Researchers have argued that the UK should invest in a large X-ray free electron laser (XFEL) that would outperform existing facilities around the world. The team is now asking other scientists to complete a short survey by the end of June to express their support. The plant is scheduled to go into operation after 2030; costs and the exact location will be determined at a later date.
The project’s scientific director, Jon Marangos of Imperial College London, underscores Britain’s intention to become a “science superpower” and increases R&D spending to 2.4% of GDP. “We cannot achieve our strategic goals without investing in large, multidisciplinary facilities,” says Marangos Chemistry world.
XFELs generate femtosecond X-ray pulses that are one hundred thousandths of the pulse duration of large synchrotron sources and that are millions of times brighter. By diffraction, such rays can reveal rapid changes in the structure of substances and illuminate their changing electronic composition spectroscopically. They give scientists the opportunity to study natural and technically important processes in more detail than ever.
Today five countries operate XFELs. Great Britain is already a partner country of the European XFEL in Hamburg. There are also branches in the USA, Japan, Switzerland and South Korea. Marangos estimates that existing facilities are receiving more than five times more access requests than they can accept. Two more are currently being built in China and another in the USA. “It is very important that the UK continues to develop its plans for XFELs,” says Marangos. “In the last decade there has been an explosion in the scientific power of these machines.”
For the past two years, scholars from many disciplines have made scientific arguments for Britain to join these nations. You are now proposing a facility with ambitious capabilities. It will be able to synchronize with many other electromagnetic radiation sources that produce ultra-fast pulses ranging from terahertz frequencies across the visible spectrum to the extreme ultraviolet.
The science plan also indicates that the UK XFEL will produce X-rays with higher spectral purity than other facilities. A major advantage of lasers is that they generate radiation with a high spectral purity. The waves emitted by lasers are mostly coherent and run in phase. However, there is still a small amount of scatter or noise in existing XFELs, explains David Dunning of the STFC Accelerator Science and Technology Center in Daresbury. The British machine hopes to use technology that will reduce this noise by an order of magnitude.
XFEL systems use self-amplified spontaneous emission (SASE), in which long passages with undulator magnets of alternating polarity force electron beams to “wiggle” from side to side. When electrons change direction, they emit light, with XFELs tailored so that their electrons create X-rays. If the electrons were just in a random cloud, the light would be completely incoherent. In SASE, the X-rays interact with the electrons, helping to align them into tight bundles that create a coherent beam.
XFELs already make beams more coherent by using separate lasers or their own X-rays to prepare or “seed” bundles before they enter the undulators. Dunning explains that seeding “dominates the noise with a clean external signal”. “Our goal would be to get a lot better,” says Dunning. “One of our main goals would be to expand laser seeding further into the soft X-ray range and achieve significantly higher repetition rates.” The new XFEL also wants to use other approaches that filter and smooth the X-ray pulse. This includes SASE with high brightness, an approach developed by British scientists such as Dunning, which will be tested this year at SwissFEL in Switzerland.
Nothing is riskier
Marangos describes the UK Science and Technologies Facilities Council (STFC) as “fairly supportive” of the idea of a new facility. The country’s overarching funding agency, UK Research and Innovation, is now advising the plan, he adds. However, in order to move to the next phase, the proposal needs to demonstrate broad community support by getting researchers to complete the relevant survey by the end of June.
The British institution will not undermine the country’s participation in the European project in Hamburg, says Marangos. Researchers will remain dependent on the European location at least until the UK facility is built in 2030, he adds. “In many ways, it should stay that way in the future,” he says. “These plans are being discussed with the other major XFELs who have plans of their own.”
Scientific team member Adam Kirrander from the University of Edinburgh emphasizes that the UK had already considered an XFEL in 2008-2010, but “held back against the high technical and scientific risks”. “Today we know that these machines work and produce great amounts of great science, and the greatest risk is not doing anything,” he says.