Thermo-mechanical analysis of Wendelstein 7-X plasma facing components

The stellarator experiment Wendelstein 7-X (W7-X) is designed for stationary plasma operation (30 min). Plasma facing components (PFCs) such as the divertor targets, baffles, heat shields and wall panels are being installed in the plasma vessel (PV) in order to protect it and other in-vessel components. The different PFCs will be exposed to different magnitude of heat loads in the range of 100 kW/m²–10 MW/m² during plasma operation. An important issue concerning the design of these PFCs is the thermo-mechanical analysis to verify their suitability for the specified operation phases. A series of finite element (FE) simulations has been performed to achieve this goal. Previous studies focused on the test divertor unit (TDU) and high heat flux (HHF) target elements. The paper presents detailed FE thermo-mechanical analyses of a prototype HHF target module, baffles, heat shields and wall panels, as well as benchmarking against tests.     

Assessment of cracks in lateral supports of the magnet system of Wendelstein 7-X

The superconducting coils of the magnet system of Wendelstein 7-X (W7-X) are bolted onto a central support ring and interconnected with five so-called lateral support elements (LSEs) per half module. After welding of the LSE hollow boxes to the coil cases cracks were found in the vicinity of the welds that could potentially limit the allowed number N of electromagnetic (EM) load cycles of the machine.In response to the appearance of first cracks during assembly, the stress intensity factor (SIF) of theoretical cracks of various sizes in potentially critical position and orientation were predicted in a fast approach. For each crack size, N was based on the SIF, derived from beam theory, and on Paris’ law parameters determined in fatigue crack growth rate (FCGR) tests, thus leading to tolerable maximal crack sizes and distances between cracks. It was proved that the actual crack dimensions remained below these values or turned out to be only superficial. Afterwards, (extended) finite element method (XFEM and FEM) and boundary element method (BEM) models were developed to project the SIF of most critical tolerated cracks, considering new FCGR tests and the local stress state in more detail. N appeared highly sensitive to the assumptions which were therefore critically reviewed.Finally, the limit for load combinations of different amplitudes was determined using Miner's rule. As a result it was shown that the predefined number of W7-X operation cycles is not jeopardized by any of the detected cracks.     

Structural analysis of W7-X: Overview

The Wendelstein 7-X (W7-X) modular stellarator is in the assembly phase at the Max-Planck-Institut für Plasmaphysik (IPP) in Greifswald, Germany. The goal of the project is to demonstrate that this type of machine is a viable option for a fusion power-plant. The “pentagonal” magnet system of the machine encompasses 50 non-planar and 20 planar superconducting coils with sophisticated support structure. Structural reliability of components as well as resulting deformations and displacements during various modes of operation have to be considered not only for the magnet system but also throughout the whole cryostat whose main components are the plasma vessel, outer vessel, ports, and thermal insulation.A reliable prediction of the W7-X structural behaviour is only possible by employing complex finite element (FE) simulations with a hierarchical set of FE models. A special strategy has been developed and implemented for the task.The design is basically completed, main parameters are defined, and most of the W7-X components are manufactured. Therefore, the focus in the analysis is being shifted to the creation of parametric FE models which allow performing fast analyses of possible non-conformities, changes in the assembly procedure, and future exploration of operational limits.This paper gives an overview of the implemented analysis strategy, the applied safety margins, and focuses on the most remarkable results.     

Influence of different detector parameters on the neutron sensitivity of OSL detectors

On the basis of a method for the calculation of the neutron sensitivity of OSL detectors with a high content of hydrogen a systematic investigation of the influence of different detector parameters on the neutron sensitivity was carried out. The detector thickness, the thickness of the contact radiator, the luminophor contents and the grain size of the used luminophor influence the neutron sensitivity, first of all in the energy range of fast neutrons. Especially the use of small grain luminophor considerably increases the sensitivity whereas the other parameters have a small influence on the neutron sensitivity.     

Expression of the alpha-galactosidase from Cyamopsis tetragonoloba (guar) by Hansenula polymorpha.

