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The propagation of small amplitude dust ion acoustic (DIA) solitary waves (SW) in four component relativistic plasma with nonthermal electrons, mobile positively charged ions and positrons, and negatively charged massive dust particles is discussed in this paper. The Korteweg-de-Vries (K-dV) nonlinear wave equation is numerically derived using the reductive perturbation approach. The role of streaming positron beam on the characteristic features of solitary waves are observed and the possible region of the formation of ion acoustic (IA) SW is analysed. The findings of this work will help in the understanding of the Earth's upper atmosphere (Ionosphere's Aurora region) as well as the space plasmas. [ABSTRACT FROM AUTHOR]

In the field of positron annihilation spectroscopy, the investigation of a thin near-surface region, modified with ion implantation, has been usually performed by slow positron beams. Experiments carried out to simulate radiation effects in Fe-based alloys, were reported widely in the past [1,2]. Radioisotope positron sources, such as 22Na, provide only a little information from the near-surface area, probing the bulk region particularly. With more and more accessible high-energy particle accelerators in research institutes, modified layers can reach up to several tens of micrometres into the bulk, enabling to use conventional 22Na positron source for their investigation. This paper addresses some practical issues of the application of unmoderated radioisotope sources for the investigation of radiation effects in solids, simulated by ion implantation. [ABSTRACT FROM AUTHOR]

Vacancy-type defects in Mg-implanted GaN were probed using monoenergetic positron beams. For the samples after annealing at 1300°C, the line shape parameter S and the positron lifetime increased under illumination with a 325-nm He-Cd laser. The observed increase in the trapping rate of positrons by vacancies was associated with the trapping of the excited electrons by the defects. Native defects in GaN grown on Si substrate were also studied. A similar illumination effect on the positron annihilation parameters was observed for GaN with the carbon concentration of 2×1016 cm−3. From the relationship between S and the photon energy, it was found that the transition of an electron from a carbon atom to the vacancies plays an important role in the charge shift of the vacancies under illumination. [ABSTRACT FROM AUTHOR]

A slow positron facility is being built in Israel, at the Hebrew University, for basic and applied research. It consists of a slow positron beam and a compact Positrons Annihilation Lifetime (PAL) spectrometer. The slow positron beam follows a traditional design, using a 22Na source, of about 40mCi, a Tungsten moderator and a unique grounded target cell, with positrons energy that can vary between 0.03 keV and 30 keV. The detection system will be comprised of High Purity Germanium and BaF2 detectors, facing each other, for low background Doppler Broadening (DB) measurements. The target cell is designed to allow a combined measurement of sample conductivity and DB, with the flexibility to add more detection options in the future. The compact PAL spectrometer includes two fast scintillation detectors read by a fast digitizer (DRS4), with a sampling rate of 5.12 GS/s. A dedicated software package was developed to emulate analogue data acquisition. Lifetime measurements were performed using a ∼25 µCi 22Na source. The time resolution was defined using a 60Co source, to be 180-200ps. First positron lifetime validation measurements of Ti resulted in positrons lifetime of 157 ± 4 ps, consistent with previously published values. [ABSTRACT FROM AUTHOR]

The intense positron beam user facility at the PULSTAR reactor of the North Carolina State University has undergone recent upgrades to address issues caused by radiation damage over the years to the Tungsten moderator and the main beam structure. The two-bank Tungsten moderator is replaced with a four-bank Platinum moderator. The effect of moderator geometry has been systematically studied using SIMION and COMSOL multiphysics and the positron transport efficiency is optimized. Initial tests showed a positron rate of nearly 6×108 e+/s. The two associated spectrometers were also modified to improve their performance. The magnetically guided spectrometer with an RF buncher (e+-PAS) has been upgraded to include a new pre-buncher and a modified chopper to significantly improve the signal to noise ratio for PALS spectroscopy. In addition, a sample changer with heating and cooling capabilities is under development to address the sample turn-around efficiency and evacuation time. Meanwhile, the electrostatically focused Ps-PAS spectrometer is under an upgrade to further shrink the beam spot size and improve the beam brightness. Magnetic shielding is being implemented between the two remoderator stages and the electrostatic lenses have been redesigned to achieve better beam focusing. After the first-phase of modifications, the on-sample spot size is expected to be improved from ~2 mm to ~0.5 mm. The second-phase of modifications involves the implementation of a third stage of brightness enhancement and a final magnetic focusing lens. The new features will allow the beam to be focused down to less than 100 μm and enable measurement with a spatial resolution of several tens of micrometers. [ABSTRACT FROM AUTHOR]

