Short Bent Crystal Research Articles

Crystal channeling investigations at medical synchrotron regimes

An experimental setup to investigate ion channeling in the hundreds MeV/u energy range is described. A short bent crystal, aligned to the incoming beam by an angular actuator, should deflect ions into a single plane pixel detector used to identify channeled and unchanneled particles. In order to enhance the footprint of channeling on the recorded signals, the incoming particle emittance is tailored on the crystalline plane acceptance by means of massive collimators. Numerical simulations of low energy carbon ions are performed with FLUKA to fully understand the measurement conditions demonstrate the feasibility of the test, to be performed in the experimental room of the National Center for Oncological Hadrontherapy accelerator complex in Pavia, Italy.

Track reconstruction and analysis of particle interactions in short bent crystals

Measurements of the interaction of positively charged particles with bent crystals were obtained by developing a new and consolidated analysis method, for the use of UA9 collaboration. The method was deployed to characterize crystals with a length of a few mm along the beam direction and a bending angle in the order of 10 μrad to 100 μrad, typically exploited in the CERN accelerators. To assess their properties and quality, the crystals have been investigated in the Super Proton Synchrotron North Area with a beam of mixed hadrons at 180 GeV. The UA9 telescopic tracker has been used to collect the data. Some of them are used in the present study to describe and validate the applied data-analysis methodology.

Use of the Reflection of Particles in Bent Crystals to Collimate a Beam in Large Hadron Colliders

A multistage collimation system for the absorption of the growing halo of circulating beams is used at the Large Hadron Collider (LHC) to protect superconducting magnets and to ensure their reliable operation. A similar system is also planned for the Future Circular Collider (FCC). Studies for the improvement of the collimation system are performed prior to the operation of the LHC with a high luminosity. Studies have shown that one of the solutions to improve the beam collimation is the use of channeling in a short bent crystal, which serves as a primary collimator throwing particles deep into the secondary collimator by means of channeling. This system is very sensitive to the angular position of the crystal and various possible vibrations. In this work, another approach to beam collimation based on the bulk reflection of particles from bent crystal-lographic planes in a sequence of crystals has been proposed. Advantages of this scheme have been justified and a multistrip crystal device has been proposed to implement this scheme.

Angular asymmetry of the nuclear interaction probability of high energy particles in short bent crystals

The rate of inelastic nuclear interactions in a short bent silicon crystal was precisely measured for the first time using a 180 GeV/c positive hadron beam produced in the North Experimental Area of the CERN SPS. An angular asymmetry dependence on the crystal orientation in the vicinity of the planar channeling minimum has been observed. For the inspected crystal, this probability is about sim 20% larger than in the amorphous case because of the atomic density increase along the particle trajectories in the angular range of volume reflection, whose dimension is determined by the crystal bending angle. Instead, for the opposite angular orientation with respect to the planar channeling, there is a smaller probability excess of sim 4%.

Positive features of crystal extraction of protons and carbon ions from the U-70 on basis of long-term experience

Works on the steering of particle beams using channeling in aligned bent crystals have been carried out at IHEP over a number of years. Comprehensive theoretical and experimental studies have led to the creation of actually operating systems on the U-70 accelerator. In particular, a slow proton beam extraction with unprecedentedly high parameters, an extraction efficiency of about 85% at a beam intensity of 10[Formula: see text] particles per cycle, has been realized on U-70 using particle channeling in short bent crystals. In recent years, successful experiments on the extraction of carbon ions were performed. At present, crystal elements are used in regular U-70 runs and provide half of the particle beams for physical experiments. Here, we summarize the results of this unique experience in the world practice of accelerators and outline its prospects.

Application of Crystal Elements for Charged Particle Beam Steering and Radiation Beam Generation on the U-70 Synchrotron

Works on the formation of particle and radiation beams using particle channeling and reflection in oriented crystals have been carried out at IHEP over a number of years. Comprehensive theoretical and experimental studies have led to the creation of actually operating systems on the U-70 accelerator. In particular, a slow proton beam extraction with unprecedentedly high parameters, an extraction efficiency of about 85% at a beam intensity of 1012 particles per cycle, has been realized on U-70 using particle channeling in short bent crystals. Experiments to implement the method of particle reflection in crystals for beam extraction and collimation have been carried out on U-70. At present, crystal elements are used in regular U-70 runs and provide half of the particle beams for physical experiments. We summarize the results of this unique experience in the world practice of accelerators and outline its prospects.

