| Popis: |
In elucidating the phenomena of breakdown it is necessary first to find the general mechanism by which the various processes of ionization interact to produce the necessary amplification of current, and then to identify the particular ionization processes themselves. It was the exact prediction, both of the form of the growth of ionization and of the breakdown potentials, when the spark parameter pd was less than about 200 (mm of mercury × cm), that first established the validity of the Townsend theory based on the continuous development of ionization by primary and secondary ionization processes; the main characteristics of this theory are given. The problem of breakdown at higher pressures when pd is 760 (mm of mercury × cm) is next discussed, and recent experimental and theoretical work on the growth of ionization currents and breakdown is described from which it is concluded that the general Townsend mechanism can also account for breakdown in this range of the spark parameter. This mechanism is then discussed in relation to other properties of breakdown involving the spatial-temporal development of currents, breakdown under impulse voltages, under non-uniform fields, and, finally, in highly compressed gases at very high voltages. |
