On the Design, Construction, Calibration, and Testing of a Custom Langmuir Probe for Use in an RF Plasma
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A particular interest of the principal investigator regarding a rare atmospheric phenomenon called ball lightning influenced the design and construction of a custom RF plasma chamber. However, the primary focus of this experiment is not on the ball lightning but instead on the interesting phenomenon that occurs when RF plasma is near its plasma frequency. At its plasma frequency, it behaves as a metamaterial which are said to exhibit interesting microwave properties. A Langmuir probe was needed to be built to collect data on the plasma density and find relationships between plasma density and how well it acts as a waveguide.
A custom plasma chamber was then designed and built for the purpose of testing the microwave attenuation/dispersion characteristics (S-parameters) of a cylindrically symmetric RF plasma (13.56 MHz). The principal investigator was interested in studying how plasma electron density affects waveguide dispersion characteristics.
Since commercially available Langmuir probes were beyond the project budget a Langmuir probe as well as the associated sensing circuitry was designed, built, tested and calibrated in-house. The necessary theoretical background needed to understand the probe and sensing circuitry is presented as well as construction of the probe and sense circuitry.