Positron Accumulator Research Articles

The Buncher and the Magnetic Lens for the LINAC Based Low Energy Positron Beams at AIST

A buncher and a magnetic lens were introduced to improve the beam flux density of a pulsed positron beam extracted from the low energy positron accumulator at National Institute of Advanced Industrial Science and Technology (AIST). The buncher made the pulse width ~ 1/4 and the magnetic lens reduced the beam cross section ~ 1/9, which resulted in about 36 times increase in the beam flux density. Possible applications for electron-positron plasma experiments are also discussed.

Testing the Weak Equivalence Principle with an antimatter beam at CERN

The goal of the AEgIS experiment is to measure the gravitational acceleration of antihydrogen – the simplest atom consisting entirely of antimatter – with the ultimate precision of 1%. We plan to verify the Weak Equivalence Principle (WEP), one of the fundamental laws of nature, with an antimatter beam. The experiment consists of a positron accumulator, an antiproton trap and a Stark accelerator in a solenoidal magnetic field to form and accelerate a pulsed beam of antihydrogen atoms towards a free-fall detector. The antihydrogen beam passes through a moiré deflectometer to measure the vertical displacement due to the gravitational force. A position and time sensitive hybrid detector registers the annihilation points of the antihydrogen atoms and their time-of-flight. The detection principle has been successfully tested with antiprotons and a miniature moiré deflectometer coupled to a nuclear emulsion detector.

Towards a spin polarized antihydrogen beam

The ASACUSA collaboration has developed a cusp trap scheme to realize an in-flight high precision microwave spectroscopy of ground-state hyperfine splitting of antihydrogen ( H) for a stringent test of CPT symmetry. Cold H atoms were successfullysynthesized by employing a cusp trap which consisted of a superconducting anti-Helmholtz coil and a stack of ring electrodes. This was achieved with an antiproton ( p) accumulator, MUSASHI, and a positron ( e+) accumulator. The principal quantum number and the time evolution of H synthesis were investigated. The latest progress was also presented.

Antihydrogen formation mechanisms

New developments in the ATHENA data analysis are presented, with some insight into the mechanisms responsible for antihydrogen production under di erent ex- perimental conditions. Studies of antihydrogen, the bound state of a positron and an antiproton, can o er new insights into the fundamental symmetries of nature from comparisons of its properties with those of hydrogen. The production and trapping of antihydrogen at low energies has recently become possible, using specialised apparatus developed at CERN (1-5). There has been no detailed study of the processes involved in the formation of antihydrogen via antiproton-positron plasma mixing in a Penning trap environment, and much has been assumed from equilibrium studies at higher plasma temperatures and in the absence of applied fields. It is the nature of the mechanisms underlying antihydrogen formation that we address in this work. In particular, we show that a careful analysis of the correlated temporal and spatial dependencies of the antihydrogen on wall annihilation signals, available from a range of experiments performed by the ATHENA collaboration, can shed light on this problem. ATHENA aimed at mixing antiprotons (pbar) and positrons (e + ) and consisted of four main subsystems: the antiproton catching trap, the positron accumulator, the antiproton/positron mixing trap, and the antihydrogen annihilation detector (see Figure 1 and (6) for the datails). The positrons ( 10 8 e + ) and antiprotons ( 10 4 pbars) were held in devices known as nested Penning traps (see e.g. (7)) which provide confinement using a combination of applied fields. A series of cylindrical electrodes, aligned along the axis of a solenoid, were used to produce electrical wells which restrict the particles axially, while the 3 T magnetic field provides transverse confinement (see Figure 2). When an antiproton and a positron, after interacting, are bound together, they form an antihy- drogen atom (Hbar) which is neutral and which thus eventually impinges on the electrode walls and annihilates. The simultaneous annihilation of the pbar on a proton/neutron (producing charged pions) and of the e + on an electron (producing two -rays) is detected by a cylindrical detector which is also

Motional sideband excitation using rotating electric fields

A form of motional sideband excitation is described in which a rotating dipole electric field is applied asymmetrically onto a Penning-type trap in the presence of a mechanism for cooling the axial motion of the trapped particles. In contrast to the traditional motional sideband excitation, which uses an oscillating electric field, the rotating field results in only one active sideband in each sense of rotation and so avoids accidental excitation of the other sideband making it applicable to Penning-type traps with a large degree of anharmonicity. Expressions are derived for the magnetron radius expansion and compression rates attainable, and approximations are made for the case of strong and weak drives. A comparison is made with data, taken using a two-stage positron accumulator presented by Isaac et al. [C. A. Isaac, C. J. Baker, T. Mortensen, D. P. van der Werf, and M. Charlton, Phys. Rev. Lett. 107, 033201 (2011)], showing good agreement between the model and experiment.

