Mirroring of 400 GeV/c protons by an ultra-thin straight crystal

/Channeling is the confinement of the trajectory of a charged particle in a crystalline solid. Positively charged particles channeled between crystal planes oscillate with a certain oscillation length, which depends on particle energy. A crystal whose thickness is half the oscillation length for planar channeling may act as a mirror for charged particles. If the incident angle of the particle trajectory with the crystal plane is less than the critical angle for channeling, under-barrier particles under go half an oscillation and exit the crystal with the reversal of their transverse momentum, i.e., the particles are mirrored by the crystal planes. Unlike the traditional scheme relying on millimeter-long curved crystals, particle mirroring enables beams teering in high energy accelerators via interactions with micrometer-thin straight crystal. The main advantage of mirroring is the interaction with a minimal amount of material along the beam, there by decreasing unwanted in coherent nuclear interactions. The effectiveness of the mirror effect for ultrarelativistic positive particles has been experimentally provenat external lines of CERN-SPS. The mirroring effect in a 26.5-mu m-thick Si crystal has been studied in the experiment with a narrow beam of 400 GeV/c protons at the CERN-PS. The reflection efficiency for a quasi-parallel beam is larger than 80%. (C) 2014 The Authors. Published by Elsevier B. V.