Natural poloidal asymmetry and neoclassical transport of impurities in tokamak plasmas

Maget, P.; Frank, J.; Nicolas, T; Agullo, O.; Garbet, X.; Lütjens, H.

doi:10.1088/1361-6587/ab53ab

Cited by 17 publications

(42 citation statements)

References 40 publications

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“…In addition, the collisional Pfirsch–Schlüter regime for the main ions is not considered as it requires , leading to different results (Fülöp & Helander 2001; Maget et al. 2020 a , b ). Some C -Mod H mode plasmas may be collisional enough to enter the Pfirsch–Schlüter regime (Theiler et al.…”

Section: Summary Of Resultsmentioning

confidence: 99%

“…Collisional background ions are not considered here, but were investigated by Fülöp & Helander (2001) and Maget et al. (2020 a , b ).…”

Section: Conservation Of Impurity Momentum and Number And Quasineutra...mentioning

confidence: 99%

“…Alternately, for the collisional Pfirsch–Schülter background ions considered by Fülöp & Helander (2001) and Maget et al. (2020 a , b ) the leading modification is a mean free path over parallel connection length correction. In addition, because CXRS measures the impurity flow to determine the radial electric field, the banana regime formulation of Helander has been recast into a form that employs the measured poloidal impurity flow in place of a term that requires solving the complicated kinetic equation for the main ion species in the presence of impurities (Espinosa & Catto 2017 a , b , 2018).…”

Section: Introductionmentioning

confidence: 99%

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Poloidal impurity asymmetries, flow and neoclassical transport in pedestals in the plateau and banana regimes

Bielajew¹,

Catto²

2023

J. Plasma Phys.

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Charge exchange recombination spectroscopy (CXRS) measures the radial electric field in the pedestal by measuring the impurity density, temperature and flow. Combined outboard and inboard CXRS measurements allow poloidal variations that arise due to the poloidal variation of the magnetic field to be determined. At present, impurity neoclassical pedestal models avoid the complications of treating finite poloidal gyroradius effects by assuming the impurity charge number is large compared with the main ion charge number. These models are extended slightly by retaining the impurity radial pressure gradient to demonstrate that no substantial effect occurs due to impurity diamagnetic effects. More importantly, the neoclassical model is significantly extended to obtain a more comprehensive treatment of the main ions in the plateau and banana regimes. A parallel impurity momentum equation is derived that is consistent with previous results in the banana regime and reduces to the proper large aspect ratio form required in the plateau regime. The implications for interpreting the CXRS measurements are discussed by writing all results in terms of the gradient drive and poloidal flow.

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Section: Summary Of Resultsmentioning

confidence: 99%

“…Collisional background ions are not considered here, but were investigated by Fülöp & Helander (2001) and Maget et al. (2020 a , b ).…”

Section: Conservation Of Impurity Momentum and Number And Quasineutra...mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Poloidal impurity asymmetries, flow and neoclassical transport in pedestals in the plateau and banana regimes

Bielajew¹,

Catto²

2023

J. Plasma Phys.

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“…This assumption relies on the fact that the parallel transport is few orders of magnitude faster than the perpendicular transport, such that electron temperature and density distribution is homogenized on each flux surface. This consideration is usually correct in plasmas with low-Z impurities; however, heavy impurities like tungsten can be subject to centrifugal [35], electrostatic [36] or friction forces [37] that induce an asymmetry of their poloidal distribution. For instance, Reinke et al derived an analytical formula for the poloidal asymmetry of the impurity density n S induced by the centrifugal force and by ion cyclotron resonance heating (ICRH):…”

Section: Asymmetric Emissivity Profilesmentioning

confidence: 99%

Implementing an X-ray tomography method for fusion devices

et al. 2021

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In fusion devices, the X-ray plasma emissivity contains essential information on the magnetohydrodynamic activity, the magnetic equilibrium and on the transport of impurities, in particular for tokamaks in the soft X-ray (SXR) energy range of 0.1–20 keV. In this context, tomography diagnostics are a key method to estimate the local plasma emissivity from a given set of line-integrated measurements. Unfortunately, the reconstruction problem is mathematically ill-posed, due to very sparse and noisy measurements, requiring an adequate regularization procedure. The goal of this paper is to introduce, with a didactic approach, some methodology and tools to develop an X-ray tomography algorithm. Based on a simple 1D tomography problem, the Tikhonov regularization is described in detail with a study of the optimal reconstruction parameters, such as the choice of the emissivity spatial resolution and the regularization parameter. A methodology is proposed to perform an in situ sensitivity and position cross-calibration of the detectors with an iterative procedure, by using the information redundancy and data variability in a given set of reconstructed profiles. Finally, the basic steps to build a synthetic tomography diagnostics in a more realistic tokamak environment are introduced, together with some tools to assess the capabilities of the 2D tomography algorithm.

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“…In recent years, special attention has been paid to the poloidal asymmetry of impurity concentrations and its impact on impurity transport [18][19][20][21][22][23]. Unlike conventional neoclassical prediction, which assumes an almost uniform impurity distribution over the flux surface [24], a strong poloidal asymmetry has repeatedly been observed in various cases and mounting evidence suggests that taking account of such asymmetry is key for a predictive model [9].…”

Section: Introductionmentioning

confidence: 99%

Gyrokinetic modelling of light to heavy impurity transport in tokamaks

et al. 2021

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Impurity transport is numerically investigated for different types of impurity, such as helium (He), argon (Ar), and tungsten (W). Both turbulent and neoclassical transports are treated self-consistently using the full-f gyrokinetic software GYSELA. For a light impurity (He), the transport is mainly controlled by turbulence, while neoclassical transport is found to be dominant in the case of a heavy impurity (W). The impact of a poloidal asymmetry of the impurity density is also studied in detail and it is found to be strong in case of a high charge impurity, due to its Boltzmann-type response. Such strong asymmetry might lead to a core accumulation of heavy impurities by reducing the thermal screening factor of neoclassical transport. The two main contributions to neoclassical transport—Pfirsch–Schlüter (PS) flux and banana–plateau (BP) flux—are also studied. Depending on their mass (A) and charge (Z), the magnitudes of each flux are determined accordingly. Tungsten shows a strong PS flux compared to the other impurities, while BP flux is dominant in the case of argon. An analytical model including the effect of poloidal asymmetry is compared with the numerical simulation and a good agreement is found between them.

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Natural poloidal asymmetry and neoclassical transport of impurities in tokamak plasmas

Cited by 17 publications

References 40 publications

Poloidal impurity asymmetries, flow and neoclassical transport in pedestals in the plateau and banana regimes

Poloidal impurity asymmetries, flow and neoclassical transport in pedestals in the plateau and banana regimes

Implementing an X-ray tomography method for fusion devices

Gyrokinetic modelling of light to heavy impurity transport in tokamaks

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