arXiv subjects

Alec G. R. Thomas

Publications and source records attributed to Alec G. R. Thomas.

8 recordsLinked to original sources

arXiv2026

Energy-optimized scaling laws for self-guided laser wakefield accelerators

Laser wakefield acceleration promises compact electron accelerators for applications in medicine, industry, and fundamental science. Yet, despite rapid progress, accurately predicting the electron energy attainable in a given experimental configuration and the acceleration length required to reach it remains an open challenge. Here we use Bayesian optimization combined with advanced particle-in-cell simulation techniques to determine the maximum electron energy that a self-guided laser wakefield accelerator driven by a laser of a given energy and wavelength can produce. By systematically optimizing the accelerator performance across a range of laser energies and wavelengths, we derive energy-optimized scaling laws. These scaling laws yield the highest electron energy over the shortest acceleration length possible, are expressed solely in terms of laser energy and wavelength, and are accompanied by the complete set of laser and plasma parameters required to enable the scaling. The resulting scaling laws provide practical guidance for designing state-of-the-art laser wakefield acceleration experiments operating at their fundamental performance limits.

physics.plasm-ph↗

arXiv2026

A Deterministic Ionization Algorithm for the OSIRIS Particle-in-Cell Framework

Ionization is critical in the formation and evolution of plasma dynamics; collisional ionization, in particular, is an often overlooked source of electrons when dealing with laser-plasma interactions. Ionization plays a crucial role in understanding the complex plasma kinetics, ranging from cold and sparse astrophysical settings to hot and dense fusion systems. In this paper, we describe the underlying theory for and development, validation, and verification of an extension to the standard particle-in-cell method to include a deterministic algorithm for collisional ionization physics. This algorithm offers improved accuracy, achieving up to two orders of magnitude decrease in the error of the ionization rate calculations, scales linearly in execution time with the number of macro-particles per cell, has been tested for physical correctness and benchmarked against several codes.

physics.plasm-ph↗

arXiv2024

Novel Signatures of Radiation Reaction in Electron-Laser Sidescattering

In this article we investigate novel signatures of radiation reaction via the angular deflection of an electron beam colliding at 90 degrees with an intense laser pulse. Due to the radiation reaction effect, the electrons can be deflected towards the beam axis for plane wave backgrounds, which is not possible in the absence of radiation reaction effects. The magnitude and size of the deflection angle can be controlled by tailoring the laser pulse shapes. The effect is first derived analytically using the Landau-Lifshitz equation, which allows to determine the important scaling behavior with laser intensity and particle energy. We then move on to full scale 3D Monte Carlo simulations to verify the effect is observable with present day laser technology. We investigate the opportunities for an indirect observation of laser depletion in such side scattering scenarios.

physics.plasm-ph↗

arXiv2024

Orbital angular momentum enhanced laser absorption and neutron generation

We experimentally demonstrate enhanced absorption of near relativistic optical vortex beams in $\mathrm{D_2O}$ plasmas to generate a record fast-neutron yield of $1.45 \times 10^6$ n/s/sr. Beams with a topological charge of 5 were shown to deliver up to a 3.3 times enhancement of fast-neutron yield over a Gaussian focused beam of the same energy but having two orders of magnitude higher intensity. This result was achieved with laser energies of 16 mJ and a pulse duration of 67 fs. The Orbital Angular Momentum (OAM) beam-target interactions in our experiment were also investigated through Particle-in-Cell (PIC) simulations. Electron density rippling resulting in enhanced plasma wave excitation on the critical surface and significantly enhanced resonance absorption is observed.

physics.plasm-ph↗

arXiv2023

Kinetic theory for spin-polarized relativistic plasmas

The investigation of spin and polarization effects in ultra-high intensity laser-plasma and laser-beam interactions has become an emergent topic in high-field science recently. In this paper we derive a relativistic kinetic description of spin-polarized plasmas, where QED effects are taken into account via Boltzmann-type collision operators under the local constant field approximation. The emergence of anomalous precession is derived from one-loop self-energy contributions in a strong background field. We are interested, in particular, in the interplay between radiation reaction effects and the spin polarization of the radiating particles. For this we derive equations for spin-polarized quantum radiation reaction from moments of the spin-polarized kinetic equations. By comparing with the classical theory, we identify and discuss the spin-dependent radiation reaction terms, and radiative contributions to spin dynamics.

physics.plasm-ph↗

arXiv2021

Modelling Chromatic Emittance Growth in Staged Plasma Wakefield Acceleration to 1 TeV using Nonlinear Transfer Matrices

A framework for integrating transfer matrices with particle-in-cell simulations is developed for TeV staging of plasma wakefield accelerators. Using nonlinear transfer matrices in terms up to ninth order in normalized energy spread $\sqrt{\langleδγ^2\rangle}$ and deriving a compact expression for the chromatic emittance growth in terms of the nonlinear matrix, plasma wakefield accelerating stages simulated using the three-dimensional particle-in-cell framework OSIRIS 4.0 were combined to model acceleration of an electron beam from 10 GeV to 1 TeV in 85 plasma stages of meter scale-length with long density ramps and connected by simple focusing lenses. In this calculation, we find that for initial relative energy spreads below $10^{-3}$, energy-spread growth below $10^{-5}$ of the energy gain per stage and normalized emittance below mm-mrad, the chromatic emittance growth can be minimal. The technique developed here may be useful for plasma collider design, and potentially could be expanded to encompass non-linear wake structures and include other degrees of freedom such as lepton spin.

physics.acc-ph↗

arXiv2021

Polarized QED cascades

By taking the spin and polarization of the electrons, positrons and photons into account in the strong-field QED processes of nonlinear Compton emission and pair production, we find that the growth rate of QED cascades in ultra-intense laser fields can be substantially reduced. While this means that fewer particles are produced, we also found them to be highly polarized. We further find that the high-energy tail of the particle spectra is polarized opposite to that expected from Sokolov-Ternov theory, which cannot be explained by just taking into account spin-asymmetries in the pair production process, but results significantly from "spin-straggling". We employ a kinetic equation approach for the electron, positron and photon distributions, each of them spin/polarization-resolved, with the QED effects of photon emission and pair production modelled by a spin/polarization dependent Boltzmann-type collision operator. For photon-seeded cascades, depending on the photon polarization, we find an excess or a shortage of particle production in the early stages of cascade development, which provides a path towards a controlled experiment. Throughout this paper we focus on rotating electric field configuration, which represent an idealized model and allows for a straightforward interpretation of the observed effects.

hep-ph↗

arXiv2019

Ultrafast Polarization of an Electron Beam in an Intense Bi-chromatic Laser Field

Here, we demonstrate the radiative polarization of high-energy electron beams in collisions with ultrashort pulsed bi-chromatic laser fields. Employing a Boltzmann kinetic approach for the electron distribution allows us to simulate the beam polarization over a wide range of parameters and determine the optimum conditions for maximum radiative polarization. Those results are contrasted with a Monte-Carlo algorithm where photon emission and associated spin effects are treated fully quantum mechanically using spin-dependent photon emission rates. The latter method includes realistic focusing laser fields, which allows us to simulate a near-term experimentally feasible scenario of a 8 GeV electron beam scattering from a 1 PW laser pulse and provide a measurement that would verify the ultrafast radiative polarization in high-intensity laser pulses that we predict. Aspects of spin dependent radiation reaction are also discussed, with spin polarization leading to a measurable (5%) splitting of the energies of spin-up and spin-down electrons.

physics.plasm-ph↗