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Surface polishing

Mechanical polishing techniques have been now used for decades for e.g. optical devices, achieving unsurpassed surface quality with surface roughness in the nano-metric scale. The aim of this R&D activity is to study and build an innovative set-up to improve, quality-wise and safety-wise, the process for surface polishing of SRF cavities.

Indeed the standard current surface treatments typically used in the community are either a Buffered Chemical Polishing (BCP) or an Electro-Polishing (EP) in a concentrated acid mixture containing highly concentrated hydrofluoric acid, extremely delicate to handle and to recycle. Combining and transferring the mechanical process technology, know-how and adapting the techniques for SRF cavities would be a major step. More precisely, the reduction of the roughness of the RF surface of the resonator will result in improvement of the RF performances of the cavity, increased efficiency, reliability and yield rate of SRF cavities surface preparation and treatment process prior to cold test in LHe. Moreover, safety would also be significantly improved. Finally, mastering of this process, jointly with advanced surface studies and RF testing will help in understanding the effect of surface state on the behaviour of superconducting material subjected to high electromagnetic RF surface fields.

All studies done so far by other laboratories were done on elliptical structure, that can be mechanically polished with standard barrel polishing machines thanks to their simple 2D geometry. No real studies have been performed yet on other type of cavities like QWR, HWR or Spoke cavities that show more complex geometries, and this is one of the main goals of this R&D project. Polishing such structures will need more complex polishing device to achieve a homogeneous polishing all over the structure.

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Picture of a Niobium polished sample by scanning electron microscopy (IPNO/CSNSM)


Contact : David LONGUEVERGNE

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IPN

Institut de Physique Nucléaire Orsay - 15 rue Georges CLEMENCEAU - 91406 ORSAY (FRANCE)
UMR 8608 - CNRS/IN2P3

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