Fast-ion losses induced by ACs and TAEs in the ASDEX Upgrade tokamak

Abstract

The phase-space of convective and diffusive fast-ion losses induced by shear Alfvén eigenmodes has been characterized in the ASDEX Upgrade tokamak. Time-resolved energy and pitch-angle measurements of fast-ion losses correlated in frequency and phase with toroidal Alfvén eigenmodes (TAEs) and Alfvén cascades (ACs) have allowed to identify both loss mechanisms. While single ACs and TAEs eject resonant fast-ions in a convective process, the overlapping of AC and TAE spatial structures leads to a large fast-ion diffusion and loss. The threshold for diffusive fast-ion losses depends on the ion energy (gyroradius). Diffusive fast-ion losses with gyroradius ≈70 mm have been observed with a single TAE for local radial displacements of the magnetic field lines larger than ≈2 mm. Multiple frequency chirping ACs cause an enhancement of the diffusive losses. The ACs and TAEs radial structures have been reconstructed by means of cross-correlation techniques between the fast-ion loss detector and the electron cyclotron emission radiometer.

Measurements of fast-ion transport by mode-particle resonances on DIII-D

“…TAEinduced losses have also been observed on JET and ASDEXUpgrade [9][10][11]. Similar to the fast-ion losses by fishbones and sawteeth, the TAE-induced losses are explained in terms of particles phase-locking with the mode and experiencing convective losses due to outward E × B drifts.…”

Numerical study on wave-induced beam ion prompt losses in DIII-D tokamak

“…[1][2][3][4][5][6][7][8][9] The losses were measured using a Fast Ion Loss Detector (FILD) with a high frequency response and were coherent with the Alfv en eigenmodes. It was shown that the coherent losses in DIII-D mainly come from trapped particles whose orbits are close to the tokamak wall.…”

Measurements of the eigenfunction of reversed shear Alfvén eigenmodes that sweep downward in frequency

“…[1][2][3] RSAEs cause fast-ion transport. [4][5][6][7] They also provide accurate information about the evolution of the q profile: When q min is an integer value, a "grand cascade" of many RSAEs with different toroidal mode numbers n is often observed. 2 In the laboratory frame, the frequency x of an RSAE is approximately 8 x…”

“…In the vast majority of published cases, [1][2][3][4][5][8][9][10][11][12][13][14][15][16][17][18][19][20][21] the modes first appear when q min ¼ m=n, then the mode frequency sweeps upward in frequency as the q profile evolves. Very rarely, 8,22,23 a mode will sweep downward to the minimum frequency, then sweep upward in the normal fashion.…”