The mercury-arc oscillator

A new device--the mercury-arc oscillator--is proposed for the conversion of low-voltage, high-current d. c. to a. c. at the voltage level of convential a.c. systems. Operation depends on the interruption of a constricted mercury column and subsequent arc formation when a low d. c. voltage (<10v) is applied to it. The phenomena involved are first discussed in relation to arc discharge in mercury-arc rectifiers, circuit breakers and EWP. Theoretical and experimental studies show that the magnetic pinch effect initiates circuit interruption and that high field emission is responsible for arc maintenance. An expression for the oscillation frequency is obtained and compared with results obtained using a 0.031 in. diameter capillary constriction over the pressure range from 106 mm Hg to 1 atmosphere. Methods of frequency control are discussed and an experimental device operating on a d.c. supply of 4-8 volts at a current of 100-160 amps with a frequency in the range 60-250 cps is described. The factors affecting duty factor are considered and typical device geometry and operating conditions for this factor to be 50% are given. There are brief discussions of frequency stability and of parallel and push-pull operating characteristics.