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Title: Controlling marginally detached divertor plasmas

Abstract

A new control system at DIII-D has stabilized the inter-ELM detached divertor plasma state for H-mode in close proximity to the threshold for reattachment, thus demonstrating the ability to maintain detachment with minimal gas puffing. When the same control system was instead ordered to hold the plasma at the threshold (here defined as Te = 5 eV near the divertor target plate), the resulting Te profiles separated into two groups with one group consistent with marginal detachment, and the other with marginal attachment. The plasma dithers between the attached and detached states when the control system attempts to hold at the threshold. The control system is upgraded from the one described in and it handles ELMing plasmas by using real time Dα measurements to remove during-ELM slices from real time Te measurements derived from divertor Thomson scattering. The difference between measured and requested inter-ELM Te is passed to a PID (proportionalintegral-derivative) controller to determine gas puff commands. While some degree of detachment is essential for the health of ITER’s divertor, more deeply detached plasmas have greater radiative losses and, at the extreme, confinement degradation, making it desirable to limit detachment to the minimum level needed to protect the target plate. However, the observed bifurcation in plasma conditions at the outer strike point with the ion B × $$\nabla $$ B drift into the divertor makes this a significant challenge. If the divertor plasma were to reattach between ELMs, there would be a long (depending on delays in the gas puff system) window of high heat flux before detachment could be re-established. Thus, good understanding of detachment behavior near the threshold for re-attachment is required to properly tune an active control system to maintain ideal divertor performance without reattaching. Furthermore, the top-of-pedestal electron densities during dithering across the bifurcation and during stable marginally detached operation are the same within uncertainty, showing the need for local real-time measurements of the divertor conditions.

Authors:
 [1];  [2];  [3];  [4];  [5];  [5];  [6];  [7];  [7];  [5];  [8]
  1. General Atomics, San Diego, CA (United States); Princeton Univ., Princeton, NJ (United States)
  2. Princeton Univ., Princeton, NJ (United States)
  3. Sandia National Lab. (SNL-CA), Livermore, CA (United States)
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  5. General Atomics, San Diego, CA (United States)
  6. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  7. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  8. Univ. of Toronto Institute for Aerospace Studies, Toronto (Canada)
Publication Date:
Research Org.:
General Atomics, San Diego, CA (United States)
Sponsoring Org.:
USDOE Office of Nuclear Energy (NE)
OSTI Identifier:
1374843
Grant/Contract Number:  
FC02-04ER54698
Resource Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 57; Journal Issue: 6; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; divertor; tokamak; control

Citation Formats

Eldon, David, Kolemen, Egemen, Barton, Joseph L., Briesemeister, Alexis R., Humphreys, David A., Leonard, Anthony W., Maingi, Rajesh, Makowski, Michael A., McLean, Adam G., Moser, Auna L., and Stangeby, Peter C.. Controlling marginally detached divertor plasmas. United States: N. p., 2017. Web. https://doi.org/10.1088/1741-4326/aa6b16.
Eldon, David, Kolemen, Egemen, Barton, Joseph L., Briesemeister, Alexis R., Humphreys, David A., Leonard, Anthony W., Maingi, Rajesh, Makowski, Michael A., McLean, Adam G., Moser, Auna L., & Stangeby, Peter C.. Controlling marginally detached divertor plasmas. United States. https://doi.org/10.1088/1741-4326/aa6b16
Eldon, David, Kolemen, Egemen, Barton, Joseph L., Briesemeister, Alexis R., Humphreys, David A., Leonard, Anthony W., Maingi, Rajesh, Makowski, Michael A., McLean, Adam G., Moser, Auna L., and Stangeby, Peter C.. Thu . "Controlling marginally detached divertor plasmas". United States. https://doi.org/10.1088/1741-4326/aa6b16. https://www.osti.gov/servlets/purl/1374843.
@article{osti_1374843,
title = {Controlling marginally detached divertor plasmas},
author = {Eldon, David and Kolemen, Egemen and Barton, Joseph L. and Briesemeister, Alexis R. and Humphreys, David A. and Leonard, Anthony W. and Maingi, Rajesh and Makowski, Michael A. and McLean, Adam G. and Moser, Auna L. and Stangeby, Peter C.},
abstractNote = {A new control system at DIII-D has stabilized the inter-ELM detached divertor plasma state for H-mode in close proximity to the threshold for reattachment, thus demonstrating the ability to maintain detachment with minimal gas puffing. When the same control system was instead ordered to hold the plasma at the threshold (here defined as Te = 5 eV near the divertor target plate), the resulting Te profiles separated into two groups with one group consistent with marginal detachment, and the other with marginal attachment. The plasma dithers between the attached and detached states when the control system attempts to hold at the threshold. The control system is upgraded from the one described in and it handles ELMing plasmas by using real time Dα measurements to remove during-ELM slices from real time Te measurements derived from divertor Thomson scattering. The difference between measured and requested inter-ELM Te is passed to a PID (proportionalintegral-derivative) controller to determine gas puff commands. While some degree of detachment is essential for the health of ITER’s divertor, more deeply detached plasmas have greater radiative losses and, at the extreme, confinement degradation, making it desirable to limit detachment to the minimum level needed to protect the target plate. However, the observed bifurcation in plasma conditions at the outer strike point with the ion B × $\nabla $ B drift into the divertor makes this a significant challenge. If the divertor plasma were to reattach between ELMs, there would be a long (depending on delays in the gas puff system) window of high heat flux before detachment could be re-established. Thus, good understanding of detachment behavior near the threshold for re-attachment is required to properly tune an active control system to maintain ideal divertor performance without reattaching. Furthermore, the top-of-pedestal electron densities during dithering across the bifurcation and during stable marginally detached operation are the same within uncertainty, showing the need for local real-time measurements of the divertor conditions.},
doi = {10.1088/1741-4326/aa6b16},
journal = {Nuclear Fusion},
number = 6,
volume = 57,
place = {United States},
year = {2017},
month = {5}
}

