DESY is one of the world's leading particle accelerator centres for research into the structure of matter. The research focus extends from particle physics to the many application areas of research with photons. These include the construction and use of x-ray lasers.
The European free-electron x-ray laser, the 'light source of superlatives', is to be developed and designed at DESY. Its highly-intensive ultrashort x-ray flashes with laser characteristics offer completely new research perspectives for scientists and industrial users alike. DESY is also involved in the next great challenge for particle physics, the International Linear Collider or ILC, an accelerator for electron-positron collisions. The ILC could enable physicists to look more deeply and accurately than ever before into the structure and origins of matter and the universe.
With its photo-injector test rig (PITZ), DESY operates a substantially smaller linear accelerator at its site in Zeuthen. It is used to develop and optimise laser-powered high-frequency electron sources for the future European x-ray laser project XFEL. The photo-injector acts as the cathode for an accelerator out of which electrons travel at a high frequency and are accelerated in the linear accelerator to almost the speed of light. In Zeuthen, however, the electrons are slowed down after around 20 m - a process in which the huge amount of kinetic energy is converted into heat.
"This heat energy has to be dissipated in correspondingly large volumes of cooling water", explains engineer Herbert Schulze, head of technical infrastructure at DESY in Zeuthen, in describing the project brief. The researchers also specify extremely precise temperature ranges, particularly for the photo-injector test rig. Supplying the entire photo-injector test rig with cooling water, not only for heat dissipation, is in itself a technical challenge.
The Grundfos Solution
In order to cool the individual components of the test rig, the planners at RCI GmbH, Berlin, have provided several cooling systems each of which operates at a different temperature. Some operate at between 4 and 12°C, some between 27 and 40°C, while other systems cool components with initial temperatures of 54 or 60°C. However the biggest challenge is to maintain a constant temperature of +/- 0.05 Kelvin in one of the systems! To build this kind of precision process-cooling system naturally imposes special conditions on the individual components, as Schulze emphasises: "We often have to pay attention to very specific qualities and tolerances. Not every manufacturer is able to comply with this." In Zeuthen they use stainless steel variable speed in-line high-pressure pumps from the CR range equipped with the latest MGE motors (CRNE).
The pumps used in the cooling circuits also have to comply with these requirements - not a problem for Grundfos pumps:
· the pumps operate continuously 365 days a year (in order to keep the temperature constant even when tests are not being carried out)
· the correct pressure must be maintained (speed-controlled pumps are generally used for this reason)
· a high constant flow rate is required (most of the pumps have inbuilt redundancy because the flow monitors will shut down the entire system in the event of even minor discrepancies)
· stainless steel is essential due to the demineralised water required in the cooling and cold water circuits (1 ìS/cm conductivity in the cooling water circuit).
Plus: the integrated frequency converter in the Grundfos pumps is beneficial in the kind of sensitive research environment that prevails at DESY because there is no external FC and so there is no need to shield naked cables.