7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Challenges to control the nonlinear wave-particle interactions using laboratoryplasmas
K. Nagaoka1,2, K. Nagasaki3, S. Kamio4, Y. Fujiwara4, Y. Katoh51
National Institute for Fusion Science, 2 Nagoya Univ. 3 Kyoto Univ., 4 UC Irvine, 5 Tohoku Univ.
e-mail (speaker): nagaoka@nifs.ac.jp
Wave-particle interactions in magnetized plasmas
attract much attention in both space plasma physics andlaboratory plasma physics research. Wave excitations
and nonlinear behaviours observed in the magnetospherehave been strongly studied so far. Recently, in-situ
measurement of the velocity distribution functions ofions and electrons due to satellites significantly progress
the study of kinetic dynamics, in particular, article
acceleration, particle losses into the loss cone, etc.
Inthe laboratory, the deformation of the velocity
distribution function of ions interacting with large
amplitude MHD burst was observed, and the energy
transfer rate was evaluated [1]. Moreover, the nonlinear
transport of energetic ions interacting with Alfven
eigenmodes (AE: eigenmode in the double-periodic
boundary of the torus geometry) was also identified
based on hybrid simulation studies [2]. Recently, external
control of such energetic ion transport was successfully
demonstrated in torus plasmas [3], which is a very
important subject for realizing the stable fusion burning
plasmas. In this paper, the laboratory experiments on
active control of wave-particle interactions are presented,
and the possibility of interdisciplinary collaboration will
be discussed.
[Active control of energetic particle transport driven
by Alfven eigenmodes]
The electron cyclotron wave obliquely injected onto theresonance layer can drive plasma current locally andchange the local magnetic shear in the plasma. This
electron cyclotron current drive (ECCD) was applied tothe plasma and clear responses of Alfven eignemodes(AEs) were observed in Heliotron J and LHD plasmas[3]. The AE responses observed in both devices may becommonly understood with the magnetic shear effect on
the AE damping, while they have different magnetic
configurations. In the case that the magnetic shear isenhanced, the mitigation of energetic ion transport isobserved as well as the AE mitigation.
[Effect of electron cyclotron heating on AE activities]
The AE responses to the application of the electron
cyclotron heating (ECH) was observed in DIII-D
tokamak, TJ-II, Heliotron J, LHD plasmas [4,5].
However, a variety of AE responses were observed, somecases enhanced the AE, some mitigated, and others madeno impact. A kinetic effect of trapped electrons wasproposed theoretically, but the mechanism of thectr-ECCD
Mag. Shear：Large＝＞Stabilizedbalanced-ECCD

co-ECCDMag. Shear：Small＝＞Destabilized

Fig. 1 AE response to the application of ECCD
on LHD experiment. []complicated AE-responses is not understood yet.
In conclusion, active control of wave-particle interaction
opened a new door in plasma physics. It was also foundthat the ECCD application is effective to the active
control of profile stiffness of energetic particles, which isrealized nonlinear excitation of AEs, which will bereported elsewhere. It is noted that active control ofwave-particle interaction in both space and laboratory
plasmas will significantly enhance deep understandingand new applications of the plasma physics.
References[1] K. Ida, et al., Comm. Phys., 5, 228 (2022).
[2] Y. Todo, et al. Nucl. Fusion, 59, 096048 (2019).
[3] S. Yamamoto, et al., Nuclear Fusion, 60, 066018(2020).
[4] Van Zeeland, et al., Plasma Phys. Control. Fusion, 50,035009 (2008).
[5] K. Nagaoka, et al., Nucl. Fusion, 53, 072004 (2013).