Material science and accelerator r&d: reflectivity and photo yield measurements of vacuum chamber technical surfaces

One of the most important problems to consider in particle accelerators is Synchrotron Radiation (SR). SR causes significant problems like heat load on the accelerator walls, photon stimulated desorption, production of secondary electrons (electron cloud effect) and consequently beam instability (coupled bunch and single bunch instabilities). Thus, it is very important to have an experimental characterization of properties of technical surfaces, in particular Reflectivity and Photo Yield (PY). PY, also known as quantum efficiency, measures the number of electrons generated per incident photon as a function of energy and incidence angle. Such material properties are essential ingredients to calculate single and multi bunch instabilities, vacuum behaviour, e—cloud instabilities, etc. There is an increasing demand from the accelerator community towards the availability of experimental data taken from representative materials and in conditions as close as possible to the one that will actually occur in the machine. In the FCC-hh contest it has been highlighted that high reflectivity could be advantageous for reducing SR induced heat load in cold dipoles. Carbon Coating of smooth vacuum chamber surfaces was suggested as a mean to reduce the heat load in cold part of the machine, by forward reflecting most SR and its deposited power towards ad hoc designed room temperature absorbers. In these Ph.D. a systematic experimental campaign has been launched and is still ongoing to study Reflectivity and Photo Yield. We identified the Optics Beamline and the Reflectometer endstation in Berlin (HZB BESSY-II), as an ideal tool to get realistic experimental values to be used in most relevant simulations. Access to this beamtime has been granted trough beamtime accepted proposals. The first experimental results will be presented and discussed here. We studied reflectivity and photo yield in UV and XUV range (from 35 eV to 1800 eV) at grazing angles (0.25, 0.5 and 1 degree), using copper samples as targets, differently prepared. We studied also the effect of Carbon Coating on reflectivity and PY.