Transparency of an instantaneously created electron-positron-photon plasma
NASA Astrophysics Data System (ADS)
Bégué, D.; Vereshchagin, G. V.
2014-03-01
The problem of the expansion of a relativistic plasma generated when a large amount of energy is released in a small volume has been considered by many authors. We use the analytical solution of Bisnovatyi-Kogan and Murzina for the spherically symmetric relativistic expansion. The light curves and the spectra from transparency of an electron-positron-photon plasma are obtained. We compare our results with the work of Goodman.
Photon-induced positron annihilation lifetime spectroscopy using an S-band compact electron linac
NASA Astrophysics Data System (ADS)
Taira, Y.; Kuroda, R.; Tanaka, M.; Kumaki, M.; Oshima, N.; O'Rourke, B. E.; Suzuki, R.; Toyokawa, H.
2014-02-01
A new photon-induced positron annihilation lifetime spectroscopy approach has been developed using an S-band compact electron linac at the National Institute of Advanced Industrial Science and Technology (AIST). The high energy (<42MeV), intense (105 photons pulse-1), and ultra-short pulse (3 ps pulse width) photon beam creates positrons throughout an entire sample via pair production. A positron lifetime spectrum can be obtained by measuring the time difference between the accelerator's RF frequency and the detection time of the annihilation gamma rays. The positron lifetimes for lead and yttria-stabilized zirconia samples have been successfully measured.
NASA Astrophysics Data System (ADS)
Bulanov, S. S.; Schroeder, C. B.; Esarey, E.; Leemans, W. P.
2013-06-01
The interaction of high-energy electrons, positrons, and photons with intense laser pulses is studied in head-on collision geometry. It is shown that electrons and/or positrons undergo a cascade-type process involving multiple emissions of photons. These photons can consequently convert into electron-positron pairs. As a result charged particles quickly lose their energy developing an exponentially decaying energy distribution, which suppresses the emission of high-energy photons, thus reducing the number of electron-positron pairs being generated. Therefore, this type of interaction suppresses the development of the electromagnetic avalanche-type discharge, i.e., the exponential growth of the number of electrons, positrons, and photons does not occur in the course of interaction. The suppression will occur when three-dimensional effects can be neglected in the transverse particle orbits, i.e., for sufficiently broad laser pulses with intensities that are not too extreme. The final distributions of electrons, positrons, and photons are calculated for the case of a high-energy e-beam interacting with a counterstreaming, short intense laser pulse. The energy loss of the e-beam, which requires a self-consistent quantum description, plays an important role in this process, as well as provides a clear experimental observable for the transition from the classical to quantum regime of interaction.
On thermalization of electron-positron-photon plasma
Siutsou, I. A.; Aksenov, A. G.
2015-12-17
Recently a progress has been made in understanding thermalization mechanism of relativistic plasma starting from a non-equilibrium state. Relativistic Boltzmann equations were solved numerically for homogeneous isotropic plasma with collision integrals for two- and three-particle interactions calculated from the first principles by means of QED matrix elements. All particles were assumed to fulfill Boltzmann statistics. In this work we follow plasma thermalization by accounting for Bose enhancement and Pauli blocking in particle interactions. Our results show that particle in equilibrium reach Bose-Einstein distribution for photons, and Fermi-Dirac one for electrons, respectively.
Photons, Electrons and Positrons Transport in 3D by Monte Carlo Techniques
2014-12-01
Version 04 FOTELP-2014 is a new compact general purpose version of the previous FOTELP-2K6 code designed to simulate the transport of photons, electrons and positrons through three-dimensional material and sources geometry by Monte Carlo techniques, using subroutine package PENGEOM from the PENELOPE code under Linux-based and Windows OS. This new version includes routine ELMAG for electron and positron transport simulation in electric and magnetic fields, RESUME option and routine TIMER for obtaining starting random number and for measuring the time of simulation.
Photons, Electrons and Positrons Transport in 3D by Monte Carlo Techniques
2014-12-01
Version 04 FOTELP-2014 is a new compact general purpose version of the previous FOTELP-2K6 code designed to simulate the transport of photons, electrons and positrons through three-dimensional material and sources geometry by Monte Carlo techniques, using subroutine package PENGEOM from the PENELOPE code under Linux-based and Windows OS. This new version includes routine ELMAG for electron and positron transport simulation in electric and magnetic fields, RESUME option and routine TIMER for obtaining starting random numbermore » and for measuring the time of simulation.« less
Resonant two-photon annihilation of an electron-positron pair in a pulsed electromagnetic wave
NASA Astrophysics Data System (ADS)
Voroshilo, A. I.; Roshchupkin, S. P.; Nedoreshta, V. N.
2016-09-01
Two-photon annihilation of an electron-positron pair in the field of a plane low-intensity circularly polarized pulsed electromagnetic wave was studied. The conditions for resonance of the process which are related to an intermediate particle that falls within the mass shell are studied. In the resonant approximation the probability of the process was obtained. It is demonstrated that the resonant probability of two-photon annihilation of an electron-positron pair may be several orders of magnitude higher than the probability of this process in the absence of the external field. The obtained results may be experimentally verified by the laser facilities of the international megaprojects, for example, SLAC (National Accelerator Laboratory), FAIR (Facility for Antiproton and Ion Research), and XFEL (European X-Ray Free-Electron Laser).
Istomin, Ya. N. Sob'yanin, D. N.
2011-10-15
The production of electron-positron pairs in a vacuum neutron star magnetosphere is investigated for both low (compared to the Schwinger one) and high magnetic fields. The case of a strong longitudinal electric field where the produced electrons and positrons acquire a stationary Lorentz factor in a short time is considered. The source of electron-positron pairs has been calculated with allowance made for the pair production by curvature and synchrotron photons. Synchrotron photons are shown to make a major contribution to the total pair production rate in a weak magnetic field. At the same time, the contribution from bremsstrahlung photons may be neglected. The existence of a time delay due to the finiteness of the electron and positron acceleration time leads to a great reduction in the electron-positron plasma generation rate compared to the case of a zero time delay. The effective local source of electron-positron pairs has been constructed. It can be used in the hydrodynamic equations that describe the development of a cascade after the absorption of a photon from the cosmic gamma-ray background in a neutron star magnetosphere.
Apparatus for photon activation positron annihilation analysis
Akers, Douglas W.
2007-06-12
Non-destructive testing apparatus according to one embodiment of the invention comprises a photon source. The photon source produces photons having predetermined energies and directs the photons toward a specimen being tested. The photons from the photon source result in the creation of positrons within the specimen being tested. A detector positioned adjacent the specimen being tested detects gamma rays produced by annihilation of positrons with electrons. A data processing system operatively associated with the detector produces output data indicative of a lattice characteristic of the specimen being tested.
Rustgi, M L; Pandey, L N; Kassaee, A; Long, S A
1989-04-01
Previous Monte Carlo calculations for the energy spectra of electrons produced in water irradiated by photons are extended to 1 GeV. All of the physical processes believed to be important in the transport of electrons and positrons above 100 keV and photons starting with the ejection of L photoelectrons are considered. The results are presented in tabular form and can be conveniently used to compute kerma in water. The contributions of several physical processes, such as Compton scattering and pair-production to electron spectra, are separately tabulated. The results are compared with those of Todo et al. (1982) for the single interactions of monoenergetic photons. It is found that the inclusion of processes such as multiple Compton scattering, bremsstrahlung production, positron annihilation in flight, Møhiller and Bhabha scattering from electrons and Molière multiple scattering from atomic nuclei make a considerable difference in the inferred electron spectrum in water.
Method for photon activation positron annihilation analysis
Akers, Douglas W.
2006-06-06
A non-destructive testing method comprises providing a specimen having at least one positron emitter therein; determining a threshold energy for activating the positron emitter; and determining whether a half-life of the positron emitter is less than a selected half-life. If the half-life of the positron emitter is greater than or equal to the selected half-life, then activating the positron emitter by bombarding the specimen with photons having energies greater than the threshold energy and detecting gamma rays produced by annihilation of positrons in the specimen. If the half-life of the positron emitter is less then the selected half-life, then alternately activating the positron emitter by bombarding the specimen with photons having energies greater then the threshold energy and detecting gamma rays produced by positron annihilation within the specimen.
NASA Astrophysics Data System (ADS)
Sarria, D.; Blelly, P.-L.; Forme, F.
2015-05-01
Terrestrial gamma ray flashes are natural bursts of X and gamma rays, correlated to thunderstorms, that are likely to be produced at an altitude of about 10 to 20 km. After the emission, the flux of gamma rays is filtered and altered by the atmosphere and a small part of it may be detected by a satellite on low Earth orbit (RHESSI or Fermi, for example). Thus, only a residual part of the initial burst can be measured and most of the flux is made of scattered primary photons and of secondary emitted electrons, positrons, and photons. Trying to get information on the initial flux from the measurement is a very complex inverse problem, which can only be tackled by the use of a numerical model solving the transport of these high-energy particles. For this purpose, we developed a numerical Monte Carlo model which solves the transport in the atmosphere of both relativistic electrons/positrons and X/gamma rays. It makes it possible to track the photons, electrons, and positrons in the whole Earth environment (considering the atmosphere and the magnetic field) to get information on what affects the transport of the particles from the source region to the altitude of the satellite. We first present the MC-PEPTITA model, and then we validate it by comparison with a benchmark GEANT4 simulation with similar settings. Then, we show the results of a simulation close to Fermi event number 091214 in order to discuss some important properties of the photons and electrons/positrons that are reaching satellite altitude.
Hard photon processes in electron-positron annihilation at 29 GeV
Gold, M.S.
1986-11-01
The hard photon processes ..mu mu gamma.. and hadrons + ..gamma.. in e/sup +/e/sup -/ annihilation at 29 GeV have been studied. The study is based on an integrated luminosity of 226 pb/sup -1/ taken at PEP with the Mark II detector. For the ..mu mu gamma.. process, a small fraction of non-planar events are observed with missing momentum along the beam direction. The resulting missing energy spectrum is consistent with that expected from higher order effects. The observed cross section is consistent with the predicted cross section for this process, sigma/sup exp/sigma/sup th/ = .90 +- .05 +- .06. The observed hard photon energy spectrum and mass distributions are found to be in agreement with O(..cap alpha../sup 3/) QED. The measured charge asymmetry is in good agreement with the predicted value, A/sub exp/A/sub th/ = .83 +- .25 +- .12. The ..mu gamma.. invariant mass distribution is used to place a limit on a possible excited muon coupling G..gamma../M* for excited muon masses in the range 1 < M* < 21 GeV of (G..gamma../M*)/sup 2/ < 10/sup -5/ GeV/sup -2/ at a 95% confidence level. In the hadrons + ..gamma.. process, evidence for final state radiation is found in an excess of events over that predicted from initial state radiation alone of 253 +- 54 +- 60 events. Further evidence for final state radiation is found in a large hadronic charge asymmetry A/sub Had+..gamma../= (-24.6 +- 5.5)%.
NASA Astrophysics Data System (ADS)
Takashima, Y.; Oki, S.; Sugiyama, H.; Kobayakawa, H.
2005-10-01
The spatial distribution of the effective dose of photons, electrons and positrons caused by beam loss around a small electron storage ring in a synchrotron radiation source is calculated. We propose a simple formula applicable to calculate the effective dose for storage rings for beam energies ranging from 200 MeV to 5 GeV. The formula is derived from Monte Carlo calculations of radiation flux using the simulation code EGS4. We apply the formula to estimate the effective dose distribution in a small synchrotron radiation facility planned by the Nagoya University.
NASA Astrophysics Data System (ADS)
Kirsebom, K.; Medenwaldt, R.; Mikkelsen, U.; Møller, S. P.; Paludan, K.; Uggerhøj, E.; Worm, T.; Elsener, K.; Ballestrero, S.; Sona, P.; Romano, J.; Connell, S. H.; Sellschop, J. P. F.; Avakian, R. O.; Avetisian, A. E.; Taroian, S. P.
1996-10-01
Detailed experimental investigations of photon multiplicities for 150 GeV electrons/positrons traversing thin diamond and Si crystals have been performed. Along axial directions up to 10 photons are emitted in 1.5 mm diamond for a radiative energy loss larger than 4 GeV. This corresponds to a mean free path for photon emission of about two orders of magnitude shorter than in an amorphous target. This is in agreement with an enhanced radiative energy loss of ˜ 30 times that in amorphous targets. The strongly enhanced photon emission leads to radiation cooling which can result in particles exiting the crystal with a reduced angle to the axis. For incidences along planar directions the average multiplicity is still above one, even for the thinnest crystals used in the present experiment, so a single-photon spectrum can only be obtained for thicknesses ≤50 μm, which, on the other hand, is comparable to the coherence lengths for GeV photons, leading to destruction of the coherent effects.
Alternative positron-target design for electron-positron colliders
Donahue, R.J. ); Nelson, W.R. )
1991-04-01
Current electron-positron linear colliders are limited in luminosity by the number of positrons which can be generated from targets presently used. This paper examines the possibility of using an alternate wire-target geometry for the production of positrons via an electron-induced electromagnetic cascade shower. 39 refs., 38 figs., 5 tabs.
The Advanced Photon Source (APS) linear accelerator as a source of slow positrons
White, M.M.; Lessner, E.S.
1996-09-01
The Advanced Photon Source linear accelerator (linac) system consists of a 200-MeV, 2856-MHz S-band electron linac, a 2-radiation-length-thick tungsten target for positron production, and a 450-MeV positron linac. The linac is briefly described, and some possibilities for its use as a slow positron source are discussed.
Electron- and positron-proton elastic scattering in CLAS
L.B. Weinstein
2009-08-01
There is a significant disagreement between measurements of the proton electric form factor, G{sup p}{sub E}, using Rosenbluth separations and polarization transfer. This disagreement, if not explained, could pose a fundamental challenge to our understanding of electron scattering or proton structure. Two-photon exchange (TPE) processes, although not fully calculable, are the most likely explanation of this disagreement. We will definitively test this assertion by comparing the electron-proton and positron-proton elastic scattering cross section in the Jefferson Lab CLAS. We will make a mixed identical electron and positron tertiary beam by passing a 5.5 GeV primary electron beam through a radiator to make a photon beam and then passing the photon beam through a converter to make electron-positron pairs. Measuring the elastic cross sections simultaneously using identical lepton beams should significantly reduce systematic uncertainties.
NASA Astrophysics Data System (ADS)
Rahman, M. M.; Alam, M. S.; Mamun, A. A.
2015-05-01
Obliquely propagating positron-acoustic solitary waves (PASWs) in a magnetized electron-positron-ion plasma (containing nonthermal hot positrons and electrons, inertial cold positrons, and immobile positive ions) are precisely investigated by deriving the Zakharov-Kuznetsov equation. It is found that the characteristics of the PASWs are significantly modified by the effects of external magnetic field, obliqueness, nonthermality of hot positrons and electrons, temperature ratio of hot positrons and electrons, and respective number densities of hot positrons and electrons. The findings of our results can be employed in understanding the localized electrostatic structures and the characteristics of PASWs in various space and laboratory plasmas.
The Calibration of the PEPPo Polarimeter for Electrons and Positrons
Adeyemi, Adeleke Hakeem; Voutier, Eric J-.M.
2013-06-01
The PEPPo (Polarized Electrons for Polarized Positrons) experiment at Jefferson Laboratory investigated the polarization transfer from longitudinally polarized electrons to longitudinally polarized positrons, with the aim of developing this technology for a low energy (~MeV) polarized positron source. Polarization of the positrons was measured by means of a Compton transmission polarimeter where incoming positrons transfer their polarization into circularly polarized photons that were subsequently analyzed by a thick polarized iron target. The measurement of the transmitted photon flux with respect to the orientation of the target polarization (+-) or the helicity (+-) of the incoming leptons provided the measurement of their polarization. Similar measurements with a known electron beam were also performed for calibration purposes. This presentation will describe the apparatus and calibrations performed at the injector at the Jefferson Laboratory to measure positron polarization in the momentum range 3.2-6.2 MeV/c, specifically to quantify the positron analyzing power from electron experimental data measured over a comparable momentum range.
ELECTRON-POSITRON FLOWS AROUND MAGNETARS
Beloborodov, Andrei M.
2013-11-10
The twisted magnetospheres of magnetars must sustain a persistent flow of electron-positron plasma. The flow dynamics is controlled by the radiation field around the hot neutron star. The problem of plasma motion in the self-consistent radiation field is solved using the method of virtual beams. The plasma and radiation exchange momentum via resonant scattering and self-organize into the 'radiatively locked' outflow with a well-defined, decreasing Lorentz factor. There is an extended zone around the magnetar where the plasma flow is ultra-relativistic; its Lorentz factor is self-regulated so that it can marginally scatter thermal photons. The flow becomes slow and opaque in an outer equatorial zone, where the decelerated plasma accumulates and annihilates; this region serves as a reflector for the thermal photons emitted by the neutron star. The e {sup ±} flow carries electric current, which is sustained by a moderate induced electric field. The electric field maintains a separation between the electron and positron velocities, against the will of the radiation field. The two-stream instability is then inevitable, and the induced turbulence can generate low-frequency emission. In particular, radio emission may escape around the magnetic dipole axis of the star. Most of the flow energy is converted to hard X-ray emission, which is examined in an accompanying paper.
Electron and Positron Stopping Powers of Materials
National Institute of Standards and Technology Data Gateway
SRD 7 NIST Electron and Positron Stopping Powers of Materials (PC database for purchase) The EPSTAR database provides rapid calculations of stopping powers (collisional, radiative, and total), CSDA ranges, radiation yields and density effect corrections for incident electrons or positrons with kinetic energies from 1 keV to 10 GeV, and for any chemically defined target material.
Electron and positron induced processes. POSMOL 2013
NASA Astrophysics Data System (ADS)
Limão-Vieira, Paulo; Campeanu, Radu; Hoshino, Masamitsu; Ingólfsson, Oddur; Mason, Nigel; Nagashima, Yasuyuki; Tanuma, Hajime
2014-09-01
POSMOL 2013, the international meeting on electron and positron induced processes comprising the XVII International Workshop on Low-Energy Positron and Positronium Physics and the XVIII International Symposium on Electron-Molecule Collisions and Swarms, was held at Kanazawa Bunka Hall, Kanazawa, Ishikawa, Japan, from 19-21 July 2013. The XVII Workshop encompassed all aspects of positron, positronium and antiproton interactions with electrons, atoms, molecules and solid surfaces, and topics related to these, whereas the XVIII Symposium encompassed all aspects of electron interactions with molecules in both gaseous and condensed phases. Particular topics include studies of electron interactions with biomolecules, electron induced surface chemistry and the study of plasma processes. Recent research on the study of electron swarms was also highlighted. Contribution to the Topical Issue "Electron and Positron Induced Processes", edited by Michael Brunger, Radu Campeanu, Masamitsu Hoshino, Oddur Ingólfsson, Paulo Limão-Vieira, Nigel Mason, Yasuyuki Nagashima and Hajime Tanuma.
Nonlinear magnetohydrodynamics of electron-positron plasmas
NASA Astrophysics Data System (ADS)
Shukla, P. K.; Dasgupta, B.; Sakanaka, P. H.
2000-05-01
A set of nonlinear magnetohydrodynamic (MHD) equations for magnetized, nonrelativistic electron-positron plasmas is derived by employing a two fluid model that is supplemented by Ampère's and Faraday's laws. The nonlinear equations show how the baroclinic driver (the Biermann battery) generates the electron positron flows and how these flows give rise to plasma currents which act as a source for the magnetic fields. The newly derived nonlinear equations form a basis for investigating waves, instabilities, as well as coherent nonlinear structures, in addition to studying exact equilibria of electron-positron jets in a magnetoplasma.
Relativistic electron-positron beams in gamma-ray bursters
NASA Technical Reports Server (NTRS)
Smith, I. A.; Epstein, Richard I.
1993-01-01
Beams of relativistic electrons and/or positrons leaving the surface of a strongly magnetized neutron star may give rise to gamma-ray bursts. The beams could be accelerated by strong, magnetically aligned electric fields that are produced by oscillations of the stellar surface. Here we investigate the particle acceleration in these electric fields, the resulting electron-positron pair cascade, and the gamma-ray emission. We find that beams of electrons and positrons moving parallel to the magnetic field are generated, with a reported differential energy distribution. These beams produce the bulk of the gamma-ray burst radiation below about 1 MeV by the resonant Compton scattering of thermal photons emitted from the stellar surface. The escaping synchrotron radiation from the cascade dominates the radiation spectrum above about 1 MeV.
Monte Carlo Code System for Electron (Positron) Dose Kernel Calculations.
CHIBANI, OMAR
1999-05-12
Version 00 KERNEL performs dose kernel calculations for an electron (positron) isotropic point source in an infinite homogeneous medium. First, the auxiliary code PRELIM is used to prepare cross section data for the considered medium. Then the KERNEL code simulates the transport of electrons and bremsstrahlung photons through the medium until all particles reach their cutoff energies. The deposited energy is scored in concentric spherical shells at a radial distance ranging from zero to twice the source particle range.
Uddin, M. J. Alam, M. S.; Mamun, A. A.
2015-02-15
Nonplanar (cylindrical and spherical) positron-acoustic (PA) Gardner solitary waves (SWs) in an unmagnetized plasma system consisting of immobile positive ions, mobile cold positrons, and superthermal (kappa distributed) hot positrons and electrons are investigated. The modified Gardner equation is derived by using the reductive perturbation technique. The effects of cylindrical and spherical geometries, superthermal parameter of hot positrons and electrons, relative temperature ratios, and relative number density ratios on the PA Gardner SWs are studied by using the numerical simulations. The implications of our results in various space and laboratory plasma environments are briefly discussed.
Electron capture from solids by positrons
Howell, R.
1987-08-01
The capture of electrons in solids is modified from that in gasses by several factors. The most important is the collective interaction of the electrons which results in a density of electron states in the solid in wide bands. Also the high density of electrons in many solids gives a high frequency of interaction as compared to gasses, and quickly destroys any electron-positron states in the metal matrix. Consequently, most positrons implanted in a metal will rapidly thermalize, and unless they reach the surface will annihilate with an electron in an uncorrelated state. Positronium formation from positrons scattered at a metal surface is analogous to ion neutralization however, most of the positronium comes from positrons passing through the surface from the bulk. The dominant motivation for studying positronium formation has been the hope that the distribution of the electrons at the surface would be obtained through the annihilation properties of positrons trapped at the surface or through analysis of the energy and angular distributions of the positronium emitted into the vacuum. These distributions have been measured and are included in this paper. 17 refs.
High-energy electron-positron photoproduction cross section close to the end of the spectrum
Di Piazza, A.; Milstein, A. I.
2010-10-15
We consider the cross section of electron-positron pair production by a high-energy photon in a strong Coulomb field close to the end of the electron or positron spectrum. We show that the cross section essentially differs from the result obtained in the Born approximation as well as from the result which takes into account the Coulomb corrections under the assumption that both electron and positron are ultrarelativistic. The cross section of bremsstrahlung in a strong Coulomb field by a high-energy electron is also obtained in the region where the final electron is not ultrarelativistic.
NASA Astrophysics Data System (ADS)
Tran, D.; Connell, J. J.; Lopate, C.; Bickford, B.
2014-12-01
Moderate energy positrons (~few to 10 MeV) have seldom been observed in the Heliosphere, due primarily to there not having been dedicated instruments for such measurements. Their detection would have implications in the study of Solar energetic particle events and the transport and modulation of the Solar wind and Galactic cosmic rays. The Positron Identification by Coincident Annihilation Photons (PICAP) system is designed specifically to measure these moderate energy positrons by simultaneously detecting the two 511-keV γ-ray photons that result from a positron stopping in the instrument and the subsequent electron-positron annihilation. This method is also expected to effectively discriminate positrons from protons by measuring the amount of energy deposited in the detectors (dE/dx versus residual energy). PICAP offers a low-mass, low-power option for measuring positrons, electrons, and ions in space. Following Monte Carlo modeling, a PICAP laboratory prototype, adaptable to a space-flight design, was designed, built, and tested. This instrument is comprised of (Si) solid-state detectors, plastic scintillation detectors, and high-Z BGO crystal scintillator suitable for detecting the 511-keV γ rays. The prototype underwent preliminary laboratory testing and calibration using radioactive sources for the purpose of establishing functionality. It has since been exposed to beams of energetic protons (up to ~200 MeV) at Massachusetts General Hospital's Francis H. Burr Proton Beam Therapy Center and positrons and electrons (up to ~10 MeV) at Idaho State University's Idaho Accelerator Center. The goal is to validate modeling and determine the performance of the instrument concept. We will present a summary of modeling calculations and analysis of data taken at the accelerator tests. This work is 95% supported by NASA Grant NNX10AC10G.
Study of electron-positron interactions
Abashian, A.; Gotow, K.; Philonen, L.
1990-09-15
For the past seven years, this group has been interested in the study of tests of the Standard Model of Electroweak interactions. The program has centered about the AMY experiment which examines the nature of the final state products in electron-positron collisions in the center of mass energy range near 60 GeV. Results of these measurements have shown a remarkable consistency with the predictions of the minimal model of 3 quark and lepton generations and single charged and neutral intermediate bosons. No new particles or excited states have been observed nor has any evidence for departures in cross sections or angular asymmetries from expectations been observed. These conclusions have been even more firmly established by the higher energy results from the LEP and SLC colliders at center of mass energies of about 90 GeV. Our focus is shifting to the neutrino as a probe to electroweak interactions. The relative merit of attempting to observe neutrinos from point sources versus observing neutrinos generally is not easy to predict. The improved ability to interpret is offset by the probably episodic nature of the emission and irreproducibility of the results. In this phase of development, it is best to be sensitive to both sources of neutrinos. As a second phase of our program at Virginia Tech, we are studying the feasibility of detecting cosmic ray neutrinos in a proposed experiment which we have called NOVA. the results of the test setup will be instrumental in developing an optimum design. A third program we are involved in is the MEGA experiment at Los Alamos, an experiment to place a limit on the rate of muon decay to electron plus photon which is forbidden by the Standard Model.
Positron source position sensing detector and electronics
Burnham, Charles A.; Bradshaw, Jr., John F.; Kaufman, David E.; Chesler, David A.; Brownell, Gordon L.
