Development of the Low Energy Particle Toroidal Accumulator project

The Low Energy Particle Toroidal Accumulator (LEPTA), a positron storage ring with electron cooling, was constructed and put in operation at the Joint Institute for Nuclear Research (Dubna). The storage ring is a generator of directed beams of ortho-positronium (o-Ps) produced upon the recombination of the beam of positrons circulating in the storage ring with a single-pass electron beam. In 2004 the storage ring was put in operation with the circulating electron beam. The source of positrons of the positron injector was tested with a new radioactive source delivered from South Africa. The positron trap was put in operation for electrons. The electron cooling system was tested with a pulsed electron beam. The progress in commissioning LEPTA is described in this paper.     

LEPTA project: Formation and injection of positron beam

The project of the Low-Energy Particle Toroidal Accumulator (LEPTA) has been developed and is put into operation at the Joint Institute for Nuclear Research (Dubna). The LEPTA facility is a small positron storage ring equipped with an electron cooling system. The project positron energy is 2?C4 keV. The main purpose of the facility is to generate an intense flux of positronium atoms (the bound state of the electron and positron). The LEPTA storage ring was commissioned in September 2004. The positron injector was designed in 2005?C2010, and the beam transport channel was constructed in 2011. The experiments on electron and positron injection from the injector into the accumulator were started in August 2011. The results are reported here.     

Betatron resonance crossing during the intense beam bunching

In the process of bunching an intense beam, the betatron oscillation frequency of particles changes due to a growth in their momentum rejection (in the presence of chromaticity) and changes in the Coulomb shift. These changes lead to the intersection of nonlinear betatron resonances. A mathematical model of the dynamics of ions in the process of bunching an intense beam has been built in order to assess the influence of transverse betatron resonances on the motion of particles. This model takes into account the influence of space charge on the longitudinal and transverse oscillations of particles in the presence of one- and two-dimensional betatron resonances. An analysis of the motion of particles near the one- and two-dimensional third-order resonances is given. Results of the numerical simulation of particle losses and emittance growth in the process of bunching an intense beam in the storage ring at the Institute for Theoretical and Experimental Physics (ITEP) are presented.     

Simplified equations for investigation of charged-particle dynamics in magnetic fields

A system of motion equations presented for charged particles in betatron magnetic fields makes it possible to conduct all particle dynamics calculations in relative units because the particle velocity components are expressed in terms of trajectory geometry using comparatively simple notation, and the conversion from relative to absolute units is easily carried out in terms of the radius of a fixed orbit and the magnetic induction of the field on it. This equation system has been used successfully to investigate particle dynamics in an electron beam extracted from a betatron and to determine the principal parameters of the beam; the results were confirmed in practice. Tomsk Polytechnic University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 29–35, March, 1998.     

Simulation of Electron Cooling Proces in a Storage Ring

A simulation of electron cooling process for the heavy ion beam in the proposed HIRFL Cooler-Storage Ring(HIRFL-CSR)is performed by taking into account the betatron and synchrotron oscilations of single particle.The continuous evolution of ion beam emittances and relative momentum spread are shown.Some factors that influence the cooling speed,like the space charge effect of electron beam,the dispersion in cooler section and the electron beam transverse temperature are presented.     

A positron injector for the LEPTA accumulator

An injector of monochromatic positrons for the low-energy positron accumulator (LEPTA) is being tested at the Joint Institute for Nuclear Research. The source of positrons is the radioactive source ²²Na. At the output of the source, positrons are slowed down in a solid target. Frozen neon is used as a moderator. For this purpose, a system of cryocooling of the source and the neon supply line have been assembled. A method of detection of slow positrons has been developed and tuned. The first experiments with the frozen moderator have been performed. A continuous beam of slow positrons with an average energy of 1.2 eV and spectrum width of 1 eV has been obtained.     

储存环内电子冷却过程模拟

考虑储存环内离子的横向振荡和纵向振荡的运动特性,模拟了HIRFL-CSR内重离子束的电子冷却过程.给出了离子束的横向发射度和纵向动量散度随时间连续变化的图象,由此分析了电子束的空间电荷效应,冷却段色散函数和横向电子束温度对冷却过程快慢的影响.     

Electron Cooling of Positrons in LEPTA

Hyperfine Interactions - Electron cooling of positrons is the essential peculiarity of the method of antihydrogen and positronium fluxes generation, which is based on low-energy positron storage...     

