The challenge of chilling to -271°C!
As the section head and work package manager for cryogenics at ESS, Philipp Arnold’s job is to create just the right cold conditions. “My work package is to take care of three cryogenic plants and all cryogenic distribution,” he explains. “That includes the Accelerator Cryogenic Plant (ACCP) which must cool the superconducting cavities down to 2K (-271°C) using helium. Cryogenics is a challenging technology.”
Luckily, Linde Kryotechnik AG in Switzerland is up to the challenge. As the world’s leading manufacturer of cryogenic equipment, its expertise in planning, designing and constructing such plants is second to none. Having been awarded the project in 2014, Linde immediately got to work on the 150 page ESS specification to develop the refrigeration plant. The solution consists of three recycle gas compressors operating at ambient temperature and one coldbox which includes Linde’s proprietary expansion turbines as well as cold compressors.
“This was a big delivery with a very detailed specification. In cryogenics, for this size of plant, you can only have tailored solutions. It’s a complicated cycle with many interdependencies. Also, we’re a green field facility and we need extensive acceptance testing,” explains Arnold.
Big in more ways than one. The coldbox is the largest single technical component in the entire ESS, and on 18th August 2017, it was delivered to the site – after what was quite a logistics undertaking. Too big for sea transport from any ports near Lund, the giant refrigerator, measuring 14 meters long and 4.7 metres high with a diameter of 3.5 metres and a weight of 50 tonnes had to travel by road from Basel to Gent for shipping to Gothenburg since the ports around Lund couldn’t handle this size of cargo. An advance team had to clear some “road furniture” such as signs and other obstacles to make it possible. In the end the transporter even had to navigate an underpass with a guideline clearance of as little as three centimetres! Arnold remembers it well: “I was here when it arrived and can verify that it took a day to get it from the entrance point to the hall where it’s housed and another day to position it precisely!”
Reliability: The potential costs of downtime
Once the facility is fully up and running and the user program begins in 2023, scientists from all over the world will be applying for their “beam time”: a, for instance, 48-hour window in which to run their potentially Nobel prize-winning experiments. If downtime occurs within that window due to a cryogenic hitch, ESS is not only running the risk of impeding scientific progression, but also of leaving users dissatisfied, as Arnold explains:
“This can’t happen very often, otherwise you could risk losing users. And many of these users will have been planning these experiments for a long time before. This is why we put so much on reliability.”
All of the scientific endeavours depend on one proton beam, which depends on one cryogenic plant, which depends on a number of components – each one essential for a reliable operation of the facility. And at the end of the day, unplanned downtime is simply not an option at ESS. Thankfully, Linde’s experience and expertise mean its solutions meet these requirements. Linde Kryotechnik AG is also currently developing a cooling plant for the target moderators planned for delivery in 2018.