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 m odes with k less than or equal to 3 cm(-1) which are typically associated w ith anomalous radial transport. High signal-to-noise fluctuations measureme nts are accomplished through use of high speed electronics to maintain a fr equency response of over 500 KHz and cryogenically cooled amplifiers and de tectors to reduce electronic noise. The optics and neutral beam-sightline g eometry 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) fibe r 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)6 5801-4].