The motional Stark effect diagnostic on NSTX.

This work describes the implementation and recent results from the motional Stark effect (MSE) collisionally induced fluorescence diagnostic on NSTX. Due to the low magnetic field on NSTX the MSE diagnostic requires a new approach for the viewing optics and spectral filter. This has been accomplished with a novel optical design that reduces the geometric Doppler broadening, and a high throughput, high resolution spectral filter to optimize signal-to-noise ratio. With these improvements the polarization fraction is approximately 30%-40% and, combined with the large throughput, a time resolution of approximately 5 ms. The MSE diagnostic presently has 16 sight lines operating, providing measurements of the magnetic field line pitch from the plasma center to near the outboard edge of the plasma.