Fusion product losses due to fishbone instabilities in deuterium JET plasmas

Abstract

During development of a high-performance hybrid scenario for future deuteriumtritium experiments on the Joint European Torus, an increased level of fast ion losses in the MeV energy range was observed during the instability of high-frequency n=1 fishbones. The fishbones are excited during deuterium neutral beam injection combined with ion cyclotron heating. The frequency range of the fishbones, 10 25 kHz, indicates that they are driven by a resonant interaction with the NBI-. The fast particle losses in a much higher energy range are measured with a fast ion loss detector, and the data show an expulsion of deuterium plasma fusion products, 1 MeV tritons and 3 MeV protons, during the fishbone bursts. An MHD mode analysis with the MISHKA code combined with the nonlinear wave-particle interaction code HAGIS shows that the loss of toroidal symmetry caused by the n=1 fishbones affects strongly the confinement of nonresonant high energy fusion-born tritons and protons by perturbing their orbits and expelling them. This modelling is in a good agreement with the experimental data.Fusion reactions as well as additional heating of fusion-grade tokamak plasmas generate large numbers of fast ions in the plasma core that can interact with the magneto-hydro-dynamic (MHD) perturbations of the plasma discharge. The MHD instabilities can eject fusion products (FP), in particular alpha-particles, which are the principal source of plasma heating in burning deuterium-tritium (D-T) plasmas. The interactions between MHD perturbations and alpha-particles could be resonant if the alpha-particles are in resonance with high-frequency waves, e.g. Toroidal Alfvén Eigenmodes (TAE) or non-resonant, when MHD perturbations are driven by thermal plasma or fast particles other than the alpha-particles. Both resonant and non-resonant interactions between alpha-particles and MHD perturbations could lead to the particle redistribution and losses [1] thus affecting the fusion plasma Q=Pout/ Pin and the first wall.

Full-orbit and drift calculations of fusion product losses due to explosive fishbones on JET

“…The pitch-angle corresponding to the ICRH H-minority fast ions is shown in solid red. Published in [2].…”

“…In the phase-space plots that follow, we will omit the embellishments in the notation for this invariant and simply write . A number of drift calculations using the HAGIS guiding-centre code [17] were carried out, and we have already published some results [2]. We have also recently developed the HALO (HAgis LOCust) code which takes mode structure from MISHKA in the same manner as HAGIS.…”

“…The energy chosen is the birth energy for the fusion products, which in this case corresponds to fast protons in the D-D reaction. Fast triton fusion products at 1 were also measured [2] but follow the same orbits so we will make no more explicit mention of them. The HAGIS drift calculation was repeated with the full-orbit LOCUST code using the same guidingcentre locations.…”

“…Explosive fishbone oscillations are also observed due to the presence of energetic particles from neutral beam and radio frequency heating. The fishbones are clearly responsible for fusion product losses [2] [3], but perhaps more concerning is the presence of main chamber hot-spots during some of the recent hybrid experiments; are the observed fusion product losses due to fishbones sufficient to explain the hot-spots?…”

“…The approximate location of the fundamental H-minority ICRH resonance is shown with the dashed line. Published in[2].…”