DEPENDENCE OF RELATIVISTIC BACKWARD-WAVE OSCILLATOR PROPERTIES ON EFFECTIVE BEAM-GAMMA

The operation of a Backward Wave Oscillator (BWO) is shown to be critically dependent on the energy of the slow space-charge wave of the electron beam. Experimental work parameterizing the dependence of microwave frequency on effective beam energy, γβ reveals that through an understanding of electron-beam dynamics, a BWO could be systematically tuned through a desired frequency range while maintaining a high power of a few hundred megawatts and narrow frequency bandwidth, which here was 400 MHz. Through variation of γβ1. 2 to 1.5 for our experiment, we observe the lack of scaling of peak microwave power with the kinetic energy of the electron beam for γβ > 1. 32. This effect was previously found in numerical simulation. We look for an explanation of this effect by examining the relationship of the beam current to space-charge-limiting current for increasing γβ Dramatic evidence of “pulse shortening,” a phenomenon known to relativistic oscillators, is also seen and some preliminary remarks are made. © 1990 IEEE