The AWAKE Experiment at CERN
Dr Edda Gschwendtner, CERN, Switzerland
AWAKE, the Advanced Proton Driven Plasma Wakefield Acceleration Experiment at CERN, pursues the demonstration of electron acceleration in plasma. The 400 GeV/c SPS proton beam, with a rms bunch length of 6 – 15 cm drives strong wakefields in a 10 m long rubidium plasma with an electron density of 10^14 – 10^15 cm3. In a first measurement campaign the AWAKE experiment has proven that the proton beam self modulates into micro-bunches, which resonantly drive the wakefields. In 2018 the experiment aims to show the acceleration of electrons in the plasma to GeV energies. An overview of the AWAKE experiment and its physics as well as the most recent result will be presented. The future experimental program, its challenges and of the technology to HEP, will be discussed.
AWAKE electron injector and diagnostics
Dr Oznur Mete Apsimon, University of Manchester and the Cockcroft Institute, UK
AWAKE is a unique experiment investigating plasma acceleration driven by 400 GeV protons from CERN’s Super Proton Synchrotron (SPS). Experiment is based on a 10m long plasma section located at the end of an SPS transfer line, which had previously served CERN Neutrinos to Gran Sasso (CNGS) experiment. The first goal of the experiment is observation of a phenomenon called the self–modulation instability which is a transverse instability leading to the modulation of 12cm long proton beam at about plasma frequency. This effect is important as the modulated bunch drives the plasma resonantly resulting into larger plasma wakefields. The second goal of this experiment is to demonstrate acceleration of a probe beam in plasma wakefields driven by modulated proton beam. A probe beam is generated externally by an electron source, which consists of an RF gun and a booster linac. 200pC electron beam reaches to 5MeV at the end of the gun and is boosted up to 16-20MeV by the linac. Electrons generated by this source will be transferred via a transfer line into the experimental area and injected into the plasma cell, synchronised with protons. Shape of the transfer line is a deciding factor on the normalised emittance budget of electrons limiting it to 2 mm mrad. Injector is equipped with pepper pot and quadrupole scan diagnostics, allowing emittance monitoring during beam set-up before the injection. In this talk, after a brief introduction, Dr Mete Apsimon will present the layout of the external electron source and performance of emittance diagnostics.
FLASHForward – plasma wakefield accelerator science for high average power applications
Dr Richard D'Arcy, DESY, Germany
The field of particle acceleration in plasma waves has seen remarkable progress in the last two decades. These days, acceleration gradients of more than 10 GV/m can be readily achieved using either ultra-short intense laser pulses or high-current density particle beams as plasma wakefield drivers. With the demonstration of first GeV electron beams and a trend towards improved reproducibility, beam quality and control over the involved plasma processes, plasma-acceleration techniques are drawing considerable interest in the traditional accelerator community. As a consequence, DESY, Germany's leading accelerator centre, has established a research programme for beam-driven plasma-based novel acceleration techniques with the goal to symbiotically combine conventional and new accelerator concepts for applications. This presentation will give an introduction into these emerging activities, show first theoretical and experimental results and outline the DESY PWFA flagship project, FLASHForward.
FLASHForward is a pioneering beam-driven plasma-wakefield experiment that aims to produce, in a few centimetres of ionized hydrogen, electron beams of energies exceeding 1.5 GeV that are of sufficient quality to demonstrate gain in a free-electron laser. The experimental beamline will allow for milestone studies assessing plasma-internal particle injection regimes, external injection, and controlled beam capturing and release for subsequent applications. The facility provides a unique combination of low-emittance GeV-class electrons from the superconducting MHz repetition rate, high-average power accelerator FLASH synchronized to a 25 TW laser interacting in a windowless, optically accessible, versatile plasma target. Experiments will commence in 2018 and are foreseen to run for the next decade, opening up new avenues in this highly dynamic research field.
Positron acceleration in plasma: challenges and progress
Dr Spencer J Gessner, CERN, Switzerland
Plasma Wakefield Acceleration (PWFA) is an exciting technology for accelerating particle beams to high energies in short distances. The ultimate application of this technology is an energy-frontier linear collider. A plasma-based linear collider has the potential to be more compact and efficient than RF-based colliders, while being less expensive. Of all the challenges on the path to a plasma-based linear collider, the acceleration of positrons in plasma is by far the most daunting. Plasmas are unique in that they are asymmetric accelerators, with light, mobile plasma electrons responding to the driving beam or laser fields, and the heavy ions remaining at rest. Many features of the plasma wakefield that are attractive for accelerating electrons are absent for positrons. In this talk, Dr Gessner will explain the physics of positron acceleration in plasma and reprise the state of research on the topic. The focus will be on the three main techniques tested so far: the quasilinear regime, nonlinear regime, and hollow channel regime. The next steps in this research will be described by S Corde in a following talk.
Positron acceleration in plasma: solutions, future experiments, and the path to a linear collider
Professor Sébastien Corde, Ecole Polytechnique, France
The concept of plasma-based particle accelerators is a promising path to overcome the limitations of conventional accelerator techniques. They hold out the promise of more compact, more affordable and higher-energy particle accelerators, and are increasingly considered as a mean to push the energy frontier of particle physics even higher. But for application to high-energy physics and to a linear collider, it is however imperative for plasma-based particle accelerators to also be capable of accelerating positrons, while most of the research effort so far has been on the acceleration of electrons. This is crucially important as positron acceleration in plasma is a much more challenging task than electron acceleration.
In this talk, Professor Corde will give a comprehensive overview of the different challenges of positron acceleration in plasma, highlighting the different routes under study, their problems and potential solutions, and the way forward to address them. Indeed, different variants of plasma-based acceleration are considered for positron acceleration in plasmas, the quasi-linear regime, the nonlinear regime and the hollow plasma channel, and they all have different advantages and flaws. Future experiments on positron acceleration and the path to a linear collider will also be discussed.