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[en] Understanding the mechanisms of the chemical erosion of carbon by hydrogen is of great importance for the application and development of plasma-facing materials, as well as the macroscopic scale modeling of plasma-surface interactions in fusion devices. In the recent years there has been a number of atomistic modeling studies, namely molecular dynamics and electronic structure calculations, on these processes. This article is an overview of these investigations, with comparison to experimental measurements as well as current theoretical understanding of the chemical erosion of carbon. Implications of the modeling are discussed along with an outlook on future studies
[en] Highlights: • In-plasma dust-surface impacts recorded with unprecedented resolution. • Experimental determination of the normal and tangential restitution coefficients. • Validation of the dominance of plastic/adhesive work over frictional dissipation. • Calibration of the analytical impact model of the MIGRAINe dust-dynamics code. - Abstract: Mechanical dust-wall collisions are unavoidable in fusion devices and their accurate modeling is essential for the understanding of dust transport. The MIGRAINe dust dynamics code features analytical models addressing all facets of dust-surface impacts, some aspects of which have not been experimentally validated thus far. Dedicated dust injection experiments have been carried out in Pilot-PSI resulting to the visualization of in-plasma tungsten dust-surface impacts with an unprecedented resolution. They allowed for a calibration of key quantities of the MIGRAINe impact model.
[en] The capability of charcoal as a sorbent for helium at cryogenic temperatures depends upon charcoal characteristics that are not well understood. Previous work by the authors has indicated that the charcoals' pumping capability for helium depends as much on their source as on their particle size distributions. To develop a correlation between the physical characteristics of charcoal and helium pumping performance, different charcoals based on wood, coal, coconut, and a petroleum by-product were obtained from commercial sources. They were bonded to an aluminum substrate, and cooled to liquid-helium temperatures in a vacuum chamber. The helium pumping speed at constant throughput versus quantity of helium absorbed was measured for each charcoal grade. Porosimetry measurements on each charcoal grade using nitrogen as the sorbent gas were made that included total surface area, adsorption and desorption isotherms, and pore area and pore volume distributions. Significant differences in helium pumping performance and in pore size distribution were observed. Comparisons are made between helium pumping performance and charcoal characteristics and a possible correlation is identified
[en] A room temperature bore superconducting (SC) solenoid magnet has been developed at Control Instrumentation Division (CnID) for carrying out liquid PbLi Magneto Hydro Dynamic (MHD) and corrosion experimental studies for ITER TBM. The SC solenoid magnet is designed to generate central bore magnetic field of 4 Tesla in a bore diameter of 300 mm and length of 800 mm with a field uniformity of 0.5% or better. The SC magnet is made up of low temperature NbTi copper composite wire whose critical temperature (Tc) is 9.8 K. The SC magnet needs to be cooled to liquid helium temperature (4.2 K) for its stable operation. Considering the operational requirement, an adiabatically stable SC magnet is under development. The adiabatically cooled SC magnet is completely immersed inside the liquid helium vessel. As the latent heat of vaporisation of liquid helium is less, heat load on liquid helium vessel needs to be reduced. In this paper we discuss about the liquid helium cryostat developed with conduction cooled thermal shield. Various heat loads on the liquid helium cryostat is calculated. Design modification of the existing cryostat to reduce the heat load and improved thermal performance is discussed. (author)