Study of NSTX electron density and magnetic field fluctuations using the FIReTIP system

The Far Infra Red Tangential Interferometry and Polarimetry (FIReTIP) system on NSTX is capable of simultaneously measuring fluctuations of electron density and magnetic field. Magnetic fields fluctuations ($\tilde {B})$ can be isolated during MHD activity such as internal kinks, since interferometry provides electron density information while polarimetry provides Faraday rotation data along the same beam path. In this paper, a comparison study of the electron density fluctuations with the fluctuations measured by the Gas Puffing Image (GPI) at the boundary plasmas will be discussed. A discussion of the $\tilde {B}$measurements from 3 channels at different tangencies including comparisons with EFIT equilibrium parameters and the structure of MHD modes will be presented.