B. Bazylev
Karlsruhe Institute of Technology
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Featured researches published by B. Bazylev.
Physica Scripta | 2007
B. Bazylev; G Janeschitz; I. Landman; S Pestchanyi; A. Loarte; G Federici; M. Merola; J. Linke; A Zhitlukhin; V Podkovyrov; N S Klimov; V Safronov
Carbon-fibre composite (CFC) and tungsten macrobrush armours are foreseen as PFC for the ITER divertor. In ITER the main mechanisms of metallic armour damage remain surface melting and melt motion erosion. In the case of CFC armour, due to rather different heat conductivities of CFC fibres a noticeable erosion of the PAN bundles may occur at rather small heat loads. Experiments carried out in the plasma gun facilities QSPA-T for the ITER like edge localized mode (ELM) heat load also demonstrated significant erosion of the frontal and lateral brush edges. Numerical simulations of the CFC and tungsten (W) macrobrush target damage accounting for the heat loads at the face and lateral brush edges were carried out for QSPA-T conditions using the three-dimensional (3D) code PHEMOBRID. The modelling results of CFC damage are in a good qualitative and quantitative agreement with the experiments. Estimation of the droplet splashing caused by the Kelvin–Helmholtz (KH) instability was performed.
Journal of Nuclear Materials | 2002
H. Würz; B. Bazylev; I. Landman; S. Pestchanyi; V.M. Safronov
Abstract Sputtering, evaporation and macroscopic erosion determine the lifetime of the ‘in vessel’ armour materials CFC, tungsten and beryllium presently under discussion for future tokamaks. For CFC armour macroscopic erosion means brittle destruction and dust formation whereas for metallic armour melt layer erosion by melt motion and droplet splashing. Available results on macroscopic erosion from hot plasma and e-beam simulation experiments and from tokamaks are critically evaluated and a comprehensive discussion of experimental and numerical macroscopic erosion and its extrapolation to future tokamaks is given. Shielding of divertor armour materials by their own vapor exists during plasma disruptions. The evolving plasma shield protects the armour from high heat loads, absorbs the incoming energy and reradiates it volumetrically thus reducing drastically the deposited energy. As a result, vertical target erosion by vaporization turns out to be of the order of a few microns per disruption event and macroscopic erosion becomes the dominant erosion source.
Journal of Nuclear Materials | 2001
H. Würz; S. Pestchanyi; B. Bazylev; I. Landman; F. Kappler
During off-normal events besides evaporation macroscopic erosion might occur. In carbon-based materials (CBMs) macroscopic erosion means brittle destruction and dust formation and in metals melt layer motion and droplet splashing. Dust, melt flow, droplet splashing and redeposited evaporated material produce complex layers with considerable surface roughness and drastically reduced heat conductivity. Moreover flaking and easy levitation of particles might occur. Subsequent ELMs when depositing their energy into such layers might enhance impurity production because of increased heating of the hot spots. For vertical targets and for first walls (FWs) macroscopic erosion is analyzed. For a simplified hot spot scenario a first estimation on maximum tolerable ELM energy is given.
Nuclear Fusion | 2015
C. Reux; V. Plyusnin; B. Alper; D. Alves; B. Bazylev; E. Belonohy; A. Boboc; S. Brezinsek; I. Coffey; J. Decker; P. Drewelow; S. Devaux; P. de Vries; A. Fil; S. Gerasimov; L. Giacomelli; S. Jachmich; E. M. Khilkevitch; V. Kiptily; R. Koslowski; U. Kruezi; M. Lehnen; I. Lupelli; P. Lomas; A. Manzanares; A. Martín de Aguilera; G. F. Matthews; J. Mlynář; E. Nardon; Emelie Nilsson
Disruptions are a major operational concern for next generation tokamaks, including ITER. They may generate excessive heat loads on plasma facing components, large electromagnetic forces in the machine structures and several MA of multi-MeV runaway electrons. A more complete understanding of the runaway generation processes and methods to suppress them is necessary to ensure safe and reliable operation of future tokamaks. Runaway electrons were studied at JET-ILW showing that their generation dependencies (accelerating electric field, avalanche critical field, toroidal field, MHD fluctuations) are in agreement with current theories. In addition, vertical stability plays a key role in long runaway beam formation. Energies up to 20 MeV are observed. Mitigation of an incoming runaway electron beam triggered by massive argon injection was found to be feasible provided that the injection takes place early enough in the disruption process. However, suppressing an already accelerated runaway electron beam in the MA range was found to be difficult even with injections of more than 2 kPa.m3 high-Z gases such as krypton or xenon. This may be due to the presence of a cold background plasma weakly coupled to the runaway electron beam which prevents neutrals from penetrating in the electron beam core. Following unsuccessful mitigation attempts, runaway electron impacts on beryllium plasma-facing components were observed, showing localized melting with toroidal asymmetries.
