Cold cathode electron guns in the LASL high power short-pulse CO2 laser program

In this paper we have described the two-sided 200 × 35 cm² cold cathode used in the LASL dual-beam module 2.5 kJ short pulse laser. The characteristics may be summarized as follows: a) Electron emission begins on both sides within ∼ 0.1 µs of application of the 50 ns rise diode voltage. b) The currents from each side of the gun are approximately equal. c) Early in the emission pulse, the electron beam fills 25 – 30 cm of the 35 cm high window; at ∼ 3.0 µs, the window is very nearly filled. d) The gun efficiency (current incident on window ÷ total emission current) is nearly unity. e) Early in the pulse, the spatial distribution of the beam at the anode window consists of 10 – 20 vertical striations ∼ 10 cm wide, and seems to originate from discrete and localized points at the blade separated by ∼ 10 cm. The effect ha~ not been satisfactorily explained. f) Later in the pulse, the striations have spread to the extent that nearly the entire window has been irradiated uniformly ± 15%. g) That portion of the beam that is incident on the top edge of the window is deflected downward because of the magnetic field of the HV feed. h) The emission current rises linearly in time after the first 0.3 µs; the plasma expansion velocity is equation 0.5 cm/µs.