RF sparking experiments at 108.5 and 216 MHz

The gap voltage in RFQ accelerating structures determines the attainable beam current. For many accelerator projects requiring a high beam current it is therefore necessary to apply a gap voltage near the breakdown voltage. The RF breakdown limit depends on many different parameters (electrode geometry, gap width, material, frequency, pulse length) and is not predictable. Experiments carried out to study breakdown phenomena with respect to the development of RFQ structures are reported. W.D. Kilpatrick´s prediction for the frequency dependence of the breakdown threshold (Rev. Sci. Instrum., vol.28, p.824-6, 1957) has not been confirmed in initial measurements