Approaching detachment in I-mode—response of core confinement and the edge pedestal in the ASDEX Upgrade tokamak

Happel, T.; Reinke, M.L.; Silvagni, D.; Bernert, M.; Grover, O.; Hennequin, Pascale; Hubbard, A.E.; Plank, U.; Trier, E.; Brida, D.; David, P.; Fischer, R.; Gil, L.; Höfler, K.; Mänz, P.; McDermott, R. M.; Merle, A.; Stroth, U.; Viezzer, E.; Willensdorfer, M.; Team, the ASDEX Upgrade; Team, the EUROfusion MST1

doi:10.1088/1741-4326/abd7b7

Cited by 9 publications

(10 citation statements)

References 83 publications

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“…Alcator C-Mod experiments were not successful in demonstrating compatibility of the I-mode regime with divertor detachment [23]. These investigations are being continued in AUG [24].…”

Section: Ar Injection Into Intrinsically Elm-free and Close-to Elm Fr...mentioning

confidence: 94%

Developments towards an ELM-free pedestal radiative cooling scenario using noble gas seeding in ASDEX Upgrade

et al. 2020

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Integrated edge-localized-mode (ELM)-free or small ELM scenarios for the demonstration fusion power plant (DEMO) are investigated in ASDEX Upgrade using argon seeding for radiative power removal mainly in the pedestal region. An important aspect is the modification of the electron pressure in the pedestal by the additional radiative power losses. Full ELM suppression could be achieved in a no-ELM H-mode scenario featuring an edge electromagnetic quasicoherent mode up to a heating power of 5 MW, where argon radiation allowed the extension of the heating power operational space. At higher powers up to 12 MW (reaching the beta limit), ELMs of reduced size prevail and detachment is obtained by the argon seeding. Control of the position of a radiating zone localized inside the X-point was found to be favorable compared to the control of the separatrix power for low P s e p / P h e a t . Integration of pedestal cooling with Ar and ELM suppression by resonant magnetic perturbations (RMP) allowed an increase of the core radiation and a partial recovery of normalized confinement to H98 = 1. This favorable behavior is finally limited by the loss of the RMP density pump-out effect, followed by an ELM-free H-mode phase and re-occurrence of ELMs. For an active tailoring of the pedestal pressure profile, precise knowledge of the radiation profile is required. Modeling of the argon radiation profile with the STRAHL code showed good agreement with bolometry only if charge exchange of neutral deuterium with argon ions was taken into account, highlighting the importance of the neutral density in the pedestal region. In view of best integration of a no-ELM scenario with divertor detachment and high heating power, the divertor compression and enrichment of argon and neon were compared using dynamic gas puff experiments. Argon shows more than a factor of 3 higher divertor enrichment compared to neon, but the absolute values decrease with higher neutral deuterium pressure.

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“…Alcator C-Mod experiments were not successful in demonstrating compatibility of the I-mode regime with divertor detachment [23]. These investigations are being continued in AUG [24].…”

Section: Ar Injection Into Intrinsically Elm-free and Close-to Elm Fr...mentioning

confidence: 94%

Developments towards an ELM-free pedestal radiative cooling scenario using noble gas seeding in ASDEX Upgrade

et al. 2020

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“…This is not due to increased radiation, but rather due to increased edge transport as nitrogen is introduced into the plasma. While complete detachment was not obtained, the inner divertor was detached along with a reduction of the heat flux on the outer divertor at a confinement factor of H 98 = 0.9 [54].…”

Section: Improved Confinement Modementioning

confidence: 95%

“…Furthermore, nitrogen seeding of I-mode discharges was tested as a way to combine the I-mode regime with a detached divertor [54]. In these experiments, the seeding rate was ramped to a maximum nitrogen core concentration of about 1.5 %.…”

Section: Improved Confinement Modementioning

confidence: 99%

Progress from ASDEX Upgrade experiments in preparing the physics basis of ITER operation and DEMO scenario development

