Evaluation of the mechanical behavior of W7-X central support connections by means of semi-automated FE analysis

The stellarator Wendelstein 7-X is under construction at the Max-Planck-Institut für Plasmaphysik in Greifswald. Its superconducting coil system is fixed by a massive structure. During machine operation the coils exert high forces and moments against each other and the central support structure (CSS). Therefore, the detailed analysis of the coil to CSS connections, the so-called central support elements (CSE), is a critical item. The major details of the design have been frozen; nevertheless, there is still need for detailed analysis of the CSEs due to assembly issues, and later on for exploring operational limits of the machine. These analyses have to be performed quickly, reliably, and shall provide results in a standardized form to enable timely responses to the assembly team. Special numerical tools – finite element (FE) parametric models of CSEs – have been developed for the purpose of such analyses. In the models, the geometry, material properties, contact conditions, loads as well as results presentation are defined in a parametric way. The use of the developed models for the definition of the final weld parameters, bolt preloads, assessment of acceptable tolerances, and optimal positions of the CSE-wedges before welding is also discussed.     

The performance of a microchannel plate at cryogenic temperatures and in high magnetic fields, and the detection efficiency for low energy positive hydrogen ions

We have conducted a systematic study of the performance of a microchannel plate at cryogenic temperatures, and in a magnetic field perpendicular to the plate surface of up to 2.5 T. We observe no change in the characteristic pulse height distribution down to temperatures near 4 K if the count rate is kept sufficiently low. With increasing count rates the onset of saturation effects can be observed to be temperature dependent. For the specific plate used, this occurs around 1 kHz at the lowest temperature. This behavior is in good agreement with calculations based on a widely used model for the gain function of microchannel plates, if the plate resistance is allowed to be temperature dependent. Additionally we have studied the detection efficiency for low energy hydrogen ions of a chevron type microchannel plate under a variety of operating conditions at room temperature, and find the detection efficiency to level off around 60% at energies above 1 keV, if the plate is operated in a saturated gain mode.     

An Inter-Comparison of Two Black Carbon Aerosol Instruments and a Semi-Continuous Elemental Carbon Instrument in the Urban Environment

Aerosol absorption coefficients were obtained using two versions of the Magee Scientific Aethalometer and a Particle Soot Absorption Photometer (PSAP) in Riverside, California during July and August of 2005. These measurements were subsequently compared to each other and to hourly elemental carbon (EC) mass concentrations as determined by a Sunset Labs semi-continuous OCEC analyzer. Measurements from all four instruments were shown to be highly correlated (R ² = 0.83 to 0.92). Differences between absorption values measured by the PSAP and the Aethalometer were found to be dominated by differences in the filter media used by the respective instruments. Comparison of optical and thermal measurements revealed that the specific attenuation cross section (σ _ATN ) of light absorbing carbon (LAC) varied as a function of the time of the day, most notably during weekdays. Minimum σ _ATN values were observed during morning rush hour when EC concentrations were at their greatest and maxima were seen in the late afternoon. These variations correlated with changes in the OC/EC ratio and the Angstrom exponent for absorption, which is consistent with changes in the mixing state of elemental carbon associated with secondary aerosol condensation on primary EC particles.     

Toxic metals in the atmosphere in Lahore, Pakistan

Aerosol mass (PM₁₀ and PM_2.5) and detailed elemental composition were measured in monthly composites during the calendar year of 2007 at a site in Lahore, Pakistan. Elemental analysis revealed extremely high concentrations of Pb (4.4 μg m^− 3), Zn (12 μg m^− 3), Cd (0.077 μg m^− 3), and several other toxic metals. A significant fraction of the concentration of Pb (84%), Zn (98%), and Cd (90%) was contained in the fine particulate fraction (PM_2.5 and smaller); in addition, Zn and Cd were largely (≥ 60%) water soluble. The 2007 annual average PM₁₀ mass concentration was 340 μg m^− 3, which is well above the WHO guideline of 20 μg m^− 3. Dust sources were found to contribute on average (maximum) 41% (70%) of PM₁₀ mass and 14% (29%) of PM_2.5 mass on a monthly basis. Seasonally, concentrations were found to be lowest during the monsoon season (July-September). Principle component analysis identified seven factors, which combined explained 91% of the variance of the measured components of PM₁₀. These factors included three industrial sources, re-suspended soil, mobile sources, and two regional secondary aerosol sources likely from coal and/or biomass burning. The majority of the Pb was found to be associated with one industrial source, along with a number of other toxic metals including As and Cr. Cadmium, another toxic metal, was found at concentrations 16 times higher than the maximum exposure level recommended by the World Health Organization, and was concentrated in one industrial source that was also associated with Zn. These results highlight the importance of focusing control strategies not only on reducing PM mass concentration, but also on the reduction of toxic components of the PM as well, to most effectively protect human health and the environment.     

