A Note on Ultra-High-Frequency Gas Breakdown

A recent paper by J. A. Pim1 describes experiments in which ultra-high-frequency sparking potentials were measured between parallel electrodes, rounded to cause breakdown in the uniform field region at the centre. Some of the curves show breakdown potentials which increase as the gap-length is reduced. In this note an attempt is made to explain why the spark does not simply transfer to a longer gap nearer to the edges of the electrodes.