Jefferson Lab is interested in the production of positrons for nuclear physics applications but also has the capability of producing low energy positrons that could be used for positron annihilation studies. Using the LERF accelerator at the Thomas Jefferson National Accelerator Facility, it is possible to produce a high brightness source of very low-energy positrons. The accelerator requirements are well within the capabilities of the installed hardware. For these experiments, we only need run at up to 120 MeV. A challenge is the production of the positrons. The gamma converter must be able to absorb the 50 kW of beam power that the linac delivers. At this low an energy, the converter, though challenging, is feasible. The transport of the low energy positrons from the production target to the next stage, where the energy is reduced even further, must have a very large acceptance to be able to efficiently transport the flux of positrons from the positron production target to the moderator. We propose to accomplish such a transport by means of a guiding solenoidal field with a novel endcap design. Finally, it is in principle possible to produce a spin polarized beam by filtering the positrons at low energy. The layout of the proposed device will be described in this presentation. [ABSTRACT FROM AUTHOR]

Preliminary results are presented from a new positron beam system currently under development at the University of Texas at Arlington for the coincident energy measurement of Doppler-shifted annihilation quanta and positron-induced Auger electrons. We report data based on an analysis of the pulses resulting from the detection of positron induced secondary electrons by a micro-channel plate detector in coincidence with the pulses resulting from the detection of associated annihilation gamma rays in a NaI(Tl) gamma detector. [ABSTRACT FROM AUTHOR]

A brief description is given of the most recent version of the PALSfit3 program. Based on previous programs (PALSfit and PATFIT) which have been used by a number of positron annihilation groups, PALSfit3 has been extended to include the option of log-normal broadening of the lifetime components. In addition more detailed graphics output has been added, and the possibility to select output in spread sheet format included. A special feature is the possibility to exclude certain channel ranges in a lifetime spectrum from the analysis, which may be valuable if spectra contain ”bumps”, for example due to scattered positrons in beam experiments. Details of PALSfit3 can be found on the PALSfit web page (www.palsfit.dk). [ABSTRACT FROM AUTHOR]

We developed a new scanning positron microbeam for spatially resolved (coincident) Doppler broadening spectroscopy ((C)DBS) at the neutron induced positron source Munich (NEPOMUC). For this purpose, positrons are moderated three times: First, positrons generated by pair production are self-moderated in annealed polycrystalline Pt foils inside the beam tube housing the positron source NEPOMUC. Then, the brightness of the primary 1 keV positron beam with 109 moderated positrons per second is enhanced by a W(100) single crystal remoderator operated in back reflection geometry. Finally, in the upgraded CDB spectrometer we apply a 100 nm thin Ni(100) foil acting as transmission remoderator to generate a positron microbeam with a minimum beam diameter of 33 µm. We demonstrate the potential of laterally resolved DBS by imaging the defect distribution around a laser beam weld of the high-strength age-hardenable Al alloy AlCu6Mn. CDBS was applied with unprecedented spatial resolution to reveal the dissolution of Cu rich precipitates and the formation of Al-vacancy-Cu-complexes. [ABSTRACT FROM AUTHOR]

We report the development of a new positron diffractometer that will be coupled to the high-intensity positron source NEPOMUC located at the research neutron source FRM II. An optional transmission-type remoderator stage utilizing a Ni (100) foil will be installed to further enhance the brightness of the positron beam. The acceleration and focus onto the remoderator foil are realized by an electrostatic lens system. At the sample position we aim to obtain an almost parallel, slightly converging beam with a diameter of less than 1mm. Simulations were run to optimize the focus onto the remoderator foil and the electrostatic acceleration up to energies of 25 keV after remoderation. [ABSTRACT FROM AUTHOR]