Positron injector for LEPTA

The low energy positron injector for the Low Energy Particle Toroidal Accumulator (LEPTA) accumulator was assembled at the Joint Institute for Nuclear Research (JINR). Key elements of the injector have been tested. The cryogenic source of slow positrons was tested with a test isotope ²²Na of the initial activity of 0.8 MBk. A continuous slow positron beam intensity of 5.8 × 10³ particle per second with an average energy of 1.2 eV and a spectrum width of 1 eV has been obtained. The achieved moderator efficiency is about 1%. The accumulation process in the positron trap was investigated with electron flux. The lifetime of the electrons in the trap, τ_life ≥ 80 s and capture efficiency ɛ ∼ 0.4, were obtained. The maximum number of accumulated particles was N _exper = 2 × 10⁸ at the initial flux of 5 × 10⁶ electrons s⁻¹. The text was submitted by the authors in English.     

Determination of the electron beam size at the Kurchatov synchrotron radiation source using an X-ray refractive lens

The electron beam size in the storage ring of the Kurchatov synchrotron radiation source at 2.5 GeV is determined using an x-ray two-dimensional parabolic refractive lens. The vertical size of the electron beam of the storage ring is found to be 270 μm, which exceeds the corresponding design value 140 μm (at a betatron coupling of 1%). The difference is explained by the imperfect geodetic arrangement of ring elements and the incomplete adjustment of the ring.     

Parameters of the electron beam in a betatron with radial comb-type poles

Expressions for the vector potential and components of the magnetic field induction vector of a betatron with radial comb-type poles are derived. The dynamics of the electron beam in the electromagnetic betatron field is investigated in the process of electron injection and acceleration. It is demonstrated that the azimuthally varying field engender beam beats. However, the amplitudes of beam particle oscillations during acceleration do not exceed their values estimated from the symmetric azimuthal component of the betatron magnetic field induction. The energy spectrum of accelerated electrons is not described by a normal law. In the electron energy spectrum, the relative number of electrons whose energy exceeds the average value is large. Application of poles with radial combs improves the efficiency of electron capture in acceleration. Results of investigations can find application in the development and adjustment of electron beam accelerating systems. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 27–34, October, 2005.     

Degenerate Landau levels for tripod-type cold atoms in U(2) Abelian gauge field

New data for positronium beam production efficiency are presented. As a converter of positrons to forward-going positronium, O₂ has been found to be as good as CO₂ from ～250 to 400 eV. Preliminary data is also presented for the production efficiency from Ar at 2.8 eV.     

Dynamics of an electron beam in the magnetic field of a betatron

Expressions for the vector potential and magnetic induction vector components have been obtained for a vertically asymmetric magnetic field of a betatron. The dynamics of the electron beam in the process of injection and acceleration in the electromagnetic field of the betatron has been investigated. It has been shown that the asymmetry of the magnetic field decreases the efficiency of the electron involvement in acceleration. The mutually related radial-vertical asymmetric oscillations of the electron beam in the asymmetric field lead to considerable losses of the beam particles on the walls and injector of the acceleration chamber. The results of these investigations may be useful in developing and tuning electron beam acceleration systems.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 42–46, December, 2004.     

BEPCⅡ Positron Source

BEPCⅡ— an upgrade project of the Beijing Electron Positron Collider (BEPC) is a factory type of e^＋e^－ collider. The fundamental requirements for its injector linac are the beam energy of 1.89GeV for on-energy injection and a 40mA positron beam current at the linac end with a low beam emittance of 1.6μm and a low energy spread of ±0.5% so as to guarantee a higher injection rate (≥50mA/min) to the storage ring. Since the positron flux is proportional to the primary electron beam power on the target, we will increase the electron gun current from 4A to 10A by using a new electron gun system and increase the primary electron energy from 120MeV to 240MeV. The positron source itself is an extremely important system for producing more positrons, including a positron converter target chamber, a 12kA flux modulator, the 7m focusing module with DC power supplies and the support. The new positron production linac from the electron gun to the positron source has been installed into the tunnel. In what follows, we will emphasize the positron source design, manufacture and tests.     