1985-01-01
A positron source, position sensing device, particularly with medical applications, in which positron induced gamma radiation is detected using a ring of stacked, individual scintillation crystals, a plurality of photodetectors, separated from the scintillation crystals by a light guide, and high resolution position interpolation electronics. Preferably the scintillation crystals are several times more numerous than the photodetectors with each crystal being responsible for a single scintillation event from a received gamma ray. The light guide will disperse the light emitted from gamma ray absorption over several photodetectors. Processing electronics for the output of the photodetectors resolves the location of the scintillation event to a fraction of the dimension of each photodetector. Because each positron absorption results in two 180.degree. oppositely traveling gamma rays, the detection of scintillation in pairs permits location of the positron source in a manner useful for diagnostic purposes. The processing electronics simultaneously responds to the outputs of the photodetectors to locate the scintillations to the source crystal. While it is preferable that the scintillation crystal include a plurality of stacked crystal elements, the resolving power of the processing electronics is also applicable to continuous crystal scintillators.
Monte Carlo Code System for Electron (Positron) Dose Kernel Calculations.
1999-05-12
Version 00 KERNEL performs dose kernel calculations for an electron (positron) isotropic point source in an infinite homogeneous medium. First, the auxiliary code PRELIM is used to prepare cross section data for the considered medium. Then the KERNEL code simulates the transport of electrons and bremsstrahlung photons through the medium until all particles reach their cutoff energies. The deposited energy is scored in concentric spherical shells at a radial distance ranging from zero to twicemore » the source particle range.« less
Advances in positron and electron scattering*
NASA Astrophysics Data System (ADS)
Limão-Vieira, Paulo; García, Gustavo; Krishnakumar, E.; Petrović, Zoran; Sullivan, James; Tanuma, Hajime
2016-10-01
The topical issue on Advances in Positron and Electron Scattering" combines contributions from POSMOL 2015 together with others devoted to celebrate the unprecedented scientific careers of our loyal colleagues and trusted friends Steve Buckman (Australian National University, Australia) and Michael Allan (University of Fribourg, Switzerland) on the occasion of their retirements. POSMOL 2015, the XVIII International Workshop on Low-Energy Positron and Positronium Physics and the XIX International Symposium on Electron-Molecule Collisions and Swarms, was held at Universidade NOVA de Lisboa, Lisboa, Portugal, from 17-20 July 2015. The international workshop and symposium allowed to achieve a very privileged forum of sharing and developing our scientific expertise on current aspects of positron, positronium and antiproton interactions with electrons, atoms, molecules and solid surfaces, and related topics, as well as electron interactions with molecules in both gaseous and condensed phases. Particular topics include studies of electron interactions with biomolecules, electron induced surface chemistry and the study of plasma processes. Recent developments in the study of swarms are also fully addressed.
Uddin, M. J. Alam, M. S.; Mamun, A. A.
2015-06-15
A theoretical investigation is made on the positron-acoustic (PA) shock waves (SHWs) in an unmagnetized electron-positron-ion plasma containing immobile positive ions, cold mobile positrons, and hot positrons and electrons following the kappa (κ) distribution. The cold positron kinematic viscosity is taken into account, and the reductive perturbation method is used to derive the Burgers equation. It is found that the viscous force acting on cold mobile positron fluid is a source of dissipation and is responsible for the formation of the PA SHWs. It is also observed that the fundamental properties of the PA SHWs are significantly modified by the effects of different parameters associated with superthermal (κ distributed) hot positrons and electrons.
NASA Astrophysics Data System (ADS)
Uddin, M. J.; Alam, M. S.; Mamun, A. A.
2015-06-01
A theoretical investigation is made on the positron-acoustic (PA) shock waves (SHWs) in an unmagnetized electron-positron-ion plasma containing immobile positive ions, cold mobile positrons, and hot positrons and electrons following the kappa (κ) distribution. The cold positron kinematic viscosity is taken into account, and the reductive perturbation method is used to derive the Burgers equation. It is found that the viscous force acting on cold mobile positron fluid is a source of dissipation and is responsible for the formation of the PA SHWs. It is also observed that the fundamental properties of the PA SHWs are significantly modified by the effects of different parameters associated with superthermal (κ distributed) hot positrons and electrons.
NLC Polarized Positron Photon Beam Target Thermal Structural Modeling
Stein, W; Sheppard, J C
2002-06-11
The NLC polarized positron photon beam target is a 0.4 radiation length thick titanium target. Energy deposition from one pulse occurs over 266 nano-seconds and results in heating of the target and pressure pulses straining the material. The 22.1 MeV photon beam has a spot size of 0.75 mm and results in a maximum temperature jump of 233 C. Stresses are induced in the material from thermal expansion of the hotter material. Peak effective stresses reach 19 Ksi (1.34 x 10{sup 8} Pa), which is lower than the yield strength of a titanium alloy by a factor of six.
High energy electron positron physics
Ali, A.; Soding, P.
1987-01-01
With the termination of the physics program at PETRA in a year from now, and with the start of TRISTAN and the SLC and later LEP, an era of e/sup +/e/sup -/ physics will come to an end and a new one begins. The field is changing from a field of a few specialists, to becoming one of the mainstream efforts of the high energy community. It seems appropriate at this moment to summarize what has been learned over the past years, in a way more useful to any high energy physicist in particular to newcomers in the e/sup +/e/sup -/ field. This is the purpose of the book. This book should be used as a reference for future workers in the field of e/sup +/e/sup -/ interactions. It includes the most relevant data, parametrizations, theoretical background, and a chapter on detectors. Contents: Foreword; Detectors for High Energy e/sup +/e/sup -/ Physics; Lepton Pair Production and Electroweak Parameters; Hadron Production, Strong and Electroweak Properties; tau Physics; Recent Results on the Charm Sector; Bottom Physics; Lifetime Measurements of tau, Charmed and Beauty Hadrons; UPSILON Spectroscopy; Hadronic Decays of the UPSILON; Quark and Gluon Fragmentation in the e/sup +/e/sup -/ Continuum; Jet Production and QCD; Two Photon Physics; Search for New Particles.
On the electron-positron cascade in AGN central engines
NASA Astrophysics Data System (ADS)
Ford, Alex; Keenan, Brett; Medvedev, Mikhail
2016-03-01
Processes around spinning supermassive black holes (BH) in active galactic nuclei (AGN) are believed to determine how relativistic jets are launched and how the BH energy is extracted. The key ``ingredient'' is the origin of plasma in BH magnetospheres. In order to explore the process of the electron-positron plasma production, we developed a numerical code which models a one-dimensional (along a magnetic field line) dynamics of the cascade. Our simulations show that plasma production is controlled by the spectrum of the ambient photon field, the B-field strength, the BH spin and mass. Implications of our results to the Galactic Center and AGNs are discussed.
Shah, Asif; Mahmood, S.; Haque, Q.
2011-11-15
Electrostatic ion acoustic solitary waves are studied in a plasma system comprising of relativistic ions, kappa distributed electrons, and positrons. The increase in the relativistic streaming factor and positron and electron kappa parameters cause the soliton amplitude to thrive. However, the soliton amplitude diminishes as the positron concentration is increased in the system. Our results are general and may be helpful, in understanding nonlinear phenomena in the presence of kappa distibuted electrons, positrons, and relativistically streaming ions.
The PEP electron-positron ring
Rees, J.R.
1988-01-01
The first stage of the positron-electron-proton (PEP) colliding-beam system which has been under joint study by a Lawrence Berkeley Laboratory-Stanford Linear Accelerator Center team for the past two years, will be the electron-positron storage ring. The physics justification for the e/sup +/e/sup minus/ ring is summarized briefly and the proposed facility is described. The ring will have six arcs having gross radii of about 220 m and six interaction regions located at the centers of straight sections about 130 m long. The longitudinal distance left free for experimental apparatus at the intersection regions will be 20 m. The range of operating beam energies will be from 5 GeV to 15 GeV. The design luminosity at 15 GeV will be 10/sup 32/cm/sup minus 2/s/sup minus 1/, and the luminosity will vary approximately as the square of the beam energy. Alternative methods under consideration for adjusting the beam cross-section are discussed. The designs of the storage ring subsystems and of the conventional facilities including the experimental halls at the interaction regions are described.
Optimization of positrons generation based on laser wakefield electron acceleration
NASA Astrophysics Data System (ADS)
Wu, Yuchi; Han, Dan; Zhang, Tiankui; Dong, Kegong; Zhu, Bin; Yan, Yonghong; Gu, Yuqiu
2016-08-01
Laser based positron represents a new particle source with short pulse duration and high charge density. Positron production based on laser wakefield electron acceleration (LWFA) has been investigated theoretically in this paper. Analytical expressions for positron spectra and yield have been obtained through a combination of LWFA and cascade shower theories. The maximum positron yield and corresponding converter thickness have been optimized as a function of driven laser power. Under the optimal condition, high energy (>100 MeV ) positron yield up to 5 ×1011 can be produced by high power femtosecond lasers at ELI-NP. The percentage of positrons shows that a quasineutral electron-positron jet can be generated by setting the converter thickness greater than 5 radiation lengths.
Photon-induced positron annihilation for standoff bomb detection
NASA Astrophysics Data System (ADS)
Bradley, D. A.; Hashim, S.; Cabello, J.; Wells, K.; Dunn, W. L.
2010-07-01
We describe an approach to detect improvised explosive devices (IEDs) by using photon-induced positron annihilation radiation (PIPAR). This system relies on back-scattered γ photons from the target and surrounding objects following exposure to high energy X-rays from a betatron. In this work we simulate the use of Bremsstrahlung source operating at 3.5 MeV, with a scintillation detector, working in PIPAR mode, in order to reduce noise produced by undesired back-scattering from the surrounding objects. In this paper, we describe the basic imaging method and preliminary results on simulating a suitable betatron source. Two types of X-ray filters copper (Cu) and aluminium (Al), have been used in the simulation to observe their differences in the deposited energy spectrum in the iron target. It was found that the use of iron target in conjunction with 2 mm Al filter is capable of detecting annihilation γ photons. An initiated experiment with an interlaced source also shows promise.
Multi-pair states in electron-positron pair creation
NASA Astrophysics Data System (ADS)
Wöllert, Anton; Bauke, Heiko; Keitel, Christoph H.
2016-09-01
Ultra strong electromagnetic fields can lead to spontaneous creation of single or multiple electron-positron pairs. A quantum field theoretical treatment of the pair creation process combined with numerical methods provides a description of the fermionic quantum field state, from which all observables of the multiple electron-positron pairs can be inferred. This allows to study the complex multi-particle dynamics of electron-positron pair creation in-depth, including multi-pair statistics as well as momentum distributions and spin. To illustrate the potential benefit of this approach, it is applied to the intermediate regime of pair creation between nonperturbative Schwinger pair creation and perturbative multiphoton pair creation where the creation of multi-pair states becomes nonnegligible but cascades do not yet set in. Furthermore, it is demonstrated how spin and helicity of the created electrons and positrons are affected by the polarization of the counterpropagating laser fields, which induce the creation of electron-positron pairs.
Quantum resonances in reflection of relativistic electrons and positrons
NASA Astrophysics Data System (ADS)
Eykhorn, Yu. L.; Korotchenko, K. B.; Pivovarov, Yu. L.; Takabayashi, Y.
2015-07-01
Calculations based on the use of realistic potential of the system of crystallographic planes confirm earlier results on existence of resonances in reflection of relativistic electrons and positrons by the crystal surface, if the crystallographic planes are parallel to the surface.The physical reason of predicted phenomena, similar to the band structure of transverse energy levels, is connected with the Bloch form of the wave functions of electrons (positrons) near the crystallographic planes, which appears both in the case of planar channeling of relativistic electrons (positrons) and in reflection by a crystal surface. Calculations show that positions of maxima in reflection of relativistic electrons and positrons by crystal surface specifically depend on the angle of incidence with respect to the crystal surface and relativistic factor of electrons/positrons. These maxima form the Darwin tables similar to that in ultra-cold neutron diffraction.
Propagation of electron and positron beams in long, dense plasmas
NASA Astrophysics Data System (ADS)
Muggli, Patric; Blue, Brent; Clayton, Chris; Decker, Franz-Joseph; Hogan, Mark; Hunag, Chengkun; Joshi, Chan; Katsouleas, Tom; Lu, Wei; Mori, Warren; O'Connell, Caollionn; Siemann, Robert; Walz, Dieter; Zhou, Miaomiao
2008-04-01
Electron beams with density larger than the plasma density can propagate through plasmas without significant emittance growth. The electron beam expels the plasma electrons from the bunch volume and propagate in a pure, uniform ion column. In contrast, positron beams attract plasma electrons that flow through the positron bunch. As a result the plasma focusing force is nonlinear, a charge halo forms around the bunch, and the bunch emittance grows. After some distance into the plasma, the bunch emittance reaches an approximately constant value, and the beam and the plasma focusing force reach a steady state. Experimental results obtained with electron and positron bunches, as well as numerical simulation results will be presented.
Photonic, Electronic and Atomic Collisions
NASA Astrophysics Data System (ADS)
Fainstein, Pablo D.; Lima, Marco Aurelio P.; Miraglia, Jorge E.; Montenegro, Eduardo C.; Rivarola, Roberto D.
2006-11-01
Plenary. Electron collisions - past, present and future / J. W. McConkey. Collisions of slow highly charged ions with surfaces / J. Burgdörfer ... [et al.]. Atomic collisions studied with "reaction-microscopes" / R. Moshammer ... [et al.]. Rydberg atoms: a microscale laboratory for studying electron-molecule tnteractions / F. B. Dunning -- Collisions involvintg photons. Quantum control of photochemical reaction dynamics and molecular functions / M. Yamaki ... [et al.]. Manipulating and viewing Rydberg wavepackets / R. R. Jones. Angle-resolved photoelectrons as a probe of strong-field interactions / M. Vrakking. Ultracold Rydberg atoms in a structured environment / I. C. H. Liu and J. M. Rost. Synchrotron-radiation-based recoil ion momentum spectroscopy of laser cooled and trapped cesium atoms / L. H. Coutinho. Reconstruction of attosecond pulse trains / Y. Mairesse ... [et al.]. Selective excitation of metastable atomic states by Femto- and attosecond laser pulses / A. D. Kondorskiy. Accurate calculations of triple differential cross sections for double photoionization of the hygrogen molecule / W. Vanroose ... [et al.]. Double and triple photoionization of Li and Be / J. Colgan, M. S. Pindzola and F. Robicheaux. Few/many body dynamics in strong laser fields / J. Zanghellini and T. Brabec. Rescattering-induced effects in electron-atom scattering in the presence of a circularly polarized laser field / A. V. Flegel ... [et al.]. Multidimensional photoelectron spectroscopy / P. Lablanquie ... [et al.]. Few photon and strongly driven transitions in the XUV and beyond / P. Lambropoulos, L. A. A. Nikolopoulos and S. I. Themelis. Ionization dynamics of atomic clusters in intense laser pulses / U. Saalmann and J. M. Rost. On the second order autocorrelation of an XUV attosecond pulse train / E. P. Benis ... [et al.]. Evidence for rescattering in molecular dissociation / I. D. Williams ... [et al.]. Photoionizing ions using synchrotron radiation / R. Phaneuf. Photo double
Properties of the electron cloud in a high-energy positron and electron storage ring
Harkay, K. C.; Rosenberg, R. A.
2003-03-20
Low-energy, background electrons are ubiquitous in high-energy particle accelerators. Under certain conditions, interactions between this electron cloud and the high-energy beam can give rise to numerous effects that can seriously degrade the accelerator performance. These effects range from vacuum degradation to collective beam instabilities and emittance blowup. Although electron-cloud effects were first observed two decades ago in a few proton storage rings, they have in recent years been widely observed and intensely studied in positron and proton rings. Electron-cloud diagnostics developed at the Advanced Photon Source enabled for the first time detailed, direct characterization of the electron-cloud properties in amore » positron and electron storage ring. From in situ measurements of the electron flux and energy distribution at the vacuum chamber wall, electron-cloud production mechanisms and details of the beam-cloud interaction can be inferred. A significant longitudinal variation of the electron cloud is also observed, due primarily to geometrical details of the vacuum chamber. Furthermore, such experimental data can be used to provide realistic limits on key input parameters in modeling efforts, leading ultimately to greater confidence in predicting electron-cloud effects in future accelerators.« less
Properties of the electron cloud in a high-energy positron and electron storage ring
Harkay, K. C.; Rosenberg, R. A.
2003-03-20
Low-energy, background electrons are ubiquitous in high-energy particle accelerators. Under certain conditions, interactions between this electron cloud and the high-energy beam can give rise to numerous effects that can seriously degrade the accelerator performance. These effects range from vacuum degradation to collective beam instabilities and emittance blowup. Although electron-cloud effects were first observed two decades ago in a few proton storage rings, they have in recent years been widely observed and intensely studied in positron and proton rings. Electron-cloud diagnostics developed at the Advanced Photon Source enabled for the first time detailed, direct characterization of the electron-cloud properties in a positron and electron storage ring. From in situ measurements of the electron flux and energy distribution at the vacuum chamber wall, electron-cloud production mechanisms and details of the beam-cloud interaction can be inferred. A significant longitudinal variation of the electron cloud is also observed, due primarily to geometrical details of the vacuum chamber. Furthermore, such experimental data can be used to provide realistic limits on key input parameters in modeling efforts, leading ultimately to greater confidence in predicting electron-cloud effects in future accelerators.
Doppler broadening of in-flight positron annihilation radiation due to electron momentum.
Hunt, A W; Cassidy, D B; Sterne, P A; Cowan, T E; Howell, R H; Lynn, K G; Golevchenko, J A
2001-06-11
We report the first observation of electron momentum contributions to the Doppler broadening of radiation produced by in-flight two-photon annihilation in solids. In these experiments an approximately 2.5 MeV positron beam impinged on thin polyethylene, aluminum, and gold targets. Since energetic positrons easily penetrate the nuclear Coulomb potential and do not cause a strong charge polarization, the experimental annihilation line shapes agree well with calculations based on a simple independent-particle model. Moreover, annihilations with the deepest core electrons are greatly enhanced.
Coherent combs of antimatter from nonlinear electron-positron-pair creation
NASA Astrophysics Data System (ADS)
Krajewska, K.; Kamiński, J. Z.
2014-11-01
Electron-positron-pair creation in collisions of a modulated laser pulse with a high-energy photon (nonlinear Breit-Wheeler process) is studied by means of strong-field quantum electrodynamics. It is shown that the driving pulse modulations lead to the appearance of comb structures in the energy spectra of produced positrons (electrons). It is demonstrated that these combs result from a coherent enhancement of probability amplitudes of pair creation from different modulations of the laser pulse, thus resembling the Young-type double-slit experiment for antimatter (matter) waves.
POsitron Electron Magnet Spectrometer (POEMS) for the Eos Mission
NASA Technical Reports Server (NTRS)
Evenson, Paul; Wefel, John P.; Guzik, T. G.; Swordy, Simon; Streitmatter, Robert; Barbier, Louis; Ormes, Jonathan; Ramaty, Reuven; Reames, Donald; Salamon, Michael
1990-01-01
The scientific objectives of the POsitron Electron Magnet Spectrometer (POEMS) experiment are briefly reviewed. These include determining the origin of primary positrons and studying particle confinement in the Galaxy, solar modulation, solar flares, the geospace environment, and atmospheric physics and chemistry. The design of the POEMS instrument is summarized.
Scattering of positrons and electrons by alkali atoms
NASA Technical Reports Server (NTRS)
Stein, T. S.; Kauppila, W. E.; Kwan, C. K.; Lukaszew, R. A.; Parikh, S. P.; Wan, Y. J.; Zhou, S.; Dababneh, M. S.
1990-01-01
Absolute total scattering cross sections (Q sub T's) were measured for positrons and electrons colliding with sodium, potassium, and rubidium in the 1 to 102 eV range, using the same apparatus and experimental approach (a beam transmission technique) for both projectiles. The present results for positron-sodium and -rubidium collisions represent the first Q sub T measurements reported for these collision systems. Features which distinguish the present comparisons between positron- and electron-alkali atom Q sub T's from those for other atoms and molecules (room-temperature gases) which have been used as targets for positrons and electrons are the proximity of the corresponding positron- and electron-alkali atom Q sub T's over the entire energy range of overlap, with an indication of a merging or near-merging of the corresponding positron and electron Q sub T's near (and above) the relatively low energy of about 40 eV, and a general tendency for the positron-alkali atom Q sub T's to be higher than the corresponding electron values as the projectile energy is decreased below about 40 eV.
Neutrino, gamma-ray, electron, and positron production in an ultrarelativistic plasma
NASA Technical Reports Server (NTRS)
Marscher, A. P.; Vestrand, W. T.; Scott, J. S.
1980-01-01
Neutrino, gamma-ray, electron and positron production resulting from inelastic proton-proton collisions in a highly relativistic plasma such as may exist in extragalactic radio or gamma-ray burst sources is examined. The source functions of primary (pions, kaons, and neutrons) and secondary (photons, electrons, positrons and neutrinos) products of relativistic nuclear collisions are computed for the cases of power law and Maxwellian relativistic proton distributions. It is shown that in plasma which is optically thin to interactions between the plasma and secondary gamma-rays, electrons and positrons, only a small fraction of the initial energy is emitted in the observable form of neutrinos and gamma rays. In an optically thick plasma on the other hand, most of the energy of the relativistic protons is found to be equally divided between gamma rays and neutrinos, although only the neutrinos may escape freely to be observed.
Extracting the Size of the Cosmic Electron-Positron Anomaly
NASA Astrophysics Data System (ADS)
Auchettl, Katie; Balazs, C.
2011-09-01
Over the last few decades, numerous observations have hinted at an excess of high energy positrons in our locality. The most recent of these experiments has been the positron fraction measured by the PAMELA satellite and the electron plus positron spectrum as measured by the Fermi-LAT satellite. Since the release of these measurements, there have been a plethora of papers where authors invoke new physics ranging from, modification of the cosmic ray propagation, supernova remnants and dark matter annihilation. Using a Bayesian likelihood analysis, we isolate the anomalous contribution of the cosmic electron-positron flux. A significant tension was found between the electron positron related data and non-electron-positron cosmic ray fluxes. Using 219 recent cosmic ray datum, we extracted the preferred values of the selected cosmic ray propagation parameters from the non-electron-positron related measurements. Based on these parameter values we calculated background predictions with uncertainties for PAMELA and Fermi-LAT. We found a deviation between the PAMELA and Fermi-LAT data and the predicted background even when uncertainties, including systematics, were taken into account. Interpreting this as a hint of new physics, we subtracted the background from the data extracting the size, shape and uncertainty of the anomalous contribution in a model independent fashion. We briefly compared the extracted signal to some theoretical results predicting such an anomaly.
Electron Photon Interaction Cross Sections
2014-11-01
Version 00 The Electron Photon Interaction Cross Sections, EPICS, provides the atomic data needed to perform coupled Electron-Photon transport calculations, to produce accurate macroscopic results, such as energy deposit and dose. Atomic data is provided for elements, Z = 1 to 100, over the energy range 10 eV to 100 GeV; note that nuclear data, such as photo-nuclear, and data for compounds, are not included. All data is in a simple computer independent text formatmore » that is standard and presented to a high precision that can be easily read by computer codes written in any computer language, e.g., C, C++, and FORTRAN. EPICS includes four separate data bases that are designed to be used in combination, these include, The Evaluated Electron Data Library (EEDL), to describe the interaction of electrons with matter. The Evaluated Photon Data Library (EPDL), to describe the interaction of photons with matter. The Evaluated Atomic Data Library (EADL), to describe the emission of electrons and photons back to neutrality following an ionizing event, caused by either electron or photon interactions. The Evaluated Excitation Data Library (EXDL), to describe the excitation of atoms due to photon interaction. All of these are available in the Extended ENDL format (ENDLX) in which the evaluations were originally performed. The first three are also available in the ENDF format; as yet ENDF does not include formats to handle excitation data (EXDL).« less
Electron Photon Interaction Cross Sections
Cullen, D. E.
2014-11-01
Version 00 The Electron Photon Interaction Cross Sections, EPICS, provides the atomic data needed to perform coupled Electron-Photon transport calculations, to produce accurate macroscopic results, such as energy deposit and dose. Atomic data is provided for elements, Z = 1 to 100, over the energy range 10 eV to 100 GeV; note that nuclear data, such as photo-nuclear, and data for compounds, are not included. All data is in a simple computer independent text format that is standard and presented to a high precision that can be easily read by computer codes written in any computer language, e.g., C, C++, and FORTRAN. EPICS includes four separate data bases that are designed to be used in combination, these include, The Evaluated Electron Data Library (EEDL), to describe the interaction of electrons with matter. The Evaluated Photon Data Library (EPDL), to describe the interaction of photons with matter. The Evaluated Atomic Data Library (EADL), to describe the emission of electrons and photons back to neutrality following an ionizing event, caused by either electron or photon interactions. The Evaluated Excitation Data Library (EXDL), to describe the excitation of atoms due to photon interaction. All of these are available in the Extended ENDL format (ENDLX) in which the evaluations were originally performed. The first three are also available in the ENDF format; as yet ENDF does not include formats to handle excitation data (EXDL).
Electromagnetic solitary pulses in a magnetized electron-positron plasma
Shukla, P. K.; Eliasson, B.; Stenflo, L.
2011-03-15
A theory for large amplitude compressional electromagnetic solitary pulses in a magnetized electron-positron (e-p) plasma is presented. The pulses, which propagate perpendicular to the external magnetic field, are associated with the compression of the plasma density and the wave magnetic field. Here the solitary wave magnetic field pressure provides the restoring force, while the inertia comes from the equal mass electrons and positrons. The solitary pulses are formed due to a balance between the compressional wave dispersion arising from the curl of the inertial forces in Faraday's law and the nonlinearities associated with the divergence of the electron and positron fluxes, the nonlinear Lorentz forces, the advection of the e-p fluids, and the nonlinear plasma current densities. The compressional solitary pulses can exist in a well-defined speed range above the Alfven speed. They can be associated with localized electromagnetic field excitations in magnetized laboratory and space plasmas composed of electrons and positrons.
Progress toward positron-electron pair plasma experiments
Stenson, E. V.; Stanja, J.; Hergenhahn, U.; Saitoh, H.; Niemann, H.; Pedersen, T. Sunn; Marx, G. H.; Schweikhard, L.; Danielson, J. R.; Surko, C. M.; Hugenschmidt, C.
2015-06-29
Electron-positron plasmas have been of theoretical interest for decades, due to the unique plasma physics that arises from all charged particles having precisely identical mass. It is only recently, though, that developments in non-neutral plasma physics (both in linear and toroidal geometries) and in the flux of sources for cold positrons have brought the goal of conducting electron-positron pair plasma experiments within reach. The APEX/PAX collaboration is working on a number of projects in parallel toward that goal; this paper provides an overview of recent, current, and upcoming activities.
