Characterization of the plasma on dielectric fiber (velvet) cathodes Available to Purchase

An investigation of the properties of the plasma and the electron beam produced by velvet cathodes in a diode powered by a $∼200kV$⁠, $∼300ns$ pulse is presented. Spectroscopic measurements demonstrated that the source of the electrons is surface plasma with electron density and temperature of $∼4×1014cm−3$ and $∼7eV$⁠, respectively, for an electron current density of $∼50A∕cm2$⁠. At the beginning of the accelerating pulse, the plasma expands at a velocity of $∼106cm∕s$ towards the anode for a few millimeters, where its stoppage occurs. It was shown by optical and x-ray diagnostics that in spite of the individual character and nonuniform cross-sectional distribution of the cathode plasma sources, the uniformity of the extracted electron beam is satisfactory. A mechanism controlling the electron current-density cross-sectional uniformity is suggested. This mechanism is based on a fast radial plasma expansion towards the center due to a magnetic-field radial gradient. Finally, it was shown that the interaction of the electron beam with the stainless-steel anode does not lead to the formation of an anode plasma.