Plasma Wakes Driven by Photon Bursts via Compton Scattering

Photon bursts with a wavelength smaller than the plasma interparticle distance can drive plasma wakes via Compton scattering. We investigate this fundamental process analytically and numerically for different photon frequencies, photon flux, and plasma magnetization. Our results show that Langmuir and extraordinary modes are driven efficiently when the photon energy density lies above a certain threshold. The interaction of photon bursts with magnetized plasmas is of distinguished interest as the generated extraordinary modes can convert into pure electromagnetic waves at the plasma-vacuum boundary. This could possibly be a mechanism for the generation of radio waves in astrophysical scenarios in the presence of intense sources of high energy photons.

Figure 1

Different regimes of Compton-plasma interaction. Left column: electrostatic field. Middle column: electron phase space. Right column: photon phase space. (a) Incoherent wake: the space charge force is too weak to pull back most of the scattered electrons, $\lambda >{\lambda }_C$ and ${\mathcal{E}}_0\sim 0.01{\mathcal{E}}_{\min }$. (b) Coherent wake: the space charge is strong enough to pull back most of the electrons, $\lambda >{\lambda }_C$ and ${\mathcal{E}}_0\sim {\mathcal{E}}_{\min }$. (c) Beam driven wake: the scattered electrons are relativistically kicked forward and formed, on top of the photon burst, a dense beam that contributes to drive the wake, $\lambda <{\lambda }_C$.

Figure 2

Amplitude of the electrostatic field as a function of the energy density of a resonant photon burst. We simulated both a burst of monoenergetic photons, circles for $n_p={10}^{18}\mathrm{c}{\mathrm{m}}^{-3}$ diamonds for $n_p=1\mathrm{c}{\mathrm{m}}^{-3}$, and crosses for a burst with an energy spread of 50% ($n_p={10}^{18}\mathrm{c}{\mathrm{m}}^{-3}$). The linear theory of Eq. (5) is displayed by the solid line.

Figure 3

Scaling of the ratio of the amplitude transverse component to the longitudinal component of the extraordinary plasma wave as a function of ${\omega }_c/{\omega }_p$. Simulations (circles) show good agreement with the theory (solid line) $|E_y/E_x|={\omega }_c/{\omega }_p$.