Cyclotron harmonic lines in the thermal magnetic fluctuation spectrum of spiraling electrons in plasmas

Journal Article · Fri Oct 01 04:00:00 EDT 1993 · Physics of Fluids B; (United States)

DOI:https://doi.org/10.1063/1.860959· OSTI ID:6022105

Stenzel, R L; Golubyatnikov, G ^[1]

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1. Department of Physics, University of California, Los Angeles, California 90024-1547 (United States)

Radio frequency (rf) magnetic fluctuations [ital [tilde B]] have been measured with loop antennas in a large pulsed discharge plasma column ([ital n][sub [ital e]][approx lt]10[sup 12] cm[sup [minus]3], [ital kT][sub [ital e]][approx lt]3 eV, [ital B][sub 0][congruent]20 G, Ar, 2[times]10[sup [minus]4] Torr, 1 m diam[times]2.5 m length). A 1/[ital f]-like noise spectrum is observed in the whistler wave regime ([omega][sub [ital ce]][sup 1/2][omega][sub [ital ci]][sup 1/2][lt][omega][lt][omega][sub [ital c][ital e]]) both in the Maxwellian afterglow plasma and in the active discharge which contains energetic (45 eV) electrons. Discrete emission lines at the electron cyclotron frequency and its harmonics are found only in the presence of spiraling energetic electrons. These are naturally present in the active discharge but have also been injected as a controlled oblique electron beam into the Maxwellian afterglow plasma. In the latter case up to 15 cyclotron harmonic lines with weak amplitude decay [ital [tilde B]][sub [ital z]]([omega]) are generated in the beam flux tube. From two-point correlation measurements it is shown that the line spectrum is due to ballistic beam modes rather than plasma eigenmodes driven unstable by the beam. The lines evolve from broadband thermal current fluctuations of the beam through a filtering effect. Those fluctuations which rotate synchronously with the ordered cyclotron motion ([omega]=[ital n][omega][sub [ital c]]) constructively interfere ([ital k][sub [parallel]]=0) and produce coherent solenoidal rf fields, while others interfere destructively. Axial and azimuthal phase velocity measurements for rf-modulated beams clearly demonstrate the filtering effect.

• OSTI ID: 6022105
• Journal Information: Physics of Fluids B; (United States), Journal Name: Physics of Fluids B; (United States) Vol. 5:10; ISSN 0899-8221; ISSN PFBPEI
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700340* -- Plasma Waves
Oscillations
& Instabilities-- (1992-)
AFTERGLOW
ANTENNAS
CYCLOTRON RESONANCE
ELECTRIC DISCHARGES
ELECTRICAL EQUIPMENT
ELECTROMAGNETIC RADIATION
ELECTRON CYCLOTRON-RESONANCE
ELECTRONS
ELEMENTARY PARTICLES
EQUIPMENT
FERMIONS
FLUCTUATIONS
INSTABILITY
LEPTONS
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
RADIATIONS
RADIOWAVE RADIATION
RESONANCE
VARIATIONS
WHISTLER INSTABILITY