Proton-driven plasma wakefield acceleration in AWAKE

Abstract

In this article, we briefly summarize the experiments performed during the first run of the Advanced Wakefield Experiment, AWAKE, at CERN (European Organization for Nuclear Research). The final goal of AWAKE Run 1 (2013-2018) was to demonstrate that 10-20 MeV electrons can be accelerated to GeV energies in a plasma wakefield driven by a highly relativistic self-modulated proton bunch. We describe the experiment, outline the measurement concept and present first results. Last, we outline our plans for the future. This article is part of the Theo Murphy meeting issue 'Directions in particle beam-driven plasma wakefield acceleration'.

Keywords: AWAKE; plasma wakefield acceleration; seeded self modulation.

Figure 1.

Schematic layout and description of the AWAKE experimental facility, beams and diagnostics. The insert panel on the bottom left shows a schematic of the spatial and temporal alignment of the proton, laser and electron bunch entering the vapour source; the bottom middle panel shows a schematic of the transverse and longitudinal proton microbunch density structure in plasma (after the self-modulation process saturated); the panel on the top right shows an experimental image obtained by the spectrometer camera, for when electrons were accelerated. (Online version in colour.)

Figure 2.

Transverse (W_r at σ_r) initial seed wakefields along the proton bunch (ξ) in plasma with an electron density of 7 × 10¹⁴ cm⁻³. The proton bunch RMS transverse size is σ_r = 0.15 mm. To speed up the calculation, the bunch length was made 10 times shorter (σ_z = 7 mm instead of ≈ 7 cm) and the bunch intensity 10 times less (3 × 10¹⁰ protons per bunch instead of 3 × 10¹¹ protons per bunch). Since the calculation is linear, the resulting wakefield amplitudes are the same. The seeding position (ξ = 0) is in the centre of the proton bunch. The green line shows the particle density along the bunch (ξ). Red areas mark wakefield phase regions that are defocusing for electrons, blue areas marks focusing regions. The bunch propagates to the left.

Figure 3.

(a) Spectrometer background image; (b) example of a spectrometer image for when electrons were accelerated. Note the change on the maximum number of counts between the two images. The same constant background was subtracted from each image.

Figure 4.

Waterfall plot of vertically summed spectrometer images during a change of plasma electrons density gradient. The upstream density is 7 × 10¹⁴ cm⁻³. The red line indicates the measured density gradient for each event. Note that integrated signals below 1000 counts are cut from the image.