Observation of beam-generated VLF hiss in a large laboratory plasma

Journal Article · Sat Oct 01 04:00:00 EDT 1977 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JA082i029p04805· OSTI ID:7277798

Stenzel, R L

The predicted instability of obliquely propagating whistler waves in a plasma penetrated by an electron beam is verified in a laboratory experiment. The observations support the model for the generation of auroral hiss and compare favorably with ground and satellite observations of VLF hiss. In contrast to the conventional small-diameter laboratory beam-plasma systems the present device is large in comparison to the characteristic whistler wavelength (lambdaapprox. =2-4 cm; beam and plasma diameter, 45 cm; length, 250 cm). Unstable whistlers can therefore propagate and grow oblique to the beam over many wavelengths before encountering the plasma boundaries. When a cold (1 eV), energetic (40 eV), low-density (n/sub b/approx. =10/sup 8/ cm/sup -3/) electron beam is injected along the magnetic field (B/sub 0/=75G) into an initially cold (kT/sub e/approx. =1/4 eV), dense (n/sub e/approx. =10/sup 10/ cm/sup -3/) background plasma, the spontaneous emission of broadband RF noise ranging from the lower hybrid frequency ..omega../sub l h/ to the electron cyclotron frequency ..omega../sub e/ is observed. By performing narrowband two-dimensional cross-correlation measurements between two small antennas the RF noise is identified from its dispersion characteristics ..omega.. (k) as whistler waves propagating near the oblique resonance angle theta=arccos (..omega../..omega../sub e/). The parallel phase velocity is close to the beam velocity (..omega../k9 or approx. =upsilon/sub b/). Although the instability amplitude is far above the thermal noise level, it is not large enough to give rise to significant nonlinear effects. The instability saturates when the higher-frequency short-wavelength electrostatic instabiliy near the electron plasma frequency (s/sub p//sup 2/>>w/sub/ e//sup 2/) forms a plateau in the beam distribution. Time- and space-resolved electron pitch angle distribution function measurements are performed. The propagation of the whistlers out of the instability region and refraction into electromagnetic whistlers are observed.

• Research Organization: TRW Systems, Redondo Beach, California 90278
• OSTI ID: 7277798
• Journal Information: J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 82:29; ISSN JGREA
• Country of Publication: United States
• Language: English

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71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
AURORAL HISS
BEAM-PLASMA SYSTEMS
BEAMS
COLD PLASMA
COLLISIONLESS PLASMA
ELECTROMAGNETIC RADIATION
ELECTRON BEAMS
INSTABILITY
LEPTON BEAMS
NOISE
PARTICLE BEAMS
PLASMA
PLASMA INSTABILITY
RADIATIONS
RADIO NOISE
RADIOWAVE RADIATION
WAVE PROPAGATION
WHISTLERS