Science and Technology Facilities Council
Atomic 'Trojan horse' could inspire a new generation of X-ray lasers and compact particle accelerators
Researchers from the UK and US have developed a ground breaking technique that could produce an electron beam up to 10,000 times brighter than the most powerful beams today.
Such an intense electron beam would make future X-ray lasers brighter, enhancing their scientific capabilities, and would be particularly applicable for use in our next generation of more compact, more powerful particle accelerators.
The experiment, published in Nature Physics, was led by the University of Strathclyde’s Professor Bernhard Hidding, who is also a member of the STFC’s Cockcroft Institute, and was carried out at the U.S Department of Energy’s Stanford Linear Accelerator Center (SLAC) in California.
Known as the ‘E-210: Trojan Horse’, the experiment involved releasing electrons from neutral atoms inside plasma, to produce a potentially much brighter, plasma-based electron source. It is referred to as the Trojan Horse technique because it’s reminiscent of the way the ancient Greeks are said to have invaded the city of Troy by hiding their forceful soldiers (electrons) inside a wooden horse (plasma), which was then pulled into the city (accelerator).
Professor Hidding recently said:
“Our experiment demonstrates the feasibility of one of the most promising methods for future electron sources and could push the boundaries of today’s technology by orders of magnitude.”
In current accelerators, electrons are generated by shining laser light onto a metallic photocathode, which displaces electrons from the metal. These electrons are then accelerated inside metal cavities, where they draw more and more energy from a radiofrequency field, resulting in a high-energy electron beam. In X-ray lasers, this electron beam drives the production of extremely bright X-ray light.
However, these metal cavities can support only a limited energy gain over a given distance, or acceleration gradient, before breaking down, and therefore accelerators for high-energy beams become very large and expensive. In recent years, scientists have looked into ways to make accelerators more compact and have demonstrated, for example, that they can replace metal cavities with plasma that allows much higher acceleration gradients, potentially shrinking the length of future accelerators by 100 to 1,000 times. The new paper expands this plasma concept to the electron source of an accelerator.
The researchers have also developed several auxiliary techniques, which would improve the quality and stability of their output beams, and to harness the technique for applications.
In a forward-looking, complementary project funded by STFC, Professor Hidding and colleagues from UK and US are already exploring the benefits to be expected from ultrabright and ultrashort electron beams for X-ray free electron lasers and other light sources at CLARA, a particle accelerator designed to develop, test and advance new technologies for the next generation of particle accelerators and free-electron-lasers, at STFC’s Daresbury Laboratory. In conjunction with further R&D at SLAC’s FACET-II facility, the Scottish Centre for the Application of Plasma-based Accelerators (SCAPA) and the Central Laser Facility (CLF), these ultrabright beams may eventually allow production of X-ray pulses short and bright enough to allow observation of electronic motion inside atoms and molecules on their natural timescale.
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