Comparison of two microwave and two probe methods for measuring plasma density

Four types of electron density measurements are compared in the same device: cylindrical probe, disk probe, microwave cavity, and microwave hairpin. The measurements are made in hot-filament discharges in a soup-pot type of plasma device with and without multidipolar surface magnetic fields with densities up to 1times10⁹ cm ^-3 and electron temperatures of 0.1-1.3 eV. The cylindrical probe and hairpin give densities that are in close agreement for all conditions. The density from the cylindrical probe, hairpin, and cavity measurements are in good agreement (les12% difference) in plasma without magnetic containment. With magnetic containment, the different methods give greater differences in the densities (les30%), perhaps as a result of the higher fraction of energetic electrons. For all conditions, the densities from the disk probe are lower than the densities from the other methods