Laser-Plasma Interactions at the Intensity Frontier: the Transition to the QED-Plasma Regime

Lead Research Organisation: Imperial College London
Department Name: Dept of Physics

Abstract

Current high-power lasers focus light to intensities up to 10^23 times higher than the intensity of sunlight at the surface of the Earth. At these extreme intensities the electrons are quickly stripped from the atoms in any matter in the laser focus, generating a plasma. However, as intensities increase from the peak reached today (2x10^22W/cm^2) to those expected to be reached on next-generation facilities such as the Extreme Light Infrastructure (>10^23W/cm^2), due to become operational by 2017, the behaviour of this plasma dramatically alters. At intensities >5x10^22W/cm^-2 the electromagnetic fields in the laser focus are predicted to accelerate the electrons in the plasma so violently that they prolifically radiate gamma-ray photons. These photons can carry away so much energy that the electron's motion is affected by the resulting energy loss and the radiation reaction force (the force the particle exerts on itself as it radiates) becomes significant in determining the plasma's macroscopic dynamics. The laser's electromagnetic fields are so strong that quantum electrodynamics effects also become important. In this case the radiation reaction force no longer behaves deterministically, i.e. instead of knowing the electron's trajectory exactly as in the classical picture, we now can only know the probability that the electron has a given trajectory. In addition, the gamma-ray photons can be converted into electron-positron pairs, these pairs can emit further photons which emit more pairs and an avalanche of antimatter production can ensue with strong consequences for the behaviour of the plasma as a whole. The interplay of radiation reaction, QED effects and ultra-relativistic plasma processes will define the physics of laser-matter interactions in this new 'QED-plasma' regime, but is currently poorly understood. We will elucidate the basic theory of laser propagation and absorption in QED-plasmas. This will provide the foundational theory describing laser matter interactions moving beyond today's intensity frontier and into the foreseeable future. This theory will be underpinned by experiments measuring the rates of the important QED processes for the first time. The new theory will then be used to design the first experiments to generate a QED plasma in the laboratory. This project will culminate in the first generation of a QED-plasma, usually only seen in extreme astrophysical environments such as pulsar magnetospheres, in the laboratory.

Publications

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Arran C (2019) Optimal parameters for radiation reaction experiments in Plasma Physics and Controlled Fusion

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Assmann R (2020) EuPRAXIA Conceptual Design Report in The European Physical Journal Special Topics

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Blackburn T (2020) Model-independent inference of laser intensity in Physical Review Accelerators and Beams

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Gould O (2019) Observing thermal Schwinger pair production in Physical Review A

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Kononenko O (2016) 2D hydrodynamic simulations of a variable length gas target for density down-ramp injection of electrons into a laser wakefield accelerator in Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment

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Sarri G (2017) Spectral and spatial characterisation of laser-driven positron beams in Plasma Physics and Controlled Fusion

 
Description We successfully measured the effect of radiation reaction in the collision of an ultra intense laser with an electron beam for the first time. This has already been published in PRX and received significant media coverage.

We have also worked on understanding the exact experimental parameters that will be needed to properly distinguish between different models of this radiation reaction process.
Exploitation Route The next generation of laser labs (e.g. ELI) will be performing similar experiments to ours, pushing the intensity frontier and we are already talking with those labs on the best ways to repeat our experiment. The gamma rays have some potential in imaging of dense material and we are investigating those with DSTL
Sectors Energy,Other

 
Description Some of the finding from our experiments have caught the public imagination and received external press coverage, including an article in the Independent, a cover article in New Scientist
First Year Of Impact 2018
Impact Types Societal

 
Description PRX press release 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact Following publication of our PRX on radiation reaction we issued a press release. Altmetrics has found that this resulted in reports by 15 new outlets, including an article in the Independent. It was tweeted about 18 times, reaching up to 22,000 followers
Year(s) Of Engagement Activity 2018
URL https://aps.altmetric.com/details/32793590/