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

Effects of fishbone-like mode on energetic particle transport and loss intokamak plasmas
Y.Q.Wang1*, G.Z.Hao1, Y.P.Zou1, Y.Q.Liu2, W.Chen1, G.Meng3, Y.F.Zhao4, Y.G.Ming1
1Southwestern Institute of Physics, Chengdu, People’s Republic of China 2General Atomics, San Diego, United Statesof America 3 Max Planck Institute for Plasma Physics, Garching, Germany 4School of Physics, Dalian University ofTechnology, Dalian, People’s Republic of Chinae-mail (speaker): wangyongqin@swip.ac.cn
Fishbone-like modes (FLM) are often observed in
the wall-stabilized high-𝛽𝑁 (above the no-wall 𝛽𝑁limit) plasmas in JT-60U [1,2] and DIII-D [3,4]. The
mode frequency essentially matches the precessional
drift frequency of trapped EPs [5,6]. FLMs, which areassociated with the XK, can be viewed as an analog tothe classical fishbone (FB) associated with the internal
kink. During a FLM burst, significant EP losses wereobserved with the simultaneous decrease of neutron rateand reduction of the plasma rotation [3,4,7,8]. Much
fewer studies have been carried out on the influence ofthe external kink or fishbone-like mode instabilities onEP confinement. More specifically, the effects of thefishbone-like mode on the EP transport and loss weremainly investigated in experiments [2,4], where it was
found that the EP transport and losses depend on themode perturbation and frequency.
The FLM has been observed in the HL-2A high-𝛽𝑁
experiments recently [9]. Therefore, systematicinvestigations have been produced on the redistribution
and loss of energetic particles (EPs) due to threedimensional (3D) FLM instability, utilizing the MHD
stability code MARS-F and the guiding center orbit
following code ORBIT. The FLM is identified as an EP
driven branch of external kink (XK) [3,6]. The
eigenmode structure of XK is employed to mimic theFLM perturbation by scanning the mode frequency.
We found that the mode frequency has more significant
effects on EP transport than amplitude. A 20 kHz FLM
induces dramatic EP transport in both the configurationand particle phase spaces and the loss fraction reaches
46% in the case as shown in Fig 1. EP loss is thedominate process in EP transport in the study
In the EP phase space, EP transport occurs mainly
near 10keV energy range and with the particle velocity
pitch Λ near 0.6. Both Λ and energy are modified by
the resonance interactions between FLM and EPs. The
simulated results are qualitatively consistent with thatobserved in DIII-D experiments [4]. In particular,experimental observations indicate a linear to quadratictransition for the dependence of the EP loss fraction withincreasing mode amplitude. The modelled enhancementof the EP loss fraction with increasing perturbation
frequency is also in qualitative agreement with thatobserved in DIII-D.

We also find the particle collisions enhance the EP
transport in phase space as shown in Fig 2. As a result,the pitch angle Λ of EP decreases, converting theparticle orbit from the passing to the trapped one. The
resonance conditions are identified which predictdomains in the particle phase space where significant
changes to the EP distribution occur. These domains inturn coincide well with that shown in the modelled EP
transport results.

Fig 1. The redistribution factor I (a) and loss fraction (b)versus the FLM frequency.

Fig 2. (a) The initial distribution of lost EPs and (b) thedistribution of lost EPs in 𝑃ζ –𝜇 phase space.
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