Excitation of Alfvén eigenmodes by fusion-born alpha-particles in D-3He plasmas on JET

Kiptily, V. G. and Ben Yaala, M., JET Contributors (2022) Excitation of Alfvén eigenmodes by fusion-born alpha-particles in D-3He plasmas on JET. Plasma Physics and Controlled Fusion, 64 (6). 064001. ISSN 0741-3335 (https://doi.org/10.1088/1361-6587/ac5d9e)

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Abstract

Alfvén eigenmode (AE) instabilities driven by alpha-particles have been observed in D-3He fusion experiments on the Joint European Torus (JET) with the ITER-like wall. For the efficient generation of fusion alpha-particles from D-3He fusion reaction, the three-ion radio frequency scenario was used to accelerate the neutral beam injection 100 keV deuterons to higher energies in the core of mixed D-3He plasmas at high concentrations of 3He. A large variety of fast-ion driven magnetohydrodynamic modes were observed, including the elliptical Alfvén eigenmodes (EAEs) with mode numbers n = -1 and axisymmetric modes with n = 0 in the frequency range of EAEs. The simultaneous observation of these modes indicates the presence of rather strong alpha-particle population in the plasma with a 'bump-on-tail' shaped velocity distribution. Linear stability analysis and Fokker-Planck calculations support the observations. Experimental evidence of the AEs excitation by fusion-born alpha-particles in the D-3He plasma is provided by neutron and gamma-ray diagnostics as well as fast-ion loss measurements. We discuss an experimental proposal for the planned full-scale D-T plasma experiments on JET based on the physics insights gained from these experiments.

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