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, τlife ≥ 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 pulsed injector of the low energy positrons for positron accumulator LEPTA has been constructed and tested at JINR. The injector is based on Na-22 radioactive source. Positrons from the source are moderated in the solid neon and injected into positron trap, where they are accumulated during about 80 seconds. For injection the positrons are extracted by the pulsed electric field and accelerated up to the required energy. ne injector will generate positrons of the energy of up to 10 keV at relative energy spread of 2.10(-3), intensity of 108 - 109 particles per pulse and at injection pulse duration of 300 nsec. 22The cryogenic source of slow positrons has been tested with a test isotope Na-22 of the initial activity of 80 MBk. The continuous slow positron beam with average energy of 1.2 eV, width of a spectrum 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 life time of the electrons in the trap, tau(life) >= 80 s and capture efficiency epsilon similar to 0.4 have been obtained. The maximum number of the accumulated particle was N-exper= 2*10(8) at the initial flux of 5.10(6) electrons per sec.The dynamics of slow positrons (electrons) in the injector and physics of the particle storage process are discussed in the report.The work is supported by RFBR grant No- 05-02-16320, the president of Russia Federation grant (MK-3948.2007.2) for supporting of young scientists and leading scientific schools.

Brief review of experimental studies of the electron cooling of a proton beam at COSY (Juelich, Germany) and S-LSR (Kyoto) are presented. Intensity of the proton beam is limited by two general effects: particle loss directly after the injection and development of instability in a deep cooled ion beam. Results of the instability investigations and the methods of the instability suppression, which allow increasing the cooled beam intensity, are described. Recent attempts of proton beam ordering in both rings are presented and discussed as well. This work is supported by RFBR grant # 05-02-16320 and INTAS grant #03-54-5584.

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.

The Low Energy Particle Toroidal Accumulator (LEPTA) was commissioned in September 2004 at JINR. The facility is dedicated to studies of particle beam dynamics in a storage ring with longitudinal magnetic field focusing (so called "stellatron"), application of circulating electron beam to electron cooling of antiprotons and ions in adjoining storage ring, electron cooling of positrons, and positronium in-flight generation. The last modes of the ring operation enables setting of numerous experiments with positronium in-flight and generation of directed and "monoenergetic" flux of antihydrogen. The positronium (Ps) atoms appear in recombination of positrons with cooling electrons inside the cooling section of the ring. An assembling of the storage ring LEPTA was completed during year 2004. Peculiarity of the storage ring is focusing of circulating particles with longitudinal magnetic field which covers whole orbit. As result, the particle motion in the ring is coupled in transverse plane. First results of the experimental study of the particle dynamics in the ring performed with circulating electron beam are presented. The beam lifetime was achieved above 20 ms at electron energy of 4 keV and vacuum pressure of 30 mTorr. The limitations of the beam lifetime and the possibility of its enhancement are discussed in the report.

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.

The Low Energy Particle Toroidal Accumulator (LEPTA) is expected to provide experiments with intense flux of positronium. The diagnostics and control system of LEPTA consists of PCs and electronic equipment grouped in accordance with their applications. Devices in CAMAC standard, instrumentation and specially designed control cards imbedded in the LEPTA equipment are used.

The cryogenic source of low energy positrons based on the 22 Na isotope has been designed and constructed at JINR. A solid neon as moderator allows to form slow positron beam of the energy of 1,2 eV and width of the spectrum of 1 eV. Afterwards such positrons are accumulated in the Penning-Malmberg trap. Description of the device and experimental results are presented. THE CRYOGENIC POSITRON SOURCE

Results of experimental studies of the electron cooling of a proton beam at COSY (Juelich, Germany) are presented. Intensity of the proton beam is limited by two general effects: particle loss directly after the injection and development of instability in a deep cooled ion beam. Results of the instability investigations performed at COSY during last years are presented in this report in comparison with previous results from HIMAC (Chiba, Japan) CELSIUS (Uppsala, Sweden) and LEAR (CERN). Methods of the instability suppression, which allow increasing the cooled beam intensity, are described. This work is supported by RFBR grant # 05-02-16320 and INTAS grant #03-54-5584.

The Low Energy Particle Toroidal Accumulator (LEPTA) was commissioned in September 2004 at JINR. The facility is dedicated to studies of particle beam dynamics in a storage ring with longitudinal magnetic field focusing (so called "stellatron"), application of circulating electron beam to electron cooling of antiprotons and ions in adjoining storage ring, electron cooling of positrons, and positronium in-flight generation. The last modes of the ring operation enables setting of numerous experiments with positronium in-flight and generation of directed and "monoenergetic" flux of antihydrogen. The positronium (Ps) atoms appear in recombination of positrons with cooling electrons inside the cooling section of the ring. An assembling of the storage ring LEPTA was completed during year 2004.Peculiarity of the storage ring is focusing of circulating particles with longitudinal magnetic field which covers whole orbit. As result, the particle motion in the ring is coupled in transverse plane. First results of the experimental study of the particle dynamics in the ring performed with circulating electron beam are presented. The beam life time was achieved above 20 ms at electron energy of 4 keV and vacuum pressure of 30 nTorr. The limitations of the beam life time and the possibility of its enhancement are discussed in the report.

