The beam emission spectroscopy diagnostic on the DIII-D tokamak

A beam emission spectroscopy system has been installed on DIII-D to provide localized density fluctuation measurements for long-wavelength turbulent modes with k less than or equal to 3 cm(-1) which are typically associated with anomalous radial transport. High signal-to-noise fluctuations measurements are accomplished through use of high speed electronics to maintain a frequency response of over 500 KHz and cryogenically cooled amplifiers and detectors to reduce electronic noise. The optics and neutral beam-sightline geometry have been optimized to allow for spatial resolution of Delta r less than or equal to 1 cm. In addition, a half-scale two-dimensional (2D) fiber array to measure the 2D turbulent density field, necessary to measure the full S(k(r),k(theta)) wavenumber spectra, has been implemented and initial results obtained. (C) 1999 American Institute of Physics. [S0034-6748(99)65801-4].