Landau damping effect due to the trapped ions in a compact electron storage ring

Theoretical analysis and experimental results show that the Landau damping due to trapped ions is greatly enhanced in the low-energy beams in compact electron storage rings. This enhancement originates mainly from the decrease in beam size in the low-energy region. This effect must indeed be the main reason why the recently developed compact rings can store a large current even though they have a low injection energy. In the typical energy region of compact rings, more positive utilization of this effect could make the damping rate of a lower-energy beam far larger than that of a higher-energy one. Therefore, if we could control the effect of the trapped ions, we might prefer to adopt lower energy in order to inject a large current in a compact ring.     

Nonparaxial gaussian beams: 2. Splitting of the singularity lines and the optical magnus effect

The Poynting vector field lines for the lowest modes of a nonparaxial Gaussian beam exhibit a number of loops and rings in the vicinity of the phase singularity lines (Airy’s fringes), with negative energy fluxes present inside these loops and rings. The positions of these fluxes are nonsymmetric with respect to rotation about the optical axis. This asymmetry leads to a local splitting of the phase singularity lines, after which the beam cross section transforms from circular to elliptic. The asymmetry of the beam cross section can be eliminated by considering a superposition of circularly polarized even and odd modes. However, this approach only uniformly redistributes the negative energy fluxes in the azimuthal direction of the cross section, rather than completely eliminates these fluxes. Any small perturbation of the resulting symmetric beam gives rise to a unique phenomenon—the optical Magnus effect in the free space, whereby the beam intensity pattern rotates upon changing the circular polarization from right to left. This effect implies the presence of a spin-orbit coupling in the nonparaxial Gaussian beam propagating in the free space.     

Cold leak tests of LHC beam screens

In order to guide the high energy proton beams inside its two 27 km long vacuum rings, the Large Hadron Collider (LHC) at CERN, Geneva, makes use of superconducting technology to create the required magnetic fields. More than 4000 beam screens, cooled at 7-20 K, are inserted inside the 1.9 K beam vacuum tubes to intercept beam-induced heat loads and to provide dynamic vacuum stability. As extremely high helium leak tightness is required, all beam screens have been leak tested under cold conditions in a dedicated test stand prior to their installation. After describing the beam screen design and its functions, this report focuses on the cold leak test sequence and discusses the results.     

Measurement of particle polarization in e+e− storage rings by means of synchrotron radiation scattering on the colliding beam

A new method for measuring the polarization of e⁺e^? in storage rings is described. It is based on the scattering of synchrotron radiation on the colliding beam. The method is simple in operation and allows a simultaneous measurement of the polarization of the electron and positron beam. This method was applied to the energy calibration of the storage ring VEPP-4 in the high precision measurements of the ?-mesons' masses with MD-1 detector.     

Superconductivity applications in high energy physics

During the past five years, several very large superconducting bubble chamber and spark chamber magnets have become operational. The economic and other factors which have led to the construction of large superconducting solenoid magnets for high energy physics research are discussed, and the technological development which made these magnets possible is summarized. Much of the recent development work on superconducting magnets for high energy physics has been directed toward the next generation of accelerators and beam storage rings. Here the goal is to develop dipole and quadrupole magnets of high field precision, low cost, high reliability, capability for slow pulsing, and minimal sensitivity to radiation heating. The status of this work and its application to future accelerators is described. Also, the application of superconducting rf cavities for linear accelerators and particle separation is reviewed briefly.     

Increasing the energy of SLC by transient wake field

This paper describes a way to make use of the field excited by the beam in the disk-loaded waveguide combined with the rf field in phase, to increase the output energy of the linear accelerator at the expense of beam duty cycle. Actually, the whole facility can be operated with both a Linac and storage rings.     

Scattering of electrons on thermal radiation photons in electron-positron storage rings

It is shown that Compton scattering on thermal radiation photons restricts the lifetime of high energy electron beams in storage rings to a level of 30 h. At a vacuum pressure of 10⁻¹⁰ Torr the probability that an electron is knocked out from the beam due to scattering on thermal photons exceeds the probability of bremsstrahlung on residual gas ( ) by one order of magnitude, i.e. this effect can cause a considerable background in detectors.     

Development of copper beam ducts with antechambers for advanced high-current particle storage rings

There has been continuous progress at the High Energy Accelerator Research Organization (KEK) in R&D on vacuum beam ducts adaptable to future high-current particle storage rings. Here we proposed copper beam ducts with antechambers to deal with the severe issues attributed to the high beam currents. The proposed antechamber scheme can withstand intense synchrotron radiation (SR), provide a beam duct with low beam impedance, and effectively reduce the electron cloud effect (ECE) in positron/proton rings. Several trial models were manufactured by a pressing or cold-drawn method, and assembled with electron beam welding. Special vacuum components, such as connection flanges, distributed pumps, and gate valves, were customized for the beam ducts. TiN coating on the inner surface of the beam duct was also investigated as a mitigating measure for the ECE. Trial models of the copper beam ducts were installed into the KEK B-factory (KEKB), and their performances were evaluated using real positron and electron beams.     

