An experiment at CERN has demonstrated a new way of accelerating electrons to high energies—one that could dramatically shrink the size of future particle accelerators and lower their costs.
The technique is the latest entrant in a hot race to develop a technology called plasma wakefield acceleration. The method uses waves in plasma, a soup of ionized atoms, to push electrons to ever-higher energies over distances much shorter than those required in today’s particle accelerators. Several laboratories have demonstrated plasma wakefield acceleration using two different approaches; most teams use laser beams to create the plasma waves needed. The latest work is the first to show that protons can also induce the waves and achieve electron acceleration—a technique that may have advantages over the others because protons can carry high energies over long distances.
In this case, researchers diverted protons that would usually be fed into the Large Hadron Collider (LHC) at CERN, Europe’s particle-physics lab near Geneva, Switzerland, and instead inserted them into the wakefield accelerator, called the Advanced Wakefield Experiment (AWAKE). The machine worked as expected and created a consistent beam of accelerated electrons. “That, for us, was a major achievement,” says Matthew Wing, a physicist at University College London, who is deputy spokesperson for AWAKE. “It essentially says that the method works, and it’s never been done before.” The work is described in Nature on August 29.
In AWAKE’s first experimental run in May, the team accelerated electrons to energies of 2 gigaelectronvolts (GeV) over 10 metres. In principle, a much larger version of the experiment that took protons from the LHC’s main ring—rather than from its lower-energy sibling—could push electrons to energies of teraelectronvolts (thousands of GeV) in a single, kilometres-long stage, Wing says.
“This would be a compelling accomplishment, as there are no laboratory sources of teraelectronvolt electrons currently available,” says James Rosenzweig, who leads the laser plasma wakefield research team at the University of California, Los Angeles.
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