A new type of plasma instability is described in an electron-beam ionized discharge. This instability occurs in gas mixtures in which the dissociative attachment rate increases strongly with electric field. It has been observed experimentally in He:H2O 740:20 and in He:CO2 1:1 and 9:1 mixtures. The values of the ionization source function S and of the electric field E at which the wave instability occurs are predicted using a Fourier analysis of the linearized kinetic rate equations. This yields the condition for instability as S < (1/α)[Eδβ/δE) − β]2, where α is the electron-ion recombination coefficient and β is the electron neutral attachment rate.
A new type of plasma instability is described in an electron-beam ionized discharge. This instability occurs in the form of current oscillations in gas mixtures in which the dissociative attachment rate increases strongly with electric field. It has been observed experimentally in He : H2O 74 : 2 and in He : CO2 1 : 1 and 9 : 1 mixtures. A theoretical analysis which describes the onset of instability is presented, and a physical explanation is given. The region of instability in parameter space of ionization source function S and electric field E is presented for certain gas mixtures. The transient phenomena in this type of discharge appear to be controlled by electron attachment, and a theoretical explanation of the observed current overshoot has been provided.
The thermal and acoustic instabilities that could possibly cause arcing in high−power pulsed and cw gas lasers have been investigated. A cubic dispersion relation is obtained from linearization of the coupled hydrodynamic and Ohmic equations in which the electrical conductivity is dependent on the neutral density. We find that when the thermal wave is unstable the acoustic waves are damped, and vice versa. The growth rate of the instability is proportional to the power density for low input powers while it goes as the cube root of the power density for high input powers.
ABSTRACT.The electromagnetic dispersion relation for two counterstreaming ion beams of arbitrary relative strength flowing parallel to a dc magnetic field is derived. The beams flow through a stationary electron background and the dispersion relation in the fluid approximation is unaffected by the electron thermal pressure. Magnetic effects on the ion beams are included but the electrons are treated as a magnetized fluid, m -*0. 6The dispersion relation is solved with a zero net current condition applied and the regions of instability in the k-U space (U is the relative velocity between the two ion beams) are presented. These results are extensions of Kovner's analysis for weak beams. The parameters are then chosen to be applicable for parallel shocks. We find that unstable waves with zero group velocity in the shock frame can exist near the leading edge v, of the shock for upstream Alfven Mach 'number's" greater than-5-r5-. -It-i-s suggested that this mechanism could generate sufficient turbulence within the shock layer to scatter the incoming ions and create the required dissipation for intermediate strength shocks.-111-
A technique for producing stimulated emission in an optically pumped atomic iron system at room temperature is described. The required iron density (∼1014 atoms/cm3) for single pass amplified spontaneous emission was produced at room temperature by two techniques: a low pressure (50 torr) discharge of iron pentacarbonyl and neon and by the flash photodecomposition of Fe(CO)5 in an argon buffer. A commercial KrF laser producing output powers near 51 Mw was modified to improve the beam quality, and the beam was focused into the reaction cell. Resonant processes involving the 3d6 4p 4p (5F°) intermediate state of iron and the KrF laser field (λ?248 nm) produced stimulated emission near 300 and 304 nm in agreement with theoretical predictions.
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