Atomic processes leading to asymmetric divertor detachment in KSTAR L-mode plasmas

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Atomic processes leading to asymmetric divertor detachment in KSTAR L-mode plasmas. / Park, Jae Sun; Groth, Mathias; Pitts, Richard; Bak, Jun Gyo; Thatipamula, S. G.; Juhn, June Woo; Hong, Suk Ho; Choe, Wonho.

In: Nuclear Fusion, Vol. 58, No. 12, 126033, 02.11.2018.

Research output: Contribution to journalArticleScientificpeer-review

Harvard

Park, JS, Groth, M, Pitts, R, Bak, JG, Thatipamula, SG, Juhn, JW, Hong, SH & Choe, W 2018, 'Atomic processes leading to asymmetric divertor detachment in KSTAR L-mode plasmas' Nuclear Fusion, vol. 58, no. 12, 126033. https://doi.org/10.1088/1741-4326/aae865

APA

Park, J. S., Groth, M., Pitts, R., Bak, J. G., Thatipamula, S. G., Juhn, J. W., ... Choe, W. (2018). Atomic processes leading to asymmetric divertor detachment in KSTAR L-mode plasmas. Nuclear Fusion, 58(12), [126033]. https://doi.org/10.1088/1741-4326/aae865

Vancouver

Author

Park, Jae Sun ; Groth, Mathias ; Pitts, Richard ; Bak, Jun Gyo ; Thatipamula, S. G. ; Juhn, June Woo ; Hong, Suk Ho ; Choe, Wonho. / Atomic processes leading to asymmetric divertor detachment in KSTAR L-mode plasmas. In: Nuclear Fusion. 2018 ; Vol. 58, No. 12.

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@article{3b97d0a18838437997b0a2e36b6c2095,
title = "Atomic processes leading to asymmetric divertor detachment in KSTAR L-mode plasmas",
abstract = "The experimentally observed in/out detachment asymmetry in KSTAR L-mode plasmas with deuterium (D) fueling and carbon walls has been investigated with the SOLPS-ITER code to understand its mechanism and identify important atomic processes in the divertor region. The simulations show that the geometrical combination of a vertical, inner target with a short poloidal connection from the X-point to the target and a much longer outer divertor leg on an inclined target lead to neutral accumulation towards the outer target, driving the outer target detachment at lower upstream density than is required for the inner target. This is consistent with available Langmuir probe measurements at both target plates, although the inner target profile is poorly resolved in these plasmas and further experiments with corroborating diagnostics are required to confirm this finding. The pressure and power loss factors defined in the two-point model (Stangeby 2018 Plasma Phys. Control. Fusion 60 4; Kotov and Reiter 2009 Plasma Phys. Control. Fusion 51 115002; Stangeby and Sang 2017 Nucl. Fusion 57 056007; Moulton et al 2017 Plasma Phys. Control. Fusion 59 6) of the divertor scrape-off layer (SOL) and the sources contributing to the loss factors are calculated through post-processing of the SOLPS-ITER results. The momentum losses are mainly driven by plasma-neutral interaction and the power losses by plasma-neutral interaction and carbon radiation. The presence of carbon impurities in the simulation enhances the pressure and power dissipation compared to the pure D case. Carbon radiation is a strong power loss channel which cools the plasma, but its effect on the pressure balance is indirect. Reduction of the electron temperature indirectly increases the momentum loss and increasing the volumetric reaction rates which are responsible for the loss of momentum. As a result, the addition of carbon saturates the momentum and power losses in the flux tube at lower upstream densities, reducing the roll-over threshold of the upstream density. The relative strengths of the various mechanisms contributing to momentum and power loss depend on the radial distance of the SOL flux tubes from the separatrix (near/far SOL) and the target (inner/outer target). This is related to the strong D2 molecule accumulation near the outer strike point, which makes the deuterium gas density at the outer target 2-10 times higher than that at the inner target. A large portion of the recycled neutral particles from both targets reach and accumulate in the outer SOL, which is predominantly attributed to the target inclination and gap structure between the central and outboard divertors and hence to the impact of geometry. The accumulated neutrals enhance the reactions involving D2, which causes momentum and power loss.",
keywords = "divertor asymmetry, divertor detachment, edge modelling, KSTAR, momentum loss, SOLPS",
author = "Park, {Jae Sun} and Mathias Groth and Richard Pitts and Bak, {Jun Gyo} and Thatipamula, {S. G.} and Juhn, {June Woo} and Hong, {Suk Ho} and Wonho Choe",
year = "2018",
month = "11",
day = "2",
doi = "10.1088/1741-4326/aae865",
language = "English",
volume = "58",
journal = "Nuclear Fusion",
issn = "0029-5515",
number = "12",

}

RIS - Download

TY - JOUR

T1 - Atomic processes leading to asymmetric divertor detachment in KSTAR L-mode plasmas

AU - Park, Jae Sun

AU - Groth, Mathias

AU - Pitts, Richard

AU - Bak, Jun Gyo

AU - Thatipamula, S. G.

