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OT08 · Non-Conventional Fishbone Instabilities Driven by Circulating Energetic Ions

V.S. Marchenko¹, Ya.I. Kolesnichenko¹, R.B. White²

¹Institute for Nuclear Research, National Academy of Sciences of Ukraine, Kyiv, 03680, Ukraine
²Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey, 08543, USA

Abstract: A new kind of fishbone instability associated with circulating energetic ions is predicted. The considered instability is essentially the energetic particle mode and arises in plasmas with on-axis safety factor q₀ close to unity and extended shear-free central core, separated from the wall by a region with finite shear. The frequency of this "quasi-interchange" fishbone mode is ω ~ k_0||v_α with k_0|| the parallel wave number in the shear-free core and ν_α the injection velocity of energetic ions. "Infernal" fishbone modes with the same properties, but m/n > 1 with m(n) the poloidal (toroidal) mode number, are investigated. A possibility to explain recent experimental observations of the m=2 fishbone oscillations accompanied by strong changes of the neutron emission during tangential neutral beam injection in the National Spherical Torus Experiment is shown.

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