Self-polarization of protons in storage rings

It has been proposed that stored proton or heavy ion beams can be polarized by spatially separating particles with opposite spin directions, using the Stern-Gerlach effect in alternating quadrupole fields. The growth rate of the vertival betatron amplitude is calculated for beam halves with opposite polarizations rotating in the horizontal plane, at intrinsic spin resonance aγ ± ν_y = integer. This polarization method would work best with rings having large diameter, low vertical emittance, low vertical betatron tune, and strong superconducting quadrupoles. Provided that suitable strong quadrupoles exist, the method might advantageously replace the present technique for obtaining polarized proton or heavy ion beams, where low energy polarized beams are first generated by a source and then accelerated through numerous depolarizing resonances up to the final energy. Although the proposed self-polarization in the present colliders and storage rings might be impractically slow, it is shown that in a purpose-built machine the vertical splitting rate of the beam might be reasonably fast compared with the beam blowup or decay.     

A geodesic beam finite element for use in the-static analysis of reinforced circular cylindrical shells

The development of a geodesic beam finite element for use with a specific circular cylindrical shell finite element in the analysis of reinforced circular cylinders is described. The basic strain and curvature change equations are given and, from these, three versions of the geodesic beam element are developed. Two of the beams have nodal degress-of-freedom identical with the shell element. They differ in the treatment of the terms relating to rotation about the principal normal. The first version ignores this parameter but, under certain circumstances, the stiffness matrix contains terms which can contribute to the strain energy under arbitrary rigid body movement of the beam. This deficiency is removed by applying an aspect of Koiter's theory which is used to transform the curvature change equations. The introduction of additional rotational degress-of-freedom, at the end nodes of the beam element, produces a variation which is capable of accurately representing and transmitting in-surface bending effects to an adjoining beam element. Numerical evaluation successfully compares finite element solutions to basic problems for straight, circular and helical beams with theoretical strain energy solutions. Finally the beam is used in conjunction with a shell element to analyse an infinitely long circular cylinder, reinforced with equispaced rings, subjected to internal pressure.     

Analysis of H− ion trajectories in a space-charge lens

The success of an electron, space-charge-corrected, solenoidal magnetic lens experiment encouraged the analysis of H⁻ trajectories in a large model-corrected solenoid. With a confined distribution of low energy electrons, the solenoid magnetic flux surfaces define electric equipotential surfaces. The field contribution from trapped electrons cancel net axial electric fields. Negatively charged beam particles then experience a defocusing force which can alleviate spherical aberration. Regions of the magnetic field can be linked by individually biased potential rings to program the correcting electric field. Given a magnetic field distribution, the electric potential distribution required to numerically correct beam particle orbits can be used to determine these ring voltages.     

Study of the properties of non-integer order vortex beams at Fraunhofer zone

The intensity and phase distributions of an optical vortex beam with non-integer values of the topological charge are analyzed in Fraunhofer region. There are two annular rings with different size and shape in the intensity patterns. The petal-like bright spots appear on the larger annular rings with higher intensity, and the small rings with lower-intensity. There are ellipse-like dark spots in the middle of the annular rings. The intensity patterns for positive and negative topological charges of vortex beams are mirrored in the x axis, and the number of bright spots and dark spots is related to the topological charge of vortex beam. In phase patters, the new born phase vortex moves gradually to the origin along the y axis, and the positions of phase vortices within the central region move regularly with the increase of the non-integer topological charge of vortex beam.     

Size filtering effect in vertical stacks of In(Ga)As/GaAs self-assembled quantum rings

We present a systematic study of closely In(Ga)As/InAs quantum rings (QRs) grown by molecular beam epitaxy (MBE). Photoluminescence (PL) experiments show a strong filtering effect in the ring being stacked and simultaneous linewidth narrowing for the appropriate layer thickness (thinner thickness). If the spacer thickness is further reduced, a strong coupling between the nanostructures is produced and the signal shifts to low energy.     

Monte Carlo simulations for the shielding of the future high-intensity accelerator facility FAIR at GSI

The Gesellschaft für Schwerionenforschung (GSI) is planning a significant expansion of its accelerator facilities. Compared to the present GSI facility, a factor of 100 in primary beam intensities and up to a factor of 10,000 in secondary radioactive beam intensities are key technical goals of the proposal. The second branch of the so-called Facility for Antiproton and Ion Research (FAIR) is the production of antiprotons and their storage in rings and traps. The facility will provide beam energies a factor of approximately 15 higher than presently available at the GSI for all ions, from protons to uranium. The shielding design of the synchrotron SIS 100/300 is shown exemplarily by using Monte Carlo calculations with the FLUKA code. The experimental area serving the investigation of compressed baryonic matter is analysed in the same way. In addition, a dose comparison is made for an experimental area operated with medium energy heavy-ion beams. Here, Monte Carlo calculations are performed by using either heavy-ion primary particles or proton beams with intensities scaled by the mass number of the corresponding heavy-ion beam.     

