The Dynamic Characteristics of a Low Pressure Discharge

Square-wave modulation of current at a frequency of 167-400 cps was imposed on a dc discharge in a tube containing mercury vapor at a pressure of $6\mu$ and argon at 3.5 mm (Hg). The intensity of $\lambda 2537$ and other data were recorded on oscillograms. Each sudden change of the arc current $i$ was accompanied by an instantaneous change in the same direction, of the longitudinal voltage gradient $E$, the electron temperature $T_e$, the 2537 output, and the ion current to the wall. These instantaneous changes were followed by much slower adjustments toward the steady-state values corresponding to the arc current. The time required for a rough adjustment was 0.2-0.5 msec when the current was increased, and 1-3 msec when it was decreased, for ratios of maximum to minimum current ranging from 1.6 to 3.9. When the current was decreased, there was an excess of ions that had to diffuse to the tube wall.