Impact of the new TCV baffled divertor upgrade on pedestal structure and performance

Sheikh, U.; Dunne, M.; Frassinetti, L.; Labit, B.; Blanchard, P.; Duval, B.P.; Février, O.; Galassi, D.; Merle, A.; Reimerdes, H.; Theiler, C.

doi:10.1016/j.nme.2021.100933

Cited by 5 publications

(7 citation statements)

References 18 publications

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“…Most of the present machines tend to work at relatively low n e sep /n e ped in type I ELMy H-modes. For example, in AUG a typical range is n e sep /n e ped ≈ 0.1-0.5 [11], in TCV n e sep /n e ped ≈ 0.1-0.4 [105], in DIII-D n e sep /n e ped ≈ 0.2-0.6 [21,22], in Alcator C-Mod n e sep /n e ped ≈ 0.1-0.35 [64,65]. These are the ranges in JET in which (i) the behaviour of the pedestal pressure can be explained via the outward shift of the density profile and (ii) the EPED1 model produces a reasonable agreement with the experimental data.…”

Section: Comparison With Other Machines and Discussion On Possible Ef...mentioning

confidence: 99%

Role of the separatrix density in the pedestal performance in deuterium low triangularity JET-ILW plasmas and comparison with JET-C

Frassinetti¹,

Thun

Chapman-Oplopoiou

et al. 2021

Nucl. Fusion

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A reduction of the pedestal pressure with increasing separatrix density over pedestal density (n e sep/n e ped) has been observed in JET. The physics behind this correlation is investigated. The correlation is due to two distinct mechanisms. The increase of n e sep/n e ped till ≈0.4 shifts the pedestal pressure radially outwards, decreasing the peeling-balloning stability and reducing the pressure height. The effect of the position saturates above n e sep/n e ped ≈ 0.4. For higher values, the reduction of the pedestal pressure is ascribed to increased turbulent transport and, likely, to resistive MHD effects. The increase of n e sep/n e ped above ≈0.4 reduces ∇n e /n e, increasing η e and the pedestal turbulent transport. This reduces the pressure gradient and the pedestal temperature, producing an increase in the pedestal resistivity. The work suggests that the increase in resistivity might destabilize resistive balloning modes, further reducing the pedestal stability.

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Section: Comparison With Other Machines and Discussion On Possible Ef...mentioning

confidence: 99%

Role of the separatrix density in the pedestal performance in deuterium low triangularity JET-ILW plasmas and comparison with JET-C

Frassinetti¹,

Thun

Chapman-Oplopoiou

et al. 2021

Nucl. Fusion

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“…We start from ELMy (type I) H-mode plasmas similar to those presented in [53] with a plasma current (I p ) = 170 kA, toroidal magnetic field (B 0 ) = 1.4 T, neutral beam heating power (P NBI ) of 0.75 MW or 1.3 MW, q 95 ∼ 5 and a Greenwald density fraction, f G ∼ 0.55. Plasmas in both ADCs and the SN were repeated with and without the polycrystalline graphite baffles recently installed in TCV.…”

Section: Experiments Overviewmentioning

confidence: 99%

“…Models and experimental data from DIII-D indicate that increasing f x and flaring should work in tandem with divertor closure to achieve a lower detachment threshold [41]. Experiments with baffles in TCV have shown easier access to detachment in L-mode [38] as well as improved core performance at high divertor neutral pressures in H-mode [53]. The exploration and assessment of the combined effect of baffling and ADCs in stable detached ELMy H-mode plasmas is the next logical step in developing advanced exhaust solutions in TCV and is the focus of this paper.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2022

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Nitrogen seeded detachment has been achieved in the Tokamak a Configuration Variable (TCV) in alternative divertor configurations (ADCs), namely X-divertor and X-point target, with and without baffles in H-mode plasmas with high core confinement. Both ADCs show a remarkable reduction in the inter-ELM particle and heat fluxes to the target compared to the standard divertor configuration. 95-98% of the inter-ELM peak heat flux to the target is mitigated as a synergetic effect of ADCs, baffling, and nitrogen seeded detachment. The effect of divertor geometry and baffles on core-divertor compatibility is investigated in detail. The power balance in these experiments is also investigated to explore the physics behind the observed reduction in heat fluxes in the ADCs.

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“…Fuelling and, thereby, a higher neutral pressure, generally degrades the pedestal pressure, p e,ped , through a degradation of the temperature pedestal, while the density pedestal height remains approximately constant, consistent with previous findings [50] that linked this degradation to an outward shift of the density profile. This outward shift and the related pedestal degradation are, however, found to be considerably more benign in the baffled divertor, presumably due to a weaker increase of p n,main , leading to a significantly higher T e,ped and, hence, higher p e,ped at high divertor neutral pressure, p n,div , figure 7, [51]. In this way, high fuelling rates, together with nitrogen seeding into the baffled divertor, resulted in an up to three-fold increase in the radiated power without significant core confinement degradation, figure 8.…”

Section: H-mode Pedestalmentioning

confidence: 95%

“…ITERH-98(y, 2) as a function of the total radiated power for various fuelling rates (symbols) and nitrogen seeding rates (marker size) with and without baffles (magenta and cyan, respectively). Reproduced from[51]. CC BY 4.0.…”

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Overview of the TCV tokamak experimental programme

et al. 2022

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The tokamak à configuration variable (TCV) continues to leverage its unique shaping capabilities, flexible heating systems and modern control system to address critical issues in preparation for ITER and a fusion power plant. For the 2019–20 campaign its configurational flexibility has been enhanced with the installation of removable divertor gas baffles, its diagnostic capabilities with an extensive set of upgrades and its heating systems with new dual frequency gyrotrons. The gas baffles reduce coupling between the divertor and the main chamber and allow for detailed investigations on the role of fuelling in general and, together with upgraded boundary diagnostics, test divertor and edge models in particular. The increased heating capabilities broaden the operational regime to include T e/T i ∼ 1 and have stimulated refocussing studies from L-mode to H-mode across a range of research topics. ITER baseline parameters were reached in type-I ELMy H-modes and alternative regimes with ‘small’ (or no) ELMs explored. Most prominently, negative triangularity was investigated in detail and confirmed as an attractive scenario with H-mode level core confinement but an L-mode edge. Emphasis was also placed on control, where an increased number of observers, actuators and control solutions became available and are now integrated into a generic control framework as will be needed in future devices. The quantity and quality of results of the 2019–20 TCV campaign are a testament to its successful integration within the European research effort alongside a vibrant domestic programme and international collaborations.

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Impact of the new TCV baffled divertor upgrade on pedestal structure and performance

Cited by 5 publications

References 18 publications

Role of the separatrix density in the pedestal performance in deuterium low triangularity JET-ILW plasmas and comparison with JET-C

Role of the separatrix density in the pedestal performance in deuterium low triangularity JET-ILW plasmas and comparison with JET-C

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

Overview of the TCV tokamak experimental programme

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