These results suggest that warfarin may not prevent ischemic stroke in Japanese hemodialysis patients with chronic sustained AF. Adequately powered studies are needed to determine the risks and benefits of anticoagulation therapy in these patients.
An integrated divertor simulation code SONIC has been developed. The self-consistent coupling of an MC impurity code IMPMC to a divertor code SOLDOR/NEUT2D is succeeded by overcoming the intrinsic problems of Monte Carlo (MC) modelling for impurity transport. MC modelling for impurity transport is required in order to take into account the kinetic effect and the complex dissociation processes of hydrocarbons. The integrated divertor code SONIC enables us to investigate the details of impurity transport including erosion/redeposition processes on the divertor plates by further coupling of an MC code EDDY. The dynamic evolution of X-point MARFE observed in JT-60U is investigated. The simulation results indicate that the hydrocarbons sputtered from the dome contribute directly to the enhanced radiation near the X-point. Without the recycling, the kinetic effect of the thermal force improves the helium compression, compared with the conventional (fluid) evaluation. This effect is, however, masked by the recycling at the divertor targets.
Sputtering due to the bombardment of C with 0.5–10 keV W ions is studied as a function of the W ion fluence by computer simulation. The simulation deals with the dynamic composition change in the surface layer due to implantation of the W ions, the associated collisional mixing and diffusion of the implanted W. The calculated results show a clear oscillation in the sputtering yield of the implanted W as a function of the ion fluence. There is a critical energy (∼ 1 keV) for the appearance of the oscillation, where the W emission yield, defined by the sum of the W sputtering yield and W reflection coefficient, is unity. Above the critical energy, the W sputtering yield oscillates around unity, whereas below the energy it monotonically increases towards a value dependent on the incident energy. The oscillation is caused by the dynamic change in the W depth profile, therefore, it is significantly influenced by the diffusion of the implanted W inside the C bulk. The diffusion suppresses the W sputtering and therefore the oscillation of the yield. Furthermore, for strong diffusion, only W deposition is calculated during the bombardment, whereas the transition from deposition to erosion is calculated without diffusion.
We performed Monte Carlo simulation of helium (He) ion induced secondary electron (SE) emission in order to compare the secondary electron image characteristics between He and gallium (Ga) scanning ion microscopes (SIM) and scanning electron microscope (SEM). For 10-50 keV He ion bombardment SE yield increases gradually with increasing the atomic number, Z2, of the target, as well as for the electron bombardment. However, for 30 keV Ga ion bombardment, SE yield shows an opposite Z2 dependence. The calculated SE yield is much larger than that for both electron and Ga ion bombardment. The incident angle dependence of the SE yield approximately obeys the inverse cosine law even at high angles of 85 degrees and more. On the other hand, for electron bombardment, the incident angle dependences are much weaker for low energy and high Z2. These indicate that the image contrast on He-SIM is clearer than those of SEM. Among the electron excitations by incident He ions, recoiled target atoms and excited electrons, the first one having narrow excitation volume dominates the SE yield, so that the spatial image resolution in SIM using zero-diameter He beams with the energies of 10-50 keV is prospected to be smaller or better (<0.1 nm) than for 30 keV Ga ion and 1 keV electron beams.
High-Z materials as tungsten are intended to be used in future fusion reactors due to their low sputtering rates and high melting points. In this context the important question is whether the use of high-Z materials is compatible with the concept of a cold radiative boundary. To investigate the local release and transport behaviour of the high-Z impurities, Mo and W test limiters were used in auxiliary heated discharges under different radiation scenarios with neon seeding. In addition, laser blow-off of tungsten as well as xenon gas puffing were performed. In some particular discharge conditions impurity accumulation was observed in the plasma core, which in the case of ohmic discharges led to minor disruptions. The connection between the accumulation and the evolution of the current density profiles is discussed. A transport analysis is made, in order to compare the observations with the neoclassical theory. It is shown that with neon the impurity-impurity driven fluxes enhance the high-Z concentration in the plasma core. However, if the source of the high-Z elements is significantly reduced, by increasing the plasma density, a development of an accumulation instability can be avoided.
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