To investigate inhomogeneous defect distributions, e.g. close to fatigue cracks or dispersive alloys with positron annihilation lifetime spectroscopy a pulsed positron beam with a diameter in the range of 1 µm and with a time resolution in the order of 250 ps is needed. The Scanning Positron Microscope (SPM) fulfills the requirements for position resolved positron lifetime measurements and was operated by the Universität der Bundeswehr München. To increase the countrate, the SPM is currently transferred to the intense positron source NEPOMUC. The SPM Interface connects the SPM to the NEPOMUC source and en-hances the beam quality to the needs of the SPM. In this contribution we will give an overview of the SPM Interface and its performance. The finale stage of the SPM Interface is the positron elevator which has been further developed. We will discuss the apparatus in detail and show measurements of the beam quality with a beam elevation of 8 keV. From our measurements we are able to predict the performance of the SPM at NEPOMUC. In the future position resolved measurements will be possible with an improved spatial resolution of about 0.3 µm and an event rate of about 3.7 kHz. [ABSTRACT FROM AUTHOR]

The APEX (A Positron Electron eXperiment) collaboration aims to magnetically confine a low-temperature electron-positron pair plasma. By using a pair of ExB plates, positrons generated by the NEPOMUC facility are drift-injected into the confinement field created by a supported permanent magnet. Fine-tuning the fields generated by electrodes and magnetic coils increased the injection efficiency to 100% and positron confinement times to more than 1s. A newly installed electron gun has been used to inject electrons, guided alongside the positron beam, into the confinement volume. This contribution describes the recent upgrades required for the first dual species experiments. [ABSTRACT FROM AUTHOR]

Though there are many applications of low energy positrons, many experiments are source limited. Using the LERF accelerator at the Thomas Jefferson National Accelerator Facility, it is possible to build a high brightness source of very low-energy positrons. The accelerator requirements are well within the capabilities of the installed hardware. The accelerator can produce 120 kW of beam with a beam energy of up to 170 MeV. For these experiments, we only need run at up to 120 MeV. The gamma-to-positron converter must be able to absorb 20% of the beam power that the linac delivers. At this low an energy the converter, though challenging, is possible. The transport of the low energy positrons from the production target to the next stage, where the energy is reduced even further, must have a very large acceptance to be able to efficiently transport the flux of positrons from the positron production target to the moderator. We propose to accomplish such a transport by means of a guiding solenoidal field with a novel endcap design. In this presentation, we will present the proposed schemes necessary to realize such a high brightness positron source. [ABSTRACT FROM AUTHOR]

We present a scheme for positron beam acceleration in CEBAF antiparallel to the normal electron path, requiring no change in polarity of the magnet systems. This feature is essential to the principal benefit: enabling extremely simple configuration changes between conventional (clockwise) e- acceleration and counter clockwise e+ acceleration. Additionally, it appears possible to configure the accelerating cavity phases to support concurrent acceleration of the electron and positron beams. The last mode also may enable use of the higher peak current electron beam for system diagnostics. The inherent penalty of the concurrent mode in acceleration efficiency and increased energy spread may render this a commissioning-only diagnostic option, but the possibility appears worthy of consideration. [ABSTRACT FROM AUTHOR]

The Polarized Electrons for Polarized Positrons (PEPPo) experiment at the injector of the Continuous Electron Beam Accelerator Facility demonstrated for the first time the efficient transfer of polarization from electrons to positrons via a two-step process: polarized bremsstrahlung radiation is induced by a polarized electron beam in a high-Z target; then the polarized bremsstrahlung produces polarized positrons via the pair-production process in the same target. Positron polarization up to 82% was measured for an initial electron beam momentum of 8.19 MeV/c, limited only by the electron beam polarization of 85%. This technique extends polarized positron capabilities from GeV to MeV electron beams, and opens access to polarized positron beam physics to a wide community. We will present the results of the PEPPo experiment and outline tentative plans for a follow-up experiment that would investigate key aspects of an approach based on PEPPo as a polarized positron source for the 12 GeV Upgrade of CEBAF. [ABSTRACT FROM AUTHOR]

