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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.As a result, 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:
 [1];  [2];  [3];  [3];  [2];  [2];  [4]
  1. Oak Ridge Assoc. Univ., Oak Ridge, TN (United States)
  2. General Atomics, San Diego, CA (United States)
  3. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); General Atomics, San Diego, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1350535
Grant/Contract Number:
AC05-00OR22725; AC02-09CH11466; FC02-04ER54698
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Review of Scientific Instruments
Additional Journal Information:
Journal Volume: 87; Journal Issue: 11; Journal ID: ISSN 0034-6748
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; plasma diagnostics; charge exchange reactions; particle distribution functions; image sensors; Maxwell equations; 46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY

Citation Formats

Chrystal, Colin, Burrell, K. H., Grierson, Brian A., Haskey, Shaun R., Groebner, R. J., Kaplan, David H., and Briesemeister, Alexis R. Improved edge charge exchange recombination spectroscopy in DIII-D. United States: N. p., 2016. Web. doi:10.1063/1.4958915.
Chrystal, Colin, Burrell, K. H., Grierson, Brian A., Haskey, Shaun R., Groebner, R. J., Kaplan, David H., & Briesemeister, Alexis R. Improved edge charge exchange recombination spectroscopy in DIII-D. United States. doi:10.1063/1.4958915.
Chrystal, Colin, Burrell, K. H., Grierson, Brian A., Haskey, Shaun R., Groebner, R. J., Kaplan, David H., and Briesemeister, Alexis R. 2016. "Improved edge charge exchange recombination spectroscopy in DIII-D". United States. doi:10.1063/1.4958915. https://www.osti.gov/servlets/purl/1350535.
@article{osti_1350535,
title = {Improved edge charge exchange recombination spectroscopy in DIII-D},
author = {Chrystal, Colin and Burrell, K. H. and Grierson, Brian A. and Haskey, Shaun R. and Groebner, R. J. and Kaplan, David H. and Briesemeister, Alexis R.},
abstractNote = {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.As a result, 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.},
doi = {10.1063/1.4958915},
journal = {Review of Scientific Instruments},
number = 11,
volume = 87,
place = {United States},
year = 2016,
month = 8
}

Journal Article:
Free Publicly Available Full Text
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  • 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 frommore » 16 to 38.As a result, 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.« less
  • 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 16more » 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.« less
  • Charge exchange spectroscopy is one of the key ion diagnostics on the DIII-D tokamak. It allows measurement of impurity densities, toroidal and poloidal rotation speeds, ion temperatures, and the radial electric field. For the 2000 experimental campaign, we have replaced the intensified photodiode array detectors on the edge portion of the system with advanced charge-coupled device (CCD) detectors mounted on faster (f/4.7) Czerny--Turner spectrometers equipped with toroidal mirrors. The combination has improved the photoelectron signal level by about a factor of 20 and the signal to noise by a factor of 2--8, depending on the absolute signal level and readoutmore » mode. A major portion of the signal level improvement comes from the improved quantum efficiency of the back-illuminated, thinned CCD detector (70% to 85% quantum efficiency for the CCD versus 10% for the image intensifier) with the remainder coming from the faster spectrometer. The CCD camera also allows shorter minimum integration times: 0.33 ms while archiving to computer memory and 0.15 ms using temporary storage on the CCD chip.« less
  • Charge exchange recombination (CER) spectroscopy has become a standard diagnostic for Tokamaks. CER measurements have been used to determine spatially and temporally resolved ion temperature, toroidal and poloidal ion rotation speed, impurity density, and radial electric field. Knowledge of the spatial profile and temporal evolution of the electric field shear in the plasma edge is crucial to understanding the physics of the {ital L} to {ital H} transition. High speed CER measurements are also valuable for edge localized mode studies. Since the 0.52 ms minimum time resolution of our present system is barely adequate to study the time evolution ofmore » these phenomena, we have developed a new charge coupled device (CCD) detector system with about a factor of 2 better time resolution. In addition, our existing system detects sufficient photons to utilize the shortest time resolution only under exceptional conditions. The new CCD detector has a quantum efficiency of about 0.65, which is a factor of 7 better than our previous image intensifier-silicon photodiode detector systems. We have also equipped the new system with spectrometers of lower {ital f}/number. This combination should allow more routine operation at the minimum integration time, as well as improving data quality for measurements in the divertor-relevant region outside of the separatrix. Construction details, benchmark data, and initial Tokamak measurements for the new system will be presented. {copyright} {ital 1997 American Institute of Physics.}« less
  • Charge exchange recombination (CER) spectroscopy has become a standard diagnostic for Tokamaks. CER measurements have been used to determine spatially and temporally resolved ion temperature, toroidal and poloidal ion rotation speed, impurity density, and radial electric field. Knowledge of the spatial profile and temporal evolution of the electric field shear in the plasma edge is crucial to understanding the physics of the L to H transition. High speed CER measurements are also valuable for edge localized mode studies. Since the 0.52 ms minimum time resolution of our present system is barely adequate to study the time evolution of these phenomena,more » we have developed a new charge coupled device (CCD) detector system with about a factor of 2 better time resolution. In addition, our existing system detects sufficient photons to utilize the shortest time resolution only under exceptional conditions. The new CCD detector has a quantum efficiency of about 0.65, which is a factor of 7 better than our previous image intensifier-silicon photodiode detector systems. We have also equipped the new system with spectrometers of lower f/number. This combination should allow more routine operation at the minimum integration time, as well as improving data quality for measurements in the divertor-relevant region outside of the separatrix. Construction details, benchmark data, and initial Tokamak measurements for the new system will be presented. {copyright} {ital 1997 American Institute of Physics.}« less