A. Kienzler

Experimental results of a 70 kA high temperature superconductor current lead demonstrator for the ITER magnet system

In the frame of the European Fusion Technology Programme, the Forschungszentrum Karlsruhe and the CRPP Villigen have designed and built a 70 kA current lead for the ITER TF Coils using High Temperature Superconductors (HTS). At the beginning of 2004 the HTS current lead was installed and tested in the TOSKA facility of the Forschungszentrum Karlsruhe. The scope of the experiment was to characterize the current lead in steady state conditions and to explore the operation limits as well. For this, the temperature profile, the contact resistances, the heat load at 4.5 K, the required 50 K He mass flow rate, and the temperature margin were evaluated. The safety margin in case of a loss of He mass flow was studied, too. The paper describes the experimental results as well as the thermal and electrical models developed.

High Temperature Superconductor Current Leads for WENDELSTEIN 7-X and JT-60SA

Forschungszentrum Karlsruhe has taken over the responsibility for the design, construction and testing of the High Temperature Superconductor (HTS) current leads for two fusion experiments, i.e. the stellarator WENDELSTEIN 7-X (W7-X) and the satellite tokamak JT-60SA. W7-X is presently under construction at the Greifswald branch of the Max-Planck-Institute for Plasma Physics and consists of 50 non-planar and 20 planar coils with a maximum conductor current of 17.6 kA. In total 14 current leads are required with a nominal current of 14 kA that are mounted upside down with the warm end at the bottom. In the frame of the Broader Approach Agreement between Japan and the EU and concomitantly to the ITER project, the satellite tokamak project JT-60SA has been agreed in 2006. The magnet system of JT-60SA consists of 18 toroidal field coils, 4 central solenoid modules and 7 poloidal field coils. In total 26 leads mounted in vertical, normal position are required. For W7-X and JT-60SA a common basic design will be used which will be adapted to the special needs of the machines. All current leads will be of the Cu-HTS binary type. The HTS part covers the range between 4.5 K and 60 K and is cooled by heat conduction from the 4.5 K end, only. The Cu heat exchanger is cooled with 50 K He and covers the range between 60 K and room temperature. The paper describes the status of the HTS current lead development for W7-X and JT-60SA.

Design and fabrication of a 70 kA current lead using Ag/Au stabilized Bi-2223 tapes as a demonstrator for the ITER TF-coil system

In the frame of the European Fusion Technology Programme, the Forschungszentrum Karlsruhe and the Centre de Recherches en Physique des Plasmas, CRPP, Villigen, develop a 70 kA current lead to demonstrate the feasibility of the usage of High Temperature Superconductors (HTS) for the current leads of the ITER TF coils. Design and fabrication of the conventional heat exchanger that covers the temperature range from 65 K to room temperature is done at the Forschungszentrum Karlsruhe. The HTS module connects the current feeder terminal at 4.5 K with the conventional heat exchanger and is cooled only by heat conduction from the cold end. Its design and fabrication has been performed by American Superconductor, AMSC. This module consists of Bi-2223 Ag/Au tapes embedded in stainless steel carriers with copper end caps. It is highly instrumented with voltage taps, temperature sensors and Hall probes. The integration with the heat exchanger and the current feeder terminal is carried out at the Forschungszentrum Karlsruhe. The current lead will be tested in the TOSKA facility in the first months of 2004. The paper describes the design, fabrication and results of pretests carried out at AMSC and Forschungszentrum Karlsruhe.

Test Results of the High Temperature Superconductor Prototype Current Leads for Wendelstein 7-X

The Karlsruhe Institute of Technology (which is a merger of former Forschungszentrum Karlsruhe and Karlsruhe University) is responsible for the design, construction and testing of the high temperature superconductor (HTS) current leads for the stellarator Wendelstein 7-X (W7-X) which is presently under construction at the Greifswald branch of the Max-Planck-Institute for Plasma Physics. The current leads are of the binary type, the HTS part covering the temperature range between 4.5 K and 60 K while the heat exchanger covers the range between 60 K and room temperature being cooled by 50 K He. In total 2 prototypes and 14 series current leads are required with a nominal current of 14 kA and a maximum current of 18.2 kA. The paper describes the design and first test results of the prototype HTS current leads.

