AVS 64th International Symposium & Exhibition
    Vacuum Technology Division Tuesday Sessions
       Session VT-TuM

Paper VT-TuM3
Vacuum System Engineering for Cornell Brookhaven ERL Test Accelerator

Tuesday, October 31, 2017, 8:40 am, Room 7 & 8

Session: Large Vacuum Systems
Presenter: Yulin Li, Cornell Laboratory for Accelerator-Based Sciences and Education
Authors: Y. Li, Cornell Laboratory for Accelerator-Based Sciences and Education
D.C. Burke, Cornell Laboratory for Accelerator-Based Sciences and Education
B. Johnson, Cornell Laboratory for Accelerator-Based Sciences and Education
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A novel electron accelerator, Cornell Brookhaven ERL Test Accelerator (CBETA), is under development by a collaboration between Cornell Laoratory of Accelerator-based Sciences and Education (CLASSE) and Brookhaven National Laboratory. As a prototype accelerator for eRHIC, many unique accelerator technologies will be tested in CBETA, including photo-cathode electron injector, 4-turn superconducting RF (SRF) Energy Recover LINAC (ERL), non-scaling Fixed-Field Alternating Gradient (NS-FFAG) optics with 4x energy acceptance. The CBETA layout consists of an existing photo-cathode injector with SRF cryomodule (ICM) and a main LINAC cryomodule (MLC), a NS-FFAG return loop that transports electron beams at four energies, 42, 78, 114 and 150 MeV in single bore beampipe, and two splitter sections where the four energy beams are separated. The total circumference of CBETA loop is about 80-m. The basic requirement of CBETA vacuum system is to achieve adequate level of vacuum and physical aperture for transporting electron beams at four different energies. Furthermore, by the nature of test accelerator, the vacuum system engineering must accommodate a very high density of beam diagnostics tools, such as 100+ beam position monitors, beam profile viewers, etc. Beam path length up to 20° RF-phase is required in the splitter sections. Aluminum alloy is chosen for beampipe construction material for its good electric conductivity (resistive-wall), no residual radioactivity (from beam losses), low magnetization (from cold work and welding etc.) as well as lower cost of fabrication (machining, extrusion, etc.). Compact non-evaporable getter (NEG) pumps are used due to the space constraints. As in situ beampipe bakeout is practically impossible, a program was carried out to measure aluminum alloy outgassing rates at various controlled processing (bakeout, purified dry nitrogen venting, etc.). As a measure of vacuum system cost reduction, metal knife-edge seal flanges made of non-coated aluminum alloy (type 6013-T6) were developed as the beam diagnostics ports. The results of the outgassing study were used to validate vacuum pumping system design via 3D simulation. In this presentation, we report the status of CBETA vacuum system design and fabrication. Measurements of aluminum alloy outgassing rate and tests of aluminum knife-edge flanges will also be discussed.