Research on Plasma Light Sources

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

9988282 Lawler Continued research on discharge plasmas for use as light sources is proposed. This research is in close collaboration with industry. The first Task is to continue experimental and theoretical investigations of barium (Ba) glow discharge plasmas for use as light sources. Barium has crucial advantages as a radiating atom in a glow discharge with an inert gas buffer. Barium has the required vapor pressure of 1 to 20 mTorr at achievable temperatures, it has a low excited configuration with a resonance level at an energy less than half of the ionization potential, and it has its dominant resonance line at the peak of the efficacy curve. The primary disadvantage of barium vapor in a lighting application is that barium is quite reactive. These studies of Ba discharges could lead to an entirely new lighting technology analogous to the low pressure sodium (Na) technology introduced in the 1960's. Low pressure Na lamps currently achieve the highest luminous efficacy of any commercially available lighting product, but unfortunately these lamps produce nearly monochromatic light. The proposed Ba lamp technology should yield a higher efficacy in applications not requiring good color. The proposed Ba lamp technology should also produce a high efficacy with reasonable color. The theoretical investigation of Ba discharges is in close collaboration with Dr. Graeme Lister, Head of Theory and Modeling at OSRAM-SYLVANIA INC. The experimental studies are entirely at the University of Wisconsin and are entirely supported by NSF. The second Task is to continue development of kinetic theory models of glow discharges. Advances in computer performance have enabled us to run Monte Carlo plasma simulations to generate Self-Consistent space charge potentials. These simulations avoid all of the fluid approximations in commonly used glow discharge models. These Self-Consistent Monte Carlo simulations also avoid any internal boundary conditions at the plasma-sheath transition. The simulation results are useful now for comparison to other, more efficient fluid and kinetic theory models. Continued development of the Self-Consistent Monte Carlo method including the introduction of multi-step ionization and gas heating, and more direct comparison to experimental results will be emphasized. ***