ERO modelling of net and gross erosion of marker samples exposed to L-mode plasmas on ASDEX Upgrade

Antti Hakola; A. Keitaanranta; Heikki Kumpulainen; Aapeli Lahtinen; Jari Likonen; M. Balden; M. Cavedon; K. Krieger; Markus Airila; M. Groth; ASDEX Upgrade Team; EUROfusion MST1 Team

doi:10.1016/j.nme.2020.100863

ERO modelling of net and gross erosion of marker samples exposed to L-mode plasmas on ASDEX Upgrade

Antti Hakola (Corresponding Author), A. Keitaanranta, Heikki Kumpulainen, Aapeli Lahtinen, Jari Likonen, M. Balden, M. Cavedon, K. Krieger, Markus Airila, M. Groth, ASDEX Upgrade Team, EUROfusion MST1 Team

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Abstract

In this paper, we report experimental and numerical investigations of gross and net erosion of gold (Au) and molybdenum (Mo), proxies for the common plasma-facing material tungsten (W), during L-mode plasma discharges in deuterium (D) in the outer strike-point region of the ASDEX Upgrade tokamak. To this end, erosion profiles of different marker spots (for Au, dimensions 1 × 1 and 5 × 5 mm²) and marker coatings (for Mo) have been determined and modelled using the ERO code. The smaller marker spots were designed to quantify the gross-erosion rate while on the bigger markers local prompt re-deposition of Au allowed obtaining data on net erosion. The experimental results indicate relatively uniform erosion profiles across the marker spots or coatings, very little re-deposition elsewhere, and the largest erosion taking place close to the strike point. Compared to W, the markers show up to 15 times higher net erosion but no major differences in the poloidal migration lengths of Au and W can be seen. Gold thus appears to be a proper choice for studying migration of W in the divertor region. The ERO simulations with different background plasmas are able to reproduce the main features of the experimental net erosion profile of Au. Of the studied parameters, electron temperature has the strongest impact on erosion: doubling the temperature enhances erosion by a factor of 2.5–3. In contrast, for Mo, the simulated net erosion is ~ 3 times smaller than what experimental data indicate. The discrepancies can be attributed to the deviations of the background plasma profiles from the measured ones as well as to the applied models or approximations for the ion temperature, plasma potential, and sheath characteristics in ERO. In addition, the surrounding areas of the marker samples being covered with impurities and W from previous experiments may have considerably reduced the actual re-deposition of Mo. All the simulations predict a toroidal tail of re-deposited particles, downstream of the markers, but the particle density seems to be below the experimental detection threshold. The comparison between the 1 × 1 mm² and 5 × 5 mm² marker spots further reveal that re-deposition drops from >50% to <40% when decreasing the marker size. This indicates that small enough marker samples can be used for accurately determining gross erosion in ASDEX Upgrade.

Original language	English
Article number	100863
Journal	Nuclear Materials and Energy
Volume	25
Early online date	1 Dec 2020
DOIs	https://doi.org/10.1016/j.nme.2020.100863
Publication status	Published - Dec 2020
MoE publication type	A1 Journal article-refereed

Funding

This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. Part of the work performed under EUROfusion WP PFC. The authors would like to thank Dr. Volker Rohde for photographs of the exposed marker samples as well as Prof. Rudolf Neu for preparing the discharge program.

Keywords

ASDEX Upgrade
Erosion
L-mode
Marker samples
Material migration

UN SDGs

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

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Hakola, A., Keitaanranta, A., Kumpulainen, H., Lahtinen, A., Likonen, J., Balden, M., Cavedon, M., Krieger, K., Airila, M., Groth, M., ASDEX Upgrade Team, & EUROfusion MST1 Team (2020). ERO modelling of net and gross erosion of marker samples exposed to L-mode plasmas on ASDEX Upgrade. Nuclear Materials and Energy, 25, Article 100863. https://doi.org/10.1016/j.nme.2020.100863

