Acceleration of electrons in the plasma wakefield of a proton bunch
2018
High-energy particle
acceleratorshave been crucial in providing a deeper understanding of fundamental particles and the forces that govern their interactions. To increase the energy or to reduce the size of the
accelerator, new
accelerationschemes need to be developed. Plasma wakefield acceleration1–5, in which the electrons in a plasma are excited, leading to strong electric fields, is one such promising novel
accelerationtechnique. Pioneering experiments have shown that an intense laser pulse6–9 or electron bunch10,11 traversing a plasma drives electric fields of tens of gigavolts per
metreand above. These values are well beyond those achieved in conventional radio-frequency
accelerators, which are limited to about 0.1 gigavolt per
metre. A limitation of laser pulses and electron
bunchesis their low stored energy, which motivates the use of multiple stages to reach very high energies5,12. The use of proton
bunchesis compelling, as they have the potential to drive wakefields and
accelerateelectrons to high energy in a single
acceleratingstage13. The long proton
bunchescurrently available can be used, as they undergo a process called self-modulation14–16, a particle–plasma interaction which longitudinally splits the
bunchinto a series of high-density microbunches, which then act resonantly to create large wakefields. The Advanced Wakefield (AWAKE) experiment at CERN17–19 uses intense
bunchesof protons, each of energy 400 gigaelectronvolts (GeV), with a total
bunchenergy of 19 kilojoules, to drive a wakefield in a 10-
metre-long plasma.
Bunchesof electrons are injected into the wakefield formed by the proton microbunches. Here we present measurements of electrons
acceleratedup to 2 GeV at the AWAKE experiment. This constitutes the first demonstration of proton-driven plasma wakefield
acceleration. The potential for this scheme to produce very high-energy electron
bunchesin a single
acceleratingstage20 means that the results shown here are a significant step towards the development of future high-energy particle accelerators21,22.
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