One goal of the JPos-17 International Workshop on Physics with Positrons was to ascertain whether it would be a good idea to expand the mission of the Thomas Jefferson National Accelerator Facility (JLab) to include science with low energy (i.e. "slow") spin polarized positrons. It is probably true that experimentation with slow positrons would potentially have wide-ranging benefits comparable to those obtained with neutron and x-ray scattering, but it is certain that the full range of these benefits will never be fully available without an infrastructure comparable to that of existing neutron and x-ray facilities. The role for Jefferson Laboratory would therefore be to provide and maintain (1) a dedicated set of machines for making and manipulating high intensity, high brightness beams of polarized slow positrons; (2) a suite of unique and easily used instruments of wide utility that will make efficient use of the positrons; and (3) a group of on-site positron scientists to provide scientific leadership, instrument development, and user support. In this note some examples will be given of the science that might make a serious investment in a positron facility worthwhile. At the same time, the lessons learned from various proposed and successful positron facilities will be presented for consideration. [ABSTRACT FROM AUTHOR]

A positron is an antiparticle of an electron that can be formed in diverse methods: natural or artificial E-decay process, fission and fusion reactions, and a pair production of electron-positron occurred in the reactor and the high energy accelerator centers. Usually a long-lifetime radio isotope is customized for the construction of a slow positron beam lines in many laboratories. The typical intensity of this beam depends upon the strength of the positron source, moderator efficiency, and guiding, pulsing, focusing and detecting systems. This article will review a few positron beam lines and their potential applications in research, especially in the Positronium Bose-Einstein Condensation. [ABSTRACT FROM AUTHOR]

Slow Positron Facility at High Energy Accelerator Research Organization (KEK) is a user dedicated facility with an energy-tunable (0.1 - 35 keV) slow positron beam created by a dedicated ~ 50 MeV linac. It operates in a short pulse (width 1-12 ns, variable, 5x106 e+/s) and a long pulse (width 1.2 µs, 5x107 e+/s) modes of 50 Hz. High energy positrons from pair creation are moderated by reemission after thermalization in W foils. The reemitted positrons are then electrostatically accelerated to a desired energy up to 35 keV and magnetically transported. A pulse-stretching section (pulse stretcher) is installed in the middle of the beamline. It stretches the slow positron pulse for the experiments where too many positrons annihilating in the sample at the same time has to be avoided. Four experiment stations for TRHEPD (total-reflection high-energy positron diffraction), LEPD (low-energy positron diffraction), Ps- (positronium negative ion), and Ps-TOF (positronium time-of-flight) experiments are connected to the beamline branches, SPF-A3, SPF-A4, SPF-B1 and SPF-B2, respectively. Recent results of these stations are briefly described. [ABSTRACT FROM AUTHOR]

A high intensity polarized positron beam, as part of the JLAB 12 GeV program and the proposed electron-ion collider (EIC), can provide a unique opportunity for testing the Standard Model (SM) and probing for new physics. The combination of high luminosity with polarized electrons and positrons incident on protons and deuterons can isolate important effects and distinguish between possible new physics scenarios in a manner that will complement current experimental e orts. A comparison of cross sections between polarized electron and positron beams will allow for an extraction of the poorly known weak neutral current coupling combination 2C3u - C3d and would complement the proposed plan for a precision extraction of the combination 2C2u - Cd at the EIC. Precision measurements of these neutral weak couplings would constrain new physics scenarios including Leptoquarks, R-parity violating supersymmetry, and electron and quark compositeness. The dependence of the charged current cross section on the longitudinal polarization of the positron beam will provide an independent probe to test the chiral structure of the electroweak interactions. A polarized positron can probe charged lepton flavor violation (CLFV) through a search for e+ → τ+ transitions in a manner that is independent and complementary to the proposed e- → τ- search at the EIC. A positron beam incident on an electron in a stationary nuclear target will also allow for a dark-photon (A') search via the annihilation process e+ + e- → A' + γ. [ABSTRACT FROM AUTHOR]