@article{123b03e721274fb49f723822fdc99fc2,

title = "ERO modelling of net and gross erosion of marker samples exposed to L-mode plasmas on ASDEX Upgrade",

abstract = "In this paper, we report experimental and numerical investigations of gross and net erosion of gold (Au) and molybdenum (Mo), proxies for the common plasma-facing material tungsten (W), during L-mode plasma discharges in deuterium (D) in the outer strike-point region of the ASDEX Upgrade tokamak. To this end, erosion profiles of different marker spots (for Au, dimensions 1 × 1 and 5 × 5 mm2) and marker coatings (for Mo) have been determined and modelled using the ERO code. The smaller marker spots were designed to quantify the gross-erosion rate while on the bigger markers local prompt re-deposition of Au allowed obtaining data on net erosion. The experimental results indicate relatively uniform erosion profiles across the marker spots or coatings, very little re-deposition elsewhere, and the largest erosion taking place close to the strike point. Compared to W, the markers show up to 15 times higher net erosion but no major differences in the poloidal migration lengths of Au and W can be seen. Gold thus appears to be a proper choice for studying migration of W in the divertor region. The ERO simulations with different background plasmas are able to reproduce the main features of the experimental net erosion profile of Au. Of the studied parameters, electron temperature has the strongest impact on erosion: doubling the temperature enhances erosion by a factor of 2.5–3. In contrast, for Mo, the simulated net erosion is ~ 3 times smaller than what experimental data indicate. The discrepancies can be attributed to the deviations of the background plasma profiles from the measured ones as well as to the applied models or approximations for the ion temperature, plasma potential, and sheath characteristics in ERO. In addition, the surrounding areas of the marker samples being covered with impurities and W from previous experiments may have considerably reduced the actual re-deposition of Mo. All the simulations predict a toroidal tail of re-deposited particles, downstream of the markers, but the particle density seems to be below the experimental detection threshold. The comparison between the 1 × 1 mm2 and 5 × 5 mm2 marker spots further reveal that re-deposition drops from >50% to <40% when decreasing the marker size. This indicates that small enough marker samples can be used for accurately determining gross erosion in ASDEX Upgrade.",

keywords = "ASDEX Upgrade, Erosion, L-mode, Marker samples, Material migration",

author = "Antti Hakola and A. Keitaanranta and Heikki Kumpulainen and Aapeli Lahtinen and Jari Likonen and M. Balden and M. Cavedon and K. Krieger and Markus Airila and M. Groth and {ASDEX Upgrade Team} and {EUROfusion MST1 Team}",

note = "Funding Information: This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. Part of the work performed under EUROfusion WP PFC. The authors would like to thank Dr. Volker Rohde for photographs of the exposed marker samples as well as Prof. Rudolf Neu for preparing the discharge program.",

year = "2020",

month = dec,

doi = "10.1016/j.nme.2020.100863",

language = "English",

volume = "25",

journal = "Nuclear Materials and Energy",

issn = "2352-1791",

publisher = "Elsevier",

}

TY - JOUR

T1 - ERO modelling of net and gross erosion of marker samples exposed to L-mode plasmas on ASDEX Upgrade

AU - Hakola, Antti

AU - Keitaanranta, A.

AU - Kumpulainen, Heikki

AU - Lahtinen, Aapeli

AU - Likonen, Jari

AU - Balden, M.

AU - Cavedon, M.

AU - Krieger, K.

AU - Airila, Markus

AU - Groth, M.

AU - ASDEX Upgrade Team

AU - EUROfusion MST1 Team

N1 - Funding Information: This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. Part of the work performed under EUROfusion WP PFC. The authors would like to thank Dr. Volker Rohde for photographs of the exposed marker samples as well as Prof. Rudolf Neu for preparing the discharge program.

