DESY (Deutsches Elektronen-Synchrotron) is the largest German research center for basic research in the natural sciences, with special emphasis upon accelerators, photon science and particle physics. DESY develops, runs and uses accelerators and detectors for photon science and particle physics.
The PETRA storage ring at DESY has been upgraded to the third generation synchrotron radiation source PETRA III (PETRA III Project), with 14 beamlines operated under ultra high vacuum (UHV) conditions. The vacuum specification requires a hydrocarbon free vacuum system and the acceptance of vibrations arising from the pumping system is very low. For these reasons ion pumps are used to pump down the beamline continuously. As the start pressure of ion pumps is below 10-6 mbar, mobile pumping stations are used for the initial pump down of the UHV system. Once the UHV state is achieved, and the ion pumps switched on, the mobile pumping stations are turned off. This required an innovative mobile dry pumping station using Edwards scroll pumps to be designed.
The DESY team approached Edwards during the design of innovative mobile dry pumping stations for the new photon beamlines. Already using Edwards scroll pumps for a number of applications within DESY, they chose the company’s XDS10 scroll pumps to provide quick rouging and pump down, enabling them to establish high vacuum within the photon beamlines and the experimental stations of beamline users.
Designing the mobile pumping station
As the mobile pumping stations can be used whenever a dry and particle free vacuum is required, they will also be provided to beamline users to pump down their experimental chambers. They additionally give the users the options of leak detection, residual gas analysis and control of their bake out systems.
The new mobile dry pumping station designed by the DESY team to meet these requirements uses two pumps, with the fore pump providing a bypass of the turbo molecular pump to enable rapid pump down of the attached vacuum chamber.
“The fore pump is a dry pump – the Edwards XDS10 scroll pump,” says Frank Wagner, Edwards’ key account manager, Scientific Deutschland Nord. “This was ideal for DESY’s requirements because it delivers sufficiently low pressure combined with good pumping speed to create the fast pump down of the system.” The XDS10 offers a high volume flow rate of up to 10m3/hr and creates an ultimate vacuum of 7 x 10-2 mbar.
Pumping begins with the fore pump only working and the valve connecting the system to the turbo molecular pump closed. When both sides are high vacuum, the main valve in the system opens, the UHV pump is activated and the fore pump is switched off. A buffer switch then allows toggling so that the fore pump is automatically restarted as needed.
This toggling system means that the fore pump runs for less than five per cent of the overall pumping time, which extends maintenance intervals and increases lifetime.
The benefits of dry pumps
The DESY team chose to use dry pumps in their design because they provide a number of important benefits. Dry pumps have no lubricants under vacuum, eliminating the need for regular oil changes and hence reducing maintenance and environmental impact. This also means there is no possibility of process contamination, vital for use in the synchrotron.
Edwards XDS pumps are an innovative design which use a bearing shield to isolate the vacuum environment from all forms of lubricant, making it not only totally dry but hermetically sealed. The shield also protects the bearing from any process vapours, ensuring that there is no possibility of contamination in any direction.
Adjustable gas ballast allows vapour to be handled and opens up the range of applications to many that were previously unsuited to scroll pumps. All of these characteristics make the pumps ideal for the demanding requirements of a synchrotron radiation source.
The Edwards XDS pumps have a wide range of applications in scientific research, including ultra high speed centrifuges, analytical instruments, lasers and scanning electron microscopes, as well as vacuum systems for photon beamlines.
“Every single component of our mobile dry pumping stations was chosen to ensure the highest performance. The Edwards pumps play a key role in these stations, and they have delivered exactly what we required,” says M. Hesse, DESY.
The Edwards XDS dry scroll pump offers a ‘fit-and-forget’ solution for its users. For the synchrotron scientists, it has provided the optimum solution for a highly demanding application.
Picture: Edwards XDS10 scroll pump