The Experts below are selected from a list of 162 Experts worldwide ranked by ideXlab platform
Marek J. Rubel - One of the best experts on this subject based on the ideXlab platform.
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The role and application of ion beam analysis for studies of plasma-facing components in Controlled Fusion devices
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2016Co-Authors: Marek J. Rubel, Per Petersson, Eduardo Alves, S. Brezinsek, J. P. Coad, Kalle Heinola, M. Mayer, A. M. WiddowsonAbstract:First wall materials in Controlled Fusion devices undergo serious modification by several physical and chemical processes arising from plasma-wall interactions. Detailed information is required for ...
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Dust particles in Controlled Fusion devices : generation mechanism and analysis
2009Co-Authors: Marek J. Rubel, V Philipps, A. Huber, Darya Ivanova, Michaele Freisinger, E. Fortuna, Z. Huang, Jochen Linke, Olaf Neubauer, H J PenkallaAbstract:Fuel inventory and generation of carbon and metal dust in a tokamak are perceived to be serious safety and economy issues for a steady-state operation of a Fusion reactor, e.g. ITER. These topics have been explored in the on-going Ph.D. work in order to contribute to the better understanding and development of methods for controlling and curtailing fuel accumulation and dust formation in Controlled Fusion devices. The work was carried out with material facing Fusion plasmas in three tokamaks: TEXTOR in Forschungszentrum Julich (Germany), Tore Supra in Cadarache (France) and JET in Culham Centre for Fusion Energy (United Kingdom). This thesis provides an account on studies of fuel removal techniques from plasmafacing components (PFCs) and on consequences of dust formation. Following issues are addressed: (a) properties of carbon and metal dust formed in the TEXTOR tokamak; (b) dust generation associated with removal of fuel and co-deposited layers from carbon PFCs from TEXTOR and Tore Supra; (c) surface morphology of wall components after different cleaning treatments; (d) surface properties of diagnostic mirrors tested at JET for ITER. The study dealt with carbon, tungsten and beryllium, i.e. with the three major elements being used for PFC in present-day devices and foreseen for a next-step machine. Some essential results are summarised by the following. (i) The amount of loose dust found on the floor of the TEXTOR liner does not exceed 2 grams with particle size range 0.1 mm – 1 mm. The presence of fine (up to 1 mm) crystalline graphite in the collected matter suggests that brittle destruction of carbon PFC could take place during off-normal events. Carbon is the main component, but there are also magnetic and non-magnetic metal agglomerates. The results obtained strongly indicate that in a carbon wall machine the disintegration of flaking co-deposits on PFC is the main source of dust: (ii) The fuel content in dust and co-deposits varies from 10% on the main limiters to 0.03% on the neutralizer plates as determined by thermal desorption and ionbeam methods: (iii) Fuel removal by annealing in vacuum or by oxidative methods disintegrates codeposits. In the case of thick layers, the treatment makes them brittle thus reducing the adherence to the target and, as a consequence, this leads to the formation of dust: (iv) Application of thermal methods for fuel removal from carbon-rich layers is effective only at high temperatures (above 800 K), i.e. in the range exceeding the allowed baking temperature of the ITER divertor: (v) Photonic cleaning by laser pulses effectively removes fuel-rich deposited layers, but it also produces debris, especially under ablation conditions: (vi) Photonic cleaning of mirrors exposed in JET results in partial recovery of reflectivity, but surfaces are modified by laser pulses. The presentation of results is accompanied by a discussion of their consequences for the future development and the application of fuel and dust removal methods in a next-step Fusion device.
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Ion beam analysis methods in the studies of plasma facing materials in Controlled Fusion devices
Vacuum, 2003Co-Authors: Marek J. Rubel, P Wienhold, D. HildebrandtAbstract:Abstract Application of ion beam analysis techniques in the studies of material transport and fuel inventory in the Controlled Fusion devices is exemplified. Enhanced proton scattering on the carbon isotopes 12 C(p,p) 12 C, 13 C(p,p) 13 C and secondary ion mass spectrometry allowed for determination of carbon erosion and re-deposition on the wall components following the experiments with a tracer ( 13 CH 4 ) injection into the plasma edge at the TEXTOR tokamak. For the assessment of the deuterium fuel accumulation in the plasma facing components depth profiling by means of nuclear reaction analysis, 3 He(d,p) 4 He, was performed. Advantages and limitations of those nuclear methods in solving experimental problems are addressed.
