Microstructure Damage in Thermal Absorbers Induced by High Energy Synchrotron Light Irradiation

Aluminium plates are used as power attenuators in beamline ID15 at the ESRF. They absorb the low-energy part of the synchrotron light to reduce the heat-load on the following beamline components. Despite of many proposed design criteria, the high heat-load generated in the zone interacting with the X-rays may result in a marked deterioration of the absorber plate. Absorber plates of an old design, that failed were investigated here. Microscopy and diffraction methods revealed that the irradiated zone recrystallized during service and that its mechanical properties deteriorated. High thermal stresses built up, which were relieved by crack formation. Today a new aluminium power attenuator with an optimised cooling system is implemented, which so far is successful. This investigation shall give evidence about possible failure sources since in case of an increase in electron storage ring current, the increase in heat-load similar absorber failures shall be prevented.