Simultaneous measurement of q and Er profiles using the motional Stark effect in high-performance DIII-D plasmas (invited)

The motional Stark effect (MSE) diagnostic was developed to provide a measurement of the magnetic pitch angle or q profile in tokamaks. The technique relies upon polarization measurements of Stark broadened D-alpha emission to determine the pitch angle of the Lorentz upsilon(b) X B electric field, where upsilon(b) is the injected neutral beam particle velocity and B is the total magnetic field. However, in many advanced confinement regimes, large values of the plasma radial electric field, E-r, are observed and can affect the interpretation of MSE measurements. Viewing fixed locations in the plasma from two different viewing angles allows one to separate the E-r field from the upsilon(b) X B field, thus providing simultaneous measurement of the E-r and q profiles. To achieve this measurement, the DIII-D MSE diagnostic was recently upgraded from 16 to 35 channels with three independent viewing angles. The new instrument provides an E-r resolution of 5-10 kV/m with a time response of 1 ms. Measurement results from the VH mode, reverse shear, and H mode plasmas are presented. (C) 1999 American Institute of Physics. [S0034-6748(99)51001-0].