Effects of extremely high fluence (∼10 30 m −2 ), mixed materials, and neutron irradiation are important issues to be pursued for ITER and beyond. But pulsed heat loadings alleviate surfaces morphology changes in some cases (He holes by ELM-like heat pulses). Particle loadings could enhance pulsed heat effects (cracking and erosion) due to surface layer embrittlement by nanometric bubbles and solute atoms. Helium bombardment would cause surface morphology changes such as W fuzz, He holes, and nanometric bubble layers, which could lead to enhanced erosion (e.g. Hydrogen induced blistering is unlikely to be an issue of ITER.
Pulsed heat loadings by transients (disruption and ELM) are the largest concerns due to surface melting, cracking, and dust formation.
It increases interest in the possibility that nanostructure formation by helium irradiation is a common phenomenon that occurs on various metals.read more read lessĪbstract: This review summarizes surface morphology changes of tungsten caused by heat and particle loadings from edge plasmas, and their effects on enhanced erosion and material lifetime in ITER and beyond. The nanostructure was also observed on the molybdenum surface that was exposed to the helium plasma. It is shown that the nanostructure formation is related to pinholes appearing on the bulk part of the material, and then, the rough structure develops to a much finer nanostructure.
#Helium electric arc simulator#
Furthermore, on the basis of the helium irradiation experiments performed in the divertor simulator NAGDIS-I, the initial formation process of the nanostructure is revealed. It is shown that the tungsten nanostructure is easily formed when the temperature is in the range 1000–2000 K, and the incident ion energy is higher than 20 eV. From the experimental results in liner divertor simulators, it is revealed that the incident ion energy and surface temperature are key parameters for the formation of the structure. This result suggests that the nanostructure on the tungsten surface formed by the bombardment of helium, which is a fusion product, could significantly change the ignition property of arcing, and ELMs become a trigger of unipolar arcing, which would be a great impurity source in fusion devices.read more read lessĪbstract: Helium irradiation on tungsten changes the surface morphology dramatically by forming a nanometre-sized fibreform structure which could bring about serious problems for fusion reactors. The unipolar arc is verified from an increase in the floating potential, a moving arc spot detected by a fast camera and arcing traces on the surface. The laser pulse width (~0.6 ms) and power (~5 MJ m−2) are similar to the heat load accompanied by type-I edge localized modes (ELMs) in ITER. By irradiating a laser pulse to the surface in the plasma, a unipolar arc, which many people have tried to verify in well-defined experiments, is promptly initiated and continued for a much longer time than the laser pulse width. The helium fluence was of the order of 1026 m−2, and the surface temperature and incident ion energy during helium irradiation were, respectively, 1900 K and 75 eV.
37, 736 (1931).Abstract: A fibreform nanostructured layer is formed on a tungsten surface by helium plasma bombardment. Jaeger, Conduction of Heat in Solids (Oxford University Press, New York, 1947), p. Note that when vapor is present, the cathode drop could be as low as the ionization potential of the vapor. Conference on Electric Welding, Detroit, April 1950. For example, see the following: Compton, Lilly, and Olmstead, Phys. This explanation of the low voltage of the arc as being due to the presence of evaporated cathode material may be applied to other cases reported in the literature. Finkelnburg, The High Current Carbon Arc, FIAT Final Report No. This phenomenon has also been observed with steel plates as anodes and tungsten rods as cathodes in both argon and helium under conditions simulating inert gas arc welding.
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