The RISK (rapid ion solver for tokamaks) code for simulating the evolution of the distribution function of neutral beam injected ions (NBI) in tokamak plasmas is described. The code has been especially developed for use in integrated modelling frameworks. Within this context, a code needs to be modular, machine independent and fast. RISK fulfils all these conditions. The RISK code solves the bounce averaged Fokker–Planck equation for the species of the injected ions by expanding the distribution function in the eigenfunctions of the collisional pitch angle scattering operator. The velocity dependent coefficient functions are calculated with a finite element solver. Finite orbit width effects are handled by an ad hoc broadening algorithm of the NBI ionization source. In order to assess the validity of the approximations employed in RISK, a comparison with a full orbit following Monte Carlo code is presented. RISK is integrated into the CRONOS transport suite of codes (Artaud et al 2010 Nucl. Fusion50 043001) and the European integrated modelling (EU-IM) framework (Falchetto et al 2014 Nucl. Fusion54 043018). The RISK implementation in this platform is discussed and exemplified to show the strength of running simulation codes in a modular and machine independent environment for simulation of fusion plasmas.
Modelling of charge-exchange induced NBI losses in the COMPASS upgrade tokamak