Steering of Sub-GeV electrons by ultrashort Si and Ge bent crystals

TL;DR

This study demonstrates the steering of sub-GeV electrons using ultrashort bent silicon and germanium crystals, revealing new insights into channeling efficiency, dechanneling length, and potential for beam manipulation.

Contribution

First experimental evidence of negative beam steering in germanium crystals and measurement of dechanneling length for the first time.

Findings

Silicon crystals achieve over 35% channeling efficiency.

Germanium crystals show nearly 10% efficiency, influenced by multiple scattering.

Dechanneling length measured, enabling optimized crystal design.

Abstract

We report the observation of the steering of 855 MeV electrons by bent silicon and germanium crystals at the MAinzer MIkrotron. 15 $\mu $m long crystals, bent along (111) planes, were exploited to investigate orientational coherent effects. By using a piezo-actuated mechanical holder, which allowed to remotely change the crystal curvature, it was possible to study the steering capability of planar channeling and volume reflection vs. the curvature radius and the atomic number, Z. For silicon, the channeling efficiency exceeds 35 %, a record for negatively charged particles. This was possible due to the realization of a crystal with a thickness of the order of the dechanneling length. On the other hand, for germanium the efficiency is slightly below 10 % due to the stronger contribution of multiple scattering for a higher-Z material. Nevertheless this is the first evidence of negative beam steering by planar channeling in a Ge crystal. Having determined for the first time the dechanneling length, one may design a Ge crystal based on such knowledge providing nearly the same channeling efficiency of silicon. The presented results are relevant for crystal-based beam manipulation as well as for the generation of e.m. radiation in bent and periodically bent crystals.