Surface analysis of the ethanol-machined aluminum alloy for the accelerator vacuum systems
Gao-Yu Hsiung1*, Chia-Mu Cheng1
1Vacuum Group, National Synchrotron Radiation Research Center, Hsinchu City, Taiwan
* Presenter:Gao-Yu Hsiung,
The aluminum alloy has been used to manufacture the beam ducts for the large accelerator ultrahigh vacuum (UHV) systems, e.g. the TPS and TLS synchrotron light sources in Taiwan. The oil-free ethanol (EL-) machining, i.e. CNC-machining with sprayed alcohol, process was applied for generating a clean surface to meet the UHV quality directly without chemical cleaning. In this study, the A6061T651 aluminum test samples and test block prepared by only the EL-machining were characterized by the XPS surface analysis, ultimate pressure after baking, and the yield of photon stimulated desorption (PSD-yield) measured at the 19B(PSD) beam line of the 1.5 GeV TLS light source. The results depict a low-carbon surface oxide layer, UHV quality at pressure ~ 10 nPa, the PSD-yield of lower than 1 molecule per 10000 photons after 1-hour photon exposure. Other samples of aluminum or stainless steel, with chemical cleaning or ozonized water cleaning, were analyzed and compared. It concludes that the EL-machining for the aluminum vacuum components or chambers possesses an ultra-clean surface and the consequent superior UHV qualities that no chemical cleaning is needed.

Keywords: ethanol machining, aluminum alloy, accelerator, ultrahigh vacuum, photon stimulated desorption