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Abstract Disruption mitigation by shattered Ne pellet injection (SPI) has been simulated for an H-mode ITER D-T discharge of 280 MJ stored energy using the 3D TOKES code. Heating of the first wall from the radiation flash during the thermal quench of the disruption initiated by the injected pellets has been assessed. The dynamics of Ne plasma expansion in the core with radiation from this plasma have been simulated for the series of pellet sizes from 5.4 × 1024 to 8.6 × 1022 Ne atoms. The threshold pellet size for irradiation of the core energy has been found. The results of SPI and massive gas injection simulations are compared. [ABSTRACT FROM AUTHOR]

Simulations of massive gas injection (MGI) into the JET plasma using noble gas (NG) have been performed using the TOKES code. The results of these simulations have been verified by comparison with JET experiment for disruption control. Further simulations performed showed that the amount of NG for triggering the thermal quench can be reduced 40 times comparing with the JET experiment. Such small amount of injected NG should generate runaway electrons (RE) with rather large probability. For mitigation of the wall damage with these RE, a special sacrificial diaphragm consisting of several W ‘nails’ with a characteristic thickness of 2 cm has been proposed. The diaphragm erosion with RE beam has been roughly estimated from above as less than 0.5 cm per disruption. Taking into account the plasma shielding may decrease erosion ∼10 times. [ABSTRACT FROM AUTHOR]

Abstract: Brittle destruction of tungsten armour under action of edge localised modes of plasma instabilities (ELMs) in ITER is an important issue determining the lifetime of the divertor. Besides, cracking of the armour produces tungsten dust with characteristic size of 1–10μm flying from the armour surface with velocities up to 10m/s. Influx of the tungsten dust into the ITER confinement decreases the temperature of the plasma, reduces the thermonuclear gain and even may run the confinement into disruption. This paper describes experiments in QSPA-Kh50 plasma gun and modeling, which has been performed for providing more insight into the physics of tungsten cracking under action of ELMs and for confirmation of the important result on stabilization of the crack development at the tungsten armour surface, predicted in our previous paper – the same authors, 2010. The threshold value of energy density deposition for start of tungsten cracking has been measured as 0.3MJ/m2 after 5–10 shots. From analytical considerations three times smaller threshold value has been predicted with increasing number of shots. [Copyright &y& Elsevier]

Abstract: The interaction of hot plasma with material in fusion devices can result in material erosion and irreversible damage. Carbon based materials are proposed for ITER divertor armour. To simulate carbon erosion under high heat fluxes, electron beam heating in the JUDITH facility has been used. In this paper, carbon erosion under energetic electron impact is modeled by the 3D thermomechanics code ‘PEGASUS-3D’. The code is based on a crack generation induced by thermal stress. The particle emission observed in thermal shock experiments is a result of breaking bonds between grains caused by thermal stress. The comparison of calculations with experimental data from JUDITH shows good agreement for various incident power densities and pulse durations. A realistic mean failure stress has been found. Pre-heating of test specimens results in earlier onset of brittle destruction and enhanced particle loss in agreement with experiments. [Copyright &y& Elsevier]

Exposure of the carbon fibre composites (CFC) NB31 and NS31 by multiple plasma pulses has been performed at the plasma guns MK-200UG and QSPA. Numerical simulation for the same CFCs under ITER type I ELM typical heat load has been carried out using the code PEGASUS-3D. Comparative analysis of the numerical and experimental results allowed understanding the erosion mechanism of CFC based on the simulation results. A modification of CFC structure has been proposed in order to decrease the armour erosion rate. [Copyright &y& Elsevier]

Abstract Fusion system codes are vital computational tools for the assessment of the key design parameters of a fusion power plant. The main goal is to capture the key physics and technology aspects, pushing the solution to comply with physics and engineering requirements and constraints. Based on that, the magnet system has to be designed to match the requirements on magnetic equilibrium as well as the technological constraints on superconductive coils. A dedicated model was developed to evaluate the coupling effects between the external poloidal field coils (PFCs) and the plasma, described in terms of its magnetic equilibrium configuration. The model first attempts to reproduce a magnetic configuration for a given set of plasma parameters within a target confining region. To achieve such an arrangement, a coil solver calculates the toroidal electrical currents in PFCs. In this paper, the mathematical details of this equilibrium model are presented and the main results referred to magnetic flux, field and coil currents are compared to a reference DEMO scenario calculation. [ABSTRACT FROM AUTHOR]

Abstract: Beryllium is foreseen as plasma facing armour for the first wall (FW) in ITER in form of Be-clad blanket modules in macrobrush design with brush size about 8–10cm. In ITER significant heat loads during transient events (TE) and runaway electrons impact are expected at the main chamber wall that may leads to the essential damage of the Be armour. The main mechanisms of metallic target damage remain surface melting, evaporation, and melt motion, which determine the life-time of the plasma facing components. The melt motion damages of Be macrobrush armour caused by the tangential friction force and the J × B forces are analyzed for bulk Be and different sizes of Be-brushes. The damage of the FW due to heat loads caused by runaway electrons is numerically simulated. [Copyright &y& Elsevier]

Abstract: The beryllium is foreseen as plasma facing armour for the first wall in the ITER in form of Be-clad blanket modules in macrobrush design with brush size about 8–10cm. In ITER significant heat loads during transient events (TE) are expected at the main chamber wall that may leads to the essential damage of the Be armour. The main mechanisms of metallic target damage remain surface melting and melt motion erosion, which determines the lifetime of the plasma facing components. Melting thresholds and melt layer depth of the Be armour under transient loads are estimated for different temperatures of the bulk Be and different shapes of transient loads. The melt motion damages of Be macrobrush armour caused by the tangential friction force and the Lorentz force are analyzed for bulk Be and different sizes of Be-brushes. The damage of FW under radiative loads arising during mitigated disruptions is numerically simulated. [Copyright &y& Elsevier]

Abstract: In recent tokamak simulation experiments with the QSPA Kh-50 facility several mechanisms of dust generation from tungsten surfaces under ITER ELM-like energy loads have been identified. Here cracking and melting are reported. The brittle destruction dominates after a few transient impacts when a network of major cracks forms on the surface. Bifurcation of major cracks results in ejection of dust particles with sizes up to ∼30μm. Dust generation occurs also after surface melting and following resolidification when fine crack networks along the grain boundaries develop. In this process the destruction is accompanied by bridge formation due to capillary tension across the fine cracks. Next impacts (even weak melt-free ones) can destroy those bridges, which produces considerable amounts of dust particles of nm-size dust. Surface modification after the repetitive plasma pulses also results in creation of nm-size dust. [Copyright &y& Elsevier]