Measuring magnetic fields in plasma gun generated flux ropes with quantum beat spectroscopy

Accurate measurement of magnetic fields is critical in numerous plasma environments, ranging from astrophysical systems to fusion energy research. Typical approaches for measuring magnetic fields in laboratory plasmas either employ perturbative probes (i.e., magnetic sensing coils) that are prone to ambient electromagnetic noise or rely on resolving individual Zeeman-split σ-peaks from full velocity distribution function (VDF) measurements. In the latter case, transient magnetic field effects are difficult to ascertain since the measurement of the full VDF from laser spectroscopic techniques, e.g., laser induced fluorescence (LIF), is inefficient and time consuming, especially in pulsed laboratory experiments where each data point used to construct the VDF is composed of several plasma pulse discharges. In this work, an alternative laser-based technique known as quantum beat spectroscopy is employed to measure weak magnetic field strengths at near single shot acquisitions from the Zeeman-split electron energy states of the (2P^o_1/2)4s ²[1/2]^o state of neutral argon. This technique is non-intrusive and unlike LIF does not require any sweeping of the laser wavelength, making this approach ideal for transient events such as probing the reconnection magnetic field strength in laboratory magnetic reconnection experiments.