Abstract Details
Abstracts
Author: Pablo Oyola
Requested Type: Poster
Submitted: 2026-03-27 14:41:08
Co-authors: V. N. Duarte, P. J. Bonofiglo, N. Bertelli, M. Podestà, J. Rueda-Rueda, K. Särkimäki, E. D. Fredrickson, R. B. White, the ASDEX Upgrade team and the NSTX-U team
Contact Info:
Princeton Plasma Physics Laboratory
100 Stellarator Rd.
Princeton, NJ 08540
USA
Abstract Text:
Fast ions generated by neutral beam injection (NBI) or radio-frequency (RF) heating can resonantly interact with background plasma and excite Alfvénic eigenmodes (AEs), in turn leading to enhanced transport and potential damage to reactor components [1]. The combined use of RF and NBI heating exhibits mixed effects on AE activity—mitigating or enhancing mode excitation in NSTX(-U) [2–4].
In low-B field spherical tokamaks (STs), and particularly for high-energy RF-accelerated ions, the guiding-center (GC) approximation breaks down, necessitating a full-orbit (FO) treatment [5]. We present benchmarks of a full-orbit RF implementation in the ASCOT5 code [6, 7] against the guiding-center Stix kick operator [8] in a conventional tokamak, ASDEX Upgrade, comparing it to experimental measurements, using the INPA diagnostic [7, 9].
Significant differences between FO and GC approaches are observed in the NSTX cases with low B-field, revealing critical impacts on the calculated fast-ion distribution and resulting AE stability. Sub-diffusive effects are observed for large ρ* particles which deviates from the quasilinear approximation underlying the current guiding center RF models. The sub-diffusive effects reduce the expected impact from the RF on the particle acceleration and could justify the lack of chirping suppression in NSTX discharges as expected from quasilinear treatment [10, 11].
[1] A. Loarte et al., PPCF 45 (2003) 1549
[2] W. W. Heidbrink et al., PPCF 48 (2006) 1347
[3] E. D. Fredrickson et al., NF 55 (2015) 013012
[4] M. Podestà et al., NF 52 (2012) 094001
[5] G. Kramer et al., PPCF 55 (2013) 025013
[6] E. Hirvijoki, PhD Thesis (2014)
[7] P. Oyola et al., in preparation
[8] T. H. Stix, NF 25 (1985) 697
[9] J. Rueda-Rueda et al., PPCF 66 (2024) 035008
[10] W. W. Heidbrink et al., PPCF 48 (2006) 1347
[11] V. N. Duarte et al., PoP 24 (2017) 122508
Characterization: 3.0
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