Measuring azimuthal magnetic field magnitudes in a plasma gun generated single flux rope with laser induced fluorescence*

It has been shown that laser induced fluorescence measurements of Zeeman split spectra offer a method to non-perturbatively measure magnetic fields in laboratory plasmas.^1,2 Laser induced fluorescence is a non-perturbative laser spectroscopic technique that uses the Doppler motion of a species and a narrow linewidth laser to measure the velocity distribution function of the particles. Prior measurements demonstrated a magnetic field resolution of 10 G is achievable.² For the results presented here, a Toptica diode laser is free-space injected parallel to the background guiding magnetic field into the PHAse Space MApping experiment (PHASMA), a helicon plasma source equipped with two plasma guns capable of generating 10 ms long flux ropes. Zeeman split Ar I σ-peaks are measured in a single flux rope in the presence of a background helicon plasma. Here we present measurements of the azimuthal magnetic field created from a single flux rope. These initial measurements show the viability of using this technique for future magnetic imaging of laboratory magnetic reconnection events arising from the merger of two flux ropes.

1. D.S. Thompson, T.E. Steinberger, A.M. Keesee, & E.E. Scime, “Laser induced fluorescence of Ar-I metastables in the presence of a magnetic field,” Plasma Sources Science and Technology, 27, 065007 (2018)

2. T. J. Gilbert, K. J. Stevenson, M. C. Paul, T. E. Steinberger, and E. E. Scime, "Magnetic field imaging in a laboratory plasma", AIP Advances 11, 055314 (2021) https://doi.org/10.1063/5.0052957