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Title: Improved cross-calibration of Thomson scattering and electron cyclotron emission with ECH on DIII-D

Abstract

Thomson scattering (TS) produces n e profiles from measurement of scattered laser beam intensity. In the case of Rayleigh scattering, it provides a first calibration of the relation n e / ITS, which depends on many factors (e.g. laser alignment and power, optics, and measurement systems). On DIII-D, the n e calibration is adjusted for each laser and optic path against an absolute n e measurement from a density-driven cutoff on the 48 channel 2nd harmonic X-mode electron cyclotron emission (ECE) system. This method has been used to calibrate Thompson densities from the edge to near the core (r/a > 0.15). Application of core electron cyclotron heating improves the quality of cutoff and depth of its penetration into the core. ECH also changes underlying MHD activity. Furthermore, on the removal of ECH power, cutoff penetrates in from the edge to the core and channels fall successively and smoothly into cutoff. This improves the quality of the TS n e calibration while minimizing wall loading.

Authors:
ORCiD logo [1];  [2];  [2];  [3];  [3];  [3]
  1. Univ. of Texas, Austin, TX (United States). Inst. for Fusion Studies
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  3. General Atomics, San Diego, CA (United States)
Publication Date:
Research Org.:
General Atomics, San Diego, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1371879
Grant/Contract Number:
FC02-04ER54698; FG03-97ER54415
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Review of Scientific Instruments
Additional Journal Information:
Journal Volume: 87; Journal Issue: 11; Related Information: M.W. Brookman, M.E. Austin, A.G. McLean, T.N. Carlstrom, A.W. Hyatt, and J. Lohr, "Improved cross-calibration of Thomson scattering and electron cyclotron emission with ECH on DIII-D", Rev. Sci. Instr. 87, 11E517 (2016); 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; 46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY

Citation Formats

Brookman, M. W., Austin, M. E., McLean, A. G., Carlstrom, T. N., Hyatt, A. W., and Lohr, J. Improved cross-calibration of Thomson scattering and electron cyclotron emission with ECH on DIII-D. United States: N. p., 2016. Web. doi:10.1063/1.4959916.
Brookman, M. W., Austin, M. E., McLean, A. G., Carlstrom, T. N., Hyatt, A. W., & Lohr, J. Improved cross-calibration of Thomson scattering and electron cyclotron emission with ECH on DIII-D. United States. doi:10.1063/1.4959916.
Brookman, M. W., Austin, M. E., McLean, A. G., Carlstrom, T. N., Hyatt, A. W., and Lohr, J. Mon . "Improved cross-calibration of Thomson scattering and electron cyclotron emission with ECH on DIII-D". United States. doi:10.1063/1.4959916. https://www.osti.gov/servlets/purl/1371879.
@article{osti_1371879,
title = {Improved cross-calibration of Thomson scattering and electron cyclotron emission with ECH on DIII-D},
author = {Brookman, M. W. and Austin, M. E. and McLean, A. G. and Carlstrom, T. N. and Hyatt, A. W. and Lohr, J.},
abstractNote = {Thomson scattering (TS) produces ne profiles from measurement of scattered laser beam intensity. In the case of Rayleigh scattering, it provides a first calibration of the relation ne / ITS, which depends on many factors (e.g. laser alignment and power, optics, and measurement systems). On DIII-D, the ne calibration is adjusted for each laser and optic path against an absolute ne measurement from a density-driven cutoff on the 48 channel 2nd harmonic X-mode electron cyclotron emission (ECE) system. This method has been used to calibrate Thompson densities from the edge to near the core (r/a > 0.15). Application of core electron cyclotron heating improves the quality of cutoff and depth of its penetration into the core. ECH also changes underlying MHD activity. Furthermore, on the removal of ECH power, cutoff penetrates in from the edge to the core and channels fall successively and smoothly into cutoff. This improves the quality of the TS ne calibration while minimizing wall loading.},
doi = {10.1063/1.4959916},
journal = {Review of Scientific Instruments},
number = 11,
volume = 87,
place = {United States},
year = {Mon Aug 08 00:00:00 EDT 2016},
month = {Mon Aug 08 00:00:00 EDT 2016}
}

