Energy loss distributions of 7 TeV protons channeled in a bent silicon crystals

The energy loss distributions of relativistic protons axially channeled through the bent <100> Si crystals, with the constant curvature radius, R = 50 m, are studied here. The proton energy is 7 TeV and the thickness of the crystal is varied from 1 mm to 5 mm, which corresponds to the reduced crystal thickness, L, from 2.1 to 10.6, respectively. The proton energy was chosen in accordance with the large hadron collider project, at the European Organization for Nuclear Research, in Geneva, Switzerland. The energy loss distributions of the channeled protons were generated by the computer simulation method using the numerical solution of the proton equations of motion in the transverse plane. Dispersion of the proton scattering angle caused by its collisions with the crystal’s electrons was taken into account. [Projekat Ministarstva nauke Republike Srbije, br. III 45006

Quantum Rainbows in Positron Transmission through Carbon Nanotubes

Here we report the results of the theoretical investigation of the transmission of channeled positrons through various short chiral single walled carbon nanotubes (SWCNT). The main question answered by this study is “What are the manifestations of the rainbow effect in the channeling of quantum particles that happens during the channeling of classical particles?” To answer this question, the corresponding classical and quantum problems were solved in parallel, critically examined, and compared with each other. Positron energies were taken to be 1 MeV when the quantum approach was necessary. The continuum positron-nanotube potential was constructed from the thermally averaged Molière’s positron-carbon potential. In the classical approach, a positron beam is considered as an ensemble of noninteracting particles. In the quantum approach, it is considered as an ensemble of noninteracting wave packages. Distributions of transmitted positrons were constructed from the numerical solutions of Newton’s equation and the time-dependent Schrödinger equation. For the transmission of 1-MeV positrons through 200-nm long SWCNT (14; 4), in addition to the central maximum, the quantum angular distribution has a prominent peak pair (close to the classical rainbows) and two smaller peaks pairs. We have shown that even though the semiclassical approximation is not strictly applicable it is useful for explanation of the observed behavior. In vicinity of the most prominent peak, i.e., the primary rainbow peak, rays interfere constructively. On one of its sides, rays become complex, which explains the exponential decay of the probability density in that region. On the other side, the ray interference alternates between constructive and destructive, thus generating two observed supernumerary rainbow peaks. The developed model was then applied for the explanation of the angular distributions of 1-MeV positrons transmitting through 200 nm long (7, 3), (8, 5), (9, 7), (14, 4), (16, 5) and (17, 7) SWCNTs. It has been shown that this explains most but not all rainbow patterns. Therefore, a new method for the identification and classification of quantum rainbows was developed relying only on the morphological properties of the positron wave function amplitude and the phase function families. This led to a detailed explanation of the way the quantum rainbows are generated. All wave packets wrinkle due to their internal focusing in a mutually coordinated way and are concentrated near the position of the corresponding classical rainbow. This explanation is general and applicable to the investigations of quantum effects occurring in various other atomic collision processes

Upgrading the ECR ion source within FAMA

Recent upgrading of the Facility for Modification and Analysis of Materials with Ion Beams-FAMA, in the Laboratory of Physics of the Vinca Institute of Nuclear Sciences, included the modernization of its electron cyclotron resonance ion source. Since the old ion source was being extensively used for more than 15 years for production of multiply charged ions from gases and solid substances, its complete reconstruction was needed. The main goal was to reconstruct its plasma and injection chambers and magnetic structure, and thus intensify the production of multiply charged ions. Also, it was decided to refurbish its major subsystems the vacuum system, the microwave system, the gas inlet system, the solid substance inlet system, and the control system. All these improvements have resulted in a substantial increase of ion beam currents, especially in the case of high charge states, with the operation of the ion source proven to be stable and reproducible

Upgrading of the CAPRICE type ECR ion source

The CAPRICE-type ECR ion source mVINIS has been upgraded by increasing its magnetic field to improve a plasma confinement and thereby enhance the source performance. This modification made it also possible to increase the internal diameter of the plasma chamber and to replace the coaxial microwave input by a waveguide. Some major subsystems such as: the vacuum system, the microwave system, the gas inlet system, the solid substance inlet system, and the control system have been also refurbished. All these improvements have resulted in a substantial increase of ion beam currents, especially in the case of high charge states, with the operation of the ion source proven to be stable and reproducible. This modification can be applied to other CAPRICE-type ion sources. © 2018 Author(s).17th International Conference on Ion Sources 2018; Geneva's International Conference Centre Geneva; Switzerland; 15 September 2017 through 20 September 2017; Code 13992

