The effectiveness of D2 pellet injection in reducing intra-ELM and inter-ELM tungsten divertor erosion rates in DIII-D during the Metal Rings Campaign

A. Cacheris; T. Abrams; L. R. Baylor; D. Shiraki; E. A. Unterberg; D. C. Donovan

doi:10.1088/1361-6587/acd026

The effectiveness of D₂ pellet injection in reducing intra-ELM and inter-ELM tungsten divertor erosion rates in DIII-D during the Metal Rings Campaign

A. Cacheris, T. Abrams, L. R. Baylor, D. Shiraki, E. A. Unterberg, D. C. Donovan

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

1 Scopus citations

Abstract

Edge localized modes (ELMs) in H-mode plasmas erode plasma-facing components (PFCs) and lead to impurities in the core, reducing confinement. This study analyzes D₂ pellet injection on the DIII-D fusion experiment used as an ELM mitigation technique applied during the 2016 tungsten Metal Rings Campaign to reduce W erosion during ELMs. The 400.9 nm photon wavelength line emission intensity of tungsten atoms (WI) filterscope channels and Langmuir probes were used to infer the gross erosion rate of tungsten-coated tiles installed in the divertor of DIII-D. D₂ mass injection rates ranging from 34 to 41 arbitrary units (A.U.) and no D₂ injection resulted in a similar total W erosion rate during ELMs (intra-ELM). On average, results show a 29% increase in the total gross W erosion rate with intermediate mass injection rates (∼13-23 A.U.) compared to the no pellets and the highest injection rate cases. On average, the fast D₂ mass injection rate cases had 15% less erosion in the inter-ELM phase than the case with no pellets. Generally, higher D₂ mass injection rates increased the ELM frequency, and the highest injection rates reduced the average erosion per ELM and fractional carbon impurities at the top of the pedestal by nearly 40% when compared to the no-pellet case. As expected, a higher D₂ pellet injection rate led to a higher plasma density and lower plasma temperature in the divertor. Additionally, an increasing divertor inter-ELM plasma electron density directly correlated to more frequent pellet injection and a decrease in both the average gross intra-ELM W erosion and the total gross intra-ELM W erosion rate. Simulations of intra-ELM erosion using the ‘free-streaming plus recycling model’ (FSRM) underestimate W erosion during pellet injection by about 30% on average. The discrepancies between the experimental measurements and the FSRM intra-ELM W erosion predictions are postulated to be due to C/W material mixing. A simple analytic mixed-material model is presented and results in better agreement with the experimental data. These results highlight the importance of incorporating the effects of a mixed-material layer in the analysis of PFC erosion.

Original language	English
Article number	085010
Journal	Plasma Physics and Controlled Fusion
Volume	65
Issue number	8
DOIs	https://doi.org/10.1088/1361-6587/acd026
State	Published - Aug 2023

Funding

This material is based upon work supported by the U.S. 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 Award(s) DE-SC0019256 (UTK), DE-FC02-04ER54698 (DIII-D), and DE-AC05-00OR22725 (ORNL). Special thanks are given to Dr Tyler Abrams and Dr David Donovan, the DIII-D team, and the University of Tennessee at Knoxville for collaboration. Disclaimer: This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

Funders	Funder number
United States Government
U.S. Department of Energy
Office of Science	DE-SC0019256
Fusion Energy Sciences
Oak Ridge National Laboratory
University of Tennessee, Knoxville	DE-AC05-00OR22725, DE-FC02-04ER54698

Keywords

Metal Rings Campaign (MRC)
between ELMs (inter-ELM)
during ELMs (intra-ELM)
edge localized modes (ELMs)
free stream recycling model (FSRM)
plasma electron ion density (n )
plasma electron/ion temperature (T )

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

Access to Document

10.1088/1361-6587/acd026

Cite this

@article{f9eef2af8abe4bfbac0f9bd480229823,

title = "The effectiveness of D2 pellet injection in reducing intra-ELM and inter-ELM tungsten divertor erosion rates in DIII-D during the Metal Rings Campaign",

abstract = "Edge localized modes (ELMs) in H-mode plasmas erode plasma-facing components (PFCs) and lead to impurities in the core, reducing confinement. This study analyzes D2 pellet injection on the DIII-D fusion experiment used as an ELM mitigation technique applied during the 2016 tungsten Metal Rings Campaign to reduce W erosion during ELMs. The 400.9 nm photon wavelength line emission intensity of tungsten atoms (WI) filterscope channels and Langmuir probes were used to infer the gross erosion rate of tungsten-coated tiles installed in the divertor of DIII-D. D2 mass injection rates ranging from 34 to 41 arbitrary units (A.U.) and no D2 injection resulted in a similar total W erosion rate during ELMs (intra-ELM). On average, results show a 29% increase in the total gross W erosion rate with intermediate mass injection rates (∼13-23 A.U.) compared to the no pellets and the highest injection rate cases. On average, the fast D2 mass injection rate cases had 15% less erosion in the inter-ELM phase than the case with no pellets. Generally, higher D2 mass injection rates increased the ELM frequency, and the highest injection rates reduced the average erosion per ELM and fractional carbon impurities at the top of the pedestal by nearly 40% when compared to the no-pellet case. As expected, a higher D2 pellet injection rate led to a higher plasma density and lower plasma temperature in the divertor. Additionally, an increasing divertor inter-ELM plasma electron density directly correlated to more frequent pellet injection and a decrease in both the average gross intra-ELM W erosion and the total gross intra-ELM W erosion rate. Simulations of intra-ELM erosion using the {\textquoteleft}free-streaming plus recycling model{\textquoteright} (FSRM) underestimate W erosion during pellet injection by about 30% on average. The discrepancies between the experimental measurements and the FSRM intra-ELM W erosion predictions are postulated to be due to C/W material mixing. A simple analytic mixed-material model is presented and results in better agreement with the experimental data. These results highlight the importance of incorporating the effects of a mixed-material layer in the analysis of PFC erosion.",

