Characterization of magnetic reconnection in the high-energy-density regime

Magnetic reconnection (MR), breaking and reorganizing the topology of magnetic field dramatically, is a fundamental process observed in many space, laboratory and astrophysical plasmas. In this talk, we report recent investigations on characterization of magnetic reconnection (MR) in the high-energy-density (HED) regime, where the plasma inflow is strongly driven and the total thermal pressure is larger than the magnetic pressure ($\beta >1)$. This extreme regime of MR occurs frequently in astrophysics and recent HED experiments. Comparing the particle-in-cell simulation results for the interactions of colliding laser-produced plasma bubbles with induced anti-parallel and parallel poloidal magnetic fields respectively, the consequences caused by MR are distinguished from those by plasma bubble collisions and two-fluid effects. It is found that the out-of-plane quadrupole magnetic field, bipolar poloidal electric field, plasma heating and even the out-of-plane electric field appear in both cases, which cannot be recognized as evidences of MR here as previously thought. The Lorentz-invariant scalar quantity $D_{e} =\gamma_{e} \mathord{\buildrel{\lower3pt\hbox{$\scriptscriptstyle\rightharpoonup$}}\over {j}} \cdot (\mathord{\buildrel{\lower3pt\hbox{$\scriptscriptstyle\rightharpoonup$}}\over {E}} +\mathord{\buildrel{\lower3pt\hbox{$\scriptscriptstyle\rightharpoonup$}}\over {v}} \times \vec{{B}})$ [$\gamma_{e} =(1-v_{e}^{2} /c^{2})^{-1/2}$ is the Lorentz factor] in the electron dissipation region is proposed as the key sign of MR occurrence in the HED regime.