R&D Of Taper Superconducting Cavity Cryomodule

Accelerator driven sub-critical(ADS)system consists of an accelerator,a spallation target and a sub-critical reactor.It not only reduce the amount of nuclear waste significantly,but also utilize the spent fuel to generate power.It has a good economy and system safety and has been recognized as one most promising technical way of nuclear waste transmutationin the world.ADS injector ? linear accelerator is mainly composed of an electron cyclotron resonance(ECR)ion source,a low energy beam transport(LEBT)line,a radio frequency quadrupole(RFQ),a medium energy beam transmission(MEBT)line,a superconducting accelerating segment and a high energy beam transmission(HEBT)line.This very prototype injector is undertaken by the Institute of Modern Physics,Chinese Academy of Sciences.The superconducting accelerating segment is composed of two HWR010 cavity cryomodules + a taper cavity cryomodule + a spoke cavity cryomodule(CM1+CM2+ CM3+CM4),which could accelerated the proton beam to 25 MeV.Cryomodule is a complex and highly integrated system which contains superconducting cavities,superconducting magnets,beam position monitors and many other equipments.Considering the limited dimension of the superconducting segment and the requirements from the cryogenic system of ADS linear accelerator,the taper type cryomodule design process is extremely challenging because it needs to optimize the compact assembly structure with different interfaces and the heat load for single cryomodule while providing a stable low temperature and vacuum environment for superconducting cavities or superconducting magnets.The core project for my doctorate thesis is a taper cavity cryomodule for ADS injector ? which operates at 4.2 K and 1.05 Bar.In the thesis,the cryomodule research status in China and abroad together with the operation experiences of early ADS injector? test cryomodules are included in the project background.The priority target of the taper type cryomodule design is ensuring the cryostat alignment,cooling process,heat load and other specifications meet the requirement of the linac system.Based on such philosophy,the whole cryomodule including a suspension support system,current leads,a cooling system,magnetic shields(normal temperature/low temperature),thermal shields and vacuum chambers are designed and realized.During the fabrication of the taper typer cryomodule,we have solved the problem of precise machining for complex shape cryomodule,achieved high precision alignment for superconducting components,analyzed the stress distribution caused by large temperature difference in the cooling process and avoided large static heat load of test cryomodules.In the meantime,standard operation procedures for efficient and reliable installation of the cryomodule system are summarized.The assembly and commissioning of the taper cryomodule have been completed and it is operating stablely online.The actual assembly operation suggested that the size tolerance of large rectangular vacuum chamber reached below 1 mm,and alignment precision of superconducting components satisfied the physical requirement ±1mm.77 K and 4.2 K temperature regions are successfully reached by using different cooling medium,through the optimization of the cooling medium distribution line,a better temperature uniformity on each cold components was realized,which reduced the stress concentration caused by large temperature differences during cooling process.Through the heat load simulation for the cryomodule,combining the heat intercept,vacuum,and multilayer insulation method,we effectively reduce the conduction heat leak,gas convective heat leak,radiation heat leak and optimize the heat load of taper cryomodule greatly,which saves the operation cost of the whole system.For the first time in the world,ADS linac produced 25 MeV high power proton beams at continuous wave mode in June 2017,and the export beam energy of taper cavity cryomodule is 18.6 MeV.The work described in this thesis not only guaranteed the success of the ADS 25 MeV linear accelerator,but also provided valuable experiences accumulation for the cryomodule design of subsequent large science facilities in China such as HIAF and CIADS project.