Dressed solitons in quantum electron-positron-ion plasmas
NASA Astrophysics Data System (ADS)
Chatterjee, Prasanta; Roy, Kaushik; Mondal, Ganesh; Muniandy, S. V.; Yap, S. L.; Wong, C. S.
2009-12-01
Nonlinear propagation of quantum ion acoustic waves in a dense quantum plasma whose constituents are electrons, positrons, and positive ions is investigated using a quantum hydrodynamic model. The Korteweg-de Vries equation is derived using reductive perturbation technique. The higher order inhomogeneous differential equation is obtained for the dressed soliton. The dynamical equation for dressed soliton is solved using the renormalization method. The conditions for the validity of the higher order correction are described. The effects of quantum parameter, positron concentration, electron to positron Fermi temperature ratio, and soliton velocity on the amplitude and width of the dressed soliton are studied.
Electron positron pair production at RHIC and LHC
Cem Gueclue, M.
2008-11-11
The STAR Collaboration at the Relativistic Heavy Ion Collider present data on electron-positron pair production accompanied by nuclear breakup at small impact parameters where the simultaneous excitation of the two ions, mainly the giant dipole resonance GDR, can occur. We calculate the electron-positron pair production cross section relevant for the STAR experimental setup, and compare our results with the other calculations. We have also predictions for the LHC energies.
Neutrino annihilation of an electron-positron pair
Samsonenko, N.V.; Lal, K.C.
1987-01-01
In this study the authors carry out the analysis of the differential cross sections of the electron-positron pair annihilation process by simultaneously taking into account the spin effects, the interference of the charged and neutral currents, and also the possible nonzero neutrino rest mass. The differential cross sections are calculated in the COM system to first order in the weak interaction coupling constant with arbitrary electron and positron spin orientations and arbitrary neutrino and antineutrino polarizations.
NASA Astrophysics Data System (ADS)
Koehn, Christoph; Ebert, Ute
2015-04-01
Thunderstorms can emit high-energy particles, photons with energies of up to at least 40 MeV, leptons (electrons, positrons) and hadrons (neutrons and protons) with energies of tens of MeV. Some of these events have been correlated with negative lightning leaders propagating upwards in the cloud. For particular lightning events we show that photons, leptons and hadrons can reach ground altitude as well as satellite altitude, and we present the number as well as the spatial and energy distribution of photons, leptons and hadrons. We have reviewed the latest literature on cross sections for collisions of photons, leptons and hadrons with air molecules and have implemented them in our Monte Carlo code. We initialize a photon beam with the characteristic energy distribution of a TGF at thunderstorm altitude and we use the Monte Carlo model to trace these photons; we include the production of secondary electrons through photoionization, Compton scattering and pair production, the production of positrons through pair production as well as the production of neutrons and protons through photonuclear processes. Subsequently we calculate the motion and energy dissipation of these leptons and hadrons with the feedback of electrons and positrons producing new photons through Bremsstrahlung and through positron annihilation at shell electrons. Additionally we provide analytic estimates for the energy losses of photons, leptons and hadrons in the energy range between 0.03 eV and 100 MeV based on the relevant cross sections. We provide the spectral analysis of how many photons, leptons and hadrons will reach ground or satellite altitude and what their energies are, depending on the initial photon energy. This is of particular interest because of campaigns measuring fluxes of all these species at 0 and 500 km altitude without knowing the actual energies of initial electrons converting into photons within a thundercloud.
Three-wave coupling in electron-positron-ion plasmas
Tinakiche, N.; Annou, R.; Tripathi, V. K.
2012-07-15
The three-wave coupling processes in electron-positron-ion plasmas are investigated. The non-linear dispersion relation is derived along with the non-linear growth rate in both resonant and non resonant processes. It is shown that the inclusion of positron affects the dielectric properties of the plasma as well as the nonlinear growth rates of parametric processes. As one increases the positron density to electron density ratio from 0 to 1, maintaining quasi neutrality of the plasma, the growth rates of stimulated Raman, Brillouin, and Compton scattering processes in an isothermal plasma tend to zero due to the ponderomotive forces acting on electrons and positrons due the pump and scattered waves being equal.
Positron creation and annihilation in tokamak plasmas with runaway electrons.
Helander, P; Ward, D J
2003-04-01
It is shown that electron-positron pair production is expected to occur in post-disruption plasmas in large tokamaks, including JET and JT-60U, where up to about 10(14) positrons may be created in collisions between multi-MeV runaway electrons and thermal particles. If the loop voltage is large enough, they are accelerated and form a beam of long-lived runaway positrons in the direction opposite to that of the electrons; if the loop voltage is smaller, the positrons have a lifetime of a few hundred ms, in which they are slowed down to energies comparable to that of the cool ( less, similar 10 eV) background plasma before being annihilated.
PEPPo: Using a Polarized Electron Beam to Produce Polarized Positrons
Adeyemi, Adeleke H.
2015-09-01
Polarized positron beams have been identified as either an essential or a significant ingredient for the experimental program of both the present and next generation of lepton accelerators (JLab, Super KEK B, ILC, CLIC). An experiment demonstrating a new method for producing polarized positrons has been performed at the Continuous Electron Beam Accelerator Facility at Jefferson Lab. The PEPPo (Polarized Electrons for Polarized Positrons) concept relies on the production of polarized e⁻/e⁺ pairs from the bremsstrahlung radiation of a longitudinally polarized electron beam interacting within a high-Z conversion target. PEPPo demonstrated the effective transfer of spin-polarization of an 8.2 MeV/c polarized (P~85%) electron beam to positrons produced in varying thickness tungsten production targets, and collected and measured in the range of 3.1 to 6.2 MeV/c. In comparison to other methods this technique reveals a new pathway for producing either high-energy or thermal polarized positron beams using a relatively low polarized electron beam energy (~10MeV) .This presentation will describe the PEPPo concept, the motivations of the experiment and high positron polarization achieved.
NASA Astrophysics Data System (ADS)
Kawanaka, Norita
2011-02-01
We investigate the observed spectrum of cosmic-ray electrons and positrons from astrophysical sources, especially pulsars, and the physical processes for making the spectrum spiky or smooth via continuous and multiple cosmic-ray injections. We find that (1) the average spectrum with the local birth rate of pulsars (including the off-axis ones) is relatively smooth, consistent with the PAMELA data, but requires an energetic source for the ATIC/PPB-BETS peak. Such a source should not occur repeatedly at the same rate. (2) A continuous injection produces a broad peak and a high energy tail above the peak, which can constrain the source duration (≲ 105 years with the current data). We also discuss the H.E.S.S. data in the TeV range which constrain the total energy of young sources.
Interpretation of AMS-02 electrons and positrons data
Mauro, M. Di; Donato, F.; Fornengo, N.; Vittino, A.; Lineros, R. E-mail: donato@to.infn.it E-mail: rlineros@ific.uv.es
2014-04-01
We perform a combined analysis of the recent AMS-02 data on electrons, positrons, electrons plus positrons and positron fraction, in a self-consistent framework where we realize a theoretical modeling of all the astrophysical components that can contribute to the observed fluxes in the whole energy range. The primary electron contribution is modeled through the sum of an average flux from distant sources and the fluxes from the local supernova remnants in the Green catalog. The secondary electron and positron fluxes originate from interactions on the interstellar medium of primary cosmic rays, for which we derive a novel determination by using AMS-02 proton and helium data. Primary positrons and electrons from pulsar wind nebulae in the ATNF catalog are included and studied in terms of their most significant (while loosely known) properties and under different assumptions (average contribution from the whole catalog, single dominant pulsar, a few dominant pulsars). We obtain a remarkable agreement between our various modeling and the AMS-02 data for all types of analysis, demonstrating that the whole AMS-02 leptonic data admit a self-consistent interpretation in terms of astrophysical contributions.
Positron annihilation in flight
NASA Astrophysics Data System (ADS)
Tudor Jones, Goronwy
1999-09-01
In this resource article, an exceptional bubble chamber picture - showing the annihilation of a positron (antielectron e+ ) in flight - is discussed in detail. Several other esoteric phenomena (some not easy to show on their own!) also manifest themselves in this picture - pair creation or the materialization of a high energy photon into an electron-positron pair; the `head-on' collision of a positron with an electron, from which the mass of the positron can be estimated; the Compton Effect ; an example of the emission of electromagnetic radiation (photons) by accelerating charges (bremsstrahlung ).
Saha, Asit E-mail: prasantachatterjee1@rediffmail.com; Pal, Nikhil; Chatterjee, Prasanta E-mail: prasantachatterjee1@rediffmail.com
2014-10-15
The dynamic behavior of ion acoustic waves in electron-positron-ion magnetoplasmas with superthermal electrons and positrons has been investigated in the framework of perturbed and non-perturbed Kadomtsev-Petviashili (KP) equations. Applying the reductive perturbation technique, we have derived the KP equation in electron-positron-ion magnetoplasma with kappa distributed electrons and positrons. Bifurcations of ion acoustic traveling waves of the KP equation are presented. Using the bifurcation theory of planar dynamical systems, the existence of the solitary wave solutions and the periodic traveling wave solutions has been established. Two exact solutions of these waves have been derived depending on the system parameters. Then, using the Hirota's direct method, we have obtained two-soliton and three-soliton solutions of the KP equation. The effect of the spectral index κ on propagations of the two-soliton and the three-soliton has been shown. Considering an external periodic perturbation, we have presented the quasi periodic behavior of ion acoustic waves in electron-positron-ion magnetoplasmas.
Positron generation using laser-wakefield electron sources
Williams, G. J. Park, J.; Pollock, B. B.; Albert, F.; Chen, Hui
2015-09-15
Positron generation, using wakefield-accelerated electrons driven into a converter target, was investigated experimentally and through Monte Carlo simulations. Using experimentally measured initial electron distributions from a 60 fs laser system, modeling shows that a collimated wakefield electron beam of moderate energy (50–200 MeV) produces a large number of positrons (∼10{sup 7}), which are emitted from the rear of a mm-scale, high-Z target with divergence angles between 50 and 150 mrad. The large perpendicular momentum of the positrons was found to be dominated by contributions from multiple small angle Coulomb scattering. Positrons were not observed above background noise for a range of targets where simulations indicate a 5–30× increase in the beam charge was necessary to exceed threshold detection. These results provide new understanding to the fundamental limitations of creating narrow-divergence, high-density positron beams from laser-wakefield platforms for use in future laboratory pair plasma experiments.
Positron Production Using a Laser-Wakefield Electron Source
NASA Astrophysics Data System (ADS)
Williams, G. Jackson; Albert, Felicie; Chen, Hui; Park, Jaebum; Pollock, Bradley
2014-10-01
Positron generation using wakefield-accelerated electrons driven into a second mm-scale target was investigated using the Callisto Laser at the Jupiter Laser Facility at Lawrence Livermore National Laboratory. This technique is in contrast to previous experiments that use direct laser-target interactions to create positron-electron pairs, and has the potential to make laser-produced positron sources widely available to smaller scale laboratories. Monte Carlo simulations show a near-collimated (<10 mrad) wakefield electron beam produces a positron beam with a significantly larger divergence angle (>100 mrad) due to multiple small angle coulomb scattering, resulting in an emitted pair density of 1013 particles/cm3. At the Callisto Laser, we did not observe a signal consistent with positrons using two different charged particle spectrometers. This could be due to a high noise environment and a large detection threshold. This work was performed under the auspices of the U.S. Department of Energy (DOE) by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and funded by the LLNL LDRD program under tracking code 13-LW-076 and 12-ERD-062.
Program EPICP: Electron photon interaction code, photon test module. Version 94.2
Cullen, D.E.
1994-09-01
The computer code EPICP performs Monte Carlo photon transport calculations in a simple one zone cylindrical detector. Results include deposition within the detector, transmission, reflection and lateral leakage from the detector, as well as events and energy deposition as a function of the depth into the detector. EPICP is part of the EPIC (Electron Photon Interaction Code) system. EPICP is designed to perform both normal transport calculations and diagnostic calculations involving only photons, with the objective of developing optimum algorithms for later use in EPIC. The EPIC system includes other modules that are designed to develop optimum algorithms for later use in EPIC; this includes electron and positron transport (EPICE), neutron transport (EPICN), charged particle transport (EPICC), geometry (EPICG), source sampling (EPICS). This is a modular system that once optimized can be linked together to consider a wide variety of particles, geometries, sources, etc. By design EPICP only considers photon transport. In particular it does not consider electron transport so that later EPICP and EPICE can be used to quantitatively evaluate the importance of electron transport when starting from photon sources. In this report I will merely mention where we expect the results to significantly differ from those obtained considering only photon transport from that obtained using coupled electron-photon transport.
NASA Technical Reports Server (NTRS)
Gould, R. J.; Rephaeli, Y.
1978-01-01
The effective average energy loss for an energetic (at least about 10 to the 15th power eV) particle traversing the microwave background radiation is evaluated. Electron-photon transformations by Compton scattering and pair production (in photon-photon collisions) are computed, with the energy loss considered to be carried away by the least energetic of the outgoing particles. Considering the most energetic of the outgoing particles as the high-energy particle, the relative probability and mean time for the particle to be a photon or electron (or positron) is evaluated. The effects of synchrotron losses for electrons and positrons are emphasized and compared with Compton losses to determine a critical energy (for given magnetic field) above which synchrotron losses dominate. Magnetic deflections are also treated for the case where the magnetic field is disordered, having a characteristic 'cell' size.
NASA Astrophysics Data System (ADS)
Zhang, Wen-Shuai; Gu, Bing-Chuan; Han, Xiao-Xi; Liu, Jian-Dang; Ye, Bang-Jiao
2015-10-01
We make a gradient correction to a new local density approximation form of positron-electron correlation. The positron lifetimes and affinities are then probed by using these two approximation forms based on three electronic-structure calculation methods, including the full-potential linearized augmented plane wave (FLAPW) plus local orbitals approach, the atomic superposition (ATSUP) approach, and the projector augmented wave (PAW) approach. The differences between calculated lifetimes using the FLAPW and ATSUP methods are clearly interpreted in the view of positron and electron transfers. We further find that a well-implemented PAW method can give near-perfect agreement on both the positron lifetimes and affinities with the FLAPW method, and the competitiveness of the ATSUP method against the FLAPW/PAW method is reduced within the best calculations. By comparing with the experimental data, the new introduced gradient corrected correlation form is proved to be competitive for positron lifetime and affinity calculations. Project supported by the National Natural Science Foundation of China (Grant Nos. 11175171 and 11105139).
QCD tests in electron-positron scattering
Maruyama, T.
1995-11-01
Recent results on QCD tests at the Z{sup o} resonance are described. Measurements of Color factor ratios, and studies of final state photon radiation are performed by the LEP experiments. QCD tests using a longitudinally polarized beam are reported by the SLD experiment.
Taira, Y.; Toyokawa, H.; Kuroda, R.; Yamamoto, N.; Adachi, M.; Tanaka, S.; Katoh, M.
2013-05-15
High-energy ultrashort gamma-ray pulses can be generated via laser Compton scattering with 90 Degree-Sign collisions at the UVSOR-II electron storage ring. As an applied study of ultrashort gamma-ray pulses, a new photon-induced positron annihilation lifetime spectroscopy approach has been developed. Ultrashort gamma-ray pulses with a maximum energy of 6.6 MeV and pulse width of 2.2 ps created positrons throughout bulk lead via pair production. Annihilation gamma rays were detected by a BaF{sub 2} scintillator mounted on a photomultiplier tube. A positron lifetime spectrum was obtained by measuring the time difference between the RF frequency of the electron storage ring and the detection time of the annihilation gamma rays. We calculated the response of the BaF{sub 2} scintillator and the time jitter caused by the variation in the total path length of the ultrashort gamma-ray pulses, annihilation gamma rays, and scintillation light using a Monte Carlo simulation code. The positron lifetime for bulk lead was successfully measured.
On-ground detection of an electron-positron annihilation line from thunderclouds.
Umemoto, D; Tsuchiya, H; Enoto, T; Yamada, S; Yuasa, T; Kawaharada, M; Kitaguchi, T; Nakazawa, K; Kokubun, M; Kato, H; Okano, M; Tamagawa, T; Makishima, K
2016-02-01
Thunderclouds can produce bremsstrahlung gamma-ray emission, and sometimes even positrons. At 00:27:00 (UT) on 13 January 2012, an intense burst of gamma rays from a thundercloud was detected by the GROWTH experiment, located in Japan, facing the Sea of Japan. The event started with a sharp gamma-ray flash with a duration of <300 ms coincident with an intracloud discharge, followed by a decaying longer gamma-ray emission lasting for ∼60 s. The spectrum of this prolonged emission reached ∼10 MeV, and contained a distinct line emission at 508±3(stat.)±5(sys.) keV, to be identified with an electron-positron annihilation line. The line was narrow within the instrumental energy resolution (∼80keV), and contained 520±50 photons which amounted to ∼10% of the total signal photons of 5340±190 detected over 0.1-10 MeV. As a result, the line equivalent width reached 280±40 keV, which implies a nontrivial result. The result suggests that a downward positron beam produced both the continuum and the line photons. PMID:26986281
On-ground detection of an electron-positron annihilation line from thunderclouds.
Umemoto, D; Tsuchiya, H; Enoto, T; Yamada, S; Yuasa, T; Kawaharada, M; Kitaguchi, T; Nakazawa, K; Kokubun, M; Kato, H; Okano, M; Tamagawa, T; Makishima, K
2016-02-01
Thunderclouds can produce bremsstrahlung gamma-ray emission, and sometimes even positrons. At 00:27:00 (UT) on 13 January 2012, an intense burst of gamma rays from a thundercloud was detected by the GROWTH experiment, located in Japan, facing the Sea of Japan. The event started with a sharp gamma-ray flash with a duration of <300 ms coincident with an intracloud discharge, followed by a decaying longer gamma-ray emission lasting for ∼60 s. The spectrum of this prolonged emission reached ∼10 MeV, and contained a distinct line emission at 508±3(stat.)±5(sys.) keV, to be identified with an electron-positron annihilation line. The line was narrow within the instrumental energy resolution (∼80keV), and contained 520±50 photons which amounted to ∼10% of the total signal photons of 5340±190 detected over 0.1-10 MeV. As a result, the line equivalent width reached 280±40 keV, which implies a nontrivial result. The result suggests that a downward positron beam produced both the continuum and the line photons.
On-ground detection of an electron-positron annihilation line from thunderclouds
NASA Astrophysics Data System (ADS)
Umemoto, D.; Tsuchiya, H.; Enoto, T.; Yamada, S.; Yuasa, T.; Kawaharada, M.; Kitaguchi, T.; Nakazawa, K.; Kokubun, M.; Kato, H.; Okano, M.; Tamagawa, T.; Makishima, K.
2016-02-01
Thunderclouds can produce bremsstrahlung gamma-ray emission, and sometimes even positrons. At 00:27:00 (UT) on 13 January 2012, an intense burst of gamma rays from a thundercloud was detected by the GROWTH experiment, located in Japan, facing the Sea of Japan. The event started with a sharp gamma-ray flash with a duration of <300 ms coincident with an intracloud discharge, followed by a decaying longer gamma-ray emission lasting for ˜60 s. The spectrum of this prolonged emission reached ˜10 MeV, and contained a distinct line emission at 508 ±3 (stat .)±5 (sys .) keV, to be identified with an electron-positron annihilation line. The line was narrow within the instrumental energy resolution (˜80 keV) , and contained 520 ±50 photons which amounted to ˜10 % of the total signal photons of 5340 ±190 detected over 0.1-10 MeV. As a result, the line equivalent width reached 280 ±40 keV, which implies a nontrivial result. The result suggests that a downward positron beam produced both the continuum and the line photons.
Simulation of tail distributions in electron-positron circular colliders
Irwin, J.
1992-02-01
In addition to the Gaussian shaped core region, particle bunches in electron-positron circular colliders have a rarefied halo region of importance in determining beam lifetimes and backgrounds in particle detectors. A method is described which allows simulation of halo particle distributions.
Search for bound-state electron+positron pair decay
NASA Astrophysics Data System (ADS)
Bosch, F.; Hagmann, S.; Hillenbrand, P.-M.; Lane, G. J.; Litvinov, Yu. A.; Reed, M. W.; Sanjari, M. S.; Stöhlker, Th.; Torilov, S. Yu.; Tu, X. L.; Walke, P. M.
2016-09-01
The heavy ion storage rings coupled to in-flight radioactive-ion beam facilities, namely the ability to produce and store for extended periods of time radioactive nuclides in high atomic charge states, for the searchof yet unobserved decay mode - bound-state electron-positron pair decay.
Resonant generation of an electron–positron pair by two photons to excited Landau levels
Diachenko, M. M. Novak, O. P.; Kholodov, R. I.
2015-11-15
We consider the resonant generation of an electron–positron pair by two polarized photons to arbitrarily low Landau levels. The resonance occurs when the energy of one photon exceeds the one-photon generation threshold, and the energy of the other photon is multiple to the spacing between the levels. The cross section of the process is determined taking into account the spins of particles. The order of magnitude of the cross section is the highest when the magnetic moments of the particles are oriented along the magnetic field.
Production of Highly Polarized Positrons Using Polarized Electrons at MeV Energies
Abbott, D.; Adderley, P.; Adeyemi, A.; Aguilera, P.; Ali, M.; Areti, H.; Baylac, M.; Benesch, J.; Bosson, G.; Cade, B.; et al
2016-05-27
The Polarized Electrons for Polarized Positrons experiment at the injector of the Continuous Electron Beam Accelerator Facility has demonstrated for the first time the efficient transfer of polarization from electrons to positrons produced by the polarized bremsstrahlung radiation induced by a polarized electron beam in a high-Z target. Positron polarization up to 82% have been measured for an initial electron beam momentum of 8.19~MeV/c, limited only by the electron beam polarization. We report that this technique extends polarized positron capabilities from GeV to MeV electron beams, and opens access to polarized positron beam physics to a wide community.
Production of Highly Polarized Positrons Using Polarized Electrons at MeV Energies
NASA Astrophysics Data System (ADS)
Abbott, D.; Adderley, P.; Adeyemi, A.; Aguilera, P.; Ali, M.; Areti, H.; Baylac, M.; Benesch, J.; Bosson, G.; Cade, B.; Camsonne, A.; Cardman, L. S.; Clark, J.; Cole, P.; Covert, S.; Cuevas, C.; Dadoun, O.; Dale, D.; Dong, H.; Dumas, J.; Fanchini, E.; Forest, T.; Forman, E.; Freyberger, A.; Froidefond, E.; Golge, S.; Grames, J.; Guèye, P.; Hansknecht, J.; Harrell, P.; Hoskins, J.; Hyde, C.; Josey, B.; Kazimi, R.; Kim, Y.; Machie, D.; Mahoney, K.; Mammei, R.; Marton, M.; McCarter, J.; McCaughan, M.; McHugh, M.; McNulty, D.; Mesick, K. E.; Michaelides, T.; Michaels, R.; Moffit, B.; Moser, D.; Muñoz Camacho, C.; Muraz, J.-F.; Opper, A.; Poelker, M.; Réal, J.-S.; Richardson, L.; Setiniyaz, S.; Stutzman, M.; Suleiman, R.; Tennant, C.; Tsai, C.; Turner, D.; Ungaro, M.; Variola, A.; Voutier, E.; Wang, Y.; Zhang, Y.; PEPPo Collaboration
2016-05-01
The Polarized Electrons for Polarized Positrons experiment at the injector of the Continuous Electron Beam Accelerator Facility has demonstrated for the first time the efficient transfer of polarization from electrons to positrons produced by the polarized bremsstrahlung radiation induced by a polarized electron beam in a high-Z target. Positron polarization up to 82% have been measured for an initial electron beam momentum of 8.19 MeV /c , limited only by the electron beam polarization. This technique extends polarized positron capabilities from GeV to MeV electron beams, and opens access to polarized positron beam physics to a wide community.
Production of Highly Polarized Positrons Using Polarized Electrons at MeV Energies.
Abbott, D; Adderley, P; Adeyemi, A; Aguilera, P; Ali, M; Areti, H; Baylac, M; Benesch, J; Bosson, G; Cade, B; Camsonne, A; Cardman, L S; Clark, J; Cole, P; Covert, S; Cuevas, C; Dadoun, O; Dale, D; Dong, H; Dumas, J; Fanchini, E; Forest, T; Forman, E; Freyberger, A; Froidefond, E; Golge, S; Grames, J; Guèye, P; Hansknecht, J; Harrell, P; Hoskins, J; Hyde, C; Josey, B; Kazimi, R; Kim, Y; Machie, D; Mahoney, K; Mammei, R; Marton, M; McCarter, J; McCaughan, M; McHugh, M; McNulty, D; Mesick, K E; Michaelides, T; Michaels, R; Moffit, B; Moser, D; Muñoz Camacho, C; Muraz, J-F; Opper, A; Poelker, M; Réal, J-S; Richardson, L; Setiniyaz, S; Stutzman, M; Suleiman, R; Tennant, C; Tsai, C; Turner, D; Ungaro, M; Variola, A; Voutier, E; Wang, Y; Zhang, Y
2016-05-27
The Polarized Electrons for Polarized Positrons experiment at the injector of the Continuous Electron Beam Accelerator Facility has demonstrated for the first time the efficient transfer of polarization from electrons to positrons produced by the polarized bremsstrahlung radiation induced by a polarized electron beam in a high-Z target. Positron polarization up to 82% have been measured for an initial electron beam momentum of 8.19 MeV/c, limited only by the electron beam polarization. This technique extends polarized positron capabilities from GeV to MeV electron beams, and opens access to polarized positron beam physics to a wide community. PMID:27284661
Production of Highly Polarized Positrons Using Polarized Electrons at MeV Energies.
