Multi-field Coupling Analysis And Experimental Study Of Discrete-Cosine-Theta Accelerator Superconducting Magnets

The study of medical accelerator technology has become a frontier in national life and health due to the development and use of particle therapy technologies such as heavy ions and protons.Superconducting magnets have become the preferred choice for accelerator magnet systems in response to the construction requirements of miniaturization,compactness,and low energy consumption of medical accelerators.The Cosine-Theta coil is further discretized into the DCT(Discrete Cosine-Theta)coil,which has emerged as a vital technology for next-generation compact medical accelerators due to its high excitation efficiency,compact construction,minimal accumulation effect of Lorentz force,and ability to achieve integrated functional magnetic fields.However,there are numerous challenges in the design and winding of DCT superconducting coils due to the complexity of conductor distribution and geometric structure.Curved DCT superconducting magnet research is still in its beginning stage,and existing models have not successfully established parametric entity models for the multi-field properties of large-curvature DCT superconducting magnets.Additionally,efficient simulation analysis and experimental testing have not been implemented.This paper combines numerical simulation and fundamental experiments to systematically study the multi-field modeling technology of new DCT superconducting magnets,such as curved type and special-shaped cross-sections.This paper focuses on the frontier topic of developing DCT superconducting magnets for new-generation accelerators.Systematic research has been done on the features of transient losses and electromagnetic-thermal-force multi-field coupling under transient operating situations.The relevant results are of significant engineering guiding relevance for the application of DCT superconducting magnet technology in accelerator devices and effectively assist the successful creation of three different types of DCT superconducting test coils.Firstly,a fully parametric entity modeling technology with variable cable spacing,variable angle position,and adjustable cross-section shape was created for the multi-field behavior simulation and analysis of various forms of DCT superconducting coils,such as curved type and anisotropic cross-sections.To calculate and analyze the multi-field behavior of DCT superconducting magnets more effectively and precisely,an electromagnetic-thermal-force multi-field coupling finite element model which considers various operating conditions,such as static and transient,was established.Secondly,magnetic field design and calculation analysis were conducted using the established parametric entity model.A magnetic field optimization method based on single-turn adjustment technology was proposed after a detailed comparison of the magnetic field distribution under the traditional line current model and the entity model for DCT coils.This comparison included the influence of various crosssectional shapes and sizes on the magnetic field distribution.The magnetic field error was obtained for DCT coils under various optimization techniques.It provides some theoretical direction for improving conductor slot processing technology.Based on these analyses,magnetic field design and optimization of a 90° DCT dipole magnet were finished.Thirdly,a loss calculation approach under time-varying magnetic fields was developed in response to the calculation and evaluation requirements of transient losses in DCT dipole magnets under fast cycle working conditions.A mathematical model and finite element model were constructed for quick assessment of eddy current losses in various structural components.The effects of structural eddy current on the quality of the magnetic field were examined,and detailed calculations of the coil hysteresis loss,coupling loss,and structural eddy current loss were made.Based on this method,a thorough discussion of the impact of AC loss on magnet thermal stability under various cooling techniques was presented,and a design strategy for cooling DCT superconducting magnets was proposed.Fourthly,a complete process was created for structural design and analysis under multiple physical fields,with a focus on the electromagnetic-thermal-force multi-field properties of DCT superconducting magnets.Stress analyses and optimization designs for various interlayer structures,process winding schemes,and extreme states under magnetism were performed using two-dimensional fine models.Based on these analytical results,the interlayer binding structure and casting process scheme of the magnet were determined.A parametric three-dimensional model that fully captures the intricate magnet structures was constructed for the assessment of the magnet’s displacement and stress distribution under a variety of challenging operating situations with various constraint techniques.A design scheme suitable for stable operation of superconducting magnet with small radius and large deflection angle was determined.Eventually,three distinct types of DCT dipole magnet test coils were created and tested,meeting the development requirements of DCT superconducting magnets with various bending angles and cross-sections.Cryogenic excitation training was applied to the superconducting test coils.In the meantime,strain gauges were employed to gather strain information from significant components of the magnet.Finally,a comparison and analysis of the performance traits of DCT magnets under various structural processes were conducted.A DCT superconducting dipole magnet prototype with an anisotropic cross-section was created and tested to meet the research and development requirements of large-scale spectrometer superconducting magnets.The rationality and applicability of the modeling technology and multi-field coupling analysis methodologies established in this study were confirmed by the comparison of test and calculation results of various magnets,providing a firm foundation for the study and development of DCT superconducting magnets.