A. Yu. Rudakov

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 2–4 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 2005–2010, 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.

Study of nonneutral plasma storage in a magnetic trap with a rotating electric field at the lepta facility

Results from experimental studies of plasma storage in a Penning-Malmberg trap at the LEPTA facility are presented. The number of stored particles is found to increase substantially when using the so-called “rotating wall” method, in which a transverse rotating electric field generated by a cylindrical segmented electrode cut into four pairs is applied to the plasma storage region. The conditions of transverse compression of the plasma bunch under the action of the rotating field and buffer gas are studied. The optimal storage parameters are determined for these experimental conditions. Mechanisms of the action of the rotating field and buffer gas on the process of plasma storage are discussed.

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.

Experimental investigations into secondary electron-electron emission from the surface of vacuum chambers

An experiment on measuring the secondary electron yield (SEY) of samples coated with titanium nitride (TiN2) is in progress at the Recuperator test bench at the Dzhelepov Laboratory of Nuclear Problems, Joint Institute for Nuclear Research. This work is related the problem of electron-cloud formation in the vacuum chambers of accelerators and is of practical importance for the NICA project. The results of the experiment on the SEY measurement will make it possible to choose the most appropriate material for coating the vacuum chamber. In this experiment samples of stainless steel with titanium nitride coating and without any coating are compared.

Secondary electron yield from stainless steel surface coated with titanium nitride

The experiment on measurement of secondary electron yield from surface of a stainless steel Kh189 sample covered with titanium nitride is performed at stand “Recuperator”. This work is related to known problem of electron clouds formation in a vacuum chamber by a propagating charge particle beam. An original method of secondary electron yield measurement was developed in this experiment. The obtained results allow one to estimate efficiency of coating nitride titanium.

Intellectual power supply and control system on the phasotron of the joint institute for nuclear research laboratory of nuclear problems implemented from one source at different currents in electromagnetic lenses

The intellectual power supply and control system is presented for the group of electromagnetic lenses in the phasotron-beam transport channel supplied from one power supply source. An intellectual power supply and control system is proposed to minimize power consumption upon the redistribution of the lens currents between the main power supply and additional local regulation power supply sources.

Precision supply system of the group of magnetic elements of the Low-Energy Particle Toroidal Accumulator

An individual power supply source is usually used for each group of identical magnetic elements in accelerators of charge particles. We discuss the power supply and control system on the basis of additional current shunts applied for the simultaneous supply of several groups of magnets in the positron storage ring of the Low-Energy Particle Toroidal Accumulator (LEPTA). Data on the use of the shunt of the linear and key converter are given. The option of the device of a power supply system with the transformation of the recuperated energy in the storage battery and supply from it of the precision power supply sources of the LEPTA correcting magnets is considered. A channel of the individual digital transformation of power supply system elements is given which allows one to build, together with a reverse precision converter, effective intellectual balanced power supply systems.

High-voltage electron cooler project for NICA collider

A high-voltage electron cooling system (ECS) with electron energy reaching 2.5 MeV for the NICA collider is being designed at the Joint Institute for Nuclear Research. The ECS is being developed in correspondence with the available experience in manufacturing similar systems from around the world. The main feature of this design is the use of two cooling electron beams (one beam per collider ring); electrons are accelerated and decelerated by a common high-voltage generator. A conceptual project of high-voltage ECS has been developed. The cooler consists of three tanks filled with SF6 gas under pressure. Two of them contain electron-beam forming systems; each system consists of two electron guns, two electron collectors, and accelerating-decelerating tubes placed in a longitudinal magnetic field generated by a solenoid. The third tank contains a high-voltage generator based on the voltage-multiplying circuit.

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, 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 pulse injector of the low energy positrons

The pulsed injector of the low energy positrons for positron accumulator LEPTA has been constructed and tested at JINR. The injector is based on 22Na 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. The 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. The cryogenic source of slow positrons has been tested with a test isotope 22Na of the initial activity of 80 MBk. The continuous slow positron beam with average energy spread 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, τlife ≥ 80 s and capture efficiency ε ~ 0.4 have been obtained. The maximum number of the accumulated particle was Nexper = 2*108 at the initial flux of 5•106 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 sceintific schools.