The ion‐acoustic instability of the helium positive column in the pressure regime 0.05 to 0.25 Torr is studied. Instability of the column is predicted by a kinetic theory which includes the effects of collisions with neutrals, but not by a hydrodynamic theory. In the regime of the experiment the ion‐acoustic instability arises from the resonant interaction of those electrons having velocities close to the phase velocities of the ion‐acoustic waves (inverse Landau damping) even though the electron‐neutral collision frequency exceeds the ion‐acoustic frequency. The helium positive column is well suited to the study of this instability mechanism because the important velocity hierarchy ion thermal velocity ion‐acoustic phase velocity electron drift velocity electron thermal velocity is naturally well established. The detection of the spontaneously excited waves is found to be crucially dependent on the bias of the detecting probe. The onset characteristics, spectral properties, spatial distribution, and saturation intensity are measured and compared with theoretical predictions.
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June 1973
Research Article|
June 01 1973
Ion‐acoustic instability in the positive column of a helium discharge
D. B. Fenneman;
D. B. Fenneman
Department of Physics and Coordinated Science Laboratory, University of Illinois, Urbana, Illinois 16801
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M. Raether;
M. Raether
Department of Physics and Coordinated Science Laboratory, University of Illinois, Urbana, Illinois 16801
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M. Yamada
M. Yamada
Department of Physics and Coordinated Science Laboratory, University of Illinois, Urbana, Illinois 16801
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Phys. Fluids 16, 871–878 (1973)
Article history
Received:
August 28 1972
Received:
February 01 1973
Citation
D. B. Fenneman, M. Raether, M. Yamada; Ion‐acoustic instability in the positive column of a helium discharge. Phys. Fluids 1 June 1973; 16 (6): 871–878. https://doi.org/10.1063/1.1694439
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