The methylotrophic yeast Hansenula polymorpha, a host organism for the production of heterologous proteins, has been applied to produce the alpha-galactosidase from the plant Cyamopsis tetragonoloba (guar). The yeast/Escherichia coli shuttle expression vector used is based on the origin of replication of the endogenous 2 microns plasmid of Saccharomyces cerevisiae and the LEU2 gene of S. cerevisiae for selection in H. polymorpha. In the expression vector, the alpha-galactosidase is controlled by the methanol-regulated promoter from the methanol oxidase gene, MOX, of H. polymorpha. The signal sequence of SUC2 (invertase) from the yeast S. cerevisiae, was used to ensure secretion of the alpha-galactosidase enzyme. After transformation and stabilization, the expression vector was stably integrated in the genome. The active alpha-galactosidase enzyme was efficiently secreted (greater than 85%) and after methanol induction, the expression level was 42 mg/l. Amino-terminal sequencing of the purified alpha-galactosidase enzyme synthesized by H. polymorpha showed that the S. cerevisiae invertase signal sequence was correctly processed by H. polymorpha. The secreted alpha-galactosidase was glycosylated and had a sugar content of 9.5%. The specific activity of the alpha-galactosidase produced by H. polymorpha was 38 U mg-1 compared to 100 U mg-1 for the guar alpha-galactosidase. Deglycosylation of the H. polymorpha alpha-galactosidase restored the specific activity completely.     

Blood Ties: Co3O4 Decorated Blood Derived Carbon as a Superior Bifunctional Electrocatalyst

A simple, versatile and cheap synthetic route is demonstrated for the preparation of Co₃O₄ decorated blood powder derived heteroatom doped porous carbon (BDHC). The inorganic hybrid performs well as an advanced bifunctional non‐precious metal electrocatalyst. The hybridization of Co₃O₄ with the blood‐derived carbon results in improved activities not only towards the oxygen reduction reaction (ORR), but also in the reverse oxygen evolution reaction (OER). An improved ORR activity and a tuned four electron transfer selectivity can be assigned to a synergistic catalytic effect due the intimate contact between Co₃O­₄ particles and the highly conductive heteroatom doped carbon support, mediated by cobalt‐nitrogen or cobalt‐phosphorous coordination sites. This heterojunction may facilitate the electron transfer by preventing an accumulation of electron density within the Co₃O­₄ particles. The straight‐forward and cheap synthesis of the highly active and durable electrocatalyst make it a promising candidate for a next‐generation bifunctional electrocatalyst for applications such as reversible fuel cells/electrolyzers or metal air batteries.     

FE analyses and tests in support of Wendelstein 7-X trim coil development

The paper presents an overview of the finite element (FE) analyses on the trim coils (TCs) and tests performed at IPP, and focuses on some specific aspects of the TC assembly. Global FE models (GM) of two types of TCs predicted the coil deformations and reaction forces on the supports. Dead weight, temperature rise during operation up to 80 °C, electromagnetic loads of 19 field configurations, and outer vessel (OV) deformations have been taken into account. In addition, local models were created for the critical winding pack (WP) regions as well as for each support clamp, and were analyzed with boundary conditions determined by the GM. The detailed WP sub-models were developed to verify the insulation strength against local stresses. The simulations were supported by various mechanical tests under static and cyclic loads. Aim of these experiments was to determine the time dependent behavior of the silicone rubber pads which are used as interfaces between TC and supports, and to check and optimize the assembly tools as well as procedures for the TCs and their supports.     

25th Anniversary Article: “Cooking Carbon with Salt”: Carbon Materials and Carbonaceous Frameworks from Ionic Liquids and Poly(ionic liquid)s

This review surveys recent work on the use of ionic liquids (ILs) and polymerized ionic liquids (PILs) as precursors to synthesize functional carbon materials. As solvents or educts with negligible vapour pressure, these systems enable simple processing, composition, and structural control of the resulting carbons under rather simple and green synthesis conditions. Recent applications of the resulting nanocarbons across a multitude of fields, such as fuel cells, energy storage in batteries and supercapacitors, catalysis, separation, and sorption materials are highlighted.     

Scope and limitations of ultrasonography in the documentation of fractures--an experimental study

Sonographic studies were performed on cadaveric bones placed in a water bath, using 7.5-MHz linear-array transducers and 3.5-MHz sector transducers. Depending on its size, the defect was revealed as an interruption of the cortical reflection of echo or a dorsal band of echoes confined to the region of the fracture. It was interesting to note that fractures and bony defects are not visualized when the transducer is placed parallel to the fracture line or the zone of bony impaction. A further remarkable aspect was the numerous artefacts adjacent to each other at several fracture margins. It may be concluded that in an experimental setting and under standardized conditions, high-resolution transducers permit the examiner to detect cortical discontinuities of 1 mm or more.