Efficient transfer of positrons from a buffer-gas-cooled accumulator into an orthogonally oriented superconducting solenoid for antihydrogen studies

Positrons accumulated in a room-temperature buffer-gas-cooled positron accumulator are efficiently transferred into a superconducting solenoid which houses the ATRAP cryogenic Penning trap used in antihydrogen research. The positrons are guided along a 9 m long magnetic guide that connects the central field lines of the 0.15 T field in the positron accumulator to the central magnetic field lines of the superconducting solenoid. Seventy independently controllable electromagnets are required to overcome the fringing field of the large-bore superconducting solenoid. The guide includes both a 15° upward bend and a 105° downward bend to account for the orthogonal orientation of the positron accumulator with respect to the cryogenic Penning trap. Low-energy positrons ejected from the accumulator follow the magnetic field lines within the guide and are transferred into the superconducting solenoid with nearly 100% efficiency. A 7 m long 5 cm diameter stainless-steel tube and a 20 mm long, 1.5 mm diameter cryogenic pumping restriction ensure that the 10−2 mbar pressure in the accumulator is isolated well from the extreme vacuum required in the Penning trap to allow for long antimatter storage times.

ASACUSA MUSASHI: New progress with intense ultra slow antiproton beam

Our group “ASACUSA MUSASHI” has established an efficient way for accumulating antiprotons and extracting them as intense ultra-slow mono-energetic beams at the CERN-AD facility. This novel beam opens new frontiers for investigating a variety of physics. For realizing H spectroscopy and the test for charge-parity-time symmetry, we have also developed the cusp trap, a combination of an anti-Helmholz superconducting coil and a multi-ring electrode trap, for trapping both antiprotons and positrons and then synthesizing antihydrogens. Recently, the cusp trap was practically used to accumulate antiprotons. The last piece for synthesizing antihydrogens in the cusp trap is the positron accumulator. We have developed a compact system to effectively accumulate positrons based on N2 gas-buffer scheme with a specially designed high precision cylindrical multi-ring electrode trap. The recent progress of the developing work is an important milestone for upcoming antihydrogen science of ASACUSA MUSASHI.

Positron transport in gases

We review the field of positron transport physics in gases, starting with a historical overview. In particular, experiments which have measured positron drift velocities and mobilities in specially constructed cells are highlighted. The relevance of understanding positron transport in current efforts to manipulate trapped clouds of positrons is emphasised. We suggest some ways in which the output of a positron accumulator might be used to develop a new and versatile technique to study positron drift.

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.

Design and operation of a two-stage positron accumulator

A compact positron accumulator based upon a simple two-stage buffer gas cooling scheme is described. Its operation to produce 10–20ns wide bursts containing around 105 positrons with cycling times in the 100msto1s range is discussed. Departures of the behavior of the accumulator from that expected of such an instrument are presented. The utility of these effects in diagnosing accumulator performance is described.

Physical Startup of the LEPTA Accumulator

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 ATHENA antihydrogen apparatus

Abstract The ATHENA apparatus that recently produced and detected the first cold antihydrogen atoms is described. Its main features, which are described herein, are: an external positron accumulator, making it possible to accumulate large numbers of positrons; a separate antiproton catching trap, optimizing the catching, cooling and handling of antiprotons; a unique high resolution antihydrogen annihilation detector, allowing an clear determination that antihydrogen has been produced; an open, modular design making variations in the experimental approach possible and a “nested” Penning trap situated in a cryogenic, 3T magnetic field environment used for the mixing of the antiprotons and positrons.

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 10 8 ‐10 9 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 22 Na 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.

