Producing the perfect light that scientists can use for their measurements of various materials is the key to running a synchrotron.
MAX IV has reached a new milestone – having light in all 11 beamlines that are either in commissioning or in regular user operation.
Stephen Molloy, Head of Operations explains: “What we want to achieve is a beam of x-rays with many, many photons of the exact same wavelength in a very small spot. In synchrotron lingo this is called having high brightness, and that is what all facilities strive towards. Delivering perfect x-ray beams to many beamlines at the same time requires controlling a lot of parameters and so far we have done really well, especially given that the machine still is quite young.”
Synchrotrons are huge ring-shaped structures in which a train of electrons in tiny bunches is stored and circulates at almost the speed of light. Synchrotrons use so-called insertion devices to produce the x-ray beams from the electrons travelling around the storage ring. These are large devices containing many powerful permanent magnets. When the electrons pass through the magnetic fields of the insertion device they start to wiggle and in doing so radiate energy in the form of x-ray light (photons). Beamlines consisting of long tubes, mirrors, and other devices are used to deliver the x-ray photons – the synchrotron light – from the insertion devices to experimental setups where scientists use those photons to study properties of materials such as their structure and composition with incredible sensitivity, in some cases down to the level of single atoms.
The energy lost in this X-ray-producing process needs to be restored so the electrons can emit new x-ray photons when passing the next insertion device, a couple of metres further along. This restoring process is done with the help of radio frequency (RF) cavities. You can think of these as huge microwave ovens, feeding the electrons with new energy. One RF cavity at MAX IV is approximately 60 times more powerful than a normal household microwave. At the 3 GeV storage ring, there are five such RF cavities installed as of now.
All the processes included in the production of the x-ray beams affect the electron beam. The more insertion devices, the larger the disturbance. It takes considerable control and a well-designed and constructed accelerator to keep the electron beam small in size and composed of electrons of the same energy. To do this every hour of every day, producing x-ray beams of impeccable quality to the scientists, is a very exciting challenge, and one that we are proving we can meet.