Reversed-direction 2-point modelling applied to divertor conditions in DIII-D

J. H. Nichols; P. C. Stangeby; A. G. McLean; J. M. Canik; A. L. Moser; M. W. Shafer; H. Q. Wang

doi:10.1088/1361-6587/ad2b90

Reversed-direction 2-point modelling applied to divertor conditions in DIII-D

J. H. Nichols, P. C. Stangeby, A. G. McLean, J. M. Canik, A. L. Moser, M. W. Shafer, H. Q. Wang

Research output: Contribution to journal › Article › peer-review

Abstract

A predictive form of the extended 2-point model known as the ‘reverse 2-point model’, Rev2PM, is applied to a range of detachment levels in the open lower divertor of DIII-D, showing that the experimentally measured electron temperature (T_e ) and pressure (p_e ) at the divertor entrance can be calculated within 50% from target measurements, if and only if a posteriori corrections for convective heat flux are included in the model. Unlike the standard 2-point model, the Rev2PM calculates upstream scrape-off layer (SOL) quantities (such as separatrix T_e and p_e ) from target conditions (such as T_e and parallel heat flux), with volumetric power and momentum losses depending solely on target T_e . The Rev2PM is tested against a database of DIII-D inter-ELM divertor Thomson scattering measurements, built from a series of 6 MW, 1.3 MA, LSN H-mode discharges with varied main ion density, drift direction, and nitrogen puffing rate. Measured target T_e ranged from 0.4-25 eV over this database, and upstream T_e ranged from 5-60 eV. Poor agreement is found between upstream measurements and Rev2PM calculations that assume purely conductive parallel heat transport. However, introducing a posteriori corrections to account for convective heat transport brings the Rev2PM calculations within 50% of the measured upstream values across the dataset. These corrections imply that up to 99% of the parallel heat flux is carried by convection in detached conditions in the DIII-D open lower divertor, though further work is required to assess any potential dependencies on device size or divertor closure.

Original language	English
Article number	045013
Journal	Plasma Physics and Controlled Fusion
Volume	66
Issue number	4
DOIs	https://doi.org/10.1088/1361-6587/ad2b90
State	Published - Apr 2024

Funding

The authors gratefully acknowledge Bart Lomanowski and Jeremy Lore for useful discussions related to this work. This material is based upon work supported by the US Department of Energy, Office of Science, Office of Fusion Energy Sciences, using the DIII-D National Fusion Facility, a DOE Office of Science user facility, under Awards DE-FC02-04ER54698, DE-AC05-00OR22725, and DE-AC52-07NA27344. This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( www.energy.gov/doe-public-access-plan ).

Funders	Funder number
DOE Office of Science user facility	DE-AC05-00OR22725, DE-FC02-04ER54698, DE-AC52-07NA27344
U.S. Department of Energy
Office of Science
Fusion Energy Sciences

Keywords

2-point model
convective heat flux
divertor Thomson scattering
divertor detachment

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10.1088/1361-6587/ad2b90

Cite this

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title = "Reversed-direction 2-point modelling applied to divertor conditions in DIII-D",

abstract = "A predictive form of the extended 2-point model known as the {\textquoteleft}reverse 2-point model{\textquoteright}, Rev2PM, is applied to a range of detachment levels in the open lower divertor of DIII-D, showing that the experimentally measured electron temperature (Te ) and pressure (pe ) at the divertor entrance can be calculated within 50% from target measurements, if and only if a posteriori corrections for convective heat flux are included in the model. Unlike the standard 2-point model, the Rev2PM calculates upstream scrape-off layer (SOL) quantities (such as separatrix Te and pe ) from target conditions (such as Te and parallel heat flux), with volumetric power and momentum losses depending solely on target Te . The Rev2PM is tested against a database of DIII-D inter-ELM divertor Thomson scattering measurements, built from a series of 6 MW, 1.3 MA, LSN H-mode discharges with varied main ion density, drift direction, and nitrogen puffing rate. Measured target Te ranged from 0.4-25 eV over this database, and upstream Te ranged from 5-60 eV. Poor agreement is found between upstream measurements and Rev2PM calculations that assume purely conductive parallel heat transport. However, introducing a posteriori corrections to account for convective heat transport brings the Rev2PM calculations within 50% of the measured upstream values across the dataset. These corrections imply that up to 99% of the parallel heat flux is carried by convection in detached conditions in the DIII-D open lower divertor, though further work is required to assess any potential dependencies on device size or divertor closure.",

