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TOKES simulations of shattered Ne pellets injection into the ITER discharge of 280 MJ thermal plasma energy was carried out taking into account shielding of the pellet. Injection was simulated to be performed through 3 upper port launchers or through 1 equatorial launcher. The shielding of pellets with 2 kPa m3 Ne has minor effects on the radiated power and on wall heat load because the injected amount is much larger than required for radiation. However, the minimum Ne amount, which radiates more than 90% of the core plasma energy (the threshold) is reduced by a factor of 2 compared to the result without shielding. The thresholds are 3 × 16 Pa m3 for upper injection and 62 Pa m3 for the equatorial injector. [ABSTRACT FROM AUTHOR]

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]

Abstract: The integrated tokamak simulation code TOKES is proposed for estimation of the ITER first wall radiation damage during massive injection of noble gas inside the core for mitigation of the disruptions. Simulations of MGI processes ab initio are almost impossible because of complexity of the problem, but one can get reliable results elaborating the TOKES scenario from JET experiments and applying it for ITER conditions. With this aim the TOKES code is used for simulation of JET shots disrupted with MGI. The TOKES scenario for the thermal quench of MGI at JET and its extrapolation to ITER have been developed basing on analysis of the available JET database and on comparison with the simulations performed. [Copyright &y& Elsevier]

Abstract: Simulations of tungsten armour cracking under small ELM-like plasma heat load, which does not cause surface melting, have been performed using the PEGASUS-3D code. A dedicated series of experiments have been performed in the QSPA-Kh50 facility for measurements of the unknown tungsten thermophysical properties and for verification of the PEGASUS-3D simulation results. The simulations revealed that a cellular crack network with average mesh size Λ ∼0.5mm formed after first ELMs and the pattern does not change further. With increasing number of repetitive ELMs loads, the average crack width Δ(n) has a maximum value Δ m . The ratio of Δ m /Λ is equal to the tungsten thermal expansion at the maximum surface temperature. Δ(n) tends to this value exponentially. The number of ELMs n m needed for Δ stabilization depends on the ELMs energy density and time duration, n m ∼300 for the simulated ELMs of 0.45MJ/m2 and 0.25ms duration. The PEGASUS-3D code is prepared for simulations of tungsten armour damage under action of ELMs of various energy deposition and time duration. These parameters of ELMs depend on ITER regimes of operation and on how successful will be the efforts on ELMs mitigation. [ABSTRACT FROM AUTHOR]

Abstract: Analysis of the peculiarities of the erosion of NB31 CFC allowed proposition of a new CFC fibre structure for considerable reduction of the erosion rate. The improvement concerns the needling and vowing fibres arrangement only and keeping the same structure of the pitch fibres – the main heat conducting component of NB31. The needling and the vowing fibres of the improved structure provide the armour stiffness, comparable to that of NB31. Numerical simulation of erosion for CFC with the improved structure has confirmed that the erosion rate is four to five times lower in comparison with that of NB31. [Copyright &y& Elsevier]

Carbon fiber composites, CFC, newly developed for the divertor armor of the future tokamak ITER, have a rather complex structure of fiber framework and carbon matrix, allowing CFC to match the thermal conductivity requirements for the tokamak stationary regimes. But for the ITER off-normal events, their behavior is still not investigated in detail. Recent experiments on electron beam facilities simulating the slow transient loads of 20 MW/m2 have shown unusually high erosion rates of CFC in the temperature range of 3000–4500 K. To understand the mechanism of the enhanced erosion, numerical simulations for the new CFC are carried out using the Pegasus code that has been generalized to describe three-dimensional effects of brittle destruction and heat transport in the carbon composites. A new erosion mechanism is discovered. The enhanced erosion is caused by local overheating in CFC materials due to preferential cracking on the fiber surface and thermal isolation of the fibers from matrix. A large difference of fiber and matrix coefficients of thermal expansion is essential for the mechanism. [Copyright &y& Elsevier]

• TOKES numerical simulations of mitigated disruption thermal quenches, caused by SPI in ITER have been performed. • Bremsstrahlung and recombination radiation contributes significantly to the core cooling upon injection of mixed pellet • The minimum Ne amount in two mixed pellets, which radiates >90 % of the core plasma energy has been found. TOKES simulations of mixed Ne/D 2 pellet injection through 1 equatorial launcher into an ITER discharge of 280 MJ thermal plasma energy was carried out. Two kinds of pellets were simulated: 'large', containing 1.1∙1024 D 2 molecules and 'small' with 2.6∙1023 D 2 molecules, both with various amount of Ne and correspondingly lower quantities of D to preserve the pellet size. It was found that the physics of the core energy radiation by the mixed pellet is different from that of the pure Ne pellet. In case of the mixed pellet injection, bremsstrahlung and recombination radiation make a significant contribution to the core cooling along with the Ne line radiation, the latter being the only mechanism for pure Ne pellet injection. The minimum Ne amount in the mixed pellet, which radiates more than 90 % of the core plasma energy (the threshold) has been found to be 1∙1020 Ne atoms for the large pellet and 2∙1021 atoms for the small one. [ABSTRACT FROM AUTHOR]

Highlights: [•] The massive gas injection (neon) is simulated with the two-dimensional tokamak code TOKES assuming the toroidal symmetry. [•] The neon injection, assimilation and transport of impurities through the entire plasma volume are modelled. [•] The output of TOKES is used by the melt motion code MEMOS to assess beryllium wall temperature and the regime with melting. [•] Complete plasma cooling occurs in minimum time of 5.7ms with avoiding Be melting at any point on the first wall. [Copyright &y& Elsevier]

Abstract: This paper is concerned with investigation of an erosion of the ITER-like divertor plasma facing components under plasma heat loads expected during the Type I ELMs in ITER. These experiments were carried out on plasma accelerator QSPA at the SRC RF TRINITI under EU/RF collaboration. Targets were exposed by series repeated plasma pulses with heat loads in a range of 0.5–1.5MJ/m2 and pulse duration 0.5ms. Erosion of CFC macrobrushes was determined mainly by sublimation of PAN-fibres that was less than 2.5μm per pulse. The CFC erosion was negligible at the energy density less than 0.5MJ/m2 and was increased to the average value 0.3μm per pulse at 1.5MJ/m2. The pure tungsten macrobrushes erosion was small in the energy range of 0.5–1.3MJ/m2. The sharp growth of tungsten erosion and the intense droplet ejection were observed at the energy density of 1.5MJ/m2. [Copyright &y& Elsevier]