Vacuum System Design and Key Technologies for the DALS Beam Test Platform Based on a Superconducting High-Repetition-Rate Accelerator

The Dalian Advanced Light Source (DALS) is a planned extreme ultraviolet (EUV) free-electron laser (FEL) facility based on a superconducting continuous-wave linear accelerator architecture. Its core objective involves generating high-brightness FEL radiation with 1 MHz repetition frequency and wavelength coverage of 6.5-180 nm using a 1 GeV electron beam. As a critical pre-research project for DALS construction, the DALS beam test platform aims to overcome key technological bottlenecks in high-quality beam generation. This work focuses on the vacuum system design and critical technologies for the room-temperature beamline section of the test platform employing superconducting high-repetition-rate accelerators. Based on beam physics requirements, systematic design and optimization were implemented through theoretical analytical calculations and Moflow+ numerical simulations. A comprehensive solution from theoretical design to engineering implementation was achieved through software simulations (SynRad+ and Workbench) and practical verification, with particular emphasis on three key technologies for superconducting accelerator beamline vacuum system adaptation: optimized design of electromagnetic field-constrained CF flange radiofrequency shielding structures, structural design and steady-state thermal analysis of non-standard vacuum chambers, and precision control with modular installation techniques for ultra-clean vacuum systems. Current vacuum test results for the room-temperature beamline section demonstrate: injection segment vacuum better than 5E-8 Pa, beam distribution and diagnostic section vacuum better than 5E-6 Pa, and differential pumping cavity vacuum downstream of superconducting modules better than 2E-8 Pa with residual gas composition (mass numbers >44) below 1% of total residual gas and low hydrogen molecule content - all meeting superconducting accelerator operational requirements. The design specifications and technical framework developed in this project provide crucial technical support for subsequent full-system vacuum engineering implementation of superconducting accelerators.