AWAKE is boosting electrons faster than ever before Maximilien Brice, Julien Ordan/CERN

Surf’s up! Electrons riding a plasma wave can be accelerated to extraordinarily high energies, which may let us build smaller particle accelerators to smash them up and learn more about the tiniest objects in the universe.

The largest particle accelerator in the world, the Large Hadron Collider at CERN, smashes protons by whizzing them around a 27 kilometre circle, but that approach doesn’t work for electrons – they have to be accelerated in a straight line.

The Advanced Proton Driven Plasma Wakefield Acceleration Experiment (AWAKE), also at CERN, takes a different approach to make that straight line shorter and cheaper. It shoots a clump of hundreds of billions of protons into a tube filled with rubidium atoms that have been stripped of electrons, forming a plasma.


Speedy electrons

This plasma splits the clump up into smaller groups, which leave waves behind them in the plasma like speed boats on a lake. When electrons are injected into the tube, they get trapped in the wakes of the proton bunches and accelerated.

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Because the acceleration happens all at once, it doesn’t take up much space. The plasma container is only 10 metres long, and the electrons at the end reached energies of 2 gigaelectronvolts (GeV).

This relatively compact machine could someday prove useful for producing medical radiation to treat cancer, says AWAKE team member Carsten Welsch. “But the hospital would need to be close to an existing facility where you already have the proton beam accelerator.”

For now, the greatest prospects for this type of accelerator are in particle physics, says Swapan Chattopadhyay at Fermilab in Illinois. Electrons are fundamental particles, meaning we think they don’t break down into anything smaller, but that may be wrong. Smashing them into quarks, another fundamental particle found inside the likes of the neutron, could bust them open to reveal any secret particles inside.

That would require electrons at energies in the hundreds of GeV first, which could be accomplished by using higher-energy protons to accelerate the electrons.

“This experiment is a proof of principle experiment at low energy,” says Chattopadhyay. “If they could make it work at higher energies, then they could have access to new types of particles and particle interactions – it’s unknown territory.”

Journal reference: Nature, DOI: 10.1038/s41586-018-0485-4

Correction: We clarified the extent of the ionization of the plasma