Description
The external heating methods such as ECRH, ICRF heating, and NBI can achieve the velocity population inversion at least for a short time. With the existence of the velocity population inversion, non-thermal radiations are generated as the results of kinetic instabilities. With using of high speed digitizers, various types of precise frequency spectrograms of non-thermal radiations have been observed during the external heating at LHD, and Heliotron-J.
• Harmonic ion cyclotron emissions at the peripheral region originated perpendicular NB [1,2]
• Harmonic ion cyclotron emissions at the peripheral region originated fusion born alpha particles during perpendicular NB when large reconnection events occur [3]
• Lower hybrid frequency and its harmonic frequency ranges accompanied with the sidebands characterized by ion cyclotron frequencies during tangential NB [4]
• Lower hybrid frequency and its harmonic frequency ranges accompanied with the sidebands characterized by ion cyclotron frequencies during perpendicular Helium NB
• Large relativistically shifted emission in harmonic electron cyclotron frequency range during ECRH/ECCD in very low dense plasmas [5]
Non-linear couplings between non-thermally emitted waves that are originated at spatially separated regions are observed. This fact suggests that we should consider the propagation, absorption, and linear and non-linear mode conversion processes as the energy cascade process of energetic particles generated via external heating methods or the nuclear fusion reaction.
References
[1]. K. Saito, H. Igami. M. Toida et al., Plasma and Fusion Research, 13, (2018) 3402043
[2]. B.C.G. Reman et al, Nucl. Fusion, 61. (2021) 066023
[3]. B.C.G. Reman et al, Nucl. Fusion, 64. (2023) 085008
[4]. E. Toida, H. Igami. K. Saito et al., Plasma and Fusion Research, 14, (2019) 3401112
[5]. H. Igami et al., “Observation of bursty non-thermal electron cyclotron waves with fast frequency sweeping during ECRH/ECCD”, at 22nd Joint WS on ECE and ECRH, (2024)
