SOLPS-ITER simulations of an X-point radiator in the ASDEX Upgrade tokamak

Pan, O.; Bernert, M.; Lunt, T.; Cavedon, M.; Kurzan, B.; Wiesen, S.; Wischmeier, M.; Stroth, U.; Team, the ASDEX Upgrade

doi:10.1088/1741-4326/ac9742

Cited by 22 publications

(11 citation statements)

References 25 publications

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“…This results in a radiating mantel around the low-temperature plasma which can be regarded as a cold XPR core. Indeed, recent SOLPS-ITER simulations of a nitrogen-seeded AUG plasma [43] support such a picture: the simulation result in figure 6 shows a 2D radiation pattern of an XPR resembling that of a black hole, with a bright radiating ring around a fainter shining core. Similarly, the experimentally observed radiation may arise at the border of the cold plasma which is identified in the model with the XPR.…”

Section: Radiating Mantel Of the Xprmentioning

confidence: 82%

Model for access and stability of the X-point radiator and the threshold for marfes in tokamak plasmas

et al. 2022

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Based on particle and energy balances, a reduced model is derived for the physical mechanisms leading to the occurrence of stable and unstable \xpres, the latter also known as marfes. The leading roles of the neutral deuterium density in the divertor region for initiating X-point radiators is highlighted. An access condition is formulated whose parameter dependencies are consistent with experimental observations and which could also apply to the process of divertor detachment. With an exponential increase of the recombination rate at low temperature, the X-point radiator becomes magnetohydrodynamically unstable, leading to a marfe and, possibly, to a disruption. A critical density for marfe occurrence is formulated with the upstream density and safety factor as leading parameters, as in the experiment. Marfes are predicted to be more likely in carbon devices than in impurity-seeded plasmas in tungsten devices. The edge plasma parameter domain where marfes occur resembles that used for active marfe avoidance schemes. Both the X-point radiator and marfe occurrence parameter can be used to guide active discharge control.

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Section: Radiating Mantel Of the Xprmentioning

confidence: 82%

Model for access and stability of the X-point radiator and the threshold for marfes in tokamak plasmas

et al. 2022

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“…by applying a fixed temperature boundary condition) to maintain the temperature gradient and prevent the carbon radiation zone from approaching the core boundary. Additionally, since fluid cross-field drifts generally result in lower electron density and higher electron temperature on the high field side [41], including drifts will compensate for the bias of the radiation spot toward the low field side core boundary during collapse.…”

Section: Quantitative Inconsistency Of Solps-iter Solutions With Expe...mentioning

confidence: 99%

Bifurcation-like transition of divertor conditions induced by X-point radiation in KSTAR L-mode plasmas ^*

et al. 2023

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Density ramps with ion grad B drift directed into lower single null KSTAR L-mode plasmas are associated with a simultaneous and abrupt reduction of the divertor particle flux on both low- and high-field-side targets when the mid-plane line averaged electron density reaches a given level. Target embedded Langmuir probe signals show a clear “cliff edge” behavior similar to that observed in the divertor target electron temperature in DIII-D H-mode plasmas. The collapse of the particle flux is observed along the whole divertor target area (from private flux region to the far SOL). The critical upstream density of this target flux cliff is invariant under fuel gas throughput modulation. The transition along the cliff occurs in tens of milliseconds. With the cliff, carbon impurities and deuterium neutrals transported through the X-point to the core produce a strong radiation spot near the X-point, seen on bolometric signals, and increase the upstream density. The experimental observations are consistent with time-dependent SOLPS-ITER simulations, which also demonstrate an abrupt transition of the target flux and upstream density with the increase in X-point radiation. The timescale of the cliff predicted by SOLPS-ITER is consistent with the experiment, although, it is influenced by gas throughput or time-dependent numerical methods. In the L-mode phase space of separatrix electron density and temperature, branches are divided based on target temperature, because the latter is strongly coupled to the radiation front and ionization front due to the monotonic characteristic of the parallel electron temperature distribution. Since the H-mode condition operates at a much higher upstream density and electron temperature in phase space, dissipation from sputtered carbon alone leads to the density limit before reaching the X-point radiation condition. This is therefore consistent with the fact that cliffs have never been observed in H-mode KSTAR experiments.

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“…Pressure balance along the field lines yields n x ≈ n u T u /T x , where the subscript 'u' denotes upstream values, here taken as the separatrix values in ASTRA. The key assumption of this model is therefore the value of T x , for which we take 7 eV as a typical value in the range of 1-10 eV obtained in AUG SOLPS-ITER simulations [105] and divertor Thomson scattering measurements [106]. Two further assumptions are that the X-point impurity concentration is equal to its upstream value, i.e.…”

Section: Model For Radiation Localized Above the X-pointmentioning

confidence: 99%

Full-radius integrated modelling of ASDEX Upgrade L-modes including impurity transport and radiation

Fajardo,

Angioni,

Dux

et al. 2024

Nucl. Fusion

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An integrated framework that demonstrates multi-species, multi-channel modelling capabilities for the prediction of impurity density profiles and their feedback on the main plasma through radiative cooling and fuel dilution is presented. It combines all presently known theoretical elements in the local description of quasilinear turbulent and neoclassical impurity transport, using the models TGLF-SAT2 and FACIT. These are coupled to the STRAHL code for impurity sources and radiation inside the ASTRA transport solver. The workflow is shown to reproduce experimental results in full-radius L-mode modelling. In particular, a set of ASDEX Upgrade L-modes with differing heating power mixtures and plasma currents are simulated, including boron (B) and tungsten (W) as intrinsic impurities. The increase of predicted confinement with higher current and the reduction of core W peaking with higher central wave heating are demonstrated. Furthermore, a highly radiative L-mode scenario featuring an X-point radiator (XPR) with two intrinsic (B, W) and one seeded argon (Ar) species is simulated, and its measured radiated power and high confinement are recovered by the modelling. The stabilizing effect of impurities on turbulence is analyzed and a simple model for the peripheral X-point radiation is introduced. A preliminary full-radius simulation of an H-mode phase of this same discharge, leveraging recent work on the role of the E×B shearing at the edge, shows promising results.

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SOLPS-ITER simulations of an X-point radiator in the ASDEX Upgrade tokamak

Cited by 22 publications

References 25 publications

Model for access and stability of the X-point radiator and the threshold for marfes in tokamak plasmas

Model for access and stability of the X-point radiator and the threshold for marfes in tokamak plasmas

Bifurcation-like transition of divertor conditions induced by X-point radiation in KSTAR L-mode plasmas ^*

Full-radius integrated modelling of ASDEX Upgrade L-modes including impurity transport and radiation

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SOLPS-ITER simulations of an X-point radiator in the ASDEX Upgrade tokamak

Cited by 22 publications

References 25 publications

Model for access and stability of the X-point radiator and the threshold for marfes in tokamak plasmas

Model for access and stability of the X-point radiator and the threshold for marfes in tokamak plasmas

Bifurcation-like transition of divertor conditions induced by X-point radiation in KSTAR L-mode plasmas *

Full-radius integrated modelling of ASDEX Upgrade L-modes including impurity transport and radiation

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Bifurcation-like transition of divertor conditions induced by X-point radiation in KSTAR L-mode plasmas ^*