Theoretical and numerical investigation of collective effects in extreme laser-plasma interaction

The proposed research project focuses on theoretical and numerical investigations of the physics of laser-matter interaction at ultra-high laser intensities, in the range 10^22-10^24 W/cm^2. These intensities will soon be achievable at multi-petawatt laser facilities, such as the 800MEuro extreme light infrastructure (ELI) and APOLLON-10P. These facilities will enable the exploration of new fundamental physical processes such as radiation reaction, relativistic electron dynamics, electron-positron pair production and the generation of relativistic ions. Electrons produce significant synchrotron radiation at laser intensities above 10^22 W/cm^2 giving rise to the radiation reaction force that strongly affects the photon emission spectrum and the overall plasma dynamics. Due to the intense electromagnetic fields involved, quantum effects will become important for laser intensities above 10^23W/cm^2, resulting in the production of copious amounts of electron-positron pairs. My proposal aims to explore the underpinning physics of these proposes theoretically and numerically. The results will be used to guide the design and interpretation of related experiments using these new ultraintense laser systems.

The proposed research project opens up new directions in ultra-relativistic plasmas that are subject to quantum electrodynamics (QED) processes. For example, to date, the role of the plasma ions on the high energy synchrotron radiation and electron-positron pair production, is poorly understood and has never been explored experimentally. It is often suggested that the interaction of a short laser pulse with plasmas is dominated by the electron dynamics and that the ions play a secondary role due to the longer timescales over which they react. Although this may be true for lower laser intensities, the situation becomes more complicated in the case of ultra-relativistic laser pulses for which the quiver electron energy could be comparable with the ion rest mass. The collective effects driven by the ion response will be investigated in both semi-classical plasmas and quantum plasmas. A kinetic theory of laser energy absorption accounting for ion response will be developed over this proposed research project. Future experiments, which will test the predictions of the theory and simulations, will also be designed.

The project involves collaboration with a number of leading researchers in high field laser-plasma interaction physics, both in the UK and in Europe. It also involves a close collaboration with an experimental team at the University of Strathclyde and with the ELI-NP high field science working group.

The proposed project focuses on theoretical and numerical investigation of the collective dynamics of charged particles in plasma physics at ultra-high laser intensities. This is an important new field of research with significant potential impact, both academic and non-academic. At the field intensities to be explored in this project, radiation reaction will not just be significant but will dominate the electron dynamics. A significant fraction of the laser energy will be converted into high energy synchrotron radiation via ultra-relativistic electrons accelerated in ultra-strong electromagnetic fields. Simulations predict that the most intense source of gamma-rays ever produce in a laboratory could be produced in this way. Such an intense and ultra-short pulse source of high energy photon radiation is likely to be applicable in industry and society (e.g. as intense, deep-penetrating probe of materials, or for medical radioisotope production or imaging). In addition, the onset radiation reaction changes the radiation pressure exerted by the laser pulse on the target plasma, which in turn changes the physics of laser-driven ion acceleration. This in turn will impact the development of such sources for hadron therapy for example. The results of the proposed result programme will be used to develop a theoretical underpinning of high field laser-plasma physics and thus the development of these unique particle and radiation sources as driven by ultra-intense laser pulses.

The proposed research project will also provide opportunities for training PhD students in numerical simulations and modelling. It will involve a substantial amount of accurate numerical simulations and data analysis. This will impact on the need for skilled scientists in the UK and thus contribute to the UK economy beyond the end of the grant.

Finally, the new regime of high field physics to be explored in this project involves quantum processes and laboratory astrophysics, which are topics of wide public interest. The project will impact on the public interest and understanding of science.