Focused Microwave Technique for Measurement of the Ionization Rate and Collision Frequency

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Abstract
A technique for the measurement of ionization rate and collision frequency in gases uses high‐powered focused microwaves. By using short pulses and focusing the energy into a small spot within a large vacuum chamber, diffusion losses are made negligible. Under these conditions the breakdown equation can be simply solved for the ionization rate in terms of easily measured parameters—the pressure, pulse width, and electric field. Experimental results with this technique are compared with published results. The agreement between the two is sufficiently good to confirm the usefulness of this technique. Due to the focusing of energy into a spot remote from walls, the walls do not enter into the ionization process. In this way a possible source of error in the measurement of ionization rate is avoided. Since the technique arranges conditions so that diffusion losses are negligible, it is not necessary to know the diffusion coefficient in order to determine the ionization rate.