Progress on the motional Stark effect with laser-induced fluoresence 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 $\times$ 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. A new plasma testbed for MSE-LIF, a spiral antenna helicon source, has been built.