The importance of the radial electric field (E{sub r}) on interpretation of motional Stark effect measurements of the q profile in DIII-D high performance plasmas

The development of enhanced confinement regimes such as negative central magnetic shear (NCS) and VH-mode illustrates the importance of the q profile and ExB velocity shear in improving stability and confinement in tokamak plasmas. Recently, it was realized that the large values of radial electric field observed in these high performance plasmas, up to 200 kV/m in DIII-D, have an effect on the interpretation of motional Stark effect (MSE) measurements of the q profile. It has also been shown that, with additional MSE measurements, one can extract a direct measurement of E{sub r} in addition to the usual poloidal field measurement. During a recent vent on DIII-D, 19 additional MSE channels with new viewing angles were added (for a total of 35 channels) in order to descriminate between the neutral beam v{sub b} x B electric field and the plasma E{sub r} field. In this paper, the system upgrade will be described and initial measurements demonstrating simultaneous measurement of the q and E{sub r} profiles will be presented.