The SHERPA project aim is to develop an efficient technique for extracting a positron beam from one of the accelerator rings composing the DAΦNE accelerator complex at the Frascati National Laboratory of INFN, setting up a new beam line delivering positron spills of O(ms) length, excellent beam energy spread and emittance. The main idea is to use coherent processes in bent crystals to slowly kick out positrons from the ring, a cheaper and less complex alternative. This non-resonant technique, already successfully used and still developed mainly in hadron accelerators, will provide a continuous multi-turn extraction of a high quality beam. In this manuscript will be given an overview of the whole experiment, describing in particular the crystal extraction principle, the accelerator optics studies, the crystal prototype and its characterization apparatus. A first estimation of the crystal extraction performance at DAΦNE is also reported