Planar channeling of 855 MeV electrons in a boron-doped (110) diamond undulator -- a case study

TL;DR

This study investigates the feasibility of using a boron-doped diamond crystal as an undulator for 855 MeV electrons, combining experimental measurements with simulations, but does not observe the expected undulator peak.

Contribution

It presents the first experimental attempt to observe planar channeling radiation in a boron-doped diamond undulator guided by detailed simulations.

Findings

Optimal observation angle identified for maximum undulator peak

No undulator peak observed in experiments

Coherent scattering suppression observed in diamond

Abstract

A 4-period diamond undulator with a thickness of 20 $\mu$m was produced with the method of Chemical Vapour Deposition (CVD), applying boron doping, on a straight diamond crystal with an effective thickness of 165.5 $\mu$m. A planar (110) channeling experiment was performed with the 855 MeV electron beam of the Mainz Microtron MAMI accelerator facility to observe the expected undulator peak. The search was guided by simulation calculations on a personal computer. The code is based on the continuum potential picture, and a classical electrodynamic expression which involves explicitly the acceleration of the particle. As a result, an unexpected optimal observation angle was figured out, for which the undulator peak is strongest and the channeling radiation from the backing crystal being significantly suppressed. However, an undulator peak was not observed. Implications for the prepared undulator structure are discussed. Scatter distributions were measured for a 75 $\mu$m Kapton, a 25 $\mu$m aluminum foils, and a 70.7 $\mu$m diamond plate in random orientation. The results were compared with Moli\`ere's scatter theory for amorphous medii. Very good agreement was found for Kapton and aluminum while for diamond the experimental width is 21\% smaller. This reduction is interpreted as coherent scattering suppression in single crystals. At tilted injection of the beam with respect to the (110) plane a clear asymmetry was observed which resembles partial beam deflection. We interpret this phenomenon heuristically as re-channeling.