About the probability of close collisions during stochastic deflection of positively charged particles by a bent crystal

Study of inelastic nuclear interactions of 400 GeV/c protons in bent silicon crystals for beam steering purposes

“…It has been obtained that a reduction factor in ACH is about twice higher than in PCH, confirming the results obtained in terms of rate in [12] and in good agreement with the results published in 2010 [9]. Another interesting result is the experimental evidence that INI probability varies with the vertical misalignment from the ACH orientation, with a peak around 60 µrad from ACH, also if the crystal is horizontally oriented in PCH, reproducing qualitatively the theoretical and simulated results published in [28]. An additional new result is the measurement of the AM/PCH reduction factor as a function of the crystal curvature.…”

“…Within 5 µrad, the reduction factor AM/PCH is 4.3 ± 0.1, while the value for AM/ACH is 8.3 ± 0.1, almost double with respect to the planar case. This behaviour was predicted in [28]. Moreover, with an angular acceptance four times larger than the critical angle, it is interesting to note that the INI rate is more uniform in the ACH case, with respect to the PCH case.…”

Relaxation of axially confined 400 GeV/c protons to planar channeling in a bent crystal

“…In the Monte Carlo a particle is considered as escaped from SD if the angle between its momentum and the atomic string exceeds the critical angle for axial channeling the usage of a bent crystal respecting condition A as a passive element in a crystal-based collimation scheme offers not only the advantage of reducing the amount of material of the primary collimator, as already been demonstrated for planar channeling at SPS [25] and, very recently, at LHC [26], but also accomplishes deflection of the whole beam to the same direction through a single pass, an operation which cannot be done via currently used scheme exploiting PC, where multiturn interaction is mandatory. A further advantage of SD, is the reduction of interactions of protons with the nuclei of the crystals as compared to planar case [27], thus reducing the amount of particles in the secondary halo. Both these features, together with the increase of angular acceptance in axial mode can be exploited in a crystal-based collimation for SPS or LHC with higher efficiency and stronger reduction of unwanted secondary particles than for planar mode.…”

Orientation dependence of the probability of close collisions during passage of high-energy negatively charged particle through a bent crystal

“…So the crystal and its orientation were the same as in [8] (x-axis coincided with the h1 1 0i crystal axis, y-axis was perpendicular to the (0 0 1) plane, z-axis coincided with the h1 1 0i crystal axis, the direction of crystal bend coincided with x-axis direction). In the present article we consider 270 GeV/c p À -mesons scattering on a bent crystal.…”

“…In the article [7] it was shown that the probability of such close collisions for high-energy negatively charged particle moving in a straight crystal increases with the decrease of w in due to axial channeling if w in < w c , where w c is a critical angle of axial channeling [5]. In the work [8] the analysis of the probability of close collisions of high-energy positively charged particle in a bent crystal as a function of the angle w in was done. This analysis shown that this probability decrease with the decrease of w in if w in < w c because for positively charged particles the smaller is the angle between particle momentum and the axis of crystal atomic string the less is particle orthogonal energy and therefore the probability to come close to atomic string.…”