Design study for large acceptance muon beamlines by using beam splitting methods

Abstract

A muon beamline scheme is designed for the Phase-I of the Experimental Muon Source (EMuS), which is a standalone facility by sharing the proton beam extracted from the Rapid Cycling Synchrotron (RCS) of China Spallation Neutron Source (CSNS). The proton beam for EMuS has a beam power of 20–25 kW and kinetic energy of 1.6 GeV with a low repetition rate of 1.25–2.5 Hz. Different from traditional muon beamline design, a sophisticated beam splitting system using combined spatial and time splitting methods has been developed for the EMuS beamline. In order to profit a graphite target of long effective length, the beamline is designed to have a large horizontal acceptance of 6000π·mm·mrad. A special electrostatic deflector with two channels splits the beam spatially into two branch beamlines, so that the reduced horizontal emittance of the split beams becomes utilizable for applications. Since the muon beam has a time structure of two bunches per pulse that inherits from the proton beam and a single bunch is required for μSR applications, a fast kicker magnet is used to separate two bunches into two endstations. All these make simultaneous muon beams in four endstations that are basically for μSR applications. Surface muons with an intensity order of 105/s and different spot sizes are available for all the four endstations. The contaminated positrons are carefully treated to reduce the background by combining the use of the electrostatic deflector and a dedicated Wien filter.