[Paper Review] Charged particle motion and radiation in strong electromagnetic fields

Arkady Gonoskov, Tom Blackburn+2 more|arXiv (Cornell University)|Jul 5, 2021

Laser-Plasma Interactions and Diagnostics6 references19 citations

TL;DR

This review synthesizes theoretical, computational, and experimental advances in charged particle dynamics and radiation emission under strong electromagnetic fields, emphasizing radiation reaction and quantum electrodynamics (QED) effects in high-intensity laser-matter interactions. It identifies the emergence of nonlinear QED phenomena such as electron-positron pair cascades and particle trapping, enabled by next-generation laser facilities, and outlines their potential for generating high-flux particle and radiation sources.

ABSTRACT

The dynamics of charged particles in electromagnetic fields is an essential component of understanding the most extreme environments in our Universe. In electromagnetic fields of sufficient magnitude, radiation emission dominates the particle motion and effects of nonlinear quantum electrodynamics (QED) are crucial, which triggers electron-positron pair cascades and counterintuitive particle-trapping phenomena. As a result of recent progress in laser technology, high-power lasers provide a platform to create and probe such fields in the laboratory. With new large-scale laser facilities on the horizon and the prospect of investigating these hitherto unexplored regimes, we review the basic physical processes of radiation reaction and QED in strong fields, how they are treated theoretically and in simulation, the new collective dynamics they unlock, recent experimental progress and plans, as well as possible applications for high-flux particle and radiation sources.

Motivation & Objective

• To synthesize current theoretical and simulation frameworks for radiation reaction and strong-field QED in extreme electromagnetic fields.
• To identify key physical phenomena—such as pair cascades, particle trapping, and field depletion—arising from nonlinear QED in high-intensity laser-matter interactions.
• To assess the role of collective dynamics in coupling single-particle QED processes with large-scale plasma behavior.
• To evaluate recent experimental progress and future prospects in probing non-perturbative QED regimes using petawatt-class lasers.
• To explore applications in generating high-flux, polarized particle and radiation sources for fundamental physics and technology.

Proposed method

• Adopting the 'cube of theories' framework, the paper maps the transition from classical to quantum, relativistic, and strong-field regimes, with emphasis on the $(c, \hbar, E_{\text{cr}})$ vertex representing strong-field QED.
• Theoretical analysis integrates classical radiation reaction (via Landau-Lifshitz approximation) and quantum radiation reaction, including multiphoton Compton and Breit-Wheeler processes.
• Numerical methods focus on QED-PIC (particle-in-cell) simulations with subcycling and resampling techniques to model particle dynamics and radiation emission in intense fields.
• The locally constant crossed-field approximation is used to model radiation spectra, with the Gaunt factor $G(\chi)$ quantifying the ratio of QED to classical radiation power.
• Key equations include the Landau-Lifshitz equation for radiation reaction, the Compton and Breit-Wheeler probability rates $P^c$ and $P^b$, and the parameter $\chi_e$ governing QED nonlinearity.
• Field strength thresholds are defined via $a_0$ and $\chi_e$, with quantum radiation reaction onset at $\chi_e \sim 1$, and classical radiation reaction at $a_0 \sim 100$.

Experimental results

Research questions

• RQ1 How do radiation reaction and QED effects alter charged particle dynamics in strong electromagnetic fields beyond classical predictions?
• RQ2 What are the conditions under which electron-positron pair cascades are triggered in high-intensity laser-plasma interactions?
• RQ3 How do collective plasma effects modify single-particle QED processes such as multiphoton Compton scattering and Breit-Wheeler pair production?
• RQ4 What are the critical thresholds for transitioning from classical to quantum radiation reaction in laser-driven systems?
• RQ5 How can next-generation high-power laser facilities enable experimental observation of non-perturbative QED phenomena in the laboratory?

Key findings

• The critical field strength $E_{\text{cr}} = m^2 c^3 / (e \hbar)$ defines the threshold for strong-field QED, where nonlinear quantum effects dominate over classical radiation reaction.
• Quantum radiation reaction becomes significant when $\chi_e \gtrsim 1$, corresponding to $a_0^{\text{qrr}} \simeq 2000\lambda$ for laser-laser interactions and $\simeq 105\lambda / \mathcal{E}_0$ for laser-electron-beam configurations.
• Electron-positron pair cascades are triggered in strong fields when $\chi_e \gtrsim 1$, leading to exponential growth of plasma density and field depletion.
• The spectral emission rate $\frac{dW}{d\hbar\omega}$ and energy transfer parameter $f_c = \hbar\omega / (\gamma m c^2)$ govern the shape of Compton spectra, with $\xi_q$ as a key shape parameter.
• QED-PIC simulations with subcycling and resampling enable accurate modeling of radiation emission and particle dynamics in intense fields, even at $a_0 \sim 1000$.
• Future facilities such as the Station of Extreme Light (100 PW) and ELI-Beamlines will enable $a_0 > 1000$, accessing the quantum radiation reaction regime and enabling observation of nonlinear QED effects in the lab.