A variable pulse-length electron beam from the back-lighted thyratron

A variable pulse-length electron beam source capable of 100´s μsec pulses to DC operation is reported. Long-pulse electron beam generation was based on the steady-state hollow cathode discharge mode of operation of the back-lighted thyratron and achieved by modification of circuit parameters that control the discharge. Three different discharge circuits were used in the experiment. An RC circuit (16 nF, 1 kΩ at -20 kV) was used to generate an electron beam with duration ≈100 μsec. The energy of the beam is associated with the cathode voltage and a current density ≈10 A/cm² was measured. To further increase the pulse-length a discharge circuit with 100 μF and 500 Ω was used. The pulse-length was extended to 50 msec FWHM. The third circuit was a pulse forming network which generated a non-decaying amplitude electron beam with a duration of 200 msec FWHM. DC operation has also been achieved. The results demonstrate the feasibility of controlling the electron beam pulse-length with modifications of external circuitry. The device is simple, robust, and compatible with a plasma environment. Applications include electron beam ionized lasers, an electron beam ion trap, electron beam assisted atomic layer epitaxy and plasma-filled microwave generators