Longitudinal beam halo measurement with an RF chopper system

It is of practical importance in a high intensity linac to measure the longitudinal beam tail width with sufficient sensitivity to a tenuous halo. In this paper, we propose a newly devised method of diagnosing the longitudinal beam tail width utilizing an RF chopper system and a downstream beam loss monitor. We have conducted a demonstration experiment at a linac to successfully show the feasibility of the measurement method. The beam loss monitor has the sensitivity to detect the fractional beam loss in the order of 10−7, which enables us to detect the width of the corresponding highly tenuous beam tail. We can also deduce the information on the longitudinal beam profile by extending the method. Although saturation calibration is required for a quantitative analysis, we have experimentally confirmed that the measurement is sensitive to provide a qualitative picture of the longitudinal beam profile.