Speaker
Description
Energetic-ion redistribution and loss induced by MHD activity are critical issues for present fusion experiments and future burning plasmas [1,2]. In future fusion power plants, energetic-particle diagnostics must operate in reactor-relevant environments where access, neutron/gamma radiation, and the use of active beam-based measurements may be limited. Radio-frequency diagnostics are therefore attractive because they can be passive, robust, and potentially compatible with high-radiation environments [3,4]. Ion cyclotron emission (ICE), driven by non-thermal energetic-ion distributions through collective wave–particle interactions near ion cyclotron harmonics, is a promising candidate for diagnosing confined, marginally confined, and loss-related energetic ions [5,6].
In this work, we present recent measurements of ICE in KSTAR neutral-beam-injection-heated plasmas using an in-vessel B-dot probe system developed for high-frequency magnetic fluctuation measurements. High-harmonic ICE bursts were observed and found to exhibit clear temporal modulation. The ICE activity is correlated with sawtooth-like events observed in core ECE measurements, suggesting that the emission is linked to rapid redistribution of energetic ions [8]. Polarization analysis of the measured magnetic fluctuations is performed to constrain the ICE wave mode and propagation properties [3,5]. The measured ICE frequencies are interpreted using the ion cyclotron resonance condition including the Doppler-shift term, allowing an estimate of a quantity related to the fast-ion parallel energy [5,6]. Wave-dispersion analysis is also performed to examine whether the observed ICE is consistent with waves excited by energetic ions redistributed toward barely confined or loss-related orbits near the plasma edge [5,6].
These results suggest that ICE can provide time-resolved information on energetic-ion redistribution beyond simple harmonic identification. In particular, the observed ICE bursts may reflect a transient energetic-ion population that becomes marginally confined or loss-related after sawtooth-induced redistribution. To test this interpretation quantitatively, TRANSP/NUBEAM simulations will be used to reconstruct the fast-ion distribution and orbit characteristics, while FIDASIM will be used to provide synthetic fast-ion diagnostic constraints for comparison with available measurements [7,8]. This work aims to establish ICE as a complementary and reactor-relevant diagnostic for energetic-ion redistribution, marginal confinement, and fast-ion-loss-related physics in KSTAR and future fusion power plants.
This work was supported by the National Research Foundation of Korea (NRF) grants funded by the Korea government (MSIT) (Nos. RS-2023-00281272, 2022R1F1A1073863, 2024-00409564, 2026-25536992, 2026-25545529), by the R&D Program of ‘Korea-US Collaboration Research for High Performance Plasma on Tungsten Divertor (EN2603)’ through the Korea Institute of Fusion Energy (KFE) funded by MSIT, and by Glocal University 30 project. The authors acknowledge Dr. Andreas Bierwage for helpful discussions on energetic-ion physics and ICE interpretation.
[1] M. H. Kim et al., Nucl. Fusion 58, 096034 (2018).
[2] M. H. Kim et al., Nucl. Fusion 60, 126021 (2020).
[3] R. Ochoukov et al., Rev. Sci. Instrum. 86, 115112 (2015).
[4] B. C. G. Reman et al., Nucl. Fusion 59, 096013 (2019).
[5] B. Chapman et al., Plasma Phys. Control. Fusion 62, 055003 (2020).
[6] N. N. Gorelenkov, Plasma Phys. Rep. 42, 430 (2016).
[7] B. Geiger et al., Plasma Phys. Control. Fusion 62, 105008 (2020).
[8] X. D. Du et al., Nucl. Fusion 60, 112001 (2020).