Development of In-situ Baking Procedures

RF cavities made from high purity niobium often show a degradation of the Q-value at higher gradients in the absence of field emission (Q-drop). Improvements in this behavior were first reported in ref [1] by in situ baking at temperatures > 100C for longer periods of time. Such Q-drop was never seen in electropolished cavities tested at KEK [2], where routinely the cavities were baked at 85C for a day in order to improve the cavity vacuum.

In-situ baking was systematically investigated at Jlab [3] -among other labs- and the effect of baking temperature and duration of baking on cavity performance for both chemically polished and electropolished cavities was explored. Besides improvements in the BCS surface resistance often improvements in quench fields were found. It was also demonstrated that the surface layer effected by the in situ baking and having modified material parameters reached to a depth of ~3000 Angstrom; after removal of this layer the “original” niobium material parameters were restored.

[1] P. Charrier,B. Coadou and B.Visientin; Proc. EPAC 1998, p. 1885

[2] K. Saito et al.;Proc. 8 th workshop on RF Superconductivity, Report LNL-INFN(Rep) 133/98, p. 830, Abano Terme, Italy (1997)

[3] P. Kneisel, -Proc. 9 th Workshop on RF Superconductivity, Report LA – 13782-C, Vol.1, p. 328, Santa Fe, New Mexico (1999)