The Experts below are selected from a list of 21510 Experts worldwide ranked by ideXlab platform
T.w. Morgan - One of the best experts on this subject based on the ideXlab platform.
-
Recrystallization-mediated crack initiation in tungsten under simultaneous high-flux hydrogen plasma loads and high-cycle Transient Heating
Nuclear Fusion 61 046018, 2021Co-Authors: T.w. Morgan, T. Vermeij, J.w. M. Vernimmen, T. Loewenhoff, J.p. M. Hoefnagels, J.a. W. Van Dommelen, M. Wirtz, G. De Temmerman, K. VerbekenAbstract:Tungsten and tungsten-based alloys are the leading material choices for the divertor plasma facing components (PFCs) in future fusion reactors. Recrystallization may occur when they undergo high heat loads, drastically modifying the predesigned grain structures and the associated desired mechanical properties. However, the influence of recrystallization on the thermal fatigue behavior of tungsten PFCs still remains unclear. In this study, ITER-grade tungsten was simultaneously exposed to a high-flux hydrogen plasma (~5×1024 m-2s-1) and high-cycle (104-105) Transient heat loads in the linear plasma device Magnum-PSI. By correlating the surface temperature distribution, obtained by analyzing temperature-, wavelength-, and surface-dependent emissivity, and the surface modifications of the plasma exposed specimens, the crack initiation heat flux factor threshold was found to be ~2 MWm-2s0.5 (equivalently, ~0.07 MJm-2 for a 1 ms pulse), which slightly decreases with increasing surface temperature (~1550 K) and increasing pulse number. Based on electron backscatter diffraction (EBSD) analyses of cross-sections near the crack initiation sites, faster recrystallization kinetics near the surface compared to literature was observed and the surface cracks preferentially initiated at high angle grains boundaries (HAGBs). Upon recrystallization, the yield strength decreases which entails increasing cyclic plastic strains. The HAGBs fraction is increased, which constrains the transfer of plastic strains at grain boundaries. The recrystallization decreases the dislocation density, which promotes heterogeneous deformation. All these mechanisms explain the reduced crack initiation threshold of recrystallized tungsten compared to its as-received counterpart. The results provide new insights into the structural failure mechanisms in tungsten PFCs exposed to extreme fusion plasmas
-
the effect of high flux h plasma exposure with simultaneous Transient heat loads on tungsten surface damage and power handling
Nuclear Fusion, 2014Co-Authors: G G Van Eden, T.w. Morgan, M. Wirtz, H J Van Der Meiden, J Matejicek, Tomas Chraska, G. De TemmermanAbstract:The performance of the full-W ITER divertor may be significantly affected by the interplay between steady-state plasma exposure and Transient events. To address this issue, the effect of a high-flux H plasma on the thermal shock response of W to ELM-like Transients has been investigated. Transient Heating of W targets is performed by means of a high-power Nd:YAG laser with simultaneous exposure to H plasma in the linear device Magnum-PSI. The effects of simultaneous exposure to laser and plasma have been compared to those sequentially and to laser only. Transient melting is found to be aggravated during plasma exposure and to occur at lower heat flux parameters. Roughness and grain growth are observed to be driven by peak temperature, rather than by the loading conditions. The temperature evolution of the W surface under a series of Transients is recorded by fast infrared thermography. By accounting for changes in the reflectivity at the damaged surface as measured by ellipsometry, a reduction in power handling capabilities of the laser/plasma affected W is concluded. The evidence of reduced power handling of the W surface under conditions as described here is of great concern with respect to the durability of W PFCs for application in fusion devices.
