Using crystals as primary beam collimators at the ILC has been contemplated (Ref 1). This application critically demands more experimental data to assess its feasibility; the proposed experiment—while at low energy compared to the ILC—will give us quality data from which to scale and provide data in an energy range for electrons where there is few, due to the lack of available beams. Channeling of electrons is much less efficient than for protons as electrons are attracted to the atomic planes and therefore have a high probability of colliding with the nuclei, leading to loss out of the channel. It may be expected that axial channeling, which by conservation of angular momentum will tend to keep particles further away from the atomic strings, has a higher efficiency, and there are some indications that it is (Ref. 2). Volume reflection (VR) is a relatively new effect the existence of which in planar orientation has been established experimentally, and the data from Ref. 2 suggests it is present in axial orientation as well. VR should work with electrons and positrons; making it an attractive process for beam-collimation e.g. in a linear e+e– collider. With VR angles being smaller than the deflection by channeling, multiple crystals are likely necessary to achieve enough deflection. The strong bending imposed on the particle trajectories by the crystalline fields cause emission of high-energy gamma rays and energy loss of the deflected electrons. We will aim to measure the energy loss of the outgoing electrons which allows estimation of the average gamma-ray energy, ideally by means of a magnetic spectrometer. This will require a certain amount of reconfiguration of the ESTB area. Over the longer term a direct measurement of the gamma-ray energy spectrum would be highly desirable. The proposed experiment aims to quantitatively measure the properties and efficiency of channeling and VR with electrons in the 10-GeV energy regime. We will also aim to measure the dechanneling vs beam energy and, if we can obtain suitable crystals in different lengths, the dechanneling length. In a second stage we plan to build and install a crystal array to explore the possibility of using it as a beam-collimation device for electrons using VR
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