An RF Technique for Plasma Number Density Measurement

It is well-known that a cylindrical plasma column in a transverse rf electric field is subject to a dipole resonance. The frequency at which this occurs can be used to determine the average electron density across the plasma section. This paper describes the experimental application of the technique to plasmas with and without a confining axial static magnetic field, and gives theoretical curves to assist in rapid reduction of the data. Higher order multipole resonances can also be excited. The feasibility of applying these to determination of the number density profile is discussed.