Comparison between theoretical and experimental resonant behaviour of a hollow cylindrical plasma

Theory using an equivalent permittivity approach predicts that a hollow cylindrical plasma column should have two resonance frequencies. Such frequencies had not yet been experimentally observed. Two hollow cylindrical discharge tubes of different sizes have been built with great care and have enabled the observation of two well-defined resonance peaks. The agreement between theory and experiments for both the frequencies and the amplitudes is very close. A comparison with the ordinary cylindrical plasma column is made and it is suggested that the method used ought to give a quite satisfactory measurement of the average plasma density.