Abbott, D; Adderley, P; Adeyemi, A; Aguilera, P; Ali, M; Areti, H; Baylac, M; Benesch, J; Bosson, G; Cade, B; Camsonne, A; Cardman, L S; Clark, J; Cole, P; Covert, S; Cuevas, C; Dadoun, O; Dale, D; Dong, H; Dumas, J; Fanchini, E; Forest, T; Forman, E; Freyberger, A; Froidefond, E; Golge, S; Grames, J; Guèye, P; Hansknecht, J; Harrell, P; Hoskins, J; Hyde, C; Josey, B; Kazimi, R; Kim, Y; Machie, D; Mahoney, K; Mammei, R; Marton, M; McCarter, J; McCaughan, M; McHugh, M; McNulty, D; Mesick, K E; Michaelides, T; Michaels, R; Moffit, B; Moser, D; Muñoz Camacho, C; Muraz, J-F; Opper, A; Poelker, M; Réal, J-S; Richardson, L; Setiniyaz, S; Stutzman, M; Suleiman, R; Tennant, C; Tsai, C; Turner, D; Ungaro, M; Variola, A; Voutier, E; Wang, Y; Zhang, Y
2016-05-27
The Polarized Electrons for Polarized Positrons experiment at the injector of the Continuous Electron Beam Accelerator Facility has demonstrated for the first time the efficient transfer of polarization from electrons to positrons produced by the polarized bremsstrahlung radiation induced by a polarized electron beam in a high-Z target. Positron polarization up to 82% have been measured for an initial electron beam momentum of 8.19 MeV/c, limited only by the electron beam polarization. This technique extends polarized positron capabilities from GeV to MeV electron beams, and opens access to polarized positron beam physics to a wide community.
Projectile Charge Effects in Differential Ionization by Positrons and Electrons
DuBois, R. D.; Gavin, J.; Lucio, O. G. de
2009-03-10
Differential data for single and double ionization of argon by positron and electron impact are presented and compared. For single ionization, coincidences between scattered projectiles, ejected electrons and recoil ions are measured as functions of the projectile scattering angle and energy loss. Differences associated with the sign of the projectile charge are indicated with regard to the scattering angle, the energy loss, and the relative intensities for binary and recoil events. Ejected electron-recoil ion coincidences are also measured as a function of the observation angle along the beam direction. From these, double to single ionization ratios are determined and compared. Differences in the magnitudes and angular dependences for positron and electron impact are attributed to the interference between the TS-1 and TS-2 double ionization mechanisms.
Pumping Electron-Positron Pairs from a Well Potential
NASA Astrophysics Data System (ADS)
Wang, Qiang; Liu, Jie; Fu, Li-Bin
2016-04-01
In the presence of very deep well potential, electrons will spontaneously occupy the empty embedded bound states and electron-positron pairs are created by means of a non-perturbative tunneling process. In this work, by slowly oscillating the width or depth, the population transfer channels are opened and closed periodically. We find and clearly show that by the non-synchronous ejections of particles, the saturation of pair number in a static super-critical well can be broken, and electrons and positrons can be pumped inexhaustibly from vacuum with a constant production rate. In the adiabatic limit, final pair number after a single cycle has quantized values as a function of the upper boundary of the oscillating, and the critical upper boundaries indicate the diving points of the bound states.
Secondary positrons and electrons in the cosmic radiation
NASA Technical Reports Server (NTRS)
Badhwar, G. D.; Stephens, S. A.
1978-01-01
An improved calculation of the secondary production and equilibrium spectrum of positrons and electrons in the Galaxy in the energy range from 1 MeV to 100 GeV has been performed. This has been done by obtaining an analytic representation of the accelerator data which describes accurately the invariant cross-section of pions, kaons, and their antiparticles from threshold energy to about 1500 GeV. This calculation takes into account the correct angular distribution of electrons in the decay of muons and the effect of nuclei-nuclei collisions. The contributions of beta-decay positrons and knock-on electrons have been included. A comparison of the present calculations with earlier calculations and experiment is presented.
Pumping Electron-Positron Pairs from a Well Potential
Wang, Qiang; Liu, Jie; Fu, Li-bin
2016-01-01
In the presence of very deep well potential, electrons will spontaneously occupy the empty embedded bound states and electron-positron pairs are created by means of a non-perturbative tunneling process. In this work, by slowly oscillating the width or depth, the population transfer channels are opened and closed periodically. We find and clearly show that by the non-synchronous ejections of particles, the saturation of pair number in a static super-critical well can be broken, and electrons and positrons can be pumped inexhaustibly from vacuum with a constant production rate. In the adiabatic limit, final pair number after a single cycle has quantized values as a function of the upper boundary of the oscillating, and the critical upper boundaries indicate the diving points of the bound states. PMID:27125998
The Contribution of Millisecond Pulsars to the Local Electron / Positron Spectrum
NASA Astrophysics Data System (ADS)
Venter, Christo; Buesching, Ingo; Harding, Alice; Kopp, Andreas; Gonthier, Peter
The high energies of gamma-ray photons (as well as the presence of lower-energy photons) coupled with the intense magnetic fields characterizing younger pulsars enable formation of electron-positron pair cascades which fills the pulsar magnetosphere with plasma and also feeds an outflowing particle wind that may create a surrounding pulsar wind nebula (PWN). Although this scenario was originally thought to be unique to the younger pulsar population, Fermi LAT demonstrated that the light curves of millisecond pulsars (MSPs) are generally very similar to those of younger pulsars, requiring copious pair production even for this older class with much lower surface magnetic fields and spin-down power. These pair cascades may thus be a primary source of Galactic electrons and positrons, and may present an astrophysical explanation for the observed enhancement in positron flux in the high-energy band. We investigate Galactic MSPs contribution to the flux of local cosmic-ray electrons and positrons. We use a population synthesis code to predict the source properties (number, position, and power) of the present-day Galactic MSPs, taking into account the latest Fermi observations to calibrate the model output. Next, we simulate pair cascade spectra from these MSPs using a model that invokes an offset-dipole magnetic field, as this increases the pair production rate relative to a standard dipole field geometry. The model source pair spectra may extend to several TeV, depending on pulsar properties, neutron star equation of state, and magnetic polar cap offset. Since MSPs are not surrounded by PWNe or supernova shells, we can assume that the pairs escape from the pulsar environment without energy loss and undergo losses only in the intergalactic medium. We lastly compute the spectrum of the transported electrons and positrons at Earth, following their diffusion and energy loss through the Galaxy. We will compare our results with the observed local interstellar spectrum and
Photonic, Electronic and Atomic Collisions
NASA Astrophysics Data System (ADS)
Fainstein, Pablo D.; Lima, Marco Aurelio P.; Miraglia, Jorge E.; Montenegro, Eduardo C.; Rivarola, Roberto D.
2006-11-01
Plenary. Electron collisions - past, present and future / J. W. McConkey. Collisions of slow highly charged ions with surfaces / J. Burgdörfer ... [et al.]. Atomic collisions studied with "reaction-microscopes" / R. Moshammer ... [et al.]. Rydberg atoms: a microscale laboratory for studying electron-molecule tnteractions / F. B. Dunning -- Collisions involvintg photons. Quantum control of photochemical reaction dynamics and molecular functions / M. Yamaki ... [et al.]. Manipulating and viewing Rydberg wavepackets / R. R. Jones. Angle-resolved photoelectrons as a probe of strong-field interactions / M. Vrakking. Ultracold Rydberg atoms in a structured environment / I. C. H. Liu and J. M. Rost. Synchrotron-radiation-based recoil ion momentum spectroscopy of laser cooled and trapped cesium atoms / L. H. Coutinho. Reconstruction of attosecond pulse trains / Y. Mairesse ... [et al.]. Selective excitation of metastable atomic states by Femto- and attosecond laser pulses / A. D. Kondorskiy. Accurate calculations of triple differential cross sections for double photoionization of the hygrogen molecule / W. Vanroose ... [et al.]. Double and triple photoionization of Li and Be / J. Colgan, M. S. Pindzola and F. Robicheaux. Few/many body dynamics in strong laser fields / J. Zanghellini and T. Brabec. Rescattering-induced effects in electron-atom scattering in the presence of a circularly polarized laser field / A. V. Flegel ... [et al.]. Multidimensional photoelectron spectroscopy / P. Lablanquie ... [et al.]. Few photon and strongly driven transitions in the XUV and beyond / P. Lambropoulos, L. A. A. Nikolopoulos and S. I. Themelis. Ionization dynamics of atomic clusters in intense laser pulses / U. Saalmann and J. M. Rost. On the second order autocorrelation of an XUV attosecond pulse train / E. P. Benis ... [et al.]. Evidence for rescattering in molecular dissociation / I. D. Williams ... [et al.]. Photoionizing ions using synchrotron radiation / R. Phaneuf. Photo double
Sato, K.; Kobayashi, Y.
2015-05-15
Enhancement of molecular sensitivity in positron emission tomography (PET) has long been discussed with respect to imaging instrumentation and algorithms for data treatment. Here, the molecular sensitivity in PET is discussed on the basis of 2-dimensional coincident measurements of 511 keV γ ray photons resultant from two-photon annihilation. Introduction of an additional selection window based on the energy sum and difference of the coincidently measured γ ray photons, without any significant instrumental and algorithmic changes, showed an improvement in the signal-to-noise ratio (SNR) by an order of magnitude. Improvement of performance characteristics in the PET imaging system was demonstrated by an increase in the noise equivalent count rate (NECR) which takes both the SNR and the detection efficiency into consideration. A further improvement of both the SNR and the NECR is expected for the present system in real clinical and in-vivo environments, where much stronger positron sources are employed.
Sato, K; Kobayashi, Y
2015-05-01
Enhancement of molecular sensitivity in positron emission tomography (PET) has long been discussed with respect to imaging instrumentation and algorithms for data treatment. Here, the molecular sensitivity in PET is discussed on the basis of 2-dimensional coincident measurements of 511 keV γ ray photons resultant from two-photon annihilation. Introduction of an additional selection window based on the energy sum and difference of the coincidently measured γ ray photons, without any significant instrumental and algorithmic changes, showed an improvement in the signal-to-noise ratio (SNR) by an order of magnitude. Improvement of performance characteristics in the PET imaging system was demonstrated by an increase in the noise equivalent count rate (NECR) which takes both the SNR and the detection efficiency into consideration. A further improvement of both the SNR and the NECR is expected for the present system in real clinical and in-vivo environments, where much stronger positron sources are employed.
Towards a Resolution of the Proton Form Factor Problem: New Electron and Positron Scattering Data
Adikaram, D.; Rimal, D.; Weinstein, L. B.; Raue, B.; Khetarpal, P.; Bennett, R.; Arrington, J.; Brooks, W.; Adhikari, K.; Afanasev, A.; et al
2015-02-10
There is a significant discrepancy between the values of the proton electric form factor, GpE, extracted using unpolarized and polarized electron scattering. Calculations predict that small two-photon exchange (TPE) contributions can significantly affect the extraction of GpE from the unpolarized electron-proton cross sections. We determined the TPE contribution by measuring the ratio of positron-proton to electron-proton elastic scattering cross sections using a simultaneous, tertiary electron-positron beam incident on a liquid hydrogen target and detecting the scattered particles in the Jefferson Lab CLAS detector. This novel technique allowed us to cover a wide range in virtual photon polarization (epsilon) and momentummore » transfer (Q2) simultaneously, as well as to cancel luminosity-related systematic errors. The cross section ratio increases with decreasing ε at Q2=1.45 GeV2. This measurement is consistent with the size of the form factor discrepancy at Q2≈1.75 GeV2 and with hadronic calculations including nucleon and Delta intermediate states, which have been shown to resolve the discrepancy up to 2-3 GeV2.« less
Towards a Resolution of the Proton Form Factor Problem: New Electron and Positron Scattering Data
Adikaram, D.; Rimal, D.; Weinstein, L. B.; Raue, B.; Khetarpal, P.; Bennett, R.; Arrington, J.; Brooks, W.; Adhikari, K.; Afanasev, A.; Amaryan, M.; Anderson, M.; Anefalos Pereira, S.; Avakian, H.; Ball, J.; Battaglieri, M.; Bedlinskiy, I.; Biselli, A.; Bono, J.; Boiarinov, S.; Briscoe, W.; Burkert, V.; Carman, D.; Careccia, S.; Celentano, A.; Chandavar, S.; Charles, G.; Colaneri, L.; Cole, P.; Contalbrigo, M.; Crede, V.; D'Angelo, A.; Dashyan, N.; De Vita, R.; De Sanctis, E.; Deur, A.; Djalali, C.; Dodge, G.; Dupre, R.; Egiyan, H.; El Alaoui, A.; El Fassi, L.; Elouadrhiri, L.; Eugenio, P.; Fedotov, G.; Fegan, S.; Filippi, A.; Fleming, J.; Fradi, A.; Garillon, B.; Gilfoyle, G.; Giovanetti, K.; Girod, F.; Goetz, J.; Gohn, W.; Golovatch, E.; Gothe, R.; Griffioen, K.; Guegan, B.; Guidal, M.; Guo, L.; Hafidi, K.; Hakobyan, H.; Hanretty, C.; Harrison, N.; Hattawy, M.; Hicks, K.; Holtrop, M.; Hughes, S.; Hyde, C. E.; Ilieva, Y.; Ireland, D.; Ishkhanov, B.; Jenkins, D.; Jiang, H.; Jo, H.; Joo, K.; Joosten, S.; Kalantarians, N.; Keller, D.; Khandaker, M.; Kim, A.; Kim, W.; Klein, A.; Klein, F.; Koirala, S.; Kubarovsky, V.; Kuhn, S.; Livingston, K.; Lu, H.; MacGregor, I.; Markov, N.; Mattione, P.; Mayer, M.; McKinnon, B.; Mestayer, M.; Meyer, C.; Mirazita, M.; Mokeev, V.; Montgomery, R.; Moody, C.; Moutarde, H.; Movsisyan, A.; Camacho, C. Munoz; Nadel-Turonski, P.; Niccolai, S.; Niculescu, G.; Osipenko, M.; Ostrovidov, A.; Park, K.; Pasyuk, E.; Pisano, S.; Pogorelko, O.; Price, J.; Procureur, S.; Prok, Y.; Protopopescu, D.; Puckett, A.; Ripani, M.; Rizzo, A.; Rosner, G.; Rossi, P.; Roy, P.; Sabati, F.; Salgado, C.; Schott, D.; Schumacher, R.; Seder, E.; Sharabian, Y.; Simonyan, A.; Skorodumina, I.; Smith, E.; Smith, G.; Sober, D.; Sokhan, D.; Sparveris, N.; Stepanyan, S.; Stoler, P.; Strauch, S.; Sytnik, V.; Taiuti, M.; Tian, Ye; Trivedi, A.; Ungaro, M.; Voskanyan, H.; Voutier, E.; Walford, N.; Watts, D.; Wei, X.; Wood, M.; Zachariou, N.; Zana, L.; Zhang, J.; Zhao, Z.; Zonta, I.
2015-02-10
There is a significant discrepancy between the values of the proton electric form factor, GpE, extracted using unpolarized and polarized electron scattering. Calculations predict that small two-photon exchange (TPE) contributions can significantly affect the extraction of GpE from the unpolarized electron-proton cross sections. We determined the TPE contribution by measuring the ratio of positron-proton to electron-proton elastic scattering cross sections using a simultaneous, tertiary electron-positron beam incident on a liquid hydrogen target and detecting the scattered particles in the Jefferson Lab CLAS detector. This novel technique allowed us to cover a wide range in virtual photon polarization (epsilon) and momentum transfer (Q2) simultaneously, as well as to cancel luminosity-related systematic errors. The cross section ratio increases with decreasing ε at Q2=1.45 GeV2. This measurement is consistent with the size of the form factor discrepancy at Q2≈1.75 GeV2 and with hadronic calculations including nucleon and Delta intermediate states, which have been shown to resolve the discrepancy up to 2-3 GeV2.
Towards a resolution of the proton form factor problem: new electron and positron scattering data.
Adikaram, D; Rimal, D; Weinstein, L B; Raue, B; Khetarpal, P; Bennett, R P; Arrington, J; Brooks, W K; Adhikari, K P; Afanasev, A V; Amaryan, M J; Anderson, M D; Anefalos Pereira, S; Avakian, H; Ball, J; Battaglieri, M; Bedlinskiy, I; Biselli, A S; Bono, J; Boiarinov, S; Briscoe, W J; Burkert, V D; Carman, D S; Careccia, S; Celentano, A; Chandavar, S; Charles, G; Colaneri, L; Cole, P L; Contalbrigo, M; Crede, V; D'Angelo, A; Dashyan, N; De Vita, R; De Sanctis, E; Deur, A; Djalali, C; Dodge, G E; Dupre, R; Egiyan, H; El Alaoui, A; El Fassi, L; Elouadrhiri, L; Eugenio, P; Fedotov, G; Fegan, S; Filippi, A; Fleming, J A; Fradi, A; Garillon, B; Gilfoyle, G P; Giovanetti, K L; Girod, F X; Goetz, J T; Gohn, W; Golovatch, E; Gothe, R W; Griffioen, K A; Guegan, B; Guidal, M; Guo, L; Hafidi, K; Hakobyan, H; Hanretty, C; Harrison, N; Hattawy, M; Hicks, K; Holtrop, M; Hughes, S M; Hyde, C E; Ilieva, Y; Ireland, D G; Ishkhanov, B S; Jenkins, D; Jiang, H; Jo, H S; Joo, K; Joosten, S; Kalantarians, N; Keller, D; Khandaker, M; Kim, A; Kim, W; Klein, A; Klein, F J; Koirala, S; Kubarovsky, V; Kuhn, S E; Livingston, K; Lu, H Y; MacGregor, I J D; Markov, N; Mattione, P; Mayer, M; McKinnon, B; Mestayer, M D; Meyer, C A; Mirazita, M; Mokeev, V; Montgomery, R A; Moody, C I; Moutarde, H; Movsisyan, A; Camacho, C Munoz; Nadel-Turonski, P; Niccolai, S; Niculescu, G; Osipenko, M; Ostrovidov, A I; Park, K; Pasyuk, E; Peña, C; Pisano, S; Pogorelko, O; Price, J W; Procureur, S; Prok, Y; Protopopescu, D; Puckett, A J R; Ripani, M; Rizzo, A; Rosner, G; Rossi, P; Roy, P; Sabatié, F; Salgado, C; Schott, D; Schumacher, R A; Seder, E; Sharabian, Y G; Simonyan, A; Skorodumina, I; Smith, E S; Smith, G D; Sober, D I; Sokhan, D; Sparveris, N; Stepanyan, S; Stoler, P; Strauch, S; Sytnik, V; Taiuti, M; Tian, Ye; Trivedi, A; Ungaro, M; Voskanyan, H; Voutier, E; Walford, N K; Watts, D P; Wei, X; Wood, M H; Zachariou, N; Zana, L; Zhang, J; Zhao, Z W; Zonta, I
2015-02-13
There is a significant discrepancy between the values of the proton electric form factor, G(E)(p), extracted using unpolarized and polarized electron scattering. Calculations predict that small two-photon exchange (TPE) contributions can significantly affect the extraction of G(E)(p) from the unpolarized electron-proton cross sections. We determined the TPE contribution by measuring the ratio of positron-proton to electron-proton elastic scattering cross sections using a simultaneous, tertiary electron-positron beam incident on a liquid hydrogen target and detecting the scattered particles in the Jefferson Lab CLAS detector. This novel technique allowed us to cover a wide range in virtual photon polarization (ϵ) and momentum transfer (Q(2)) simultaneously, as well as to cancel luminosity-related systematic errors. The cross section ratio increases with decreasing ϵ at Q(2)=1.45 GeV(2). This measurement is consistent with the size of the form factor discrepancy at Q(2)≈1.75 GeV(2) and with hadronic calculations including nucleon and Δ intermediate states, which have been shown to resolve the discrepancy up to 2-3 GeV(2).
Towards a Resolution of the Proton Form Factor Problem: New Electron and Positron Scattering Data
Adikaram, D.; Rimal, D.; Weinstein, L. B.; Raue, B.; Khetarpal, P.; Bennett, R. P.; Arrington, J.; Brooks, W. K.; Adhikari, K. P.; Afanasev, A. V.; Dupre, R.; El Alaoui, A.; El Fassi, L.; Hafidi, K.; Moody, C. I.
2015-02-10
There is a significant discrepancy between the values of the proton electric form factor, G(E)(p), extracted using unpolarized and polarized electron scattering. Calculations predict that small two-photon exchange (TPE) contributions can significantly affect the extraction of G(E)(p). from the unpolarized electron-proton cross sections. We determined the TPE contribution by measuring the ratio of positron-proton to electron-proton elastic scattering cross sections using a simultaneous, tertiary electron-positron beam incident on a liquid hydrogen target and detecting the scattered particles in the Jefferson Lab CLAS detector. This novel technique allowed us to cover a wide range in virtual photon polarization (epsilon) and momentum transfer (Q(2)) simultaneously, as well as to cancel luminosity-related systematic errors. The cross section ratio increases with decreasing epsilon at Q(2) = 1.45 GeV2. This measurement is consistent with the size of the form factor discrepancy at Q(2) approximate to 1.75 GeV2 and with hadronic calculations including nucleon and Delta intermediate states, which have been shown to resolve the discrepancy up to 2-3 GeV2.
Observation of double electron-positron pair production by {gamma} rays reexamined
Maidana, N. L.; Oliveira, J. R. B.; Rizzutto, M. A.; Added, N.; Vanin, V. R.; Brualla, L.; Fernandez-Varea, J. M.
2009-04-15
An experiment was conducted to observe triple- and quadruple-escape peaks, at a photon energy equal to 6.128 MeV, in the spectra recorded with a high-purity Ge detector working in coincidence with six bismuth germanate detectors. The peak intensities may be explained having recourse to only the bremsstrahlung cascade process of consecutive electron-positron pair creation; i.e., the contribution of simultaneous double pair formation (and other cascade effects) is much smaller. The experimental peak areas are in reasonably good agreement with those predicted by Monte Carlo simulations done with the general-purpose radiation-transport code PENELOPE.
Nonlinear propagation of broadband intense electromagnetic waves in an electron-positron plasma
Marklund, M.; Eliasson, B.; Shukla, P. K.
2006-08-15
A kinetic equation describing the nonlinear evolution of intense electromagnetic pulses in electron-positron (e-p) plasmas is presented. The modulational instability is analyzed for a relativistically intense partially coherent pulse, and it is found that the modulational instability is inhibited by the spectral pulse broadening. A numerical study for the one-dimensional kinetic photon equation is presented. Computer simulations reveal a Fermi-Pasta-Ulam-type recurrence phenomenon for localized broadband pulses. The results should be of importance in understanding the nonlinear propagation of broadband intense electromagnetic pulses in e-p plasmas in laser-plasma systems as well as in astrophysical plasma settings.
Bruno Touschek: From Betatrons to Electron-Positron Colliders
NASA Astrophysics Data System (ADS)
Bernardini, Carlo; Pancheri, Giulia; Pellegrini, Claudio
Bruno Touschek's life as a physicist spanned the period from World War II to the 1970s. He was a key figure in the developments of electron-positron colliders and storage rings, and made important contributions to theoretical high energy physics. Storage rings, initially developed for high energy physics, are being widely used in many countries as synchrotron radiation sources and are a tool for research in physics, chemistry, biology, environmental sciences and cultural heritage studies. We describe Touschek's life in Austria, where he was born, in Germany, where he participated in the construction of a betatron during WWII, and in Italy, where he proposed and led to completion the first electron-positron storage ring in 1960, in Frascati. We highlight how his central European culture influenced his lifestyle and work, and his main contributions to physics, such as the discovery of the Touschek effect and beam instabilities in the larger storage ring ADONE.
Bruno Touschek: From Betatrons to Electron-Positron Colliders
NASA Astrophysics Data System (ADS)
Bernardini, Carlo; Pancheri, Giulia; Pellegrini, Claudio
Bruno Touschek’s life as a physicist spanned the period from World War II to the 1970s. He was a key figure in the developments of electron-positron colliders and storage rings, and made important contributions to theoretical high energy physics. Storage rings, initially developed for high energy physics, are being widely used in many countries as synchrotron radiation sources and are a tool for research in physics, chemistry, biology, environmental sciences and cultural heritage studies. We describe Touschek’s life in Austria, where he was born, in Germany, where he participated in the construction of a betatron during WWII, and in Italy, where he proposed and led to completion the first electron-positron storage ring in 1960, in Frascati. We highlight how his central European culture influenced his lifestyle and work, and his main contributions to physics, such as the discovery of the Touschek effect and beam instabilities in the larger storage ring ADONE.
Collisionless Reconnection in an Electron-Positron Plasma
Bessho, N.; Bhattacharjee, A.
2005-12-09
Electromagnetic particle-in-cell simulations of fast collisionless reconnection in a two-dimensional electron-positron plasma (without an equilibrium guide field) are presented. A generalized Ohm's law in which the Hall current cancels out exactly is given. It is suggested that the key to fast reconnection in this plasma is the localization caused by the off-diagonal components of the pressure tensors, which produce an effect analogous to a spatially localized resistivity.
Electronic and positronic guiding-center drift ions.
Dubin, Daniel H E
2004-05-14
A novel type of guiding-center drift ion is described. These ions occur only in strong magnetic fields. They consist of a neutral atom to which either an electron or positron is weakly bound, at a sufficiently large radius that it may be described by ExB drift dynamics. Such ions may occur naturally in astrophysical plasmas and may have been formed in recent antihydrogen experiments, where their presence would provide proof that deeply bound H atoms are being created.
Electron Cloud in the Wigglers of the Positron Damping Ring of the International Linear Collider
Wang, L.; /SLAC
2007-07-06
The ILC positron damping ring comprises hundreds of meters of wiggler sections, where many more photons than in the arcs are emitted, and with the smallest beampipe aperture of the ring. A significant electron-cloud density can therefore be accumulated via photo-emission and via beam-induced multipacting. In field-free regions the electron-cloud build up may be suppressed by adding weak solenoid fields, but the electron cloud remaining in the wigglers as well as in the arc dipole magnets can still drive single-bunch and multi-bunch beam instabilities. This paper studies the electron-cloud formation in an ILC wiggler section for various scenarios, as well as its character, and possible mitigation schemes.
NASA Astrophysics Data System (ADS)
Ali Shan, S.; El-Tantawy, S. A.
2016-07-01
In this work, we examine the nonlinear propagation of planar ion-acoustic freak waves in an unmagnetized plasma consisting of cold positive ions and superthermal electrons subjected to cold positrons beam. For this purpose, the reductive perturbation method is used to derive a nonlinear Schrödinger equation (NLSE) for the evolution of electrostatic potential wave. We determine the domain of the plasma parameters where the rogue waves exist. The effect of the positron beam on the modulational instability of the ion-acoustic rogue waves is discussed. It is found that the region of the modulational stability is enhanced with the increase of positron beam speed and positron population. Second as positrons beam increases the nonlinearities of the plasma system, large amplitude ion acoustic rogue waves are pointed out. The present results will be helpful in providing a good fit between the theoretical analysis and real applications in future laboratory plasma experiments.
