Publications (8)7.27 Total impact
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Article: Integrated ELM Modelling
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ABSTRACT: This paper presents a short overview of current trends and progress in integrated ELM modelling. First, the concept of integrated ELM modelling is introduced, various interpretations of it are given and the need for it is discussed. Then follows an overview of different techniques and methods used in integrated ELM modelling presented roughly according to physics approached in use and in order of increasing complexity. The paper concludes with a short discussion of open issues and future modelling requirements within the field of integrated ELM modelling. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)Beiträge aus der Plasmaphysik 08/2006; 46(7‐9):726 - 738. -
Article: Predictive transport modelling of type I ELMy H-mode dynamics using a theory-motivated combined ballooning–peeling model
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ABSTRACT: This paper discusses predictive transport simulations of the type I ELMy high confinement mode (H-mode) with a theory-motivated edge localized mode (ELM) model based on linear ballooning and peeling mode stability theory. In the model, a total mode amplitude is calculated as a sum of the individual mode amplitudes given by two separate linear differential equations for the ballooning and peeling mode amplitudes. The ballooning and peeling mode growth rates are represented by mutually analogous terms, which differ from zero upon the violation of a critical pressure gradient and an analytical peeling mode stability criterion, respectively. The damping of the modes due to non-ideal magnetohydrodynamic effects is controlled by a term driving the mode amplitude towards the level of background fluctuations. Coupled to simulations with the JETTO transport code, the model qualitatively reproduces the experimental dynamics of type I ELMy H-mode, including an ELM frequency that increases with the external heating power. The dynamics of individual ELM cycles is studied. Each ELM is usually triggered by a ballooning mode instability. The ballooning phase of the ELM reduces the pressure gradient enough to make the plasma peeling unstable, whereby the ELM continues driven by the peeling mode instability, until the edge current density has been depleted to a stable level. Simulations with current ramp-up and ramp-down are studied as examples of situations in which pure peeling and pure ballooning mode ELMs, respectively, can be obtained. The sensitivity with respect to the ballooning and peeling mode growth rates is investigated. Some consideration is also given to an alternative formulation of the model as well as to a pure peeling model.Plasma Physics and Controlled Fusion 06/2004; 46(8):1197. · 2.42 Impact Factor -
Article: Predictive transport modelling and MHD stability analysis of mixed type I-II ELMy H-mode JET plasmas
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ABSTRACT: Mixed type I-II ELMy H-mode, a mode operation with small, frequent type II edge localized modes (ELMs) interrupted by occasional large type I ELMs, has been observed in various experimental situations. This paper combines two simple models for type I and type II ELMs, respectively (used e.g. in Lönnroth et al 2003 Plasma Phys. Control. Fusion 45 1689) into an improved scheme for modelling of mixed type I-II ELMy H-mode, which has been implemented in the 1.5D core transport code JETTO together with simple schemes for modelling of pure type I and type II ELMy H-modes based on the same ideas. In the ELM modelling, transport during the ELMs is enhanced by edge-localized radially Gaussian-shaped perturbations to the transport coefficients. Type I and type II ELMs are represented by perturbations with different widths and amplitudes and controlled by different stability limits derived from magnetohydrodynamic (MHD) stability analysis. Some justification from theory and numerical analysis is given for the representation of each ELM type. Predictive transport simulations with JETTO demonstrate that the experimental dynamics of mixed type I-II ELMy H-mode can be qualitatively reproduced using the present model. For completeness, the modelling of mixed type I-II ELMy H-mode is compared with reference simulations of pure type I and pure type II ELMy H-mode and the differences, e.g. in confinement are explained. In addition, this paper presents the results of MHD stability analysis of a number of situations experimentally found to be favourable for the occurrence of type II ELMs, namely situations with strong external neutral gas puffing, a quasi-double-null magnetic configuration, high poloidal β (ratio of the total pressure to the kinetic pressure) and combinations of high edge safety factor q95 and high triangularity δ. The results of the analysis of the given scenarios are such that the model used in this paper can explain why these situations can be favourable for mixed type I-II or pure type II ELMy H-mode.Plasma Physics and Controlled Fusion 03/2004; 46(5):767. · 2.42 Impact Factor -
Article: Edge localized mode physics and operational aspects in tokamaks
