30MeV 100 MA Superconducting Linear Accelerator Beam Dynamic Design

With the increasing demand for nuclear physics research and accelerator-driven subcritical systems,there is an urgent need for the development of high-power proton linear accelerators.Increasing the beam intensity is a key factor in achieving high-power accelerators,but high beam currents can lead to strong space charge effects.Controlling beam loss under strong space charge effects is a major challenge,significantly increasing the difficulty of structural design for high-current superconducting linear accelerators.This paper focuses on the physics-based design methodology for high-current proton accelerators,based on beam dynamics.Through numerical simulations,it investigates the characteristics of low-energy beam transport using the equipartition design（EP design）method and the equal tune depression design（ET design）method.Additionally,based on practical engineering requirements,the physical design of a 30 Me V,100 m A superconducting linear accelerator is completed,providing guidance for the design of high-current proton accelerators in future high-flux neutron source facilities.This paper first analyzes the evolution of various parameters,including RMS emittance growth,99.99%emittance growth,halo formation,and RMS size,under different beam intensity conditions for two design methods based on the full-period structure.For both design approaches,the emittance growth increases gradually as the beam intensity increases.Under a beam intensity of 100m A,the longitudinal RMS emittance growth and 99.99%emittance growth in the ET design show significant improvements,while the transverse RMS emittance growth and 99.99%emittance growth remain similar to those in the EP design.To meet engineering requirements,a full-period structure consisting of 27 cells,each containing a single solenoid and single cavity,is designed for a 100m A superconducting segment.Secondly,based on the ET design method,the dynamic design of a 100m A superconducting linear accelerator with matching sections between cryomodule is conducted,followed by multi-particle simulation.The results of the multi-particle tracking simulations show that the RMS emittance growth is approximately 23.6%in the X direction,23.6%in the Y direction,and 22.9%in the Z direction.The 99.99%emittance growth is 171.8%in the X direction,181.8%in the Y direction,and 176.6%in the Z direction.Under a beam intensity of 100m A,both the transverse and longitudinal RMS emittance growth are around 23.6%,while the99.99%emittance growth is less than 182%.To validate the error tolerance of the accelerator’s structural design,error analysis is conducted using multi-particle simulations.The error analysis includes parameters such as beam emittance growth,beam loss,halo evolution,centroid,and beam size.The results demonstrate that,after calibration,there is no beam loss under standard error conditions.Under double the standard error,the beam loss is measured at4.5×10^-6,which still satisfies the requirement of beam loss below 1W/m.The comprehensive simulation results indicate that the ET design has a clear advantage for beam intensities greater than 30m A.With the insertion of matching sections,the RMS emittance growth for a 100m A superconducting linear accelerator using the ET design method is around 24%,while the 99.99%emittance growth is approximately 175%.Therefore,for high-current low-energy accelerators,both the insertion of matching sections and the choice of design method have a significant impact that cannot be ignored.Based on these conclusions,for such high-current low-energy superconducting linear accelerators,the ET design method can effectively enhance beam quality and acceleration efficiency.