An accessible microwave cavity experiment for plasma density determination

Plasmas are indissociable from microwave science. Effectively, the most fundamental properties of any plasma arise from its plasma frequency. However, combining plasma physics with electromagnetic (EM) wave propagation is challenging for physics students. An EM cavity poses an excellent opportunity to understand the behavior of EM standing waves, the issues related to transmitted and reflected power in waveguides, coupling, and how free charges in the plasma affect its resonant frequency and quality factor, interlinking the properties of matter with wave propagation. The inclusion of an external magnetic field allows students to explore the underlying principles of magnetic confinement in a linear geometry. (paper)