Electromagnetic Design And Fabrication Of High Temperature Superconducting Coil With New End Structure

In September 2012,Chinese high energy physicists proposed to build a Circular Electron Positron Collider with a circumference of 100 km.The first phase of the collider is the Circular Electron Positron Collider(CEPC),and the second phase is the Super Proton-Proton Collider(SPPC).Thousands of the high-field superconducting magnets would be required to bend and focus high-energy proton beam Compared with low-temperature superconductor,High-temperature superconductor(HTS)has the characteristics of higher critical current density,higher upper critical magnetic field and higher critical temperature.This paper has carried out a preliminary exploration on the application of HTS in the field of accelerator magnets.The main contents are as follows:1)The electromagnetic design of iron-based superconducting dipole magnet with main magnetic field of 12 T for SPPC has been finished.Racetrack coil configuration was adopted in this magnet and a field quality of 1/10000 was reached.With the utilizing of elliptic curve in the end of the racetrack magnet,the high-order component of magnetic field was effectively reduced.Bending ways of hard-way bending(hard bending/bending along narrow surface)and soft-way bending(bending along wide surface)of the magnet were designed and compared.2)The preliminary design of a 16 T superconducting dipole coil has been completed.The scheme of 13 T background magnet with 3 T inserted coil was designed.ReBCO coil was inserted into the 50 mm gap provided by the background magnet.By optimizing the end of the coil,the Angle between the broad side of tape and the magnetic lines of flux in the high-field area was effectively reduced.This design not only increased the critical current density of ReBCO tape to 40%higher than that under the vertical field,but also improved the field strength and field uniformity with the inserted coil at the same time.The influence of the position of the inserted coil and the iron yoke on the magnetic field uniformity was analyzed and optimized.3)This paper presents a novel end structure called Balloon-end based on racetrack superconducting coils.ReBCO coils were inserted into the 10 mm gap between the two racetrack coils,and the ReBCO tape was wound at an opposite angle to achieve the bending radius of 20 mm.In the process of tension optimization,based on the concept of curvature continuity,a segment of easing curve was adopted and combined with the inverse angle arc to form a new end structure.We wound a series of Balloon-end coils with 100 mm straight section with different insulation schemes,curing and winding processes.They all reached the design current in the test at 77 K.The critical current of the inserted coil in the 4.2 K test reached 800 A,which proved the feasibility of the new end scheme.ReBCO and iron-based superconducting tape were used to make LPF1-B inserted coils with a straight section of 730 mm.The metal stainless steel insulation scheme was adopted.These two ReBCO coils reach the design current in the 77 K test and the test under the high background magnetic field.The research results mainly include:analyzing various factors affecting field uniformity and current density in the magnet design optimization and reaching the expected design indexes.The new end scheme of Balloon-end is put forward,and the included Angle of wire and magnetic field together with the stress in winding process are optimized at the same time.The insertion of HTS coils in small space with large bending radius is realized,and the parallel field provided by the background magnet is fuly utilized,providing higher current and safe margin Experiments have been carried out to prove the feasibility of the new structure under various insulation schemes,and it is expected to be used in the high magnetic field dipole magnet.The design of 16 T diode magnet is completed,and the parallel field insertion and correction of high order components of the background magnet field are realized.The relationship between the variable of the coil and magnetic field uniformity,maximum magnetic field,width of wire and Angle of magnetic field is summarized and analyzed,and the design index is achieved.