Microwave Diagnostic Results from the Gaseous Electronics Conference RF Reference Cell

Area of Science:

• Plasma Physics
• Gas Discharge Physics

Background:

• Microwave interferometry is a versatile technique for measuring electron density.
• Gaseous Electronics Conference (GEC) reference reactors are standard experimental devices.

Purpose of the Study:

• To compare electron density measurements from different research groups using microwave interferometry in GEC reactors.
• To investigate the agreement and discrepancies in electron density data across various pressures and gases.

Main Methods:

• Utilized microwave interferometry for electron density measurements.
• Analyzed data from three independent research groups operating GEC reference reactors.
• Investigated time-resolved electron density changes.

Main Results:

• Excellent agreement in electron density data was observed at higher pressures (above 33.3 Pa) in argon, helium, and nitrogen.
• Discrepancies emerged at lower pressures (13.3 Pa) and in specific helium discharge conditions (133 Pa, >200 mA).
• Time-resolved measurements showed a dramatic electron density rise in helium after rf power cutoff, unlike argon and nitrogen.

Conclusions:

• Microwave interferometry is a reliable method for electron density diagnostics in GEC reactors, particularly at higher pressures.
• Observed divergences may be linked to the transition between alpha (bulk ionization) and gamma (secondary electron emission) discharge modes, influenced by electrode material.
• Time-resolved data highlights distinct post-excitation plasma decay dynamics across different gases.