Optimal annular computer-generated holograms for the generation of optical vortices

We analyze a method for efficiently generating optical vortices by use of annular computer-generated holograms and a spatial light modulator. We found that there exists an optimal annular width by which the reconstructed vortex ring in the focal plane has the steepest gradient and the worthless subbright rings can be largely suppressed. We fitted a general formula for determining the value of this optimal annular width and propose a method for designing a multiring structure of optical vortices and specialized interferometric vortex patterns. Finally, we discuss the situation of a Gaussian beam as illuminated light and find that there exists an optimal beam waist that results in the best energy efficiency.     

Strong intrabeam scattering in heavy ion and proton beams

The growth of a beam of particles due to intrabeam scattering has been studied over long periods of time for a beam of gold ions and for a beam of protons, and as a function of the beam energy. In strong intrabeam scattering, the beam dimensions may grow by several-fold, and the accelerator aperture is large enough to contain the beam as it grows. The final state of the beam, after the initial large growth rates have subsided, has certain interesting features. Some simple general results were found to hold in the high energy limit. The dependence of the final beam state on the beam intensity, coupling and the choice of transition energy has also been studied.     

Beam induced quench of superconducting solenoid

The beam induced quench of a superconducting solenoid was studied to estimate the effect of the energy deposition due to the high energy proton beam. The solenoid was directly exposed to 12 GeV proton beam with a typical beam duration time of 250 ms. The experimental results were compared with the MPZ/Cold-End energy calculation and a computer simulation solving the thermal equation. They can be well reproduced by the simulation result with reasonable parameters.     

Encircled energy in systems with truncated-Gaussian apertures of different Fresnel numbers. I. Generalization of the Q2n function of E. Wolf and the Yn function of H. H. Hopkins

In his works on diffraction [Proc. R. Soc. London Ser. A204, 533 (1951)], E. Wolf introduced the Q2n function, which enters his expressions for the encircled energy. This quantity specifies the fraction of the total energy within various rings in receiving planes parallel to the geometrical focal plane. In addition to the Q2n function, another special function, called the Yn function, was used in his formulation, which had been introduced by H. H. Hopkins [Proc. Phys. Soc. London Sect. B62, 22 (1949)]. The purpose of this study is to generalize both the Q2n and Yn functions for evaluating the encircled energy in systems of focused truncated Gaussian beams by apertures of different Fresnel numbers and different levels of beam truncation. The generalized Q and Y functions are functions of more than one variable and are applicable to all nonnegative integers m; they may therefore be called the Qm and the Ym functions. Computed results are shown graphically in the form of contour lines of the encircled energy. Part II of this study [J. Opt. Soc. Am. A24, 2033 (2007)] contains an analysis of maximizing beam energy concentration on a target.     

高能电子束辐照对NBR/PVC胶圈胶料性能的影响

采用高能电子束对丁腈橡胶/聚氯乙烯(NBR/PVC)胶圈胶料进行辐照,研究不同辐照剂量对NBR/PVC胶圈胶料性能的影响。实验结果表明,生橡胶经高能电子束辐照后,焦烧时间随辐照剂量增大逐渐减小;NBR/PVC硫化胶经高能电子束辐照后,冲击弹性提高33%~67%,硬度提高4%~10%,拉伸强度提高8%左右,断裂伸长率下降6.7%~34.4%。单因素试验结果显示,50k~60kGy剂量辐照时,硫化胶拉伸强度提高幅度较大,压缩、拉伸永久变形和磨耗量下降,同时弹性、硬度均有提升。综合考虑,50k~60kGy剂量为辐照NBR/PVC胶圈硫化胶的最适剂量。     

The effect of the ion beam energy on the properties of indium tin oxide thin films prepared by ion beam assisted deposition

Indium tin oxide (ITO) thin films have been deposited onto polycarbonate substrates by ion beam assisted deposition technique at room temperature. The structural, optical and electrical properties of the films have been characterized by X-ray diffraction, atomic force microscopy, optical transmittance, ellipsometric and Hall effect measurements. The effect of the ion beam energy on the properties of the films has been studied. The optical parameters have been obtained by fitting the ellipsometric spectra. It has been found that high quality ITO film (low electrical resistivity and high optical transmittance) can be obtained at low ion beam energy. In addition, the ITO film prepared at low ion beam energy gives a high reflectance in IR region that is useful for some electromagnetic wave shielding applications.