G. Pintsuk (Sp), J. Compan, T. Hirai, J. Linke, M. Rödig, Research Centre Juelich (Germany)
Thermo-mechanical and thermo-physical degradation of plasma facing materials like tungsten and carbon fibre
composites, caused by neutron irradiation, are important issues in the field of nuclear fusion research. A major
role therein plays the electron beam facility JUDITH due to its worldwide unique ability to perform thermal fatigue
and thermal shock testing on irradiated and toxic samples. In thermal fatigue tests it was shown, that material
degradation caused by neutron irradiation reduces the maximum applicable heat flux and shortens the lifetime of
a component. This is mainly caused by radiation effects, e.g. reduction of thermal conductivity, especially for
carbon based materials, and an embrittlement of tungsten based materials.
For the investigation of the influence of these effects on the thermal shock resistance short transient events like
edge localised modes (ELMs) and disruptions were simulated on potential plasma facing materials like pure
tungsten or W-La203 as well as graphite and one, two or three directional carbon fibre composites (CFCs). These
were part of irradiation experiments termed ‘PARIDE 3’ (T = 200°C; ~0.2 dpa / carbon) and ‘PARIDE 4’ (T = 200°
C; ~1 dpa / carbon), which were carried out within the EU R&D programme at the high flux reactor (HFR) in
Petten (The Netherlands).
In situ observations were done on particle erosion, surface temperature and absorbed current. In combination
with microscopic investigations of the surface morphology of the loaded area (4 x 4 mm2) and weight loss
measurements a drastic quantitative increase of particle erosion after neutron irradiation was found for carbon
based materials, in particular under disruption like conditions. For tungsten, the onset of crack formation, partly
severe cracking and melting of plasma sprayed tungsten was observed. A detailed qualification and quantification
of the material response was done by metallographic means.