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Dust particles in Controlled Fusion devices: morphology, observations in the plasma and influence on the plasma performance
Nuclear Fusion, 2001Co-Authors: Marek J. Rubel, Marco Cecconello, Jenny-ann Malmberg, Gennady Sergienko, Wolfgang Biel, James R. Drake, Anders Hedqvist, A. Huber, V PhilippsAbstract:The formation and release of particle agglomerates, i.e. debris and dusty objects, from plasma facing components and the impact of such materials on plasma operation in Controlled Fusion devices has been studied in the Extrap T2 reversed field pinch and the TEXTOR tokamak. Several plasma diagnostic techniques, camera observations and surface analysis methods were applied for in situ and ex situ investigation. The results are discussed in terms of processes that are decisive for dust transfer: localized power deposition connected with wall locked modes causing emission of carbon granules, brittle destruction of graphite and detachment of thick flaking co-deposited layers. The consequences for large next step devices are also addressed.
V Philipps - One of the best experts on this subject based on the ideXlab platform.
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Dust particles in Controlled Fusion devices : generation mechanism and analysis
2009Co-Authors: Marek J. Rubel, V Philipps, A. Huber, Darya Ivanova, Michaele Freisinger, E. Fortuna, Z. Huang, Jochen Linke, Olaf Neubauer, H J PenkallaAbstract:Fuel inventory and generation of carbon and metal dust in a tokamak are perceived to be serious safety and economy issues for a steady-state operation of a Fusion reactor, e.g. ITER. These topics have been explored in the on-going Ph.D. work in order to contribute to the better understanding and development of methods for controlling and curtailing fuel accumulation and dust formation in Controlled Fusion devices. The work was carried out with material facing Fusion plasmas in three tokamaks: TEXTOR in Forschungszentrum Julich (Germany), Tore Supra in Cadarache (France) and JET in Culham Centre for Fusion Energy (United Kingdom). This thesis provides an account on studies of fuel removal techniques from plasmafacing components (PFCs) and on consequences of dust formation. Following issues are addressed: (a) properties of carbon and metal dust formed in the TEXTOR tokamak; (b) dust generation associated with removal of fuel and co-deposited layers from carbon PFCs from TEXTOR and Tore Supra; (c) surface morphology of wall components after different cleaning treatments; (d) surface properties of diagnostic mirrors tested at JET for ITER. The study dealt with carbon, tungsten and beryllium, i.e. with the three major elements being used for PFC in present-day devices and foreseen for a next-step machine. Some essential results are summarised by the following. (i) The amount of loose dust found on the floor of the TEXTOR liner does not exceed 2 grams with particle size range 0.1 mm – 1 mm. The presence of fine (up to 1 mm) crystalline graphite in the collected matter suggests that brittle destruction of carbon PFC could take place during off-normal events. Carbon is the main component, but there are also magnetic and non-magnetic metal agglomerates. The results obtained strongly indicate that in a carbon wall machine the disintegration of flaking co-deposits on PFC is the main source of dust: (ii) The fuel content in dust and co-deposits varies from 10% on the main limiters to 0.03% on the neutralizer plates as determined by thermal desorption and ionbeam methods: (iii) Fuel removal by annealing in vacuum or by oxidative methods disintegrates codeposits. In the case of thick layers, the treatment makes them brittle thus reducing the adherence to the target and, as a consequence, this leads to the formation of dust: (iv) Application of thermal methods for fuel removal from carbon-rich layers is effective only at high temperatures (above 800 K), i.e. in the range exceeding the allowed baking temperature of the ITER divertor: (v) Photonic cleaning by laser pulses effectively removes fuel-rich deposited layers, but it also produces debris, especially under ablation conditions: (vi) Photonic cleaning of mirrors exposed in JET results in partial recovery of reflectivity, but surfaces are modified by laser pulses. The presentation of results is accompanied by a discussion of their consequences for the future development and the application of fuel and dust removal methods in a next-step Fusion device.
