Abstract
Experimental studies of a plasma-filled X-band backward-wave oscillator (BWO) are presented. Depending on the background gas pressure, microwave frequency upshifts of up to 1 GHz appeared along with an enhancement by a factor of 7 in the total microwave power emission. The bandwidth of the microwave emission increased from <or=0.5 GHz to 2 GHz when the BWO was working at the RF power enhancement pressure region. The RF power enhancement appeared over a much wider pressure range in a high beam current case (10-100 mT for 3 kA) than in a lower beam case (80-115 mT for 1.6 kA). The plasma-filled BWO has higher power output than the vacuum BWO over a broader region of magnetic guide field strength. Trivelpiece-Gould modes (T-G modes) are observed with frequencies up to the background plasma frequency in a plasma-filled BWO. Mode competition between the T-G modes and the X-band Tm/sub 01/ mode prevailed when the background plasma density was below 6*10/sup 11/ cm/sup -3/. At a critical background plasma density of approximately=8*10/sup 11/ cm/sup -3/ power enhancement appeared in both X-band and the T-G modes. Power enhancement of the S-band in this mode collaboration region reached up to 8 dB. Electric fields measured by the Stark-effect method were as high as 34 kV/cm while the BWO power level was 80 MW. These electric fields lasted throughout the high-power microwave pulse.<<ETX>>
Highlights
INTENSE relativistic electron beam excitation of slow wave structures has been an active subject since Nation [ l ] confirmed the possibility in 1972
In the vacuum BWO rf signal appeared -140 ns after the beam turned on, this time delay was independent of the beam current for I = 3 kA, 2 kA, and 1.6 kA
Microwave frequency upshifted 1 GHz in the microwave power enhancement background helium pressure region for both 1.6 kA and 3 kA of beam current. This is less than the theory of [14], which predicts a 2.5 GHz upshift at np = 8 x 10l1 cmW3(Our plasma density measurements indicate np 2 (84~1.5x) 10l1 cmP3.) The background plasma increases the beam electron kinetic energy by reducing the space charge potential produced by the beam in the BWO
Summary
INTENSE relativistic electron beam excitation of slow wave structures has been an active subject since Nation [ l ] confirmed the possibility in 1972. This work studies (a) the effect background plasma has on microwave frequency f and bandwidth Af ; (b) the plasma modes (Trivelpiece-Gould modes) in the plasmafilled BWO and their effect on the BWO waveguide mode (TMol); and (c) measuring the electric field properties in the plasma-filled BWO through the atomic light emission (spectroscopic method). EM waves with f > f,, which can axially bunch the electron beam These are the usual TMon modes of the plasma-filled BWO system, modified by addition of the plasma [14]. Behavior of the electric field in the plasma filled BWO, in a region where the relativistic electron beam, high power rf and plasma interact, could add important information for understanding the basic mechanisms of plasma-filled slow wave devices.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