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Works referenced in this record:

Integrated modeling applications for tokamak experiments with OMFIT
journal, July 2015


Initial operation of the divertor Thomson scattering diagnostic on DIII-D
journal, February 1997

  • Carlstrom, T. N.; Hsieh, C. L.; Stockdale, R.
  • Review of Scientific Instruments, Vol. 68, Issue 2
  • DOI: 10.1063/1.1147893

Divertor heat flux mitigation in the National Spherical Torus Experiment
journal, February 2009

  • Soukhanovskii, V. A.; Maingi, R.; Gates, D. A.
  • Physics of Plasmas, Vol. 16, Issue 2
  • DOI: 10.1063/1.3068170

MARFE phenomena in the HT-7 tokamak
journal, June 2000


Initial results of the high resolution edge Thomson scattering upgrade at DIII-D
journal, October 2012

  • Eldon, D.; Bray, B. D.; Deterly, T. M.
  • Review of Scientific Instruments, Vol. 83, Issue 10
  • DOI: 10.1063/1.4738656

Plasma detachment in JET Mark I divertor experiments
journal, March 1998


Electron pressure balance in the SOL through the transition to detachment
journal, August 2015


Modeling of ELM events and their effect on impurity enrichment
journal, March 2003


High heat flux Langmuir probe array for the DIII-D divertor plates
journal, October 2008

  • Watkins, J. G.; Taussig, D.; Boivin, R. L.
  • Review of Scientific Instruments, Vol. 79, Issue 10
  • DOI: 10.1063/1.2982423

Current convective instability in detached divertor plasma
journal, September 2016

  • Krasheninnikov, S. I.; Smolyakov, A. I.
  • Physics of Plasmas, Vol. 23, Issue 9
  • DOI: 10.1063/1.4962568

The Filterscope
journal, March 2003

  • Colchin, R. J.; Hillis, D. L.; Maingi, R.
  • Review of Scientific Instruments, Vol. 74, Issue 3
  • DOI: 10.1063/1.1537038

Strike point control for the National Spherical Torus Experiment (NSTX)
journal, September 2010


The ITER divertor Thomson scattering system: engineering and advanced hardware solutions
journal, February 2012


Scaling radiative divertor solutions to high power in DIII-D
journal, April 2012


Heat flux management via advanced magnetic divertor configurations and divertor detachment
journal, August 2015


Marfe: an edge plasma phenomenon
journal, August 1984


E×B circulation at the tokamak divertor X point
journal, May 2001

  • Schaffer, M. J.; Bray, B. D.; Boedo, J. A.
  • Physics of Plasmas, Vol. 8, Issue 5
  • DOI: 10.1063/1.1352597

Progress in quantifying the edge physics of the H mode regime in DIII-D
journal, December 2001


MARFE phenomena in the HT-7 tokamak
journal, June 2000


The ITER divertor Thomson scattering system: engineering and advanced hardware solutions
journal, February 2012


Modeling of ELM events and their effect on impurity enrichment
journal, March 2003


    Works referencing / citing this record:

    OMFIT Tokamak Profile Data Fitting and Physics Analysis
    journal, January 2018


    A scalable real-time framework for Thomson scattering analysis: Application to NSTX-U
    journal, April 2019

    • Laggner, F. M.; Diallo, A.; LeBlanc, B. P.
    • Review of Scientific Instruments, Vol. 90, Issue 4
    • DOI: 10.1063/1.5088248

    MANTIS: A real-time quantitative multispectral imaging system for fusion plasmas
    journal, December 2019

    • Perek, A.; Vijvers, W. A. J.; Andrebe, Y.
    • Review of Scientific Instruments, Vol. 90, Issue 12
    • DOI: 10.1063/1.5115569

    Plasma detachment in divertor tokamaks
    journal, February 2018