Light has always been the most important tool for humanity to advance the understanding of nature. We only tend to believe what is visible to our eyes. An intriguing light source is synchrotron radiation. Scientists love it due to its high intensity and brilliance, defined properties, and wide frequency range from X-ray over the visible regime up to infrared radiation. It allows completely new investigations and developments of matter, materials, and medical drugs. Governments invest billions of dollars in research facilities to make it available to their scientists. But how does it work?
Based on Einstein’s Special Theory of Relativity, synchrotron radiation is generated in large storage rings when electron bunches move on a circle at relativistic velocities, i.e., with almost the speed of light. “Imagine being on a stand of a circular racetrack. Every time a car passes by you, you can hear its boasting sound thrilling you. A synchrotron is similar. The racetrack is a storage ring of about hundred meters in diameter. Similar to the cars making the sound on a racetrack, electron bunches fly on a circle inside the ring. Every time they pass by a beamline, they emit the brilliant radiation that scientists use for their experiments,” explains Rafael Molena Seraphim, head of the vacuum group at the Brazilian Synchrotron Light Laboratory LNLS. “However, the electrons travel about 5 million times faster than a formula one race car.”
The ring consists of metallic tubes inside which electrons are guided by magnets to steer their way. To ensure that no air molecules collide with the electrons and hinder their relativistic movement, the tubes are kept at ultra-high vacuum (UHV) of 10-12 mbar. This atmosphere is comparable to the moon’s surface. In a nutshell, a synchrotron is Einstein’s relativistic racetrack for particles in a moon-like atmosphere.
The SIRIUS ring in Brazil is one of the latest fourth-generation synchrotrons. Its construction started in 2015, and it is the most sophisticated and complex infrastructure ever built in the country. It accelerates electrons to relativistic energies of 3 GeV inside a storage ring of 518m circumference. Removing the air from the large storage ring is a challenge and requires a lot of time for pumping. Furthermore, a clean environment needs to be maintained despite multiple scientists performing experiments at the same time.
The main strategy to build a complex UHV system is to divide it into distinct segments separated by section valves. By this, individual parts of the ring can be vented for maintenance works while keeping the rest at UHV pressures. Yet, the critical aspect of the section valves is not when they are closed but when they are open during the operation of the synchrotron. The electrons fly in small packages through the ring carrying an alternating current of radio frequency (RF). “The open valves must mimic the design of the tubes as much as possible to avoid any RF disturbances for the electron current,” highlights Rafael Seraphim. “Otherwise, it is like oil in the curve of the racetrack. Surely, the car would crash at high speed, or the electrons lose their optimum track.”
VAT has a long-standing history of providing specialized vacuum valves for the operation of storage rings. These range from the series 54.1 all-metal angle valves for venting and pumping purposes to the series 47 and 48 gate valves. “Our all-metal valves are elastomer-free and specifically suitable for the challenging radiative environment inside a storage ring. However, we are always flexible to adapt the valves to our customer’s specific needs. Already in the early planning phase of SIRIUS in 2012, I flew to Brazil to understand the specific architecture and requirements of the project,” recalls Jürg Öhri. “We started a very open and constructive collaboration.”
In the following, VAT developed the series 47 XHV RF all-metal gate valve with a specific radiofrequency bridge. When open, it bridges two vacuum tubes of the ring by a special metallic spring to ensure that the connection exactly matches the electrical properties of the SIRIUS ring. The electrons flying by the open valve do not see a difference to the plain tube used in the rest of the ring anymore.
The multi-user environment of a synchrotron is another challenge requiring additional safety measures: “The beamlines are booked by many scientists who perform creative novel experiments. In case something goes wrong, we need to protect the synchrotron from any contamination that might enter from the malfunctioning experiment at the beamline,” defines beamline engineer Gustavo Rodrigues the task. To achieve this, VAT also provided a safety system consisting of malfunction detectors and an ultrafast series 77.3 shutter valve which disconnects the beamline from the storage ring within only 10 ms. In other words, the racetrack remains free of contamination.
The vacuum valves are among the most complex components inside a synchrotron. Until 2021 LNLS Engineers installed almost 300 VAT valves in the SIRIUS ring. The VAT high-tech solutions are part of the reason why the first beamlines of the SIRIUS are now in operation with scientists performing their experiments. In the end, there is the possibility for up to 38 beamlines. “By their in-depth know-how on synchrotron vacuum design together with their flexibility to adapt components to their specific use case, VAT has been a strong technology partner in realizing SIRIUS operation within 2020,” summarizes Rafael Seraphim. “It is always fascinating to see these complex scientific infrastructures growing mature. We are the world market leader for complex scientific vacuum facilities with about 90% of the UHV valves inside synchrotron rings made by us. However, each project has distinct challenges and requirements, and we are always ready to tackle them”, elucidates Jürg Öhri, sales engineer at VAT. “We are proud to be one of the key partners to make SIRIUS happen and to help providing researchers with the most modern scientific infrastructure”, concludes Jürg Öhri.
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