Characterization of a channel spark discharge and the generated electron beam

We report on an experimental study of a channel spark discharge (CSD) and the generated electron beam. The CSD was operated at a discharge voltage U-d <= 30 kV and a discharge current I-d <= 3.5 kA. The CSD system consists of a glass tube placed between a hollow cathode and a grounded anode electrode. The parameters of the CSD operation, the potential distribution along the glass tube, and the generated beam were studied by electrical, optical, and spectroscopic diagnostics in the Ar gas pressure range of P=0.005-2 Pa. At P >= 0.5 Pa, electrons with energy similar to eU(d) appeared prior to the start of the main CSD with a current amplitude <= 10(-4)I(d). These high-energy electrons are responsible for the initiation of the CSD inside the glass tube. The generation of the electron beam which was composed of low-energy electrons with a current amplitude up to 3 kA occurred during a fast fall in the discharge voltage. Decreasing the Ar gas pressure below 0.1 Pa allows one to increase significantly the beam duration and the part of the high-energy electrons in the beam, and to increase the efficiency of the electron beam generation up to 75%. The high-current CSD inside the glass tube is accompanied by the formation of a plasma consisting of protons, Ar II, Ar III, C II-IV, and O II-IV ions. The plasma electron density and temperature were found to be in the ranges of 10(15)-10(16) cm(-3) and 10-15 eV, respectively.