Physical Startup of the LEPTA Accumulator

Abstract

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 LEPTA setup (Low Energy Particle Toroidal Accumulator), whose purpose is to generate intense fluxes of positronium ions and performing experimental research on positronium, is under construction at the Joint Institute of Nuclear Research [1-4] (Fig. 1). It consists of a positron injector, an accumulator and system for detecting the positron flux. The injector includes a β + -emitting source based on 22 Na and a Penning-type trap for preliminary accumulation of positrons and subsequently injecting them, in one revolution, into the accumulator. A low-activity test source of positrons for adjusting the setup has been fabricated; its parameters are being measured.The key component of the setup is the accumulator with a 17.2 m perimeter. The purpose of the accumulator is to accumulate ~10 keV positrons and to cool them electronically. The positronium atoms are formed when electrons and positrons recombine in the cooling section. The principle of operation and the construction of the main components of the accumulator were proposed in [2], where a similar accumulator was proposed for generating atoms of antihydrogen. As a result of the low positron energy, it was proposed at the circulating beam be focused by a longitudinal magnetic field in combination with an additional spiral quadrapole field. Such a field geometry is characteristic for a modified betatron and its modifications -the stomatron [5]. But, in contrast to the stomatrons, developed and studied in the USA [6,7], the structure of the LEPTA accumulator does not possess azimuthal symmetry, and the spiral quadrapole field is present only on a short part of the orbit in the rectilinear section. In addition, in [2] an innovative injection scheme was proposed, making it possible to solve the main problem of stomatrons -introducing the beam into a longitudinal magnetic field without substantial perturbation of the beam parameters.The physical startup of the accumulator with circulating electron beam was conducted in September 2004. The main components of the accumulator were tested beforehand with a pulsed electron beam. In the present paper, the methods used to adjust the components of the accumulator and to obtain a circulating beam are presented.