Magnetohydrodynamic spin waves in degenerate electron-positron-ion plasmas
NASA Astrophysics Data System (ADS)
Mushtaq, A.; Maroof, R.; Ahmad, Zulfiaqr; Qamar, A.
2012-05-01
Low frequency magnetosonic waves are studied in magnetized degenerate electron-positron-ion plasmas with spin effects. Using the fluid equations of magnetoplasma with quantum corrections due to the Bohm potential, temperature degeneracy, and spin magnetization energy, a generalized dispersion relation for oblique magnetosonic waves is derived. Spin effects are incorporated via spin force and macroscopic spin magnetization current. For three different values of angle θ, the generalized dispersion relation is reduced to three different relations under the low frequency magnetohydrodynamic assumptions. It is found that the effect of quantum corrections in the presence of positron concentration significantly modifies the dispersive properties of these modes. The importance of the work relevant to compact astrophysical bodies is pointed out.
Magnetohydrodynamic spin waves in degenerate electron-positron-ion plasmas
Mushtaq, A.; Maroof, R.; Ahmad, Zulfiaqr; Qamar, A.
2012-05-15
Low frequency magnetosonic waves are studied in magnetized degenerate electron-positron-ion plasmas with spin effects. Using the fluid equations of magnetoplasma with quantum corrections due to the Bohm potential, temperature degeneracy, and spin magnetization energy, a generalized dispersion relation for oblique magnetosonic waves is derived. Spin effects are incorporated via spin force and macroscopic spin magnetization current. For three different values of angle {theta}, the generalized dispersion relation is reduced to three different relations under the low frequency magnetohydrodynamic assumptions. It is found that the effect of quantum corrections in the presence of positron concentration significantly modifies the dispersive properties of these modes. The importance of the work relevant to compact astrophysical bodies is pointed out.
Threshold for Trapping Positrons in the Wake Driven by a Ultra-relativistic Electron Bunch
Wang, X.; Muggli, P.; Katsouleas, T.; Ischebeck, R.; Hogan, M. J.; Joshi, C.; Mori, W. B.
2009-01-22
We have recently proposed a new concept for generating, injecting and accelerating positrons in a plasma using a double-pulse electron bunch. Monte Carlo simulations show that the number of the positrons produced in a foil target has an exponentially decay energy spectrum. The energy threshold for the trapping of these positrons in a ultra-relativistic electron wake is investigated numerically. For a typical 28.5 GeV electron drive bunch, the trapping threshold for the positrons is a few MeV, and therefore a majority of positrons generated in the foil target are focused and accelerated by the plasma wake.
Spatial wave functions of photon and electron
Khokhlov, D. L.
2010-12-01
The quantum mechanical model of the photon and electron is considered. The photon is conceived of as a particle moving with the speed of light which is accompanied by the wave function of the photon spreading out with an infinite speed. The wave function of the electron is introduced in terms of virtual photons tied to the electron. A description of electrostatic and magnetostatic interactions is given through the wave functions of electrons. The approach provides an explanation of the results of recent experiments measuring the speed of propagation of the bound magnetic field.
Acceleration of positrons by a relativistic electron beam in the presence of quantum effects
Niknam, A. R.; Aki, H.; Khorashadizadeh, S. M.
2013-09-15
Using the quantum magnetohydrodynamic model and obtaining the dispersion relation of the Cherenkov and cyclotron waves, the acceleration of positrons by a relativistic electron beam is investigated. The Cherenkov and cyclotron acceleration mechanisms of positrons are compared together. It is shown that growth rate and, therefore, the acceleration of positrons can be increased in the presence of quantum effects.
Nonlinear electrostatic drift waves in dense electron-positron-ion plasmas
NASA Astrophysics Data System (ADS)
Haque, Q.; Mahmood, S.; Mushtaq, A.
2008-08-01
The Korteweg-de Vries-Burgers (KdVB)-type equation is obtained using the quantum hydrodynamic model in an inhomogeneous electron-positron-ion quantum magnetoplasma with neutral particles in the background. The KdV-type solitary waves, Burgers-type monotonic, and oscillatory shock like solutions are discussed in different limits. The quantum parameter is also dependent on the positron concentration in dense multicomponent plasmas. It is found that both solitary hump and dip are formed and their amplitude and width are dependent on percentage presence of positrons in electron-ion plasmas. The height of the monotonic shock is decreased with the increase of positron concentration and it is independent of the quantum parameter in electron-positron-ion magnetized quantum plasmas. However, the amplitude of the oscillatory shock is dependent on positron concentration and quantum parameter in electron-positron-ion plasmas.
Nonlinear electrostatic drift waves in dense electron-positron-ion plasmas
Haque, Q.; Mahmood, S.; Mushtaq, A.
2008-08-15
The Korteweg-de Vries-Burgers (KdVB)-type equation is obtained using the quantum hydrodynamic model in an inhomogeneous electron-positron-ion quantum magnetoplasma with neutral particles in the background. The KdV-type solitary waves, Burgers-type monotonic, and oscillatory shock like solutions are discussed in different limits. The quantum parameter is also dependent on the positron concentration in dense multicomponent plasmas. It is found that both solitary hump and dip are formed and their amplitude and width are dependent on percentage presence of positrons in electron-ion plasmas. The height of the monotonic shock is decreased with the increase of positron concentration and it is independent of the quantum parameter in electron-positron-ion magnetized quantum plasmas. However, the amplitude of the oscillatory shock is dependent on positron concentration and quantum parameter in electron-positron-ion plasmas.
Optical distortions in electron/positron storage rings
Brown, K.L.; Donald, M.; Servranckx, R.
1983-01-01
We have studied the optical distortions in the PEP electron/positron storage ring for various optical configurations using the computer programs DIMAT, HARMON, PATRICIA, and TURTLE. The results are shown graphically by tracing several thousand trajectories from one interaction region to the next using TURTLE and by tracing a few selected rays several hundred turns using the programs DIMAT and PATRICIA. The results show an interesting correlation between the calculated optical cleanliness of a particular lattice configuration and the observed operating characteristics of the machine.
Low-energy scattering of electrons and positrons in liquids
NASA Technical Reports Server (NTRS)
Schrader, D. M.
1990-01-01
The scattering of low energy electrons and positrons is described for the liquid phase and compared and contrasted with that for the gas phase. Similarities as well as differences are noted. The loci of scattering sites, called spurs in the liquid phase, are considered in detail. In particular, their temporal and spatial evolution is considered from the point of view of scattering. Two emphases are made: one upon the stochastic calculation of the distribution of distances required for slowing down to thermal velocities, and the other upon the calculation of cross sections for energy loss by means of quantum mechanics.
Relativistic wave-breaking limit of electrostatic waves in cold electron-positron-ion plasmas
NASA Astrophysics Data System (ADS)
Karmakar, Mithun; Maity, Chandan; Chakrabarti, Nikhil; Sengupta, Sudip
2016-06-01
A one-dimensional nonlinear propagation of relativistically strong electrostatic waves in cold electron-positron-ion (EPI) plasmas has been analyzed. The motion of all the three species, namely, electron, positron, and ion has been treated to be relativistic. The maximum permissible electric field amplitude - so called "wave-breaking limit" of such an electrostatic wave before wave-breaking has been derived, showing its dependence on the relativistic Lorentz factor associated with the phase velocity of the plasma wave, on the electron/positron to ion mass ratio, and on the ratio of equilibrium ion density to equilibrium electron/positron density.
Positrons for linear colliders
Ecklund, S.
1987-11-01
The requirements of a positron source for a linear collider are briefly reviewed, followed by methods of positron production and production of photons by electromagnetic cascade showers. Cross sections for the electromagnetic cascade shower processes of positron-electron pair production and Compton scattering are compared. A program used for Monte Carlo analysis of electromagnetic cascades is briefly discussed, and positron distributions obtained from several runs of the program are discussed. Photons from synchrotron radiation and from channeling are also mentioned briefly, as well as positron collection, transverse focusing techniques, and longitudinal capture. Computer ray tracing is then briefly discussed, followed by space-charge effects and thermal heating and stress due to showers. (LEW)
LOVO Electrons: The Special Electrons of Molecules in Positron Annihilation Process
NASA Astrophysics Data System (ADS)
Ma, Xiaoguang; Wang, Lizhi; Yang, Chuanlu
2014-05-01
The electrons in the lowest occupied valence orbital (LOVO) of molecules have been found to dominate the gamma-ray spectra in the positron-electron annihilation process. The mechanism of this phenomenon is revealed in the present work for the first time. Theoretical quantitative analyses are applied to all noble gas atoms and molecules CH4, O2, C6H6, and C6H14. More than 70% of LOVO electrons and less than 30% of highest occupied molecular orbital (HOMO) electrons distribute within the full width at half-maximum (FWHM) region of the momentum spectra averagely. This indicates that the LOVO electrons have at least 2 times of probabilities than the HOMO electrons within this area. The predicted positron annihilation spectra are then generally dominated by the innermost LOVO electrons instead of the outmost HOMO electrons under the plane-wave approximation.
FTL Quantum Models of the Photon and the Electron
Gauthier, Richard F.
2007-01-30
A photon is modeled by an uncharged superluminal quantum moving at 1.414c along an open 45-degree helical trajectory with radius R = {lambda}/2{pi} (where {lambda} is the helical pitch or wavelength). A mostly superluminal spatial model of an electron is composed of a charged pointlike quantum circulating at an extremely high frequency ( 2.5 x 1020 hz) in a closed, double-looped hehcal trajectory whose helical pitch is one Compton wavelength h/mc. The quantum has energy and momentum but not rest mass, so its speed is not limited by c. sThe quantum's speed is superluminal 57% of the time and subluminal 43% of the time, passing through c twice in each trajectory cycle. The quantum's maximum speed in the electron's rest frame is 2.515c and its minimum speed is .707c. The electron model's helical trajectory parameters are selected to produce the electron's spin ({Dirac_h}/2{pi})/2 and approximate (without small QED corrections) magnetic moment e({Dirac_h}/2{pi})/2m (the Bohr magneton {mu}B) as well as its Dirac equation-related 'jittery motion' angular frequency 2mc2/({Dirac_h}/2{pi}), amplitude ({Dirac_h}/2{pi})/2mc and internal speed c. The two possible helicities of the electron model correspond to the electron and the positron. With these models, an electron is like a closed circulating photon. The electron's inertia is proposed to be related to the electron model's circulating internal Compton momentum mc. The internal superluminalily of the photon model, the internal superluminahty/subluminality of the electron model, and the proposed approach to the electron's inertia as ''momentum at rest'' within the electron, could be relevant to possible mechanisms of superluminal communication and transportation.
Small Explorer (SMEX) POsitron Electron Magnet Spectrometer (POEMS)
NASA Technical Reports Server (NTRS)
LHeureux, Jacques; Evenson, Paul A.; Aleman, R. (Technical Monitor)
1995-01-01
This report covers the activities of Louisiana State University (LSU) under subcontract 26053-EX between LSU and the Bartol Research Institute (Bartol), which began January 1, 1994. The purpose of this subcontract was for LSU to participate in and support Bartol in the work to define the SMEX (Small Explorer)/POEMS (Positron Electron Magnet Spectrometer) spaceflight mission under NASA Contract NAS5-38098 between NASA and Bartol. The conclusions of this study were that for a 1998 launch into a 600km altitude, 98 degrees, approximately sun synchronous orbit, (a) the total radiation dose would be typically a few k-rad per year, certainly less than 20 k-rad per year for the anticipated shielding and potential solar flare environment, (b) detector counting rates would be dominated by the South Atlantic Anomaly (SAA) and the horns of the Van Allen belts, (c) the galactic electron and positron 'signal' can be extracted from the albedo background and the trapped populations by detailed evaluation of the geomagnetic transmission function (cut-off) for each event, (d) POEMS could make significant contributions to magnetospheric science if sufficient downlink capacity were provided and, (e) a fully functioning, cost efficient, data processing and analysis facility design was developed for the mission. Overall, POEMS was found to be a relatively simple experiment to manifest, operate and analyze and had potential for fundamental new discoveries in cosmic, heliospheric, solar and magnetospheric science.
Relativistic, perpendicular shocks in electron-positron plasmas
NASA Technical Reports Server (NTRS)
Gallant, Yves A.; Hoshino, Masahiro; Langdon, A. B.; Arons, Jonathan; Max, Claire E.
1992-01-01
One-dimensional particle-in-cell plasma simulations are used to examine the mechanical structure and thermalization properties of collisionless relativistic shock waves in electron-positron plasmas. Shocks propagating perpendicularly to the magnetic field direction are considered. It is shown that these shock waves exist, and that they are completely parameterized by the ratio of the upstream Poynting flux to the upstream kinetic energy flux. The way in which the Rankine-Hugoniot shock jump conditions are modified by the presence of wave fluctuations is shown, and they are used to provide a macroscopic description of these collisionless shock flows. The results of a 2D simulation that demonstrates the generality of these results beyond the assumption of the 1D case are discussed. It is suggested that the thermalization mechanism is the formation of a synchrotron maser by the coherently reflected particles in the shock front. Because the downstream medium is thermalized, it is argued that perpendicular shocks in pure electron-positron plasmas are not candidates as nonthermal particle accelerators.
Nonlinear propagation of ion-acoustic waves in electron-positron-ion plasma with trapped electrons
NASA Astrophysics Data System (ADS)
Alinejad, H.; Sobhanian, S.; Mahmoodi, J.
2006-01-01
A theoretical investigation has been made for ion-acoustic waves in an unmagnetized electron-positron-ion plasma. A more realistic situation in which plasma consists of a negatively charged ion fluid, free positrons, and trapped as well as free electrons is considered. The properties of stationary structures are studied by the reductive perturbation method, which is valid for small but finite amplitude limit, and by pseudopotential approach, which is valid for large amplitude. With an appropriate modified form of the electron number density, two new equations for the ion dynamics have been found. When deviations from isothermality are finite, the modified Korteweg-deVries equation has been found, and for the case that deviations from isothermality are small, calculations lead to a generalized Korteweg-deVries equation. It is shown from both weakly and highly nonlinear analysis that the presence of the positrons may allow solitary waves to exist. It is found that the effect of the positron density changes the maximum value of the amplitude and M (Mach number) for which solitary waves can exist. The present theory is applicable to analyze arbitrary amplitude ion-acoustic waves associated with positrons which may occur in space plasma.
Nonlinear propagation of ion-acoustic waves in electron-positron-ion plasma with trapped electrons
Alinejad, H.; Sobhanian, S.; Mahmoodi, J.
2006-01-15
A theoretical investigation has been made for ion-acoustic waves in an unmagnetized electron-positron-ion plasma. A more realistic situation in which plasma consists of a negatively charged ion fluid, free positrons, and trapped as well as free electrons is considered. The properties of stationary structures are studied by the reductive perturbation method, which is valid for small but finite amplitude limit, and by pseudopotential approach, which is valid for large amplitude. With an appropriate modified form of the electron number density, two new equations for the ion dynamics have been found. When deviations from isothermality are finite, the modified Korteweg-deVries equation has been found, and for the case that deviations from isothermality are small, calculations lead to a generalized Korteweg-deVries equation. It is shown from both weakly and highly nonlinear analysis that the presence of the positrons may allow solitary waves to exist. It is found that the effect of the positron density changes the maximum value of the amplitude and M (Mach number) for which solitary waves can exist. The present theory is applicable to analyze arbitrary amplitude ion-acoustic waves associated with positrons which may occur in space plasma.
Electron-positron pairs in physics and astrophysics: From heavy nuclei to black holes
NASA Astrophysics Data System (ADS)
Ruffini, Remo; Vereshchagin, Gregory; Xue, She-Sheng
2010-02-01
+e- annihilation to hadronic channels, in addition to the Dirac electromagnetic channel; (B) ongoing Earth-based experiments to detect electron-positron production in strong fields by focusing coherent laser beams and by electron-beam-laser collisions; and (C) the multiyear attempts to detect electron-positron production in Coulomb fields for a large atomic number Z>137 in heavy-ion collisions. These attempts follow the classical theoretical work of Popov and Zeldovich, and Greiner and their schools. We then turn to astrophysics. We first review the basic work on the energetics and electrodynamical properties of an electromagnetic black hole and the application of the Schwinger formula around Kerr-Newman black holes as pioneered by Damour and Ruffini. We only focus on black hole masses larger than the critical mass of neutron stars, for convenience assumed to coincide with the Rhoades and Ruffini upper limit of 3.2 M⊙. In this case the electron Compton wavelength is much smaller than the space-time curvature and all previous results invariantly expressed can be applied following well established rules of the equivalence principle. We derive the corresponding rate of electron-positron pair production and introduce the concept of dyadosphere. We review the recent progress in describing the evolution of optically thick electron-positron plasma in the presence of supercritical electric field, which is relevant both in astrophysics as well as in ongoing laser beam experiments. In particular we review the recent progress based on the Vlasov-Boltzmann-Maxwell equations to study the feedback of the created electron-positron pairs on the original constant electric field. We evidence the existence of plasma oscillations and its interaction with photons leading to energy and number equipartition of photons, electrons and positrons. We finally review the recent progress obtained by using the Boltzmann equations to study the evolution of an electron-positron-photon plasma towards thermal
NASA Astrophysics Data System (ADS)
Rafat, A.; Rahman, M. M.; Alam, M. S.; Mamun, A. A.
2016-08-01
Obliquely propagating electron-acoustic solitary waves (EASWs) in a magnetized electron-positron-ion plasma (containing nonextensive hot electrons and positrons, inertial cold electrons, and immobile positive ions) are precisely investigated by deriving the Zakharov-Kuznetsov equation. It is found that the basic features (viz. polarity, amplitude, width, phase speed, etc.) of the EASWs are significantly modified by the effects of the external magnetic field, obliqueness of the system, nonextensivity of hot positrons and electrons, ratio of the hot electron temperature to the hot positron temperature, and ratio of the cold electron number density to the hot positron number density. The findings of our results can be employed in understanding the localized electrostatic structures and the characteristics of EASWs in various astrophysical plasmas.
NASA Technical Reports Server (NTRS)
Zdziarski, A. A.; Lightman, A. P.
1985-01-01
A nonthermal model for power-law X-ray and gamma-ray sources is considered. An initial, primary distribution of relativistic electrons is injected and cooled via Compton scattering of soft photons (produced either externally or by the synchrotron mechanism). The scattered photons, constituting a primary gamma-ray source, produce electron-positron pairs that act as a secondary electron injection, which in turn produce a secondary photon spectrum. Pairs formed by a part of the photon spectrum optically thin to pair production are taken into account. The distribution of particles and photons is obtained, and numerical results as well as analytical solutions to certain special cases are presented. For the case of a delta-function primary electron injection it is found that the photon spectrum in the X-ray region is well approximated by a power law, with the energy spectral index alpha(X) lying in the relatively narrow range 0.5-0.9 as the compactness parameter L(x)/R (where L(x) is the X-ray luminosity and R is the source radius) varies over many orders of magnitude. This is proposed as a possible mechanism to explain the universal X-ray spectra observed from active galactic nuclei.
Weibel instabilities in relativistic electron-positron plasmas
Yang, T.-Y.B.; Gallant, Y.; Arons, J.; Langdon, A.B.
1992-07-20
Wisps have long been observed in the Crab Nebula. Modern observations reveal a whole series of wisps to the northwest, and at least one much fainter wisp to the southeast. Recently, a conceptual model of the wisps in the Crab Nebula has been proposed based on the shock structure of a relativistic magnetosonic shock wave in a electron-positron-proton plasma. The ion overshoot, downstream compressional oscillations, and possibly the pair overshoot can be identified with the wisps. In this paper, we study the linear stability properties of the Weibel instability, which are collective electromagnetic oscillations driven by pitch-angle anisotropy of the distribution functions. This instability can cause pitch-angle scattering of the charged particles and the isotropization of the distribution functions.
The electronics for the Donner 600-Crystal Positron Tomograph
Cahoon, J.L.; Huesman, R.H.; Derenzo, S.E.; Geyer, A.B.; Uber, D.C.; Turko, B.T.; Budinger, T.F.
1986-02-01
The data acquisition system, designed for the Donner 600-Crystal Positron Tomograph, is described. Coincidence timing resolution of less than five nanoseconds full width at half maximum and data rates in excess of one million events per second are achieved by using high-speed emitter coupled logic circuits, first-in first-out memory to derandomize data flow, and parallel architecture to increase throughput. These data rates allow the acquisition of adequate transmission data in a reasonable amount of time. Good timing resolution minimizes accidental coincidences and permits data rates greater than 100,000 image-forming events per second for high-speed dynamic emission tomography. Additional scatter and accidental rejection are accomplished for transmission data by using an orbiting source and a look-up table for valid events. Calibration of this complex electronic system is performed automatically under computer control.
Electronics for the Donner 600-Crystal Positron Tomograph
Cahoon, J.L.; Huesman, R.H.; Derenzo, S.E.; Geyer, A.B.; Uber, D.C.; Turko, B.T.; Budinger, T.F.
1985-10-01
The data acquisition system, designed for the Donner 600-Crystal Positron Tomograph, is described. Coincidence timing resolution of less than five nanoseconds full width at half maximum and data rates in excess of one million events per second are achieved by using high-speed emitter coupled logic circuits, first-in first-out memory to derandomize data flow, and parallel architecture to increase throughput. These data rates allow the acquisition of adequate transmission data in a reasonable amount of time. Good timing resolution minimizes accidental coincidences and permits data rates greater than 100,000 image-forming events per second for high-speed dynamic emission tomography. Additional scatter and accidental rejection are accomplished for transmission data by using an orbiting source and a look-up table for valid events. Calibration of this complex electronic system is performed automatically under computer control. 4 refs., 5 figs.
Design Considerations for High Energy Electron -- Positron Storage Rings
DOE R&D Accomplishments Database
Richter, B.
1966-11-01
High energy electron-positron storage rings give a way of making a new attack on the most important problems of elementary particle physics. All of us who have worked in the storage ring field designing, building, or using storage rings know this. The importance of that part of storage ring work concerning tests of quantum electrodynamics and mu meson physics is also generally appreciated by the larger physics community. However, I do not think that most of the physicists working tin the elementary particle physics field realize the importance of the contribution that storage ring experiments can make to our understanding of the strongly interacting particles. I would therefore like to spend the next few minutes discussing the sort of things that one can do with storage rings in the strongly interacting particle field.
Solitary and shock waves in magnetized electron-positron plasma
Lu, Ding; Li, Zi-Liang; Abdukerim, Nuriman; Xie, Bai-Song
2014-02-15
An Ohm's law for electron-positron (EP) plasma is obtained. In the framework of EP magnetohydrodynamics, we investigate nonrelativistic nonlinear waves' solutions in a magnetized EP plasma. In the collisionless limit, quasistationary propagating solitary wave structures for the magnetic field and the plasma density are obtained. It is found that the wave amplitude increases with the Mach number and the Alfvén speed. However, the dependence on the plasma temperature is just the opposite. Moreover, for a cold EP plasma, the existence range of the solitary waves depends only on the Alfvén speed. For a hot EP plasma, the existence range depends on the Alfvén speed as well as the plasma temperature. In the presence of collision, the electromagnetic fields and the plasma density can appear as oscillatory shock structures because of the dissipation caused by the collisions. As the collision frequency increases, the oscillatory shock structure becomes more and more monotonic.
Surface waves in magnetized quantum electron-positron plasmas
NASA Astrophysics Data System (ADS)
Misra, A. P.; Ghosh, N. K.; Shukla, P. K.
2010-02-01
The dispersion properties of electrostatic surface waves propagating along the interface between a quantum magnetoplasma composed of electrons and positrons, and vacuum are studied by using a quantum magnetohydrodynamic plasma model. The general dispersion relation for arbitrary orientation of the magnetic field and the propagation vector is derived and analyzed in some special cases of interest (viz. when the magnetic field is directed parallel and perpendicular to the boundary surface). It is found that the quantum effects facilitate the propagation of electrostatic surface modes in a dense magnetoplasma. The effect of the external magnetic field is found to increase the frequency of the quantum surface wave. The existence of a singular wave on the boundary surface is also proved, and its properties are analyzed numerically. It is shown that the new wave characteristics appear due to the Rayleigh type of the wave.
Fragmentation production of charmed hadrons in electron-positron annihilation
Novoselov, A. A.
2010-10-15
Processes involving the production of D* mesons and {Lambda}{sub c} baryons in electron-positron annihilation at the energies of 10.58 and 91.18 GeV are considered. At the energy of 10.58 GeV, the production of pairs of B mesons that is followed by their decay to charmed particles is analyzed along with direct charm production. The violation of scaling in the respective fragmentation functions is taken into account in the next-to-leading-logarithmic approximation of perturbative QCD. The required nonperturbative fragmentation functions are extracted numerically from experimental data obtained at B factories and are approximated by simple analytic expressions. It is shown that the difference in the nonperturbative fragmentation functions for transitions to mesons and baryons can readily be explained on the basis of the quark-counting rules.
Alinejad, H.; Mamun, A. A.
2011-11-15
A theoretical investigation is carried out to understand the basic features of linear and nonlinear propagation of ion-acoustic (IA) waves subjected to an external magnetic field in an electron-positron-ion plasma which consists of a cold magnetized ion fluid, Boltzmann distributed positrons, and superthermal electrons. In the linear regime, the propagation of two possible modes (fast and slow) and their evolution are investigated. It is shown that the electron superthermality and the relative fraction of positrons cause both modes to propagate with smaller phase velocities. Also, two special cases of dispersion relation are found, which are related to the direction of the wave propagation. In the nonlinear regime, the Korteweg-de Vries (KdV) equation describing the propagation of fast and slow IA waves is derived. The latter admits a solitary wave solution with only negative potential in the weak amplitude limit. It is found that the effects of external magnetic field (obliqueness), superthermal electrons, positron concentration, and temperature ratio significantly modify the basic features of solitary waves.
Andreev, Pavel A.
