Resumen de Computational analysis of ion cyclotron resonance frequency heating for jet experiments
Heating plasmas to a relevant fusion temperature is one of the key aspects of magnetically confined fusion plasmas. Radio frequency (RF) heating with electromagnetic waves in the ion cyclotron range of frequencies (ICRF) has been proven to be an efficient auxiliary method in present fusion devices such as tokamaks. Moreover, the International Thermonuclear Experimental Reactor (ITER) will be provided with ICRF antennas as one of the main heating mechanisms. For that, the study of different heating schemes to optimise the fusion performance is of utmost importance.
During the 2015-2019 Joint European Torus (JET) campaigns many efforts have been devoted to the exploration of high-performance plasma scenarios envisaged for D-T operation in JET. Experiments in D, H and T are expected to lead in 2020 to the first experiments with 50%:50% D-T mixtures. These last campaigns at JET have been focused on enhancing the fusion performance of the baseline and hybrid scenarios with the final goal of improving ITER's future operation. This thesis reports on the modelling study of plasma heating through ICRF waves and NBI for recent experiments at JET with special emphasis on plasma performance.
The modelling has been performed mainly with the ICRF code PION. Simulations are in excellent agreement with experimental results which proves the reliability of the results shown in this thesis. The assessment of the results offer an overview to understand and optimise plasma performance for high-performance hybrid discharges that were performed with D plasma and H minority.
Impurity accumulation control with ICRF waves was found to be efficient only for a range of central resonance locations while impurity accumulation occurred for off-axis resonance. Contribution to temperature screening from fast ions was calculated to be negligible when finite orbit widths (FOW) are taken into account, as opposed to previous studies that did not take into account FOW. Small differences in H concentration have a large impact on power partition between H and D. The lower the H concentration the larger the power channeled to D which is shown to substantially enhance the D-D fusion rate. The study of a neutron record high-performance discharge shows high bulk ion heating and low H concentration as key ingredients for increased fusion performance.
Of especial relevance for ITER is the study of the D-T prediction from high-performance discharges. This analysis compares two ICRF schemes, H and 3He minority. It is shown that 3He is a strong absorber and provides higher bulk ion heating as compared to H. However, ICRF fusion enhancement is computed to be larger in H, as this scheme has a stronger 2nd harmonic heating. In D-T, ICRF fusion enhancement is computed to be significantly lower with regards to D-D plasmas due to different fusion cross sections. Results in preparation of the T and D-T campaigns at JET show that the extrapolation from T to D-T plasmas is not straightforward. PION predicts the T density to have a large impact on the T velocity distribution function for the ITER relevant 2nd$ T harmonic heating scheme. Larger concentrations of T lead to higher bulk ion heating, therefore, it is expected D-T bulk ion heating to be lower.
