If you fly over MAX IV right now and look down, you’ll see a large circular building. The reason for this size and shape is the 528-meter-long 3GeV storage ring which precisely guides bunches of electrons traveling at velocities approaching the speed of light. As the electrons pass through arrays of magnets called insertion devices, they produce bright X-rays which are then used by beamline scientists to do many different types of experiments.
In an article published this month in the Journal of Synchrotron Radiation, the 3 GeV ring team led by Pedro Tavares describe the results for the first year of operation. This important milestone in the MAX IV project provides validation for many of the brand-new concepts that were implemented in the MAX IV design in order to improve the performance of the machine and reduce downtime.
An example of this is the magnet blocks used to steer the electrons around the storage ring. These are anymore compact than in previous generations of synchrotrons owing to a design that allowed the magnets to be brought very close together. At the design phase, it was questioned whether this would work or not, and if it would be possible to monitor the magnetic fields with magnets so close together. The first-year commissioning tests show that over the course of the year, the system worked even better than expected with unprecedented stability and requiring less energy to operate the machine.
Stability was a strong consideration from the very beginning and the ring was designed to make the beam as stable as possible. Most synchrotrons have special magnets in order to quickly correct the beam if there is any instability or drift. The beam going through the 3 GeV ring showed similar stability to other world-leading synchrotrons before the correction magnets were turned on.
Another success from the commissioning was the NEG coating that MAX IV uses to trap molecules in the electron tube in order to create an ultra-high vacuum. Not only did the NEG coating work well but a new neon venting system from CERN and trailed at MAX IV this summer meant that vacuum could be restored in sections of the ring after maintenance much more quickly than before.
Of course, the commissioning was not without challenges. One of the biggest problems when designing something new and so much smaller than previous versions is finding parts that fit together. This caused a few headaches during the design and commissioning process, but the problems were eventually overcome. Likewise, with anything brand new there are always teething problems in the beginning. An example is the Radio Frequency cavities that provide energy to the electrons needed time to be conditioned before they would work as expected.
These results have been highly anticipated by the international synchrotron community as they look to MAX IV to see if the design decisions taken had paid off. As for the first year, it certainly looks very positive.
Pedro F. Tavares, Eshraq Al-Dmour, Åke Andersson, Francis Cullinan, Brian N. Jensen, David Olsson, David K. Olsson, Magnus Sjöström, Hamed Tarawneh, Sara Thorin & Alexey Vorozhtsov
J. Synchrotron Rad. (2018). 25, 1291–1316
First published: 27 August 2018