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Loading of deuterium and helium by Pilot-PSI plasma and their detection by in-situ LIBS
No full textLaser-induced breakdown spectroscopy (LIBS) is a promising method for quantifying the fuel content of the plasma-facing components of ITER both in between plasma discharges (in-situ) and after maintenance operations. The aim of the present study is to test the applicability of in-situ LIBS for monitoring deuterium (D) and helium (He) content of W samples exposed to fusion relevant plasma fluxes in the linear plasma device Pilot-PSI.
The D loading was performed during 1000 s of plasma exposure at low (200-300 °C) surface temperatures. Despite of low intensity and noisy LIBS spectra, H and D lines, at 656.1 and 656.3 nm, respectively, could be fitted with Lorentzian contours and reliably resolved at 1.2 mbar background pressure of argon.
In the case of He loading, the samples were also exposed to plasma during 1000 s while the surface temperature reached values up to 720 °C at the center. Already at 10–2 mbar residual pressure of the device, the He I line at 587.6 nm was visible for the first 2–3 laser shots.
We demonstrated that in-situ LIBS is a reliable method for detection of He and D retention in ITER-relevant materials. Nevertheless, for measuring relative and absolute concentrations of D and He in the ITER-relevant samples, further studies are needed
Thiophene Rings Improve the Device Performance of Conjugated Polymers in Polymer Solar Cells with Thick Active Layers
No full textDeveloping novel materials that tolerate thickness variations of the active layer is critical to further enhance the efficiency of polymer solar cells and enable large-scale manufacturing. Presently, only a few polymers afford high efficiencies at active layer thickness exceeding 200 nm and molecular design guidelines for developing successful materials are lacking. It is thus highly desirable to identify structural factors that determine the performance of semiconducting conjugated polymers in thick-film polymer solar cells. Here, it is demonstrated that thiophene rings, introduced in the backbone of alternating donor-acceptor type conjugated polymers, enhance the fill factor and overall efficiency for thick (>200 nm) solar cells. For a series of fluorinated semiconducting polymers derived from electron-rich benzo[1,2-b: 4,5-b\u27] dithiophene units and electron-deficient 5,6-difluorobenzo[2,1,3] thiazole units a steady increase of the fill factor and power conversion efficiency is found when introducing thiophene rings between the donor and acceptor units. The increased performance is a synergistic result of an enhanced hole mobility and a suppressed bimolecular charge recombination, which is attributed to more favorable polymer chain packing and finer phase separation
Implementation of the full viscoresistive magnetohydrodynamic equations in a nonlinear finite element code
Get PDFNumerical simulations form an indispensable tool to understand the behavior of a hot plasma that is created inside a tokamak for providing nuclear fusion energy. Various aspects of tokamak plasmas have been successfully studied through the reduced magnetohydrodynamic (MHD) model. The need for more complete modeling through the full MHD equations is addressed here. Our computational method is presented along with measures against possible problems regarding pollution, stability, and regularity. The problem of ensuring continuity of solutions in the center of a polar grid is addressed in the context of a finite element discretization of the full MHD equations. A rigorous and generally applicable solution is proposed here. Useful analytical test cases are devised to verify the correct implementation of the momentum and induction equation, the hyperdiffusive terms, and the accuracy with which highly anisotropic diffusion can be simulated. A striking observation is that highly anisotropic diffusion can be treated with the same order of accuracy as isotropic diffusion, even on non-aligned grids, as long as these grids are generated with sufficient care. This property is shown to be associated with our use of a magnetic vector potential to describe the magnetic field. Several well-known instabilities are simulated to demonstrate the capabilities of the new method. The linear growth rate of an internal kink mode and a tearing mode are benchmarked against the results of a linear MHD code. The evolution of a tearing mode and the resulting magnetic islands are simulated well into the nonlinear regime. The results are compared with predictions from the reduced MHD model. Finally, a simulation of a ballooning mode illustrates the possibility to use our method as an ideal MHD method without the need to add any physical dissipation.</p
Short- and long-range energy strategies for Japan and the world after the Fukushima nuclear accident
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Effect of rhenium addition on tungsten fuzz formation in helium plasmas
No full textThe effect of the addition of rhenium to tungsten on the formation of a nanostructure referred to as ‘fuzz’ when exposed to helium plasmas at fusion relevant ion fluxes was investigated in the Magnum and Pilot PSI devices at the FOM Institute DIFFER. The effect rhenium had on fuzz growth was seen to be dependent on time, temperature and flux. Initial fuzz growth was seen to be highly dependent on grain orientation, with rhenium having little effect. Once the fuzz was fully developed, the effect of grain orientation disappeared and the rhenium had an inhibiting effect on growth. This could be beneficial for inhibiting fuzz growth in a future fusion reactor, where transmutation of tungsten to rhenium is expected. It also appears that erosion or annealing of the fuzz is limiting growth of fuzz at higher temperatures in the range of ∼1340 °C
Design and characterization of a prototype divertor viewing infrared video bolometer for NSTX-U
No full textIon bombardment measurements and simulations of a low temperature VHF PECVD SiH4-H2 discharge in the a-Si:H to μc-Si:H transition regime
No full textWe studied ion bombardment during amorphous silicon layer deposition for hydrogen dilutions 5 to 59 with mass resolved IED measurements and simulations. The trends in the peak position of H2+ and SiHy+ IEDs with increasing hydrogen dilution show good agreement between measurements and simulations. A difference in asymmetry of the discharge between simulations and measurements results in a roughly 6 eV lower peak position for the simulations. An increasing SiHy+ ion flux with increasing hydrogen dilution is measured. We hypothesize that this is due to amorphous silicon etching that is enhanced by Hy+ ion bombardment
