Beam-generated plasma formation near a dielectric target irradiated by a pulsed electron beam in the forevacuum pressure range

We have investigated the formation of electron beam-generated (EBG) plasma near a dielectric (ceramic) target and an insulated metal target, and the compensation of the negative charge accumulated on the insulated metal target when the targets are irradiated by an intense pulsed electron beam in the forevacuum pressure range (4–15 Pa). It is shown that the density of the EBG plasma near the irradiated ceramic target (or the irradiated insulated metal target) is greater than the plasma density for a beam propagating freely in a vacuum chamber (or for the grounded metal target). The EBG plasma near the target is formed with a certain delay with respect to the electron beam current pulse, because of which the negative potential of the insulated target is also compensated by a delay. The delay time in the formation of the EBG plasma and in the compensation of the target negative potential decreases with increasing gas pressure. Expressions have been proposed for estimating this delay time.