Microwave Measurements of the Properties of a dc Hydrogen Discharge

Microwave measurements of the properties of thin cross-sectional elements of a dc hydrogen discharge have been made. These measurements were accomplished by exposure of portions of the discharge in the gap between the cones of an S-band re-entrant cavity operating in the TM010 mode. The equipment and techniques for making the microwave measurements employing the re-entrant cavity are described. Measurements in the positive column of a dc hydrogen discharge showed the following results: Electron density increases with increasing tube current and also with increasing gas pressure in the pressure range measured (2 to 8-mm Hg). Electron collision frequency is approximately equal to 4.6×109 multiplied by the gas pressure in mm Hg, and is independent of tube current. When measurements were made in the negative glow region, several anomalous effects including a negative frequency shift were observed. These have been explained qualitatively as being caused by plasma resonance phenomena. The fact that these plasma resonance phenomena were also observed at a frequency of 8550 Mc demonstrates that the electron density in portions of the negative glow is at least 300 times greater than the density in the positive column.