Mitsuhashi, T.M. JACoW Geneva, Switzerland 978-3-95450-192-2 10.18429/JACoW-IBIC2017-WEPCC10 English 369-372 WEPCC10 ion scattering background simulation synchrotron Contribution to a conference proceedings 2018 2018-03 https://doi.org/10.18429/JACoW-IBIC2017-WEPCC10 http://jacow.org/ibic2017/papers/wepcc10.pdf In beam halo measurements by means of a coronagraph viewing visible SR light, the theoretical image contrast is dominated by leakage of the diffracted fringe pattern from the Lyot stop. On other hand, the noise background in an actual coronagraph also contains light scattered from imperfections in the first objective lens. Most of this light is due to Mie-scattering from dig imperfections on the surface of objective which can reduce the image contrast to the 10⁻³ range for a lens with 60/40 scratch and dig figures. By introducing a high-quality objective lens into the system the theoretical value of 10-5-10-6 image contrast can be recovered for the Lyot coronagraph. In this paper, Mie-scattering due to dig imperfections is analyzed theoretically and results from measurements of the Mie scattering are presented.