Laser-driven plasma pinching in $e^{-}{e}^{+}$ cascade

The cascaded production and dynamics of electron-positron plasma in ultimately focused laser fields of extreme intensity are studied by three-dimensional particle-in-cell simulations with the account of the relevant processes of quantum electrodynamics (QED). We show that, if the laser facility provides a total power above 20 PW, it is possible to trigger not only a QED cascade but also pinching in the produced electron-positron plasma. The plasma self-compression in this case leads to an abrupt rise of the peak density and magnetic (electric) field up to at least ${10}^{28}{\mathrm{cm}}^{-3}$ and 1/20 (1/40) of the Schwinger field, respectively. Determining the actual limits and physics of this process might require quantum treatment beyond the used standard semiclassical approach. The proposed setup can thus provide extreme conditions for probing and exploring fundamental physics of the matter and vacuum.

Figure 1

Plasma-field parameters at nonlinear stage of interaction vs laser power: (a) maximum pair density; (b) maximum photon (solid line) and electron (dashed line) energy; (c) currents through plane $z=0$ in cylinders $\rho =0.44\lambda$ (solid line) and $\rho =0.1\lambda$ (dashed line); (d) maximum magnetic field at linear (dashed line) and nonlinear (solid line) stage of interaction.

Figure 2

Plasma-field dynamics for 27 PW. (a) Temporal evolution, $f\left(t\right)$: laser pulse envelope; $B/B_0$: magnetic field in the plane $z=0$ at $\rho =1/60\lambda$; $n_p$: maximum pair density; $J_z$, current through the cylinder with radius $0.1\lambda$. Electric [(b), (f), (j))] and magnetic [(c), (g), (k)] fields, and positron [(d), (h), (l)] and photon [(e), (i), (m)] distributions at the stages of (b)–(e) linear QED cascade, (f)–(i) plasma column pinching, and (j)–(m) pinch breakdown due to bending instability. For convenience only the central part of the simulation region is shown.

Figure 3

(a)–(f) Magnetic field [(a), (c), (e)] and pair density distribution [(b), (d), (f)] at the moment of maximum compression and start of bending instability for different resolutions: (a), (b) $n_{\lambda }=115$; (c), (d) $n_{\lambda }=460$; (e), (f) $n_{\lambda }=1840$. (g)–(i) Pinch temporal evolution for different $n_{\lambda }$: (g) magnetic field, (h) pair density, and (i) electric field. Colored dots show the moment of maximum compression and the starting moment of bending instability.

Figure 4

Typical particle trajectories for (a) 19 PW and (b) 27 PW; (c) phase plane $B\text{−}x$ for two trajectories shown in panels (a) and (b). Blue dots show starting points of the trajectories. Dashed lines depict electric (black) and magnetic (blue) fields of an e-dipole wave. Blue dotted line shows self-consistent magnetic field at the nonlinear stage.

Figure 5

$\gamma$ photons: (a) spectra and (b) angular distributions for 19 and 27 PW e-dipole waves.