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Thick Co-Deposits and Dust in Controlled Fusion Devices with Carbon Walls: Fuel Inventory and Growth Rate of Co-Deposited Layers
Physica Scripta, 2003Co-Authors: M Rubel, V Philipps, P Wienhold, T. Tanabe, M. Freisinger, J. Linke, J. Von Seggern, E. WesselAbstract:Recent results regarding the formation of co-deposits, fuel accumulation and overall material transport at the TEXTOR tokamak are described. Two categories of brittle flaking co-deposits were identified: (i) smooth stratified layers of a thickness of up to 50 mum and a fuel content of up to 16 at.%. (ii) granular and columnar structures reaching 1 mm in thickness and containing around 0.5 at.% of fuel species. They were formed on the blades of the toroidal belt pump limiter (similar to 15000 s of plasma operation) and on the neutraliser plates of this limiter (similar to 90000 s), respectively. A comparison is made to the fuel inventory measured in other Controlled Fusion devices with carbon walls
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Erosion and redeposition of wall material in Controlled Fusion devices
Vacuum, 2002Co-Authors: V Philipps, A. Kirschner, P Wienhold, M RubelAbstract:Processes of erosion and redeposition and their impact on plasma facing materials in devices for magnetically confined Fusion are discussed. Volatile molecules formed in the erosion process are partly pumped out but the majority of species released from the wall components returns to the surface causing the modification of its morphology. Prompt redeposition and redeposition after global transport reduce the gross erosion at any surface. Detailed analysis shows that erosion and deposition can coexist on otherwise erosion-dominated surfaces due to local inhomogenities. The erosion yield of redeposited material of sub-monolayer thickness significantly differs from that observed for thick targets. On deposition dominated areas one observes the formation of thick co-deposits containing a mixture of trapped fuel atoms (hydrogen isotopes) and species removed originally from the wall. This leads to a large and long-term fuel accumulation (tritium inventory) in a device. Reduced mechanical integrity of such layers stimulates their flaking and peeling-off if a critical thickness has been reached. This, in turn, results in the formation of hydrogen-rich dust particles.
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Erosion and redeposition of wall material in Controlled Fusion devices
Vacuum, 2002Co-Authors: V Philipps, A. Kirschner, P Wienhold, M RubelAbstract:Processes of erosion and redeposition and their impact on plasma facing materials in devices for magnetically confined Fusion are discussed. Volatile molecules formed in the erosion process are partly pumped out but the majority of species released from the wall components returns to the surface causing the modification of its morphology. Prompt redeposition and redeposition after global transport reduce the gross erosion at any surface. Detailed analysis shows that erosion and deposition can coexist on otherwise erosion-dominated surfaces due to local inhomogenities. The erosion yield of redeposited material of sub-monolayer thickness significantly differs from that observed for thick targets. On deposition dominated areas one observes the formation of thick co-deposits containing a mixture of trapped fuel atoms (hydrogen isotopes) and species removed originally from the wall. This leads to a large and long-term fuel accumulation (tritium inventory) in a device. Reduced mechanical integrity of such layers stimulates their flaking and peeling-off if a critical thickness has been reached. This, in turn, results in the formation of hydrogen-rich dust particles. (C) 2002 Elsevier Science Ltd. All rights reserved
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Dust particles in Controlled Fusion devices: morphology, observations in the plasma and influence on the plasma performance
Nuclear Fusion, 2001Co-Authors: Marek J. Rubel, Marco Cecconello, Jenny-ann Malmberg, Gennady Sergienko, Wolfgang Biel, James R. Drake, Anders Hedqvist, A. Huber, V PhilippsAbstract:The formation and release of particle agglomerates, i.e. debris and dusty objects, from plasma facing components and the impact of such materials on plasma operation in Controlled Fusion devices has been studied in the Extrap T2 reversed field pinch and the TEXTOR tokamak. Several plasma diagnostic techniques, camera observations and surface analysis methods were applied for in situ and ex situ investigation. The results are discussed in terms of processes that are decisive for dust transfer: localized power deposition connected with wall locked modes causing emission of carbon granules, brittle destruction of graphite and detachment of thick flaking co-deposited layers. The consequences for large next step devices are also addressed.
M Rubel - One of the best experts on this subject based on the ideXlab platform.
