Fig. 1. (a) Experimental setup. (b) Configuration of Ω-shaped coil. (c) Configuration of closed-loop coil.

Fig. 2. Temporal evolution of the measured B-field strength at the position of the B-dot probe. The vertical error bars correspond to the standard deviation of two shots.

Fig. 3. Calculated two-dimensional magnetic field distribution in the x–y plane at z = 0: (a) Ω-shaped coil; (b) closed-loop coil.

Fig. 4. Shadowgraphs in the x–y plane: (a) before laser shot; (b) at a delay time t = 3.5 ns; (c) at a delay time t = 6.0 ns. The dark regions demonstrate that the plasma density is so high that the probe light cannot penetrate it.

Fig. 5. (a) Comparison between the observed spectra from the Ω-shaped and closed-loop coils and the Cu I spectrum obtained from the NIST Atomic Spectra Database at T_e = 0.8 eV. (b) Comparison between the observed spectrum from the closed-loop coil and calculated spectra: the red dashed curve is the Voigt fitting for the closed-loop coil spectrum at 521.47 nm, and the green dotted curve is one typical PrismSPECT Cu I line shape convolved with instrumental broadening computed at T_e = 0.8 eV and n_e = 2 × 10¹⁷ cm⁻³. (c) Comparison between the observed spectrum from the Ω-shaped coil and the calculated Voigt spectrum.

Fig. 6. FWHM of line at transition (3) as a function of electron density n_e computed with PrismSPECT at T_e = 0.8 eV.

Table 1. Summary of spectra.