Electron density characterisation using plasma loaded microwave cavity resonators

Gas discharge tubes present a convenient and cost-effective way to produce plasmas for studying electromagnetically active systems. Their electron density can be tuned over a given range by varying the discharge voltage. Furthermore, the plasma column can be magnetised to exhibit gyrotropic properties. These characteristics have led to the increasing use of gas discharge tubes in the fields of photonics and topological materials. Although sometimes estimated through analytical investigation and simulations, the plasma proprieties of these gas tubes often remain imprecisely determined. We present a scalable, reproducible and economic method to determine plasma frequency and electron density tuning range in non-magnetised and magnetised gas discharge tubes. Experiments and simulations are carried out for 0-50mT magnetic fields and 2-18 GHz microwave frequencies for multiple gas discharge tubes with plasma frequencies in the 3-10GHz range.