Validity of diffusion theory in radio frequency breakdown in molecular gases in longitudinal magnetic field

Abstract

The breakdown of a gas excited by a radio frequency voltage of frequency 5.6 MHz has been studied in a cylindrical discharge tube 7.2 cm long and 2.9 cm in dia and fitted with two internal electrodes at a distance of 2.5 cm in hydrogen, oxygen and air within the pressure range of a few microns to 2 torr in the presence of a longitudinal magnetic field varying from zero to 800 G. Experimental results indicate that the breakdown is diffusion controlled and the values of (a/P) at differentE/P values calculations obtained by Brown as well as by Kihara’s theory have been compared with (a/P) values obtained in the literature. It is concluded that the diffusion theory is also valid when the frequency of the exciting voltage is scaled down to radio frequency provided the collision frequency is much higher than the exciting frequency. The change of diffusion length in the presence of longitudinal magnetic field has been obtained from measuredE/P values and comparison with theoretical values indicates that there is quantitative agreement for small (H/P) values whereH is the magnetic field. The calculated values of pressure at which the breakdown voltage shows a minimum in the presence of magnetic field is in very good agreement with experimental values. It is concluded that in the presence of magnetic field also the loss of electrons takes place predominantly by the process of diffusion.