Experimental study of positron production from a 2.55-mm-thick silicon crystal target using 8-GeV electron beams with high-bunch charges

We have investigated quenching phenomena of channeling radiation through positron production from a silicon crystal hit by a single-bunch electron beam with high-bunch charge at the 8-GeV electron/positron injector linac. The crystal axis, <1 1 0>, was aligned to the electron beam with a precise goniometer, and positrons produced in the forward direction with a momentum of 20 MeV/c were detected with a magnetic spectrometer. Positron yields were measured by varying the charge in a bunch with a typical bunch length of ∼10 ps from 0.1 nC to 2 nC. The corresponding instantaneous current density ranged from 0.15 x 104 to 1.2 x 104 A/cm2. The results show that, at these current densities, the positron yield is proportional to the bunch charge within the experimental accuracy, which implies that no non-linear phenomena are observed in channeling radiation