AN INSTABILITY OF A BEAM-GENERATED PLASMA IN A UNIFORM MAGNETIC FIELD.
Abstract
The purpose of this research was to study the instability, to identify the cause, and to determine under what conditions the interactions of the beam and plasma might be used for amplifiers of microwaves. A cold-beam - cold-plasma model was analyzed and numerical values were computed for wave propagation and growth. The nature of a beam-generated plasma was studied experimentally. Wave propagation on the plasma column was observed using a slotted-line technique and gain was observed between two cavities spaced along the column. The theory shows that growing waves could be produced at low frequencies as a result of coupling of the beam to a foward wave on the plasma column or oscillations could occur at a higher frequency as a result of the coupling of the beam to a backward wave of the plasma which exists above the cyclotron frequency. In the former case, reflections at the ends of the plasma column could provide feedback to convert the growing waves to oscillations. It was observed experimentally that the lower-frequency oscillations predominate in the spectrum of signals of the instability, particularly at low voltages and high magnetic fields. There was a close correspondence between the theoretical conditions necessary to obtain some forward-wave gain and the experimental conditions at which the instability begins. Standing waves observed under these conditions indicate the presence of reflections. Gain of the order of 1 db-cm was measured at 1000 Mc. Higher values were prevented by the appearance of the instability. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 1965
- Accession Number
- AD0480185
Entities
People
- James E. Simpson
Organizations
- Stanford University