The Advanced Proton Driven Plasma Wakefield Acceleration Experiment.

The Advanced Proton Driven Plasma Wakefield Acceleration Experiment (AWAKE) aims at studying plasma wakefield generation and electron acceleration driven by proton bunches. It is a proof-of-principle R&D experiment at CERN and the world׳s first proton driven plasma wakefield acceleration experiment. The AWAKE experiment will be installed in the former CNGS facility and uses the 400 GeV/c proton beam bunches from the SPS. The first experiments will focus on the self-modulation instability of the long
(rms ~12 cm) proton bunch in the plasma. These experiments are planned for the
end of 2016. Later, in 2017/2018, low energy (~15 MeV) electrons will be externally injected into the sample wakefields and be accelerated beyond 1 GeV.

AWAKE is a proof-of-concept acceleration experiment with the aim to inform a design for high energy frontier particle accelerators and is currently being built at CERN. The AWAKE experiment is the world׳s first proton driven plasma wakefield acceleration experiment, which will use a high-energy proton bunch to drive a plasma wakefield for electron beam acceleration. A 400 GeV/c proton beam will be extracted from the CERN Super Proton Synchrotron, SPS, and utilized as a drive beam for wakefields in a 10 m long plasma cell to accelerate electrons with amplitudes up to the GV/m level. Figure 1 shows the AWAKE facility in the CERN accelerator complex. In order to drive the plasma wakefields efficiently, the length of the drive bunch has to be on the order of the plasma wavelength λpe, which corresponds to ≈1 mm for the plasma density used in AWAKE (1014–1015 electrons/cm3). The proton beam for AWAKE has a bunch length of sigma_z = 12 cm, therefore the experiment relies on the self-modulation instability (SMI), which modulates the proton driver at the plasma wavelength in the first few meters of plasma. The SMI is a transverse instability that arises from the interplay between transverse components of the plasma wakefields and the wakefields being driven by regions of different bunch densities. The modulation period s is approximately λpe  and the modulated bunch resonantly drives the plasma wakefields. The occurrence of the SMI can be detected by characterizing the longitudinal structure of the proton beam when exiting the plasma cell.

 
Figure 1: CERN accelerator complex.

In the AWAKE master schedule, the experiment to obtain evidence for the SMI corresponds to Phase 1, and is expected to start by the end of 2016. In Phase 2, AWAKE aims at the first demonstration of proton-driven plasma wakefield acceleration of an electron witness beam; this programme is planned to start by the end of 2017. At a later phase it is foreseen to have two plasma cells in order to separate the modulation of the proton bunch from the acceleration stage. Simulations show that this would optimize the acceleration of external electrons and reach even higher gradients.

This text is extracted from: AWAKE, The Advanced Proton Driven Plasma Wakefield Acceleration Experiment at CERN.

Installation of the plasma cell:



AWAKE proton beam commissioning:



Some pictures of the AWAKE facility: