Improved heat and particle flux mitigation in high core confinement, baffled, alternative divertor configurations in the TCV tokamak

Raj, Harshita; Theiler, C.; Thornton, A.; Février, O.; Gorno, S.; Bagnato, F.; Blanchard, P.; Colandrea, C.; Oliveira, H. De; Duval, B. P.; Labit, B.; Perek, A.; Reimerdes, H.; Sheikh, U.; Vallar, M.; Vincent, Benjamin

doi:10.1088/1741-4326/ac94e5

Cited by 9 publications

(7 citation statements)

References 65 publications

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“…In tokamak à configuration variable (TCV), gas baffles of varied shape were installed to increase the divertor closure. They resulted in an increase in the divertor neutral pressure while decreasing divertor-core coupling and facilitating access to detachment [15][16][17], in line with design predictions [18]. Similar baffling approaches have also been applied to Alcator C-Mod [19].…”

Section: Introductionsupporting

confidence: 53%

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Performance assessment of a tightly baffled, long-legged divertor configuration in TCV with SOLPS-ITER

et al. 2023

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Numerical simulations explore a possible tightly baffled, long-legged divertor (TBLLD) concept in a future upgrade of the Tokamak à configuration variable (TCV). The SOLPS-ITER code package is used to compare the exhaust performance of several TBLLD configurations with results from unbaffled and baffled TCV configurations. The investigated TBLLDs feature a range of radial gaps between the separatrix and the divertor baffles, with a smaller gap resulting in tighter baffling. All modelled TBLLDs are predicted to lead to a denser and colder plasma in front of the targets and increase the power handling by factors of 2-3 compared to the present, baffled, divertor and by up to a factor of 12 compared to the original, unbaffled, configuration. This improved TBLLD performance is attributed to an increased neutral confinement with more plasma-neutral interactions in the divertor region. Both power handling capability and neutral confinement increase with tighter baffling. The core compatibility of TBLLDs with nitrogen seeding is also evaluated and the detachment window, with acceptable core pollution, for these TBLLDs is explored, showing a reduction of the required upstream impurity concentration to achieve detachment by up to 18% with tighter baffling.

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Section: Introductionsupporting

confidence: 53%

“…Nitrogen is well adopted for medium-size devices and widely used as the impurity species in TCV. Both L-mode and H-mode detachment have been achieved with nitrogen seeding [17,45,46]. Nitrogen is therefore also used in this study of a TBLLD in TCV.…”

Section: Compatibility With Nitrogen Seedingmentioning

confidence: 99%

Performance assessment of a tightly baffled, long-legged divertor configuration in TCV with SOLPS-ITER

et al. 2023

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“…The simulation setup follows the previously published work by Fil et al [17,18] 5 . The original simulations performed were interpretive simulations of TCV tokamak [23,24], discharge # 52065, which is a single null L-mode unbaffled [25,26] density ramp discharge that has been extensively reported in literature [3,5,7,9,27,28]. In the simulation, the upstream density is scanned by a fuelling puff, similarly to [17,18].…”

Section: Simulation Setup and Theorymentioning

confidence: 99%

Investigating the impact of the molecular charge-exchange rate on detached SOLPS-ITER simulations

et al. 2023

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Plasma-molecular interactions generate molecular ions which react with the plasma and contribute to detachment through molecular activated recombination (MAR), reducing the ion target flux, and molecular activated dissociation (MAD), both of which create excited atoms. Hydrogenic emission from these atoms have been detected experimentally in detached TCV, JET and MAST-U deuterium plasmas. The TCV findings, however, were in disagreement with SOLPS-ITER simulations for deuterium indicating a molecular ion density ($D_2^+$) that was insufficient to lead to significant hydrogenic emission, which was attributed to underestimates of the molecular charge exchange rate ($D_2+D^+\rightarrow D_2^++D$) for deuterium (obtained by rescaling the hydrogen rates by their isotope mass).In this work, we have performed new SOLPS-ITER simulations with the default rate setup and a modified rate setup where ion isotope mass rescaling was disabled. This increased the $D_2^+$ content by $>\times 100$. By disabling ion isotope mass rescaling: 1) the total ion sinks are more than doubled due to the inclusion of MAR; 2) the additional MAR causes the ion target flux to roll-over during detachment; 3) the total $D\alpha$ emission in the divertor increases during deep detachment by roughly a factor four; 4) the neutral atom density in the divertor is doubled due to MAD, leading to a 50\% increase in neutral pressure; 5) total hydrogenic power loss is increased by up to 60\% due to MAD. These differences result in an improved agreement between the experiment and the simulations in terms of spectroscopic measurements, ion source/sink inferences and the occurrence of an ion target flux roll-over. Extrapolating simplified scalings of divertor molecular densities (TCV \& MAST-U) to reactor-relevant densities suggests the underestimation of molecular charge exchange could strongly impact divertor physics (neutral atom density, ions sinks) and hydrogen emission (which has implications for detachment control) in deeply detached conditions, warranting further study.

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“…The first generation of TCV baffles were designed to maximise the core-to-divertor neutral compression in the standard SN geometry whilst remaining compatible with a variety of other divertor geometries [8] (see, for example, the study of long-legged ADCs with baffles [22]). The SF-LFS features an even higher flux expansion in the null-point region than the SN, and so requires the development of a baffleoptimised geometry to maximise neutral compression whilst minimising plasma-baffle interaction.…”

Section: Development Of Baffled Sf-lfs Configurationmentioning

confidence: 99%

Power exhaust and core-divertor compatibility of the baffled snowflake divertor in TCV

Gorno¹,

Colandrea²,

Février³

et al. 2023

Plasma Phys. Control. Fusion

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A baffled Snowflake Minus Low-Field Side (SF-LFS) is geometrically-optimised in TCV, increasing divertor neutral pressure, to evaluate the roles of divertor closure (comparing with an unbaffled SF-LFS) and magnetic geometry (comparing with a baffled Single Null, SN) in power exhaust and core-divertor compatibility. Ohmically-heated L-mode discharges in deuterium, with a line-averaged core density of approximately 4 x 10^19 m^-3, are seeded with nitrogen to approach detached conditions. Baffles in the SF-LFS configuration are found to reduce the peak outer target heat flux by up to 23%, without significantly affecting the location of the inter-null radiation region or the core-divertor compatibility. When compared to the baffled SN, the baffled SF-LFS exhibits a reduction in outer target heat flux by up to 66% and the ability to balance the strike-point distribution of heat flux. These benefits are less significant with N_2 seeding, with similar peak target quantities (such as heat flux, electron temperature and ion flux) and divertor radiated power. Despite a radiating region located farther from the confined plasma for the SF-LFS than the baffled SN, no change in core confinement is observed. Core effective charge even indicates an increase in core impurity penetration for the SF-LFS. These experiments constitute a good reference for detailed model validations and extrapolations, exploring important physics such as core impurity shielding and the dependence of divertor cross-field transport on magnetic geometry.

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Improved heat and particle flux mitigation in high core confinement, baffled, alternative divertor configurations in the TCV tokamak

Cited by 9 publications

References 65 publications

Performance assessment of a tightly baffled, long-legged divertor configuration in TCV with SOLPS-ITER

Performance assessment of a tightly baffled, long-legged divertor configuration in TCV with SOLPS-ITER

Investigating the impact of the molecular charge-exchange rate on detached SOLPS-ITER simulations

Power exhaust and core-divertor compatibility of the baffled snowflake divertor in TCV

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