Continuous-Wave Laser Thomson Scattering Diagnostic for Low Temperature Plasmas

Colorado State University, Fort Collins CO

Investigators

Abstract

This project will aim to develop a novel diagnostic to quantitatively study electron populations in a low temperature plasma. Plasma, often referred to as the fourth-state of matter, is a gas that contains charged species such as electrons and ions. Low temperature plasmas that also contain energetic atoms and molecules, referred to as radicals, can enable many technological applications. The properties of low temperature plasmas are largely governed by electrons and an ongoing challenge in plasma science has been to develop diagnostic techniques to measure the temperature and number density of electrons. The present project addresses this need through the development of a diagnostic, referred to as continuous-wave Laser Thomson scattering (CW LTS), to quantitatively measure the electrons. With CW LTS, a high-power laser beam illuminates the plasma to be studied and the laser light photons are elastically scattered by the plasma electrons (like colliding billiard balls). The scattered photons are then detected allowing one to infer electron properties of the plasma. The project will benefit basic investigations of low temperature plasmas as well as technological applications including processing plasmas for the semiconductor industry, plasma thrusters for space exploration, and atmospheric pressure plasmas. The project will also aim to attract students from underrepresented groups to participate in the development of a CO2 laser demonstration for outreach to local K-12 students. The project seeks to develop a new paradigm for Laser Thomson scattering (LTS) based on using continuous-wave (CW), high-power (>kW) light sources to achieve higher scattering counts and improved detection limits as compared to conventional systems with pulsed lasers. Since the signal stream is continuous, the CW LTS approach will attempt to advance LTS from measuring time-average electron parameters to capturing temporally resolved dynamics up to ~10-100 kHz. This would represent an unprecedented and powerful advance of LTS towards studying plasma dynamics such as ionization and recombination in pulsed discharges, plasma waves, and oscillations such as the breathing mode in Hall effect thrusters. The diagnostic advances will be shared in publications and conferences and will be integrated into undergraduate and graduate courses at Colorado State University. Students from underrepresented minority groups will be sought to work on the project both for graduate thesis research and for undergraduate research experience. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.