Key Technology Study Of Superconducting Combined Multipoles For HIAF-HFRS

With the development of modern heavy-ion accelerators,high intensity and high energy have become the main goals pursued,which puts forwards higher requirements for the superconducting accelerator magnets.HIAF(High Intensity heavy-ion Accelerator Facility)is the next-generation high-intensity heavy-ion accelerator built by the Institute of Modern Physics,Chinese Academy of Sciences.HFRS(High Energy FRagment Separator)is the radioactive beamline used for ion fragmentation analysis.The design requires a magnetic stiffness of 25 Tm.It is composed of 11 superconducting dipole magnets and 39 sets of superconducting combined multipole lenses.Very large acceptability and high resolution require a superconducting magnet with both a large aperture(φ330 mm)and a high integration field uniformity(plus or minus eight parts per million).To solve the problems of the traditional iron-dominated superconducting multipole magnet based on cold iron yoke structure,such as large cold mass,long cooling time,difficult installation,poor compactness,etc.,a coil-dominated superconducting magnet design was proposed,called DCT(Discrete Cosine Theta)coil,which uses the discrete streamline coils with approximate cos(mθ))current density distribution to generate multipole magnetic field.It has the advantages of lightweight,high field quality,and compact structure,which is more in line with the design requirements of HIAF-HFRS.It is the first time that this technique has been applied in an accelerator scientific facility on a large scale in China.This paper focuses on the research and development of the prototype of the HFRS superconducting combined multipole magnets,and carries out a series of key technology research on the DCT superconducting coil.The main research contents include:Based on the principle of multipole magnetic field generation and the current-line model,a fast modeling algorithm for DCT coils is developed,and a set of electromagnetic design programs for DCT coils is developed,which has the characteristics of fast calculation speed and accurate calculation results.Using this program,the electromagnetic design of HFRS series superconducting multipole magnets is completed,and the harmonic field analysis and the field quality robustness analysis of the magnet under the controllable accuracy of the structure deformation and conductor wiring are carried out.On the basis of the electromagnetic optimization design,the multi-physics simulation research on the stability of structure,operation and quench safety of the HFRS-DCT superconducting multipole magnet is further carried out,which lays a theoretical and design foundation for the actual development of the prototype.Through systematic DCT coil process iteration experiments,the exploration of key technologies and processes of the DCT coil magnets such as coil space curve modeling and wiring,bobbin and wire slot CNC machining,coil winding,inter-turn and interpole transition and casting molding was completed.Finally completed the production of the first HFRS-DCT superconducting combined multipole magnet prototype.Focusing on the design,development and technical exploration of the full-scale prototype of the DCT-type superconducting multipole magnet of HFRS,the innovations of this paper are:Based on the principle of magnetic field generation and the current construction of DCT coils,a complete,flexible and efficient DCT accelerator magnet fast calculation and design program is written.The program combines random error sampling technology to verify the robustness of the magnetic field quality of the DCT superconducting coils.Based on the improvement of excitation efficiency,process optimization and safety,and referring to the structure of conventional power cables and Litzy wires,a 6+1superconducting inter-turn insulated cable with nonlinear quench-back protection function is creatively proposed.Developed a multi-layer DCT nested superconducting combined coil fabrication technology based on the additive and subtractive material manufacturing and highprecision wiring technology.Finally,the prototype of HFRS superconducting combined multipole magnet was successfully developed.By completing the first domestic DCT superconducting multipole magnet prototype,this paper has mastered the design method,technical route and process parameters of this type of superconducting magnet.The low-temperature excitation test of the prototype reaches 110% of the designed magnetic field.In addition to the reliability of the conductive combined multipole magnet scheme,the effectiveness of the nonlinear quench-back quench protection has also been successfully verified to ensure the quench safety.It lays a solid foundation for the batch development and application of this type of superconducting magnet in HIAF device or similar devices.