Modelling of JET hybrid plasmas with emphasis on performance of combined ICRF and NBI heating

Modelling of JET hybrid plasmas with emphasis on performance of combined ICRF and NBI heating

Modelling of JET hybrid plasmas with emphasis on performance of combined ICRF and NBI heating 150 150 amit

During the 2015-2016 JET campaigns many efforts have been devoted to the exploration of high-performance plasma scenarios envisaged for DT operation in JET. In this paper we review various key recent hybrid discharges and model the combined ICRF+NBI heating. These deuterium discharges with deuterium beams had the ICRF antenna frequency tuned to match the cyclotron frequency of minority H at the centre of the tokamak coinciding with the second harmonic cyclotron resonance of D. The modelling takes into account the synergy between ICRF and NBI heating through the second harmonic cyclotron resonance of D beam ions which allows us to assess its impact on the neutron rate RNT . For discharges carried out with a fixed ICRF antenna frequency and different toroidal magnetic field to vary the resonance position, we evaluate the influence of the resonance position on the heating performance and central impurity control. The H concentration was varied in different discharges in order to test its role in the heating performance. It was found that discharges with a resonance beyond ∼ 0.15 m from the magnetic axis R0 suffered from MHD activity and impurity accumulation in these plasma conditions. According to our modelling, the ICRF enhancement of RNT increases with the ICRF power absorbed by deuterons as the H concentration decreases. We find that in the recent hybrid discharges this ICRF enhancement varied due to a variation of H concentration and was in the range of 10-25%. The modelling of a recent record high-performance hybrid discharge shows that ICRF fusion yield enhancement of ∼30% and ∼15% can be achieved in the ramp-up phase and during the main heating phase, respectively. We extrapolate the results to DT and find that the best performing hybrid discharges correspond to an equivalent fusion power of ∼7.0 MW in DT. Finally, an optimization analysis of the bulk ion heating for the DT scenario reveals around 15-20% larger bulk ion heating for the 3He minority scenario as compared to the H minority scenario.

Collection:
Journals
Journal:
Nuclear Fusion
Publisher:
IOP (Institute of Physics)
Published date:
09/05/2018