Quantum rainbows in positron channeling in carbon nanotubes

Carbon nanotubes are the sheets of carbon atoms rolled up into cylinders with the atoms lying at the hexagonal crystal lattice sites. It has been predicted that they can be used to channel positively charged particles. This means that nanotubes could be used for guiding such beams. It has been also shown that the rainbow effect plays an important role in proton and positron channeling in nanotubes. This plenary speech is devoted to channeling of positrons of kinetic energy of 1 MeV in (11, 9) chiral single-wall carbon nanotubes of lengths between 50 and 200 nm. We present the classical and quantum spatial and angular distributions of transmitted positrons. In the classical calculations, the approach is via the equations of motion, and in the quantum calculations, the time-dependent Schrödinger equations is solved. The solutions of these quations are obtained numerically. In the quantum calculations, the initial beam is taken to be an ensemble on noninteracting Gaussian wave packets. The spatial and angular distributions are generated using the computer simulation method. The analysis is concentrated on the rainbow effects, which is clearly seen in the spatial and angular distributions. The obtained classical and quantum rainbows are analyzed in detail and compared with each other. We give a full quantum mechanical explanation of the quantum rainbows.IV Serbian Ceramic Society Conference - Advanced Ceramics and Application : new frontiers in multifunctional material science and processing : program and the book of abstracts; September 21-23, 2015; Belgrad

Rainbows with Crystals and Nanotubes

This review paper is devoted to the crystal rainbow effect, which occurs in ion channeling in crystals and nanotubes. We begin with a description of crystal rainbows. Then, we analyze the evolution of the angular distribution of channeled ions with the crystal thickness. The analysis includes the rainbow cycles, and the effects of spatial focusing and angular focusing of channeled ions. This leads us to the theory of crystal rainbows. It is shown that it is the proper theory of ion channeling. After that, we describe how the effect of spatial focusing of channeled ions can be used for a subatomic microscopy. Further, the rainbow effect occurring with carbon nanotubes is considered. Finally, we demonstrate how an ion beam can be guided by a bent carbon nanotube

Concept of an accelerator-driven subcritical research reactor within the TESLA accelerator installation

Study of a small accelerator-driven subcritical research reactor in the Vinca Institute of Nuclear Sciences was initiated in 1999. The idea was to extract a beam of medium-energy protons or deuterons from the TESLA accelerator installation, and to transport and inject it into the reactor. The reactor core was to be composed of the highly enriched uranium fuel elements. The reactor was designated as ADSRR-H. Since the use of this type of fuel elements was not recommended any more, the study of a small accelerator-driven subcritical research reactor employing the low-enriched uranium fuel elements began in 2004. The reactor was designated as ADSRR-L. We compare here the results of the initial computer simulations of ADSRR-H and ADSRR-L. The results have confirmed that our concept could be the basis for designing and construction of a low neutron flux model of the proposed accelerator-driven subcritical power reactor to be moderated and cooled by lead. Our objective is to study the physics and technologies necessary to design and construct ADSRR-L. The reactor would be used for development of nuclear techniques and technologies, and for basic and applied research in neutron physics, metrology, radiation protection and radiobiology. (c) 2006 Elsevier B.V. All rights reserved.7th International Conference on Accelerator Applications, Aug 28-Sep 01, 2005, Venice, Ital

Crystal rainbows

This review is devoted to ion transmission through axial channels of thin crystals. In this process the rainbows occur. The effect is called the crystal rainbow effect. We shall describe its origin and present the experiments in which it has been observed. We shall explain also how the crystal rainbows can be classified using catastrophe theory. This classification has resulted in a universal, simple and accurate approximation to the continuum potential in the channels. Besides, the periodicity of the angular distributions of transmitted ions with the reduced crystal thickness will be considered. It will be introduced via the effect of zero-degree focusing of channeled ions. In addition, we shall mention the doughnut effect in ion channeling, which has proven to be the rainbow effect with tilted crystals. All these considerations will demonstrate clearly the usefulness of the theory of crystal rainbows, which is the proper theory of ion channeling in thin crystals. (C) 2003 Elsevier Science B.V. All rights reserved.22nd Werner Brandt Workshop, Jun, 2002, Namur, Belgiu

Influence of Cyclotron Magnet Gap Size on Stripping Extraction

The stripping extraction system of a cyclotron is prized by the range and quality of beams it delivers. The gap size of a cyclotron magnet is one of the parameters which significantly influence the design as well as the output characteristics of the stripping extraction system. The vertical dimension of the beam as well as of the extraction system elements placed inside a vacuum chamber is limited by the magnet gap size. Beside this direct influence, the indirect effect of the magnet gap size on stripping extraction occurs through the magnetic field and its impact on the beam dynamics in the extraction region. The performance of the extraction system is optimized by the proper placement of the point of beam exit from the cyclotron. It is shown that the optimal position of the exit point strongly depends on the magnet gap size. The performance of the optimized stripping extraction system for a smaller gap size is found to be somewhat better

Analytical Prediction of Ion Stripping Extraction From Isochronous Cyclotrons

Accelerated ion beams are often extracted from a cyclotron by stripping some of ions electrons at the end of the acceleration process. Stripping extraction system is commonly designed and optimized using computer simulations of beam dynamics at a later stage of a cyclotron project. However, minor changes in the distance between the magnet poles are proven to cause large displacements of the optimal position of high-energy transport line. It is shown that simple analytical formulas give good prediction of the position and direction of beam exit after stripping extraction and are useful tool for preliminary facility layout planning