  The idea of using fixed-target annihilations of a high-energy positron beam
on a target for producing a new, very feebly interacting particle has been
exploited by the PADME experiment at LNF using the extracted beam from the
LINAC in the BTF facility. Extracting the beam from a synchrotron would improve
by several orders of magnitude the duty-cycle of the LINAC, thus greatly
extending the physics reach of such experiments. The option of substituting or
complementing the standard, slow 1/3 of integer resonant extraction technique
by using coherent phenomena in a bent crystal, like the channeling has been
studied by the SHERPA experiment. Both using the DAFNE main positron ring or
the smaller damping ring (accumulator) as pulse extender of the LINAC have been
considered.
  We here propose to demonstrate the feasibility of this technique performing
an experiment on the DAFNE positron main ring, installing in a suitable vacuum
goniometer a thin Silicon crystal, bent in the (110) direction in order to
provide a ~1 mrad kick, and then simulating the extraction process with a
virtual septum: instead of performing a real extraction, the crossing of the
gap of a septum magnet is simulated by detecting positrons at its position (at
phase advance close to 1/4) by means of a Silicon pixel detector inserted in
the ring, in a secondary vacuum of a Roman pot.
