Studies On Secondary-Beam Transport With Super Large Emittance And Broad Momentum Spread

Secondary beams are widely applied for research and studies in physics,material and life science,medical science and so on.Compared with primary beams,secondary beams own the properties of low production yield and complex transport.To obtain high quality secondary beams,which means beams with high intensity and polarization,low contamination of other species,the design of beam transportation system is critical.This thesis focuses on the physics design and studies related with the transportation of beam with super large emittance and broad momentum spread.It includes periodic transport,charge/particle type selection,momentum selection,adiabatic transition,and small beam spot focusing and so on.The beam transport of a super large emittance is largely affected by the higher-order effect,mainly contributed from very large beam divergence,broad momentum spread,and the fringe field effect of large aperture magnets,which makes it hard to describe the transport by paraxial optics.Most detailed studies largely depend on multiparticle simulations with more-or-less realistic field distributions.The main work of the thesis is about the beamline design for the MOMENT and CSNS EMuS projects,but also includes the solenoid field correction on MICE project.MOMENT is an accelerator-based neutrino project aiming to measure the lepton CP violating phase to an unprecedented precision.The beamline needs to transport a mixed ?/? beam with emittance around 100 ?mm-rad to produce a high-flux neutrino beam.It is composed of several sections,such as the charge selection section,pion decay channel,bending section,adiabatic taper and the muon decay channel.In the charge selection section,different selection methods based on magnetic horns,dipoles and curved solenoids were studied and compared.In the bending section,the scenarios by mounting adjacent solenoids with the same or opposite polarity were studied.In the adiabatic taper section,the factors that affect the adiabatic matching process between the target area and the beamline were studied and the magnetic field pattern was optimized.In the two decay channels,periodic focusing structure based on superconducting solenoids was applied,and the condition for the stop-band emerging and the relationship between the stop-band width and the focusing parameters were studied.The matching between two adjacent sections was optimized.The simulation results of the energy spectra of a possible neutrino beam at the far detectors were also given.CSNS EMuS is a muon source project based on China Spllation Neutron Source(CSNS).Usually muon sources share proton beams with neutron sources in tandem,while EMuS is a stand-alone facility by using a fractional proton beam with a low repetition rate,which provides more flexibilities on the choice of the target size and shape,and the collection method of the secondary beams.Those merits open the opportunity to obtain high quality muon beams even with relatively low power proton beam.EMuS is planned to run in three different modes:surface muon mode,polarized decay muon mode and high-momentum muon mode,in which the reference momentum and momentum acceptance are different.The trunk muon beamline that are based on superconducting solenoid focusing should be able to transport all three beams by different settings.Two branch beamlines were designed to transfer surface muon beam and polarized decay muon beam from the main beamline to two ?SR spectrometers,respectively.The beamlines should have high transmission,and need to realize the required beam manipulations,such as momentum selection,removing of contaimed positrons,and small spot focusing at the samples.In addition,the author also carried out studies about superconducting solenoid fieldmap alignment for the international muon cooling experiment project(MICE).By introducing the equivalent matrix method,the relationship between the fieldmap misalignments and the beam center offsets can be exactly described by formulas.The formula was also verified with beams of large emittance and large dispersion.