AU - Juhn, June Woo

AU - Hong, Suk Ho

AU - Choe, Wonho

PY - 2018/11/2

Y1 - 2018/11/2

N2 - The experimentally observed in/out detachment asymmetry in KSTAR L-mode plasmas with deuterium (D) fueling and carbon walls has been investigated with the SOLPS-ITER code to understand its mechanism and identify important atomic processes in the divertor region. The simulations show that the geometrical combination of a vertical, inner target with a short poloidal connection from the X-point to the target and a much longer outer divertor leg on an inclined target lead to neutral accumulation towards the outer target, driving the outer target detachment at lower upstream density than is required for the inner target. This is consistent with available Langmuir probe measurements at both target plates, although the inner target profile is poorly resolved in these plasmas and further experiments with corroborating diagnostics are required to confirm this finding. The pressure and power loss factors defined in the two-point model (Stangeby 2018 Plasma Phys. Control. Fusion 60 4; Kotov and Reiter 2009 Plasma Phys. Control. Fusion 51 115002; Stangeby and Sang 2017 Nucl. Fusion 57 056007; Moulton et al 2017 Plasma Phys. Control. Fusion 59 6) of the divertor scrape-off layer (SOL) and the sources contributing to the loss factors are calculated through post-processing of the SOLPS-ITER results. The momentum losses are mainly driven by plasma-neutral interaction and the power losses by plasma-neutral interaction and carbon radiation. The presence of carbon impurities in the simulation enhances the pressure and power dissipation compared to the pure D case. Carbon radiation is a strong power loss channel which cools the plasma, but its effect on the pressure balance is indirect. Reduction of the electron temperature indirectly increases the momentum loss and increasing the volumetric reaction rates which are responsible for the loss of momentum. As a result, the addition of carbon saturates the momentum and power losses in the flux tube at lower upstream densities, reducing the roll-over threshold of the upstream density. The relative strengths of the various mechanisms contributing to momentum and power loss depend on the radial distance of the SOL flux tubes from the separatrix (near/far SOL) and the target (inner/outer target). This is related to the strong D2 molecule accumulation near the outer strike point, which makes the deuterium gas density at the outer target 2-10 times higher than that at the inner target. A large portion of the recycled neutral particles from both targets reach and accumulate in the outer SOL, which is predominantly attributed to the target inclination and gap structure between the central and outboard divertors and hence to the impact of geometry. The accumulated neutrals enhance the reactions involving D2, which causes momentum and power loss.

AB - The experimentally observed in/out detachment asymmetry in KSTAR L-mode plasmas with deuterium (D) fueling and carbon walls has been investigated with the SOLPS-ITER code to understand its mechanism and identify important atomic processes in the divertor region. The simulations show that the geometrical combination of a vertical, inner target with a short poloidal connection from the X-point to the target and a much longer outer divertor leg on an inclined target lead to neutral accumulation towards the outer target, driving the outer target detachment at lower upstream density than is required for the inner target. This is consistent with available Langmuir probe measurements at both target plates, although the inner target profile is poorly resolved in these plasmas and further experiments with corroborating diagnostics are required to confirm this finding. The pressure and power loss factors defined in the two-point model (Stangeby 2018 Plasma Phys. Control. Fusion 60 4; Kotov and Reiter 2009 Plasma Phys. Control. Fusion 51 115002; Stangeby and Sang 2017 Nucl. Fusion 57 056007; Moulton et al 2017 Plasma Phys. Control. Fusion 59 6) of the divertor scrape-off layer (SOL) and the sources contributing to the loss factors are calculated through post-processing of the SOLPS-ITER results. The momentum losses are mainly driven by plasma-neutral interaction and the power losses by plasma-neutral interaction and carbon radiation. The presence of carbon impurities in the simulation enhances the pressure and power dissipation compared to the pure D case. Carbon radiation is a strong power loss channel which cools the plasma, but its effect on the pressure balance is indirect. Reduction of the electron temperature indirectly increases the momentum loss and increasing the volumetric reaction rates which are responsible for the loss of momentum. As a result, the addition of carbon saturates the momentum and power losses in the flux tube at lower upstream densities, reducing the roll-over threshold of the upstream density. The relative strengths of the various mechanisms contributing to momentum and power loss depend on the radial distance of the SOL flux tubes from the separatrix (near/far SOL) and the target (inner/outer target). This is related to the strong D2 molecule accumulation near the outer strike point, which makes the deuterium gas density at the outer target 2-10 times higher than that at the inner target. A large portion of the recycled neutral particles from both targets reach and accumulate in the outer SOL, which is predominantly attributed to the target inclination and gap structure between the central and outboard divertors and hence to the impact of geometry. The accumulated neutrals enhance the reactions involving D2, which causes momentum and power loss.

KW - divertor asymmetry

KW - divertor detachment

KW - edge modelling

KW - KSTAR

KW - momentum loss

KW - SOLPS

UR - http://www.scopus.com/inward/record.url?scp=85056279061&partnerID=8YFLogxK

U2 - 10.1088/1741-4326/aae865

DO - 10.1088/1741-4326/aae865

M3 - Article

VL - 58

JO - Nuclear Fusion

JF - Nuclear Fusion

SN - 0029-5515

IS - 12

M1 - 126033

ER -

ID: 31436777