Metastable helium density probe for remote plasmas

Area of Science:

• Plasma Physics
• Atomic Physics
• Diagnostic Techniques

Background:

• Helium metastable atoms are crucial species in various plasma applications.
• Accurate measurement of their density is essential for understanding and controlling plasma processes.
• Existing diagnostic methods may have limitations in remote or complex plasma environments.

Purpose of the Study:

• To develop and validate a modified electrostatic probe for spatially determining helium metastable atom density.
• To assess the probe's effectiveness in a remote plasma setting.
• To quantify the achievable measurement sensitivity and identify operational limitations.

Main Methods:

• A modified guard ring electrostatic probe was designed and implemented.
• Opposite polarity voltages were applied to the inner probe and guard ring to shield charged particles.
• Secondary electron current generated by de-exciting metastable atoms was measured, with photoelectrons minimized through shielding and orientation.

Main Results:

• The modified probe successfully measured helium metastable atom densities.
• Measured densities were on the order of 10(7) cm(-3).
• Comparisons with simulated metastable distributions revealed limitations of the technique.

Conclusions:

• The modified electrostatic probe is a viable tool for measuring helium metastable atom density in remote plasmas.
• The technique offers a sensitivity of approximately 10(7) cm(-3).
• Further refinement and understanding of limitations are necessary for broader application.