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Title: Spectroscopic imaging of limiter heat and particle fluxes and the resulting impurity sources during Wendelstein 7-X startup plasmas

Abstract

A combined IR and visible camera system [G. A. Wurden et al., “A high resolution IR/visible imaging system for the W7-X limiter,” Rev. Sci. Instrum. (these proceedings)] and a filterscope system [R. J. Colchin et al., Rev. Sci. Instrum. 74, 2068 (2003)] were implemented together to obtain spectroscopic data of limiter and first wall recycling and impurity sources during Wendelstein 7-X startup plasmas. Both systems together provided excellent temporal and spatial spectroscopic resolution of limiter 3. Narrowband interference filters in front of the camera yielded C-III and Hα photon flux, and the filterscope system provided H α, H β, He-I, He-II, C-II, and visible bremsstrahlung data. The filterscopes made additional measurements of several points on the W7-X vacuum vessel to yield wall recycling fluxes. Finally, the resulting photon flux from both the visible camera and filterscopes can then be compared to an EMC3-EIRENE synthetic diagnostic [H. Frerichs et al., “Synthetic plasma edge diagnostics for EMC3-EIRENE, highlighted for Wendelstein 7-X,” Rev. Sci. Instrum. (these proceedings)] to infer both a limiter particle flux and wall particle flux, both of which will ultimately be used to infer the complete particle balance and particle confinement time τ P.

Authors:
 [1]; ORCiD logo [2];  [1];  [1];  [1];  [3];  [4];  [3];  [3];  [3]; ORCiD logo [4]
  1. Univ. of Wisconsin, Madison, WI (United States)
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  3. Max Planck Inst. of Plasma Physics, Greifswald (Germany)
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Univ. of Wisconsin, Madison, WI (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Max Planck Inst. of Plasma Physics, Greifswald (Germany)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24); European Commission (EC)
Contributing Org.:
W7-X Team
OSTI Identifier:
1415400
Report Number(s):
LA-UR-17-24683
Journal ID: ISSN 0034-6748; TRN: US1800799
Grant/Contract Number:
AC52-06NA25396; AC05-00OR22725; SC0014210; FG02-93ER54222; 633053
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; cameras; limiters; photons; plasma diagnostics; calibration

Citation Formats

Stephey, L., Wurden, G. A., Schmitz, O., Frerichs, H., Effenberg, F., Biedermann, C., Harris, J., König, R., Kornejew, P., Krychowiak, M., and Unterberg, E. A. Spectroscopic imaging of limiter heat and particle fluxes and the resulting impurity sources during Wendelstein 7-X startup plasmas. United States: N. p., 2016. Web. doi:10.1063/1.4959274.
Stephey, L., Wurden, G. A., Schmitz, O., Frerichs, H., Effenberg, F., Biedermann, C., Harris, J., König, R., Kornejew, P., Krychowiak, M., & Unterberg, E. A. Spectroscopic imaging of limiter heat and particle fluxes and the resulting impurity sources during Wendelstein 7-X startup plasmas. United States. doi:10.1063/1.4959274.
Stephey, L., Wurden, G. A., Schmitz, O., Frerichs, H., Effenberg, F., Biedermann, C., Harris, J., König, R., Kornejew, P., Krychowiak, M., and Unterberg, E. A. Mon . "Spectroscopic imaging of limiter heat and particle fluxes and the resulting impurity sources during Wendelstein 7-X startup plasmas". United States. doi:10.1063/1.4959274. https://www.osti.gov/servlets/purl/1415400.
@article{osti_1415400,
title = {Spectroscopic imaging of limiter heat and particle fluxes and the resulting impurity sources during Wendelstein 7-X startup plasmas},
author = {Stephey, L. and Wurden, G. A. and Schmitz, O. and Frerichs, H. and Effenberg, F. and Biedermann, C. and Harris, J. and König, R. and Kornejew, P. and Krychowiak, M. and Unterberg, E. A.},
abstractNote = {A combined IR and visible camera system [G. A. Wurden et al., “A high resolution IR/visible imaging system for the W7-X limiter,” Rev. Sci. Instrum. (these proceedings)] and a filterscope system [R. J. Colchin et al., Rev. Sci. Instrum. 74, 2068 (2003)] were implemented together to obtain spectroscopic data of limiter and first wall recycling and impurity sources during Wendelstein 7-X startup plasmas. Both systems together provided excellent temporal and spatial spectroscopic resolution of limiter 3. Narrowband interference filters in front of the camera yielded C-III and Hα photon flux, and the filterscope system provided Hα, Hβ, He-I, He-II, C-II, and visible bremsstrahlung data. The filterscopes made additional measurements of several points on the W7-X vacuum vessel to yield wall recycling fluxes. Finally, the resulting photon flux from both the visible camera and filterscopes can then be compared to an EMC3-EIRENE synthetic diagnostic [H. Frerichs et al., “Synthetic plasma edge diagnostics for EMC3-EIRENE, highlighted for Wendelstein 7-X,” Rev. Sci. Instrum. (these proceedings)] to infer both a limiter particle flux and wall particle flux, both of which will ultimately be used to infer the complete particle balance and particle confinement time τP.},
doi = {10.1063/1.4959274},
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}
}

