An Upgrade of the DIII-D MSE Diagnostic that Utilizes the Counter-Injected Neutral Beam for Improved Current Profile Reconstruction

The motional Stark effect (MSE) diagnostic is being upgraded this year to take advantage of the new \hbox{DIII-D} neutral beam arrangement. Our three existing MSE views will be maintained as they are while a fourth view will be added to image the counter-injected neutral beam. The fourth view will use two separate imaging systems for coverage of the plasma from the magnetic axis to the low-field edge. These systems each contain a single polarization preserving fold mirror and a lens relay system to transfer light to a polarimeter. The details of this design are discussed. The addition of the new views will eliminate a gap in the profile where the existing MSE views cannot accurately discriminate $B_z$ and $E_r$. Uncertainty in $E_r(R)$ will be reduced by a factor of 2 in the core and 5-6 in the edge. Uncertainty in $B_z(R)$ will be reduced by 20-30\%, and the radial resolution will improve by about a factor of 3 in the core.