Development of wall current monitor on FETS-FFA test ring

Conceptual design studies of the FETS-FFA demonstration ring have been actively performed to confirm the reliability of a Fixed Field Alternating gradient (FFA) accelerator for a future high-power spallation neutron source, called ISIS-II. A wall Current Monitor (WCM) is a choice of non-destructive intensity monitor to evaluate the circulating proton beams from 3 MeV (about 1MHz in revolution frequency) to 12 MeV(about 2MHz in revolution frequency) in the FETS-FFA test ring. As the beam orbit shifts radially with beam energy in FFAs, the aperture of FETS-FFA WCM will be about 700mm horizontally. The maximum mean circulating beam current is about 100mA and tomographic and Schottky measurements require a bandwidth of 370MHz (100 harmonics). This is a challenge for such a large monitor. A half-width demonstration WCM (demo-WCM) was designed and manufactured to benchmark numerical simulations and to understand monitor responses. Whilst measured frequency band was lower than expected, 1% intensity resolution was achieved in the demo-WCM. In this paper, the detail design study as well as the signal response of the demo-WCM will be presented.