High heat flux testing of beryllium components with improved diagnostics

Beryllium is one of the most interesting materials to be used in nuclear fusion devices due to its promising properties. However, testing of beryllium components is quite challenging because of its toxicity and the required safety procedures. Within this paper an overview of high heat flux thermal fatigue tests carried out in the electron beam facility JUDITH 2 (Juelich Divertor Test Facility in the Hot Cells) at Forschungszentrum Juelich (FZJ) on actively cooled beryllium mock ups is given. The performance of the mock ups was documented by temperature measurements as well as optical inspections before and after testing. Special attention was paid to the temperature diagnostics during the tests for two different reasons. Firstly, local overheating of the beryllium tiles, which are the proof of bonding failures, is detected by temperature measurements. Secondly, temperature information is exceptionally important to meet the required safety standards because of the toxicity of beryllium. In order to avoid evaporation of beryllium, a temperature limit for an automatic safety shut down of the electron beam facility JUDITH 2 was set to a certain value. Finally examples of the temperature distribution under different loading conditions for the beryllium mock ups are presented within this paper.