K. Verbeken - One of the best experts on this subject based on the ideXlab platform.
-
Recrystallization-mediated crack initiation in tungsten under simultaneous high-flux hydrogen plasma loads and high-cycle Transient Heating
Nuclear Fusion 61 046018, 2021Co-Authors: T.w. Morgan, T. Vermeij, J.w. M. Vernimmen, T. Loewenhoff, J.p. M. Hoefnagels, J.a. W. Van Dommelen, M. Wirtz, G. De Temmerman, K. VerbekenAbstract:Tungsten and tungsten-based alloys are the leading material choices for the divertor plasma facing components (PFCs) in future fusion reactors. Recrystallization may occur when they undergo high heat loads, drastically modifying the predesigned grain structures and the associated desired mechanical properties. However, the influence of recrystallization on the thermal fatigue behavior of tungsten PFCs still remains unclear. In this study, ITER-grade tungsten was simultaneously exposed to a high-flux hydrogen plasma (~5×1024 m-2s-1) and high-cycle (104-105) Transient heat loads in the linear plasma device Magnum-PSI. By correlating the surface temperature distribution, obtained by analyzing temperature-, wavelength-, and surface-dependent emissivity, and the surface modifications of the plasma exposed specimens, the crack initiation heat flux factor threshold was found to be ~2 MWm-2s0.5 (equivalently, ~0.07 MJm-2 for a 1 ms pulse), which slightly decreases with increasing surface temperature (~1550 K) and increasing pulse number. Based on electron backscatter diffraction (EBSD) analyses of cross-sections near the crack initiation sites, faster recrystallization kinetics near the surface compared to literature was observed and the surface cracks preferentially initiated at high angle grains boundaries (HAGBs). Upon recrystallization, the yield strength decreases which entails increasing cyclic plastic strains. The HAGBs fraction is increased, which constrains the transfer of plastic strains at grain boundaries. The recrystallization decreases the dislocation density, which promotes heterogeneous deformation. All these mechanisms explain the reduced crack initiation threshold of recrystallized tungsten compared to its as-received counterpart. The results provide new insights into the structural failure mechanisms in tungsten PFCs exposed to extreme fusion plasmas
Chun Ming Leung - One of the best experts on this subject based on the ideXlab platform.
-
infrared emission from isolated dust clouds in the presence of very small dust grains
Icarus, 1991Co-Authors: D C Lis, Chun Ming LeungAbstract:Models of the effects of small grain-generated temperature fluctuations on the IR spectrum and surface brightness of externally heated interstellar dust clouds are presently constructed on the basis of a continuum radiation transport computer code which encompasses the Transient Heating of small dust grains. The models assume a constant fractional abundance of large and small grains throughout the given cloud. A comparison of model results with IRAS observations indicates that the observed 12-25 micron band emissions are associated with about 10-A radius grains, while the 60-100 micron emission is primarily due to large grains which are heated under the equilibrium conditions.
-
size and density distribution of very small dust grains in the barnard 5 cloud
The Astrophysical Journal, 1991Co-Authors: D C Lis, Chun Ming LeungAbstract:The effects of the temperature fluctuations in small graphite grains on the energy spectrum and the IR surface brightness of an isolated dust cloud heated externally by the interstellar radiation field were investigated using a series of models based on a radiation transport computer code. This code treats self-consistently the thermal coupling between the Transient Heating of very small dust grains and the equilibrium Heating of conventional large grains. The model results were compared with the IRAS observations of the Barnard 5 (B5) cloud, showing that the 25-micron emission of the cloud must be produced by small grains with a 6-10 A radius, which also contribute about 50 percent to the observed 12-micron emission. The remaining 12 micron flux may be produced by the polycyclic aromatic hydrocarbons. The 60-and 100-micron radiation is dominated by emission from large grains heated under equilibrium conditions.