keywords = "Metal Rings Campaign (MRC), between ELMs (inter-ELM), during ELMs (intra-ELM), edge localized modes (ELMs), free stream recycling model (FSRM), plasma electron ion density (n ), plasma electron/ion temperature (T )",

author = "A. Cacheris and T. Abrams and Baylor, {L. R.} and D. Shiraki and Unterberg, {E. A.} and Donovan, {D. C.}",

note = "Publisher Copyright: {\textcopyright} 2023 The Author(s). Published by IOP Publishing Ltd",

year = "2023",

month = aug,

doi = "10.1088/1361-6587/acd026",

language = "English",

volume = "65",

journal = "Plasma Physics and Controlled Fusion",

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T1 - The effectiveness of D2 pellet injection in reducing intra-ELM and inter-ELM tungsten divertor erosion rates in DIII-D during the Metal Rings Campaign

AU - Cacheris, A.

AU - Abrams, T.

AU - Baylor, L. R.

AU - Shiraki, D.

AU - Unterberg, E. A.

AU - Donovan, D. C.

PY - 2023/8

Y1 - 2023/8

N2 - Edge localized modes (ELMs) in H-mode plasmas erode plasma-facing components (PFCs) and lead to impurities in the core, reducing confinement. This study analyzes D2 pellet injection on the DIII-D fusion experiment used as an ELM mitigation technique applied during the 2016 tungsten Metal Rings Campaign to reduce W erosion during ELMs. The 400.9 nm photon wavelength line emission intensity of tungsten atoms (WI) filterscope channels and Langmuir probes were used to infer the gross erosion rate of tungsten-coated tiles installed in the divertor of DIII-D. D2 mass injection rates ranging from 34 to 41 arbitrary units (A.U.) and no D2 injection resulted in a similar total W erosion rate during ELMs (intra-ELM). On average, results show a 29% increase in the total gross W erosion rate with intermediate mass injection rates (∼13-23 A.U.) compared to the no pellets and the highest injection rate cases. On average, the fast D2 mass injection rate cases had 15% less erosion in the inter-ELM phase than the case with no pellets. Generally, higher D2 mass injection rates increased the ELM frequency, and the highest injection rates reduced the average erosion per ELM and fractional carbon impurities at the top of the pedestal by nearly 40% when compared to the no-pellet case. As expected, a higher D2 pellet injection rate led to a higher plasma density and lower plasma temperature in the divertor. Additionally, an increasing divertor inter-ELM plasma electron density directly correlated to more frequent pellet injection and a decrease in both the average gross intra-ELM W erosion and the total gross intra-ELM W erosion rate. Simulations of intra-ELM erosion using the ‘free-streaming plus recycling model’ (FSRM) underestimate W erosion during pellet injection by about 30% on average. The discrepancies between the experimental measurements and the FSRM intra-ELM W erosion predictions are postulated to be due to C/W material mixing. A simple analytic mixed-material model is presented and results in better agreement with the experimental data. These results highlight the importance of incorporating the effects of a mixed-material layer in the analysis of PFC erosion.

AB - Edge localized modes (ELMs) in H-mode plasmas erode plasma-facing components (PFCs) and lead to impurities in the core, reducing confinement. This study analyzes D2 pellet injection on the DIII-D fusion experiment used as an ELM mitigation technique applied during the 2016 tungsten Metal Rings Campaign to reduce W erosion during ELMs. The 400.9 nm photon wavelength line emission intensity of tungsten atoms (WI) filterscope channels and Langmuir probes were used to infer the gross erosion rate of tungsten-coated tiles installed in the divertor of DIII-D. D2 mass injection rates ranging from 34 to 41 arbitrary units (A.U.) and no D2 injection resulted in a similar total W erosion rate during ELMs (intra-ELM). On average, results show a 29% increase in the total gross W erosion rate with intermediate mass injection rates (∼13-23 A.U.) compared to the no pellets and the highest injection rate cases. On average, the fast D2 mass injection rate cases had 15% less erosion in the inter-ELM phase than the case with no pellets. Generally, higher D2 mass injection rates increased the ELM frequency, and the highest injection rates reduced the average erosion per ELM and fractional carbon impurities at the top of the pedestal by nearly 40% when compared to the no-pellet case. As expected, a higher D2 pellet injection rate led to a higher plasma density and lower plasma temperature in the divertor. Additionally, an increasing divertor inter-ELM plasma electron density directly correlated to more frequent pellet injection and a decrease in both the average gross intra-ELM W erosion and the total gross intra-ELM W erosion rate. Simulations of intra-ELM erosion using the ‘free-streaming plus recycling model’ (FSRM) underestimate W erosion during pellet injection by about 30% on average. The discrepancies between the experimental measurements and the FSRM intra-ELM W erosion predictions are postulated to be due to C/W material mixing. A simple analytic mixed-material model is presented and results in better agreement with the experimental data. These results highlight the importance of incorporating the effects of a mixed-material layer in the analysis of PFC erosion.

KW - Metal Rings Campaign (MRC)

KW - between ELMs (inter-ELM)

KW - during ELMs (intra-ELM)

KW - edge localized modes (ELMs)

KW - free stream recycling model (FSRM)

KW - plasma electron ion density (n )

KW - plasma electron/ion temperature (T )

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DO - 10.1088/1361-6587/acd026

M3 - Article

AN - SCOPUS:85163879810

SN - 0741-3335

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JO - Plasma Physics and Controlled Fusion

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