Reduced model for resonance overlap threshold governing transport of fast ions by TAEs
This work introduces a reduced model to predict the “resonance overlap threshold” governing transport of Fast Ions (FIs) by Toroidal Alfven Eigenmodes (TAEs) in tokamak plasmas. TAE-FI resonance occurs within distinct “resonance regions” of particle phase space, which grow wider when the TAE mode amplitude increases. If these resonance regions are separate then FI transport is limited and localised; if multiple resonance regions overlap then large-scale stochastic transport of FIs can occur, jeopardising confinement. Predicting the resonance overlap threshold between these two scenarios is an important problem in the field of FI transport modelling. Current workflows rely on computationally expensive orbit-following codes; the new reduced resonance overlap model (RROM) provides a much simpler and faster alternative, for ease of implementation in integrated models. Results from the RROM are benchmarked against HALO code simulations and existing theory. This model provides a useful step in increasing efficiency of predictive modelling for next-generation fusion reactors.