Nuclear Fusion | 2015
J. W. Coenen; G. Arnoux; B. Bazylev; G. F. Matthews; A. Autricque; I. Balboa; M. Clever; R. Dejarnac; I. Coffey; Y. Corre; S. Devaux; L. Frassinetti; E. Gauthier; J. Horacek; S. Jachmich; M. Komm; M. Knaup; K. Krieger; S. Marsen; A. Meigs; Ph. Mertens; R.A. Pitts; T. Puetterich; M. Rack; M. Stamp; G. Sergienko; P. Tamain; V. Thompson; Jet-Efda Contributors
The original goals of the JET ITER-like wall included the study of the impact of an all W divertor on plasma operation (Coenen et al 2013 Nucl. Fusion 53 073043) and fuel retention (Brezinsek et al 2013 Nucl. Fusion 53 083023). ITER has recently decided to install a full-tungsten (W) divertor from the start of operations. One of the key inputs required in support of this decision was the study of the possibility of W melting and melt splashing during transients. Damage of this type can lead to modifications of surface topology which could lead to higher disruption frequency or compromise subsequent plasma operation. Although every effort will be made to avoid leading edges, ITER plasma stored energies are sufficient that transients can drive shallow melting on the top surfaces of components. JET is able to produce ELMs large enough to allow access to transient melting in a regime of relevance to ITER. Transient W melt experiments were performed in JET using a dedicated divertor module and a sequence of I-P = 3.0 MA/B-T = 2.9 T H-mode pulses with an input power of P-IN = 23 MW, a stored energy of similar to 6 MJ and regular type I ELMs at Delta W-ELM = 0.3 MJ and f(ELM) similar to 30 Hz. By moving the outer strike point onto a dedicated leading edge in the W divertor the base temperature was raised within similar to 1 s to a level allowing transient, ELM-driven melting during the subsequent 0.5 s. Such ELMs (delta W similar to 300 kJ per ELM) are comparable to mitigated ELMs expected in ITER (Pitts et al 2011 J. Nucl. Mater. 415 (Suppl.) S957-64). Although significant material losses in terms of ejections into the plasma were not observed, there is indirect evidence that some small droplets (similar to 80 mu m) were released. Almost 1 mm (similar to 6 mm(3)) of W was moved by similar to 150 ELMs within 7 subsequent discharges. The impact on the main plasma parameters was minor and no disruptions occurred. The W-melt gradually moved along the leading edge towards the high-field side, driven by j x B forces. The evaporation rate determined from spectroscopy is 100 times less than expected from steady state melting and is thus consistent only with transient melting during the individual ELMs. Analysis of IR data and spectroscopy together with modelling using the MEMOS code Bazylev et al 2009 J. Nucl. Mater. 390-391 810-13 point to transient melting as the main process. 3D MEMOS simulations on the consequences of multiple ELMs on damage of tungsten castellated armour have been performed. These experiments provide the first experimental evidence for the absence of significant melt splashing at transient events resembling mitigated ELMs on ITER and establish a key experimental benchmark for the MEMOS code.
Fusion Technology | 1997
Hermann WÜrz; Nicolai Arkhipov; Vitali Bakhtin; B. Bazylev; I. Landman; Valeri Safronov; Dima Toporkov; Sergej Vasenin; Anatoli Zhitlukhin
In evaluating the lifetime of plasma-facing components for the International Thermonuclear Experimental Reactor (ITER) against nonnormal high heat loads, credit is taken from the existence of a plasma shield that protects the target from excessive evaporation. Formation and physical properties of plasma shields are studied at the dual plasma gun facility, 2MK-200, under conditions simulating ITER hard disruptions and edge-localized modes (ELMs). The experimental results are used for validation of the theoretical modeling of the plasma/surface interaction. The important features of the non-local thermodynamic equilibrium plasma shield, such as temperature and density distribution, its evolution, the conversion efficiency of the energy of the plasma stream into total and soft X-ray radiation from highly ionized evaporated target material, and the energy balance in the plasma shield, are reproduced quite well. Thus, realistic modeling of ITER disruptive plasma/wall interaction is now possible. Because of the rather small target erosion in the simulation experiments, material erosion for ITER typical disruptions and ELMs cannot be evaluated from these simulation experiments. This requires additional simulation experiments with hot plasma streams of longer pulse duration and a separate numerical analysis, which can now be performed with validated theoretical models.
