Figure 2

(a–c) 2D maps of the plasma electron density 40 ns after the laser irradiation on target (located on the left edge of the images at \(x = 0\)), for various strengths of the applied external magnetic field, as indicated. The color scale shown in (a) applies for all images. The images in (b,c) are reconstructed from two different shots with same parameters but obtained by moving the target within the diagnostic field of view, such that we can reconstruct a larger span of the plasma evolution. Patching this way two images obtained on two different shots is possible because the reproducibility of the results is very high, which is due to the external magnetic field generation having less than 1% variation from shot-to-shot². (d) Corresponding radially integrated electron density as a function of the distance from the target, i.e. the 1D densities are obtained from 2D maps as shown in (a–c) and integrated over the axis Y. The lines correspond, respectively, to the case of a free expansion (black, dashed), 10 (thin red) and 30 T (thick blue). The maximum noise level is about \(1 \times 10^{16}\) cm\(^{-1}\), i.e. much lower than experimental data.