2015-06-15
We discuss the complete theory of spin-1/2 electron-positron quantum plasmas, when electrons and positrons move with velocities mach smaller than the speed of light. We derive a set of two fluid quantum hydrodynamic equations consisting of the continuity, Euler, spin (magnetic moment) evolution equations for each species. We explicitly include the Coulomb, spin-spin, Darwin and annihilation interactions. The annihilation interaction is the main topic of the paper. We consider the contribution of the annihilation interaction in the quantum hydrodynamic equations and in the spectrum of waves in magnetized electron-positron plasmas. We consider the propagation of waves parallel and perpendicular to an external magnetic field. We also consider the oblique propagation of longitudinal waves. We derive the set of quantum kinetic equations for electron-positron plasmas with the Darwin and annihilation interactions. We apply the kinetic theory to the linear wave behavior in absence of external fields. We calculate the contribution of the Darwin and annihilation interactions in the Landau damping of the Langmuir waves. We should mention that the annihilation interaction does not change number of particles in the system. It does not related to annihilation itself, but it exists as a result of interaction of an electron-positron pair via conversion of the pair into virtual photon. A pair of the non-linear Schrodinger equations for the electron-positron plasmas including the Darwin and annihilation interactions is derived. Existence of the conserving helicity in electron-positron quantum plasmas of spinning particles with the Darwin and annihilation interactions is demonstrated. We show that the annihilation interaction plays an important role in the quantum electron-positron plasmas giving the contribution of the same magnitude as the spin-spin interaction.
NASA Astrophysics Data System (ADS)
Andreev, Pavel A.
2015-06-01
We discuss the complete theory of spin-1/2 electron-positron quantum plasmas, when electrons and positrons move with velocities mach smaller than the speed of light. We derive a set of two fluid quantum hydrodynamic equations consisting of the continuity, Euler, spin (magnetic moment) evolution equations for each species. We explicitly include the Coulomb, spin-spin, Darwin and annihilation interactions. The annihilation interaction is the main topic of the paper. We consider the contribution of the annihilation interaction in the quantum hydrodynamic equations and in the spectrum of waves in magnetized electron-positron plasmas. We consider the propagation of waves parallel and perpendicular to an external magnetic field. We also consider the oblique propagation of longitudinal waves. We derive the set of quantum kinetic equations for electron-positron plasmas with the Darwin and annihilation interactions. We apply the kinetic theory to the linear wave behavior in absence of external fields. We calculate the contribution of the Darwin and annihilation interactions in the Landau damping of the Langmuir waves. We should mention that the annihilation interaction does not change number of particles in the system. It does not related to annihilation itself, but it exists as a result of interaction of an electron-positron pair via conversion of the pair into virtual photon. A pair of the non-linear Schrodinger equations for the electron-positron plasmas including the Darwin and annihilation interactions is derived. Existence of the conserving helicity in electron-positron quantum plasmas of spinning particles with the Darwin and annihilation interactions is demonstrated. We show that the annihilation interaction plays an important role in the quantum electron-positron plasmas giving the contribution of the same magnitude as the spin-spin interaction.
Observation of exclusive electron-positron production in hadron-hadron collisions.
Abulencia, A; Adelman, J; Affolder, T; Akimoto, T; Albrow, M G; Ambrose, D; Amerio, S; Amidei, D; Anastassov, A; Anikeev, K; Annovi, A; Antos, J; Aoki, M; Apollinari, G; Arguin, J-F; Arisawa, T; Artikov, A; Ashmanskas, W; Attal, A; Azfar, F; Azzi-Bacchetta, P; Azzurri, P; Bacchetta, N; Badgett, W; Barbaro-Galtieri, A; Barnes, V E; Barnett, B A; Baroiant, S; Bartsch, V; Bauer, G; Bedeschi, F; Behari, S; Belforte, S; Bellettini, G; Bellinger, J; Belloni, A; Benjamin, D; Beretvas, A; Beringer, J; Berry, T; Bhatti, A; Binkley, M; Bisello, D; Blair, R E; Blocker, C; Blumenfeld, B; Bocci, A; Bodek, A; Boisvert, V; Bolla, G; Bolshov, A; Bortoletto, D; Boudreau, J; Boveia, A; Brau, B; Brigliadori, L; Bromberg, C; Brubaker, E; Budagov, J; Budd, H S; Budd, S; Budroni, S; Burkett, K; Busetto, G; Bussey, P; Byrum, K L; Cabrera, S; Campanelli, M; Campbell, M; Canelli, F; Canepa, A; Carillo, S; Carlsmith, D; Caron, B; Carosi, R; Casarsa, M; Castro, A; Catastini, P; Cauz, D; Cavalli-Sforza, M; Cerri, A; Cerrito, L; Chang, S H; Chen, Y C; Chertok, M; Chiarelli, G; Chlachidze, G; Chlebana, F; Cho, I; Cho, K; Chokheli, D; Chou, J P; Choudalakis, G; Chuang, S H; Chung, K; Chung, W H; Chung, Y S; Ciljak, M; Ciobanu, C I; Ciocci, M A; Clark, A; Clark, D; Coca, M; Compostella, G; Convery, M E; Conway, J; Cooper, B; Copic, K; Cordelli, M; Cortiana, G; Crescioli, F; Almenar, C Cuenca; Cuevas, J; Culbertson, R; Cully, J C; Cyr, D; Daronco, S; D'Auria, S; Davies, T; D'Onofrio, M; Dagenhart, D; de Barbaro, P; Cecco, S De; Deisher, A; Lentdecker, G De; Dell'orso, M; Paoli, F Delli; Demortier, L; Deng, J; Deninno, M; Pedis, D De; Derwent, P F; Giovanni, G P Di; Dionisi, C; Ruzza, B Di; Dittmann, J R; Dituro, P; Dörr, C; Donati, S; Donega, M; Dong, P; Donini, J; Dorigo, T; Dube, S; Efron, J; Erbacher, R; Errede, D; Errede, S; Eusebi, R; Fang, H C; Farrington, S; Fedorko, I; Fedorko, W T; Feild, R G; Feindt, M; Fernandez, J P; Field, R; Flanagan, G; Foland, A; Forrester, S; Foster, G W; Franklin, M; 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Wang, S M; Warburton, A; Waschke, S; Waters, D; Wester, W C; Whitehouse, B; Whiteson, D; Wicklund, A B; Wicklund, E; Williams, G; Williams, H H; Wilson, P; Winer, B L; Wittich, P; Wolbers, S; Wolfe, C; Wright, T; Wu, X; Wynne, S M; Yagil, A; Yamamoto, K; Yamaoka, J; Yamashita, T; Yang, C; Yang, U K; Yang, Y C; Yao, W M; Yeh, G P; Yoh, J; Yorita, K; Yoshida, T; Yu, G B; Yu, I; Yu, S S; Yun, J C; Zanello, L; Zanetti, A; Zaw, I; Zhang, X; Zhou, J; Zucchelli, S
2007-03-16
We present the first observation of exclusive e(+)e(-) production in hadron-hadron collisions, using pp[over] collision data at (square root) s = 1.96 TeV taken by the run II Collider Detector at Fermilab, and corresponding to an integrated luminosity of 532 pb(-1). We require the absence of any particle signatures in the detector except for an electron and a positron candidate, each with transverse energy E(T) > 5 GeV and pseudorapidity |eta| < 2. With these criteria, 16 events are observed compared to a background expectation of 1.9+/-0.3 events. These events are consistent in cross section and properties with the QED process pp[over] --> p + e(+)e(-) + p[over] through two-photon exchange. The measured cross section is 1.6(-0.3)(+0.5)(stat) +/- 0.3(syst) pb. This agrees with the theoretical prediction of 1.71+/-0.01 pb.
Investigation into electron cloud effects in the International Linear Collider positron damping ring
Crittenden, J.A.; Conway, J.; Dugan, G.F.; Palmer, M.A.; Rubin, D.L.; Shanks, J.; Sonnad, K.G.; Boon, L.; Harkay, K.; Ishibashi, T.; Furman, M.A.; Guiducci, S.; Pivi, M.T.F.; Wang, L.; Crittenden, J.A.; Conway, J.; Dugan, G.F.; Palmer, M.A.; Rubin, D.L.; Shanks, J.; Sonnad, K.G.; Boon, L.; Harkay, K.; Ishibashi, T.; Furman, M.A.; Guiducci, S.; Pivi, M.T.F.; Wang, L.
2014-02-28
We report modeling results for electron cloud buildup and instability in the International Linear Collider positron damping ring. Updated optics, wiggler magnets, and vacuum chamber designs have recently been developed for the 5 GeV, 3.2-km racetrack layout. An analysis of the synchrotron radiation profile around the ring has been performed, including the effects of diffuse and specular photon scattering on the interior surfaces of the vacuum chamber. The results provide input to the cloud buildup simulations for the various magnetic field regions of the ring. The modeled cloud densities thus obtained are used in the instability threshold calculations. We conclude that the mitigation techniques employed in this model will suffice to allow operation of the damping ring at the design operational specifications
Solitary wave propagation in quantum electron-positron plasmas
NASA Astrophysics Data System (ADS)
Misra, A. P.; Ghosh, N. K.; Bhowmik, C.
2008-10-01
Existence of large amplitude stationary solitary wave structures in an unmagnetized electron-positron (e-p) plasma is studied using a quantum hydrodynamic (QHD) model that includes the quantum force (tunnelling) associated with the Bohm potential and the Fermi-dirac pressure law. It is found that in a quasi-neutral pair (e-p) plasma, where the dispersion is only due to the the quantum tunnelling effects, the large amplitude stationary solitary structure exists only when the normalized Mach speed,M <√2. Such solitary structures do not exist in absence of the Bohm potential term in an unmagnetized quasineutral pair (e-p) plasma. The system is shown to support only rarefactive stationary solitary waves. For such waves the amplitude, being independent of the quantum parameter H (the ratio of the electron plasmon to electron Fermi energy), decreases with the Mach number M, whereas the width increases with both M and H. The present theory is applicable to analyze the formation of localized coherent solitary structures at quantum scales in dense astrophysical objects as well as in intense laser fields.
Lu, Ding; Li, Zi-Liang; Xie, Bai-Song
2013-09-01
The effects of ion mobility and positron fraction on the solitary waves of the laser field envelope and the potential of the electrostatic field in weak relativistic electron-positron-ion plasma are investigated. The parameter region for the existence of solitary waves is obtained analytically, and a reasonable choice of parameters is clarified. Both cases of mobile and immobile ions are considered. It is found that the amplitudes of solitary waves in the former case are larger compared to the latter case. For small plasma density, the localized solitary wave solutions in terms of the approximate perturbation analytical method are very consistent with those by exact numerical calculations. However, as the plasma density increases the analytical method loses its validity more and more. The influence of the positron fraction on the amplitudes of solitary waves shows a monotonous increasing relation. The implications of our results to particle acceleration are also discussed briefly. PMID:24125373
Sadiq, Safeer; Mahmood, S.; Haque, Q.; Ali, Munazza Zulfiqar
2014-09-20
The propagation of electrostatic waves in a dense magnetized electron-positron-ion (EPI) plasma with nonrelativistic and ultrarelativistic degenerate electrons and positrons is investigated. The linear dispersion relation is obtained for slow and fast electrostatic waves in the EPI plasma. The limiting cases for ion acoustic wave (slow) and ion cyclotron wave (fast) are also discussed. Using the reductive perturbation method, two-dimensional propagation of ion acoustic solitons is found for both the nonrelativistic and ultrarelativistic degenerate electrons and positrons. The effects of positron concentration, magnetic field, and mass of ions on ion acoustic solitons are shown in numerical plots. The proper form of Fermi temperature for nonrelativistic and ultrarelativistic degenerate electrons and positrons is employed, which has not been used in earlier published work. The present investigation is useful for the understanding of linear and nonlinear electrostatic wave propagation in the dense magnetized EPI plasma of compact stars. For illustration purposes, we have applied our results to a pulsar magnetosphere.
Ultrashort megaelectronvolt positron beam generation based on laser-accelerated electrons
NASA Astrophysics Data System (ADS)
Xu, Tongjun; Shen, Baifei; Xu, Jiancai; Li, Shun; Yu, Yong; Li, Jinfeng; Lu, Xiaoming; Wang, Cheng; Wang, Xinliang; Liang, Xiaoyan; Leng, Yuxin; Li, Ruxin; Xu, Zhizhan
2016-03-01
Experimental generation of ultrashort MeV positron beams with high intensity and high density using a compact laser-driven setup is reported. A high-density gas jet is employed experimentally to generate MeV electrons with high charge; thus, a charge-neutralized MeV positron beam with high density is obtained during laser-accelerated electrons irradiating high-Z solid targets. It is a novel electron-positron source for the study of laboratory astrophysics. Meanwhile, the MeV positron beam is pulsed with an ultrashort duration of tens of femtoseconds and has a high peak intensity of 7.8 × 1021 s-1, thus allows specific studies of fast kinetics in millimeter-thick materials with a high time resolution and exhibits potential for applications in positron annihilation spectroscopy.
Numerical simulation study of positron production by intense laser-accelerated electrons
Yan, Yonghong; Dong, Kegong; Wu, Yuchi; Zhang, Bo; Gu, Yuqiu; Yao, Zeen
2013-10-15
Positron production by ultra-intense laser-accelerated electrons has been studied with two-dimensional particle-in-cell and Monte Carlo simulations. The dependence of the positron yield on plasma density, plasma length, and converter thickness was investigated in detail with fixed parameters of a typical 100 TW laser system. The results show that with the optimal plasma and converter parameters a positron beam containing up to 1.9 × 10{sup 10} positrons can be generated, which has a small divergence angle (10°), a high temperature (67.2 MeV), and a short pulse duration (1.7 ps)
Photon-induced near field electron microscopy
NASA Astrophysics Data System (ADS)
Park, Sang Tae; Zewail, Ahmed H.
2013-09-01
Ultrafast electron microscopy in the space and time domains utilizes a pulsed electron probe to directly map structural dynamics of nanomaterials initiated by an optical pump pulse, in imaging, di raction, spectroscopy, and their combinations. It has demonstrated its capability in the studies of phase transitions, mechanical vibrations, and chemical reactions. Moreover, electrons can directly interact with photons via the near eld component of light scattering by nanostructures, and either gain or lose light quanta discretely in energy. By energetically selecting those electrons that exchanged photon energies, we can map this photon-electron interaction, and the technique is termed photon-induced near eld electron microscopy (PINEM). Here, we give an account of the theoretical understanding of PINEM. Experimentally, nanostructures such as a sphere, cylinder, strip, and triangle have been investigated. Theoretically, time-dependent Schrodinger and Dirac equations for an electron under light are directly solved to obtain analytical solutions. The interaction probability is expressed by the mechanical work done by an optical wave on a traveling electron, which can be evaluated analytically by the near eld components of the Rayleigh scattering for small spheres and thin cylinders, and numerically by the discrete dipole approximation for other geometries. Application in visualization of plasmon elds is discussed.
Wakefields generated by collisional neutrinos in neutral-electron-positron-ion plasma
Tinakiche, Nouara
2015-12-15
A classical fluid description is adopted to investigate nonlinear interaction between an electron-type neutrino beam and a relativistic collisionless unmagnetized neutral-electron-positron-ion plasma. In this work, we consider the collisions of the neutrinos with neutrals in the plasma and study their effect on the generation of wakefields in presence of a fraction of ions in a neutral-electron-positron plasma. The results obtained in the present work are interpreted and compared with previous studies.
Enhanced Correlation of Electron-Positron Pair in Two and Three Dimensions
NASA Astrophysics Data System (ADS)
Tang, Suo; Xie, Bai-Song; Wang, Hong-Yu; Liu, Jie; Fu, Li-Bin; Yu, Ming-Young
2014-01-01
Early time electron-positron correlation in vacuum pair-production in an external field is investigated. The entangled electron and positron wave functions are obtained analytically in the configuration and momentum spaces. It is shown that, relative to that of the one-dimensional theory, two- and three-dimensional calculations yield enhanced spatial correlation and broadened momentum spectra. In fact, at early times the electron and positron almost coincide spatially. The correlation also depends on the direction of the applied field. For the spatial correlation, the transverse correlation is stronger than the longitudinal correlation.
Linear electrostatic waves in a three-component electron-positron-ion plasma
Mugemana, A. Moolla, S.; Lazarus, I. J.
2014-12-15
Analytical linear electrostatic waves in a magnetized three-component electron-positron-ion plasma are studied in the low-frequency limit. By using the continuity and momentum equations with Poisson's equation, the dispersion relation for the electron-positron-ion plasma consisting of cool ions, and hot Boltzmann electrons and positrons is derived. In the linear regime, the propagation of two possible modes and their evolution are studied. In the cases of parallel and perpendicular propagation, it is shown that these two possible modes are always stable. The present investigation contributes to nonlinear propagation of electrostatic waves in space and the laboratory.
Entanglement Dynamics of Electrons and Photons
NASA Astrophysics Data System (ADS)
Wu, Xiang-Yao; Liu, Xiao-Jing; Lu, Jing-Bin; Li, Tian-Shun; Zhang, Si-Qi; Liang, Yu; Ma, Ji; Li, Hong
2016-08-01
Entanglement is a fundamental feature of quantum theory as well as a key resource for quantum computing and quantum communication, but the entanglement mechanism has not been found at present. We think when the two subsystems exist interaction directly or indirectly, they can be in entanglement state. such as, in the Jaynes-Cummings model, the entanglement between the atom and the light field comes from their interaction. In this paper, we have studied the entanglement mechanism of electron-electron and photon-photon, which are from the spin-spin interaction. We found their total entanglement states are relevant both space state and spin state. When two electrons or two photons are far away, their entanglement states should be disappeared even if their spin state is entangled.
Gyrokinetic stability theory of electron-positron plasmas
NASA Astrophysics Data System (ADS)
Helander, P.; Connor, J. W.
2016-06-01
> The linear gyrokinetic stability properties of magnetically confined electron-positron plasmas are investigated in the parameter regime most likely to be relevant for the first laboratory experiments involving such plasmas, where the density is small enough that collisions can be ignored and the Debye length substantially exceeds the gyroradius. Although the plasma beta is very small, electromagnetic effects are retained, but magnetic compressibility can be neglected. The work of a previous publication (Helander, Phys. Rev. Lett., vol. 113, 2014a, 135003) is thus extended to include electromagnetic instabilities, which are of importance in closed-field-line configurations, where such instabilities can occur at arbitrarily low pressure. It is found that gyrokinetic instabilities are completely absent if the magnetic field is homogeneous: any instability must involve magnetic curvature or shear. Furthermore, in dipole magnetic fields, the stability threshold for interchange modes with wavelengths exceeding the Debye radius coincides with that in ideal magnetohydrodynamics. Above this threshold, the quasilinear particle flux is directed inward if the temperature gradient is sufficiently large, leading to spontaneous peaking of the density profile.
Weibel instability in colliding electron-positron-ion plasmas
NASA Astrophysics Data System (ADS)
Silva, Luis
2008-04-01
The new regimes accessed in ultra intense laser plasma interactions and recent developments in relativistic astrophysics are giving rise to an increased interest in the Weibel instability. In fact, whenever colliding streams of plasmas (arbitrary mixtures of electrons-positrons-ions) are present, a fraction of the kinetic energy of the plasma flows can be converted to a sub-equipartition magnetic field. In this talk, and using a combination of particle-in-cell simulations and relativistic kinetic theory, I will first describe the recent theoretical advances in our understanding of the Weibel instability and the connection with the electromagnetic beam plasma instability. Emphasis will be given to the coupling with longitudinal modes, leading to the formation of tilted filaments, and to the effects of the collisions and the merging of the Weibel instability with the resistive filamentation instability. In light of these results, the relevance of Weibel instability to ultra intense laser matter interactions (e.g. fast ignition) and to astrophysical scenarios (e.g. in gamma ray bursters and for cluster magnetic fields) will be discussed. Finally, the role of the Weibel instability in the formation of relativistic shocks and in particle acceleration in these structures will also be addressed.
Electronic and photonic power applications
Walko, R.J.; Ashley, C.S.; Brinker, C.J.; Reed, S.T.; Renschler, C.L. ); Shepodd, T.J. ); Ellefson, R.E.; Gill, J.T. ); Leonard, L.E. )
1990-01-01
Efficient conversion of radioactive decay to electrical power has been the goal of a number of past research efforts. One of these was the Elgin-Kidde nuclear battery. In this concept promethium-147 was used as a beta source which was then mixed with a phosphor to produce a radioluminescent (RL) source of light. The light source was coupled to silicon photovoltaic converters to create electricity. This photoelectric approach is being revisited using tritium based solid state compounds and advanced gas concepts to produce RL light sources being disclosed at this conference. Efficient conversion of the RL light energy to electrical energy imposes certain requirements on the semiconductor converter. These requirements will be discussed. Projections of power source electrical and physical characteristics will be presented based on reasonable design parameter assumptions. The words Power Supply'' usually evoke a vision of a rotating machine or chemical battery. However, today's technology is making increasing use of photonics, where information and even power can be moved through optical fibers. Brighter volumetric RL light sources open a whole new range of photonics-based applications, while solid state tritiated compounds provide the foundation for improved mechanical adaptability and safety. 4 refs., 6 figs., 1 tab.
The stationary non-equilibrium plasma of cosmic-ray electrons and positrons
NASA Astrophysics Data System (ADS)
Tomaschitz, Roman
2016-06-01
The statistical properties of the two-component plasma of cosmic-ray electrons and positrons measured by the AMS-02 experiment on the International Space Station and the HESS array of imaging atmospheric Cherenkov telescopes are analyzed. Stationary non-equilibrium distributions defining the relativistic electron-positron plasma are derived semi-empirically by performing spectral fits to the flux data and reconstructing the spectral number densities of the electronic and positronic components in phase space. These distributions are relativistic power-law densities with exponential cutoff, admitting an extensive entropy variable and converging to the Maxwell-Boltzmann or Fermi-Dirac distributions in the non-relativistic limit. Cosmic-ray electrons and positrons constitute a classical (low-density high-temperature) plasma due to the low fugacity in the quantized partition function. The positron fraction is assembled from the flux densities inferred from least-squares fits to the electron and positron spectra and is subjected to test by comparing with the AMS-02 flux ratio measured in the GeV interval. The calculated positron fraction extends to TeV energies, predicting a broad spectral peak at about 1 TeV followed by exponential decay.
NASA Astrophysics Data System (ADS)
Baurichter, A.; Kirsebom, K.; Kononets, Yu. V.; Medenwaldt, R.; Mikkelsen, U.; Møller, S. P.; Uggerhøj, E.; Worm, T.; Elsener, K.; Ballestrero, S.; Sona, P.; Romano, J.; Connell, S. H.; Sellschop, J. P.; Avakian, R. O.; Avetisian, A. E.; Taroian, S. P.
1997-11-01
Presented is the first experimental demonstration of a dramatic radiative redistribution in transverse states for multi-GeV electrons/positrons, interacting with strong crystalline fields. Detailed analysis of energy loss, photon multiplicities, and scattering distributions leads to new physical insight into open questions such as radiative cooling/heating of the beams in aligned crystals, validity of the constant-field approximation, radiative capture of random particles (``feed in'') into channeled states, and the Landau-Pomeranchuk effect in multiphoton radiation spectra.
Shock waves and double layers in a quantum electron-positron-ion plasma
NASA Astrophysics Data System (ADS)
Dip, P. R.; Hossen, M. A.; Salahuddin, M.; Mamun, A. A.
2016-02-01
The ion-acoustic (IA) shock waves and double layers (DLs) in an unmagnetized, dissipative, quantum electron-positron-ion (EPI) plasma (composed of a viscous heavy ion fluid, Fermi electrons and positrons) have been theoretically investigated. The higher-order Burgers and Gardner equations are derived by employing the reductive perturbation method. The basic features of the IA shock waves and the DLs are identified by analyzing the solutions of both the higher-order Burgers and Gardner equations. The ratio of the Fermi temperature of the positron to that of the electron, the Fermi pressure of electrons and positrons, the viscous force, the plasma particle number densities, etc. are found to change remarkably the basic features (viz. amplitude, width, phase speed, etc.) of the IA waves. The results of our investigation may be helpful in understanding the nonlinear features of localized IA waves propagating in quantum EPI plasmas which are ubiquitous in astrophysical, as well as laboratory, environments.
Unitarity and electron-positron pairs created by strong external fields
NASA Astrophysics Data System (ADS)
Ionescu, Dorin Cezar
1994-05-01
Lowest-order perturbative calculations of the electron-positron production probability in relativistic heavy-ion collisions exceed unitarity bounds for the heaviest collision systems at extreme relativistic energies and sufficiently small impact parameters. Starting with the exponential representation of the time-evolution operator in the Furry picture, we derive manifestly unitary and gauge-invariant expressions for transition amplitudes and probabilities associated with the created electron-positron pairs by employing the Magnus expansion to first order. The time-evolved ground state of the electron-positron field around the heavy nuclei is expressed as a superposition of the unperturbed vacuum state and virtual excitation modes consisting of electron-positron pairs.
Neutrino emissivity from electron-positron annihilation in hot matter in a strong magnetic field
Amsterdamski, P.; Haensel, P. )
1990-10-15
The neutrino emissivity due to electron-positron annihilation in a strong magnetic field is computed. A strong magnetic field can significantly increase the neutrino emissivity at {ital T}{similar to}10{sup 9} K.
Electromagnetic drift waves in nonuniform quantum magnetized electron positron ion plasmas
NASA Astrophysics Data System (ADS)
Ren, Haijun; Wu, Zhengwei; Cao, Jintao; Chu, Paul K.
2008-03-01
Electromagnetic drift waves in a nonuniform quantum magnetized electron positron ion (EPI) plasma are studied. By using the quantum hydrodynamic equations with magnetic fields of the Wigner Maxwell system, we obtained a new dispersion relation in which ions' motions are not considered. The positrons component (featured by the parameter ξ), density gradient of electrons, and of positrons are shown to have a significant impact on the dispersion relation. Our results should be relevant to dense astrophysical objects, e.g. white dwarf and pulsar magnetospheres, as well as low-temperature laboratory EPI plasmas.
Antiproton, positron, and electron imaging with a microchannel plate/phosphor detector.
Andresen, G B; Bertsche, W; Bowe, P D; Bray, C C; Butler, E; Cesar, C L; Chapman, S; Charlton, M; Fajans, J; Fujiwara, M C; Gill, D R; Hangst, J S; Hardy, W N; Hayano, R S; Hayden, M E; Humphries, A J; Hydomako, R; Jørgensen, L V; Kerrigan, S J; Kurchaninov, L; Lambo, R; Madsen, N; Nolan, P; Olchanski, K; Olin, A; Povilus, A P; Pusa, P; Sarid, E; Seif El Nasr, S; Silveira, D M; Storey, J W; Thompson, R I; van der Werf, D P; Yamazaki, Y
2009-12-01
A microchannel plate (MCP)/phosphor screen assembly has been used to destructively measure the radial profile of cold, confined antiprotons, electrons, and positrons in the ALPHA experiment, with the goal of using these trapped particles for antihydrogen creation and confinement. The response of the MCP to low energy (10-200 eV, <1 eV spread) antiproton extractions is compared to that of electrons and positrons.
