Modelling of ICRF heating for JET T and D-T plasmas

Abstract

A tritium (T) campaign is planned in preparation for the deuterium-tritium (D-T) campaign at the Joint European Torus (JET). These experiments will be the first experiments involving T with the ITER-like plasma-wall facing components materials. They will give a unique opportunity to test one of the most promising ion cyclotron resonance frequency (ICRF) heating schemes for ITER plasmas: the 2nd tritium (T) harmonic resonance (ω = 2ωT). This paper provides two key contributions related to modelling of the performance of this scheme at JET. First, we assess the heating performance of the 2nd T harmonic resonance and, second, we model different ICRF schemes for the T campaign in support for the D-T campaign, i.e., identify differences and similarities from the heating point of view between T and D-T plasmas in order to predict the performance of ω = 2ωT in the D-T scenario. In our modelling we use a selected hybrid record discharge as reference, i.e., using its experimental profiles. We consider two ICRF schemes (6 MW), i.e. ω = ω3He = 2ωT (no 3He), with a central resonance and three NBI power outputs (15, 25 and 35 MW) in two plasma compositions ( 100% T and 50%:50% D-T). Note that isotope effects are not taken into account in these simulations. For this study, the ICRF and NBI heating are modelled with the ICRF code PION and the beam code PENCIL which take into account the ICRF+NBI synergy. The analysis of the T velocity distribution function shows that a stronger tail is formed in those plasmas with lower tritium density. This fact has an important impact on the slowing-down process of fast tritons with the background species. The T plasma shows a higher and more peaked ion-ion collisional power density at the plasma centre as compared to D-T plasma. In the T plasma, ICRF heating drives fast tritons at the plasma centre with an average energy substantially lower than in the other case. On the other hand, the use of 3He as a minority makes the fast ion T energy considerably lower due to strong 3He absorption. Fast ion average energies reached at the plasma centre are similar in all species mixture cases. As a result, there is a strong heating similarity between T and D-T. However, it is crucial to study the generation of a strong T tail as a result of particle-wave interaction which is not possible under this scheme and needs to be studied in plasmas without 3He in preparation of JET D-T campaign and ITER. Therefore, both schemes (ω = ω3He = 2ωT and ω=2ωT) need to be tested.