A muon facility—EMuS (Experimental Muon Source)—at China Spallation Neutron Source (CSNS) has been studied since 2007. CSNS, which is designed to deliver a proton beam power of 100 kW at Phase-I, and will serve multidisciplinary research based on neutron scattering techniques, has just completed construction, and is ready to open to general users from September 2018. As an additional platform to CSNS, EMuS aims to provide different muon beams for multiple applications, among which, magnetism study by μSR techniques is a core part. By using innovative designs, such as a long target in conical shape situating in superconducting capture solenoids and forward collection method, EMuS can provide very intense muon beams with a proton beam of 5 kW and 1.6 GeV, from surface muons, decay muons, and high momentum muons to slow muons. In this article, the design aspects of EMuS, including general design, target station, muon beamlines, and μSR spectrometer, as well as prospects for applications on magnetism studies, will be reviewed.

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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.

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