Antiproton, positron, and electron imaging with a microchannel plate/phosphor detector
Andresen, G. B.; Bowe, P. D.; Hangst, J. S.; Bertsche, W.; Butler, E.; Charlton, M.; Humphries, A. J.; Joergensen, L. V.; Kerrigan, S. J.; Madsen, N.; Werf, D. P. van der; Bray, C. C.; Chapman, S.; Fajans, J.; Povilus, A. P.; Cesar, C. L.; Lambo, R.; Fujiwara, M. C.; Gill, D. R.; Collaboration: ALPHA Collaboration; and others
2009-12-15
A microchannel plate (MCP)/phosphor screen assembly has been used to destructively measure the radial profile of cold, confined antiprotons, electrons, and positrons in the ALPHA experiment, with the goal of using these trapped particles for antihydrogen creation and confinement. The response of the MCP to low energy (10-200 eV, <1 eV spread) antiproton extractions is compared to that of electrons and positrons.
Production of free electron-positron pairs in relativistic heavy-ion collisions
NASA Astrophysics Data System (ADS)
Ionescu, D. C.; Eichler, J.
1993-08-01
The production of free electron-positron pairs in relativistic heavy-ion collisions is investigated within first-order time-dependent perturbation theory. An analytic expression for the differential pair-production cross section is obtained by employing Furry-Sommerfeld-Maue wave functions for the description of continuum states in the external field of the target nucleus. The angular distributions of electrons and positrons and cross sections are calculated and compared with previous results.
Excitation of the half-cyclotron waves by the counterstreaming electron-positron beams
Shokri, B.; Khorashadizadeh, S.M.
2005-08-15
The dispersion relation of the half-cyclotron waves excited by the interaction of the two counterstreaming electron-positron-plasma beams is obtained. Furthermore, obtaining the growth rate and the threshold for the instability development, the excitation of the half-cyclotron waves in a system of two rotating monoenergetic electron-positron counterstreaming beams flowing parallel to the external magnetic field is investigated.
Enigmatic electrons, photons, and ``empty`` waves
MacGregor, M.H.
1995-08-22
A spectroscopic analysis is made of electrons and photons from the standpoint of physical realism. In this conceptual framework, moving particles are portrayed as localized entities which are surrounded by ``empty`` waves. A spectroscopic model for the electron Stands as a guide for a somewhat similar, but in essential respects radically different, model for the photon. This leads in turn to a model for the ``zeron``. the quantum of the empty wave. The properties of these quanta mandate new basis states, and hence an extension of our customary framework for dealing with them. The zeron wave field of a photon differs in one important respect from the standard formalism for an electromagnetic wave. The vacuum state emerges as more than just a passive bystander. Its polarization properties provide wave stabilization, particle probability distributions, and orbit quantization. Questions with regard to special relativity are discussed.
Heat Deposition in Positron Sources for ILC
Bharadwaj, V.; Pitthan, R.; Sheppard, J.; Vincke, H.; Wang, J.W.; /SLAC
2006-03-15
In the International Linear Collider (ILC) positron source, multi-GeV electrons or multi-MeV photons impinge on a metal target to produce the needed positrons in the resulting electromagnetic showers. The incoming beam power is hundreds of kilowatts. Various computer programs -- such as FLUKA or MARS -- can calculate how the incoming beam showers in the target and can track the particle showers through the positron source system. Most of the incoming energy ends up as heat in the various positron source elements. This paper presents results from such calculations and their impact on the design of a positron source for the ILC.
NASA Astrophysics Data System (ADS)
Abdrashitov, S. V.; Bogdanov, O. V.; Dabagov, S. B.; Pivovarov, Yu L.; Tukhfatullin, T. A.
2016-07-01
We consider the radiator-converter approach at 200 MeV channeled electrons (the SPARC_LAB LNF facility energies) for the case of using W crystalline radiator and W amorphous converter. A comparison of the positron production by the axial channeling radiation and the bremsstrahlung is performed. The positron stopping in the convertor is studied by means of computer simulations. It is shown that for the maximum yield of positrons the thickness of the W amorphous converter should be taken 0.35 cm in the case of using the axial channeling radiation resulting to total yield of positrons 5 10-3 e+/e- and 0.71 cm in the case of using the bremsstrahlung resulting to total yield of positrons 3.3 10-3 e+/e-.
Small amplitude Kinetic Alfven waves in a superthermal electron-positron-ion plasma
NASA Astrophysics Data System (ADS)
Adnan, Muhammad; Mahmood, Sahahzad; Qamar, Anisa; Tribeche, Mouloud
2016-11-01
We are investigating the propagating properties of coupled Kinetic Alfven-acoustic waves in a low beta plasma having superthermal electrons and positrons. Using the standard reductive perturbation method, a nonlinear Korteweg-de Vries (KdV) type equation is derived which describes the evolution of Kinetic Alfven waves. It is found that nonlinearity and Larmor radius effects can compromise and give rise to solitary structures. The parametric role of superthermality and positron content on the characteristics of solitary wave structures is also investigated. It is found that only sub-Alfvenic and compressive solitons are supported in the present model. The present study may find applications in a low β electron-positron-ion plasma having superthermal electrons and positrons.
NASA Astrophysics Data System (ADS)
Wang, Xiaodan; Wang, Yunliang; Liu, Tielu; Zhang, Fan
2016-06-01
> Two-dimensional nonlinear magnetosonic solitary and shock waves propagating perpendicular to the applied magnetic field are presented in quantum electron-positron-ion plasmas with strongly coupled classical ions and weakly coupled quantum electrons and positrons. The generalized viscoelastic hydrodynamic model is used for the ions and a quantum hydrodynamic model is introduced for the electrons and positrons. In the weakly nonlinear limit, a modified Kadomstev-Petviashvili (KP) equation with a damping term and a KP-Burgers equation have been derived in the kinetic regime and hydrodynamic regime, respectively. The analytical and numerical solutions of the modified KP and KP-Burgers equations are also presented and analysed with the typical parameters of a white dwarf star and pulsar magnetosphere, which show that the quantum plasma beta and the variation of positron number density have remarkable effects on the propagation of magnetosonic solitary and shock waves.
NASA Astrophysics Data System (ADS)
Rahman, Ata-Ur; Ali, S.; Mushtaq, A.; Qamar, A.; Qamar
2013-10-01
The dynamics and propagation of ion acoustic (IA) waves are considered in an unmagnetized collisionless plasma, whose constituents are the relativistically degenerate electrons and positrons as well as the inertial cold ions. At a first step, a linear dispersion relation for IA waves is derived and analysed numerically. For nonlinear analysis, the reductive perturbation technique is used to derive a Korteweg-deVries equation, which admits a localized wave solution in the presence of relativistic degenerate electrons and positrons. It is shown that only compressive IA solitary waves can propagate, whose amplitude, width and phase velocity are significantly modified due to the positron concentration. The latter also strongly influences all the relativistic plasma parameters. Our present analysis is aimed to understand collective interactions in dense astrophysical objects, e.g. white dwarfs, where the lighter species electrons and positrons are taken as relativistically degenerate.
Quantum Mesoscopic Physics of Electrons and Photons
NASA Astrophysics Data System (ADS)
Akkermans, Eric
2013-03-01
We first review basic notions of coherent quantum transport at the mesoscopic scale for both electronic and photonic systems. We then show that successful descriptions developed for coherent electronic transport (e.g. weak localization and UCF) and thermodynamics (persistent currents), noise and full counting statistics can be extended and applied to the study of Quantum Electrodynamics of quantum conductors and of quantum optics based on photons emitted by such conductors. In this context, we discuss the two following specific problems : (1) Ramsey fringes and time domain interference for particle creation form a quantum vacuum with a specific application to dynamical Coulomb blockade. In that setup, the current noise of a coherent conductor is biased by two successive voltage pulses. An interference pattern between photon assisted processes is observed which is explained by the contribution of several processes to the probability to emit photons after each pulse. Recent experiments in this context will be discussed. (2) Quantum emitter coupled to a fractal environment. A new and unexpected type of oscillatory structures for the probability of spontaneous emission has been obtained which results from the fractal nature of the quantum vacuum. When applied to the case of a tunnel junction as a quantum emitter of photons, the same oscillatory structure arises for the conductance of the tunnel junction. This work was supported by the Israel Science Foundation Grant No.924/09
Alinejad, H.
2012-05-15
The linear and nonlinear propagation of ion-acoustic waves are investigated in a magnetized electron-positron-ion (e-p-i) plasma with nonthermal electrons. In the linear regime, the propagation of two possible modes and their evolution are studied via a dispersion relation. In the cases of parallel and perpendicular propagation, it is shown that these two possible modes are always stable. Then, the Korteweg-de Vries equation describing the dynamics of ion-acoustic solitary waves is derived from a weakly nonlinear analysis. The influence on the solitary wave characteristics of relevant physical parameters such as nonthermal electrons, magnetic field, obliqueness, positron concentration, and temperature ratio is examined. It is observed that the increasing nonthermal electrons parameter makes the solitary structures much taller and narrower. Also, it is revealed that the magnetic field strength makes the solitary waves more spiky. The present investigation contributes to the physics of the nonlinear electrostatic ion-acoustic waves in space and laboratory e-p-i plasmas in which wave damping produces an electron tail.
High-field electron-photon interactions
Hartemann, F V
1999-02-26
Recent advances in novel technologies (including chirped-pulse amplification, femtosecond laser systems operating in the TW-PW range, high-gradient rf photoinjectors, and synchronized relativistic electron bunches with subpicosecond durations and THz bandwidths) allow experimentalists to study the interaction of relativistic electrons with ultrahigh-intensity photon fields. Ponderomotive scattering can accelerate these electrons with extremely high gradients in a three-dimensional vacuum laser focus. The nonlinear Doppler shift induced by relativistic radiation pressure in Compton backscattering is shown to yield complex nonlinear spectra which can be modified by using temporal laser pulse shaping techniques. Colliding laser pulses, where ponderomotive acceleration and Compton backscattering are combined, could also yield extremely short wavelength photons. Finally, one expects strong radiative corrections when the Doppler-upshifted laser wavelength approaches the Compton scale. These are discussed within the context of high-field classical electrodynamics, a new discipline borne out of the aforementioned innovations.
The electron-cloud instability in the arcs of the PEP-II positron ring
Furman, Miguel A.; Lambertson, Glen R.
1998-03-01
We have applied our simulation code ''POSINST'' to evaluate, in linear approximation, the contribution to the growth rate of the electron-cloud instability (ECI) from the pumping sections and the dipole bending magnets in the arcs of the PEP-II positron ring. A key ingredient in our model is a detailed description of the secondary emission process off the TiN-coated chambers. Another important element is the analytic computation of the electric field produced by the beam, including the effects from surface charges. Space-charge forces of the electron cloud upon itself are also included, although these forces are negligible under nominal conditions. Bunch-length effects are optionally included by slicing the bunch into several kicks. We conclude that the growth rate is dominated by the pumping sections and scales linearly with the photoelectric yield Y'. For Y' = 1, our present estimate is in the range {approx} 1000-1300 s{sup -1}, depending upon the value of the photon reflectivity R. This is in the range controllable by the transverse feedback system. The contributions to the growth rate from other magnets and from other sections of the ring remain to be evaluated.
Study of secondary electrons and positrons produced by Terrestrial Gamma-ray Flashes
NASA Astrophysics Data System (ADS)
Sarria, D.; Blelly, P.-L.; Forme, F.
2015-12-01
Terrestrial Gamma ray Flahes are emissions of X and gamma rays, correlated to thunderstorms. By interacting with the atmosphere, the photons produce a large number of electrons and positrons. Some of these reach altitudes above ˜ 100 km that their interactions with the atmosphere become negligible, and they are then guided by Earth's magnetic field lines, forming the so called Terrestrial Electron Beams. The GBM instrument of the Fermi Space Telescope made a particularly interesting measurement of such an event that happened the 12/09/2009. We perform Monte-Carlo simulations to study this event in detail and we focus on the resulting time histograms. In agreement with previous works, we show that the histogram measured by Fermi GBM can be reproduced from simulations. We then show that the time histogram can be decomposed into three populations of leptons, coming from the hemisphere opposite from the TGF, and mirroring back to the satellite with interactions with the atmosphere or not, and that these we can be clearly distinguished both with their pitch angles.
Towards laboratory-produced relativistic electron-positron pair-plasmas
Chen, H; Wilks, S C; Meyerhofer, D D; Beiersdorfer, P; Cauble, R; Dollar, F; Falk, K; Hazi, A; Murphy, C D; Park, J; Seely, J; Szabo, C I; Shepherd, R; Tommasini, R; Zulick, K
2010-08-31
Relativistic pair-plasmas and jets are believed to exist in many astrophysical objects and are often invoked to explain energetic phenomena related to Gamma Ray Bursts and Black Holes. On earth, positrons from radioactive isotopes or accelerators are used extensively at low energies (sub-MeV) in areas related to surface science positron emission tomography and basic antimatter science. Experimental platforms capable of producing the high-temperature pair-plasma and high-flux jets required to simulate astrophysical positron conditions have so far been absent. In the last few years, we performed extensive experiments generating positrons with intense lasers where we found that relativistic electron and positron jets are produced by irradiating a solid gold target with an intense picosecond laser pulse. The positron temperatures in directions parallel and transverse to the beam both exceeded 0.5 MeV, and the density of electrons and positrons in these jets are of order 10{sup 16} cm{sup -3} and 10{sup 13} cm{sup -3}, respectively. With the advent of high-energy ultra-short laser pulses, we expect that a charge-neutral, relativistic pair-plasma is achievable, a novel regime of laboratory-produced hot dense matter. This talk will present some details of the laser-produced pair-plasma experiments.
NASA Astrophysics Data System (ADS)
Marjanović, S.; Banković, A.; White, R. D.; Buckman, S. J.; Garcia, G.; Malović, G.; Dujko, S.; Petrović, Z. Lj
2015-04-01
The recent availability of cross sections for positron (and positronium) interactions has made it possible to calculate transport properties and rates of collisions, and study in a quantitative fashion some aspects of positron-induced processes and their effects on living tissue. This paper models the interaction of primary positrons, and their secondary electrons, with water vapour (and subsequently liquid) using complete sets of cross sections predominately based on experimental binary collision data. We use a simple procedure to represent the presence of organic molecules where we look for dissociation of methane as a prototype of organic molecule dissociation. We isolate this particular process in order to establish whether the degree of damage is directly associated with the energy deposited in the tissue or whether some specific processes may cause excessive damage even with little energy deposition. We thus report on the relative contributions of initial positrons and secondary electrons in inducing dissociation, the spatial and energy profiles of individual collisional events, and positron/secondary electron tracks. It was found that secondary electrons induce 2-3 times more dissociations than the original positrons and with a longer range.
The scaling of electron and positron generation in intense laser-solid interactions
Chen, Hui; Link, A.; Fiuza, F.; Hazi, A.; Heeter, R. F.; Kemp, A. J.; Kemp, G. E.; Nagel, S. R.; Park, J.; Tommasini, R.; Williams, G. J.; Sentoku, Y.; Audebert, P.; Hill, M.; Hobbs, L.; Kerr, S.; Meyerhofer, D. D.; Myatt, J.
2015-05-15
This paper presents experimental scalings of the electrons and positrons produced by intense laser-target interactions at relativistic laser intensities (10{sup 18}–10{sup 20} W cm{sup −2}). The data were acquired from three short-pulse laser facilities with laser energies ranging from 80 to 1500 J. We found a non-linear (≈E{sub L}{sup 2}) scaling of positron yield [Chen et al., Phys. Rev. Lett. 114, 215001 (2015)] and a linear scaling of electron yield with the laser energy. These scalings are explained by theoretical and numerical analyses. Positron acceleration by the target sheath field is confirmed by the positron energy spectrum, which has a pronounced peak at energies near the sheath potential, as determined by the observed maximum energies of accelerated protons. The parameters of laser-produced electron-positron jets are summarized together with the theoretical energy scaling. The measured energy-squared scaling of relativistic electron-positron jets indicates the possibility to create an astrophysically relevant experimental platform with such jets using multi-kilojoule high intensity lasers currently under construction.
Monte Carlo electron/photon transport
Mack, J.M.; Morel, J.E.; Hughes, H.G.
1985-01-01
A review of nonplasma coupled electron/photon transport using Monte Carlo method is presented. Remarks are mainly restricted to linerarized formalisms at electron energies from 1 keV to 1000 MeV. Applications involving pulse-height estimation, transport in external magnetic fields, and optical Cerenkov production are discussed to underscore the importance of this branch of computational physics. Advances in electron multigroup cross-section generation is reported, and its impact on future code development assessed. Progress toward the transformation of MCNP into a generalized neutral/charged-particle Monte Carlo code is described. 48 refs.
NASA Astrophysics Data System (ADS)
Ruan, Shi-Sen; Wu, Shan; Raissan, Majid; Cheng, Ze
2013-08-01
This article presents the first study of the head-on collision between two magnetoacoustic solitary waves (MASWs) in magnetized quantum plasma consisting of electrons, positrons, and ions, using the extended Poincaré-Lighthill-Kou (PLK) method. The effects of the magnetic field intensity, the positron to ion number density ratio, the quantum parameter, the Fermi temperature ratio, and plasma number density on the solitary wave collisions are investigated. It is shown that these factors significantly modify the phase shift.
Study on Momentum Density of Electrons and Fermi Surface in Niobium by Positron Annihilation
NASA Astrophysics Data System (ADS)
Kubota, Takeshi; Kondo, Hitoshi; Watanabe, Kazuhiro; Murakami, Yasukazu; Cho, Yang-Koo; Tanigawa, Shoichiro; Kawano, Takao; Bahng, Gun-Woong
1990-12-01
The three dimensional electron-positron momentum density in niobium has been reconstructed from measurements of two dimensional angular correlation of positron annihilation radiations (2D-ACAR) followed by the image reconstruction technique based on a direct Fourier transformation. We determined the position of the Fermi surface sheets; \\varGamma-centered hole octahedron, multiply connected jungle-gym arms and N-centered hole ellipsoids. The Fermi surface topology is in good agreement with the theory.
THz Hot-Electron Photon Counter
NASA Technical Reports Server (NTRS)
Karasik, Boris S.; Sergeev, Andrei V.
2004-01-01
We present a concept for the hot-electron transition-edge sensor capable of counting THz photons. The main need for such a sensor is a spectroscopy on future space telescopes where a background limited NEP approx. 10(exp -20) W/H(exp 1/2) is expected at around 1 THz. Under these conditions, the rate of photon arrival is very low and any currently imaginable detector with sufficient sensitivity will operate in the photon counting mode. The Hot-Electron Photon Counter based on a submicron-size Ti bridge has a very low heat capacity which provides a high enough energy resolution (approx.140 GHz) at 0.3 K. With the sensor time constant of a few microseconds, the dynamic range would be approx. 30 dB. The sensor couples to radiation via a planar antenna and is read by a SQUID amplifier or by a 1-bit RSFQ ADC. A compact array of the antenna-coupled counters can be fabricated on a silicon wafer without membranes.
The magnetic toroidal sector: a broad-band electron-positron pair spectrometer
NASA Astrophysics Data System (ADS)
Hagmann, Siegbert; Hillenbrand, Pierre-Michel; Litvinov, Yuri; Spillmann, Uwe
2016-05-01
At the future relativistic storage-ring HESR at FAIR the study of electron-positron pairs from non-nuclear, atomic processes will be one of the goals of the experimental program with kinematically complete experiments focusing on momentum spectroscopy of coincident emission of electrons and positrons from free-free pairs and corresponding recoil ions. The underlying production mechanisms belong to central topics of QED in strong fields. We present first results on the electron-optical properties of a magnetic toroidal sector configuration enabling coincident detection of free-free electron-positron pairs; this spectrometer is suitable for implementation into a storage ring with a supersonic jet target and covering a wide range of lepton emission into the forward hemisphere. The simulation calculations are performed using the OPERA code.
Khan, S. A.; Ayub, M. K.; Ahmad, Ali
2012-10-15
Quantum plasma oscillations are studied in a strongly magnetized, ultra-dense plasma with degenerate electrons and positrons. The dispersive role of electron and positron quantum effects on low frequency (in comparison to electron cyclotron frequency) shear electromagnetic wave is investigated by employing hydrodynamic formulation. In the presence of ions, the density balance changes, and the electromagnetic wave (with frequency lower than the ion cyclotron frequency) is shown to couple with electrostatic ion mode under certain conditions. For such low frequency waves, it is also seen that the contribution of electron and positron degeneracy pressure is dominant as compared to their diffraction effects. The results are analyzed numerically for illustrative purpose pointing out their relevance to the dense laboratory (e.g., super-intense laser-dense matter interactions) and astrophysical plasmas.
NASA Astrophysics Data System (ADS)
Khan, S. A.; Ayub, M. K.; Ahmad, Ali
2012-10-01
Quantum plasma oscillations are studied in a strongly magnetized, ultra-dense plasma with degenerate electrons and positrons. The dispersive role of electron and positron quantum effects on low frequency (in comparison to electron cyclotron frequency) shear electromagnetic wave is investigated by employing hydrodynamic formulation. In the presence of ions, the density balance changes, and the electromagnetic wave (with frequency lower than the ion cyclotron frequency) is shown to couple with electrostatic ion mode under certain conditions. For such low frequency waves, it is also seen that the contribution of electron and positron degeneracy pressure is dominant as compared to their diffraction effects. The results are analyzed numerically for illustrative purpose pointing out their relevance to the dense laboratory (e.g., super-intense laser-dense matter interactions) and astrophysical plasmas.
Positron and electron scattering from alkane molecules. Normal- and cyclo-octane
NASA Astrophysics Data System (ADS)
Sueoka, O.; Makochekanwa, C.; Kimura, M.
2006-03-01
Total cross-sections (TCSs) for 0.2 1000 eV positrons and 0.4 1000 eV electrons colliding with normal-octane and cyclo-octane molecules have been studied using a relative measurement method. The TCS curves for positron and electron vary smoothly and compare well with other alkane molecules, in order of increasing carbon number. For positron scattering, weak humps at 1.5 2.5 eV for both normal- and cyclo-octane were observed. In the energy range lower than 2.2 eV, positron TCSs are roughly equal to or larger than electron TCSs. For electron scattering, a resonance peak at 8 eV and a shoulder at 25.0 eV were observed for both molecules. Over all the energy range, the TCS values for normal-octane are larger than those of cyclo-octane. The positron and electron TCS data for normal- and cyclo-octane molecules are briefly compared with those for normal- and cyclo-hexane.
Environmental assessment for the proposed B-Factory (Asymmetric Electron Positron Collider)
Not Available
1993-11-01
This document presents the potential environmental consequences associated with the construction and operation of an Asymmetric Electron Positron Collider, also known as a B-Factory. DOE proposes to modify either the existing Positron-Electron Project at the Stanford Linear Accelerator Center (SLAC) or the Cornell Electron Storage Ring (CESR) at Cornell University. PEP and CESR provide the most technically promising and practical options for a B-Factory. A B-Factory can be constructed by modifying the existing facilities and with minor or no conventional construction. Details involved with the upgrade along with two alternatives to the proposed action are described.
Code System for Monte Carlo Simulation of Electron and Photon Transport.
2015-07-01
Version 01 PENELOPE performs Monte Carlo simulation of coupled electron-photon transport in arbitrary materials and complex quadric geometries. A mixed procedure is used for the simulation of electron and positron interactions (elastic scattering, inelastic scattering and bremsstrahlung emission), in which hard events (i.e. those with deflection angle and/or energy loss larger than pre-selected cutoffs) are simulated in a detailed way, while soft interactions are calculated from multiple scattering approaches. Photon interactions (Rayleigh scattering, Compton scattering,more » photoelectric effect and electron-positron pair production) and positron annihilation are simulated in a detailed way. PENELOPE reads the required physical information about each material (which includes tables of physical properties, interaction cross sections, relaxation data, etc.) from the input material data file. The material data file is created by means of the auxiliary program MATERIAL, which extracts atomic interaction data from the database of ASCII files. PENELOPE mailing list archives and additional information about the code can be found at http://www.nea.fr/lists/penelope.html. See Abstract for additional features.« less
Code System for Monte Carlo Simulation of Electron and Photon Transport.
2015-07-01
Version 01 PENELOPE performs Monte Carlo simulation of coupled electron-photon transport in arbitrary materials and complex quadric geometries. A mixed procedure is used for the simulation of electron and positron interactions (elastic scattering, inelastic scattering and bremsstrahlung emission), in which hard events (i.e. those with deflection angle and/or energy loss larger than pre-selected cutoffs) are simulated in a detailed way, while soft interactions are calculated from multiple scattering approaches. Photon interactions (Rayleigh scattering, Compton scattering, photoelectric effect and electron-positron pair production) and positron annihilation are simulated in a detailed way. PENELOPE reads the required physical information about each material (which includes tables of physical properties, interaction cross sections, relaxation data, etc.) from the input material data file. The material data file is created by means of the auxiliary program MATERIAL, which extracts atomic interaction data from the database of ASCII files. PENELOPE mailing list archives and additional information about the code can be found at http://www.nea.fr/lists/penelope.html. See Abstract for additional features.
Particle Acceleration and Magnetic Field Generation in Electron-Positron Relativistic Shocks
NASA Technical Reports Server (NTRS)
Nishikawa, K.-I.; Hardee, P.; Richardson, G.; Preece, R.; Sol, H.; Fishman, G. J.
2004-01-01
Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., Buneman, Weibel and other two-stream instabilities) created in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic electron-positron jet front propagating into an ambient electron-positron plasma with and without initial magnetic fields. We find small differences in the results for no ambient and modest ambient magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. The non-linear fluctuation amplitudes of densities, currents, electric, and magnetic fields in the electron-positron shock are larger than those found in the electron-ion shock studied in a previous paper. This comes from the fact that both electrons and positrons contribute to generation of the Weibel instability. Additionally, we have performed simulations with different electron skin depths. We find that growth times scale inversely with the plasma frequency, and the sizes of structures created by the Weibel instability scale proportional to the electron skin depth. This is the expected result and indicates that the simulations have sufficient grid resolution. While some Fermi acceleration may occur at the jet front, the majority of electron and positron acceleration takes place behind the jet front and cannot be characterized as Fermi acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying nonuniform, small-scale magnetic fields which contribute to the electron's (positron's) transverse deflection behind the jet head. This small scale magnetic field structure is appropriate to the generation
Particle Acceleration and Magnetic Field Generation in Electron-Positron Relativistic Shocks
NASA Technical Reports Server (NTRS)
Nishikawa, K.-L.; Hardee, P.; Richardson, G.; Preece, R.; Sol, H.; Fishman, G. J.
