Pure research

The world's strongest laser center, the "Extreme Light Infrastructure" (ELI), is currently being built with EU funds near the Czech capital Prague. It is expected to be available to scientists from around the world for fundamental research within a few years.

What CERN means for particle physicists, ELI aims to become for laser research. Even the construction of the facility, which will cost several hundred million euros, presents experts with challenges previously unknown. The problem: The apparatus, about the size of a football field, reacts very sensitively to contamination. The high-energy laser beams, which travel through an ultra-high vacuum, burn particles and gases into the walls or sinter them, thus transforming them into substances that deposit like a coating. The deflection mirrors would become blind, and the entire facility would become unusable. Cleanliness is therefore of the utmost importance. Complicating matters is the fact that dozens of different suppliers deliver the individual components, all of which must meticulously adhere to the specified purity standards. "That is a huge effort," says Markus Keller, an expert at the Fraunhofer Institute for Production Technology and Automation IPA.

Many companies have now turned to the IPA. Because the institute not only has the world's largest research cleanroom of ISO Class 1, but its scientists also possess the necessary know-how in all questions of purity. And for this project, led by Keller, all facets are required, from cleaning to validation, from clean packaging to training. It concerns both organic contaminants and particles. And it is about ensuring that no materials used outgas. The approach is accordingly versatile.

Some parts, such as a vacuum valve weighing half a ton, are cleaned in Stuttgart, carefully packaged, and shipped. For other components, transportation would be too complicated. For example, more than 100 stainless steel pipes are needed, each 6 meters long and 40 centimeters in diameter. These will later carry the laser beams through the ultra-high vacuum.

These pipes can only be connected on-site, requiring a provisional cleanroom. This means: wall coating, flooring, rust protection — nothing must outgas. The IPA selects the optimal building materials. Above all, no dirt may be inside the pipes. To monitor cleanliness, the IPA provides the necessary equipment and analyzes the returned samples for particles, organic dirt, and gases. Finally, Keller and his colleagues train the employees of the involved companies so they can meet the requirements. Because the superlaser does not tolerate mistakes. Once the apparatus is set up, no further cleaning work is possible. The pipes through which the beam passes remain hermetically sealed.