The Accelerator Physics Design Of The Spectrometer Ring

As one of the ”12th Five-Year Plan” national major science and technology infrastructure construction projects,the High Intensity Heavy-ion Accelerator Facility(HIAF)will build a heavy ion science comprehensive research facility with advanced beam index,focusing on nuclear physics,atomic physics and multidisciplinary researches and applications.The HIAF project will provide an international leading experimental platform for nuclear physics and nuclear astrophysics basic research,atomic physics and heavy ion beam application researches,and aims to improve China’s nuclear physics researches at the nuclear level enter into the international advanced level.As an essential part of the HIAF project,the Spectrometer Ring(SRing)is the key device to obtain high-quality rare isotope beams(RIBs)and use the beams for atomic physics and nuclear physical experimental researches.In order to meet a variety of the requirements of the physical experiments,three operation modes have been designed:the isochronous mode,the normal mode and the internal target mode.In the isochronous mode,the SRing operates under a special linear ion-optics and could be used to measure the mass of nuclei with half-life shorter than tens of microseconds with high precision.In the normal mode,the SRing could be used to prepare high-quality radioactive ion beams(RIBs)with electron and stochastic cooling systems for the Schottky mass measurement.In the internal target mode,the SRing could prepare high-quality and highintensity highly-charged heavy ion beams for atomic and nuclear physical experimental researches.We carefully analyze the physical experiments performed by the SRing for the hardware design indicators and the requirements of the beam parameters,point out the specific design indexes for the SRing,refine the operation schemes of the three modes and finish the accelerator physics design scheme.The design of the isochronous mode focuses on the improvement of the mass resolving power.The important point the normal mode is to cool the RIBs with rapid rate.The design emphasis of the internal target mode is to ensure the collision luminosity of the heavy ion beams with electrons,gas molecules and laser light,and guarantee the heavy ion beams could be decelerated in the mode.Based on the operation scheme and design indicators of the three operation modes,we finish the accelerator physics design including the linear ion-optics,the injection design,the extraction design,the nature chromaticity correction,the dynamic aperture calculation and the isochronous higher-order correction scheme.The accelerator physics design should take the three modes into account and make sure the storage ring will have a compact structure which could decrease the engineering budget.According to the present design schemes of the dipole,quadrupole and sextupole magnets,the fringe field and higher order field distribution of the magnets are obtained by the program OPERA-3D.The fringe field and higher order filed distribution have been taken into the calculation to study their influences on the linear ion-optics,dynamic aperture and the isochronous higher-order correction.A method which takes advantage of the program MAD-X is proposed to solve the fringe field effects on the linear ion-optics.According to the results of the dynamic aperture tracking,the high-order harmonic component of the magnetic field and the alignment errors for the magnets are put forward.Taking the fringe field effects of the dipole and quadrupole magnets and the effects of the high-order harmonic component of the dipole magnets into account,the program GICOSY is used to recalculate the linear ion-optics and higher-order corrections for the isochronous mode.This method could eliminate the influence of the fringe field effects and the higher-order magnetic field errors on the isochronous mass resolving power.Finally,the program MOCADI is used to track the particles,check the numerical computing results calculated by GICOSY and get the optimized correction results.The accelerator physics design of the SRing is based on the development and operation experiences of the existing device the CSRe at IMP.It draws on the design philosophies of the storage ring in the world such as the ESR at the GSI.The requirements of the physical experiment proposed at the present stage and the potential physical experiential objectives are also fully considered to ensure the reliability and rationality of the design scheme for the SRing.