11
A diamond
window
to the plasma
Heating plasma
for Wendel-
stein 7-X
The window between the tube and the exterior is another critical component of the gyrotron.
It is made of artificial diamond with a high level of purity to ensure that the thermal losses will
be kept as low as possible. These diamond windows, which have been manufactured by Diamond
Materials and Element Six, in collaboration with the Karlsruhe Institute für Technologie,
using the chemical vapour deposition (CVD) technique, are unique worldwide and excellently
suited for microwave and millimetre-wave heating applications with their diameters of up to
120 millimetres and thicknesses of 1.8 millimetres.
The diamond window requires reliable cooling, but a water-based technique risks corrosion.
For that reason, silicone oil was successfully used as coolant for the first time. During their
longstanding cooperation, Reuter Technologie and the Karlsruhe Institute for Technology have
developed their skills in soldering diamond and copper with special copper-silver-titanium
solders. Soldering provides the basis for constructing a diamond window, which after further
soldering is mounted in a stainless steel housing and used in a standard millimetre wavelength
transfer line. Soldering together these two very different materials to produce a vacuum-tight
seal represented a special challenge during the manufacture of the diamond windows with their
integrated cooling.
Currently, work is underway to develop a 1.5-megawatt gyrotron for continuous operation at
Wendelstein 7-X and to upgrade the transmission lines for the use of twelve instead of now
10 microwave sources. Part of this project to increase the heating power at Wendelstein 7-X is a
new industrial contract with Thales for the construction of a 1.5-megawatt prototype source.
The design of this gyrotron is based on the successful Wendelstein 7-X gyrotron, which also
forms the basis for the European gyrotron for the international experimental reactor ITER.
High-performance microwave tube for continuous operation
All these improvements in the concept and the technical details have opened up new
ways for manufacturing high-power microwave tubes required in communications
technology, materials technology, the International Thermonuclear Experimental
Reactor (ITER) fusion experiment, and the first fusion power plant “DEMO”. Thales
Electron Devices, as the primary contractor, has gained extensive knowledge through
the execution of these contracts and is now significantly better positioned in the
market. With the acquired expertise, Diamond Materials and Reuter Technologie have
also clearly improved their position for winning future contracts.
Photo: IPP, Wolfgang Filser