The LEPTA setup (Low Energy Particle Torroidal Accumulator) is being constructed at the Joint Institute of Nuclear Research. The main purpose of this setup is to generate intense fluxes of positronium ions and perform experiments in positronium physics. The main component of the setup is the low-energy positron accumulator with a electronic cooling system. A special feature of the accumulator is that it uses a longitudinal magnetic field to focus a circulating beam. The physical startup of the accumulator was performed in September 2004. The results of the adjustment of the main components of the accumulator, the method for obtaining a circulating beam, and the first results of measurements of its parameters are presented.

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.

Results of experimental studies of the electron cooling of a proton beam at COSY (Juelich, Germany) and an ion beam at HIMAC (Chiba, Japan) are presented. Intensity of the ion beam is limited by two general effects: particle loss directly after the injection and development of instability in a deep cooled ion beam. Methods of the instability suppression, which allow increasing the cooled beam intensity, are described.

Low Energy Particle Toroidal Accumulator, which is under construction in JINR, is a storage ring with particle focusing provided by longitudinal magnetic field. The general goals of this installation are electron cooling of positrons, positronium generation and experiments with an intensive positronium flux. Current status of the project realisation is presented. Results of tests of general elements of the ring with modeling electron beam are discussed.

The project of Low Energy Particle Toroidal Accumulator (LEPTA) is dedicated to construction of a positron storage ring with electron cooling of positrons circulating in the ring. Such a peculiarity of LEPTA enables it automatically to be a generator of positronium (Ps) atoms, which appear in recombination of positrons with cooling electrons inside the cooling section of the ring. The project has a few goals: • Dynamics in the modified betatron • Electron cooling with circulating beam • Electron cooling of positrons • Positronium generation in flight • Positronium physics • Feasibility of antihydrogen generation in flight All key elements of the ring: kicker, electron beam injection system, helical quadrupole, septum magnet are tested and expected design parameters were achieved for those elements. LEPTA construction has been completed and circulating electron beam has been achieved. This work is supported by RFBR grant #02-02-16911 and INTAS grant #03-54-5584. INTRODUCTION The Low Energy Particle Toroidal Accumulator (LEPTA) is proposed for the electron cooling of positrons and generation of antihydrogen and positronium in flight [1÷5]. The LEPTA facility (Fig.1) includes small positron storage ring with circumference of 17.2 m equipped with electron cooling system and positron injector consisting of a low energy positron source based on β -active sodium isotope and penning-type trap for preliminary storing of positrons. The energy of positron beam circulating in the ring is planned to be at 10 keV, the value of focusing magnetic field is equal to 400 G. The peculiarity of the LEPTA ring is the longitudinal focusing magnetic field for both circulating positron beam and cooling electron beam. The longitudinal magnetic field provides the positron magnetisation and, as a consequence, long lifetime of the circulating positrons. However, to form closed orbit of circulating beam one needs to use additional helical quadrupole coil. In the presence of longitudinal magnetic field the beam superposition and separation requires especial design of injection complex. Figure 1: Design of the LEPTA. 1 – positron source, 2 – positron trap, 3 – positron transfer section, 4 – septum solenoids, 5 – kicker (inside septum solenoid), 6 – toroidal solenoids, 7 – solenoid and helical quadrupole inside it, 8 – electron cooling section, straight solenoid, 9 – experimental channel, 10 – electron gun, 11 – collector of the electrons, 12 – vacuum pumps 23 Proceedings of RuPAC XIX, Dubna 2004

The ITEP-TWAC is a new heavy ion accumulator facility under construction at ITEP in Moscow [B. Sharkov et al., Nucl. Instr. Meth. A415, 20(1998)]. The TWAC project directs on development and promotion of high intensity and high power heavy ion beam technology. The main goal of the TWAC project is accumulation in the storage ring of intense ion beam, its longitudinal compression and using the extracted beam for plasma experiments.An electron cooler with electron energy of 380keV provides a small ion bunch size during charge-exchange injection into the U10 accumulator ring [I. Meshkov et al., Design project of electron cooling system for TWAC accumulator ring (Dubna, 2001)]. The cooling time is compared with the storage time during charge-exchange multi-turn injection. The electron cooler allows us to significantly improve the beam parameters at the target (specific energy, specific power and so on) and to suppress the beam losses by an order of magnitude. The application of electron cooling allows an increase in of the final power of an extracted ion beam on a target by a factor 2-3.

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.

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.