PPPL-5217

Effects of energetic particle phase space modifications by 
instabilities on integrated modeling

Authors:   M. Podesta, M. Gorelenkova, E. Fredrickson, N. N. Gorelenkov, R. B.White

Abstract:  Tokamak plasmas can feature a large population of energetic particles (EP) from Neutral Beam injection or fusion reactions. In turn, energetic particles can drive instabilities, which a ffect the driving EP population leading to a distortion of the original EP distribution function and of quantities that depend on it. The latter include, for example, Neutral Beam (NB) current drive and plasma heating through EP thermalization. Those e ffects must be taken into account to enable reliable and quantitative simulations of discharges for present devices as well as predictions for future burning plasmas. Reduced models for EP transport are emerging as an eff ective tool for long time-scale integrated simulations of tokamak plasmas, possibly including the eff ects of instabilities on EP dynamics. Available models diff er in how EP distribution properties are modifi ed by instabilities, e.g. in terms of gradients in real or phase space. It is therefore crucial to assess to what extent di fferent assumptions in the transport models a ffect predicted quantities such as EP profi le, energy distribution, NB driven current and energy/momentum transfer to the thermal populations. A newly developed kick model, which includes modi fications of the EP distribution by instabilities in both real and velocity space, is used in this work to investigate these issues. Coupled to TRANSP simulations, the kick model is used to analyze NB-heated NSTX and DIII-D discharges featuring unstable Alfven eigenmodes (AEs). Results show that instabilities can strongly a ffect the EP distribution function, and modi fications propagate to macroscopic quantities such as NB-driven current profi le and NB power transferred to the thermal plasma species. Those important aspects are only qualitatively captured by simpler fast ion transport models that are based on radial di ffusion of energetic ions only.
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Submitted to:  Nuclear Fusion
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