The Energy Spectrum of the Electron Beam of a Betatron

The process of extraction of an electron beam through the glass wall of a sealed-off acceleration chamber has been investigated. It has been shown that the electron beam extracted from the MIB-6E small-sized betatron has a nonuniform cross-sectional distribution of the particle flux density. This nonuniformity is due to the imperfection of the beam extraction devices and to the flaws in design of the extraction window of the accelerator chamber. The electrons extracted through the glass wall of the window lose a major portion of their energy. At the outlet of the chamber of the small-sized betatron, the spectrum of the electrons is not line. The half-width of the spectral line of the electron beam is, at best, 6% for a window glass thickness of 0.5 mm and about 15% for a glass thickness of 4 mm. The results of this study may find practical implementation in developing extracted electron beam formation systems.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 51–55, January, 2005.     

Crossed beam measurement of binding energies of positronium compounds: A proposal

We describe an experiment to establish the chemical stability and measure the binding energies of compounds containing positronium atoms. The method consists of crossing a monoenergetic beam of low energy (1–25 eV) positrons with a supersonic adiabatic expansion molecular beam, and, after a dissociative attachment reaction takes place, detecting the resulting ¡gnature ion while measuring its kinetic energy. Except for the use of a positron beam instead of an electron beam, this is similar to electron impact MS/IKES (mass spectrometry/ion kinetic energy spectrometry). The start signal for the IKES measurement is provided by the remoderation of the positron beam. Among the benefits of the proposed research are the study of: (1) a new class of resonances, those involving temporarily bound positrons to molecules in excited electronic states; and (2) the surprising sub-threshold fragmentation observed by Surko and Hulett in positron-molecule scattering.     

Numerical simulation of particle dynamics in a storage ring by using BETACOOL program

The BETACOOL program, developed by electron cooling group of the Joint Institute for Nuclear Research (JINR), is a set of algorithms based on common format of input and output files. The program is oriented toward simulation of the ion beam dynamics in a storage ring in the presence of cooling and heating effects. The version presented in this report includes three basic algorithms: simulation of root-mean-square (rms) parameters of the particle distribution function evolving in time, simulation of the distribution function evolution using the Monte Carlo method, and a tracking algorithm based on a molecular dynamics technique. The general processes investigated with the program are intrabeam scattering in the ion beam, electron cooling, and interaction with residual gas and an internal target.     

Production and use of low-energy,monoenergetic positron beams from electron LINACS

Low-energy intense positron beams derived from pair production can be made at high-energy electron linacs and such beams are in operation or under installation at several linac facilities. Using a pulsed position beam made at a 100 MeV electron linac, we have measured the intensity and velocity distribution of positronium emitted from materials by measuring the time-of-flight of annihilating positronium. The time-of-flight data are augmented by positron lifetime and angular correlation measurements performed with the beam. Positronium spectra have been measured for a number of metallic samples. Several new observations have been made including details of the energy distribution of positronium emission formed by a thermalized positron and a conduction electron and the production of positronium from energetic positrons scattered out of the sample.This paper is based upon an invited talk given by R.H.H. at the International Symposium Production of Low-Energy Positrons with Accelerators and Applications Justus-Liebig-Universität Giessen, FRG (25–27 September, 1986)     

The Dynamics of Electron Orbits during the Acceleration of Electrons in a Betatron

This paper presents a system of equations that describe the motion of charged particles in the electromagnetic field of a betatron. This system of equation was successfully used to study the behavior of the electron orbits and to determine the principal parameters of the electron beam in the electromagnetic field of a betatron during the electron acceleration and deceleration. The results of this study may find application in developing systems designed to accelerate electron beams. It has been shown that in the course of acceleration there is no damping of the betatron oscillations by the law B _z ^–1/2 and, correspondingly, no decrease in beam cross section. In contrast to the existing belief, the initial departure of the kinetic energy (momentum) of the injected electrons from the energy (momentum) of the electrons following the equilibrium orbit is not preserved in the course of acceleration. In the betatron chamber, the electron beam, when accelerated, does not constrict to form a ring but occupies a broad zone, whose dimensions are determined by the initial double amplitudes of the vertical and horizontal oscillations. Despite the large double amplitude of the oscillations of the beam particles, the average energy of the electrons differs from the energy of the electrons following the equilibrium orbit only slightly, and the departure of the average energy from the energy of the equilibrium electrons varies proportionally to the (varying) field of the betatron.