Fore-vacuum plasma-cathode electron sources

This paper presents a review of physical principles, design, and performances of plasma-cathode direct current (dc) electron beam guns operated in so called fore-vacuum pressure (1 - 15 Pa). That operation pressure range was not reached before for any kind of electron sources. A number of unique parameters of the e-beam were obtained, such as electron energy (tip to 25 kV), dc beam current (up 0.5 A), and total beam power (Lip to 7 kW). For electron beam generation at these relatively high pressures, the following special features are important: high probability of electrical breakdown within the accelerating gap, a strong influence of back-streaming ions oil both the emission electrode and the emitting plasma, generation of secondary plasma in the beam propagation region, and intense beam-plasma interactions that lead in turn to broadening of the beam energy spectrum and beam defocusing. Yet other unique peculiarities can occur for the case of ribbon electron beams, having to do with local maxima in the lateral beam current density distribution. The construction details of several plasma-cathode electron sources and some specific applications are also presented.