Experiment of positron generation using a crystal target at the KEK electron/positron linac

We have performed an experiment of positron generation using a crystal targ et at an electron/positron linac at KEK. The target consists of a tungsten crystal to emit photons and an amorphous tungsten for pair creation, whose thicknesses are 0.5 and 2.0 radiation length, respectively. When the (III)c rystal axis is oriented parallel to the 3 GeV incident electron beam, the p ositron yield is enhanced by 40% compared to values for the disoriented cry stal. No effect of injecting intense ultra-short electron bunches on the cr ystalline structure is observed. The crystal orientation dependence of the positron yield as well as the enhancement factor can be explained by a simu lation assuming a coherent bremsstrahlung process of the electron in the cr ystal. (C) 2001 Elsevier Science B.V. All rights reserved.