Positron production in axially oriented single crystals: comparison of theory with experiment

The theory of radiation from high energy electrons moving near a crystalline axis is outlined. The intensity of radiation in thick crystal is discussed. Starting from the energy ε ∼ 1 GeV the contribution of channeling radiation dominates. For energies a few GeV the development of the electron-photon showers in axially aligned single crystals is described including the formula for the intensity spectrum. Both channeling radiation and bremsstrahlung are taken into account. Some characteristics of the positron yield measured in recent experiments are calculated. Theoretical estimations display a rather good agreement with experimental results obtained using 3 to 10 GeV electrons aligned to the <111> - axis of the tungsten crystals. Such comparison verified that the accuracy of our approach is quite sufficient to make a reliable choice for optimal parameters of the positron source using axially aligned crystals for future linear colliders. (author)