Analysis of Ion Cyclotron Heating and Current Drive at ω≈2ωcH for Sawtooth Control in JET Plasmas

Ion cyclotron heating and current drive at w 2w cH in JET deuterium plasmas with a hydrogen concentration nH/(nD+nH)in the range of 5-15%are analysed.Second-harmonic hydrogen damping is found to be maximised by placing the resonance on the low-field-side (LFS) of the torus, which minimises competing direct electron damping and parasitic high-harmonic D damping in the presence of D beams. The shape of the calculated current perturbation and the radial localisation of the heating power densityfor the LFS resonance are consistent with the experimentally observed evolution of the sawtooth period when the resonance layer moves near the q=1 surface. Since the calculated driven current is dominated bya current of diamagnetic type caused byfinite orbit widths of trapped resonating ions,it is not too sensitive to the ICRF phasing. Control of sawteeth with ion cyclotron current drive using the LFS w 2w cH resonance in the present experimental conditions can thus be best obtained by varying the resonance location rather than the ICRF phasing. Due to differences in fast ion orbits,collisional electron heating and fast ion pressure profiles are significantlymore peaked for a LFS resonance than for a high field-side (HFS)resonance. For the HFS w 2w cH resonance,an enhanced neutron rate is observed in the presence of D beam ions,which is consistent with parasitic D damping at the w 5w cD resonance in the plasma centre.
Name Size  
EFDP01072 1.40 Mb