Real-time simulation of the NBI fast-ion distribution

Knowledge of the fast-ion distribution arising from neutral beam injection (NBI) is important for transport analysis and magnetic equilibrium reconstruction. For advanced plasma control, which will be essential for the operation of future fusion devices, it is very beneficial to know this distribution function already in real-time during the discharge.
Several numerical codes exist, that can calculate this beam ion distribution in good agreement with experimental data, such as the Monte-Carlo code NUBEAM. The high accuracy of these codes has, however, to be paid with relatively intensive numerical efforts, which compromises their use in real-time applications. In this contribution, we present the novel code RABBIT (Rapid Analytical Based Beam Injection Tool). RABBIT currently takes ≈20 ms per time step, which is roughly a factor of 1000 faster than NUBEAM, while benchmarks still indicate a good agreement between both.
Several applications of the model on different machines are carried out. RABBIT is run in real-time in the discharge control system of ASDEX Upgrade to improve active plasma control. In addition, RABBIT is embedded in the IDE code suite for accurate equilibrium reconstructions in between shots. This facilitates the development of advanced scenarios, where a tailoring of the q-profile is desired.
On DIII-D, RABBIT is foreseen to be used in experiments with the goal to demonstrate real-time control of Alfvén eigenmodes (AE). Precisely, the neutron rate predicted by RABBIT is compared to its measurement to detect neutron deficit attributable to fast-ion transport. In conjunction with direct AE detection with ECE diagnostics, when detrimental conditions are observed, counter-measures to stabilize AEs can be activated during the discharge. This could be of great importance for future fusion reactors, where strong AE activity is expected.