Title: On planar (110) channeling of 855 MeV electrons in a boron-doped diamond undulator

Abstract: A 4-period diamond undulator with a thickness of 20 $\mu$m was produced with the method of Chemical Vapour Deposition (CVC), applying boron doping, on a straight diamond crystal with an effective thickness of 165.5 $\mu$m. A planar (110) channeling experiment, performed with the high quality 855 MeV electron beam of the Mainz Microtron MAMI accelerator facility, failed to observe the expected undulator peak. Simulation calculations which are based on the continuum potential picture revealed unexpected results for radiation spectra at the chosen observation direction. They suggest, in addition, that at an optimized observation angle, for which the undulator peak is the strongest, the channeling radiation from the rather thick backing crystal can be significantly suppressed. A byproduct of this case study was the experimental observation that beam deflection can be achieved even with a flat 50 $\mu$m thick diamond crystal.