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A simplified model describing turbulent plasma transport in the far scrape-off layer has been proposed for calculation of the plasma heat and particle fluxes to the first wall (FW) of the DEMO tokamak. The model has been implemented in the TOKES code for simulation of the heat flux distribution along the tokamak FW. First simulations of the wall heat flux, using this model, predict more pronounced “hot spots” at the top of the DEMO wall in comparison with the exponential heat flux decay model, commonly used for simulation of the flux. [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]

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 castellated targets of pure tungsten, lanthanum tungsten and CFC under plasma heat loads expected during the Type I ELMs and disruptions in ITER. These experiments were carried out on a plasma gun QSPA-T at the SRC RF TRINITI under EU/RF collaboration. The targets were exposed by series repeated plasma pulses with heat loads in the range of 0.2–2.5MJ/m2 and a pulse duration of 0.5ms. The erosion value as a function of pulse number and energy density were obtained. The erosion of lanthanum tungsten started at the lower energy density as compared with pure tungsten and was mainly due to a melt layer movement and a droplets ejection. Characteristics of ejected droplets were measured. The erosion of CFC macrobrushes under ELM and disruption heat loads was determined mainly by damage of PAN-fibers. [Copyright &y& Elsevier]

Abstract: The behavior of a preheated at 650°C tungsten targets under repetitive ELM-like plasma pulses is studied in simulation experiments with the quasi-stationary plasma accelerator QSPA Kh-50. The targets have been exposed up to 350 pulses of the duration 0.25ms and the surface heat loads either 0.45MJ/m2 or 0.75MJ/m2, which is below and above the melting threshold, respectively. The development of surface morphology of the exposed targets as well as cracking and swelling at the surface is discussed. First comparisons of obtained experimental results with corresponding numerical simulations of the code PEGASUS-3D are presented. [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]