Fig. 1. (a) A composite image of collisionless shock formed in the SNRs^[18]. Color stands for the observation wavelength, as shown in the color bar. (b) The experimental configurations to simulate the astrophysical CPFs. Here, two schemes are used to generate counter-streaming flows. Case I is a symmetrical one, where both flows are directly ablating both facing surfaces of the foils. Case II is an unsymmetrical one, where only one foil is ablating by one bunch and the other side foil is heated by the X-ray from laser–target interaction. The probe beam (outwards) transversely passes through the interaction region for optical diagnostics.

Fig. 2. The evolution of the counter-streaming flows obtained by a Nomarski interferometer. The red circle in the raw images stands for the laser focal spot. When both flows coming from the opposing foils interpenetrate each other at the midplane at 2 ns shown in Abel inversion image, the plasma density increases by the unanticipated factor of 3 (from to ), indicating that a shock has been generated. The width is measured as about , much smaller than the MFPs. Obviously, it is collisionless. Subsequently (), the collisionless shock is dissipated by the growing filamentation structures.

Fig. 3. Collisionless shock formation and evolution in unsymmetrical CPFs^[30]. (a) and (b) show the interferogram obtained at 5 ns and 9 ns, respectively. (c) and (d) are the corresponding shadowgraphs of (a) and (b). (e) and (f) show the density profile and the intensity profile at 9 ns.

Fig. 4. Collisionless shock formation and evolution in the symmetrical CPFs. (a) and (b) are the interferograms (lower) and electron density distributions (upper) obtained by the Abel inversion, taken at 6 ns and 10 ns, respectively. (c) and (d) are the electron density profiles plotted along the flow direction^[20].

Fig. 5. The evolution of the filamentation instability in CPFs. Interferogram with magnification of 2.5 times shows initial conditions of both flows at 3.5 ns. A series of shadowgraph with larger magnification of 4 times is applied to measure the evolution of the Weibel instability. The intensity profile shows the typical features of the evolution of the filaments.

Fig. 6. The observed neutron signals from D–D nuclear reaction in collisional case^{[36, 40]}.