Limits and challenges of manufacturing micro moulds

Due to the ongoing miniaturisation in industrial sectors like automotive, electronics or medical, the development of new manufacturing processes which are suitable for micro system technologies gains more and more importance. The miniaturisation of components leads to challenges in the manufacturing of micro parts. One application area is the manufacturing of moulds for the micro powder injection moulding (μPIM) process. This process requires good surface qualities and a sufficient demoulding behaviour of the moulds. Micro milling, micro electrical discharge machining (μEDM) and micro laser beam machining (μLBM) are appropriate processes for the manufacturing of micro structures in different materials. Abrasive micro peening can be used for further precision treatment. Depending on the desired structure a single process or the combination of several processes has to be chosen to obtain superior surface qualities of the moulds. This paper deals with challenges and limits of the manufacturing processes among others exemplified on a gearwheel mould.

Construction and operation performance of the 80 kA current leads used for the test of the ITER toroidal field model coil in the TOSKA facility

For the test of the ITER TFMC in the TOSKA facility of the Forschungszentrum Karlsruhe, two 80 kA current leads were designed and manufactured. Based on the experience coming from the performance of the 30 kA forced-flow current leads, the 80 kA leads were designed in a continuous manner. During the TFMC experiment, various optimization runs were performed at 0, 40 and 80 kA. It could be demonstrated that the leads were operated with the designed mass flow rates. Especially, the Nb/sub 3/Sn inserts used in the lower part of the heat exchanger behave as expected. The slightly different mass flow rate of both terminals can be explained by different RRR of the copper of the heat exchanger. The 80 kA current leads display the highest operating sc coil current reported up to now.

OberfläChennachbearbeitung von Mikroformeinsätzen Für das Mikropulverspritzgießen

Kurzfassung Die Produktion von keramischen und metallischen Mikrokomponenten mittels Mikropulverspritzgießen (μPIM) stellt hohe Anforderungen an die Formeinsatz-Werkzeuge bezüglich der Verschleißbeständigkeit und Oberflächenqualität. Daher wurden im Rahmen der hier vorgestellten Forschungskooperation Formeinsätze aus einem Ultrafeinkornhartmetall durch EDM (Electro Discharge Machining) strukturiert und zusätzlich die Oberflächen durch Mikrostrahlen bearbeitet sowie im Anschluss der Verschleiß in einem Modellprüfstand unter Beanspruchung durch keramische Formmasse charakterisiert. Die Untersuchungen zeigten, dass insbesondere die durch EDM erzeugte spröde Randschicht sich negativ auf das Verschleißverhalten auswirkt. Eine Entfernung dieser Randschicht durch das Mikrostrahlen verbesserte die Oberflächenqualität und erhöhte zudem den Verschleißwiderstand.

Burr Minimization and Removal by Micro Milling Strategies or Micro Peening Processes

Micro milled mold inserts made from hardened and tempered steel can have burrs in the size order of 50 μm at the edges. These burrs often prevent the easy demolding of green bodies from micro powder injection molds. Further surface treatments on the molds are necessary to improve surface quality thus facilitating demolding processes. In the present study, three different processes: micro milling, abrasive micro peening and ultrasonic wet peening, have been investigated for their suitability as viable solutions for reducing or eliminating burrs. The tool used for the micro milling process is capable of removing existing burrs but creates new burrs which are inherent to the tool movement over the machined surface. While abrasive micro peening leads to a reduction of burrs on the mold surface, the material below the impacted surface is plastically deformed. Ultrasonic wet peening showed the best effectiveness at removal of burrs of a wide variety of complex geometries in a short processing time and without plastic deformation of the edge zones.