Shooting an underground movie of real life
Switzerland has a long tradition in underground engineering and is world-renowned for the construction of the Gotthard tunnel in the 19th century. One of the latest high-tech tunnels of the country is the Swiss Free Electron Laser (SwissFEL) at the Paul Scherrer Institute (PSI) that generates ultrashort X-ray pulses inside a tunnel of 740m in length. It is the new tool for scientists worldwide to investigate biochemical processes governing our human lives. The SwissFEL’s X-rays are extremely brilliant, and they might even allow following chemical reactions in living cells in real-time in the future, a thrilling prospect for every biologist!
The scientists at the PSI are directors who want to shoot movies about the natural processes governing our daily lives. The chemical structures are visible to soft X-Ray radiation, but the reactions – for example, the light absorption in chlorophyll - happen on a very short timescale of a few femtoseconds. That is about ten trillion times faster than the image repetition rate of consumer TVs. Hence, X-ray pulses need to be very short to visualize these fast biological changes. The pulses are generated by the acceleration of small electron bunches inside the 740m long tube. The tube is held at ultra-high vacuum (UHV) of 10-12 mbar to ensure an unhindered movement of the electrons on the inside, without interference with any ambient air molecules. The vacuum conditions need to be maintained at all operating times because the traveling path of the electrons is the crucial key to the generation of ultrashort X-ray pulses. Once at high speed, these electrons are guided by magnets on a wave-like trajectory. This curved motion is what causes them to emit X-Ray radiation.
The X-ray pulses are the camera for the scientific directors, and they are guided into endstations where scientists perform their experiments. The latest Maloja endstation uses the soft X-ray spectrum at the Athos beamline of the SwissFEL to get a real-time view of the chemical and electronic structure changes of single atoms, molecules, and nanoparticles after controlled manipulation. “For experiments to work, it is crucial to align the beams from the SwissFEL very accurately with our samples and any other laser beams that we use to manipulate and probe the materials under investigation”, explains PSI senior scientist Dr. Kirsten Schnorr. “This is often very tedious and time-consuming work, and we cannot expect the other operators at the SwissFEL to wait for us to finish.” Therefore, we required a solution to enable the experimental preparation of the endstation while the rest of the SwissFEL environment continued its operation.
Customized VAT valves specific to customer needs
A common solution is the implementation of a segment valve that separates the endstation from the ultra-high vacuum part of the SwissFEL. “However, we could not find any valve on the market which would allow us to go through with our three different alignment beams,“ recalls Dr. Schnorr. “When you are part of a complex technological environment like SwissFEL, and you need a customized solution of reliable quality, you cannot just go to the next workshop. We need to be sure that it always works and will not impede the UHV of the main facility. Luckily, we knew that VAT had already been involved in the SwissFEL project, and we asked them for help.”
VAT is a long-standing partner of the PSI and has supplied several high-quality components at UHV grade to the SwissFEL project. These range from gate valves of the 01.0 & 10.8 series, across 54.0 all-metal angle valves, to fine dosing valves of the 59.0 type. “When it comes to ultra-high vacuum applications in sophisticated scientific environments like the SwissFEL, VAT is usually an integral part of the project. We provide a unique product catalog when it comes to UHV valves,” explains Andreas Dostmann, Sales Manager at VAT.
“Yet, when Dr. Schnorr approached me regarding a gate valve with three alignment windows at defined angles, I knew this was not a product off-the-shelf. Thus, I decided to ask our engineers to design it specifically for the Maloja station.” After some quick technical exchange with PSI about the technical requirements, VAT designed the gate valve, chose the proper window materials to ensure an unhindered laser penetration, and delivered the assembled gate valve to the Maloja endstation for installation.
The shared ambition for progress
“We are very happy with our new alignment gate valve at the Maloja endstation. Now, we can thoroughly prepare our sophisticated experiments with up to 10 femtosecond resolution without any implications on the main facility. When opening the gates towards the SwissFEL, we can instantly use the fascinating properties of the ultrashort X-Ray pulses and enjoy our well-prepared experiments at work,” summarizes Kirsten Schnorr. “We are very grateful for the flexibility at VAT to design a customized solution specific to our needs at minimum development time.”
“I know that we have the know-how in-house to solve these kinds of technical problems quickly,” knows Andreas Dostmann. “But even more important, our company always had the ambition to contribute to technological progress by customized solutions. We do not mind putting the engineering hours into finding the one perfect solution for each individual customer.” This is one of the reasons why the Paul Scherrer Institute is one of the oldest clients of VAT, having a single-digit customer number.
While the tunnel design of the SwissFEL creates an association with Gotthard going right through Alpes, the endstations are named after Swiss passes that take you over the alpine summits. And it fits their purpose: The scientists aim high with their goal of visualizing our biological processes, i.e., what makes us human. Like the serpentines of the Maloja pass, they will need to take turns on their way to the top. VAT will help where they can!