In these proceedings, the possibilities for studying the nucleon spin structure with positrons and electrons are presented. An overview of existing results based on the usage of charged-lepton beams of both charges is given, and the corresponding advantages are highlighted. Also, possibilities for future experiments with an electron and a positron beam are discussed. [ABSTRACT FROM AUTHOR]

Positron annihilation lifetime spectroscopy (PALS) has been widely used to determine the free volume and void properties in polymeric materials. Recently, a two dimensional positron annihilation lifetime spectroscopy (2DPALS) system has been developed for membrane applications. The system measures the coincident signals between the lifetime and the energy which could separate the 2γ and 3γ annihilations and improve the accuracy in the determination of the free volume and void properties. When 2D-PALS is used in coupling with a variable mono-energy slow positron beam, it could be applied to a variety of material characterization. Results of free volumes and voids properties in a multi-layer polymer membrane characterized using 2D-PALS are presented. [ABSTRACT FROM AUTHOR]

Despite the widespread use of positron technology the efficiency of positron utilization is less than 1 %. The low efficiency is primarily due to positron destruction during moderation. Emitted positrons must be filtered through a moderator material to restrict the re-emitted positrons to a useable and defined energy range. The quantum mechanical nature of solidified hydrogen holds the potential to increase the moderator efficiency an order of magnitude over solid neon-the current leader in moderator efficiency. However the characteristics of solid hydrogen as a positron moderator have never been investigated. This paper discusses the design of an experimental cryostat to create solid hydrogen targets for positron beam studies. The design is constrained by the sublimation pressure of the solid hydrogen target exceeding the vacuum pressure of the positron accelerator, and the ability to control hydrogen crystal growth and quality. Thermal control calculations of the test section and heat exchangers are presented. [ABSTRACT FROM AUTHOR]

A brief discussion of the DVCS program at the Jefferson Lab 12 GeV energy upgrade is given with emphasis on what can be learned from using both polarized electron and positron beams in measurements of deeply virtual Compton scattering on protons. [ABSTRACT FROM AUTHOR]

Positron beams have many applications and there are many different concepts for positron sources. In this paper, only positron source techniques for linear colliders are covered. In order to achieve high luminosity, a linear collider positron source should have a high beam current, high beam energy, small emittance and, for some applications, a high degree of beam polarization. There are several different schemes presently being developed around the globe. Both the differences between these schemes and their common technical challenges are discussed. [ABSTRACT FROM AUTHOR]

We review recent total cross section results from the University of Trento for positron scattering from the molecules carbon dioxide, tetrahydrofuran, 3-hydroxy-tetrahydrofuran, formic acid and methanol and ethanol. Where possible comparison is made to other experimental data and with results from state of the art scattering calculations. These comparisons indicate that at low positron energies the scattering process is dominated by the dipole polarisability and, if applicable, the permanent dipole moment of the species in question. [ABSTRACT FROM AUTHOR]

An intense slow positron beam is in its early stages of operation at the 1-MW open-pool PULSTAR research reactor at North Carolina State University. The positron beam line is installed in a beam port that has a 30-cm×30-cm cross sectional view of the core. The positrons are created in a tungsten converter/moderator by pair-production using gamma rays produced in the reactor core and by neutron capture reactions in cadmium cladding surrounding the tungsten. Upon moderation, slow (∼3 eV) positrons that are emitted from the moderator are electrostatically extracted, focused and magnetically guided until they exit the reactor biological shield with 1-keV energy, approximately 3-cm beam diameter and an intensity exceeding 6×108 positrons per second. A magnetic beam switch and transport system has been installed and tested that directs the beam into one of two spectrometers. The spectrometers are designed to implement state-of-the-art PALS and DBS techniques to perform positron and positronium annihilation studies of nanophases in mater. [ABSTRACT FROM AUTHOR]

We are building the SOPHI experiment in Saclay, which is a device based on a small 5 MeV electron linac [1] to produce positrons via pair production on a tungsten target. This device should provide 108 slow e+/s, i.e. a factor 300 greater than the strongest activity Na22 based setup. The SOPHI system has been finalized at the end of 2006 and the main components have been studied and built during 2007 [2]. The experiment is currently being assembled and first results are expected for autumn 2008. The electron linac, positron beam production and transport system will be presented, and expected positron production rate reported. [ABSTRACT FROM AUTHOR]

