ISSN:
1573-8620
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Maschinenbau
,
Physik
Notizen:
Abstract The conditions for periodicity of the spatial distribution of plasma oscillation intensity upon excitation by an electron beam are investigated. It is established that periodicity is observed in the presence of a boundary reflecting primary or emitting secondary electrons which form a reflected wave. If there is no such boundary, then the oscillations build up in accordance with the principles of the theory of convective plasma instability. Merrill and Webb [1] first discovered that in gas discharge tubes at low pressure, regions of intense plasma oscillation and regions scattering of primary electrons emitted from the cathode have a spatially periodic structure. A theory to account for these results was developed in [2] on the basis of the notion of velocity modulation of primary electrons on passage through an oscillating double layer at the boundary of the plasma and bunching near the focal plane (in much the same way as in a klystron). Later [3, 4] it was noted that periodicity of oscillation intensity distribution is observed in some cases, but not in others. In [5] it was shown that the presence of a second boundary electrode affects the nature of intensity distribution (the first boundary is the cathode) if it reflects primary electrons or emits secondary electrons and thus leads to the formation of reflected waves. When the interelectrode distance exceeded the mean free path of beam electrons in the gas, the oscillation distribution had the form of a smooth curve with a maximum somewhere in the central region between the electrodes. However, when the distance between electrodes is less than the mean free path, periodicity appears, as described in [1]. Theory [2] does not reflect this aspect of the phenomenon, since it assumes that the medium is bounded only on one side (semibounded) in the direction of motion of the beam. It is of great interest from the theoretical viewpoint to have information on the spatial distribution of the oscillations, since this makes it possible to draw conclusions concerning the nature of plasma instability as a result of which the oscillations are excited. In this article, experiments are described that confirm the role of reflected electrons in the formation of a periodic oscillation intensity. Moreover, data on the buildup of oscillations are presented and a comparison is made with the conclusions of convective instability theory.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF00915606
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