Characterization of interphase adhesion in multi-layer coating systems

Multi-layer coating systems are the state of the art for painting of metal and plastic surfaces e.g. in the automotive industry. Utilizing such systems consisting of several specialized coating materials, a high adhesion and a good corrosion protection can be reached, along with good barrier properties, chemical and scratch resistance as well as appealing surface appearance. The interphase regions between single layers of such systems represent areas of a potential weakness, where a delamination and a premature coating degradation can start. To test in a short time the protective properties of the coating, a special hydrothermal cyclic loading test procedure was developed, which causes accelerated build-up of internal stress within the coating system. Using an electrochemical impedance spectroscopy with various optimized electrode geometries, it was possible to detect the early stages of coating degradation and to compare different coating systems. Internal stress measurements contributed additionally to a better understanding of the coating degradation.     

Comparison of photon transport efficiency in simple scintillation electron detector configurations for scanning electron microscope

The purpose of this paper is to find some general rules for the design of robust scintillation electron detectors for a scanning electron microscope (SEM) that possesses an efficient light-guiding (LG) system. The paper offers some general instructions on how to avoid the improper design of highly inefficient LG configurations of the detectors. Attention was paid to the relevant optical properties of the scintillator, light guide, and other components used in the LG part of the scintillation detector. Utilizing the optical properties of the detector components, 3D Monte Carlo (MC) simulations of photon transport efficiency in the simple scintillation detector configurations were performed using the computer application called SCIUNI to assess shapes and dimensions of the LG part of the detector. The results of the simulation of both base-guided signal (BGS) configurations for SE detection and edge-guided signal (EGS) configurations for BSE detection are presented. It is demonstrated that the BGS configuration with a matted disc scintillator exit side connected to the cylindrical light guide without optical cement is almost always a sufficiently efficient system with a mean LG efficiency of about 20%. It is simulated that poorly designed EGS strip configurations have an extremely low mean LG efficiency of only 0.01%, which can significantly reduce detector performance. On the other hand, no simple nonoptimized EGS configuration with a light guide widening to a circular or square profile, with a polished cemented scintillator and with an indispensable hole in it has a mean LG efficiency lower than 6.5%.     

Structural analysis of W7-X: From design to assembly and operation

The Wendelstein 7-X (W7-X) modular stellarator is in the assembly phase at the Max-Planck-Institut für Plasmaphysik in Greifswald, Germany. The design of the “basic machine”, i.e. without in-vessel components, diagnostics and periphery, is largely completed, structural parameters such as bolt preload, initial conditions for contact elements, etc. are defined, and most of the components are manufactured and partly assembled. Therefore, the focus of structural analysis was shifted towards fast analyses of non-conformities, changes in the assembly procedure, and exploration of operational limits. Assembly-related work is expected to continue until commissioning of the machine, however, with decreasing intensity. In parallel the analysis requirements for in-vessel components, diagnostics and periphery will increase.This paper focuses on the most remarkable results, on special problems which had to be solved, on strategic issues like parameterization, complex finite element model structuring and benchmarking with alternative models in different codes, on assumptions of reasonable safety margins and expected tolerances, and on confirmation of analysis results by tests. Finally it highlights some lessons learned so far, which might be relevant also for other large fusion machines, and gives an outlook on future work.