Deflection of 100 MeV positron beam by repeated reflections in thin crystals

The phenomenon of the deflection of a charged particle beam due to channelling in a bent crystal is thoroughly investigated and successfully applied for the extraction of the beam in high-energy accelerators, at the energies of about $10$ GeV and higher. However, a big practical interest lies in the task of bending and extracting charged particles with energies below $1$ GeV, for example, for the production of ultrastable beams of low emittance for medical and biological applications. That is why a novel crystal technique, namely thin straight crystal targets, is investigated in this article, using crystals as elements for extraction and collimation of the circulating beam in a ring accelerator. The advantages of reflection in straight crystals in comparison with bent crystal channelling consist in the small length of straight crystals along the beam that reduces the amount of nuclear interactions and improves the background. Experimental results were obtained for the bending of a $100$ MeV positron beam with using five sequential straight crystals.