[Triumf-seminars] TRIUMF Accelerator Seminar today at 15:00

[TRIUMF Seminars]

Date/Time: Mon 2017-03-20 at 15:00

Location:  ISAC II Conf Rm     

Speaker:   Tobi Junginger (Marie-Curie-International-Outgoing Fellow - TRIUMF/HZB)

Title:     Characterizing SRF materials using muon spin rotation and relaxation

Abstract: Superconducting radiofrequency (SRF) cavities have been used to increase the energy of charged particles since more than 50 years. Currently the material of choice is niobium, the element with the largest critical temperature and critical field. For example TRIUMF uses niobium technology for the ISAC-II heavy ion and the ARIEL electron accelerator. Specific surface treatments have increased the performance of this technology close to its fundamental limitations in terms of maximum accelerating gradient and quality factor. Current SRF material research is going in two directions: pushing niobium even closer to its fundamental limitations and investigating potential new materials which might yield an even better performance. Of particular interest is to understand how flux enters these materials. For this purpose TRIUMF scientists have pioneered muon spin rotation and relaxation as a method to characterize SRF materials. In this talk I will show how the experiment has been constantly further developed over the past years and now enables to probe the field of first flux entry and the pinning strength. These parameters directly determine the performance of SRF cavities. The former is setting the limit for the maximum achievable accelerating gradient, while the latter determines how efficiently flux can be expelled related to the maximum achievable quality factor. In a recent experiment we have shown that an overlayer of a higher Tc material on niobium pushes the field of first flux entry and therefore the potential maximum accelerating gradient by about 40%, independent of layer thickness or material. The hypothesis for this observation is that the overlayer induces superheating in the underlying niobium by the proximity effect.





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