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Thick Co-Deposits and Dust in Controlled Fusion Devices with Carbon Walls: Fuel Inventory and Growth Rate of Co-Deposited Layers
Physica Scripta, 2003Co-Authors: M Rubel, V Philipps, P Wienhold, T. Tanabe, M. Freisinger, J. Linke, J. Von Seggern, E. WesselAbstract:Recent results regarding the formation of co-deposits, fuel accumulation and overall material transport at the TEXTOR tokamak are described. Two categories of brittle flaking co-deposits were identified: (i) smooth stratified layers of a thickness of up to 50 mum and a fuel content of up to 16 at.%. (ii) granular and columnar structures reaching 1 mm in thickness and containing around 0.5 at.% of fuel species. They were formed on the blades of the toroidal belt pump limiter (similar to 15000 s of plasma operation) and on the neutraliser plates of this limiter (similar to 90000 s), respectively. A comparison is made to the fuel inventory measured in other Controlled Fusion devices with carbon walls
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Erosion and redeposition of wall material in Controlled Fusion devices
Vacuum, 2002Co-Authors: V Philipps, A. Kirschner, P Wienhold, M RubelAbstract:Processes of erosion and redeposition and their impact on plasma facing materials in devices for magnetically confined Fusion are discussed. Volatile molecules formed in the erosion process are partly pumped out but the majority of species released from the wall components returns to the surface causing the modification of its morphology. Prompt redeposition and redeposition after global transport reduce the gross erosion at any surface. Detailed analysis shows that erosion and deposition can coexist on otherwise erosion-dominated surfaces due to local inhomogenities. The erosion yield of redeposited material of sub-monolayer thickness significantly differs from that observed for thick targets. On deposition dominated areas one observes the formation of thick co-deposits containing a mixture of trapped fuel atoms (hydrogen isotopes) and species removed originally from the wall. This leads to a large and long-term fuel accumulation (tritium inventory) in a device. Reduced mechanical integrity of such layers stimulates their flaking and peeling-off if a critical thickness has been reached. This, in turn, results in the formation of hydrogen-rich dust particles.
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Erosion and redeposition of wall material in Controlled Fusion devices
Vacuum, 2002Co-Authors: V Philipps, A. Kirschner, P Wienhold, M RubelAbstract:Processes of erosion and redeposition and their impact on plasma facing materials in devices for magnetically confined Fusion are discussed. Volatile molecules formed in the erosion process are partly pumped out but the majority of species released from the wall components returns to the surface causing the modification of its morphology. Prompt redeposition and redeposition after global transport reduce the gross erosion at any surface. Detailed analysis shows that erosion and deposition can coexist on otherwise erosion-dominated surfaces due to local inhomogenities. The erosion yield of redeposited material of sub-monolayer thickness significantly differs from that observed for thick targets. On deposition dominated areas one observes the formation of thick co-deposits containing a mixture of trapped fuel atoms (hydrogen isotopes) and species removed originally from the wall. This leads to a large and long-term fuel accumulation (tritium inventory) in a device. Reduced mechanical integrity of such layers stimulates their flaking and peeling-off if a critical thickness has been reached. This, in turn, results in the formation of hydrogen-rich dust particles. (C) 2002 Elsevier Science Ltd. All rights reserved
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carbon particles emission brittle destruction and co deposit formation experience from electron beam experiments and Controlled Fusion devices
Physica Scripta, 2001Co-Authors: J. Linke, M Rubel, Jenny-ann Malmberg, James R. Drake, R Duwe, H J Penkalla, M Rodig, E. WesselAbstract:Graphite erosion leading to the formation of carbon clusters and dust particles under high power deposition has been studied using an electron beam facility and in various types of Controlled Fusion devices with carbon walls. It is shown that brittle destruction of graphite takes place in both systems and it results in the production of debris of a sub-millimeter to millimeter size. In electron beam experiments fine grain graphites and carbon fiber composite have been subjected to intense transient heat loads with deposited energy densities of up to several tens of MJ m-2 in order to simulate plasma disruptions (5 ms pulse duration) or vertical displacement events (100–1000 ms pulse duration). In a reversed field pinch the brittle destruction has been caused by a pronounced mode activity (and related power loads to the wall, over 1 GW m-2) at the very edge of the plasma during wall locking phase of discharges. Particles or dust generated during the thermal load tests and in Fusion devices have been collected and analyzed using optical and various electron microscopy methods.
