SPARK GAP SWITCHES FOR RADAR 



581 



gaps could switch peak powers in the megawatt range for long periods of 

 time with stable operating characteristics. Under the urge for still higher 

 {)ovvers than those which were handled by the aluminum cathode gaps, 

 experiments were undertaken to develop a mercury cathode type of gap. 

 The main difficulty in the way of using mercury as a cathode is a mechani- 

 cal one, as the conditions of operation of spark gap switches, particularly for 



26" PRESSURE OF 



75% HYDROGEN 



25%ARG0N 



KOVAR CUP 



0.080" MOLYBDENUM 



SINTERED IRON 



POWDER SATURATED 



WITH MERCURY 



Fig. 14 — Schematic drawing of an iron sponge mercury cathode unit gap— actual size. 



airborne radar, demand that the sparking surface be rendered substantially 

 quiescent. Preliminary experiments were made with metal baffles as damp- 

 ing agents and with metal wicks to furnish a mercury sparking surface. The 

 latter led to the development of a sintered iron sponge saturated with 

 mercury as the best means of obtaining a satisfactory cathode. 



The constructional details of one of the earliest tubes of this type are given 

 in the sketch, Fig. 14. The sintered iron sponge, a cross section of which is 



