J.-H. Feist

Rf ion sources for fusion applications: design, development and performance

Abstract The use of rf ion sources in neutral beam injection (NBI) systems offers reduced maintenance and cost due to the absence of filaments. For the first time high-power rf positive ion sources have been put in operation recently in a real NBI system on a tokamak. The performance of the new system is equivalent to that of a conventional one with arc discharge sources. Due to the relevance for ITER, rf sources are also being investigated in context with negative ions: 8.5 mA/cm2 H− have been achieved so far in a non-optimised version.

Design and construction of WENDELSTEIN 7-X

Abstract Following the approval by EURATOM and the German government WENDELSTEIN 7-X (W7-X) is presently the largest fusion project under construction. W7-X is a helical advanced stellarator (HELIAS) which produces the confining magnet field only by magnet coils that enables steady-state operation. W7-X aims to demonstrate that the HELIAS configuration has the potential for a future power reactor. The successful application of new technologies for manufacturing prototypes and the positive results gained from tests allowed to design the machine in detail and to order major components. The geometry of the non-planar magnet coils has a considerable impact on the design of the machine in particular on the shape of the plasma vessel, positioning of the plasma-facing components and the size and orientation of the ports. The requirement for steady-state operation has consequences for many subsystems of W7-X. The magnet coils need to be superconducting and cooled to liquid helium temperature. Gyrotrons shall continuously provide 10 MW of ECR heating power. The divertor must be cooled to withstand heat loads of up to 10 MW/m 2 . The schedule of W7-X is determined by the delivery dates of the non-planar coils, the plasma vessel and the outer vessel. Start of commissioning and scientific operation is scheduled for spring 2006.

Progress in the Design, Manufacture and Testing of the W7-X Superconducting Magnets

The W7-X machine is a low-shear stellarator of the Wendelstein line being assembled in Greifswald, Germany. The manufacture of its superconducting magnets is in a well advanced phase. After the acceptance tests in the factory, the magnets are tested in cold conditions in a dedicated facility at CEA Saclay. This paper gives an overview of the status of the manufacture of the W7-X coils, including the production of the superconductor, the windings and casings for the magnets, the final assembly and in-factory test procedures. Several design changes and re-work have been implemented in the course of the manufacture due to more detailed engineering analyses or weaknesses and quality problems found in some components. The status of the cold tests of the coils will also be presented

Final design and construction of the Wendelstein7-X coils

The Stellarator of the Wendelstein 7-X (W7-X) experiment contains a system of 50 non-planar and 20 planar superconducting coils. The coils were designed by the IPP. The coil manufacturing and inspection is shared between several European enterprises and consortiums. The coils consist of the winding pack embedded in a stainless steel casing and of the related instrumentation. Design details, tolerances and guarantee values and differences between the coils types are described in the contribution. The features of the superconductor are described separately. Finally, the contribution indicates measures adopted by the W7-X project to ensure the quality of the coil design and manufacturing.

Assembly and test of the W7-X demo-cryostat

An overview is given on the status of the demo-cryostat project for the WENDELSTEIN 7-X stellarator. Construction and assembly of the prototype are finished, and the test period is near completion. The intention of this project was to get experience with design and construction of W7-X-components, as well as with assembly of this complex system. The goal is now practically achieved, and it could be demonstrated that the W7-X cryostat can be built with reasonable effort. Many of the solutions found can be adopted directly for W7-X, or are starting points for further improvements. A short description is given of the cryostat, its assembly, and of the most important tests which were performed so far.

Large-area radio frequency plasma sources for fusion applications

Four powerful inductively coupled radio frequency (rf) plasma generators producing 90 A, 55 kV hydrogen beams were manufactured for the second injector of ASDEX Upgrade. The design of the source and the power supply was optimized based on the experience with a prototype source. During conditioning of the first two sources, it was demonstrated that power efficiency, transmission of the beam power and reliability meet all requirements. The start of the neutral beam injection with the second injector is scheduled for October 1997. Recently, also negative ions in rf sources are being investigated within a collaboration with CEA Cadarache. In this development project a positive ion prototype rf source is being utilized with a small extraction area (48 cm2) and a 700 G cm magnetic filter. Without cesium a current density of 4.5 mA/cm2 was achieved so far at elevated pressure (1.6 Pa), the H−-current density being proportional to the rf power. At medium pressure (0.6 Pa) the current density is lower approximatel...

Large Scale Titanium Getter Pumps for the ASDEX-Upgrade Neutral Beam Injectors

For the ASDEX-Upgrade neutral beam injectors, each of which will deliver 6 MW of hydrogen, titanium getter pumps will be used as the fast pumping system. Each injector has a pumping speed of 2.800.000 l/s installed. The design of the pumps is based on the experience made with the smaller systems for ASDEX and Wendelstein 7-AS. Titanium is evaporated from compound wires onto cast aluminum surfaces, which are corrugated to enhance the pumping speed. The pumping speed measured at the testbed for two pumps confirms the design value. The capacity is enough for 1000 beam pulses at full power.

Quality management for WENDELSTEIN 7-X

The WENDELSTEIN 7-X stellarator is the next step device in the stellarator line of IPP Garching and is being built in the new branch institute of IPP at Greifswald. Start of operation is scheduled for 2006. The W7-X project is presently the largest scientific project in Germany with a total spending of 300 MEU during the construction phase. From the beginning of the design up to the end of operation, the project will last for almost 40 years. More than 350 people are expected to work on W7-X during the operational phase. An experiment of this size needs an industrial type management. An essential central function within this management is performed by the quality management division. This division is responsible for the following subtasks: system co-ordination, documentation, quality planning and quality assurance. A quality system is established for the W7-X construction project which is based on the DIN EN ISO 9000 family. The basis of the quality system is a quality manual together with the necessary procedures and instructions. Quality planning and assurance is carried out in close co-operation with the various technical divisions.

DESIGN OF THE NEUTRAL BEAM INJECTION SYSTEM FOR ASDEX-UPGRADE

For the ASDEX-Upgrade tokamak additional heating by long pulse neutral injection is forseen with a power of 6 MW when injecting hydrogen and 9 MW when injecting deuterium. This paper gives an overview of the injection system with the main emphasis on the mechanical parts. Additionally the basic concepts of the electrical systems and of the system control will be described.

A High Power RF Plasma Source for ASDEX Upgrade Neutral Beam Injection

In order to demonstrate the qualification for the second injector of ASDEX Upgrade (AUG) a large 1 MHz/120 kW RF plasma source has been tested at the long pulse testbed.