Plasma wakes driven by Compton scattering: Non-linear regime and particle acceleration

TL;DR

This work demonstrates that plasma wakes driven by Compton scattering of photon bursts constitute a non-ponderomotive pathway to wakefield acceleration, extending linear theory to nonlinear regimes where the wake amplitude scales with photon energy density. A key finding is that perfectly collimated photon drivers can sustain wakes propagating at the speed of light and potentially trap and accelerate electrons, with depletion and diffraction acting as practical limits, while non-collimated drivers introduce a subluminal phase velocity and dephasing constraints. Two-dimensional simulations reveal a distinctive DC magnetic field behind the wake, yielding consistent transverse focusing that differs from laser wakefields. The results have implications for astrophysical settings around luminous compact objects interacting with tenuous plasmas, and outline laboratory challenges, suggesting that linear Compton wakes may be observable under attainable conditions, with nonlinear wakes requiring extreme energy densities and long propagation distances.

Abstract

We investigate plasma wake generation via Compton scattering from photon bursts, a non-ponderomotive process relevant when the photon wavelength is smaller than the interparticle distance but larger than the Compton wavelength. In this regime, electrons can reach relativistic velocities. We extend linear theory to the nonlinear regime, showing that plasma waves can reach the wave-breaking limit. Perfectly collimated drivers produce wakes propagating at the speed of light, allowing electron phase-locking (limited by driver depletion). Non-collimated drivers induce subluminal phase velocities, limiting acceleration via dephasing. Two-dimensional simulations reveal unique transverse fields compared to laser wakefields, with a DC magnetic field leading to consistent focusing. The work considers observational prospects in laboratory and astrophysical scenarios such as around highly luminous compact objects (e.g., pulsars, gamma-ray bursts) interacting with tenuous interstellar or intergalactic plasmas, where conditions favor Comptondominated wakefield acceleration.

Figures (13)

• Figure 1: Amplitude of the function $\mathcal{A}$ as a function of $k_pL$, given by Eq.(\ref{['eq: ampltrig']}) plotted in solid line for $R = 10^{-8}$ in blue and for $R=0.5$ in black. For a long driver $k_pL\gg1$, if $Rk_pL\lesssim 1$, the wake amplitude does not decrease. For a symmetric driver $R=0.5$, the wake amplitude falls as $\mathcal{A}\propto 1/k_pL$, shown in dashed line.
• Figure 2: Amplitude of the function $\mathcal{A}$ as a function of $R$, given by Eq.\ref{['eq: ampltrig']} plotted in solid line for $k_pL\simeq47$. 1D PIC simulation results are displayed with ($\times$).
• Figure 3: Amplitude of the wake field (black) and normalized fluid momentum of the plasma electrons (blue) for a resonant driver with energy density of $\mathcal{E}_0=eE_0/\sigma_T$. The simulation results are represented with a solid line and the theory, solution of Eq.(\ref{['eq: nonlinear']}), with a dashed line.
• Figure 4: Amplitude of the wakefield as a function of the driver energy density. Simulations are denoted with $(\times)$, the numerical solution of Eq (\ref{['eq: nonlinear']}) is in solid line, Eq. (\ref{['eq: Rel E']}) with $\hat{\gamma}$ obtained from Eq. (\ref{['eq: hatgamma']}) in dashed line, and linear theory is in dot-dashed line.
• Figure 5: Wavelength of the wake as a function of the driver energy density. Simulations are denoted with $(\times)$, the solid line is the numerical solution of Eq (\ref{['eq: nonlinear']}).