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Title: Mitigation of divertor heat flux by high-frequency ELM pacing with non-fuel pellet injection in DIII-D

Abstract

Experiments have been conducted on DIII-D investigating high repetition rate injection of non-fuel pellets as a tool for pacing Edge Localized Modes (ELMs) and mitigating their transient divertor heat loads. Effective ELM pacing was obtained with injection of Li granules in different H-mode scenarios, at frequencies 3–5 times larger than the natural ELM frequency, with subsequent reduction of strike-point heat flux. However, in scenarios with high pedestal density (~6 × 10 19 m –3), the magnitude of granule triggered ELMs shows a broad distribution, in terms of stored energy loss and peak heat flux, challenging the effectiveness of ELM mitigation. Furthermore, transient heat-flux deposition correlated with granule injections was observed far from the strike-points. As a result, field line tracing suggest this phenomenon to be consistent with particle loss into the mid-plane far scrape-off layer, at toroidal location of the granule injection.

Authors:
ORCiD logo [1]; ORCiD logo [1];  [1];  [1];  [1];  [2];  [2];  [3]; ORCiD logo [1];  [4];  [4];  [1];  [3];  [2]
  1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  3. General Atomics, San Diego, CA (United States)
  4. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); General Atomics, San Diego, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24); USDOE Office of Nuclear Energy (NE)
Contributing Org.:
DIII-D team
OSTI Identifier:
1349223
Alternate Identifier(s):
OSTI ID: 1374820
Grant/Contract Number:
AC02-09CH114661; AC05-00OR227252; FC02-04ER546983; FG02-06ER54867; AC52-07NA273444; FC02-04ER54698; AC02-09CH11466; AC05-00OR22725; AC52-07NA27344
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nuclear Materials and Energy
Additional Journal Information:
Journal Volume: 12; Related Information: DIII-D data shown in this paper can be obtained in digital format by following the links at https://fusion.gat.com/global/D3D_DMP.; Journal ID: ISSN 2352-1791
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Bortolon, A., Maingi, R., Mansfield, D. K., Nagy, A., Roquemore, A. L., Baylor, L. R., Commaux, N., Jackson, G. L., Lunsford, R., Lasnier, C. J., Makowski, M. J., Nazikian, R., Osborne, T. H., and Shiraki, D.. Mitigation of divertor heat flux by high-frequency ELM pacing with non-fuel pellet injection in DIII-D. United States: N. p., 2017. Web. doi:10.1016/j.nme.2017.01.003.
Bortolon, A., Maingi, R., Mansfield, D. K., Nagy, A., Roquemore, A. L., Baylor, L. R., Commaux, N., Jackson, G. L., Lunsford, R., Lasnier, C. J., Makowski, M. J., Nazikian, R., Osborne, T. H., & Shiraki, D.. Mitigation of divertor heat flux by high-frequency ELM pacing with non-fuel pellet injection in DIII-D. United States. doi:10.1016/j.nme.2017.01.003.
Bortolon, A., Maingi, R., Mansfield, D. K., Nagy, A., Roquemore, A. L., Baylor, L. R., Commaux, N., Jackson, G. L., Lunsford, R., Lasnier, C. J., Makowski, M. J., Nazikian, R., Osborne, T. H., and Shiraki, D.. Thu . "Mitigation of divertor heat flux by high-frequency ELM pacing with non-fuel pellet injection in DIII-D". United States. doi:10.1016/j.nme.2017.01.003. https://www.osti.gov/servlets/purl/1349223.
@article{osti_1349223,
title = {Mitigation of divertor heat flux by high-frequency ELM pacing with non-fuel pellet injection in DIII-D},
author = {Bortolon, A. and Maingi, R. and Mansfield, D. K. and Nagy, A. and Roquemore, A. L. and Baylor, L. R. and Commaux, N. and Jackson, G. L. and Lunsford, R. and Lasnier, C. J. and Makowski, M. J. and Nazikian, R. and Osborne, T. H. and Shiraki, D.},
abstractNote = {Experiments have been conducted on DIII-D investigating high repetition rate injection of non-fuel pellets as a tool for pacing Edge Localized Modes (ELMs) and mitigating their transient divertor heat loads. Effective ELM pacing was obtained with injection of Li granules in different H-mode scenarios, at frequencies 3–5 times larger than the natural ELM frequency, with subsequent reduction of strike-point heat flux. However, in scenarios with high pedestal density (~6 × 1019 m–3), the magnitude of granule triggered ELMs shows a broad distribution, in terms of stored energy loss and peak heat flux, challenging the effectiveness of ELM mitigation. Furthermore, transient heat-flux deposition correlated with granule injections was observed far from the strike-points. As a result, field line tracing suggest this phenomenon to be consistent with particle loss into the mid-plane far scrape-off layer, at toroidal location of the granule injection.},
doi = {10.1016/j.nme.2017.01.003},
journal = {Nuclear Materials and Energy},
number = ,
volume = 12,
place = {United States},
year = {Thu Mar 23 00:00:00 EDT 2017},
month = {Thu Mar 23 00:00:00 EDT 2017}
}

