skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: A synthetic diagnostic for beam emission spectroscopy in the helically symmetric experiment stellarator

Abstract

The Helically Symmetric Experiment (HSX) has a number of active spectroscopy diagnostics. Due to the relatively large beam width compared to the plasma minor radius, it is difficult to achieve good spatial resolution at the core of the HSX plasma. This is due to the fact that the optical sightline cuts through many flux surfaces with varying field vectors within the beam. It is important to accurately model the beam width effects in order to compare the experimental results with theoretical models. We've developed a synthetic diagnostic for this purpose. This synthetic diagnostic calculates the effect of spot size and beam width on the measurements of quantities of interest, including radial electric field, flow velocity, and Stark polarization.

Authors:
 [1];  [1];  [1]
  1. Univ. of Wisconsin, Madison, WI (United States). Dept. of Electrical and Computer Engineering and HSX Plasma Lab.
Publication Date:
Research Org.:
Univ. of Wisconsin, Madison, WI (United States). Dept. of Electrical and Computer Engineering
Sponsoring Org.:
USDOE
OSTI Identifier:
1287267
Grant/Contract Number:
FG02-93ER54222
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Review of Scientific Instruments
Additional Journal Information:
Journal Volume: 87; Journal Issue: 11; Conference: 21st Topical Conference on High-Temperature Plasma Diagnostics, Madison, Wisconsin, USA, June 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; HSX

Citation Formats

Dobbins, T. J., Kumar, S. T. A., and Anderson, D. T. A synthetic diagnostic for beam emission spectroscopy in the helically symmetric experiment stellarator. United States: N. p., 2016. Web. doi:10.1063/1.4960068.
Dobbins, T. J., Kumar, S. T. A., & Anderson, D. T. A synthetic diagnostic for beam emission spectroscopy in the helically symmetric experiment stellarator. United States. doi:10.1063/1.4960068.
Dobbins, T. J., Kumar, S. T. A., and Anderson, D. T. Wed . "A synthetic diagnostic for beam emission spectroscopy in the helically symmetric experiment stellarator". United States. doi:10.1063/1.4960068. https://www.osti.gov/servlets/purl/1287267.
@article{osti_1287267,
title = {A synthetic diagnostic for beam emission spectroscopy in the helically symmetric experiment stellarator},
author = {Dobbins, T. J. and Kumar, S. T. A. and Anderson, D. T.},
abstractNote = {The Helically Symmetric Experiment (HSX) has a number of active spectroscopy diagnostics. Due to the relatively large beam width compared to the plasma minor radius, it is difficult to achieve good spatial resolution at the core of the HSX plasma. This is due to the fact that the optical sightline cuts through many flux surfaces with varying field vectors within the beam. It is important to accurately model the beam width effects in order to compare the experimental results with theoretical models. We've developed a synthetic diagnostic for this purpose. This synthetic diagnostic calculates the effect of spot size and beam width on the measurements of quantities of interest, including radial electric field, flow velocity, and Stark polarization.},
doi = {10.1063/1.4960068},
journal = {Review of Scientific Instruments},
number = 11,
volume = 87,
place = {United States},
year = {Wed Aug 03 00:00:00 EDT 2016},
month = {Wed Aug 03 00:00:00 EDT 2016}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record

Save / Share:
  • The Helically Symmetric Experiment (HSX) has a number of active spectroscopy diagnostics. Due to the relatively large beam width compared to the plasma minor radius, it is difficult to achieve good spatial resolution at the core of the HSX plasma. This is due to the fact that the optical sightline cuts through many flux surfaces with varying field vectors within the beam. In order to compare the experimental results with theoretical models it is important to accurately model the beam width effects. A synthetic diagnostic has been developed for this purpose. This synthetic diagnostic calculates the effect of spot sizemore » and beam width on the measurements of quantities of interest, including radial electric field, flow velocity, and Stark polarization.« less
  • An eight channel electron cyclotron emission imaging (ECEI) diagnostic system is being developed for use on the helically symmetric experiment (HSX) stellarator. The system utilizes a linear Schottky diode mixer/receiver array, coupled with low cost conventional ECE radiometer IF boards under development at U.C. Davis, to measure the second harmonic x-mode radiation from the plasma. The array is fed with a fixed local oscillator, with single sideband operation enabled via a dichroic plate high pass filter whose cutoff frequency equals that of the local oscillator. A multithrow, high speed ({lt}100 ns switching times) microwave switch is utilized to sequentially connectmore » the output from each mixer channel to the broadband IF receiver system, thus making the array capable of generating a high resolution two-dimensional image of the HSX electron temperature profile at rates exceeding 50 kHz. Instrument details of the system will be described. {copyright} {ital 1999 American Institute of Physics.}« less
  • The multichannel interferometer system on the helically symmetric experiment (HSX) stellarator is reconfigured to perform far-forward collective scattering measurements of electron density fluctuations. The collective scattering system has nine viewing chords with 1.5 cm spacing. Scattered power is measured using a homodyne detection scheme. Far-forward collective scattering provides a line-integrated measurement of fluctuations within the divergence of the probe beam covering wavenumber range: k{sub perpendicular}<2 cm{sup -1}. The perpendicular wavenumber consists of poloidal and radial contributions that vary with chord position. Both coherent modes and broadband fluctuation are measured. When HSX is operated without quasihelical symmetry at B{sub T}=1 Tmore » and n{sub e}{approx}4x10{sup 12} cm{sup -3}, a coherent electrostatic fluctuation is observed.« less
  • The interferometer system on the Helically Symmetric eXperiment (HSX) stellarator uses an expanded beam and linear detector array to realize a multichord measurement. Unlike conventional interferometry which determines the plasma phase shift with respect to a reference, directly evaluating the phase between two adjacent chords can be employed to measure the change in plasma phase with impact parameter. This approach provides a measure of the equilibrium density gradient or the density gradient fluctuations and is referred to as differential interferometry. For central chords, measurements are spatially localized due to a geometrical weighting factor and can provide information on core densitymore » gradient fluctuations. The measurement requires finite coherence between fluctuations in the two spatially offset chords. This technique is applied on the HSX stellarator to measure both broadband turbulence and coherent modes. Spatial localization is exploited to isolate core turbulence changes associated with change in magnetic configuration or heating location.« less
  • Gyrokinetic simulations of plasma microturbulence in the Helically Symmetric eXperiment are presented. Using plasma profiles relevant to experimental operation, four dominant drift wave regimes are observed in the ion wavenumber range, which are identified as different flavors of density-gradient-driven trapped electron modes. For the most part, the heat transport exhibits properties associated with turbulence driven by these types of modes. Additionally, long-wavelength, radially localized, nonlinearly excited coherent structures near the resonant central flux surface, not predicted by linear simulations, can further enhance flux levels. Integrated heat fluxes are compatible with experimental observations in the corresponding density gradient range. Despite lowmore » shearing rates, zonal flows are observed to regulate turbulence but can be overwhelmed at higher density gradients by the long-wavelength coherent structures.« less