On the challenge of plasma heating with the JET metallic wall

Neutral beam injection (NBI) will be one of the main sources of heating and non-inductive current drive in ITER. Due to high level of injected power the beam induced heat loads present a potential threat to the integrity of the first wall of the device, particularly in the presence of non-axisymmetric perturbations of the magnetic field. Neutral beam injection can also destabilize Alfvén eigenmodes and energetic particle modes, and act as a source of plasma rotation. Therefore, reliable and accurate simulation of NBI is important for making predictions for ITER, as well as for any other current or future fusion device. This paper introduces a new beamlet-based neutral beam ionization model called BBNBI. It takes into account the fine structure of the injector, follows the injected neutrals until ionization, and generates a source ensemble of ionized NBI test particles for slowing down calculations. BBNBI can be used as a stand-alone model but together with the particle following code ASCOT it forms a complete and sophisticated tool for simulating neutral beam injection. The test particle ensembles from BBNBI are found to agree well with those produced by PENCIL for JET, and those produced by NUBEAM both for JET and ASDEX Upgrade plasmas. The first comprehensive comparisons of beam slowing down profiles of interest from BBNBI+ASCOT with results from PENCIL and NUBEAM/TRANSP, for both JET and AUG, are presented. It is shown that, for an axisymmetric plasma, BBNBI+ASCOT and NUBEAM agree remarkably well. Together with earlier 3D studies, these results further validate using BBNBI+ASCOT also for studying phenomena that require particle following in a truly three-dimensional geometry.

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“…1 in Refs. [28] and [29], respectively) have been modelled in detail in BBNBI as described in Sec. 2.1.…”

Section: Comparisons Against Established Nbi Codesmentioning

confidence: 99%

Modelling neutral beams in fusion devices: Beamlet-based model for fast particle simulations

Asunta

Govenius

Budny

et al. 2015

Computer Physics Communications

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“…It is essential to adapt the heating systems to the WEST configuration, and also to verify the adequacy of these heating schemes with H-mode operation in terms of power coupling, fast particle confinement and ELM resilience in a metallic environment. It will complement active efforts carried out in metallic environments on JET-ILW [13], ASDEX Upgrade [14,15], Alcator C-Mod [16] and FTU [17].…”

Section: High Frequency Plasma Heatingmentioning

confidence: 85%

“…The ideal MHD stability limit in the WEST scenarios studied has been calculated using the linear MHD code MISHKA [13]. The pedestal width is assumed to be around 5% of the minor radius such that ped = 2.3 cm.…”

Section: L-h Power Threshold Pedestal and Elmsmentioning

confidence: 99%

WEST Physics Basis

et al. 2015

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56 075020) is used to pave the way towards ITER divertor procurement and operation. It consists in implementing a divertor configuration and installing ITER-like actively cooled tungsten monoblocks in the Tore Supra tokamak, taking full benefit of its unique long-pulse capability. WEST is a user facility platform, open to all ITER partners. This paper describes the physics basis of WEST: the estimated heat flux on the divertor target, the planned heating schemes, the expected behaviour of the L-H threshold and of the pedestal and the potential W sources. A series of operating scenarios has been modelled, showing that ITER-relevant heat fluxes on the divertor can be achieved in WEST long pulse H-mode plasmas.

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“…At present, numerous codes 35,36 are capable of iterating between the first two, mostly considering an isotropic background equilibrium and ignoring finite orbit e ects, although significant e orts to circumvent these limitations have recently been developed 37 . The most di cult challenges that remain in simulating ICRH in tokamaks and stellarators relate to the coupling between the antenna and the edge plasma, which involves strongly nonlinear e ects associated with the large radiofrequency (RF) voltages (tens of kilovolts) present at the antenna surface, and the turbulent nature of the edge-plasma region 38 . This coupling strongly influences not only the e ectiveness of the heating, but also the integrity of the antenna, which is subject to electrical arcs and ion bombardment due to the rectification of the RF voltage in the plasma sheath close to the antenna, and can strongly modify the properties of the edge plasma.…”

Section: Heating and Current Drive By Wavesmentioning

confidence: 99%

Computational challenges in magnetic-confinement fusion physics

et al. 2016

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Magnetic-fusion plasmas are complex self-organized systems with an extremely wide range of spatial and temporal scales, from the electron-orbit scales (⇠10 11 s, ⇠10 5 m) to the di usion time of electrical current through the plasma (⇠10 2 s) and the distance along the magnetic field between two solid surfaces in the region that determines the plasma-wall interactions (⇠100 m). The description of the individual phenomena and of the nonlinear coupling between them involves a hierarchy of models, which, when applied to realistic configurations, require the most advanced numerical techniques and algorithms and the use of state-of-the-art high-performance computers. The common thread of such models resides in the fact that the plasma components are at the same time sources of electromagnetic fields, via the charge and current densities that they generate, and subject to the action of electromagnetic fields. This leads to a wide variety of plasma modes of oscillations that resonate with the particle or fluid motion and makes the plasma dynamics much richer than that of conventional, neutral fluids.T he most straightforward way for describing plasmas would be the microscopic particle approach: solving the equations of motion for the many individual particles that form the plasma in externally imposed electromagnetic fields and in the fields that the particles themselves generate. However, this is computationally impossible to apply to realistic magnetic-fusion plasmas, which typically contain 10 22 -10 23 particles. (For a review of the basic concepts of magnetically confined fusion plasmas, see ref. 1.)A statistical treatment leads to the kinetic model, based on the Vlasov equation (equation (1)), essentially Liouville's theorem applied to the specific plasma environment, with interactions that are dominated by electromagnetic fields and a separation between particle collisions -that is, interactions at microscopic scales-and long-range fields. The Vlasov equation describes the evolution of f s (x,v,t), the single-particle phase-space distribution function of the species labelled 's' (electrons or ions), under the e ect of the longrange electric and magnetic fields E and B, which evolve according to Maxwell's equations with plasma charge and current densities as sources:Here, x, v, q s and m s stand for the position, velocity, charge and the mass of a particle of species 's' , respectively. In the Vlasov model, collisions are neglected, an approximation that is generally justified for fusion plasmas because small-scale e ects based on Coulomb interactions become very weak at high temperatures. In fact, Coulomb collisions' cross-sections for the exchange of momentum and energy, and related quantities such as the electrical resistivity ⌘, scale with T 3/2 . In ITER core plasmas (see ref. 1), for example, T ⇡ 10 keV (⇡10 8 K) and the electron-electron ('ee'), electron-ion ('ei') and ion-ion ('ii') collisional exchanges of momentum and energy ('E') occur over relatively long characteristic times:2)-justifying the collisi...

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On the challenge of plasma heating with the JET metallic wall

Cited by 21 publications

References 49 publications

Modelling neutral beams in fusion devices: Beamlet-based model for fast particle simulations

Modelling neutral beams in fusion devices: Beamlet-based model for fast particle simulations

WEST Physics Basis

Computational challenges in magnetic-confinement fusion physics

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