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Manuscript Title: Parallel Code NSBC: Simulations of Relativistic Nuclei Scattering by a Bent Crystal
Authors: A.A. Babaev
Program title: NSBC (Nuclei Scattering by Bent Crystal)
Catalogue identifier: AEQT_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 185(2014)368
Programming language: C++ (g++, icc compilers).
Computer: Multiprocessor systems (clusters).
Operating system: Any OS based on LINUX; the program was tested under Novell SLES 10.
Has the code been vectorised or parallelized?: Yes. The code contains MPI directives
RAM: About 1MB per processor
Keywords: Accelerators, Nuclei beam, Channeling, Quasichanneling, Bent crystal, Crystal collimation.
Classification: 7.10, 11.10.

External routines: MPI library for GNU C++, Intel C++ compilers

Nature of problem:
Here we deal with planar channeling of fast particles in a bent crystal. The channeled projectile moves along bent planes being in such a way deflected at large angles from the initial direction of motion. This effect is recognized as accelerator techniques to shape the beam. Other attractive phenomenon is known as volume reflection of quasichanneled projectiles. Volume reflected projectiles can also be deflected at essential angles. In general, channeled and reflected particles are deflected in opposite directions and initial beam is split into two beams. Hence, there is the practical interest to model the beam tracking in a bent crystal, to obtain the characteristic angles of deflection and to estimate the number of particles which can be effectively deflected at large angles.

Solution method:
Initially the beam of relativistic nuclei hitting the bent crystal is considered. The velocity of a particle is defined by two components. The component along the beam direction is relativistic, while the transverse component is nonrelativistic. The particle trajectory in a crystal is defined by the continuous potential of bent planes. Hence, to obtain the trajectory the classical equation of motion is solved numerically. The initial position of a nucleus in the channel is suggested to be random that can be obtained from the uniform distribution. To take into account the multiple scattering of projectiles on crystal both electrons and nuclei the corrections to the trajectory is introduced from time to time. Finally, at the projectile fly-out from the crystal one can obtain the transverse velocity as well as the deflection angle.

As known the theory of the channeling effect implies the critical Lindhard angle θL. Channeling takes place when the angle θ0 between the bent planes and the velocity of a particle at the crystal entrance face undergoes the condition |θ0| < θL. The quasichanneling appears when |θ0| exceeds the value θL but remains close to this value. Thus, it is not recommended to input large values of the crystal orientation angle |θC| which defines the range of angles θ0 (see in Section 2). Nevertheless, in our simulations we found the program gives correct results in the broad range of crystal orientation angles, for example, -18θL ≤ θC ≤ 4θL for 400 GeV protons. Characteristic values of critical angle θL are about 10 μrad for the energy of projectile about 100 GeV/uamu.

Additional comments:
The distribution file contains a user manual, readme.pdf, a utility to generate the beam of particles Beam_Generator.exe, the pdf presentation that is commented in the Sample A.

Running time:
In general, the running time T depends on the number of both processors N and particles P hitting the crystal, as well as on the crystal thickness. It can be estimated by the ratio T[min]=3.10-5R[μrad].P/(N - 1) for the 2.66 GHz processors, where αRis the crystal bending angle. In our tests the simulations were performed for a few thousands of particles into the crystal of up to several mm thickness. The number of the 2.66 GHz processors used counted up to 30. The running time of about 5 min was registered in the above mentioned conditions.