F Engelmann - One of the best experts on this subject based on the ideXlab platform.
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Controlled Fusion and Plasma Physics
Plasma Physics and Controlled Fusion, 2007Co-Authors: F EngelmannAbstract:This new book by Kenro Miyamoto provides an up-to-date overview of the status of Fusion research and the important parts of the underlying plasma physics at a moment where, due to the start of ITER construction, an important step in Fusion research has been made and many new research workers will enter the field. For them, and also for interested graduate students and physicists in other fields, the book provides a good introduction into Fusion physics as, on the whole, the presentation of the material is quite appropriate for getting acquainted with the field on the basis of just general knowledge in physics. There is overlap with Miyamoto's earlier book Plasma Physics for Nuclear Fusion (MIT Press, Cambridge, USA, 1989) but only in a few sections on subjects which have not evolved since. The presentation is subdivided into two parts of about equal length. The first part, following a concise survey of the physics basis of thermonuclear Fusion and of plasmas in general, covers the various magnetic configurations studied for plasma confinement (tokamak; reversed field pinch; stellarator; mirror-type geometries) and introduces the specific properties of plasmas in these devices. Plasma confinement in tokamaks is treated in particular detail, in compliance with the importance of this field in Fusion research. This includes a review of the ITER concept and of the rationale for the choice of ITER's parameters. In the second part, selected topics in Fusion plasma physics (macroscopic instabilities; propagation of waves; kinetic effects such as energy transfer between waves and particles including microscopic instabilities as well as plasma heating and current drive; transport phenomena induced by turbulence) are presented systematically. While the emphasis is on displaying the essential physics, deeper theoretical analysis is also provided here. Every chapter is complemented by a few related problems, but only partial hints for their solution are given. A selection of references, mostly to articles covering original research, allows the interested reader to go deeper into the various subjects. There are a few quite relevant areas which are essentially not covered in the book (plasma diagnostics; fuelling). The discussion of particle and power exhaust is limited to tokamaks and is somewhat scarce. Other points which I did not find fully satisfactory are: the index is too selective and does not really allow easy access to any specific subject. Cross references between different sections treating related topics are not always given. There are quite a lot of typographical errors which as far as cross references are concerned may be disturbing. A list of the symbols used would be a helpful supplement, especially since some of them appear with different meanings. There are apparent imperfections in the structure of certain chapters. While the English is sometimes unusual, this generally does not affect the readability. Overall, the book can be warmly recommended to all interested in familiarizing themselves with the physics of magnetic Fusion.
W M Tang - One of the best experts on this subject based on the ideXlab platform.
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predicting disruptive instabilities in Controlled Fusion plasmas through deep learning
Nature, 2019Co-Authors: Julian Katesharbeck, Alexey Svyatkovskiy, W M TangAbstract:Nuclear Fusion power delivered by magnetic-confinement tokamak reactors holds the promise of sustainable and clean energy1. The avoidance of large-scale plasma instabilities called disruptions within these reactors2,3 is one of the most pressing challenges4,5, because disruptions can halt power production and damage key components. Disruptions are particularly harmful for large burning-plasma systems such as the multibillion-dollar International Thermonuclear Experimental Reactor (ITER) project6 currently under construction, which aims to be the first reactor that produces more power from Fusion than is injected to heat the plasma. Here we present a method based on deep learning for forecasting disruptions. Our method extends considerably the capabilities of previous strategies such as first-principles-based5 and classical machine-learning7–11 approaches. In particular, it delivers reliable predictions for machines other than the one on which it was trained—a crucial requirement for future large reactors that cannot afford training disruptions. Our approach takes advantage of high-dimensional training data to boost predictive performance while also engaging supercomputing resources at the largest scale to improve accuracy and speed. Trained on experimental data from the largest tokamaks in the United States (DIII-D12) and the world (Joint European Torus, JET13), our method can also be applied to specific tasks such as prediction with long warning times: this opens up the possibility of moving from passive disruption prediction to active reactor control and optimization. These initial results illustrate the potential for deep learning to accelerate progress in Fusion-energy science and, more generally, in the understanding and prediction of complex physical systems. Using data from plasma-based tokamak nuclear reactors in the US and Europe, a machine-learning approach based on deep neural networks is taught to forecast disruptions, even those in machines on which the algorithm was not trained.