In this blog post, we share some recent installations of UHV/XHV pump technologies in electron synchrotrons and how these special pumps perform.
Electron synchrotrons provide powerful sources of X-ray and UV light for various research fields in physics, medicine, surface science, material science, biophysics, mineralogy, and catalysis. The synchrotron radiation is generated when high energy electrons are deflected in an electromagnetic field. The electron then emits a light quant in its original direction due to the rule of conservation of energy.
The ALBA Synchrotron
ALBA (Spanish and Catalan for “daybreak”) is a third generation synchrotron located near Barcelona/Spain. Founded in 2003, construction began in 2006. It was inaugurated in 2010 and the first beamlines were in operation for scientific use in 2012. A linear accelerator (LINAC), like ALBA, accelerates the electrons to an energy above 100 MeV. In the booster ring, electrons receive their final energy of 3 GeV and get injected into the storage ring. The storage ring has a circumference of 268,8 m with the vacuum vessel itself being 72 x 28 mm in diameter. The beam energy is 3 GeV.
Picture 1 Aerial view of the ALBA synchrotron (source: www.lightsources.org)
Like most current synchrotrons, ALBA’s vacuum chambers are made of stainless steel. For a stable beam, collisions between the beam and residual gas molecules have to be kept at a minimum. This requires pressures in the low 10-10 mbar range. All vacuum components have to be cleaned and free of hydrocarbons and dust particles. Roughing is done by dry turbomolecular pump stations. The vacuum systems of the booster and the storage ring are baked to 180–200 C to reduce the degassing from the walls. The main UHV pumps are ion getter pumps and NEG (Non-Evaporable Getter) pumps. A report on the commissioning of the ALBA vacuum system can be found by clicking here. For more information on the world wide synchrotron locations see lightsources.org.
Presently ALBA currently operates 8 different beam lines. Applications include X-ray microscopy, spectroscopy, scattering and crystallography. Three new beamlines are under construction. 'LOREA' for photoemission spectroscopy, 'XAIRA' for macromolecular crystallography, and 'NOTOS' for X-ray absorption and powder diffraction metrology. A fourth one named 'FAXTOR' is in design and you can learn more about it here.
The UHV (Ultra High Vacuum) in these beam lines is achieved by ion sputter pumps of the diode principle. Learn more about this in our blog posts 'Working Principles of High- and Ultra High Vacuum Pumps’ and 'Working With Ion Getter Pumps'.
Pump sizes vary from 75 to 800 l/s. All pumps follow the diode principle. Some use the conventional pump elements with both cathodes of titanium, while some use the differential electrode system where one of the cathode plates uses tantalum. These special elements have an enhanced pumping speed and stability for noble gases like argon.
The Argonne National Laboratory
The Argonne National Laboratory (ANL) is located near Chicago, Illinois (USA). Founded in 1946, it is one of the largest National Laboratories of the Department of Energy (DOE). ANL operates the synchrotron APS (Advanced Photon Source). APS got its first beam in 1995 and has more than 60 beamlines today. The storage ring has a circumference of 1100 m, and the electron energy is up to 7 GeV! The APS was most recently involved in research for COVID-19 vaccine (for more on this, please click here).
Picture 2: Aerial view of the APS (source: https://www.aps.anl.gov/About/Welcome)
After 25 years of successful operation, APS is upgrading their facility to become the most productive X-ray light source in the world from 2023. The brightness of the X-ray beam will be 500 times higher than any currently available, enabling scientists to conduct previously impossible experiments. Part of the upgrade work is done during regular shutdowns while the main upgrade will be done during a complete shutdown at the end of 2023. For more information, check out this article by the University of Chicago..
Part of this project includes an improvement and renewal of the UHV vacuum system. More than 600 ion pumps will be applied, the majority with integrated NEG pumps.
How NEG pumps work
Getter pumps have been used in UHV technology for more than 50 years. They use titanium which is evaporated by high current and forms an active film inside the pump or vacuum chamber. This film gathers chemically reactive gasses like O2, N2 or H2 by forming a compound with ultra low partial pressure. The active getter film has to be renewed constantly, but in the UHV pressure regime this just happens daily or even weekly.
Picture 3: Titanium Sublimator (courtesy of Gamma Vacuum)
The new NEG (Non Evaporable Getter) is made of a special alloy mainly containing zirconium and vanadium. This material has to be activated once in vacuum at temperatures of 400°C for at least an hour. After cooling down to room temperature, all reactive gasses will be pumped on the surface by forming stable chemical compounds with ultra low partial pressure. Only hydrogen — the most present gas in UHV — will be pumped by migrating into the bulk material.
The NEG has two advantages over the titanium sublimation pump:
- It does not need to be evaporated and therefore doesn’t coat the interior of the pump, or even the vacuum chamber
- It can be regenerated by heating it again. Then compounds of pumped gas will migrate into the bulk material forming a fresh reactive surface. In contrast, hydrogen will be released again and can be pumped off by an external pump. This regeneration process can be done up to 150 times. At pressures of 10-10 mbar, regeneration intervals can be up to a year.
- NEG pumps can be installed inside the vacuum system, see picture 4, or already inside an ion pump.
Picture 4: NEG cartridge (courtesy of Gamma Vacuum)
Activation of the NEG can be done manually by external power supplies with a power of approx. 100 W. A convenient way to do this is by controlling and automating the process with a special NEG controller.
Picture 5: NEG controller SPCN (Gamma Vacuum)
More information with educational videos about the different UHV pumping technologies can be found here.
In this short blog post, we’ve shared how and why classic ion pumps are essential to provide ultra high vacuum in most advanced synchrotron facilities. We’ve also shared how new NEG pumps have become mature in this application and support ion pumps by boosting the pumping speed inside the vacuum chamber, especially for hydrogen.
Interested in learning more about other types of vacuum pumps? Download our free guide to learn the advantages, disadvantages and application uses of different vacuum pumps. Simply click the link below to get your copy.