G. De Temmerman - One of the best experts on this subject based on the ideXlab platform.
-
Recrystallization-mediated crack initiation in tungsten under simultaneous high-flux hydrogen plasma loads and high-cycle Transient Heating
Nuclear Fusion 61 046018, 2021Co-Authors: T.w. Morgan, T. Vermeij, J.w. M. Vernimmen, T. Loewenhoff, J.p. M. Hoefnagels, J.a. W. Van Dommelen, M. Wirtz, G. De Temmerman, K. VerbekenAbstract:Tungsten and tungsten-based alloys are the leading material choices for the divertor plasma facing components (PFCs) in future fusion reactors. Recrystallization may occur when they undergo high heat loads, drastically modifying the predesigned grain structures and the associated desired mechanical properties. However, the influence of recrystallization on the thermal fatigue behavior of tungsten PFCs still remains unclear. In this study, ITER-grade tungsten was simultaneously exposed to a high-flux hydrogen plasma (~5×1024 m-2s-1) and high-cycle (104-105) Transient heat loads in the linear plasma device Magnum-PSI. By correlating the surface temperature distribution, obtained by analyzing temperature-, wavelength-, and surface-dependent emissivity, and the surface modifications of the plasma exposed specimens, the crack initiation heat flux factor threshold was found to be ~2 MWm-2s0.5 (equivalently, ~0.07 MJm-2 for a 1 ms pulse), which slightly decreases with increasing surface temperature (~1550 K) and increasing pulse number. Based on electron backscatter diffraction (EBSD) analyses of cross-sections near the crack initiation sites, faster recrystallization kinetics near the surface compared to literature was observed and the surface cracks preferentially initiated at high angle grains boundaries (HAGBs). Upon recrystallization, the yield strength decreases which entails increasing cyclic plastic strains. The HAGBs fraction is increased, which constrains the transfer of plastic strains at grain boundaries. The recrystallization decreases the dislocation density, which promotes heterogeneous deformation. All these mechanisms explain the reduced crack initiation threshold of recrystallized tungsten compared to its as-received counterpart. The results provide new insights into the structural failure mechanisms in tungsten PFCs exposed to extreme fusion plasmas
-
the effect of high flux h plasma exposure with simultaneous Transient heat loads on tungsten surface damage and power handling
Nuclear Fusion, 2014Co-Authors: G G Van Eden, T.w. Morgan, M. Wirtz, H J Van Der Meiden, J Matejicek, Tomas Chraska, G. De TemmermanAbstract:The performance of the full-W ITER divertor may be significantly affected by the interplay between steady-state plasma exposure and Transient events. To address this issue, the effect of a high-flux H plasma on the thermal shock response of W to ELM-like Transients has been investigated. Transient Heating of W targets is performed by means of a high-power Nd:YAG laser with simultaneous exposure to H plasma in the linear device Magnum-PSI. The effects of simultaneous exposure to laser and plasma have been compared to those sequentially and to laser only. Transient melting is found to be aggravated during plasma exposure and to occur at lower heat flux parameters. Roughness and grain growth are observed to be driven by peak temperature, rather than by the loading conditions. The temperature evolution of the W surface under a series of Transients is recorded by fast infrared thermography. By accounting for changes in the reflectivity at the damaged surface as measured by ellipsometry, a reduction in power handling capabilities of the laser/plasma affected W is concluded. The evidence of reduced power handling of the W surface under conditions as described here is of great concern with respect to the durability of W PFCs for application in fusion devices.
Ulrich Wiesner - One of the best experts on this subject based on the ideXlab platform.
-
Block Copolymer Self-Assembly Directed Hierarchically Structured Materials from Nonequilibrium Transient Laser Heating
Macromolecules, 2019Co-Authors: Kwan Wee Tan, Ulrich WiesnerAbstract:We highlight two recent approaches operating far from equilibrium for the synthesis of hierarchical porous thin film materials by coupling block copolymer-directed self-assembly with Transient laser Heating. In first block copolymer-induced writing by Transient Heating experiments, or B-WRITE, an all-organic block copolymer–resols hybrid film is heated by submillisecond carbon dioxide laser irradiation, directly generating 3D mesoporous continuous resin structures and shapes. Harnessing the highly unique resin materials properties under laser Heating conditions, in the second approach block copolymer-directed resin templating is coupled with nanosecond pulsed excimer laser annealing to generate complementary crystalline silicon nanostructures. The underlying structure formation mechanisms for such laser-induced organic and inorganic nanostructured materials are discussed, emphasizing that the nonequilibrium nature of these Transient laser annealing approaches opens up vast and new processing windows beyon...
