Numerically, we use the FLASH code[

Numerically, we use the FLASH code[25], which is an adaptive mesh refinement (AMR) program, developed by the Flash Center at the University of Chicago. The FLASH code has been well-known in astrophysics and space geophysics, to create a reference to the MHD solution in our experiments. Here, we employ the single fluid resistive MHD, two dimensional Eulerian code FLASH. And the equation of state (Eos) and opacity tables of targets are based on the IONMIX4 database[26]. In terms of its capabilities, the FLASH code can handle laser ablation, magnetic field dynamics and non-ideal material properties in a single consistent run, it is robust against shocks. In order to better simulate the experiments, the initial conditions (laser, target materials, etc.) are consistent with the experiments, and outflow boundaries are imposed on all sides. The computational domain (X–Y plane) is set as 4000 μm × 1400 μm, and the maximum resolution is 2 μm × 2 μm. We used a FLASH simulation to reproduce the cases with the external magnetic field and without the magnetic field in the experiment.Figure 2 shows side viewing images from the electrons distribution during 0 to 9 ns in FLASH simulation results. Timing from the moment of the nanosecond laser injection. The center of the laser beam is at (x, y, z) = (0, 0, 0) in Figs. 1. In the left panels of Fig. 2(a, c, e) the magnetic field was null and, in the right panels of Fig. 2(b, d, f), the external magnetic field was 1.0 × 105 Gauss. Figure 2 indicate that the electron density is on the order of 1020 cm-3 in our region of interest (near the modulation layer). At the delay time of 3 ns, the plasma outflow passed through the region of Al modulation layer. When the time delay is 6 ns, the KHI has been formed around the interaction region between the plasma outflow and the Al modulation in Fig 2(c, d). When the time delay is 9ns, we can see from Fig. 2(f) that the plasma outflow moved in the positive direction along the Y-axis far from the Al modulation layer. This makes the interaction area between the plasma outflow and the Al modulation layer smaller and smaller, that is, the velocity shear layer between the plasma outflow and the Al modulation layer will gradually disappear. 下面详细分析有无磁场时密度分布的不同之处。