Stroth

Team²

2022

Nucl. Fusion

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An overview of recent results obtained at the tokamak ASDEX Upgrade (AUG) is given. A work flow for predictive profile modelling of AUG discharges was established which is able to reproduce experimental H-mode plasma profiles based on engineering parameters only. In the plasma center, theoretical predictions on plasma current redistribution by a dynamo effect were confirmed experimentally. For core transport, the stabilizing effect of fast ion distributions on turbulent transport is shown to be important to explain the core isotope effect and improves the description of hollow low-Z impurity profiles. The L–H power threshold of hydrogen plasmas is not affected by small helium admixtures and it increases continuously from the deuterium to the hydrogen level when the hydrogen concentration is raised from 0 to 100%. One focus of recent campaigns was the search for a fusion relevant integrated plasma scenario without large edge localised modes (ELMs). Results from six different ELM-free confinement regimes are compared with respect to reactor relevance: ELM suppression by magnetic perturbation coils could be attributed to toroidally asymmetric turbulent fluctuations in the vicinity of the separatrix. Stable improved confinement mode plasma phases with a detached inner divertor were obtained using a feedback control of the plasma β. The enhanced D α H-mode regime was extended to higher heating power by feedback controlled radiative cooling with argon. The quasi-coherent exhaust regime was developed into an integrated scenario at high heating power and energy confinement, with a detached divertor and without large ELMs. Small ELMs close to the separatrix lead to peeling-ballooning stability and quasi continuous power exhaust. Helium beam density fluctuation measurements confirm that transport close to the separatrix is important to achieve the different ELM-free regimes. Based on separatrix plasma parameters and interchange-drift-Alfvén turbulence, an analytic model was derived that reproduces the experimentally found important operational boundaries of the density limit and between L- and H-mode confinement. Feedback control for the X-point radiator (XPR) position was established as an important element for divertor detachment control. Stable and detached ELM-free phases with H-mode confinement quality were obtained when the XPR was moved 10 cm above the X-point. Investigations of the plasma in the future flexible snow-flake divertor of AUG by means of first SOLPS-ITER simulations with drifts activated predict beneficial detachment properties and the activation of an additional strike point by the drifts.

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“…With the same B T , the stored energy of the I-modes is less than that of the H-mode but more than that of the L-mode [9,13]. Detachment in I-mode operations has been successfully achieved in the AUG tokamak with nitrogen seeding under a constant heating power [19], which confirms the potential of I-mode operation in divertor protection. Moreover, the I-mode also leads to a larger power decay length λ sol than the H-mode does [20], as well as a longer power fall-off length λ q , although it is shorter than that of the L-mode [21].…”

Section: Introductionmentioning

confidence: 54%

Numerical analysis of divertor target heat load of I-modes in comparison with H-modes of EAST

Wang¹,

Wang²,

Liu³

et al. 2023

Plasma Phys. Control. Fusion

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Due to substantial edge transport of particles, I-mode operations offer a high potential for divertor heat load mitigation. In this work, divertor parameters of I-mode operations on EAST have been investigated by SOLPS-ITER code, and the comparison with H-mode operations has also been made, with modeling the operated I- and H-mode processes on EAST. The simulation finds that, for the same separatrix electron density on outer mid-plane (OMP) n_(e,OMP)^sep, the upstream electron density of the I-mode is higher than that of H-modes with no density pedestal, while the upstream temperature of the I-mode is almost the same as that of H-mode with the temperature pedestal similar to that of H-modes. As a combined result, temperature and energy flux peaks of the I-mode are thus lower than those of H-modes at the divertor target. Further parameter scanning investigation reveals that, under low density condition (n_(e,OMP)^sep=1.16×〖10〗^19 m^(-3)), the peak energy flow at the target is reduced by ~ 34.1%, comparing the I-mode case to the H-mode, while the peak target temperature is dropped by ~ 54.6%. Under high density condition (n_(e,OMP)^sep=4.04×〖10〗^19 m^(-3)), on the other hand, energy flux and temperature peaks are weakened by ~ 28% and ~ 30.1%, respectively. The upstream density at detachment onset of an I-mode is also lower than that of an H-mode, by a fraction of 18.5%. These results suggest that the I-mode operation is more appropriate for divertor heat load mitigation than the H-mode.

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Approaching detachment in I-mode—response of core confinement and the edge pedestal in the ASDEX Upgrade tokamak

Cited by 9 publications

References 83 publications

Developments towards an ELM-free pedestal radiative cooling scenario using noble gas seeding in ASDEX Upgrade

Developments towards an ELM-free pedestal radiative cooling scenario using noble gas seeding in ASDEX Upgrade

Progress from ASDEX Upgrade experiments in preparing the physics basis of ITER operation and DEMO scenario development

Numerical analysis of divertor target heat load of I-modes in comparison with H-modes of EAST

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