Authors: M. Podesta
Abstract:
Alfvenic instabilities (AEs) are well known as a potential cause
of enhanced fast ion transport in fusion devices. Given a specific
plasma scenario, quantitative predictions of (i) expected unstable
AE spectrum and (ii) resulting fast ion transport are required to
prevent or mitigate the AE-induced degradation in fusion
performance. Reduced models are becoming an attractive tool to
analyze existing scenarios as well as for scenario prediction in
time-dependent simulations. In this work, a neutral beam heated
NSTX discharge is used as reference to illustrate the potential of
a reduced fast ion transport model, known as kick model, that has
been recently implemented for interpretive and predictive analysis
within the framework of the time-dependent tokamak transport code
TRANSP. Predictive capabilities for AE stability and saturation
amplitude are rst assessed, based on given thermal plasma
profiles only. As an example of the flexibility of the model
within TRANSP, changes in the mode's behavior are discussed when
neutral beam injection parameters are varied. Predictions are then
compared to experimental results, and the interpretive
capabilities of the model further discussed. Overall, the reduced
model captures the main properties of the instabilities and
associated effects on the fast ion population. Additional
information from the actual experiment enables further tuning of
the model's parameters to achieve a close match with measurements.
Submitted to: Plasma Physics and Controlled Fusion
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