| AVS 65th International Symposium & Exhibition | |
| Vacuum Technology Division | Tuesday Sessions |
| Session VT-TuM |
| Session: | Large Vacuum Systems and Accelerator Vacuum Technology |
| Presenter: | Xianghong Liu, Cornell Laboratory of Accelerator-based Sciences and Education |
| Authors: | Y. Li, Cornell Laboratory of Accelerator-based Sciences and Education X. Liu, Cornell Laboratory of Accelerator-based Sciences and Education A. Lyndaker, Cornell Laboratory of Accelerator-based Sciences and Education K. Smolenski, Cornell Laboratory of Accelerator-based Sciences and Education A. Woll, Cornell Laboratory of Accelerator-based Sciences and Education L. Smieska, Cornell Laboratory of Accelerator-based Sciences and Education |
| Correspondent: | Click to Email |
A major upgrade project (CHESS-U) will elevate performance of Cornell High Energy Synchrotron Source (CHESS) to a state-of-the-art 3rd generation light source. In the CHESS-U project, ~80 meters of Cornell Electron Storage Ring (CESR) will be upgraded with a Double Bend Achromat (DBA) lattice and CHESS compact undulators (CCUs), together with new CHESS front-ends and X-ray beamlines. Tremendous progresses have been made in the design, construction, and test of all required new accelerator components (such as magnets, vacuum chambers, etc.), and we are on schedule for the CHESS-U installation in late 2018.
One of the most challenging vacuum components is the crotch absorbers at the synchrotron radiation (SR) exit ports at the ends of dipole bending chambers. CHESS-U is designed for 250-mA maximum beam current at 6-GeV beam energy. The crotches need to safely absorb 5.1 kW of SR power generated by the dipole magnets at small angles of incidence, while allowing the undulator beams produced by the canted CCUs to pass. We present a design for a compact crotch which can effectively dissipate this high SR power and will be compatible with the ultra-high vacuum system of CESR.
The crotch is a composite of a 5-mm thick beryllium outer ring, which acts as a SR diffuser, and an axially water cooled copper cylinder, similar to the existing CHESS crotches that have been in operation for decades. The outer beryllium ring is bonded to the copper cylinder via vacuum furnace braze using Cusiltin (60% Ag - 30% Cu - 10% Sn) braze alloy. Thermal analysis has shown no surface temperatures higher than 325°C. However, the calculated maximum thermal stress (on the surface of the beryllium) is near beryllium’s ultimate strength. As a practical validation of the CHESS-U crotch design, an existing CHESS crotch was removed from CESR for microscopic inspection. Though the CHESS crotch was exposed to slightly higher SR power (5.7 kW) during operations, no sign of fracture, surface melting, or other visible defect was detected on the beryllium surface. To ensure the good bonding of the beryllium diffuser ring to the copper cylinder, scanning X-ray fluorescence (XRF) inspections of the brazed crotches were performed at CHESS A1 beamline. The XRF inspection verified the presence of a continuous braze layer (corresponding to 10-30 μm thickness of Cusiltin) between the beryllium and the copper, indicating good braze joint. Five CHESS-U crotch assemblies have been successfully fabricated and XRF inspected, to fulfill the need for 4 crotches required for the CHESS-U project.