Fuelling and density control for DEMO

Vincenzi, P.; Koechl, F.; Garzotti, L.; King, D.; Tindale, E.; Bolzonella, T.; Lang, P. T.; Pégouriè, B.; Romanelli, M.; Wenninger, R.

doi:10.1088/0029-5515/55/11/113028

Cited by 19 publications

(14 citation statements)

References 32 publications

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“…However, though pellets are there to increase the density, recycling from the walls still provides the main source of fuel required to maintain a baseline density. Interestingly, DEMO modeling currently relies on there being a density pedestal structure, even though due to its size, it will be more opaque than ITER for similar plasma densities [82].…”

Section: Iter and Demomentioning

confidence: 99%

Overview of density pedestal structure: role of fueling versus transport

Mordijck¹

2020

Nucl. Fusion

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How much of the density pedestal structure is determined by fueling versus transport is still an open question. In most current tokamaks, the scrape-off layer is not opaque enough to screen the neutrals and limit their penetration past the separatrix. As such, recycled neutrals and additional gas puffing can directly affect the pedestal structure through ionization. However, in ITER and other future burning plasma magnetic confinement devices, the ionization source will be pushed further out into the scrape-off layer. This poses the question: how much of the density pedestal structure is governed by this edge ionization source versus plasma transport effects? Theoretically, several turbulent modes have been identified which could provide a 'pinch-like' up-gradient transport mechanism. Up-gradient transport is necessary in a source-free region to obtain a peaked density profile, which is often observed in the core of tokamaks. In an opaque scrape-off layer, without the existence of such a pinch, the density pedestal structure would eventually disappear. Not only would this limit our ability to fuel a fusion reactor, it would also affect the pedestal stability. In this paper we will give an overview of the state-of-the-art on what sets the density pedestal structure based on experimental observations as well as theoretical models. We will complement these studies with new results from Alcator C-Mod and DIII-D where the opaqueness is increased to reach values similar to those in ITER.

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Section: Iter and Demomentioning

confidence: 99%

Overview of density pedestal structure: role of fueling versus transport

Mordijck¹

2020

Nucl. Fusion

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“…The first design of the pellet fueling system of EU-DEMO used the same pellet size as that planned for ITER (6 × 10 21 at. ), and the first calculations of penetration/ deposition profiles done in this frame [72]. However, for minimizing the difficulties in the plasma control that were resulting from a too large density increment [59], the pellet particle content was reduced down to 2×10 21 at.…”

Section: Fueling Systems Of Future Devicesmentioning

confidence: 99%

Pellet Core Fueling in Tokamaks, Stellarators and Reversed Field Pinches

GEULIN¹,

Pégouriè²

2022

Plasma and Fusion Research

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In a reactor grade device, the role of core fueling is to replace the D and T consumed in the fusion reactions (almost negligible) and to compensate the plasma losses through the separatrix -including the material expelled out by the ELMs. For this purpose, deep material deposition is an advantage and pellet injection the best candidate for fueling the future machines. Fueling by pellet injection consists in two phases: First, the pellet ablation itself, then the ablated material homogenization and drift in the discharge. The former is a self-regulated process, which depends only of the local plasma characteristics. The second is a global phenomenon, which depends on the whole magnetic configuration. In this paper, we discuss first the basics of the ablation physics, emphasizing the role of the fast particles -ions and electrons -resulting from NBI or wave heating; then we describe the homogenization process and associated ∇B-induced drift. The drift acceleration and damping processes are described as well as the influence of the magnetic configuration (tokamak, stellarator and reversed field pinch) on the predominance of a given damping process and its consequence on the resulting deposition profile. We finally review the last results relative to pellet fueling in these different kind of devices and present the ongoing projects for future large-scale machines.

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“…Incidentally, such a configuration might be easily extended, in principle, to accommodate more compact TSG drivers on the single gun-barrel of an injector based on a screw extruder, with the aim of improving the repetition rate. The injection frequency required to maintain a stationary volumeaveraged plasma density of  10 20 m -3 in DEMO, is predicted to be less than  4 Hz, for ITER standard-sized pellets (6x10 21 particles each, corresponding to cylindrical pellets having diameter and length of 5 mm) injected from the HFS at speeds in the 300 to 1000 m/s range [29]. Accommodating four compact TSG drivers on the same barrel does not seem to be a prohibitive task.…”

Section: The Enea-ornl High-speed Pellet Injectormentioning

confidence: 99%

Core Fueling of DEMO by Direct Line Injection of High-Speed Pellets From the HFS

Frattolillo

Baylor

Bombarda

et al. 2018

IEEE Trans. Plasma Sci.

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Pellet injection represents to date the most realistic candidate technology for core fueling of a DEMO tokamak fusion reactor. Modelling of both pellet penetration and fuel deposition profiles, for different injection locations, indicates that effective core fuelling can be achieved launching pellets from the inboard high field side at speeds not less than 1 km/s. Inboard pellet fueling is commonly achieved in present tokamaks, using curved guide tubes; however, this technology might be hampered at velocities  1 km/s. An innovative approach, aimed at identifying suitable inboard "direct line" paths, to inject high-speed pellets (in the 3 to 4 km/s range), has been recently proposed as a potential complementary solution. The fuel deposition profiles achievable by this approach have been explored using the HPI2 simulation code. The results presented here show that there are possible geometrical schemes providing good fueling performance. The problem of neutron flux in a direct line of sight injection path is being investigated, though preliminary analyses indicate that, perhaps, this is not a serious problem. The identification and integration of straight injection paths suitably tilted may be a rather difficult task, due to the many constraints and to interference with existing structures. The suitability of straight guide tubes to reduce the scatter cone of high-speed pellets, is therefore of main interest. A preliminary investigation,, aimed at addressing these technological issues, has been recently started. A possible implementation plan, using an existing ENEA-ORNL facility is shortly outlined. Index Terms-DEMO tokamak fusion reactor, HFS highspeed pellet injection, straight guide tubes Manuscript received June 2017. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

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Fuelling and density control for DEMO

Cited by 19 publications

References 32 publications

Overview of density pedestal structure: role of fueling versus transport

Overview of density pedestal structure: role of fueling versus transport

Pellet Core Fueling in Tokamaks, Stellarators and Reversed Field Pinches

Core Fueling of DEMO by Direct Line Injection of High-Speed Pellets From the HFS

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