Physica Scripta | 2011
B. Bazylev; Yu. Igitkhanov; J W Coenen; V. Philipps; Y. Ueda
Tungsten, in the form of a macrobrush, is seen as one of the candidate materials for the ITER divertor. The melting of tungsten, melt motion and melt splashing are expected to be the main mechanisms of surface damage, which determines the lifetime of plasma-facing components. Experiments with long-time plasma action at the metallic surface in a strong magnetic field demonstrate that the J×B force generated by thermo-emission electrons dominates in the acceleration of the melt layer and leads to high target damage. In this paper, numerical simulations of tungsten target damage caused by the long-time plasma heat loads supporting the TEXTOR experiments are performed by the MEMOS code. The calculated tungsten target damage is in good agreement with the target damage observed in the TEXTOR experiments, which allows projections of surface damage to be made at ITER and DEMO conditions.
Physica Scripta | 2011
N S Klimov; V L Podkovyrov; D V Kovalenko; A M Zhitlukhin; V A Barsuk; I. Mazul; Radmir Giniyatulin; V Ye Kuznetsov; B. Riccardi; A. Loarte; M. Merola; V.S. Koidan; J. Linke; I. Landman; S Pestchanyi; B. Bazylev
This paper concerns the experimental study of damage of ITER divertor plasma-facing components (PFCs) under a combination of pulsed plasma heat loads (representative of controlled ITER type I edge-localized modes (ELMs)) and quasi-stationary heat loads (representative of the high heat flux (HHF) thermal fatigue expected during ITER normal operations and slow transient events). The PFCs tungsten armor damage under pulsed plasma exposure was driven by (i) the melt layer motion, which leads to bridges formation between neighboring tiles and (ii) the W brittle failure giving rise to a stable crack pattern on the exposed surface. The crack width reaches a saturation value that does not exceed some tens of micrometers after several hundreds of ELM-like pulses. HHF thermal fatigue tests have shown (i) a peeling-off of the re-solidified material due to its brittle failure and (ii) a significant widening (up to 10 times) of the cracks and the formation of additional cracks.
Physica Scripta | 2009
B. Bazylev; I. Landman; A. Loarte; N S Klimov; V Podkovyrov; V Safronov
Tungsten in the form of macrobrush is foreseen as one of the candidate materials for the ITER divertor. Melting of tungsten, the melt motion and melt splashing are expected to be the main mechanisms of damage determining the lifetime of plasma-facing components. Experimental investigations of droplet emission from the W melt layer for ELM-like heat loads were carried out at the plasma gun facility QSPA-T. Distribution functions of droplet velocity and droplet sizes for different heat loads were determined.In the paper, the main physical mechanism (the Kelvin?Helmholtz instability) of the melt splashing under the heat loads being applied at QSPA-T and those anticipated after the ITER transients is analyzed. Analytical distribution functions for droplet sizes and droplet velocities are defined. Numerical simulations demonstrated a reasonable agreement with the experimental data on the droplet sizes and droplet velocities and allowed projections of the melt splashing at ITER conditions.
Journal of Nuclear Materials | 1996
H. Würz; I. Landman; B. Bazylev; F. Kappler; G. Piazza; S. Pestchanyi
Abstract During plasma disruptions and ELMs a plasma shield from vaporized target material is formed in front of the divertor plates within a few microseconds which protects the divertor against further excessive evaporation. For calculations of plasma shield formation and material erosion the one dimensional (1 D) radiation magnetohydrodynamics (MHD) code FOREV-1 with 1 1 2 D MHD model was developed. Experimental results on plasma shield formation obtained at the 2MK-200 disruption simulation facility were used to check the adequacy of the physical models used in FOREV-1. It was demonstrated that the theoretical models adequately describe the complex physical processes during plasma shield formation. Plasma shield formation and material erosion in a tokamak is a 2 D problem requiring a 2 1 2 D MHD model. For modeling of this situation the 2 D code FOREV-2 is under development. First results are presented here.