Lifetime measurement of a particular deep crack failure on a flat-type divertor mockup under cyclic high heat flux loading conditions

Plasma facing components (PFCs) are key to enduring high heat flux (HHF) loading from high-temperature plasma in nuclear fusion reactors. Understanding their thermal-mechanical behavior and cracking failure mechanisms related to structural designs and fabrication technologies during high heat flux loading is of great significance for improving their servicing performance and R&D (Research and Development) levels. In this study, a particular deep cracking failure process on the tungsten layer of a flat-type divertor mockup during 1800 cycles of 10 MW m-2 HHF loadings is completely monitored and measured with a special improved digital image correlation (DIC) technique. It is found that the DIC measurement under the HHF loading environment is improved successfully to capture fine deformation and strain fields with a spatial resolution less than 0.35 mm so that field strain on a 1 mm thick copper interlayer and deep crack initiation at several microns scale on the tungsten layer are measured out. Based on both full field and local strain and displacement measurements of the target divertor mockup, the thermal mechanical behaviors from deformation to crack initiation and propagation are successfully measured and traced. It is revealed that for the baseline copper interlayer design of a flat-type divertor mockup, the accumulation of plastic strain in the copper interlayer during ratcheting damage induces enough tensile stress on the tungsten layer during HHF cycles, leading to cracking and fracture failures even in its elastic state earlier than the copper LCF lifetime. Current SDC-IC rules fail to cover this kind of ratcheting cracking failure mode in the design stage. New design models or mechanical validation rules to resolve this design blind spot should be established in the future.

Characteristics of Radiation of High-Pressure Short-Arc Xenon Gas-Discharge Lamp

The paper is devoted to the study of changes in characteristics of ultra-high pressure short-arc xenon lamps when a tungsten layer is sprayed onto the quartz shell, as a result of heating and local electrode erosion. The paper analyzes the mechanisms of phenomena occurring in the super-high pressure xenon discharge and the cathode spot, which affect the sputtering of the electrode material. The main negative effects of tungsten deposits appearing on the lamp shell inner surface are considered: a decrease in the optical transparency and mechanical strength of quartz glass, an increase of the bulb temperature, a change in spectral characteristics and spatial distribution of radiation of a gas-discharge lamp. The original method developed for studying the parameters of radiation of a gas-discharge lamp and based on the superposition of the optical axis of the photometer with the axis of the lamp passing through the cathode spot and the considered shell segment, transparent or sprayed, allowed us to compare radiation characteristics of the lamp without changing the plasma parameters. The thermodynamic analysis carried out within the research confirmed the absence of chemical interaction of tungsten layer with quartz glass. Spectral distribution of xenon discharge radiation in the visible and IR ranges is different for a transparent bulb and the bulb with a tungsten spot, which is due to the size of tungsten layer particles on the lamp bulb. A study of spatial distribution of radiation from a gas-discharge lamp showed a decrease in the intensity of radiation in a solid angle bounded by a tungsten spot. At the same time, in this region, there was observed an increase in the temperature of the quartz shell, leading to the appearance of a longitudinal gradient of the temperature field of the gas-discharge lamp.