Thyratron Design & Circuit Techniques To Overcome The Adverse Effects Of High Inverse Voltages

Abstract

It is well known that hydrogen thyratrons can hold-off inverse voltages which are equal in magnitude to their forward voltage hold-off ratings with impunity, provided that a sufficient time is allowed to lapse after forward conduction has ceased. However, circuits exist where it is not feasible to avoid the application of appreciably large inverse voltages at the thyratron anode immediately upon the cessation of forward current. Bi-directional hollow-anode thyratrons which can conduct peak reverse currents of many kiloamps are oftcn used to overcqme this problem [l], [2]. However, there arc instances where large inverse currents cannot be tolerated, either because of the effect produced at the load, or because of recovery time considerations, and the use of hollow-anode thyratrons must therefore be ruled out. Applications where such circuits can be found include medium-to-high power copper vapour lasers and certain types of kicker magnets. This paper describes the phenomena of thyratron arc-back and anode erosion which can result from high inverse voltage. The mechanisms by which these phenomena affect thyratron performance are discussed. A relatively simple saturable anode inductor is shown to alleviate greatly the phenomenon of arc-back, by providing a delay between the cessation of forward current and the application of inverse voltage. The performance of an experimental thyratron in a high repetition rate circuit with appreciable inverse voltage is also described. Lifetest results indicate that substantial improvement in operating life has been obtained by controlling the adverse effects of anode erosion, induced by high inverse voltages.