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  • A combined IR and visible camera system [G. A. Wurden et al., “A high resolution IR/visible imaging system for the W7-X limiter,” Rev. Sci. Instrum. (these proceedings)] and a filterscope system [R. J. Colchin et al., Rev. Sci. Instrum. 74, 2068 (2003)] were implemented together to obtain spectroscopic data of limiter and first wall recycling and impurity sources during Wendelstein 7-X startup plasmas. Both systems together provided excellent temporal and spatial spectroscopic resolution of limiter 3. Narrowband interference filters in front of the camera yielded C-III and H{sub α} photon flux, and the filterscope system provided H{sub α}, H{sub β},more » He-I, He-II, C-II, and visible bremsstrahlung data. The filterscopes made additional measurements of several points on the W7-X vacuum vessel to yield wall recycling fluxes. The resulting photon flux from both the visible camera and filterscopes can then be compared to an EMC3-EIRENE synthetic diagnostic [H. Frerichs et al., “Synthetic plasma edge diagnostics for EMC3-EIRENE, highlighted for Wendelstein 7-X,” Rev. Sci. Instrum. (these proceedings)] to infer both a limiter particle flux and wall particle flux, both of which will ultimately be used to infer the complete particle balance and particle confinement time τ{sub P}.« less
  • Observations on confinement in the first experimental campaign on the optimized Stellarator Wendelstein 7-X are summarized. In this phase W7-X was equipped with five inboard limiters only and thus the discharge length restricted to avoid local overheating. Stationary plasmas are limited to low densities <2–3 centerdot 10 19 m -3. With the available 4.3 MW ECR Heating core T e ~ 8 keV, T i ~ 1–2 keV are achieved routinely resulting in energy confinement time τ E between 80 ms to 150 ms. For these conditions the plasmas show characteristics of core electron root confinement with peaked T e-profilesmore » and positive E r up to about half of the minor radius. Lastly, profiles and plasma currents respond to on- and off-axis heating and co- and counter ECCD respectively.« less
    Cited by 4
  • Cited by 4
  • The design for a set of four high-efficiency vacuum ultraviolet/extreme ultraviolet (VUV/XUV) spectrometers has been developed, which shall be used for plasma impurity monitoring and impurity transport studies on the stellarator experiment Wendelstein 7-X (W7-X). The new high-efficiency XUV overview spectrometer (HEXOS) system covers the wavelength range from 2.5 to 160 nm, divided into four subsections with some overlapping, thus achieving a complete coverage of prominent spectral lines from the relevant impurity elements. Taking into account spectrometer geometries and detector geometries, toroidal holographic diffraction gratings are numerically optimized to maximize the total throughput while maintaining good spectral resolution. The performancemore » of the spectrometers is tested and optimized by means of ray tracing calculations. In order to prove the potential for line identification as well as the expected levels of signal intensity and noise figures of the new systems, spectra are simulated using the impurity transport code STRAHL. Under typical plasma conditions on W7-X the new spectrometers will allow clear identification of all relevant impurity elements in the plasma. The large collected photon flux results in a high accuracy for the measured line intensities, even when operating the spectrometers at spectra rates of 1000/s.« less
  • Confinement transitions in the Wendelstein 7-AS stellarator [H. Renner et al., Plasma Phys. Controlled Fusion 31, 1579 (1989)] can be induced by varying either the internal plasma current or the external magnetic field. In this paper we report on experiments where closely matched confinement states (good and bad) were constructed using the latter method. Analysis using the former scheme has been reported upon previously [S. Zoletnik et al., Plasma Phys. Controlled Fusion 44, 1581 (2002)]. The electron temperature, along with the major spectral characteristics of magnetic and small-scale electron density fluctuations, changes dramatically at the transition from good to badmore » confinement. The fluctuation power is intermittent, and core bursts traveling in the electron diamagnetic drift (DD) direction are correlated between the bottom and top of the plasma, especially during degraded confinement. A corresponding top-bottom correlation for the edge ion DD direction turbulence feature was not found. Strong correlations are observed both between the two density fluctuation signals and between magnetic and density fluctuations in bad compared to good confinement. The correlation time of the bursts is of order 100 {mu}s, similar to the lifetime observed during edge localized modes.« less