A possible excitation mechanism for observed superthermal ion cyclotron emission from tokamak plasmas

Journal Article · Tue Dec 01 04:00:00 EST 1992 · Physics of Fluids B; (United States)

DOI:https://doi.org/10.1063/1.860304· OSTI ID:7028028

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)

Intense superthermal ion cyclotron emission (ICE) has been observed from tokamak plasmas. The power spectrum displays narrow peaks at multiple harmonics of the background ion cyclotron frequency (Cottrell and Dendy, Phys. Rev. Lett. {bold 60}, 33 (1988)) in Ohmic deuterium plasmas, and the radiation appears to be driven by the fusion ion population in the edge plasma. Theoretical investigation of this phenomenon may be rewarding, in terms of the information about the behavior of energetic ions in tokamaks that can be extracted from ICE observations. The interpretation presented here is based on the resonant excitation of fast Alfven waves with ion Bernstein waves supported by an energetic ion species ({alpha}), in the presence of a more numerous thermal ion species ({ital i}). Because the ion cyclotron frequencies may be commensurate ({ital l}{Omega}{sub {alpha}}={ital s}{Omega}{sub {ital i}} for some low integers {ital l},{ital s}), and observations indicate that {omega} is comparable in magnitude to {Omega}{sub {ital i}}, the standard theory (Belikov and Kolesnichenko, Sov. Phys. Tech. Phys. {bold 20}, 1146 (1976)) which assumes {omega}{much gt}{Omega}{sub {ital i}} is not immediately applicable, and is accordingly extended here to the low-frequency regime. The results show that excitation of the fast Alfven wave at proton cyclotron harmonics can occur for fusion proton concentrations {ital n}{sub {alpha}}/{ital n}{sub {ital i}} as low as 10{sup {minus}7}, and that multiple cyclotron harmonics can be simultaneously unstable. Furthermore, while fusion protons born at 3.0 MeV are above the energy threshold required to drive the instability, the other primary fusion products in deuterium---1.0 MeV tritons and 0.82 MeV helium-3 nuclei---fall below it, consistent with the observation that radiation at cyclotron harmonics of the latter is not detected.

• OSTI ID: 7028028
• Journal Information: Physics of Fluids B; (United States), Journal Name: Physics of Fluids B; (United States) Vol. 4:12; ISSN 0899-8221; ISSN PFBPE
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700340* -- Plasma Waves
Oscillations
& Instabilities-- (1992-)
ALFVEN WAVES
BARYONS
BERNSTEIN MODE
CLOSED PLASMA DEVICES
CYCLOTRON RESONANCE
DEUTERIUM
ELEMENTARY PARTICLES
ENERGY-LEVEL TRANSITIONS
EXCITATION
FERMIONS
HADRONS
HYDROGEN ISOTOPES
HYDROMAGNETIC WAVES
INSTABILITY
ION CYCLOTRON-RESONANCE
ISOTOPES
LIGHT NUCLEI
MAGNETOACOUSTIC WAVES
NUCLEI
NUCLEONS
ODD-ODD NUCLEI
OSCILLATION MODES
PLASMA INSTABILITY
PLASMA MICROINSTABILITIES
PROTONS
RESONANCE
STABLE ISOTOPES
THERMONUCLEAR DEVICES
TOKAMAK DEVICES