Optimization Design Of CiADS Superconducting Linac

The China Initiative Accelerator Driven System(CiADS)is the first dedicated research platform for nuclear waste processing under construction in the world.Its superconducting proton accelerator has a beam intensity of 5 m A and a beam power of2.5 MW.For large-scale high-power superconducting proton linear accelerators,two key issues that need to be solved urgently in physical design are beam loss control and engineering cost optimization.This paper summarizes and analyzes the design and operation experience of similar international superconducting linac in the world.Through the systematic multiparticle simulation,the optimimal physical design research of the CiADS superconducting accelerator is carried out.Details as follows:(1)Quantify the design principles of 90-degree periodic phase advance and smooth focusing and solve the contradiction between beam physics and engineering cost.Among the design principles generally followed at present,the periodic phase advance less than 90 degrees and smooth focusing proposed based on envelope instability are the main factors that limit the acceleration efficiency.In this thesis,a quantitative analysis of the 90-degree periodic phase advance and smooth focusing principle under the acceleration effect is carried out.First,under the condition of acceleration effect,the influence of the periodic phase advance greater than 90 degrees is simulated and analyzed,and the results show that the beam emittance and beam halo parameters are related to the number of working points that period phase advance greater than 90 degrees and the change speed of the phase advance;secondly,the design principle of smooth focusing is quantitatively studied,and the influence of different beam intensity and unit phase advance on beam emittance and beam loss is analyzed.Compared with the 0deg/m phase advance difference,when the difference of phase advance per meter is less than 4deg/m,the beam RMS emittance change is less than 5%,and the 99.99%emittance change is less than 10%.Based on the above research results,combined with the design requirements and hardware boundaries of the CiADS superconducting proton linac,the superconducting acceleration section structure design that focus both beam loss control and engineering cost is completed.(2)Reduce and control beam loss through "peak-to-peak" matching and transverse acceptance optimization.The feature of the superconducting linac is that the low-energy section adopts a quasi-periodic structure,and the high-energy section adopts a full-period structure.The mismatch between non-periodic transition sections between cryomodules is one of the main sources of beam halo.Based on numerical simulation and CAFe commissioning experience,this thesis verifies that the peak-to-peak matching optimization method with the minimum envelope oscillation as the optimization goal is an effective method to reduce the emittance growth and beam loss probability of the matching section.To avoid the influence of beam loss on the performance of the superconducting cavity,the thesis uses the method of limiting the aperture of the normal temperature magnet to reduce the transverse acceptance and achieves the purpose of controlling the beam loss in the superconducting cavity.(3)Innovative error weight method is adopted to complete error study systematically.Element error is one of the important factors leading to beam loss.In this thesis,based on the different characteristics of element position,type,error characteristics and other factors that have different effects on beam,it innovatively adopts the principle of error weight distribution to analyze the normalized error of each element,and completes the effect of the error of each element in the CiADS superconducting section.The systematic error study of the CiADS superconducting section is completed.The key factors affecting beam loss are found,and the error requirement for key components(superconducting cavity)is reduced.This thesis further completed the element error distribution scheme and orbit correction scheme for beam loss control.In summary,this thesis takes the CiADS superconducting accelerator under construction as the research object and verifies the rationality and robustness of the accelerator design through quantitative design principles,"peak-to-peak" matching,transverse acceptance optimization,and systematic error study.Finally,the design scheme combining beam physics and engineering cost is got.