Development of the Aluminum Beam Ducts for the Synchrotron Light Source with Ultra-Low Emittance
Gao-Yu Hsiung1*, Hsin-Pai Hsueh1, Shen-Nung Hsu1, June-Rong Chen1
1Vacuum Group, National Synchrotron Radiation Research Center (NSRRC), Hsinchu City, Taiwan
* Presenter:Gao-Yu Hsiung,
The next generation synchrotron light source with ultra-low emittance, typically < 500 pm rad, requests the beam duct with the inner aperture much smaller than 20 mm for the ultrahigh vacuum (UHV) system of the electron storage ring as well as a smooth cross section with much lower impedance. The aluminum extruded beam ducts of 10 mm inner-diameter and 1 m ~ 2 m in-length have been developed for this purpose. The inner surface of the duct was oil-free machined by deep drilling in ethanol to obtain a clean oxide layer that the consequent lower thermal outgassing rate was achieved. To mitigate the impedance of the flange connection, a special designed aluminum (Al-) flange without knife edge and a diamond-edge (DE-) gasket were developed. The inner diameters of both the Al-flange and the DE-gasket are 10 mm, the same as that of the beam duct. The sealing of the DE-gasket has been proved the leak-tight under a leak rate of 1E-9 Torr l/s. The ultimate pressure at both ends of the 1 m in-length aluminum beam duct, with and without pumping, after baking at 150 °C for 24 hours has reached to 2E-10 Torr and 6E-10 Torr, respectively. The thermal outgassing rate of the Al-beam duct, measured via the throughput method, has achieved 7E10-14 Torr l/(s cm2), lower than other materials such as the stainless steel or copper. The result consists with the calculation model for the pressure distribution. This developments not only fulfill the ultrahigh vacuum performance but also minimize the broad-band impedance of the flange connection are applicable for the future light source.

Keywords: light source, ultra-low emittance, aluminum, diamond-edge gasket, ultrahigh vacuum