Abstract
Alfvén eigenmodes (AEs) driven by energetic alpha particles can lead to enhanced fast ion transport and losses, thereby degrading the plasma performance in ITER and future magnetic confinement fusion reactors. Unexpectedly, AEs with negative toroidal mode numbers, which are currently not considered for ITER, were observed in dedicated experiments with fusion-born alpha particles on the tokamak Joint European Torus (JET). The paper provides evidence for a complex interplay between fast ions, monster sawtooth crashes and AEs. Our results highlight the need for an improved description of the synergies between different fast ion phenomena in future burning plasmas.
Highlights
This paper reports on sawtooth-induced Alfven eigenmodes (AEs) with toroidal mode numbers n < 0 and n = 0, which were unexpectedly observed in recent experiments in D-3He plasmas with fusion-born alpha particles on the world-largest magnetic confinement fusion device, the tokamak Joint European Torus (JET)
Dedicated fast-ion experiments in mixed D-3He plasmas with n(3He)/ne ≈ 20%–25% were recently performed on JET [11]
Deuterium ions from neutral beam injection (NBI) with characteristic pitch, λ = v||/v ≈ +0.62 (v|| is the ion velocity along the confining magnetic field B) and ENBI ≈ 100 keV were accelerated to high energies with waves in the ion cyclotron range of frequencies (ICRF), using the three-ion
Summary
This paper reports on sawtooth-induced AEs with toroidal mode numbers n < 0 (i.e. opposite to the ion-diamagnetic direction) and n = 0 (i.e. an axisymmetric mode), which were unexpectedly observed in recent experiments in D-3He plasmas with fusion-born alpha particles on the world-largest magnetic confinement fusion device, the tokamak JET (major radius R0 ≈ 3.0 m, minor radius a ≈ 0.9 m).
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