Fig. 1. (a) Schematic diagram of initial plasma density (local); (b) current in the foam target at 75T₀. The simulation window size is . The units of plasma density and current are , and , respectively (a) 泡沫靶密度分布示意图(局部); (b) 75 泡沫间隙的准静态电流(模拟窗口大小为 ; 图中密度无量纲单位为 , 电流无量纲单位为 )

Fig. 2. Magnetic field distribution in foam region at 150 : (a) Bubble radius is 0.075 ; (b) bubble radius is 0.15 ; (c) bubble radius is 0.6 . The unit of magnetic field is 150 的泡沫区磁场分布　(a) 泡沫孔径0.075 ; (b) 泡沫孔径0.15 ; (c) 泡沫孔径0.6 (磁场无量纲单位为 )

Fig. 3. Trajectory of 50 electrons whose initial positions randomly distributed on the front surface of the target: (a) Planar target; (b) foam target. The labeled number is the kinetic energy of the electrons moving to the area behind the target. The red line is the trajectory of one of the accelerated electrons50个初始位置随机分布在靶前表面的电子的轨迹(a)平面靶; (b)泡沫靶; 图中标注数字为运动到靶后区域单个电子的动能, 红色线表示其中一个电子加速后的轨迹

Fig. 4. Evolution of electron energy and position with time in multiple acceleration of electron. Here, the x = (40, 42) region marked with yellow is the foam region 电子多次加速过程中的能量和位置随时间演化, 图中x = (40, 42) 黄色标记区域为泡沫靶区

Fig. 5. Spatial distribution of electron energy density for (a) planar target, and bubble target with bubble size of (b) 0.075 , (c) 0.15 , (d) 0.6 . The unit of electron energy density is 平面靶和不同孔径泡沫靶的电子能量密度空间分布　(a)平面靶; (b)泡沫孔径0.075 ; (c)泡沫孔径0.15 ; (d)泡沫孔径0.6 ; 电子能量密度无量纲单位为

Fig. 6. (a) Electron energy spectra of foam targets with different bubble radii; (b) electron energy spectra of foam targets with different foam thicknesses(a)不同孔径泡沫靶的超热电子能谱; (b)不同厚度泡沫靶的超热电子能谱