Ultrafast Synchrotron-Enhanced Thermalization of Laser-Driven Colliding Pair Plasmas

We report on the first self-consistent numerical study of the feasibility of laser-driven relativistic pair shocks of prime interest for high-energy astrophysics. Using a QED-particle-in-cell code, we simulate the collective interaction between two counterstreaming electron-positron jets driven from solid foils by short-pulse ($\sim 60\mathrm{fs}$), high-energy ($\sim 100\mathrm{kJ}$) lasers. We show that the dissipation caused by self-induced, ultrastrong ($>10^6\mathrm{T}$) electromagnetic fluctuations is amplified by intense synchrotron emission, which enhances the magnetic confinement and compression of the colliding jets.

Figure 1

(a) Transversely averaged particle densities at the rear of the left target prior to the collision (${\omega }_{0}t=555$). (b) Time evolution of the total radiated energy (blue) and power (red) normalized to the laser energy. (c),(d) Electron and positron $p_x-p_y$ phase spaces at the center of the pair plasma ($x=155c/{\omega }_0$) prior to the collision (${\omega }_{0}t=555$).

Figure 2

(a),(b) Magnetic field (averaged over a laser cycle) in the overlap region at ${\omega }_{0}t=705$. (b) Positron density at ${\omega }_{0}t=705$. (c) Time evolution of the electromagnetic energies (normalized to the laser energy) integrated in the overlap region and comparison with the theoretical growth rate (dashed line). (d) Evolution of the particle (${ϵ}_{\pm }$), photon (${ϵ}_{\gamma }$), and magnetic (${ϵ}_{B_z}$) energies (normalized to the total kinetic energy) in the collision region.

Figure 3

(a) Electron and (b) positron $p_x-p_y$ phase spaces at the center of the domain at the time of maximum compression (${\omega }_{0}t=690$). (c) Corresponding electron (red) and positron (blue) $\gamma$ distributions and comparison with the best-fitting Maxwell-Jüttner distributions (dashed lines). (d) Positron $p_x-p_y$ phase space without radiation losses.

Figure 4

Space-time evolution of the $y$-averaged positron density with (a) and without (b) radiation losses.

Figure 5

Space-time evolution of the $y$-averaged positron (a) compression ratio and (b) Lorentz factor. (c) Magnetic field $B_z$ (top) and quantum parameter ${\chi }_{+}$ (bottom) at ${\omega }_{0}t=400$. (d) $y$-averaged profiles of $|E_x|$, $|E_y|$, $c|B_z|$ (normalized to $m_{e}c{\omega }_0/e$) and $n_{+}/n_{\max }$ at ${\omega }_{0}t=400$.