Use Of Bent Crystals Research Articles

The GALORE project

Bent crystals are a compact and versatile tool to manipulate ultra-relativistic particle beams in accelerators. Indeed, the unrivaled steering power achievable exploiting channeling of particles between the atomic planes is comparable to that of a 10^{2-3} Tesla magnetic dipole. Since the first experiments in the 1980s, extensive research has been delivering important results for new physics experiments and applications in accelerators. The substantial technological development, accompanied by reliable Monte Carlo simulations, has increased the steering efficiency from a few % to the intrinsic maximum efficiency of sim 80%, limited by scattering of the particles with nuclei inside the crystal. The recently started two-year (2022–2023) project GALORE of INFN aims to assess experimentally the possibility to overcome this hard limit by developing a new generation of bent crystals, featuring an innovative geometry characterized by a crystalline microstructure which influences particle dynamic in the crystal lattice to boost efficiency close to 100%. The manufacturing process will exploit well-established techniques developed for silicon microelectronics, and experimental testing will be carried out at the extracted beamlines of CERN North Area with high-energy hadron beams. The success of this project could strongly impact the employment of bent crystal in frontier energy accelerators, boosting performance of already proposed schemes as well as enabling completely inedited use of bent crystal in particle physics experiment in accelerators.Graphic

The CpFM, an in-vacuum Cherenkov beam monitor for UA9 at SPS

The use of bent crystals for beam manipulation in particle accelerators is a well-assessed concept rapidly evolving into practical application. The experiments of the UA9 collaboration at the CERN-SPS have played a key role for a quantitative understanding of channeling and volume reflection mechanisms. Investigation of the channeling process close to a circulating beam ideally requires in vacuum detectors resolving the single particle, which should be located inside the vacuum pipe itself. Cherenkov radiators are potential candidates for such functionality due the reduced electro-magnetic interaction of the radiator material with the circulating charges and their compatibility with vacuum requirements in the beam pipe. For this purpose, we developed a device called Cherenkov detector for proton Flux Measurement (CpFM) that aims at counting the number of deflected protons of the beam halo surrounding the circulating beam with an accuracy of 15%. After a detailed description of the detection chain and its simulation, we present results of beam tests of different configurations, the calibration of the final device and the results of its first operation in the SPS.

USE OF CRYSTALS FOR BEAM DEFLECTION IN PARTICLE ACCELERATORS

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.

CRYSTAL-BASED COLLIMATION IN MODERN HADRON COLLIDERS

The use of bent crystals for beam manipulations in particle accelerators or in external beam-lines is an old concept, still under scrutiny. In the last three decades, the knowledge on the features of crystal-particle interaction has been continuously growing on the basis of a large number of experimental findings. In all cases, the results of measurements have been found in agreement and, sometimes, have been anticipated by numerical models and simulations. Bent crystals can impart angular deviations to the incoming particles, through channelling or volume reflection mechanisms. The efficiency of the latter mechanism has been found to be intrinsically large, whilst the channelling efficiency has been improved by the increased technological expertise in crystal cutting and bending. In this paper we review the recent milestones of the worldwide effort to propose a routine use of bent crystal in particle accelerators, with a specific attention to the proposals of promoting the use of bent crystals as primary element in a collimation system.

The schemes of proton extraction from IHEP accelerator using bent crystals

IHEP Protvino has pioneered the wide practical use of bent crystals as optical elements in high energy beams for beam extraction and deflection on permanent basis since 1989. In the course of IHEP experiments, crystal channeling has been developed into efficient instrument for particle steering at accelerators, working in predictable, reliable manner with beams of very high intensity over years. Crystal systems extract 70GeV protons from IHEP main ring with efficiency of 85% at intensity of 1012, basing on multi-pass mechanism of channeling proposed theoretically and realized experimentally at IHEP. Today, six locations on the IHEP 70GeV main ring of the accelerator facility are equipped by crystal extraction systems, serving mostly for routine applications rather than for research and allowing a simultaneous run of several particle physics experiments, thus significantly enriching the IHEP physics program. The long successful history of large-scale crystal exploitation at IHEP should help to incorporate channeling crystals into accelerator systems worldwide in order to create unique systems for beam delivery. We report recent results from the research and exploitation of crystal extraction systems at IHEP.

Use of oriented polycrystalline films in x-ray optics

X-ray diffractors having doubly curved crystal planes can have a high collection efficiency for radiation from a point source and can provide point-to-point focusing of monochromatic x rays as shown by some of the authors. These kinds of diffractors can be used to form x-ray microprobes that can give lower detection limits than electron microprobes or to make wavelength dispersive spectrometers with better signal and signal/background ratio than conventional ones employing the Johann or Johansson geometry. However, fabrication of diffractors of the desired geometry by the use of bent crystals has been difficult. In this paper, we explore the use of oriented polycrystalline films to fabricate doubly curved diffractors for x rays of short wavelength.Oriented polycrystalline films (OPF) have been of interest for many applications, e.g., magnetic recording media, non-linear optical device components, inexpensive large-area substrates for semiconductor device fabrication, etc. These films consist of small monocrystalline grains that have a high degree of preferential orientation of one crystallographic axis relative to the substrate surface.

X-ray microscopy of laser-produced plasmas with the use of bent crystals

X-ray spectroscopical and microscopical methods are used for the determination of the spectral and spatial distribution of X-ray intensity of laser-produced plasmas. The use of Bragg reflections of two-dimensionally bent crystals enables the X-ray microscopical imaging in narrow spectral ranges (Δλ/λ = 10−4 to 10−2) with wavelengths 0.1 nm < λ > 2.6 nm. It is possible to adapt, in the X-ray microscope, the distances, magnification, position, and width of the spectral window to the special conditions of the laser facility. Manufacturing and testing of the two-dimensionally bent crystals requires a great deal of effort. It was demonstrated that a spatial resolution of about 5 μm was achieved, and that the experimentally determined reflectivity was found to be in close agreement with the dynamical theory of X-ray interferences. Due to high luminosity of the X-ray microscope, in experiments with laser-produced plasmas it was necessary to attenuate the radiation with aperture-limiting diaphragms or filters down to 0.01–1% of the original intensity in the case of a magnification of about one. Emission of the resonance line W 1–2, the intercombination line of helium-like ions, and Lyman alpha line were imaged simultaneously with a three-channel microscope. Such images form the foundation for establishing the Ne(r), Tz(r) maps.