Plasma and Diagnostics Preparation for α-Particle Studies in JET DT

Full text: A deuterium-tritium (DT) experimental campaign DTE2 on JET scheduled for 2019-2020, will be done in the Be/W vessel and will address essential operational, technical, diagnostic and scientific issues in support of ITER. In preparation for the campaign, developments were performed on JET aiming at studies of α-particles. For studying AEs driven entirely by α-particles, a scenario similar to the TFTR beam "afterglow" was developed for JET. In DT plasmas, after NBI is switched off, α-particles will be the only energetic ions during the time interval between slowingα-down times for NBI-produced ions and α-particles. Detection of α-driven AEs in this time window may help in diagnosing the temporal evolution of the pressure profile and slowingα-down time of α-particles. JET advanced tokamak scenarios with q ≈ 1.5-2.5 were chosen and discharges have been successfully developed. The transport modelling extrapolated to DT predicted that α-particle ≈ 0.1% could be achieved comparable to that in successful TFTR experiments. In "hybrid" scenario plasmas with q₀ ≥ 1, fast ion losses in the MeV energy range were observed during n = 1 fishbones driven by a resonant interaction with D beam ions in the energy range ≤ 120 keV. The losses are identified as an expulsion of DD fusion products, 1 MeV tritons and 3 MeV protons. A mode analysis with the MISHKA code combined with the study of nonlinear waveα-particle interaction with HAGIS show that the loss of toroidal symmetry strongly affects the confinement of high energy tritons and protons by perturbing their orbits and expelling them in a good agreement with experiment. The extrapolation to the case of α-particles in DTE2 hybrid scenarios with similar fishbones has shown an additional α-particle loss of ∼ 1%. (author)