Development of an RF coaxial resonator for investigating multipactor discharges on metal and dielectric surfaces

Multipactor discharge is a phenomenon in which electrons impact one or more material surfaces in resonance with an alternating electric field. The discharge can occur for a wide range of frequencies, from the MHz range to tens of GHz, and in wide array of geometries if the impacted surface has a secondary electron emission (SEE) yield larger than one. The discharge can take place on a single surface or between two surfaces. A novel coaxial resonator to investigate two-surface multipactor discharges on metal and dielectric surfaces in the gap region under high vacuum (HV) conditions ($10^{-8}$ mbar) has been developed and tested at LAL. The RF coaxial resonator is $\sim$19 cm in length with an outer diameter of 11 cm. A pulsed RF source delivers up to 30 W average power over a wide frequency range 650–900 MHz to the RF resonator. The incident and reflected RF signals are monitored by calibrated RF diodes. An electron probe provides temporal measurements of the multipacting electron current with respect to the RF power. These experiments were successful in identifying multipacting and allowed us the evaluation of a home made sputtered titanium nitride (TiN) thin layers as a Multipactor suppressor.