Mechanism of the optogalvanic effect in a hollow-cathode discharge

Conference · Fri Jun 17 04:00:00 EDT 1983

OSTI ID:6091293

Keller, R A; Warner, B E; Zalewski, E F; Dyer, P; Engleman, R Jr; Palmer, B A

There are two significantly different mechanisms proposed for the origin of the optogalvanic effect in a hollow-cathode discharge: (1) laser excitation of atoms to higher electronic states leads to an increased cross section for electron impact ionization, with the result that the excited atom becomes ionized and the conductivity of the discharge increases; and (2) laser excitation of atoms to higher electronic states perturbs the equilibrium established between the electron temperature and the atomic excitation temperature. Superelastic collisions between the electrons and the laser-excited atoms restore the equilibrium, with the excess energy ending up in an increased electron temperature and therefore an increased conductivity of the discharge. Both mechanisms undoubtedly proceed simultaneously and what needs to be determined is their relative importance at different discharge conditions and different excitation conditions. This is important because laser isotope enrichment schemes have been proposed using selective excitation in a hollow-cathode discharge. In order for these schemes to work, (1) must be the predominant mechanism. We have measured the optogalvanic signal, concentration of uranium atoms, impedance of the discharge, and electron temperature as a function of the discharge current in a neon-filled uranium hollow-cathode discharge. The hollow cathode operating characteristics are used as input parameters in a simple discharge model. Predictions of electron density, changes in electron temperature, and discharge impedance compare well with experimental observations. Our model and experimental observations yield a qualitative understanding of the optogalvanic effect in a hollow-cathode discharge and estimate the relative importance of the two optogalvanic mechanisms.

• Research Organization: Los Alamos National Lab., NM (USA); Lawrence Livermore National Lab., CA (USA); National Bureau of Standards, Washington, DC (USA)
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 6091293
• Report Number(s): UCRL-88533; CONF-830646-1; ON: DE83013583
• Country of Publication: United States
• Language: English

Related Subjects

050503 -- Nuclear Fuels-- Uranium Enrichment-- Laser Excitation-- (-1989)
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
640301* -- Atomic
Molecular & Chemical Physics-- Beams & their Reactions
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ACTINIDES
CATHODES
ELECTRIC DISCHARGES
ELECTRODES
ELECTROMAGNETIC RADIATION
ELEMENTS
EMISSION
ENERGY-LEVEL TRANSITIONS
EXCITATION
FLUIDS
GALVANOMAGNETIC EFFECT
GASES
HOLLOW CATHODES
IONIZATION
ISOTOPE SEPARATION
LASER ISOTOPE SEPARATION
LASER RADIATION
MAGNETO-OPTICAL EFFECTS
METALS
NEON
NONMETALS
PHOTOEMISSION
RADIATIONS
RARE GASES
SECONDARY EMISSION
SEPARATION PROCESSES
URANIUM