Study of a plasma-filled X-band backward wave oscillator
The plasma-filled Backward Wave Oscillator (BWO) is a very promising but poorly understood high power microwave device. The goal of this experimental investigation was to measure the electric field in a plasma-filled BWO by the spectroscopic analysis of the plasma light emission. The measurement was done directly in the region where the plasma, relativistic electron beam and RF interact. The author also hoped to shed some light on how the microwave frequency, power and bandwidth depended on the background plasma density. The vacuum BWO microwave output was 100 MW at a frequency of 8.5 GHz and bandwidth ({Delta}f/f{sub 0}) of 6%. The efficiency of converting the beam kinetic energy into electromagnetic radiation was 5%. When the BWO was filled with background plasma, up to a factor of 7 enhancement in the microwave power output over its vacuum counterpart appeared at a background plasma density of 8 {times} 10{sup 11} cm{sup {minus}3}, with a frequency upshift of 1 GHz and a bandwidth ({Delta}f/f{sub 0}) of 24%. Mode switching appeared at a background helium plasma density of 10{sup 12} cm{sup {minus}3}. The electric field strength, measured by the Stark shift, peaked at 34 kV/cm and lasted as long as the microwave pulse. Trivelpiece-Gould modes appeared at 2 GHz to 5 GHz in the plasma-filled BWO. Mode competition between the Trivelpiece-Gould mode and the X-band TM{sub 01} mode occurred when the background plasma density was below 6 {times} 10{sup 11} cm{sup {minus}3}. At a critical background plasma density of n{sub cr} {approx_equal} 8 {times} 10{sup 11} cm{sup {minus}3}, power enhancement appeared in both X-band and the Trivelpiece-Gould modes. When the background plasma density increased from 6 {times} 10{sup 11} cm{sup {minus}3} to 8 {times} 10{sup 11} cm{sup {minus}3}, power enhancement of the S-band in this mode collaboration region reached up to 8 dB.
- Research Organization:
- California Univ., Irvine, CA (United States)
- OSTI ID:
- 102822
- Resource Relation:
- Other Information: TH: Thesis (Ph.D.); PBD: 1992
- Country of Publication:
- United States
- Language:
- English
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