A Microwave Method for the Study of Steady and Fluctuating Plasma Number Densities

A method for the measurement of dc and ac components of number density in cylindrical gas-discharge columns has been studied. The technique is based on a dipole resonance, occurring below the electron plasma frequency. It is excited by an rf signal transmitted along a stripline enclosing the plasma column. By working on the side of the resonance curve, a fluctuating output signal is obtained corresponding to the density fluctuations. The simple theory of the resonance has been extended to take account of stripline size, of the glass surrounding the column, and of a radial variation in number density. The method is considerably more sensitive than cavity perturbation techniques, and the results compare reasonably well with number density measurements made by other methods.