Wendelstein 7-X and fusion - Max-Planck-Institut für Plasmaphysik

12
Large corporations
Target elements during thermographic testing
Facts:
Research institutes:
Max Planck Institute for Plasma Physics
Industrial partner:
Plansee SE (Reutte, Austria)
Contracts:
Development and production of elements
for the first wall, particularly within the field
of divertors
Thus, the development of high-performance divertors has become necessary. Plansee
SE has designed so called “target elements” for the divertors, which must be continuously
capable of withstanding 10 megawatts per square metre. A sophisticated combination
of carbon-fibre-reinforced carbon and water-cooled metal blocks, also known as
heat sinks, had to be been developed. Significant steps in this development were made
in close collaboration with the Max Planck Institute for Plasma Physics.
• Joining the carbon-fibre-reinforced carbon to the water-cooled heat sink made of a
metal alloy has turned out to be extraordinarily demanding. The carbon is in contact
with the plasma and exposed to an extremely high heat load; pressurized cooling water
circulates through the heat sink. For joining the two elements, the carbon had to
be coated with a structured copper layer and then welded onto the heat sink to ensure
good thermal conductivity from the surface of the carbon layer to the heat sink.
At the same time, it was necessary to compensate for the different thermal expansion
coefficients of the two materials. Plansee has patented the procedure.
• The water-cooled heat sinks must dissipate tremendous quantities of heat under
conditions of continuous operation. The pressurized cooling water must be circulated
through the body of the metal heat sink. For this purpose, the cooling channel had to
be designed such that turbulent flow occurs and more heat is dissipated.
• Quality assurance for this complex structural element composed of several materials
presented a huge challenge for the production of altogether 890 elements,
representing 18,000 tiles. The Max Planck Institute for Plasma Physics, together with
its contractor Plansee, developed a quality assurance plan based on both systematic
and randomized high-performance tests. Because standard procedures were not
available for non-destructive checking of joints, the company developed special test
methods on the basis of ultrasonic, X-ray and thermographic testing.
The heat load of 10 million Watt per square metre mentioned above are higher than that
placed on the edges of the wing of the space shuttle when it re-enters the atmosphere
(6 million watts per square metre), which, however, “only” occurs for several hundred
seconds in that case. Carbon-fibre-reinforced carbon tiles are also used in that application.
Space technology and fusion technology have been combined for the development
of materials exposed to high temperatures. Under the management of the IPP, an important
joint European project promoted by the EU under the name EXTREMAT (http://
www. Extremat org.) has been carried out. Plansee played a leading role among the 30
project partners, which are predominantly from the industrial sector.
Using a technology that was introduced for the French fusion experiment, Tore Supra,
Plansee and the Max Planck Institute for Plasma Physics have refined it for Wendelstein
7-X and improved its quality and reliability. These heat-conducting carbon-fibrereinforced
carbon-metal composites are certain to find a wide range of applications.