Free electron lasers driven by plasma accelerators: status and near-term prospects

Journal article

Radiation reaction is the recoil of a charge upon emitting radiation. This effect is expected to play a significant role in the dynamics of charges, particularly electrons, and the radiation they produce in strong-field environments. Of particular interest are environments in which the electric field strength approaches the Schwinger field, E_sch=(m_e^2 c^3)/eℏ=1.38×10^16 Vcm^-1 defined as the field strength which can induce electron-positron pair production from vacuum. Electric field strengths approaching the Schwinger field may be generated by astrophysical bodies, such as pulsars and quasars. In such environments, classical theories of radiation reaction are expected to break down. Thus, a quantum description of radiation reaction is needed to accurately model radiation generation and other related processes such as pair production in these environments. The subject of this thesis is an experiment, conducted at the Central Laser Facility in 2021, the aim of which was to measure radiation reaction. The experiment utilised an all-optical set-up in which an energetic electron beam (peak energy ≈1 GeV) generated by a wakefield accelerator collided with a tightly focussed, counter-propagating laser pulse. In this thesis, I introduce and discuss a Bayesian analysis procedure which I have developed. This allows the post-collision electron spectrum and the spectrum of gamma radiation emitted during the col- lision to be used to quantitatively compare different models of radiation reaction, whilst also retrieving information concerning the collision conditions which could not be measured during the experiment. We find evidence of radiation reaction to 8σ, the highest degree of significance of any all-optical experi- ment to date. Using the Bayesian framework, we find that a quantum model of radiation reaction is more consistent with the spectrum of emitted radiation and the electron energy loss measured experimentally than a classical or a semiclassical model.Open Acces

Authors: Emma, C; Van Tilborg, J; Assmann, R; Barber, S; Cianchi, A

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Cambridge University Press
• Journal: High Power Laser Science and Engineering
• Volume: 9
• Pages: e57
• Article number: e57
• Publication date: 2021-09-10
• DOI: 10.1017/hpl.2021.39
• EISSN: 2052-3289
• ISSN: 2095-4719
• Language: English
• Keywords: Milestone; Beam (structure); Nuclear physics; Laser; Electron; Beamline; Physics; Undulator; Optics; Plasma; Plasma acceleration