THE CHARACTERISTICS OF PULSED HOLLOW-CATHODE DISCHARGES USED FOR PSEUDOSPARK SWITCH TRIGGERING

The complex interaction between trigger discharge and main switch disc harge in high-power gas discharge switches influences both, the switch ing characteristics, and the switch and trigger lifetime. Any attempts to improve either of these parameters has to take into account the pr essure and geometry dependence of a particular trigger geometry. Yet, although not very intensely investigated in detail for this particular purpose, pulsed hollow cathode discharges are commonly used for low-p ressure gas discharge triggering like in pseudospark switches. Measure ments of the electron current flowing to the cathode backplane of a ps eudospark switch from the pulsed hollow cathode trigger discharge show , that maximum current densities are peaked around the symmetry axis o f the trigger electrode, an effect which is more pronounced at low pre ssures. Delayed (and slowed-down) increase of the current density at l arger radii leads to increasing delay and jitter, provided the trigger coupling holes in the cathode backplane are located off-axis. The ele ctron current density increases with decreasing diameter of the trigge r electrode, and with increasing pressure of the working gas. In addit ion, it is shown that a preionization (keep-alive) current in the trig ger electrode region shows a distinct influence on the trigger current distribution, proofing that there exists an optimum keep-alive curren t depending on geometry and gas pressure.