Short microwave pulses in long pulse REB systems

Summary form only given. It is pointed out that high-power microwave experiments employing long-pulse (≳50-ns) relativistic electron beams (REBs) have not produced long microwave pulses. Effects that could limit the microwave pulse length are being studied. In particular, it is found that the presence of the microwave pulse modifies the DC space charge of the beam. At high powers, the modifications can adversely affect beam propagation prior to the onset of the normal saturation mechanism, beam trapping. Theory is being developed to quantitatively determine the magnitude of this effect. The DC space charge of hollow beam injection has been electrostatically examined in both one and two dimensions. A purely electrostatic model of the beam will not explain high-power pulse shorting. The theory of the effect of the AC field on the DC space charge predicts an increase in the beam density. Linear theory expressions have been derived to predict the added space charge depression of the beam, given the AC field. The added AC/DC depression produces both a loss of useful beam power and an alteration in the dispersion relation. At high beam currents, the effect can be expected to disrupt beam propagation, resulting in operation as a relaxation oscillator