Phase contrast issues operating pinhole cameras with low-emittance beams

In the framework of SOLEIL-II, the project of SOLEIL's storage ring upgrade towards lower emittances, preliminary studies were performed to pinpoint the resolution limits of the exisiting pinhole cameras. However, while reducing the vertical emittance from the SOLEIL's nominal 50 pm.rad value to 8 pm.rad, unexpected filaments were observed in the image plane of the pinhole cameras, severely spoiling the reliability of the emittance measurement. Investigations, on the existing pinhole cameras as well as on the Metrology beamline of SOLEIL, revealed that those filaments correspond to a phase contrast imaging of the UHV Aluminium window, located before the pinhole. In this work, we first report on experimental measurements performed to identify the origin of this issue and on our attempts of mitigation using a phase blurrer. We then report on SRW simulations targetting the reproduction of these experimental results and further oriented to predict the impact of this effect on SOLEIL-II pinhole cameras configurations.