A beam emission spectroscopy system has been installed on DIII-D to provide localized density fluctuation measurements for long-wavelength turbulent modes with kр3 cm Ϫ1 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 ⌬r р1 cm. In addition, a half-scale two-dimensional ͑2D͒ fiber array to measure the 2D turbulent density field, necessary to measure the full S(k r ,k ) wavenumber spectra, has been implemented and initial results obtained.

The levels in 26 Na with single particle character have been observed for the first time using the d( 25 Na,pγ) reaction at 5 MeV/nucleon. The measured

Multi-field/-scale interactions of turbulence with neoclassical tearing mode magnetic islands in the DIII-D tokamak

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The beam emission spectroscopy optical fluctuation diagnostic requires the highest possible quantum efficiency detector at 656 nm to minimize the photon statistical baseline limit to the detectable fluctuation level. A photoconductive photodiode detector with an extremely low-noise preamplifier and a reactive feedback circuit provides quantum efficiencies up to 70%–80% for a useful frequency range of at least 0–150 kHz with incident powers of ∼10 nW. The diodes are chosen for negligible leakage current and hence do not require active cooling. These detectors have provided increase in the sensitivity to plasma fluctuation amplitude by a factor of ∼14 over photomultipliers and a factor of 4 over large area avalanche photodiodes.