The magnetoacoustic cyclotron instability of an extended shell distribution of energetic ions

Journal Article · Thu Jul 01 00:00:00 EDT 1993 · Physics of Fluids B; (United States)

DOI:https://doi.org/10.1063/1.860781· OSTI ID:6423545

Dendy, R O; Lashmore-Davies, C N; Kam, K F ^[1]

---

1. AEA Fusion, Culham Laboratory (Euratom/UKAEA Fusion Association), Abingdon, Oxfordshire, OX14 3DB (United Kingdom)

The magnetoacoustic cyclotron instability is a mechanism by which waves on the perpendicular fast Alfven-ion Bernstein branch can be excited through cyclotron resonance with an energetic ion population. It is a candidate emission mechanism for the superthermal ion cyclotron radiation, apparently associated with the products of fusion reactions, that has been observed from tokamak plasmas. In the present paper, an extended shell model is adopted for the energetic ion distribution function, [ital f][sub [alpha]]([bold v])[similar to][ital n][sub [alpha]] exp[[minus]([ital v][minus][ital v][sub 0])[sup 2]/[ital v][sub [ital T]][sup 2]]. An analytical formulation of the dispersion relation is obtained, whose numerical solution yields quantitative information on the role of [ital v][sub [ital T]] in stabilizing wave growth at ion cyclotron harmonics. The results show that, for typical plasma parameters of interest, the degree of instability is significantly depressed, relative to its level for [ital v][sub [ital T]]=0, once [ital v][sub [ital T]]/[ital v][sub 0][congruent]0.1. Gaps appear in typical multiple cyclotron harmonic excitation patterns for 0.1[le][ital v][sub [ital T]]/[ital v][sub 0][le]0.2, and most harmonics are stable for [ital v][sub [ital T]]/[ital v][sub 0][ge]0.25. Thus the energetic ion shell-driven magnetoacoustic cyclotron instability typically occurs only when the shell is relatively narrow in velocity space.

• OSTI ID: 6423545
• Journal Information: Physics of Fluids B; (United States), Vol. 5:7; ISSN 0899-8221
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
MAGNETOACOUSTIC WAVES
CYCLOTRON INSTABILITY
SHELL MODELS
ALFVEN WAVES
BERNSTEIN MODE
CYCLOTRON RESONANCE
DISPERSION RELATIONS
DISTRIBUTION FUNCTIONS
NUMERICAL SOLUTION
FUNCTIONS
HYDROMAGNETIC WAVES
INSTABILITY
MATHEMATICAL MODELS
NUCLEAR MODELS
OSCILLATION MODES
PLASMA INSTABILITY
PLASMA MICROINSTABILITIES
RESONANCE
700340* - Plasma Waves
Oscillations
& Instabilities- (1992-)