A promising method of accelerating electrons using waves of plasma now has enough efficiency to power a new generation of shorter, more economical accelerators. Think 20 feet instead of two miles.
Scientists from the Department of Energy’s SLAC National Accelerator Laboratory and the University of California, Los Angeles say their research could greatly expand use of particle accelerators in fields as diverse as medicine, national security, industry and high-energy physics research.
The achievement marks a milestone in demonstrating the practicality of plasma wakefield acceleration, a technique in which electrons gain energy basically by surfing on a wave of electrons within an ionized gas.
“Many of the practical aspects of an accelerator are determined by how quickly the particles can be accelerated,” said physicist Mike Litos, lead author. “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.”
Researchers boosted bunches of electrons to energies 400 to 500 times higher than they could reach traveling the same distance in a conventional accelerator, by using SLAC’s Facility for Advanced Accelerator Experimental Tests (FACET).
Plasma Wakefield Blowout Regime
Plasma wakefields have been relevant to accelerator physicists for 35 years. It is one of the most promising ways for powering smaller, cheaper accelerators of the future.
The researchers sent pairs of electron bunches having 5 billion to 6 billion electrons each into a laser-generated column of plasma inside an oven of hot lithium gas.
The first bunch in each pair was the drive bunch; it blasted all the free electrons away from the lithium atoms, leaving the positively charged lithium nuclei behind, a configuration known as the “blowout regime.”
The blasted electrons then fell back behind the second bunch of electrons, known as the trailing bunch, forming a “plasma wake” that propelled the trailing bunch to higher energy.
“These results have an additional significance beyond a successful experiment,” said Mark Hogan, SLAC accelerator physicist. “Reaching the blowout regime with a two-bunch configuration has enabled us to increase the acceleration efficiency to a maximum of 50 percent – high enough to really show that plasma wakefield acceleration is a viable technology for future accelerators.”
Before plasma wakefield acceleration can be applied beyond experimental uses, Hogan said, the trailing bunches must be shaped and spaced just right so all the electrons in a bunch receive exactly the same boost in energy, while maintaining the high overall quality of the electron beam.