The application of positron annihilation lifetime spectroscopy (PALS) and Doppler broadening spectroscopy (DBS) to the study of animal or human tissue has only recently been reported [G. Liu, et al. phys. stat. sol. (C) 4, Nos. 10, 3912–3915 (2007)]. We have initiated a study of normal brain section and brain section with glioma derived from a rat glioma model. For the rat glioma model, 200,000 C6 cells were implanted in the basal ganglion of adult Sprague Dawley rats. The rats were sacrificed at 21 days after implantation. The brains were harvested, sliced into 2 mm thick coronal sections, and fixed in 4% formalin. PALS lifetime runs were made with the samples soaked in formalin, and there was not significant evaporation of formalin during the runs. The lifetime spectra were analyzed into two lifetime components. While early results suggested a small decrease in ortho-Positronium (o-Ps) pickoff lifetime between the normal brain section and brain section with glioma, further runs with additional samples have showed no statistically significant difference between the normal and tumor tissue for this type of tumor. The o-Ps lifetime in formalin alone was lower than either the normal tissue or glioma sample. So annihilation in the formalin absorbed in the samples would lower the o-Ps lifetime and this may have masked any difference due to the glioma itself. DBS was also used to investigate the difference in positronium formation between tumor and normal tissue. Tissue samples are heterogeneous and this needs to be carefully considered if PALS and DBS are to become useful tools in distinguishing tissue samples. [ABSTRACT FROM AUTHOR]

The baseline design of the positron source for the International Linear Collider (ILC) incorporates a helical undulator and pair-production target in order to generate the unprecedented quantities of positrons required to sustain the intended ILC physics programme. This configuration is challenging but readily achievable by using novel adaptations of existing technologies to avoid problems inherent in conventional positron sources in which the stresses in the target(s) and activation of the target station are both serious problems. In addition, a highly polarized positron beam, essential for realizing the full potential of the ILC, can be produced by a simple upgrade to the baseline design. A major contribution to the international design effort is being led by the UK-based HeLiCal collaboration. The collaboration is responsible for the design and prototyping of the helical undulator itself, which is a short period device with a small aperture, and also leads development of the start to end simulations of the polarised particles to ensure that high levels of polarization are maintained from the sources, through the beam transport systems and up to the interaction point(s). Members of the collaboration are also involved in the EUROTeV-funded research programme to produce a design for a pair-production target which can operate reliably in the high photon flux of the undulator. This paper will provide an update on the work of the collaboration, focusing on the design, construction and testing of components of the polarized positron source, and will also discuss future plans. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Positron traps have been demonstrated to have the capability for producing high-quality positron beams and intense positron pulses for a variety of scientific and technological applications including atomic physics experiments and probes for materials science. Techniques for accumulating positrons in traps have now advanced to the point where the development of commercial trap-based positron beam systems is feasible. Trap-based beams offer advantages over conventional positron beam systems, including the ability to produce ultra-cold positron beams, giant positron pulses, and ultra-short pulses. They also enable high-efficiency brightness enhancement schemes. The design and performance of a new trap-based positron beam system is described. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

High quality positron beams are currently used for a variety of applications in science and technology. One of the most demanding applications is as analytical tools for surface and materials science, where ultra-short positron pulses (<200 ps) and microscopic beams (< 1 micron in diameter) are desirable. Positron traps offer a qualitatively new method for beam formation and manipulation that has significant advantages in efficiency, flexibility, and cost over current beam conditioning techniques. One important capability is brightness enhancement by radial compression of the positron plasma using the rotating wall technique developed for electron and ion plasmas. A second capability is the production of ultra-short positron pulses required for positron annihilation lifetime spectroscopy. This can be accomplished using a trap by means of the simple technique of quadratic potential bunching, thus avoiding multiple stages of rf bunching currently used to produce pulsed positron beams. [ABSTRACT FROM AUTHOR]