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

JET Contributors, V. G. Kiptily, M. Ben Yaala

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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.

Original languageEnglish
Article number064001
Number of pages16
JournalPlasma Physics and Controlled Fusion
Volume64
Issue number6
DOIs
Publication statusPublished - 21 Apr 2022

Keywords

  • fast-ion diagnostics
  • fusion-born alpha-particles
  • MHD instabilities
  • tokamak

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