Addesa, F.M. Burmistrov, L. Cavoto, G. Dubos, S. Garattini, M. Iacoangeli, F. Montesano, S. Puill, V. Scandale, W. Stocchi, A. JACoW Geneva, Switzerland 978-3-95450-192-2 10.18429/JACoW-IBIC2017-WEPCF04 English 419-422 WEPCF04 ion proton detector extraction experiment Contribution to a conference proceedings 2018 2018-03 https://doi.org/10.18429/JACoW-IBIC2017-WEPCF04 http://jacow.org/ibic2017/papers/wepcf04.pdf The UA9 experiment at CERN-SPS investigates the manipulation of high energy hadron beams using bent silicon crystals since 2009. Monitoring and characterization of channeled beams in the high energy accelerators environment ideally requires in-vacuum and radiation hard detectors. For this purpose the Cherenkov detector for proton Flux Measurement (CpFM) was designed and developed. It features a fused silica bar in the beam pipe vacuum which intercepts charged particles and generates Cherenkov light. In this contribution the SE-CpFM (Slow Extraction CpFM) detector is described in detail. It has been installed in early 2016 in the TT20 extraction line of SPS to study the feasibility of the crystal-assisted extraction from the SPS. Before the installation the detector has been fully characterized in 2015, during the UA9 data taking in the H8-SPS extraction line with 180 GeV pions. The single particle detection efficiency and the photoelectron yield per proton have been estimated and are shown in this contribution.