JET-P(95)33
Recent Results of ICRF Heating on JET
During ICRF heating experiments, the new four-strap A2 antennas on JET have coupled 16.5MW of power into single null divertor plasmas (fig 1). In combined heating experiments a maximum of 32MW has been achieved by adding 15MW of hydrogen minority ICRH to 17MW of neutral beam injection (NBI). This combined heating power is a record for the present campaign and was achieved in a high density, strongly radiating, reactor-like scenario with 'grassy' ELMs. Central electron temperatures close to 15keV have been obtained with both RF-only and combined heating in ELM-free plasmas which were created with high flux expansion in the divertor region and which were substantially triangular ( δ ~- 0.3). Similar discharges were used to obtain the highest D-D reactivity in JET with NBI. The addition of hydrogen minority ICRH to these plasmas increases both the reactivity and the H-factor obtained by comparing the thermal energy content to the ITERH93-P scaling. RF-only H-modes have been produced in plasmas with currents (Ip) up to 4. 7MA and the power thresholds a.re similar those with NBI. At lp = 4.7MA and a toroidal field (Bt) of 3.2T, a plasma energy content of 7MJ was achieved with 8M\V of 51.3MHz ICRH in 0π0π phasing. The heating efficiency, as determined from power modulation experiments, is close to 100% with 0π0π and 0ππ0 phasing. The efficiency decreases for phasings such as 00ππ and monopole which produce average values of the parallel wavevector less than 3.5m-1. However, the recent introduction of a separator limiter at the centre of one antenna has improved its heating efficiency for perpendicularly launched waves and such separators will be fitted to all antennas in the near future.