title: Improved edge charge exchange recombination spectroscopy in DIII-D.
abstract: The charge exchange recombination spectroscopy diagnostic on the DIII-D tokamak has been upgraded with the addition of more high radial resolution view chords near the edge of the plasma (r/a > 0.8). The additional views are diagnosed with the same number of spectrometers by placing fiber optics side-by-side at the spectrometer entrance with a precise separation that avoids wavelength shifted crosstalk without the use of bandpass filters. The new views improve measurement of edge impurity parameters in steep gradient, H-mode plasmas with many different shapes. The number of edge view chords with 8 mm radial separation has increased from 16 to 38. New fused silica fibers have improved light throughput and clarify the observation of non-Gaussian spectra that suggest the ion distribution function can be non-Maxwellian in low collisionality plasmas.
authors.affiliation: Oak Ridge Associated Universities, Oak Ridge, Tennessee 37831, USA.
authors.forename: C
authors.initials: C
authors.lastname: Chrystal
authors.affiliation: General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA.
authors.forename: K H
authors.initials: KH
authors.lastname: Burrell
authors.affiliation: Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543-0451, USA.
authors.forename: B A
authors.initials: BA
authors.lastname: Grierson
authors.affiliation: Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543-0451, USA.
authors.forename: S R
authors.initials: SR
authors.lastname: Haskey
authors.affiliation: General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA.
authors.forename: R J
authors.initials: RJ
authors.lastname: Groebner
authors.affiliation: General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA.
authors.forename: D H
authors.initials: DH
authors.lastname: Kaplan
authors.affiliation: Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: A
authors.initials: A
authors.lastname: Briesemeister