TUESDAY, 6 JULY 2021CERN, the European Organization for Nuclear Research, boasts the world’s largest particle physics laboratory and is located in Geneva, Switzerland. It houses the Large Hadron Collider (LHC), a huge machine that creates high-energy particles and smashes them together at high velocities. With a whopping circumference of 27 kilometres, the LHC is the world’s biggest and most powerful particle accelerator.
The LHC is a synchrotron; a type of cyclic particle accelerator. Subatomic particles such as protons and electrons are accelerated to very high speeds and focused into beams. Many experiments conducted in the LHC involve creating and observing high-energy proton beam collisions. Colliders like the LHC have been responsible for some of the most important breakthroughs in particle physics, including the discovery of the Higgs boson. The Higgs boson has long been predicted by the standard model — a single theory which describes all known forces apart from gravity — but was not observed until 2012.
Still, there is a lesser-known area of synchrotron science which has become a crucial research tool: synchrotron radiation. Also known as synchrotron light, this radiation is emitted when charged particles are accelerated. Once an unwanted by-product of particle accelerators, synchrotron light is now used to facilitate highly specialised experiments, which have important applications in many areas of science. Synchrotron light sources — facilities producing this radiation — are capable of generating light 100 billion times brighter than the Sun. This radiation enables scientists to study samples on sub-nanometre scales.
Synchrotron Light | Whilst colliders like the LHC use proton beams in their experiments, synchrotron light sources make use of electrons instead. Since electrons are lighter than protons, it takes less energy to accelerate them. In synchrotron light sources, electrons are generated by an electron gun, accelerated to near-light speeds, and then focused into a high-energy beam. The final stage of acceleration involves circulating the electron beam around a ring of superconducting electromagnets. The powerful magnetic fields generated by these electromagnets pull the particles into a circular path. When electrons that are travelling at very high speeds are accelerated in this manner, they emit synchrotron radiation.
This radiation is then projected out of the ring and captured by beamlines. Beamlines consist of an optics cabin, an experimental cabin, and a control cabin. In the optics cabin, the light is fine-tuned before entering the experimental cabin. Here, synchrotron light facilitates experiments using microscopes and other high-tech gadgets, allowing a glimpse into the atomic world. Finally, at the control cabin, scientists begin to conduct their work.
Synchrotron light is a powerful research tool as it is very bright and highly tunable. These sources generate radiation across the electromagnetic spectrum, ranging in frequency from microwaves up to x-rays. This versatility is handy, as each beamline is optimised for every experiment. Accompanied by sophisticated analytical techniques, synchrotron light is our key to unlocking the complex structure of matter, uncovering otherwise inaccessible information.
A Brief History of Particle Accelerators | The first particle accelerator was built by physicists Cockroft and Walton in 1930, at the Cavendish Laboratory in Cambridge. One year later, the American nuclear physicist Lawrence designed a more compact machine: the cyclotron, the first circular particle accelerator. Lawrence was awarded the 1939 Nobel Prize in Physics for his invention.
The cyclotron was the most powerful particle accelerator until the 1940s, when it was surpassed by the much larger synchrotron. Soviet experimental physicist Veksler, and American physicist McMillan, are both credited for devising the synchrotron. Initially a waste product, some time passed before scientists realised the potential of synchrotron light. Almost 30 years after the invention of the synchrotron, the first light source was constructed at the Synchrotron Radiation Centre in Wisconsin, US.
Diamond Light Source | Colliders like the LHC have made important contributions to particle physics, furthering our understanding of galaxies, black holes, and dark matter. In other research areas, the use of synchrotron light extends further, facilitating advancements in medicine, paleontology, engineering, and more.
There are now over 50 synchrotron light sources worldwide, with more under construction. The UK’s own synchrotron centre, Diamond Light Source, is located at the Harwell Science and Innovation Campus in Oxfordshire. This glamorous-sounding facility has been in operation since 2007. The 3 GeV synchrotron is encased in a silver ring-like building, covering an area of over 43,000 square meters. This futuristic toroidal structure wouldn’t look out of place in a Star Wars film.
Diamond is in its third developmental phase, due to be complete in a few years. The centre will accommodate a grand total of 33 beamlines. As it stands, the facility hosts a third generation synchrotron; compared to earlier models, these machines are capable of producing more intense and malleable light. This is because third generation machines make use of special arrays of magnets called undulators. These magnets are periodically placed along the ring, guiding electrons through a wiggling path, to produce even more synchrotron light.
There are plans for a Diamond-II upgrade, which will involve the replacement and improvement of instruments and computer technology, greatly increasing the performance quality. These renovations herald a bright future for synchrotron science, paving the way for more pioneering research
Artificial Heart Valves | Researchers at the University of Cambridge studied the properties of polymers to determine their suitability for artificial heart valves. Polymers are compounds consisting of very large molecules, and can be naturally occurring or man-made. In recent years, polymers have become increasingly popular in biomedical applications, as they are inert, non-toxic and have good elasticity properties.
Artificial heart valves have been used since the 1960’s to replace defective natural valves. The function of these is to allow blood to flow through the heart in only one direction. The valves open and close to enable blood flow, and are thus able to withstand repeated loading and unloading of pressure.
At Diamond, researchers investigated the properties of special copolymers for use in prosthetic heart valves. One of the beamlines was used to study real-time microstructural changes within samples being subject to repeated pressure cycles. These experiments yielded exciting results and inspired novel designs for artificial heart valves.
Debris Particles from Fukushima | In 2011, northeastern Japan was hit by a magnitude 9.0 earthquake, followed by a powerful 33 feet high tsunami wave. The natural disaster was one of the most destructive and deadly in Japanese history. The tsunami resulted in extensive flooding and power cuts throughout the northeast. Fukushima’s nuclear plant was left without power, causing the cooling mechanism to fail. Disastrously, the fuel rods partially melted, releasing radioactive debris into the surrounding area.
Working alongside the Japan Atomic Energy Agency, researchers from the University of Bristol collected and examined samples from the restricted zone. The team used a unique combination of beamlines at Diamond to investigate the long-term physical and chemical properties of the radioactive debris.
The specialist techniques offered at Diamond enabled the research group to learn more about radioactive debris and the processes that caused the accident. In future incidents, similar methodology can be used to assess the dangers associated with restricted radioactive zones.
Fran Seymour is an undergraduate student in Physical Natural Sciences at Gonvillle and Caius College. Artwork by Mary Holmes.