Multi-mode Alfvénic fast particle transport and losses: numerical versus experimental observation

In many discharges at A SDEX Upgrade (A UG ) fast particle losses can be observed due to Alfvénic gap modes, reversed shear Alfvén eigenmodes or core-localized beta Alfvén eigenmodes. For the first time, simulations of experimental conditions in the A UG fusion device are performed for different plasma equilibria (particularly for different, also non-monotonic q profiles). The numerical tool is the extended version of the H AGIS code (Pinches et al 1998 Comput. Phys. Commun. 111 133–49 , Brüdgam 2010 PhD Thesis ), which also computes the particle motion in the vacuum region between the vessel wall in addition to the internal plasma volume. For this work, a consistent fast particle distribution function was implemented to represent the strongly anisotropic fast particle population as generated by I CRH minority heating. Furthermore, H AGIS was extended to use more realistic eigenfunctions, calculated by the gyrokinetic eigenvalue solver L IGKA (Lauber et al 2007 J. Comput. Phys. 226 447–65 ). The main aim of these simulations is to allow fast ion loss measurements to be interpreted with a theoretical basis. Fast particle losses are modelled and directly compared with experimental measurements (García-Muñoz et al 2010 Phys. Rev. Lett. 104 185002 ). The phase space distribution and the mode-correlation signature of the fast particle losses allows them to be characterized as prompt, resonant or diffusive (non-resonant). The experimental findings are reproduced numerically. It is found that a large number of diffuse losses occur in the lower energy range (at around 1/3 of the birth energy) particularly in multiple mode scenarios (with different mode frequencies), due to a phase space overlap of resonances leading to a so-called domino (Berk et al 1995 Nucl. Fusion 35 1661 ) transport process. In inverted q profile equilibria, the combination of radially extended global modes and large particle orbits leads to losses with energies down to 1/10th of the birth energy.