Scientists have unveiled a theory according to which a technique for accelerating particles on waves of plasma is efficient enough to power a new generation of shorter, more economical particle accelerators. Scientists from the Department of Energy’s SLAC National Accelerator Laboratory and the University of California, Los Angeles have shown that a promising technique for accelerating electrons on waves of plasma is efficient enough to power a new generation of shorter, more economical accelerators.
The new system, called a Wakefield accelerator, could allow scientists to make tiny but powerful particle colliders that could fit on any university campus. That, in turn, could make it feasible to look for as-yet-unknown subatomic particles lurking in the universe. This achievement is a milestone in demonstrating the practicality of plasma wakefield acceleration, a technique in which electrons gain energy by essentially surfing on a wave of electrons within an ionized gas.
Their results, described in Nature, could eventually lead to an expansion in the use of plasma wakefield acceleration in areas such as medicine, national security, industry and high-energy physics research.
“Many of the practical aspects of an accelerator are determined by how quickly the particles can be accelerated,” says SLAC accelerator physicist Mike Litos, lead author of the paper. “To put these results in context, we have now shown that we could use this technique to accelerate an electron beam to the same energies achieved in the 2-mile-long SLAC linear accelerator, in less than 20 feet.”
Most current accelerators use a structure called an “rf cavity”, a carefully designed “box” through which the particle beam passes. The cavity transfers electromagnetic energy into the kinetic energy of particles, accelerating them. However, there is a limit to the amount of energy that an rf cavity can transfer to particles. This is because, despite operating in a vacuum, there is a risk that increasing electromagnetic fields can lead to lightning-like discharges of energy. However, even routine experiments in places like the LHC require more energy than a single rf cavity can provide. That is why the current solution is to use very many cavities arranged in a straight line, if it is a linear machine such as the SLAC, or using the same cavity very many times if it is in a circular machine, such as the LHC.
In other words previous experiments had demonstrated multi-bunch acceleration, but the team at SLAC was the first to reach the high energies of the blowout regime, where maximum energy gains at maximum efficiencies can be found. Of equal importance, the accelerated electrons wound up with a relatively small energy spread.
The plasma source used in the experiment was developed by a team of scientists led by Chandrashekhar Joshi, director of the Neptune Facility for Advanced Accelerator Research at UCLA.