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Title: Advances in radiated power control at DIII-D

Abstract

Feedback control of radiated power from the lower divertor P rad, div, L has been implemented in the DIII-D Plasma Control System (PCS). A realtime sensor for P rad, div, L has been constructed from 12 foil bolometer channels which agrees with standard post-shot analysis to within 20%. Results with the 12-channel sensor are compared to initial proof-of-concept tests with a single channel as a proxy for P rad, div, L, showing that the upgraded sensor is necessary to overcome limitations of the proxy channel strategy in DIII-D. Using N 2 seeding under feedback control, P rad, div, L has been increased by up to 150% above unseeded levels, and a radiated power fraction frad of 80% has been demonstrated, although feedback controlled gas flow is steadier at $$f_{rad}$$ = 55%. Spatial coverage is broad enough to enable P rad control during the strike point sweeps which are commonly used to generate pseudo-2D divertor Thomson measurements in DIII-D divertor experiments. Use of this control reveals challenges that may affect next step devices, which will require actively controlled extrinsic impurity seeding in order to manage heat loads. When operating at high $$f_{rad}$$, changes in pedestal Te (caused by ELMs in these experiments but could come from other disturbances) resulted in large perturbations to Prad which were destabilizing to the feedback controller.

Authors:
ORCiD logo [1];  [2];  [3];  [3];  [4];  [3];  [4];  [3]; ORCiD logo [3]; ORCiD logo [3]
  1. General Atomics, San Diego, CA (United States); Princeton Univ., NJ (United States)
  2. Princeton Univ., NJ (United States)
  3. General Atomics, San Diego, CA (United States)
  4. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1529181
Report Number(s):
LLNL-JRNL-777067
Journal ID: ISSN 2352-1791; 970087
Grant/Contract Number:  
AC52-07NA27344; FC02-04ER54698; AC02-09CH11466; SC001587
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nuclear Materials and Energy
Additional Journal Information:
Journal Volume: 18; Journal Issue: C; Journal ID: ISSN 2352-1791
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Eldon, D., Kolemen, E., Humphreys, D. A., Hyatt, A. W., Järvinen, A. E., Leonard, A. W., McLean, A. G., Moser, A. L., Petrie, T. W., and Walker, M. L. Advances in radiated power control at DIII-D. United States: N. p., 2019. Web. doi:10.1016/j.nme.2019.01.010.
Eldon, D., Kolemen, E., Humphreys, D. A., Hyatt, A. W., Järvinen, A. E., Leonard, A. W., McLean, A. G., Moser, A. L., Petrie, T. W., & Walker, M. L. Advances in radiated power control at DIII-D. United States. doi:10.1016/j.nme.2019.01.010.
Eldon, D., Kolemen, E., Humphreys, D. A., Hyatt, A. W., Järvinen, A. E., Leonard, A. W., McLean, A. G., Moser, A. L., Petrie, T. W., and Walker, M. L. Fri . "Advances in radiated power control at DIII-D". United States. doi:10.1016/j.nme.2019.01.010. https://www.osti.gov/servlets/purl/1529181.
@article{osti_1529181,
title = {Advances in radiated power control at DIII-D},
author = {Eldon, D. and Kolemen, E. and Humphreys, D. A. and Hyatt, A. W. and Järvinen, A. E. and Leonard, A. W. and McLean, A. G. and Moser, A. L. and Petrie, T. W. and Walker, M. L.},
abstractNote = {Feedback control of radiated power from the lower divertor Prad, div, L has been implemented in the DIII-D Plasma Control System (PCS). A realtime sensor for Prad, div, L has been constructed from 12 foil bolometer channels which agrees with standard post-shot analysis to within 20%. Results with the 12-channel sensor are compared to initial proof-of-concept tests with a single channel as a proxy for Prad, div, L, showing that the upgraded sensor is necessary to overcome limitations of the proxy channel strategy in DIII-D. Using N2 seeding under feedback control, Prad, div, L has been increased by up to 150% above unseeded levels, and a radiated power fraction frad of 80% has been demonstrated, although feedback controlled gas flow is steadier at $f_{rad}$ = 55%. Spatial coverage is broad enough to enable Prad control during the strike point sweeps which are commonly used to generate pseudo-2D divertor Thomson measurements in DIII-D divertor experiments. Use of this control reveals challenges that may affect next step devices, which will require actively controlled extrinsic impurity seeding in order to manage heat loads. When operating at high $f_{rad}$, changes in pedestal Te (caused by ELMs in these experiments but could come from other disturbances) resulted in large perturbations to Prad which were destabilizing to the feedback controller.},
doi = {10.1016/j.nme.2019.01.010},
journal = {Nuclear Materials and Energy},
issn = {2352-1791},
number = C,
volume = 18,
place = {United States},
year = {2019},
month = {1}
}

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Cited by: 1 work
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Figures / Tables:

Figure 1 Figure 1: DIII-D cross section and control schematic. Cross section overlays: limiting surfaces (black), sample plasma last closed flux surfaces (blue and cyan at 2000 and 5000 ms), bolometer proxy channel (thick dashed magenta), bolometer channels used by upgraded sensor (red and magenta), unused bolometer channels (faint gray), and gasmore » injection ports (green arrows).« less

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