In order to separate the fundamental synchrotron radiation from the high harmonics emitted by an undulator, a low photon energy-pass filter has been designed and built, ensuring a high spectral purity on the vacuum ultraviolet (VUV) SU5 beamline at Super-ACO. It consists of an absorption cell filled with rare gases and separated from the ultrahigh vacuum of the storage ring and of the beamline by a double differential pumping obtained with thin capillaries. Its conception has been optimized by numerical computation of pumping speed. Admission pressures in the range of 100 Pa in the central part of the filter have been used without any degradation of the upstream or downstream ultrahigh vacuum. The measured attenuation factors above the energy cutoff are above 105 and 102 (and certainly above 103 with ultimate pressure of Ne) for argon and neon absorbing gases, respectively, with no measurable attenuation of fundamental radiation. A sophisticated numerical simulation of the pressure distribution, taking into account the geometry of the whole absorption cell including the first pair of capillaries, has been developed. The corresponding calculated attenuation factors are in very good agreement with the measurements, and thus allow reliable predictions of the expected attenuation factors for any given configuration of the filter.

As part of the R&D toward the production of high flux of polarised Gamma-rays we have designed and built a non-planar four-mirror optical cavity with a high finesse and operated it at a particle accelerator. We report on the main challenges of such cavity, such as the design of a suitable laser based on fiber technology, the mechanical difficulties of having a high tunability and a high mechanical stability in an accelerator environment and the active stabilization of such cavity by implementing a double feedback loop in a FPGA.

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A Study of the dimensional accuracy obtained by low cost 3D printing for possible application in medicine K Kitsakis, P Alabey, J Kechagias et al. Abstract. In the recent year additive manufacturing (3D printing) has revolutionized mechanical engineering by allowing the quick production of mechanical components with complex shapes. So far most of these components are made in plastic and therefore can not be used in accelerator beam pipes. We have investigated samples printed using a metal 3D printer to study their behavior under vacuum. We report on our first tests showing that such samples are vacuum compatible and comparing pumping time.