The quest for high gradients in accelerating structures is a real economical challenge for the electron linac TESLA.
To achieve the optimum RF performance, the cavity surface is cleaned by chemical etching, two process are available: electropolishing (EP) or buffer chemical polishing (BCP). Since the resolution of the "Q slope" problem by cavity baking, the maximum accelerator field in cavities is now limited by the thermal breakdown.
The electropolishing gives the best result with roughly a maximum accelerator field value around 40 MV/m for a single-cell cavity (10 MV/m more than BCP). Nevertheless, compared to BCP, the EP process needs a more sophisticated set up and the final achievement of the cavity surface is more sensitive.
For these reasons we have planned to work on the quench improvement of a BCP cavity, all the more we have early observed that the quench position was sensitive to the chemical bath purity and could be moved after a cavity baking.
In this way we have investigated the modification of the RF superconducting parameters ( RBCS, Rres, TC, l , Equench ) after baking from 100 to 800°C. We will present the preliminary results and we will discuss about the material purity evolution ( gas load on the surface, oxygen diffusion inside the material ).
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