Electromagnetic Design And Mechanical Analysis Of The Toroidal Field Coils And The High-temperature Superconducting Insert Coils For Fusion Devices

In fusion devices,toroidal field(TF)magnets are crucial in defining the fusion device shape and in generating the toroidal magnetic field that confines the plasma.The energy gain and fusion power density of the fusion device also have a scalar law relationship with the toroidal magnetic field,and the cost of a tokamak machine roughly increases as the cube of the major radius.At the same time,if the centerline of the TF coil is not properly designed,the in-plane bending moment generated by the electromagnetic force during the operation of the TF coil will further increase the shear stress on the insulation and the peak stress on the coil case.Therefore,the most important principle in the design of the TF coil centerline is:constant tension,no bending moment and the highest possible increase in the strength of the toroidal magnetic field generated by the TF coil within the limited radial space.However,the tension on the centerline obtained by conventional TF coil centerline design methods is often not completely constant,for example,the tension non-constancy of the centerline,designed based on the famous Princeton-D,is as high as 20.2%.Therefore,this paper uses a trapezoidal prism current model and an iterative design method based on a semi-analytic formulation of the centerline magnetic field to accurately calculate the magnetic field on the centerline,and then does iterative optimisation of the centerline shape to design an optimised D-shaped centerline for the TF coil.Reduced tension non-constancy on the centre line to 0.1%.Afterwards,the effects of the number of TF coils N and the radius of the outer leg r2 on the centerline of the TF coils were analysed and it was found that:1)as N increases,the ripple decreases and the height and length of the TF coils keep increasing;2)expanding r2,although it allows more space for the internal components of the fusion device,also further increases the height and length of the TF coils and raises the cost of the fusion device.Plasma disruption and vertical displacement events are extreme cases of fast transient electromagnetic processes in fusion devices which generate large eddy currents and electromagnetic loads on the conducting structures surrounding the plasma,for which electromagnetic and eddy current analysis of TF magnets under plasma disruption conditions is carried out.The analysis shows that the eddy current on the TF case is mainly concentrated on the straight leg near the plasma side under the plasma rupture condition and the electromagnetic force caused by the induced eddy currents is much smaller than that of the toroidal field coil during steady operation.The central solenoidal(CS)coil of a fusion device provides the magnetic flux that excites and maintains the plasma.The magnetic flux that can be provided by the central solenoid is important for improving the performance of the fusion device.In order to improve the magnetic flux of the CS coils as much as possible,the Institute of Plasma Physics is currently planning to use high-temperature superconducting(HTS)CS coils in future fusion devices.Although HTS CS coils can increase magnetic flux by raising the highest field,there are still many challenges in the application of HTS CS coil in fusion devices due to the shielding current effect caused by the inherent anisotropy and E-J nonlinearity of high temperature superconductors.This paper will investigate the effect of shielding currents on magnetic fields,AC losses and stress strains based on high field high temperature superconducting insert coils.A study of the shield current effect on high field HTS insert coils during excitation shows that:1)the shield current induced field(SCIF)generated by the shield current reduces the magnetic field strength of the insert coil;2)the shield current effect causes the AC losses in the insert coil to be concentrated at the ends of the coil away from the mid-plane;and 3)the twisting forces at the ends of the tape caused by the shield current further increase the stress-strain level in the insert coil.Finally,a 16T high background field test coil for conductor testing is designed based on gradient nonlinear optimization algorithm.By optimizing the design,a uniform magnetic field with a strength of 16 T and an inhomogeneity of 0.5%is generated in a 50 mm diameter area in the center of the test device.Mechanical analysis of the 16T test coils under winding,cooling and electromagnetic load shows that a certain winding preload helps to overcome the expansion of the coils in the radial direction under electromagnetic forces and improves the cooling performance of the coils.The work in this paper provides methodological references and implications for the optimization of the centerline of TF coils and the application of HTS CS coils in future fusion devices,the electromagnetic mechanical analysis of TF coils in accident conditions and the optimal design of superconducting coils.