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Charged particles interacting with a bent crystal can be trapped in channeling states and deflected by the atomic planes of the crystal lattice. The use of bent crystals for beam manipulation in particle accelerators is a well assessed concept rapidly evolving into practical applications. In the last three decades, a large number of experimental findings have contributed to clarify our knowledge and to improve our control of crystal–particle interactions. Bent crystals can impart angular deflections to the incoming particles, through channeling or volume reflection mechanisms. The efficiency of the latter mechanism has been found to be intrinsically very large, whilst the channeling efficiency has been improved by the increased technological expertize in crystal cutting and bending. In this paper, we review the recent milestones of the worldwide effort to propose a routine use of bent crystals in particle accelerators, with a specific attention to the proposals of promoting the use of bent crystals as primary element in beam halo collimation systems.

Crystals were used at Fermilab accelerators for slow extraction and halo collimation in the Tevatron collider, and for channeling radiation generation experiments at the FAST electron linac facility. Here we overview past experience and major outcomes of these studies and discuss opportunities for new crystal acceleration R&D program.

In this review article we discuss the recent progress in studying ballistic transport for charge carriers in graphene through highly inhomogeneous magnetic field known as magnetic barrier in combination with gate voltage induced electrostatic potential. Starting with cases for a single or double magnetic barrier we also review the progress in understanding electron transport through the superlattices created out of such electromagnetic potential barriers and discuss the possibility of experimental realization of such systems. The emphasis is particularly on the analogy of such transport with propagation of light wave through medium with alternating dielectric constant. In that direction we discuss electron analogue of optical phenomena like Fabry–Perot resonances, negative refraction, Goos–Hänchen effect, beam collimation in such systems and explain how such analogy is going to be useful for device generation. The resulting modification of band structure of Dirac fermions, the emergence of additional Dirac points was also discussed accompanied by brief section on the interconvertibility of electric and magnetic field for relativistic Dirac fermions. We also discuss the effect of such electromagnetic potential barrier on bilayer graphene (BLG) in a similar framework.

We present a semi-analytical model using the equations of general relativistic magnetohydrodynamics (GRMHD) for jets emitted by a rotating black hole. We assume steady axisymmetric outflows of a relativistic ideal fluid in Kerr metrics. We express the conservation equations in the frame of the FIDucial Observer (FIDO or ZAMO) using a 3+1 space–time splitting. Calculating the total energy variation between a non-polar field line and the polar axis, we extend to the Kerr metric the simple criterion for the magnetic collimation of jets obtained for a nonrotating black hole by Meliani et al.¹⁰ We show that the black role rotation induced a more efficient magnetic collimation of the jet.

High energy ion colliders are large research tools in nuclear physics for studying the quark–gluon–plasma (QGP). The collision energy and high luminosity are important design and operational considerations. The experiments also expect flexibility with frequent changes in the collision energy, detector fields, and ion species. Ion species range from protons, including polarized protons in RHIC, to heavy nuclei like gold, lead, and uranium. Asymmetric collision combinations (such as protons against heavy ions) are also essential. For the creation, acceleration, and storage of bright intense ion beams, limits are set by space charge, charge change, and intrabeam scattering effects, as well as beam losses due to a variety of other phenomena. Currently, there are two operating ion colliders: the Relativistic Heavy Ion Collider (RHIC) at BNL and the Large Hadron Collider (LHC) at CERN.

I review some accelerator physics topics for circular as well as linear colliders, considering both lepton and hadron beams.

The ELI-NP facility, currently being built in Bucharest, Romania, will deliver an intense and almost monochromatic gamma beam with tunable energy between 0.2 and 20 MeV. The challenging energy bandwidth of $\le$0.5% will be adjusted through the collimation system, while the main beam parameters will be measured through a devoted gamma-beam characterization system.${}^{\mathrm{\text{1}}}$ The gamma-beam characterization system, designed by the EuroGammaS collaboration, consists of four elements: a Compton spectrometer that measures the gamma energy spectrum; a sampling calorimeter for a fast combined measurement of the beam average energy and its intensity, which will be used also as a monitor during machine commissioning and development; a nuclear resonant scattering system for absolute energy inter-calibration of the other detectors; and a gamma beam profile imager to be used for alignment and diagnostics purposes. The collimation and characterization system will be presented in this article. These systems have already been built and tested, while the delivery at ELI-NP facility and the final commissioning is scheduled by Fall 2018.

Crystals were used at Fermilab accelerators for slow extraction and halo collimation in the Tevatron collider, and for channeling radiation generation experiments at the FAST electron linac facility. Here we overview past experience and major outcomes of these studies and discuss opportunities for new crystal acceleration R&D program.

The collimation based on bent crystals represents an opportunity to increase the cleaning efficiency and reduce the beam impedance in high energy accelerators, starting from LHC, whose luminosity is now limited (at the 40% of the nominal value) by the collimation system. The basic idea of the crystal based collimation is to replace the amorphous primary collimator with a silicon bent crystal able to deflect the beam halo outside the beam towards an absorber. The UA9 experiment is testing this scheme on the CERN SPS circulating beam. The 120 GeV/c proton beam is stimulated to create a halo that impinges on the selected crystal; the particles deflected by the crystal are directed on to a tungsten absorber located ~ 70 m after. The experiment combines the standard beam diagnostic system (beam loss monitors and ionisation detectors) with a silicon microstrip tracking system that will be placed in two roman pots located between the crystal and the absorber. The tracking system presented in this paper represents one of the UA9 novelties with respect to the past similar experiment: it will measure the position and angle of the deflected particles allowing one to clearly recognise the crystal behaviour.

High energy ion colliders are large research tools in nuclear physics for studying the quark–gluon–plasma (QGP). The collision energy and high luminosity are important design and operational considerations. The experiments also expect flexibility with frequent changes in the collision energy, detector fields, and ion species. Ion species range from protons, including polarized protons in RHIC, to heavy nuclei like gold, lead, and uranium. Asymmetric collision combinations (such as protons against heavy ions) are also essential. For the creation, acceleration, and storage of bright intense ion beams, limits are set by space charge, charge change, and intrabeam scattering effects, as well as beam losses due to a variety of other phenomena. Currently, there are two operating ion colliders: the Relativistic Heavy Ion Collider (RHIC) at BNL and the Large Hadron Collider (LHC) at CERN.

I review some accelerator physics topics for circular as well as linear colliders, considering both lepton and hadron beams.