| Superconducting radio-frequency (RF) technology is a crucial enabling basis foradvanced accelerator, and plays an irreplaceable role especially in the new generationof high energy accelerators, continuous wave free electron laser (CW-FEL) or intensecurrent energy recovery LINAC (ERL) and so on. For example, TESLA type1300MHz9-cell superconducting cavities have been adopted in the main LINAC ofEuropean X-ray free electron laser (EURO-XFEL). An optimized1300MHz7-cellcavity structure has been finally decided for main LINAC of Cornell University’sintense current ERL facility based on years of research on superconducting cavitytechnology.In this paper, we proposed a new type superconducting cavity structure for anERL-based FEL facility. The resonant frequency and cell number were decided to be1500MHz and5-cell with the compromise of accelerating efficiency, higher ordermodes damping, and other issues such as sensitive factors. The geometry parametersand final structure have been obtained by several radio-frequency simulation softwaretools like Superfish, CST (Computer Simulation Technology) and so on. A largerbeam pipe was employed to propagate the higher order modes (HOMs) out of thecavity for damping the dangerous HOMs. The simulation results showed that thequality factors of dipole mode and quadruple mode were damped to be lower than104and1010, respectively, which means that the HOMs property satisfied with therequirements of hundreds-mA current class ERL.It is confirmed that the R/Q of the fundamental mode TM010to be550to havea reasonable cryogenic losses. In order to avoid the risk of field emission, theparameters Epk/Eaccand Bpk/Eaccwere optimized respectively to be2.06and4.22.Multipacting simulation results by MultiPac showed that there was no multipacting inthe designed structure at the field in the medium accelerating gradient (15~20MV/m)range. It was concluded that RF property of the designed cavity could meet therequirements of ERL-based FEL very well. |
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