Simulation of Observed EGAM Induced Beam-ion Losses in DIII-D

In DIII-D a non-perturbative beam-driven instability, the energetic particle geodesic acoustic mode (EGAM) is often observed when counter-going beams are injected in the current ramp-up phase of the discharge. The EGAM is an $n=0$ mode in the plasma core with a frequency about 50\% below the ideal GAM and it is an excellent mode to validate codes that are used to predict fast-ion losses in burning plasmas. When the EGAM appears the 2.5 MeV neutron emission drops 10\% to 15\%. This signal is dominated by beam-ion collisions with the thermal plasma and indicates a decrease in the fast-ion population. Recently, accurate measurements have been made of EGAM induced losses with a fast-ion loss detector (FILD) mounted below the mid-plane in DIII-D. We report on state-of-the-art full-orbit following fast-ion loss simulations for the first 50 ms of beam injection using the 3-D beam birth deposition from TRANSP. A very good qualitative agreement between simulation and experiment was found.