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, h110i, 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 · 10 to 1.2 · 10 A/cm. 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. 2006 Elsevier B.V. All rights reserved. PACS: 41.75.Ht; 61.80.Fe; 61.85.+p; 52.38.Hb