Emission of Photons at the Interaction of a High-Energy Electron Beam with a Sequence of Bent Single Crystals

A radiation source based on the emission of electrons and positrons moving in a short bent crystal has been recently discovered. The emission of particles is due to oscillations of their trajectories near the point of reflections, where trajectories approach a tangent to bent atomic planes. In the experiment performed with the secondary electron beam of the U70 accelerator, it has been shown that the emission intensity can be increased by using a sequence of oriented bent crystals. Passing through six 2.5-mm-long silicon crystals, 7-GeV electrons lose on average 2.0 GeV on emission. This value is several times larger than that in an amorphous medium. Thus, an intense source of radiation has been demonstrated with prospects of application at accelerators.

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

An investigation on the mechanism of relaxation of axially confined 400 GeV/c protons to planar channeling in a bent crystal was carried out at the extracted line H8 from CERN Super Proton Synchrotron. The experimental results were critically compared to computer simulations, showing a good agreement. We firmly individuated a necessary condition for the exploitation of axial confinement or its relaxation for particle beam manipulation in high-energy accelerators. We demonstrated that with a short bent crystal, aligned with one of its main axis to the beam direction, it is possible to realize either a total beam steerer or a beam splitter with adjustable intensity. In particular, in the latter case, a complete relaxation from axial confinement to planar channeling takes place, resulting in beam splitting into the two strongest skew planar channels.

Observation of nuclear dechanneling length reduction for high energy protons in a short bent crystal

Deflection of 400 GeV/c protons by a short bent silicon crystal was studied at the CERN SPS. It was shown that the dechanneling probability increases while the dechanneling length decreases with an increase of incident angles of particles relative to the crystal planes. The observation of the dechanneling length reduction provides evidence of the particle population increase at the top levels of transverse energies in the potential well of the planar channels.

Double volume reflection of a proton beam by a sequence of two bent crystals

The doubling of the angle of beam deflection due to volume reflection of protons by a sequence of two bent silicon crystals was experimentally observed at the 400 GeV proton beam of the CERN SPS. A similar sequence of short bent crystals can be used as an efficient primary collimator for the Large Hadron Collider.

Volume reflection of high-energy protons in short bent crystals

Characteristics of volume reflection for high-energy protons in short bent crystals are considered by simulation. The deflection efficiency and angle depend on the bend radius of the crystal. The concurrent process of volume capture of particles into channeling states limits the reflection efficiency. The optimal parameters of a crystal for using it as a beam reflector were determined.It was shown that the deflection efficiency of high-energy proton beams by the sequence of reflections in short bent crystals is high for small deflection angles. This allows considering possible applications of crystal reflectors for the beam collimation of hadrons colliders and for high-energy physics experiments.

Volume Reflection of a Proton Beam in a Bent Crystal

Volume reflection predicted in the mid-1980s by Taratin and Vorobiev has been observed for the first time in the interactions of a 70 GeV proton beam with a short bent crystal. Incident protons deviate from convex atomic planes in the bulk of the crystal as a result of coherent interaction with bent lattice around the tangency point of particle trajectory with a curved atomic plane. The deflection angle 2theta(R) was found to be (39.5+/-2.0) microrad, or (1.65+/-0.08)theta(c) in terms of the critical angle for channeling. The process has a large probability with respect to channeling and takes place in the angular range equal to the bend angle of atomic planes. It could possibly open new fields of application of crystals in high-energy particle beam optics.

High-efficiency beam extraction and collimation using channeling in very short bent crystals.

A silicon crystal was used to channel and extract 70 GeV protons from the U-70 accelerator with an efficiency of 85.3+/-2.8%, as measured for a beam of approximately 10(12) protons directed towards crystals of approximately 2 mm length in spills of approximately 2 s duration. The experimental data follow very well the prediction of Monte Carlo simulations. This demonstration is important in devising a more efficient use of the U-70 accelerator in Protvino and provides crucial support for implementing crystal-assisted slow extraction and collimation in other machines, such as the Tevatron, RHIC, the AGS, the SNS, COSY, and the LHC.

High-efficiency multipass extraction of 70-GeV protons from an accelerator with a short bent crystal

Using channeling in a 5-mm crystal with a bending angle of 1.5 mrad, a radical increase in the efficiency of beam extraction from accelerator was achieved due to an increased number of particle encounters with crystal. The measured world-highest efficiency of crystal extraction, over 40%, is in good agreement with theory predictions. The extracted beam intensity of 6×10 11 ppp was obtained, five orders of magnitude higher than previous results.