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ABSTRACT: Recent progress in experimental and theoretical studies of edge localized mode (ELM) physics is reviewed for the reactor relevant plasma regimes, namely the high confinement regimes, that is, H-modes and advanced scenarios.Theoretical approaches to ELM physics, from a linear ideal magnetohydrodynamic (MHD) stability analysis to non-linear transport models with ELMs are discussed with respect to experimental observations, in particular the fast collapse of pedestal pressure profiles, magnetic measurements and scrape-off layer transport during ELMs.High confinement regimes with different types of ELMs are addressed in this paper in the context of development of operational scenarios for ITER. The key parameters that have been identified at present to reduce the energy losses in Type I ELMs are operation at high density, high edge magnetic shear and high triangularity. However, according to the present experimental scaling for the energy losses in Type I ELMs, the extrapolation of such regimes for ITER leads to unacceptably large heat loads on the divertor target plates exceeding the material limits. High confinement H-mode scenarios at high triangularity and high density with small ELMs (Type II), mixed regimes (Type II and Type I) and combined advanced regimes at high βp are discussed for present-day tokamaks. The optimum combination of high confinement and small MHD activity at the edge in Type II ELM scenarios is of interest to ITER. However, to date, these regimes have been achieved in a rather narrow operational window and far from ITER parameters in terms of collisionality, edge safety factor and βp.The compatibility of the alternative internal transport barrier (ITB) scenario with edge pedestal formation and ELMs is also addressed. Edge physics issues related to the possible combination of small benign ELMs (Type III, Type II ELMs, quiescent double barrier) and high performance ITBs are discussed for present-day experiments (JET, JT-60U, DIII-D) in terms of their relevance for ITER. Successful plasma edge control, at high triangularity (~0.5) and high density (~0.7nGR), in ITB scenarios in JET is reported.Active control of ELMs by edge current, pellet injection, impurities and external magnetic perturbations creating an ergodic zone localized at the separatrix are discussed for present-day experiments and from the perspective of future reactors.Plasma Physics and Controlled Fusion 11/2003; 45(12A):A93. · 2.42 Impact Factor -
Article: Edge localized mode physics and operational aspects in tokamaks
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ABSTRACT: Recent progress in experimental and theoretical studies of edge localized mode (ELM) physics is reviewed for the reactor relevant plasma regimes, namely the high confinement regimes, that is, H-modes and advanced scenarios. Theoretical approaches to ELM physics, from a linear ideal magnetohydrodynamic (MHD) stability analysis to non-linear transport models with ELMs are discussed with respect to experimental observations, in particular the fast collapse of pedestal pressure profiles, magnetic measurements and scrape-off layer transport during ELMs. High confinement regimes with different types of ELMs are addressed in this paper in the context of development of operational scenarios for ITER. The key parameters that have been identified at present to reduce the energy losses in Type I ELMs are operation at high density, high edge magnetic shear and high triangularity. However, according to the present experimental scaling for the energy losses in Type I ELMs, the extrapolation of such regimes for ITER leads to unacceptably large heat loads on the divertor target plates exceeding the material limits. High confinement H-mode scenarios at high triangularity and high density with small ELMs (Type II), mixed regimes (Type II and Type I) and combined advanced regimes at high βp are discussed for present-day tokamaks. The optimum combination of high confinement and small MHD activity at the edge in Type II ELM scenarios is of interest to ITER. However, to date, these regimes have been achieved in a rather narrow operational window and far from ITER parameters in terms of collisionality, edge safety factor and βp.Plasma Physics and Controlled Fusion, v.45, A93-A113 (2003). -
Article: Edge localized modes control: experiment and theory
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ABSTRACT: The paper reviews recent theoretical and experimental results focussing on the identification of the key factors controlling ELM energy and particle losses both in natural ELMs and in the presence of external controlling mechanisms. Present experiment and theory pointed out the benefit of the high plasma shaping, high q95 and high pedestal density in reducing the ELM affected area and conductive energy losses in Type I ELMs. Small benign ELMs regimes in present machines (EDA, HRS, Type II, Grassy, QH, Type III in impurity seeded discharges at high δ ) and their relevance for ITER are reviewed. Recent studies of active control of ELMs using stochastic boundaries, small pellets and edge current generation are presented.Journal of Nuclear Materials. -
Article: ELM Control by Resonant Magnetic Perturbations: Overview of Research by the ITPA Pedestal and Edge Physics Group
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Article: ITER ELM Control Requirements, ELM Control Schemes and Required R&D
Top co-authors
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Institutions
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2006
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The University of York
York, ENG, United Kingdom
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2003–2004
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Culham Centre for Fusion Energy
Abingdon, ENG, United Kingdom
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