Study On Rf Impedance And Wakefield Of High Repetition Frequency Hard X-ray Free Electron Laser Facility

The advent of the Hard X-ray Free Electron Laser(HXFEL)has enabled the generation of short,strong,coherent X-ray pulses for a wide range of scientific applications in physics,biology,and chemical research.The Shanghai High Repetition Rate Hard X-ray Free Electron Laser and Extreme Optics Facility(SHINE)under construction is the first high repetition rate hard X-ray free electron facility in China.After the facility is completed,it will become the most efficient and advanced free electron facility in the world.One of the electronic laser user devices,providing high-resolution imaging,ultra-fast process exploration,advanced structure for physics,chemistry,life science,materials science,energy science and other disciplines Analysis and other cutting-edge research methods,forming a unique,multi-disciplinary advanced scientific research platform.In order to provide an electron beam with a high repetition rate of 1 MHz,SHINE selects a high-Q and low-loss superconducting cavity as an accelerating structure to accelerate particles.The superconducting cavity needs to work in a low temperature environment.When the beam passes through the entire superconducting module,it will not only excite the longitudinal impedance and wakefield,which will bring additional low temperature thermal load to the entire module.It also stimulates the transverse impedance and wake field leading to an increase in the emittance of the beam.These effects all affect the operation of the device,and their study is crucial.The European Hard X-ray Free Electron Laser(The European XFEL)is a hard Xray free electron device that has been built and is running in the world.It is also a free electron laser device based on a superconducting linear accelerator with a repetition rate of up to 4.5 MHz.It is currently planned to install a corrugated structure on the SASE1 line of The European XFEL.When the beam passes through such a corrugated structure,not only the longitudinal wakefield can be excited to control the bandwidth of the SASE radiation,but also the transverse wakefield can be excited,as a two-color scheme kicker.However,due to the very small gap of the corrugated structure,the wakefield impacted beam particles will experience large betatron oscillations after hitting the corrugated structure,which will lead to energy deposition in the undulator beamline,which may cause the undulator to demagnetize,especially This is even more dangerous at high repetition rates.Moreover,SHINE will also install the same corrugated structure at the exit of the linear accelerator in the future,so this problem will also be encountered.Therefore,it is particularly urgent to study the beam loss caused by the wakefield to particles passing through the folded structure,and how to reduce this beam loss to protect the downstream undulator.Based on the above practical engineering requirements,this paper discusses in detail the longitudinal impedance and low-temperature thermal load caused by the wake field in the 1.3 GHz Tesla and 3.9 GHz superconducting modules in SHINE,and the obtained results are directly used for the cooling works for SHINE superconducting cryomodules.The transverse impedance and wakefield-induced emittance increase of 1.3 GH in Tesla superconducting modules are also calculated,including single-bunch emittance increase caused by short-range transverse wakefield,and long-range transverse wakefield.The resulting multi-bunch emittance increases.And the problem of coupler RF kick and emittance growth caused by 1.3GHz superconducting cavity coupler is studied,and a reasonable arrangement of the 8 cavities in the cryomodule is given to optimize the emittance growth,and the conclusion becomes the SHINE linac Physical parametric design.This paper also studies the beam loss caused by the corrugated structure in the European hard X-ray free electron laser device in detail,proposes a new method to simulate the wake field effect in BDSIM equivalently,and presents two different schemes for the beam Loss simulation:double-plate corrugated structure under FODO optics and single-plate corrugated structure under low β ptics.The final results show that the latter scheme accommodates the passage of more particles.In order to further reduce the peak energy loss caused by the impact of particles in the beam halo on the downstream undulator section,the possibility of adding a collimator between the corrugated structure and the undulator section was investigated,and the results showed that the energy peak was reduced by a factor of 100,And the cooling power of the collimator under the high repetition frequency electron bunch is calculated.In view of the importance of the collimator,SHINE will also install a collimator in the future,and the structure between the collimator and the connecting section is complex,and the calculation of the wake field is complicated.Based on the preliminary design of the current SHINE collimator and the inter-segment structure,this paper analyzes the calculation method of the longitudinal wake field in detail,and compares the longitudinal wake field of multiple collimator gaps.The final result can be used as a solution for the engineering design and processing of SHINE collimators.To sum up,this paper is based on the research on impedance and wakefield of high repetition frequency hard X-ray free electron laser devices SHINE and Eu-XFEL.The superconducting cavity,low temperature module,corrugated structure,collimator and segment are introduced in detail.The impedance and wake field of the inter-structure and the resulting longitudinal and transverse effects have been used in practical engineering applications or a reliable basis for engineering design.