The research program will deliver a suite of validated energetic particle (EP) modeling tools for time-dependent integrated tokamak simulations that can be used to model plasma discharges featuring a substantial EP content, such as burning plasmas. ‘Neoclassical’ EP dynamic is well described by present theories. (Here we adopt the term neoclassical to refer to fast ion collisional transport in the absence of instabilities). However, microturbulence and MHD – not included in neoclassical theory - can enhance EP transport, which in turn affects heating and current drive performance and discharge evolution/stability. The effects of instabilities on the EP dynamic need to be included for quantitative interpretive and predictive time-dependent simulations through codes such as TRANSP.
European facilities offer opportunities for the validation of EP transport models that are not presently available on US devices. The planned D-T campaign on JET will provide unique data to validate models under burning plasma conditions. Data from ASDEX-Upgrade, in which NB ions are accelerated by ICRH, can be used as a proxy for alphas under very well diagnosed experimental conditions. The TCV device offers excellent flexibility in terms of heating schemes (ECH vs NBI) and plasma shaping, which can be exploited to vary in a controlled way the E/Te and Te/Ti ratios (E: NB injection energy) and NB deposition profile to assess the role of microturbulence and EP-driven modes on EP transport. Scenario development for alpha particle physics studies in NBI and NBI+ICRH heated plasmas is presently one of the main activities in view of the JET D-T campaign, in parallel with the commissioning of diagnostics to monitor EP behavior and activity of EP-driven instabilities. The research activities align well with the EU plans by providing validated tools for reliable interpretation of burning plasma regimes on JET and their extrapolation to ITER. Notably, JET plans envision to study alpha physics in the transient phase after NB switch-off (“after-glow”) in which the drive from alphas can overcome the drive/damping from NB ions, thus enabling the unambiguous assessment of AE drive by alphas. Because of the lack of measurements critical for EP studies (e.g. q-profile, rotation), reliable modeling of the transient after-glow phase requires an assessment of time-dependent capabilities with reduced inputs.
The proposed activities focus on two main goals: (i) leverage the unique opportunity that the coming JET D-T experiments will offer for studying burning plasma regimes, and (ii) validate reduced-physics EP transport models for burning plasma scenarios in TRANSP. Research on ASDEX-Upgrade and TCV will complement validation activities with additional data from well-diagnosed experiments on EP transport by instabilities and EP interaction with RF waves. The project includes four US institutions coordinated by PPPL, starting from the ongoing JET/PPPL collaboration on fast ion loss measurements, EP transport and scenario development. Results are expected to expand – and be coordinated with - work by the US EP and RF SciDAC Centers towards burning plasma regimes, as well as to contribute to ITPA-EP Joint Activities.
