Analysis of ion cyclotron heating and current drive at omega= 2omega(cH) for sawtooth control in JET plasmas
Ion cyclotron heating and current drive at omega=2omega(cH) in JET deuterium plasmas with a hydrogen concentration n(H)/(n(D)+n(H)) in the range of 5-15% are analysed, comparing results of numerical computer modelling with experiments. 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 density for 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 by a current of diamagnetic type caused by finite 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 omega=2omega(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 significantly more peaked for a LFS resonance than for a high-field side (HFS) resonance. For the HFS omega=2omega(cH) resonance, an enhanced neutron rate is observed in the presence of D beam ions, which is consistent with parasitic D damping at the omega=5omega(cD) resonance in the plasma centre.
Bibliographic Reference: An article published in: Plasma Physics and Controlled Fusion, 44 (August 2002) 1521-1542
Availability: This article can be accessed online by subscribers, and can be ordered online by non-subscribers, at: http://stacks.iop.org/0741-3335/44/1521
Record Number: 200215626 / Last updated on: 2002-12-02
Original language: en
Available languages: en