Fig. 1. Experimental setup at the LULI2000 facility. A laser beam was used to drive the target (graphite pin) and generate a BW in air. A 2ω probe beam was used transversely to the propagation of the BW for the interferometry diagnostic. SOP and 2D self-emission diagnostics collected the light coming from the same direction. High- and low-dispersion optical spectrometers gathered the self-emission light at 3 and 4 mm from TCC along the laser axis from the top access point. The magnetic field was perpendicular or parallel to the BW propagation axis. Part of the coil casing is removed here for better visualization.

Fig. 2. 2D self-emission snapshots of the BW plasma in the 580–850 nm range as a function of time and magnetic field. The graphite pin target is outside the field of view to the left of the images. The shaded area on the center-left image indicates the approximate volume and position probed by the optical spectrometers (150 × 150 × 50 μm³, 3 and 4 mm for the perpendicular and parallel magnetic field to the spectrometers’ line of view, respectively).

Fig. 3. Time-resolved spectra collected by the HD spectrometer for two bandwidths (left: 493–504 nm, right: 563–573 nm). Both orientations of the magnetic field are presented: (a) and (d) at 0 T, (b) and (e) at 20 T (parallel to the line of sight), and, (c) and (f) at 20 T (perpendicular to the line of sight). The shaded bands in (a) and (d) indicate the time range over which the signal was integrated (see Fig. 4). The Zeeman splitting is particularly apparent by comparing images (d) and (e), as shown by the arrows.

Fig. 4. Time-integrated lineouts from 140 to 160 ns for all values and orientations of the magnetic field: (a) 493–504 nm, (b) 563–573 nm. The dashed vertical lines correspond to the theoretical NII lines from NIST.

Fig. 5. PPPB simulations for the NII transitions overlaid on time-integrated (over 50 ns) lineouts for 5, 10 and 20 T: (a) perpendicular and (b) parallel to the magnetic field orientation. Solid curves represent the values indicated in the legend, while the shaded areas correspond to simulations with δn_e = ±0.2 × 10¹⁸ cm⁻³ relative to them (here, curves with higher intensities correspond to higher densities). The electron temperature is T_e = 5 eV for all simulated spectra. A linear background has been added to account for the bremsstrahlung emission of the plasma, and the spectra are normalized for each magnetic field and orientation. The dashed vertical lines correspond to the theoretical NII lines from NIST.

Fig. 6. Same as Fig. 5, but with a variation in electron temperature indicated by the shaded areas for 1 or 2 eV. Here, curves with lower intensities correspond to higher T_e. The plasma conditions for the simulated spectrum with the solid line are n_e = 1.6 × 10¹⁸ cm⁻³ and T_e = 5 eV. A linear background has been added to account for the bremsstrahlung emission of the plasma and the spectra are normalized for each magnetic field orientation. The dashed vertical lines correspond to the theoretical NII lines from NIST.

Fig. 7. Same as Fig. 5, but with a variation in the magnetic field indicated by the shaded areas for 2 or 3 T. Here, curves with lower intensities correspond to higher B. The plasma conditions for the simulated spectra are n_e = 1.6 × 10¹⁸ cm⁻³ and T_e = 5 eV.

Fig. 8. Time-integrated spectra (over 50 ns) compared to the NII, CII and combined PPPB simulations; n_e = 1.4 × 10¹⁸ cm⁻³, T_e = 5 eV and n_e = 1.6 × 10¹⁸ cm⁻³, T_e = 5 eV for B_‖ of (a) 10 and (b) 15 T, respectively. A linear background has been added to account for the bremsstrahlung emission of the plasma. The dashed vertical lines correspond to the theoretical NII lines from NIST.

Fig. 9. Time-integrated spectra (over 50 ns) compared to the NII PPPB simulations for a parallel magnetic field orientation and the conditions shown in the legend. The similarity in the line shapes for certain combinations of n_e and T_e necessitate the use of independent diagnostics to choose the appropriate values. The dashed vertical lines correspond to the theoretical NII lines from NIST.