keywords = "2-point model, convective heat flux, divertor Thomson scattering, divertor detachment",

author = "Nichols, {J. H.} and Stangeby, {P. C.} and McLean, {A. G.} and Canik, {J. M.} and Moser, {A. L.} and Shafer, {M. W.} and Wang, {H. Q.}",

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AU - Nichols, J. H.

AU - Stangeby, P. C.

AU - McLean, A. G.

AU - Canik, J. M.

AU - Moser, A. L.

AU - Shafer, M. W.

AU - Wang, H. Q.

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N2 - A predictive form of the extended 2-point model known as the ‘reverse 2-point model’, Rev2PM, is applied to a range of detachment levels in the open lower divertor of DIII-D, showing that the experimentally measured electron temperature (Te ) and pressure (pe ) at the divertor entrance can be calculated within 50% from target measurements, if and only if a posteriori corrections for convective heat flux are included in the model. Unlike the standard 2-point model, the Rev2PM calculates upstream scrape-off layer (SOL) quantities (such as separatrix Te and pe ) from target conditions (such as Te and parallel heat flux), with volumetric power and momentum losses depending solely on target Te . The Rev2PM is tested against a database of DIII-D inter-ELM divertor Thomson scattering measurements, built from a series of 6 MW, 1.3 MA, LSN H-mode discharges with varied main ion density, drift direction, and nitrogen puffing rate. Measured target Te ranged from 0.4-25 eV over this database, and upstream Te ranged from 5-60 eV. Poor agreement is found between upstream measurements and Rev2PM calculations that assume purely conductive parallel heat transport. However, introducing a posteriori corrections to account for convective heat transport brings the Rev2PM calculations within 50% of the measured upstream values across the dataset. These corrections imply that up to 99% of the parallel heat flux is carried by convection in detached conditions in the DIII-D open lower divertor, though further work is required to assess any potential dependencies on device size or divertor closure.

AB - A predictive form of the extended 2-point model known as the ‘reverse 2-point model’, Rev2PM, is applied to a range of detachment levels in the open lower divertor of DIII-D, showing that the experimentally measured electron temperature (Te ) and pressure (pe ) at the divertor entrance can be calculated within 50% from target measurements, if and only if a posteriori corrections for convective heat flux are included in the model. Unlike the standard 2-point model, the Rev2PM calculates upstream scrape-off layer (SOL) quantities (such as separatrix Te and pe ) from target conditions (such as Te and parallel heat flux), with volumetric power and momentum losses depending solely on target Te . The Rev2PM is tested against a database of DIII-D inter-ELM divertor Thomson scattering measurements, built from a series of 6 MW, 1.3 MA, LSN H-mode discharges with varied main ion density, drift direction, and nitrogen puffing rate. Measured target Te ranged from 0.4-25 eV over this database, and upstream Te ranged from 5-60 eV. Poor agreement is found between upstream measurements and Rev2PM calculations that assume purely conductive parallel heat transport. However, introducing a posteriori corrections to account for convective heat transport brings the Rev2PM calculations within 50% of the measured upstream values across the dataset. These corrections imply that up to 99% of the parallel heat flux is carried by convection in detached conditions in the DIII-D open lower divertor, though further work is required to assess any potential dependencies on device size or divertor closure.

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ER -

Reversed-direction 2-point modelling applied to divertor conditions in DIII-D

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