The empretron, a mercury pool arc tube allowing operation at repetition rates in the kilocycle range

The empretron is a new mercury pool arc tube for switching applications. The arc between the mercury pool cathode and the main anode is initiated by a vacuum spark. The spark discharge occurs between two continuously replenishable electrodes, one being an electrode partly immersed in the mercury pool and the other, the starter electrode, a mercury reservoir supported above the mercury pool. Starting is accomplished by applying a high-voltage pulse to the starter electrode. The resulting spark discharge develops into an arc between the cathode and the main anode. The minimum energy necessary for arc initiation, 10–
³
to 10-
₂
joules per start, is determined by the stray capacitance between the starter electrode and the mercury pool. Operation at repetition rates up to 5,000 cps (cycles per second) has been demonstrated. This is about one order of magnitude higher than the upper limit of 400 cps for the conventional ignitron.