RABBIT: Real-time simulation of the NBI fast-ion distribution

A novel code is presented, which is capable of computing the NBI fast-ion distribution in real-time. We discuss the approximations needed to arrive at this goal: a simplified beam geometry is used for calculating the beam attenuation. Finite-orbit-width effects are taken into account by an orbit average of the beam deposition. The time-dependent solution of the Fokker-Planck equation (2D in velocity) is then calculated based on analytic expressions. This code currently takes approximate to 25 ms per time step, which is roughly a factor of 1000 faster than the more sophisticated NUBEAM code. Nevertheless, good agreement between both codes is found in a comprehensive benchmark.