Speaker
Description
Projecting fast ion dynamics from present devices to a fusion reactor requires a combination of experimental results and numerical models. Confidence in the models relies on their extensive validation to ensure that the underlying physics is correct, as well as to assess their range of validity and possible limitations. Experiments on TCV have revisited the physics of well-known instabilities such as fishbones to gather a database for model validation. In parallel, several existing analysis and modeling tools have been combined in a single workflow to enable comprehensive tests and validation. Experimentally, the effects of fishbones on fast ions from Neutral Beam Injection (NBI) are characterized via diagnostics for confined and lost ions, namely neutron counters, Fast Ion D-Alpha (FIDA) and a Fast Ion Loss Detector (FILD) [1]. Mode properties are inferred from magnetic sensors and soft X-rays detectors covering the poloidal cross-section. Experimental data are used to guide modeling of the fast ion transport and loss induced by fishbones. Modeling is conducted via the particle-following code Orbit and with the combined TRANSP+kick model [2]. Results are in qualitative agreement with measurements from FIDA and FILD, indicating a redistribution of particles from the core – where the fishbone amplitude peaks – to mid-radius. Depending on the mode amplitude, fast ions near the co-passing/lost and trapped/lost boundaries can reach FILD, with characteristic values of energy and pitch that vary in time as the mode frequency and amplitude evolve [1]. The possibility to reconstruct modifications of the fast ion distribution induced by fishbones directly from experimental FIDA and FILD data is explored, by both forward modeling [1] and inversion techniques [3]. The results from modeling and forward/inverse analysis will be compared to assess the ability to infer the fast ion distribution response to the instability, as well as to assess the limitations of each method. The possible extension of those methods to more complex instabilities such as Alfvénic modes on TCV [4] will also be discussed.
[1] Q. Kernel et al., Experimental characterization of fishbones and associated energetic particle transport via correlated FIDA and FILD measurements on the TCV tokamak (this conference).
[2] M. Podestà et al., Plasma Phys. Control. Fusion 59 (2017) 095008.
[3] M. Rud et al., Resonant mode-particle interaction priors for energetic particle phase-space tomography (this conference).
[4] A. Jansen van Vuuren et al., Experimental investigations of Alfvén eigenmode control in TCV fast-ion plasmas (this conference).