We report on the implementation of a new spectroscopic approach to measure magnetic fields in plasmas that is particularly applicable for dense plasma. In the new method [1], the magnetic field is inferred from the comparison of the line-shapes of different fine-structure components of the same multiplet, which practically have the same Stark and Doppler broadenings, but different magnetic-induced contribution to the line-shapes. In the present work we utilize the Al III 4s-4p doublet at 5696 Å and 5722 Å for the magnetic field measurements. The plasma is obtained by irradiating an aluminum target by 10-nanosecond laser beam of a power density of ~ 10⁹ W/cm².  The ablated plasma has an electron temperature of a few eV and an electron density in the range of n_e ~ 10¹⁷ cm^-3 (when no external magnetic field is applied). The plasma expands in an external magnetic field produced by a microsecond pulsed-power system. The presence of the external magnetic field at the time of the plasma creation and expansion has major consequences on the structure of the plume and its dynamics, as can be inferred from time-dependent line-shape and-intensity, and time-of-flight measurements. In particular, we find a significant increase of the electron density, allowing for expending our magnetic field measurements to plasma with n_e ≥ 10¹⁸ cm^-3. In this density range and for the peak magnetic field generated here (up to ~ 20 T), the Al III 4s-4p line-shapes are dominated by Stark broadening and do not exhibit Zeeman splitting. Thus, the magnetic field in the plasma is determined using the new method. Advanced line-shape analysis [2] allows for the simultaneous determination of  both the magnetic field and electron density.

 [1] E. Stambulchik, K. Tsigutkin, and Y. Maron, Physical Review Letters, 98, 225001 (2007).

[2] E. Stambulchik, and Y. Maron, Journal of Quantitative Spectroscopy & Radiative Transfer, 99, 730-749 (2006).