PY - 2020/12

Y1 - 2020/12

N2 - In this paper, we report experimental and numerical investigations of gross and net erosion of gold (Au) and molybdenum (Mo), proxies for the common plasma-facing material tungsten (W), during L-mode plasma discharges in deuterium (D) in the outer strike-point region of the ASDEX Upgrade tokamak. To this end, erosion profiles of different marker spots (for Au, dimensions 1 × 1 and 5 × 5 mm2) and marker coatings (for Mo) have been determined and modelled using the ERO code. The smaller marker spots were designed to quantify the gross-erosion rate while on the bigger markers local prompt re-deposition of Au allowed obtaining data on net erosion. The experimental results indicate relatively uniform erosion profiles across the marker spots or coatings, very little re-deposition elsewhere, and the largest erosion taking place close to the strike point. Compared to W, the markers show up to 15 times higher net erosion but no major differences in the poloidal migration lengths of Au and W can be seen. Gold thus appears to be a proper choice for studying migration of W in the divertor region. The ERO simulations with different background plasmas are able to reproduce the main features of the experimental net erosion profile of Au. Of the studied parameters, electron temperature has the strongest impact on erosion: doubling the temperature enhances erosion by a factor of 2.5–3. In contrast, for Mo, the simulated net erosion is ~ 3 times smaller than what experimental data indicate. The discrepancies can be attributed to the deviations of the background plasma profiles from the measured ones as well as to the applied models or approximations for the ion temperature, plasma potential, and sheath characteristics in ERO. In addition, the surrounding areas of the marker samples being covered with impurities and W from previous experiments may have considerably reduced the actual re-deposition of Mo. All the simulations predict a toroidal tail of re-deposited particles, downstream of the markers, but the particle density seems to be below the experimental detection threshold. The comparison between the 1 × 1 mm2 and 5 × 5 mm2 marker spots further reveal that re-deposition drops from >50% to <40% when decreasing the marker size. This indicates that small enough marker samples can be used for accurately determining gross erosion in ASDEX Upgrade.

AB - In this paper, we report experimental and numerical investigations of gross and net erosion of gold (Au) and molybdenum (Mo), proxies for the common plasma-facing material tungsten (W), during L-mode plasma discharges in deuterium (D) in the outer strike-point region of the ASDEX Upgrade tokamak. To this end, erosion profiles of different marker spots (for Au, dimensions 1 × 1 and 5 × 5 mm2) and marker coatings (for Mo) have been determined and modelled using the ERO code. The smaller marker spots were designed to quantify the gross-erosion rate while on the bigger markers local prompt re-deposition of Au allowed obtaining data on net erosion. The experimental results indicate relatively uniform erosion profiles across the marker spots or coatings, very little re-deposition elsewhere, and the largest erosion taking place close to the strike point. Compared to W, the markers show up to 15 times higher net erosion but no major differences in the poloidal migration lengths of Au and W can be seen. Gold thus appears to be a proper choice for studying migration of W in the divertor region. The ERO simulations with different background plasmas are able to reproduce the main features of the experimental net erosion profile of Au. Of the studied parameters, electron temperature has the strongest impact on erosion: doubling the temperature enhances erosion by a factor of 2.5–3. In contrast, for Mo, the simulated net erosion is ~ 3 times smaller than what experimental data indicate. The discrepancies can be attributed to the deviations of the background plasma profiles from the measured ones as well as to the applied models or approximations for the ion temperature, plasma potential, and sheath characteristics in ERO. In addition, the surrounding areas of the marker samples being covered with impurities and W from previous experiments may have considerably reduced the actual re-deposition of Mo. All the simulations predict a toroidal tail of re-deposited particles, downstream of the markers, but the particle density seems to be below the experimental detection threshold. The comparison between the 1 × 1 mm2 and 5 × 5 mm2 marker spots further reveal that re-deposition drops from >50% to <40% when decreasing the marker size. This indicates that small enough marker samples can be used for accurately determining gross erosion in ASDEX Upgrade.

KW - ASDEX Upgrade

KW - Erosion

KW - L-mode

KW - Marker samples

KW - Material migration

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U2 - 10.1016/j.nme.2020.100863

DO - 10.1016/j.nme.2020.100863

M3 - Article

AN - SCOPUS:85097576797

SN - 2352-1791

VL - 25

JO - Nuclear Materials and Energy

JF - Nuclear Materials and Energy

M1 - 100863

ER -

ERO modelling of net and gross erosion of marker samples exposed to L-mode plasmas on ASDEX Upgrade

Abstract

Funding

Keywords

UN SDGs

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