| AVS 62nd International Symposium & Exhibition | |
| Vacuum Technology | Tuesday Sessions |
| Session VT-TuA |
| Session: | Gas Dynamics and Modeling, Pumping and Outgassing |
| Presenter: | Yulin Li, Cornell University |
| Correspondent: | Click to Email |
During summer 2014 accelerator shutdown, a pair of Cornell Compact Undulators (CCUs) was installed at Cornell Electron Storage Ring (CESR), together with a 3.5-long vacuum chamber with 5-mm vertical aperture. In a canted arrangement, these CCUs provide much brighter X-ray beams to 5 (out of 12) user stations at Cornell High Energy Synchrotron Source (CHESS). To take full advantage of the brighter sources, one of CHESS beamline, namely A1 beamline, was re-designed entirely and constructed with new vacuum chambers along ~25-m length. Similar to most 3rd generation light sources, the new CHESS A1 beamline deployed a windowless design without any vacuum barrier between CESR and A1 user station. However, the windowless design poses potential risks to CESR ultra-high vacuum (UHV) systems from potential vacuum excursions at the user station. Differential pumping and various protection interlocks are incorporated in the A1 beamline to mitigate the risks. In this paper, vacuum responses to large gas loads in A1 beamline front-end section were simulated using a test-particle Monte-Carlo program, MolFlow+ [1]. The front-end sector of the A1 beamline is constructed of UHV-compatible components with all-metal seals, including an X-ray optics box, beam shutters, two collimators, and all-metal gate valves etc. Vacuum pumping consists of a large turbo-molecular pump (1300 l/s) at the mirror box, and 6 additional sputtering-ion pumps (SIPs) and non-evaporable getters (NEGs) with pumping speed ranging from 45 to 200 l/s. To simulate vacuum incidents, a very large gas load (0.1 torr×liter/sec) is introduced at the X-ray optics box. The vacuum pressure profiles are simulated along the front-end sector to assess the impact of the large gas load to CESR UHV system, for various pumping conditions. To evaluate the A1 front-end sector as a vacuum delay-line, time-dependent pressure profiles are also simulated with MolFlow+. The simulation results indicate that CESR UHV system is immune from vacuum incidents at CHESS user stations and the A1 front-end sector acts as effective delay line.
This work is supported by the National Science Foundation, under Grant# DMR-1332208 and 0936384. Mr. Aaron Lyndaker of CHESS provided a 3D model of A1 front-end used in the simulations.
[1] MolFlow+ is available from CERN’s web-site: http://test-molflow.web.cern.ch/