Development of the Motional Stark Effect with Laser-Induced Fluorescence (MSE-LIF) Diagnostic

The motional Stark effect with laser-induced fluorescence (MSE- LIF) diagnostic is under development to extend the MSE magnetic pitch angle diagnostic to lower fields ( $<$ 0.5 T) and enable measurement of magnetic field magnitude as well as direction. The technique involves injecting a low energy-spread neutral hydrogen beam (30 kV, 30 mA) into plasma, and using a collinear laser to excite transitions from the n=2 to n=3 atomic states in the beam atoms. The subsequent fluorescence from the same transition (Balmer-alpha, near 650 nm for the Doppler-shifted beam) is observed, and its splitting and polarization due to the E = v X B electric field in the beam frame is used to determine the background magnetic field magnitude and direction. This poster will present recent results from MSE-LIF development, including magnetic field measurements at very low field ($<$ 0.01 T) in neutral gas based on an enhanced LIF phenomenon, a comprehensive collisional-radiative model which determines the population fractions in the n=1, 2 and 3 states of the beam as the states mix in applied magnetic and electric fields, as well as upgrades to the experimental apparatus that will enable measurements in intermediate fields (0.01 - 0.2 T) in plasma.