The ATHENA positron accumulator

A positron accumulator has been constructed for use in the ATHENA anti-hydrogen experiment in CERN. Employing a solid neon moderator plated on to a 50 mCi 22 Na source, a low energy beam of 7 10 6 positrons/s is guided into a 0.14 T magnetic field where they are trapped and cooled down to room temperature using nitrogen as a buffer gas. Plasmas of up to 2 10 8 positrons in 450 s, with an FWHM of 4 mm after compressing with the rotating electrical wall technique have been observed. In order to transfer the plasma to the main ATHENA (3 T) magnet, where the recombination trap is situated, a transfer section has been constructed consisting of a valve and a pulsed magnet with a pumping restriction inside. This magnet pulses to 1.2 T during the transfer. Preliminary tests have yielded transfer efficiencies in the order of 50%. # 2002 Elsevier Science B.V. All rights reserved.

A Positron Accumulator for Antihydrogen Synthesis

A Positron Accumulator for Antihydrogen Synthesis

Low-energy positron scattering from atoms and molecules using positron accumulation techniques

Positron scattering from atoms and molecules is studied at low values of incident positron energy. The experiments use a cold magnetized positron beam formed in a positron accumulator. A discussion of positron scattering in a magnetic field is presented along with differential cross-sections (DCS) for positron–atom collisions and positron–molecule total vibrational excitation cross-sections. Absolute values of the DCS for elastic scattering from argon and krypton are measured at energies ranging from 0.4 to 2.0 eV. The first low-energy positron–molecule vibrational excitation cross-sections have been measured (i.e., for carbon tetrafluoride at energies ranging from 0.2 to 1 eV). Using information gained from these experiments a second generation scattering apparatus is described, which was designed and built specifically for scattering experiments using a magnetized positron beam. This apparatus has a number of improvements, including an order of magnitude higher throughput, better energy separation between elastic and inelastic scattering events, and improved measurement of the absolute pressure of the test-gases. Analysis techniques for the data taken in these experiments using a retarding potential energy analyzer and possible extensions of these experiments are also discussed.

Atomic and molecular physics using positron accumulation techniques – Summary and a look to the future

An overview is presented of current techniques to accumulate and cool large numbers of positrons from a radioactive 22 Na source and neon moderator, and the first operation of a new generation of positron accumulator is described. Experiments are discussed that use these techniques to study the interaction of positrons with atoms and molecules at low energies (i.e., below the threshold for positronium formation), including systematic studies of the dependence of positron annihilation on chemical composition. By measuring the Doppler-broadening of gamma-ray annihilation radiation, the quantum state of the annihilating electrons in atoms and molecules was identified. These experiments indicate that positrons annihilate with approximately equal probability on any valence electron. Annihilation with inner shell electrons is infrequent, but is measurable at the level of a few percent in heavier atoms. Measurements of annihilation rates in molecules as a function of positron temperature revealed a number of interesting trends that are briefly discussed. We have developed a new technique to make a cold, bright positron beam. This technique is now being used for a new generation of scattering experiments in the range of energies 61 eV. Other possible experiments to study aspects of atomic and molecular physics using positron accumulation techniques and this cold positron beam are briefly discussed. ” 2000 Elsevier Science B.V. All rights reserved.

Unexpected Role of Chaotic Transport in a Positron Accumulator

Unexpected Role of Chaotic Transport in a Positron Accumulator

Construction and commissioning of the positron accumulator ring for the APS

The injector for the Advanced Photon Source (APS) incorporates a 450-MeV positron accumulator ring (PAR) to accumulate and damp positrons from the 60Hz linac during each cycle of the 2-Hz synchrotron. An overview of PAR hardware is presented. Commissioning of the PAR is well underway using electrons. Studies have produced a modified lattice model using three free parameters that agrees well with measurements. Principle problems are high leakage fields from the septum and ion trapping.

A status update on the advanced photon source project — Summer 1993

The Advanced Photon Source Project has passed the mid-point in its construction. The linac and synchrotron booster enclosures are complete. A portion of the experiment hall has been completed and put into use to support accelerator component assembly, test, and installation. Plans for the user lab/office modules and the central laboratory/office complex are well advanced. Installation of the linac injection system has been completed and commissioning is beginning. Installation and commissioning of the positron accumulator ring, the booster synchrotron, the storage ring, and the rf power systems will follow. Accelerator operations capable of supporting the commissioning of the experimental beamlines is planned for the summer of 1995. A strong research program is continuing to produce results supportive of both accelerator and beamline construction and operations. Collaborative Access Teams have been formed to conduct research with the initial set of 32 beamlines that will be available at the completion of the first phase of construction.