Journal Article:
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  • Experiments have been conducted on DIII-D investigating high repetition rate injection of non-fuel pellets as a tool for pacing Edge Localized Modes (ELMs) and mitigating their transient divertor heat loads. Effective ELM pacing was obtained with injection of Li granules in different H-mode scenarios, at frequencies 3-5 times larger than the natural ELM frequency, with subsequent reduction of strike-point heat flux [Bortolon et al, Nucl. Fus., 56, 056008, 2016]. However, in scenarios with high pedestal density (~6×10 19 m -3), the magnitude of granule triggered ELMs shows a broad distribution, in terms of stored energy loss and peak heat flux,more » challenging the effectiveness of ELM mitigation. Furthermore, transient heat-flux deposition correlated with granule injections was observed far from the strike-points. Field line tracing suggest this phenomenon to be consistent with particle loss into the mid-plane far scrape-off layer, at toroidal location of the granule injection.« less
  • . The injection of high repetition rate deuterium pellets is shown to trigger high-frequency edge localized modes (ELMs) in otherwise low natural ELM frequency H-mode deuterium discharges in the DIII-D tokamak. The resulting triggered ELMs have significantly lower energy and particle fluxes to the divertor than the natural ELMs. The plasma global energy confinement and density are not strongly affected by the pellet perturbations. The plasma core impurity density is strongly reduced with the application of the pellets. These experiments were performed in plasmas designed to match the ITER baseline configuration in shape and normalized operation with input power justmore » above the H-mode power threshold. This strongly reduced ELM intensity shows promise for exploitation in ITER to control ELM size while maintaining high plasma purity and performance.« less
  • A newly installed Lithium Granule Injector (LGI) was used to pace edge localized modes (ELM) in DIII-D. ELM pacing efficiency was studied injecting lithium granules of nominal diameter 0.3–0.9mm, speed of 50–120 m s -1 and average injection rates up to 100 Hz for 0.9mm granules and up to 700 Hz for 0.3mm granules. The efficiency of ELM triggering was found to depend strongly on size of the injected granules, with triggering efficiency close to 100% obtained with 0.9mm diameter granules, lower with smaller sizes, and weakly depending on granule velocity. Robust ELM pacing was demonstrated in ITER-like plasmas formore » the entire shot length, at ELM frequencies 3–5 times larger than the ‘natural’ ELM frequency observed in reference discharges. Within the range of ELM frequencies obtained, the peak ELM heat flux at the outer strike point was reduced with increasing pacing frequency. The peak heat flux reduction at the inner strike point appears to saturate at high pacing frequency. Lithium was found in the plasma core, with a concurrent reduction of metallic impurities and carbon. Altogether, high frequency ELM pacing using the lithium granule injection appears to be compatible with both H-mode energy confinement and attractive H-mode pedestal characteristics, but further assessment is need« less