Phase space effects on fast ion distribution function modeling in tokamaks
Authors: M. Podesta , M. Gorelenkova, E. D.
Fredrickson, N. N. Gorelenkov and R. B. White
Abstract: Integrated simulations of tokamak
discharges typically rely on classical physics to model energetic
particle (EP) dynamics. However, there are numerous cases in which
energetic particles can su ffer additional transport that is not
classical in nature. Examples include transport by applied 3D
magnetic perturbations and, more notably, by plasma instabilities.
Focusing on the e ffects of instabilities, ad-hoc models can
empirically reproduce increased transport, but the choice of
transport coefficients is usually somehow arbitrary. New
approaches based on physics-based reduced models are being
developed to address those issues in a simpli ed way, while
retaining a more correct treatment of resonant wave-particle
interactions. The kick model implemented in the tokamak transport
code TRANSP is an example of such reduced models. It includes
modi fications of the EP distribution by instabilities in real and
velocity space, retaining correlations between transport in energy
and space typical of resonant EP transport. The relevance of EP
phase space modi fications by instabilities is first discussed in
terms of predicted fast ion distribution. Results are compared
with those from a simple, ad-hoc diff usive model. It is then
shown that the phase-space resolved model can also provide
additional insight into important issues such as internal
consistency of the simulations and mode stability through the
analysis of the power exchanged between energetic particles and
the instabilities.
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