Enhanced Catalytic Probe Design for Mapping Radical Density in the Plasma Afterglow

Area of Science:

• Plasma Science
• Chemical Engineering
• Surface Science

Background:

• Electrified chemical processes increasingly require sensors for plasma-activated species like radicals.
• Radical probes offer in situ quantification of radical density via exothermal recombination heat.
• Distinguishing recombination heat from other heat fluxes is a significant challenge.

Purpose of the Study:

• To develop and validate an advanced radical probe for accurate radical density quantification in plasma afterglows.
• To improve heat flux analysis in radical probe measurements by incorporating a heat sink.
• To differentiate between recombination heating and other heat fluxes like radiation and conduction.

Main Methods:

• Utilized a dual thermocouple setup with a catalytic unit and a reference thermocouple.
• Integrated a monitored temperature heat sink to determine conductive and radiative heat fluxes.
• Employed simultaneous in-reactor probe measurements and infrared imaging of reactor wall temperature.

Main Results:

• Demonstrated the advantage of a dual thermocouple setup over a single thermocouple for radiation heat analysis.
• Successfully quantified conductive and radiative heat fluxes using the heat sink addition.
• Mapped nitrogen atom densities in a plasma afterglow, confirming the probe's accuracy.

Conclusions:

• The developed radical probe provides accurate, spatially resolved radical density measurements.
• The heat flux analysis method reduces ambiguities and enhances measurement reliability.
• Confirmed three-body recombination as the primary N radical recombination pathway with a rate constant of k_rec = (2.0 ± 0.9)·10^-44 m^6/s.