Journal Article:
Free Publicly Available Full Text
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  • Thomson scattering produces n{sub e} profiles from measurement of scattered laser beam intensity. Rayleigh scattering provides a first calibration of the relation n{sub e} ∝ I{sub TS}, which depends on many factors (e.g., laser alignment and power, optics, and measurement systems). On DIII-D, the n{sub e} calibration is adjusted against an absolute n{sub e} from the density-driven cutoff of the 48 channel 2nd harmonic X-mode electron cyclotron emission system. This method has been used to calibrate Thomson n{sub e} from the edge to near the core (r/a > 0.15). Application of core electron cyclotron heating improves the quality of cutoffmore » and depth of its penetration into the core, and also changes underlying MHD activity, minimizing crashes which confound calibration. Less fueling is needed as “ECH pump-out” generates a plasma ready to take up gas. On removal of gyrotron power, cutoff penetrates into the core as channels fall successively and smoothly into cutoff.« less
  • An alternative method of absolute calibration of Thomson scattering (TS) systems is described. The method is based on the measurements of electron cyclotron emission (ECE) from the plasma. If the plasma density reaches some critical value the emission at some frequencies is cut off and an abrupt loss of signal is registered by the ECE diagnostic. These critical values are calculated from the frequencies of the ECE channels in which cutoffs are observed, using the dispersion relation for the wave propagation. The radial positions of the ECE channels are bound to the measured magnetic field in the tokamak and, therefore,more » are known. The derived critical density values at certain positions in plasma are used to calculate absolute calibration coefficients for the core TS system. For that data points from the TS diagnostic are interpolated in time and space to these critical density values. This calibration technique is implemented in situ on the Alcator C-Mod tokamak during plasma operation. We use a nine-channel ECE diagnostic to calibrate the eight-channel core TS system. The uncertainty of the TS density calibration is {<=}10%, which is less than that from the gas scattering calibrations. Good agreement exists between TS density profiles and measurements from the visible continuum diagnostic and interferometry. Given the wide availability of ECE diagnostics on most tokamaks and other fusion devices, this technique should be suitable on many other experiments.« less
  • The measurement of accurate temperature profiles is critical for transport analysis and equilibrium reconstruction in the DIII-D tokamak. Recent refinements in the Michelson interferometer diagnostic have produced more precise electron temperature measurements from electron cyclotron emission and made them available for a wider range of discharge conditions. Replacement of a lens-relay with a low-loss corrugated waveguide transmission system resulted in an increase in throughput of 6 dB and a reduction of calibration error from 15{percent} to 5{percent}. The waveguide exhibits a small polarization scrambling fraction of 0.05 at the quarter-wavelength frequency and very stable transmission characteristics over time. Further reductionmore » in error was realized through special signal processing of the calibration and plasma interferograms. {copyright} {ital 1997 American Institute of Physics.}« less
  • We present the first simultaneous measurements of the Thomson scattering and electron cyclotron emission radiometer diagnostics performed at TCABR tokamak with Alfven wave heating. The Thomson scattering diagnostic is an upgraded version of the one previously installed at the ISTTOK tokamak, while the electron cyclotron emission radiometer employs a heterodyne sweeping radiometer. For purely Ohmic discharges, the electron temperature measurements from both diagnostics are in good agreement. Additional Alfven wave heating does not affect the capability of the Thomson scattering diagnostic to measure the instantaneous electron temperature, whereas measurements from the electron cyclotron emission radiometer become underestimates of the actualmore » temperature values.« less
  • In many high-performance discharges in the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. {bold 8}, 441 (1985)] high electron density prevents determining the electron temperature from the second harmonic electron cyclotron emission (ECE). A technique for obtaining central electron temperatures from optically gray third harmonic ECE is presented that does not require knowledge of the reflective properties of the vessel wall. The temperature values derived from ECE spectra measured with an absolutely calibrated Michelson interferometer agree with independent measurements by Thomson scattering. As part of this work, a method of determining the optical depth of thirdmore » harmonic frequencies in a low aspect ratio tokamak is also demonstrated. The optical depth measurements are in agreement with calculations correct to first order in the Larmor radius. {copyright} {ital 1996 American Institute of Physics.}« less