Microwave Measurements of the Properties of a dc Hydrogen Discharge

Abstract

Laser induced stimulated emission for hydrogen atom density measurements in a hydrogen pulsed microwave dischargeMicrowave 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 TMoio 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 4.6X10 9 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.

The Townsend Ionization Coefficients in Crossed Electric and Magnetic Fields

“…(ii) Microwave measurements of the properties of electric discharges in hydrogen enable the collision frequency vc=ujL (at 1 rom Hg pressure) to bedetermined (Rose and Brown 1955;Udelson, Creedon, and French 1957) That the values of Vc obtained by these various methods are different is to be expected, because a collision between an electron and a molecule is defined differently for the different methods (Healey and Reed 1941). For the deter- mination of the effective cross section a collision is defined as an event in which an electron suffers an appreciable change either in direction of motion or in velocity, whereas for the drift velocity analysis, a collision is defined as an event in which, on the average, an electron loses all its momentum in any specified direction.…”

Electron density and ionization rate in thermally ionized gases produced by medium strength shock waves

“…The attenuation caused by a gas discharge in our microwave system was compared with results of Udelson, Creedon & French (1957). Instead of the shock tube, a discharge tube of the same diameter was passed through the waveguide and a d.c. discharge in hydrogen was produced using a power supply of variable voltage (0-5000 V), which enabled us to raise the discharge current to a maximum of 7-5mA.…”

An Investigation of the Plasma Composition in Plasma-enhanced Hot Filament Catalytic Chemical Vapor Deposition of Carbon Nanotubes

“…The model assumed two temperatures, translational/rotational T g and electronic T e temperatures, each describing a Maxwell/Boltzmann distribution for its respective mode. The structure of direct current glow discharge was well known [29,30], since the highest concentration of ions lied in the plasma region of negative glow discharge. In the positive column, the concentration of electrons and ions was about two to three orders of magnitude lower around 10 9 -10 10 cm -3 0 k [30].…”