Our research focuses on the testing and analyses of materials and components for extreme environments, especially high temperature applications like in fusion reactor devices. Fife main topics and three main armour materials are investigated. The three main armour materials are beryllium (Be), different forms of carbon (e.g. graphite or carbon fibre reinforced carbon) and tungsten (W). These materials have suitable properties, the most important one being their high thermal conductivity.
The main topics are all related to the thermal loading conditions that are expected in future fusion reactors. These loads are applied using high power electron beams.
|… is mainly related to interface damages and hence to components that consist of an armour material, which absorbs the thermal load, and an actively cooled heat sink material. Typical heat sink materials are copper, copper alloys or steel. Different joining techniques (brazing, explosion bonding, diffusion bonding, HIPing, …) are used to connect heat sink and armour. During operation thermal cycling leads to cyclic mechanical stresses at the interface which typically result in fatigue damage and hence overheating and detachment of armour tiles.more|
|… is mainly related to surface near damages (micrometers up to hundreds of micrometers) and is therefore tested using components as well as materials (also without active cooling, e.g. small blocks of pure tungsten). The thermal shock pulse increases the surface temperature of the material by several hundred degrees in a millisecond. This results in steep temperature gradients which produce high local stresses due to thermal expansion. Comparison of the performance of materials is done by low pulse number tests more and high pulse number tests.more|
Neutron irraddiation effects...
… degrade material properties and therefore influence the performance in both of the former fields. The D-T fusion reaction results in high fluxes of 14 MeV neutrons which lead to micro structural modifications, transmutation and activation of materials. Neutron irradiation of components is performed by collaboration partners (e.g. in the HFR-Petten).
The components are then transported to our test facilities and tested, mostly in thermal fatigue experiments.more
|… load the armour materials simultaneously with the thermal loads (and partially transport the thermal energy). Apart from neutrons also hydrogen/deuterium, helium and other species (e.g. eroded beryllium atoms) strike armour surfaces. In contrast to neutrons these particles do not penetrate deep into the material, but lead to complex plasma surface interactions that can significantly alter the surfaces of plasma facing materials. In order to simulate high particle fluxes, samples are exposed to plasma or ion gun facilities. more|
Finite element simulation
… is firstly used as supporting technique to predict temperatures in experiments more , but also gains increasing importance as tool to spot positions of highest stresses in components. These are the weak points were failure is likely to occur.more