A technique to improve crystal channeling efficiency of charged particles

Abstract

It is shown that a narrow plane cut near the crystal surface considerably increases the probability of capture into the stable channeling motion of positively charged particles entering a crystal at angles smaller than a quarter of the critical channeling angle with respect to the crystal planes. At smallest incidence angles the capture probability reaches 99 percent. A pair of crystals bent in orthogonal planes and provided with the cuts allows to reach a 99.9 percent efficiency of single-pass deflection of a proton beam with an ultra small divergence. Conditions necessary for efficient single-pass deflection of protons from the LHC beam halo are also discussed. KEYWORDS: Accelerator modelling and simulations (multi-particle dynamics; single-particle dynamics); Beam-line instrumentation (beam position and profile monitors; beam-intensity monitors; bunch length monitors); Instrumentation for particle accelerators and storage ringshigh energy (linear accelerators, synchrotrons); Detector alignment and calibration methods (lasers, sources, particle-beams).

Planar channeling and quasichanneling oscillations in a bent crystal

“…This program was validated in particular in the simulation of single-pass experiments at CERN SPS [34], in which a good agreement of experimental and simulation results was achieved [26]. The model implemented in this program [4,30,31,35] was also successfully applied to the explanation of different experiments on channeling radiation [24,25,35]. The effect of multiple volume reflection in a single-piece bent crystal was also predicted in the frame of this model [36][37][38] and demonstrated in several experiments [39][40][41].…”

“…Such oscillations are described below. The second can be realized in making a narrow plane cut perpendicularly to the crystal planes, resulting in an increase in channeling efficiency up to 99% [4,5]. The idea consists in focusing the particles in the cut to the centers of interplanar channels and their consequent recapture under channeling mode, far away from the crystal planes.…”

Quantitative theory of channeling particle diffusion in transverse energy in the presence of nuclear scattering and direct evaluation of dechanneling length

“…In particular, they correctly describe both the rechanneling process and the large transverse energy fluctuations at the upper under-barrier region ε ⊥ ∼ ε ⊥max , in which the diffusion equation looses its applicability. Monte Carlo approach have also demonstrated its efficiency in simulation of the new effects of channeling probability increase by the crystal cut [23], positive miscut influence of collimation [24] and other possibilities of the latter [25], multiple new radiation features in both crystal undulators [2,26,27] and bent crystals [28,29], the effects of planar channeling and quasichanneling oscillations in the deflection angle distribution of particles passed through a bent crystal [30] and many effects in the field of atomic strings [31,32,33,34,35,36,37]. However the main purpose of this paper was to demonstrate that despite all the achievements of Monte Carlo method, the diffusion equation approach, refined in present paper, can supplement the simulation results with the enlightening treatment of the collective statistical behavior of channeling particles, which can not be described by the sum of two exponents decaying with nuclear and electron dechanneling lengths.…”

“…has a clear semiclassical meaning, being equal to the multiplied by 2π quantum number of transverse oscillatory motion in the state corresponding to the considered transverse energy ε ⊥ . Both Eqs (22),(23). and the standard transformations[19] allows one to extract further the Sturm-Liouville operator in Eq (20).…”

On the deflection of a positron beam by the miscut surface of an oriented crystal

“…The possibility of using crystals with narrow plane cut in them was also discussed [10]. In this work, the pos sibility of the deflection of a beam propagating along the lateral surface of a crystal is studied.…”