Design and prototype test of a high-sensitivity reentrant-cavity based Schottky pickup

Schottky diagnostics is an important measure for the debunched beam during the injection phase of the Xi'an Proton Application Facility (XiPAF). The existing capacitive Schottky pickup has a relatively low sensitivity and a poor signal-to-noise ratio for the low-intensity beam. A resonant Schottky pickup based on the principle of a reentrant cavity is proposed. The effects of cavity geometric parameters on cavity properties are systematically studied. A prototype was built and tested to validate the simulation results. The prototype has a resonance frequency of 24.23 MHz, a Q value of 635, and a shunt impedance of 19.75 kΩ. The resonant Schottky pickup has the capability to detect as few as 2.3 × 10⁶ protons with an energy of 7 MeV and a momentum spread of about 1% at the injection phase of XiPAF. The sensitivity is two orders of magnitude higher than the existing capacitive pickup.