The Field Emission Initiated Vacuum Arc. I. Experiments on Arc Initiation

Abstract

It is known that electrical breakdown between metal electrodes can be initiated by field emission. The present work concerns a further study of that initiation process under conditions of excellent vacuum and a clean cathode surface.As the field current density from the single crystal tungsten emitter is continuously increased, the normal emission is terminated by an explosive vacuum arc. Since this breakdown occurs in less than a microsecond, the experimental observations were obtained by use of pulse electronic techniques. The magnitude of the electric field, current density, and work function at the cathode were simultaneously determined prior to breakdown. From this investigation it has been established that: (1) the vacuum arc was initiated at a critical value of the field current density of the order of ${10}^{8}$ amperes/${\mathrm{cm}}^{2}$;(2) breakdown was predictable and not random; in fact easily recognizable conditions preceding arc formation have been established; at current densities just below the critical value, an electron emission process was observed, which apparently involved both high electric fields and high temperatures;(3) arc formation did not require cathode bombardment by material from the anode or from residual gases;(4) breakdown was independent of the applied microsecond voltage in the range $5<V<60$ kv, provided the critical current density was not exceeded;(5) the current during arc exceeded the initiating field current by a factor of at least 100.