental investigation of the potentials modified by radio frequency sheaths during ion cyclotron range of frequency on EAST

Recent ion cyclotron range of frequency (ICRF) experiments combined with lower hybrid wave (LHW) on EAST show that LHW coupling can be strongly modified when the LHW launcher is connected magnetically to a powered ICRF antenna. Using Langmuir probes, investigation of radio frequency (RF)-enhanced potential and local plasma parameters under an applied ICRF pulse is carried out on EAST. When the ICRF antenna connected to the probe is powered, localized high positive peaks appear on the floating potential. The dependence of floating potential modifications on various parameters is investigated. These initial results are shown to be consistent with RF sheath physics. A new four-strap antenna is modelled with the high frequency structural simulator (HFSS) code for evaluation of the parallel electrical fields (E-parallel to) and sheath potentials. It is found that the E-parallel to fields with the (0, 0, pi, pi) phase are much higher than those with other phases. Only the (0, pi, pi, 0) phasing has a significant reduction potential compared with the original two-strap antenna at the dipole phase.Recent ion cyclotron range of frequency (ICRF) experiments combined with lower hybrid wave (LHW) on EAST show that LHW coupling can be strongly modified when the LHW launcher is connected magnetically to a powered ICRF antenna. Using Langmuir probes, investigation of radio frequency (RF)-enhanced potential and local plasma parameters under an applied ICRF pulse is carried out on EAST. When the ICRF antenna connected to the probe is powered, localized high positive peaks appear on the floating potential. The dependence of floating potential modifications on various parameters is investigated. These initial results are shown to be consistent with RF sheath physics. A new four-strap antenna is modelled with the high frequency structural simulator (HFSS) code for evaluation of the parallel electrical fields (E-parallel to) and sheath potentials. It is found that the E-parallel to fields with the (0, 0, pi, pi) phase are much higher than those with other phases. Only the (0, pi, pi, 0) phasing has a significant reduction potential compared with the original two-strap antenna at the dipole phase.A