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UK researchers achieve first ever acceleration of electrons in a proton-driven plasma wave

August 29th 2018 - UK researchers have played a key role in the first successful acceleration of electrons using a wave generated by protons zipping through a plasma.  The breakthrough by the AWAKE (Advanced WAKEfield Experiment) collaboration at CERN could radically change the design of future particle accelerators.

Professor Matthew Wing (UCL) is Deputy Spokesperson for the AWAKE collaboration and Principal Investigator for AWAKE-UK: “We have accelerated particles to greater energies and over shorter distances than was possible with current technology, which could result in accelerators of much reduced length and therefore cost.  This is a crucial next step in achieving high-energy collisions to probe the fundamental laws of nature.”

The AWAKE proof-of-concept compact accelerator project injects a ‘drive’ beam of protons from CERN’s SPS accelerator into a plasma column.  As the particles travel through the plasma, they generate a type of wave called a wakefield that rapidly picks up energy before a second beam of electrons is accelerated by the wakefield.

Plasma wakefield research is focused on the capacity to reach high accelerator gradients over short distances. The accelerator gradient for conventional accelerators is limited to around 100 MeV (million electronvolts) per metre. 

This new result has shown that electrons injected into AWAKE at relatively low energies of around 19 MeV, “rode” the plasma wave, and were accelerated by a factor of around 100, to an energy of 2 GeV (billion electronvolts) over a distance of only 10 metres. 

Professor Carsten Welch (Liverpool) is the Scientific Project manager for AWAKE-UK: “The Universities of Lancaster, Liverpool and Manchester, together with UCL, have made significant contributions to this result including developing the booster section of the initial electron line, simulation studies into the beam and plasma dynamics, as well as beam monitors to fully characterise the initial and accelerated electron beam. These contributions help to fully understand and optimise this novel accelerating scheme.”

While previous wakefield acceleration experiments have relied on electrons or lasers to drive the wake, AWAKE is the world’s first to use protons.

“Drive beams of protons penetrate deeper into the plasma than drive beams of electrons and lasers,” said Professor Allen Caldwell from the Max Planck Institute for Physics in Germany, Spokesperson of the AWAKE collaboration. “Therefore, wakefield accelerators relying on protons for their drive beams can accelerate electrons for a greater distance, consequently allowing them to attain higher energies.”

UK participation in AWAKE is supported by the Science and Technology Facilities Council (STFC).

Professor Grahame Blair, STFC’s Executive Director of Programmes, said: “I would like to congratulate the AWAKE collaboration for this exciting result! AWAKE has successfully demonstrated that electrons can be accelerated to 2 GeV in just 10 metres by using a high-energy proton beam as a driver. The measured accelerating gradient is significantly higher than what can be achieved with conventional accelerators and has exciting prospects for an entirely new range of experiments and applications.”

AWAKE has made rapid progress since inception. The plasma cell was installed in early 2016. A few months later, the first drive beams of protons was injected into the plasma cell to commission the experimental apparatus, and a proton-driven wakefield was observed for the first time in late 2016.

The collaboration will now carry out detailed studies to further optimise the beam-plasma interaction and achieve even higher acceleration gradients which is essential to understand the potential of this new way of accelerating electron beams.

Additional information https://www.nature.com/articles/s41586-018-0485-4

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