I. A. Seleznev

Storage ring with longitudinal magnetic field LEPTA (Stellatron)

The project of the Low Energy Particle Toroidal Accumulator (LEPTA) is dedicated to the construction of a positron storage ring with electron cooling of positrons circulating in the ring. Such a specific feature of LEPTA automatically enables it to be a generator of positronium (Ps) atoms, which appear in the recombination of positrons with cooling electrons inside the cooling section of the ring. The project has the following goals: particle dynamics in the modified betatron, electron cooling with a circulating beam, positronium generation in flight, positronium physics, and feasibility of antihydrogen generation in flight. All key elements of the ring—the kicker, electron beam injection system, helical quadrupole, septum magnet—have been tested, and the expected design parameters have been achieved for these elements. The construction of LEPTA has been completed, and the circulating electron beam has been achieved. This paper discusses the issues of particle dynamics in such an accelerator, the results of numerical simulation and experimental findings of the research into beam dynamics, measurement of betatron number and beam lifetime.

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.

Perspectives of LEPTA

The Low Particle Toroidal Accumulator (LEPTA) project is under development at JINR. The ring assembling is completed. The test experiments with circulating electron beam are in progress and the results are presented. Assembling and test of the positron injector is started. The program of experiment on directed o‐Ps flux generated at LEPTA is listed in the report. The first experiment that is under preparation presently has the goal to measure p‐Ps life time by interference of ortho‐ and para‐ states of Ps in magnetic field.

Formation of an intense electron beam in guns with a small-diameter cathode

In the given work the experimental results of formation of the electron beam with a current up to 4 A in the electron gun with the cathode of a small diameter - 13 mm are presented. The gun is intended for generation of intense electron beams in systems of electron cooling used for fast and deep cooling of ions in the scheme with large factor of expansion in a decreasing magnetic field.

Low-energy positron injector

The LEPTA low-energy positron accumulator, which is to be used for producing directed fluxes of positronium and antihydrogen atoms, is under development at the Joint Institute of Nuclear Research. The monochromatic positron injector, operating in the pulsed mode, in the accumulator must generate a positron beam with intensity 108–109 particles in a pulse with duration less than 300 nsec, the positron energy is 10 keV, the relative energy spread in the beam is less than 2·10–3, and the beam radius is 0.5 cm.Radioactive 22Na serves as a positron source. The positrons at the exit from the source are decelerated in a solid target and enter the magnetic trap. There they are once again decelerated in a gas to thermal velocity and accumulate in ~100 sec. For injection into the accumulator, the positrons are pulled out of the trap by a pulsed electric field and acclerated up to the required energy.

Low-energy positron accumulator for generating directed positron fluxes (LEPTA project)

The LEPTA (Low Energy Particle Toroidal Accumulator) under construction at the Joint Institute of Nuclear Research is described. The goal of this project is to produce a small accumulator for 10-keV positrons with electronic cooling of the circulating positron beam. The main purpose of the accumulator is to generate an intense flux of the electron–positron ground state, so-called positronium. The parameters of the first experiments on a positronium flux and the current status of the work on this project are discussed.

DELSY project: Dubna electron synchrotron

The DELSY (Dubna electron synchrotron) accelerator complex, including a 1.2-GeV electron storage ring, is under construction at JINR. This complex is a high-luminosity source of synchrotron radiation. It contains a linear accelerator-injector and a family of free-electron lasers operating in a wide spectral range from infrared radiation (λ ≈ 100 μm) to high-energy x-rays (εω ≈ 0 keV). The DELSY source will make it possible to expand current research performed at JINR on the condensed-state and atomic physics, biology and medicine, crystallography and x-ray spectroscopy, nuclear physics, and metrology. The project is being implemented in three phases.