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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