Cavity Enhanced Thomson Scattering System for Low Temperature Plasmas

Electrons play a very key role in plasma chemistry and dynamics of low temperature plasmas. Improved capability for measuring electron number density, ne, and electron energy distribution function, EEDF, in weakly ionized low temperature plasmas would benefit both fundamental study and application areas. For example, the capability would directly benefit emerging research targeted at modifying and controlling the EEDF to optimize plasma source performance. Laser Thomson Scattering (LTS) is one of the few non-intrusive diagnostics for ne and EEDF; however, challenges of low signal levels and optical interferences place limits on the applicability of the technique. The proposed effort is to develop a novel laser Thomson scattering (LTS) system for measurement of weakly-ionized low temperature plasmas. In the proposed scheme, a high power (intra-cavity) beam of power ~100 kW provides several orders of magnitude higher (average) power relative to the illumination sources used in conventional LTS experiments. The brighter light source will provide elevated counts of scattered photons and improved sensitivity (allowing measurement of densities as low as ~109-1010 cm-3), thereby providing a significant improvement relative to the state-of-the-art. The Phase I effort will provide proof of concept and riskmitigation results. Commercial Application and other Benefits: Currently there are very limited commercial offerings for sensitive plasma diagnostics of electrons. The proposed instrument will allow sensitive measurements in a versatile manner that can be employed in many user facilities. Commercialization of the proposed instrument will therefore be of strong benefit to the plasma science community (university, government, industry). From a broader perspective, the diagnostics enabled by the instrument will benefit the nations economy by improving plasma sources and processes used in the semi-conductor, electric propulsion, and manufacturing industries. The proposal includes support letters expressing interest in our instrument.