Abstract

The need for high accelerating gradients for the future Compact Linear Collider (CLIC) imposes considerable constraints on the materials of the accelerating structures. The surfaces exposed to high pulsed RF currents are subjected to cyclic thermal stresses possibly resulting in surface break up by fatigue. Since no fatigue data exists in literature up to very large numbers of cycles, a comprehensive study has been initiated.  
Low cycle fatigue data (up to 10^7 cycles) has been collected by means of a pulsed laser surface heating apparatus. High cycle fatigue data up to 7x10^10 cycles, has been collected in high frequency bulk fatigue tests using an ultrasonic apparatus. It is found that the appearance of surface fatigue damage in the laser experiments, and of fatigue cracks in the bulk specimen, happen at similar stress levels for similar numbers of cycles. This allows the two experimental techniques to be connected and to predict the surface damage at a high number of cycles. 
In this talk an introduction to Ultrasound fatigue testing, the updated CLIC fatigue parameters and a status report of the laser and ultrasound test results are presented.

Samuli gave an introduction to fatigue and presented fatigue issues at CLIC. In particular, he presented the ultrasound fatigue testing and gave an overview of all different fatigue tests for different materials relevant for CLIC so far. Finally, he showed some future plans. 

Sergio presented the results of the laser fatigue testing.
Laser fatigue testing seems to be relevant for RF applications. RF and laser temperature and stress profiles are very similar, and laser and 'high-cycle' ultrasound fatigue studies show comparable results. More data is needed to determine the best material.