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Title: SOL effects on the pedestal structure in DIII-D discharges

Abstract

SOLPS analysis explains the differences in pedestal structure associated with different ion ∇B drift directions in DIII-D. Core transport models predict that fusion power scales roughly as the square of the pressure at the top of the pedestal, so understanding the effects that determine pedestal structure in steady-state operational scenarios is important to projecting scenarios developed in DIII-D to ITER and other devices. Both experiments and modeling indicate that scrape off layer (SOL) conditions are important in optimizing the pedestal structure for high-beta steady-state scenarios. The SOLPS code is used to provide interpretive analysis of the pedestal and SOL to examine the nature of flows and fueling on the pedestal structure including the effects of drifts in the fluid model. This analysis shows that flows driven by the ion ∇B drift are outward when this drift is toward the x-point in a single-null divertor configuration (favorable ∇B direction for reduced H-mode power threshold), and inward when the drift is away from the x-point (unfavorable ∇B direction). It is hypothesized that these flows decrease the density gradient in the pedestal in the favorable direction, thereby stabilizing the kinetic ballooning mode (KBM) and increasing the pedestal width. Comparisons of pedestal structures inmore » similarly shaped DIII-D steady-state plasmas confirm this change, showing increased density pedestal width and lower peak density and lower separatrix density with the favorable drift direction. The pedestal temperature is higher in the lower density case, resulting in an increased pedestal pressure, which indicates that the increased particle flux does not significantly degrade energy confinement. Modeling of cases with constant ∇B drift direction but changing between the more open lower divertor and more closed upper divertor show that there is increased fueling inside the pedestal with the more open geometry. As a result, the pedestal fueling rate for both attached and detached cases is always lower with more closed divertor geometry than in any cases with more open geometry.« less

Authors:
ORCiD logo [1];  [2]; ORCiD logo [1];  [2]; ORCiD logo [1];  [2]; ORCiD logo [1];  [1];  [2]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. General Atomics, La Jolla, CA (United States)
Publication Date:
Research Org.:
General Atomics, San Diego, CA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1394293
Alternate Identifier(s):
OSTI ID: 1373410
Grant/Contract Number:  
FC02-04ER54698; AC05-00OR22725
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 57; 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; pedestal structure; SOL modeling; drift effects; divertor closure

Citation Formats

Sontag, Aaron C., Chen, Xi, Canik, John, Leonard, Anthony, Lore, Jeremy D., Moser, Auna L., Murakami, M., Park, J. M., and Petty, Clinton. SOL effects on the pedestal structure in DIII-D discharges. United States: N. p., 2017. Web. doi:10.1088/1741-4326/aa6cb6.
Sontag, Aaron C., Chen, Xi, Canik, John, Leonard, Anthony, Lore, Jeremy D., Moser, Auna L., Murakami, M., Park, J. M., & Petty, Clinton. SOL effects on the pedestal structure in DIII-D discharges. United States. doi:10.1088/1741-4326/aa6cb6.
Sontag, Aaron C., Chen, Xi, Canik, John, Leonard, Anthony, Lore, Jeremy D., Moser, Auna L., Murakami, M., Park, J. M., and Petty, Clinton. Wed . "SOL effects on the pedestal structure in DIII-D discharges". United States. doi:10.1088/1741-4326/aa6cb6. https://www.osti.gov/servlets/purl/1394293.
@article{osti_1394293,
title = {SOL effects on the pedestal structure in DIII-D discharges},
author = {Sontag, Aaron C. and Chen, Xi and Canik, John and Leonard, Anthony and Lore, Jeremy D. and Moser, Auna L. and Murakami, M. and Park, J. M. and Petty, Clinton},
abstractNote = {SOLPS analysis explains the differences in pedestal structure associated with different ion ∇B drift directions in DIII-D. Core transport models predict that fusion power scales roughly as the square of the pressure at the top of the pedestal, so understanding the effects that determine pedestal structure in steady-state operational scenarios is important to projecting scenarios developed in DIII-D to ITER and other devices. Both experiments and modeling indicate that scrape off layer (SOL) conditions are important in optimizing the pedestal structure for high-beta steady-state scenarios. The SOLPS code is used to provide interpretive analysis of the pedestal and SOL to examine the nature of flows and fueling on the pedestal structure including the effects of drifts in the fluid model. This analysis shows that flows driven by the ion ∇B drift are outward when this drift is toward the x-point in a single-null divertor configuration (favorable ∇B direction for reduced H-mode power threshold), and inward when the drift is away from the x-point (unfavorable ∇B direction). It is hypothesized that these flows decrease the density gradient in the pedestal in the favorable direction, thereby stabilizing the kinetic ballooning mode (KBM) and increasing the pedestal width. Comparisons of pedestal structures in similarly shaped DIII-D steady-state plasmas confirm this change, showing increased density pedestal width and lower peak density and lower separatrix density with the favorable drift direction. The pedestal temperature is higher in the lower density case, resulting in an increased pedestal pressure, which indicates that the increased particle flux does not significantly degrade energy confinement. Modeling of cases with constant ∇B drift direction but changing between the more open lower divertor and more closed upper divertor show that there is increased fueling inside the pedestal with the more open geometry. As a result, the pedestal fueling rate for both attached and detached cases is always lower with more closed divertor geometry than in any cases with more open geometry.},
doi = {10.1088/1741-4326/aa6cb6},
journal = {Nuclear Fusion},
number = 7,
volume = 57,
place = {United States},
year = {Wed May 24 00:00:00 EDT 2017},
month = {Wed May 24 00:00:00 EDT 2017}
}

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