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Title: Real-time pedestal optimization and ELM control with 3D fields and gas flows on DIII-D

Abstract

The capabilities of the DIII-D tokamak's plasma control system (PCS) were expanded to allow for pedestal optimization and edge localized mode (ELM) control. Three proof of principle control schemes are presented herein that were successfully implemented and tested. These use multiple inputs from real-time (RT) diagnostics like a $$D_\alpha$$ based ELM monitor and edge profile measurements from Thomson scattering (TS) as well as 3D, i.e. non-axisymmetric, magnetic fields and gas puffs as actuators to regulate the density pedestal. The first scheme targets to optimize the access of ELM suppression induced by non-axisymmetric magnetic perturbations (MPs). The conducted set of experiments identifies a path dependence of plasma confinement on the applied MP amplitude. The controller aims to transition into ELM suppression at the minimum 3D field amplitude and reduces it further afterwards, allowing for partial confinement recovery. Another pedestal control scheme is deployed to compensate the density 'pump-out' in MP ELM suppression by regulating the gas puff. This uses RT TS diagnostic data, extracting the pedestal height from the electron density ($$n_{\mathrm{e}}$$) profiles and enables studies of the transition into and out of MP ELM suppression at constant density. A limit cycle behavior of edge rotation and MP amplitude persists under these conditions. The third control scheme combines MPs and gas puffs as actuators to perform pedestal density trajectory control to access Super high confinement mode (H-mode) and furthermore, allowing the integration of a radiative divertor in this regime. While MPs mainly impact the pedestal top density, the control scheme allows to loosen the tight coupling of pedestal top and separatrix density evolution. With respect to ITER, the achieved results emphasize the need for an advanced control system to keep MP amplitude close to but above the ELM suppression threshold at all times, enabling high confinement and, respectively, at high fusion energy gain factor (Q). Lastly, pedestal control enables detailed physics studies in present-day tokamaks and allows the exploration of core-edge integrated plasma scenarios.

Authors:
ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [3]; ORCiD logo [2]; ORCiD logo [3]; ORCiD logo [2];  [4]; ORCiD logo [3]; ORCiD logo [3]; ORCiD logo [2];  [2]; ORCiD logo [3]; ORCiD logo [2]; ORCiD logo [2]; ORCiD logo [5]; ORCiD logo [6]
+ Show Author Affiliations
  1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Princeton Univ., NJ (United States)
  2. General Atomics, San Diego, CA (United States)
  3. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  4. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  6. Princeton Univ., NJ (United States)
Publication Date:
Research Org.:
General Atomics, San Diego, CA (United States); Princeton Univ., NJ (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
Contributing Org.:
DIII-D team
OSTI Identifier:
1631424
Alternate Identifier(s):
OSTI ID: 1615725; OSTI ID: 1631484
Grant/Contract Number:  
FC02-04ER54698; AC02-09CH11466; AC52-07NA27344; AC05-00OR22725; SC0015878; SC0015480
Resource Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 60; Journal Issue: 7; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Tokamak; super H-mode; edge localized modes; 3D fields

Citation Formats

Laggner, F. M., Eldon, D., Nelson, A. O., Paz-Soldan, C., Bortolon, A., Evans, T. E., Fenstermacher, M. E., Grierson, B. A., Hu, Q., Humphreys, D. A., Hyatt, A. W., Nazikian, R., Meneghini, O., Snyder, P. B., Unterberg, E. A., and Kolemen, E. Real-time pedestal optimization and ELM control with 3D fields and gas flows on DIII-D. United States: N. p., 2020. Web. doi:10.1088/1741-4326/ab88e1.
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Laggner, F. M., Eldon, D., Nelson, A. O., Paz-Soldan, C., Bortolon, A., Evans, T. E., Fenstermacher, M. E., Grierson, B. A., Hu, Q., Humphreys, D. A., Hyatt, A. W., Nazikian, R., Meneghini, O., Snyder, P. B., Unterberg, E. A., & Kolemen, E. Real-time pedestal optimization and ELM control with 3D fields and gas flows on DIII-D. United States. doi:https://doi.org/10.1088/1741-4326/ab88e1
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Laggner, F. M., Eldon, D., Nelson, A. O., Paz-Soldan, C., Bortolon, A., Evans, T. E., Fenstermacher, M. E., Grierson, B. A., Hu, Q., Humphreys, D. A., Hyatt, A. W., Nazikian, R., Meneghini, O., Snyder, P. B., Unterberg, E. A., and Kolemen, E. Wed . "Real-time pedestal optimization and ELM control with 3D fields and gas flows on DIII-D". United States. doi:https://doi.org/10.1088/1741-4326/ab88e1.
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@article{osti_1631424,
title = {Real-time pedestal optimization and ELM control with 3D fields and gas flows on DIII-D},
author = {Laggner, F. M. and Eldon, D. and Nelson, A. O. and Paz-Soldan, C. and Bortolon, A. and Evans, T. E. and Fenstermacher, M. E. and Grierson, B. A. and Hu, Q. and Humphreys, D. A. and Hyatt, A. W. and Nazikian, R. and Meneghini, O. and Snyder, P. B. and Unterberg, E. A. and Kolemen, E.},
abstractNote = {The capabilities of the DIII-D tokamak's plasma control system (PCS) were expanded to allow for pedestal optimization and edge localized mode (ELM) control. Three proof of principle control schemes are presented herein that were successfully implemented and tested. These use multiple inputs from real-time (RT) diagnostics like a $D_\alpha$ based ELM monitor and edge profile measurements from Thomson scattering (TS) as well as 3D, i.e. non-axisymmetric, magnetic fields and gas puffs as actuators to regulate the density pedestal. The first scheme targets to optimize the access of ELM suppression induced by non-axisymmetric magnetic perturbations (MPs). The conducted set of experiments identifies a path dependence of plasma confinement on the applied MP amplitude. The controller aims to transition into ELM suppression at the minimum 3D field amplitude and reduces it further afterwards, allowing for partial confinement recovery. Another pedestal control scheme is deployed to compensate the density 'pump-out' in MP ELM suppression by regulating the gas puff. This uses RT TS diagnostic data, extracting the pedestal height from the electron density ($n_{\mathrm{e}}$) profiles and enables studies of the transition into and out of MP ELM suppression at constant density. A limit cycle behavior of edge rotation and MP amplitude persists under these conditions. The third control scheme combines MPs and gas puffs as actuators to perform pedestal density trajectory control to access Super high confinement mode (H-mode) and furthermore, allowing the integration of a radiative divertor in this regime. While MPs mainly impact the pedestal top density, the control scheme allows to loosen the tight coupling of pedestal top and separatrix density evolution. With respect to ITER, the achieved results emphasize the need for an advanced control system to keep MP amplitude close to but above the ELM suppression threshold at all times, enabling high confinement and, respectively, at high fusion energy gain factor (Q). Lastly, pedestal control enables detailed physics studies in present-day tokamaks and allows the exploration of core-edge integrated plasma scenarios.},
doi = {10.1088/1741-4326/ab88e1},
journal = {Nuclear Fusion},
number = 7,
volume = 60,
place = {United States},
year = {2020},
month = {5}
}
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DOI:  https://doi.org/10.1088/1741-4326/ab88e1
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