2004-01-01
Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., Buneman, Weibel and other two-stream instabilities) created in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic electron-positron jet front propagating into an ambient electron-positron plasma with and without initial magnetic fields. We find small differences in the results for no ambient and modest ambient magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. The non-linear fluctuation amplitudes of densities, currents, electric, and magnetic fields in the electron-positron shock are larger than those found in the electron-ion shock studied in a previous paper at the comparable simulation time. This comes from the fact that both electrons and positrons contribute to generation of the Weibel instability. Additionally, we have performed simulations with different electron skin depths. We find that growth times scale inversely with the plasma frequency, and the sizes of structures created by the Weibel instability scale proportional to the electron skin depth. This is the expected result and indicates that the simulations have sufficient grid resolution. While some Fermi acceleration may occur at the jet front, the majority of electron and positron acceleration takes place behind the jet front and cannot be characterized as Fermi acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying nonuniform: small-scale magnetic fields which contribute to the electron's (positron's) transverse deflection behind the jet head. This small scale magnetic field structure
Particle Acceleration and Magnetic Field Generation in Electron-Positron Relativistic Shocks
NASA Technical Reports Server (NTRS)
Nishikawa, K.-I.; Hardee, P.; Richardson, G.; Preece, R.; Sol, H.; Fishman, G. J.
2005-01-01
Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., Buneman, Weibel, and other two-stream instabilities) created in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a three-dimensional relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic electron-positron jet front propagating into an ambient electron-positron plasma with and without initial magnetic fields. We find small differences in the results for no ambient and modest ambient magnetic fields. New simulations show that the Weibel instability created in the collisionless shock front accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. Furthermore, the nonlinear fluctuation amplitudes of densities, currents, and electric and magnetic fields in the electron-positron shock are larger than those found in the electron-ion shock studied in a previous paper at a comparable simulation time. This comes from the fact that both electrons and positrons contribute to generation of the Weibel instability. In addition, we have performed simulations with different electron skin depths. We find that growth times scale inversely with the plasma frequency, and the sizes of structures created by tine Weibel instability scale proportionally to the electron skin depth. This is the expected result and indicates that the simulations have sufficient grid resolution. While some Fermi acceleration may occur at the jet front, the majority of electron and positron acceleration takes place behind the jet front and cannot be characterized as Fermi acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying nonuniform, small-scale magnetic fields, which contribute to the electron s (positron s) transverse deflection behind the jet head. This
Photon/Electron Benchmarks for Intercode Comparisons
Hughes, Henry Grady III; Sweezy, Jeremy Ed; Lemaire, Sebastien
2015-07-21
The goal of this work was to improve accuracy and efficiency of two Monte-Carlo transport codes (MCNP and DIANE) with an emphasis on γ+electron physics. The approach involved intercode comparisons + measurements for gamma/e^{-} energy deposition in a cylinder with a photon source and different materials (C, Pb) and the bombardment of 15-MeV electrons on thick targets (Al, Be, Pb). Comparisons of the codes DIANE and MCNP6 showed good agreement (differences < 3%) for gamma-electron energy deposition in a 2D cylinder, except for the first 0.1 μm of lead (difference < 10%). Comparisons with measurements showed generally good agreement, often better than 10%; best-performing codes/options are problem-dependent; and single-event discrepancies are in active use in reviewing electron elastic scattering.
Wakefields generated by collisional neutrinos in neutral-electron-positron plasma
Tinakiche, Nouara
2013-02-15
A classical fluid description is adopted to investigate nonlinear interaction between an electron-type neutrino beam and a relativistic collisionless unmagnetized neutral-electron-positron plasma. In this work, we consider the collisions of the neutrinos with neutrals in the plasma and study their effect on the generation of wakefields in this plasma.
Positron-electron decay of 28Si at an excitation energy of 50 MeV
NASA Astrophysics Data System (ADS)
Buda, A.; Bacelar, J. C.; Balanda, A.; van der Ploeg, H.; Sujkowski, Z.; van der Woude, A.
1993-03-01
The electron-position pair decay of 28Si at 50 MeV excitation produced by the isospin T=0 (α + 24Mg) and the mixed isospin T=0,1 (3He + 25Mg) reactions has been studied using a special designed Positron-Electron pair spectrometer PEPSI.
NASA Technical Reports Server (NTRS)
Wu, Jianshi; Derrickson, J. H.; Parnell, T. A.; Strayer, M. R.
1999-01-01
We study the screening effects of the atomic electrons in the electromagnetic production of electron-positron pairs in relativistic nucleus-atom collisions for fixed target experiments. Our results are contrasted with those obtained in bare collisions, with particular attention given to its dependence on the beam energy and the target atom.
Ceeh, Hubert; Weber, Josef Andreas; Weber, Josef Andreass; Böni, Peter; Leitner, Michael; Benea, Diana; Chioncel, Liviu; Ebert, Hubert; Minár, Jan; Vollhardt, Dieter; Hugenschmidt, Christoph
2016-01-01
We employ a positron annihilation technique, the spin-polarized two-dimensional angular correlation of annihilation radiation (2D-ACAR), to measure the spin-difference spectra of ferromagnetic nickel. The experimental data are compared with the theoretical results obtained within a combination of the local spin density approximation (LSDA) and the many-body dynamical mean-field theory (DMFT). We find that the self-energy defining the electronic correlations in Ni leads to anisotropic contributions to the momentum distribution. By direct comparison of the theoretical and experimental results we determine the strength of the local electronic interaction U in ferromagnetic Ni as 2.0 ± 0.1 eV. PMID:26879249
Ceeh, Hubert; Weber, Josef Andreass; Böni, Peter; Leitner, Michael; Benea, Diana; Chioncel, Liviu; Ebert, Hubert; Minár, Jan; Vollhardt, Dieter; Hugenschmidt, Christoph
2016-01-01
We employ a positron annihilation technique, the spin-polarized two-dimensional angular correlation of annihilation radiation (2D-ACAR), to measure the spin-difference spectra of ferromagnetic nickel. The experimental data are compared with the theoretical results obtained within a combination of the local spin density approximation (LSDA) and the many-body dynamical mean-field theory (DMFT). We find that the self-energy defining the electronic correlations in Ni leads to anisotropic contributions to the momentum distribution. By direct comparison of the theoretical and experimental results we determine the strength of the local electronic interaction U in ferromagnetic Ni as 2.0 ± 0.1 eV. PMID:26879249
NASA Technical Reports Server (NTRS)
Gidley, D. W.; Rich, A.; Van House, J. C.; Zitzewitz, P. W.
1981-01-01
A positronium-formation experiment with a high sensitivity to a possible relation between the helicity of beta particles emitted in nuclear beta decay and the optical asymmetry of biological molecules is presented. The experiment is based on a mechanism in which the electrons in optically active molecules possess a helicity of less than 0.001, too weak to detect in radiolysis experiments, the sign of which depends on the chirality of the isomer. A helicity-dependent asymmetry is sought in the formation of the triplet ground state of positronium when a low-energy beam of polarized positrons of reversible helicity interacts with an optically active substance coating a channel electron multiplier. Asymmetries between positronium decays observed at positive and negative helicities for the same substance can thus be determined with a sensitivity of 0.0001, which represents a factor of 100 improvement over previous positronium experiments.
An arbitrary amplitude fast magnetosonic soliton in quantum electron-positron-ion plasmas
NASA Astrophysics Data System (ADS)
Hussain, S.; Mushtaq, A.; Mahmood, S.
2013-02-01
Nonlinear fast magnetosonic waves are studied in a collisionless homogenous, magnetized electron-positron-ion (e-p-i) plasma. The multi-component quantum magneto-hydrodynamic model is used in which ions are assumed to be dynamic whereas electron and positron quantum fluids are taken to be inertialess. The Sagdeev potential approach is used to obtain arbitrary amplitude magnetosonic structures in dense e-p-i plasmas. It is found that the wave amplitude as well as the width of the magnetosonic structure depends on different plasma parameters such as the electron to positron density ratio, plasma beta, quantum parameter and the Alfvénic Mach number. The numerical results have also been obtained for illustration.
Nonlinear ion-acoustic structures in dusty plasma with superthermal electrons and positrons
El-Tantawy, S. A.; El-Bedwehy, N. A.; Moslem, W. M.
2011-05-15
Nonlinear ion-acoustic structures are investigated in an unmagnetized, four-component plasma consisting of warm ions, superthermal electrons and positrons, as well as stationary charged dust impurities. The basic set of fluid equations is reduced to modified Korteweg-de Vries equation. The latter admits both solitary waves and double layers solutions. Numerical calculations indicate that these nonlinear structures cannot exist for all physical parameters. Therefore, the existence regions for both solitary and double layers excitations have been defined precisely. Furthermore, the effects of temperature ratios of ions-to-electrons and electrons-to-positrons, positrons and dust concentrations, as well as superthermal parameters on the profiles of the nonlinear structures are investigated. Also, the acceleration and deceleration of plasma species have been highlight. It is emphasized that the present investigation may be helpful in better understanding of nonlinear structures which propagate in astrophysical environments, such as in interstellar medium.
Generation of neutral and high-density electron-positron pair plasmas in the laboratory.
Sarri, G; Poder, K; Cole, J M; Schumaker, W; Di Piazza, A; Reville, B; Dzelzainis, T; Doria, D; Gizzi, L A; Grittani, G; Kar, S; Keitel, C H; Krushelnick, K; Kuschel, S; Mangles, S P D; Najmudin, Z; Shukla, N; Silva, L O; Symes, D; Thomas, A G R; Vargas, M; Vieira, J; Zepf, M
2015-01-01
Electron-positron pair plasmas represent a unique state of matter, whereby there exists an intrinsic and complete symmetry between negatively charged (matter) and positively charged (antimatter) particles. These plasmas play a fundamental role in the dynamics of ultra-massive astrophysical objects and are believed to be associated with the emission of ultra-bright gamma-ray bursts. Despite extensive theoretical modelling, our knowledge of this state of matter is still speculative, owing to the extreme difficulty in recreating neutral matter-antimatter plasmas in the laboratory. Here we show that, by using a compact laser-driven setup, ion-free electron-positron plasmas with unique characteristics can be produced. Their charge neutrality (same amount of matter and antimatter), high-density and small divergence finally open up the possibility of studying electron-positron plasmas in controlled laboratory experiments. PMID:25903920
Jet algorithms in electron-positron annihilation: perturbative higher order predictions
NASA Astrophysics Data System (ADS)
Weinzierl, Stefan
2011-02-01
This article gives results on several jet algorithms in electron-positron annihilation: Considered are the exclusive sequential recombination algorithms Durham, Geneva, Jade-E0 and Cambridge, which are typically used in electron-positron annihilation. In addition also inclusive jet algorithms are studied. Results are provided for the inclusive sequential recombination algorithms Durham, Aachen and anti- k t , as well as the infrared-safe cone algorithm SISCone. The results are obtained in perturbative QCD and are N3LO for the two-jet rates, NNLO for the three-jet rates, NLO for the four-jet rates and LO for the five-jet rates.
Acoustic double layer structures in dense magnetized electron-positron-ion plasmas
NASA Astrophysics Data System (ADS)
Akhtar, N.; Mahmood, S.
2011-11-01
The acoustic double layer structures are studied using quantum hydrodynamic model in dense magnetized electron-positron-ion plasmas. The extended Korteweg-de Vries is derived using reductive perturbation method. It is found that increase in the ion concentration in dense magnetized electron-positron plasmas increases the amplitude as well as the steepness of the double layer structure. However, increase in the magnetic field strength and decrease in the obliqueness of the nonlinear acoustic wave enhances only the steepness of the double layer structures. The numerical results have also been shown by using the data of the outer layer regions of white dwarfs given in the literature.
Acoustic double layer structures in dense magnetized electron-positron-ion plasmas
Akhtar, N.; Mahmood, S.
2011-11-15
The acoustic double layer structures are studied using quantum hydrodynamic model in dense magnetized electron-positron-ion plasmas. The extended Korteweg-de Vries is derived using reductive perturbation method. It is found that increase in the ion concentration in dense magnetized electron-positron plasmas increases the amplitude as well as the steepness of the double layer structure. However, increase in the magnetic field strength and decrease in the obliqueness of the nonlinear acoustic wave enhances only the steepness of the double layer structures. The numerical results have also been shown by using the data of the outer layer regions of white dwarfs given in the literature.
Visible and dark matter genesis and cosmic positron and electron excesses
Gu Peihong; Sarkar, Utpal; Zhang Xinmin
2009-10-01
Dark and baryonic matter contribute comparable energy density to the present universe. The dark matter may also be responsible for the cosmic positron and electron excesses. We connect these phenomena with the Dirac seesaw for neutrino masses. In our model (i) the dark matter relic density is a dark matter asymmetry generated simultaneously with the baryon asymmetry so that we can naturally understand the coincidence between the dark and baryonic matter and (ii) the dark matter mostly decays into the leptons so that its decay can interpret the anomalous cosmic rays with positron and electron excesses.
Electron and positron scattering on rubidium at 200 eV
Chin, J. H.; Ratnavelu, K.; Zhou, Y.
2014-03-05
The recent implementation of the coupled-channels-optical method (CCOM) [1,2], in the study of the electron and positron-Rubidium(Rb) scattering at intermediate energies [3,4], shows that the continuum effect remains important as the energy increases, even to 100 eV. Here, we study the effect of the continuum in electron and positron scattering on Rb at an even higher energy namely 200 eV. The total, elastic and inelastic integral and differential cross sections are therefore calculated and compared to the available experimental [5] and theoretical data [6,7].
Coupled electron-photon radiation transport
Lorence, L.; Kensek, R.P.; Valdez, G.D.; Drumm, C.R.; Fan, W.C.; Powell, J.L.
2000-01-17
Massively-parallel computers allow detailed 3D radiation transport simulations to be performed to analyze the response of complex systems to radiation. This has been recently been demonstrated with the coupled electron-photon Monte Carlo code, ITS. To enable such calculations, the combinatorial geometry capability of ITS was improved. For greater geometrical flexibility, a version of ITS is under development that can track particles in CAD geometries. Deterministic radiation transport codes that utilize an unstructured spatial mesh are also being devised. For electron transport, the authors are investigating second-order forms of the transport equations which, when discretized, yield symmetric positive definite matrices. A novel parallelization strategy, simultaneously solving for spatial and angular unknowns, has been applied to the even- and odd-parity forms of the transport equation on a 2D unstructured spatial mesh. Another second-order form, the self-adjoint angular flux transport equation, also shows promise for electron transport.
NASA Astrophysics Data System (ADS)
Adnan, Muhammad; Williams, Gina; Qamar, Anisa; Mahmood, Shahzad; Kourakis, Ioannis
2014-09-01
The propagation of linear and nonlinear electrostatic waves is investigated in a magnetized anisotropic electron-positron-ion (e-p-i) plasma with superthermal electrons and positrons. A two-dimensional plasma geometry is assumed. The ions are assumed to be warm and anisotropic due to an external magnetic field. The anisotropic ion pressure is defined using the double adiabatic Chew-Golberger-Low (CGL) theory. In the linear regime, two normal modes are predicted, whose characteristics are investigated parametrically, focusing on the effect of superthermality of electrons and positrons, ion pressure anisotropy, positron concentration and magnetic field strength. A Zakharov-Kuznetsov (ZK) type equation is derived for the electrostatic potential (disturbance) via a reductive perturbation method. The parametric role of superthermality, positron content, ion pressure anisotropy and magnetic field strength on the characteristics of solitary wave structures is investigated. Following Allen and Rowlands [J. Plasma Phys. 53, 63 (1995)], we have shown that the pulse soliton solution of the ZK equation is unstable to oblique perturbations, and have analytically traced the dependence of the instability growth rate on superthermality and ion pressure anisotropy.
Electron and Positron Scattering with a Few Alkyne Molecules - Theoretical Cross sections
NASA Astrophysics Data System (ADS)
Patel, U. R.; Joshipura, K. N.; Kothari, H. N.
2016-05-01
Electron molecule scattering processes play an important role in the understanding of the electron driven physiochemical phenomena in diverse environments such as biological media, planetary atmospheres, interstellar clouds and plasmas. In modeling and simulating effects induced by electrons traversing through matter, the relevant cross section data are required as an input. An alternative probe, positron has also been used for the similar study of atoms, molecules and matter in bulk. Interaction of positrons with atoms and molecules differs from electron interactions due to opposite sign of charge and absence of exchange potential. In the present paper, our aim is to apply an identical theoretical method1,2 to electrons as well as positrons interacting with alkyne molecules like acetylene (HC ≡ CH), 1- Butyne (HC ≡ C- CH2 CH3) and Propyne (HC ≡ C- CH3) . We have carried out calculations of total scattering cross sections by starting with complex potential approach followed by the solution of the Schrodinger equation using numerical method. Ionization cross sections are deduced as in1,2. Comparisons have been made with available theoretical and experimental results for both electron (e-) and positron (e+) . The study will be extended to alkanes and alkenes.
Theory of photon and electron induced reactions
Onley, D.S.; Wright, L.E.
1992-01-01
During the first year and half of the current grant from the Department of Energy we have made considerable progress on the following aspects of the general investigation of electron and photon induced reactions: (1) photo- and electro-production of mesons; (2) Coulomb distortion effects on (e,e{prime}{gamma}) and (e,e{prime}) and (e,e{prime}p) in the quasi-elastic region, (3) studies involving the relativistic shell model, and (4) quark models. We will report on each of these developments in this paper.
Measurement of Separate Cosmic-Ray Electron and Positron Spectra with the Fermi Large Area Telescope
NASA Technical Reports Server (NTRS)
Ferrara, E. C.; Harding, A. K.; McEnery, J. E.; Moiseev, A. A.; Ackemann, M.
2012-01-01
We measured separate cosmic-ray electron and positron spectra with the Fermi Large Area Telescope. Because the instrument does not have an onboard magnet, we distinguish the two species by exploiting Earth's shadow, which, is offset in opposite directions for opposite charges due to Earth's magnetic field. We estimate and subtract the cosmic-ray proton background using two different methods that produce consistent results. We report the electron-only spectrum, the positron-only spectrum, and the positron fraction between 20 and 200 Ge V. We confirm that the fraction rises with energy in the 20-100 Ge V range. The three new spectral points between 100 and 200 GeV are consistent with a fraction that is continuing to rise with energy.
Study of defects in electron irradiated CuInSe{sub 2} by positron lifetime spectroscopy
Polity, A.; Krause-Rehberg, R.; Staab, T.E.; Puska, M.J.; Klais, J.; Moeller, H.J.; Meyer, B.K.
1998-01-01
CuInSe{sub 2} was studied in the as-grown state and after low-temperature (4 K) 2 MeV electron irradiation. The positron bulk lifetime of 235 ps was measured for the unirradiated sample. The positron bulk lifetime was theoretically calculated and is in good agreement with the experimental value. In addition, the defect-related lifetimes for mono-, di-, and trivacancies are theoretically determined. An increased average positron lifetime indicated after electron irradiation the appearance of open-volume defects, most probably of divacancy type. The disappearance of this defect was observed during annealing below 250 K. Other defects were formed leading to a divacancy signal at least stable up to 600 K in the temperature range above 450 K. {copyright} {ital 1998 American Institute of Physics.}
Measurement of Separate Cosmic-Ray Electron and Positron Spectra with the Fermi Large Area Telescope
NASA Technical Reports Server (NTRS)
Ackermann, M.; Ajello, M.; Allafort, A.; Baldini, L.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Brogland, A. W.; Bouvier, A.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Ferrara, E. C.; Harding, A. K.; McEnery, J. E.
2011-01-01
We measured separate cosmic-ray electron and positron spectra with the Fermi Large Area Telescope. Because the instrument does not have an onboard magnet, we distinguish the two species by exploiting the Earth's shadow, which is offset in opposite directions for opposite charges due to the Earth's magnetic field. We estimate and subtract the cosmic-ray proton background using two different methods that produce consistent results. We report the electron-only spectrum, the positron-only spectrum, and the positron fraction between 20 GeV and 200 GeV, We confirm that the fraction rises with energy in the 20-100 GeV range and determine for the first time that it continues to rise between 100 and 200 GeV,
NASA Astrophysics Data System (ADS)
Gill, T. S.; Bala, Parveen; Bains, A. S.
2015-05-01
A rigorous theoretical study based on Zakharov Kuznetsov (ZK) equation of ion-acoustic solitary waves (IASWs), their stability analysis in a magnetized e- p- i plasma is presented. The plasma model consists of inertial ions, magnetic field, electrons and positrons obeying q-nonextensive velocity distribution. Reductive perturbation method is used to derive ZK equation. The solitary wave structures are dependent on chosen plasma model, whose parameters influence the solitary characteristics. Particularly, nonextensivity, proportion of positron concentration, magnetic field and difference between electron and positron temperatures play crucial role in the solitary structures. The present work is also extended to give stability analysis and parametric ranges for the existence of stable and unstable solitons. This research work may be useful to understand the physics of nonlinear electrostatic excitations in different astrophysical and cosmic scenarios like stellar polytropes, hadron matter and quark-gluon plasma.
Ion acoustic shock waves in plasmas with warm ions and kappa distributed electrons and positrons
Hussain, S.; Mahmood, S.; Hafeez Ur-Rehman
2013-06-15
The monotonic and oscillatory ion acoustic shock waves are investigated in electron-positron-ion plasmas (e-p-i) with warm ions (adiabatically heated) and nonthermal kappa distributed electrons and positrons. The dissipation effects are included in the model due to kinematic viscosity of the ions. Using reductive perturbation technique, the Kadomtsev-Petviashvili-Burgers (KPB) equation is derived containing dispersion, dissipation, and diffraction effects (due to perturbation in the transverse direction) in e-p-i plasmas. The analytical solution of KPB equation is obtained by employing tangent hyperbolic (Tanh) method. The analytical condition for the propagation of oscillatory and monotonic shock structures are also discussed in detail. The numerical results of two dimensional monotonic shock structures are obtained for graphical representation. The dependence of shock structures on positron equilibrium density, ion temperature, nonthermal spectral index kappa, and the kinematic viscosity of ions are also discussed.
Ackermann, M; Ajello, M; Allafort, A; Atwood, W B; Baldini, L; Barbiellini, G; Bastieri, D; Bechtol, K; Bellazzini, R; Berenji, B; Blandford, R D; Bloom, E D; Bonamente, E; Borgland, A W; Bouvier, A; Bregeon, J; Brigida, M; Bruel, P; Buehler, R; Buson, S; Caliandro, G A; Cameron, R A; Caraveo, P A; Casandjian, J M; Cecchi, C; Charles, E; Chekhtman, A; Cheung, C C; Chiang, J; Ciprini, S; Claus, R; Cohen-Tanugi, J; Conrad, J; Cutini, S; de Angelis, A; de Palma, F; Dermer, C D; Digel, S W; do Couto E Silva, E; Drell, P S; Drlica-Wagner, A; Favuzzi, C; Fegan, S J; Ferrara, E C; Focke, W B; Fortin, P; Fukazawa, Y; Funk, S; Fusco, P; Gargano, F; Gasparrini, D; Germani, S; Giglietto, N; Giommi, P; Giordano, F; Giroletti, M; Glanzman, T; Godfrey, G; Grenier, I A; Grove, J E; Guiriec, S; Gustafsson, M; Hadasch, D; Harding, A K; Hayashida, M; Hughes, R E; Jóhannesson, G; Johnson, A S; Kamae, T; Katagiri, H; Kataoka, J; Knödlseder, J; Kuss, M; Lande, J; Latronico, L; Lemoine-Goumard, M; Llena Garde, M; Longo, F; Loparco, F; Lovellette, M N; Lubrano, P; Madejski, G M; Mazziotta, M N; McEnery, J E; Michelson, P F; Mitthumsiri, W; Mizuno, T; Moiseev, A A; Monte, C; Monzani, M E; Morselli, A; Moskalenko, I V; Murgia, S; Nakamori, T; Nolan, P L; Norris, J P; Nuss, E; Ohno, M; Ohsugi, T; Okumura, A; Omodei, N; Orlando, E; Ormes, J F; Ozaki, M; Paneque, D; Parent, D; Pesce-Rollins, M; Pierbattista, M; Piron, F; Pivato, G; Porter, T A; Rainò, S; Rando, R; Razzano, M; Razzaque, S; Reimer, A; Reimer, O; Reposeur, T; Ritz, S; Romani, R W; Roth, M; Sadrozinski, H F-W; Sbarra, C; Schalk, T L; Sgrò, C; Siskind, E J; Spandre, G; Spinelli, P; Strong, A W; Takahashi, H; Takahashi, T; Tanaka, T; Thayer, J G; Thayer, J B; Tibaldo, L; Tinivella, M; Torres, D F; Tosti, G; Troja, E; Uchiyama, Y; Usher, T L; Vandenbroucke, J; Vasileiou, V; Vianello, G; Vitale, V; Waite, A P; Winer, B L; Wood, K S; Wood, M; Yang, Z; Zimmer, S
2012-01-01
We measured separate cosmic-ray electron and positron spectra with the Fermi Large Area Telescope. Because the instrument does not have an onboard magnet, we distinguish the two species by exploiting Earth's shadow, which is offset in opposite directions for opposite charges due to Earth's magnetic field. We estimate and subtract the cosmic-ray proton background using two different methods that produce consistent results. We report the electron-only spectrum, the positron-only spectrum, and the positron fraction between 20 and 200 GeV. We confirm that the fraction rises with energy in the 20-100 GeV range. The three new spectral points between 100 and 200 GeV are consistent with a fraction that is continuing to rise with energy.
Chapman, J D; Schneider, R F; Urbain, J L; Hanks, G E
2001-01-01
Radiotherapy prescription can now be customized to target the major mechanism(s) of resistance of individual tumors. In that regard, functional imaging techniques should be exploited to identify the dominant mechanism(s). Tumor biology research has identified several mechanisms of tumor resistance that may be unique to radiation treatments. These fall into 3 broad areas associated with (1) tumor hypoxic fraction, (2) tumor growth rate, (3) and the intrinsic radiosensitivity of tumor clonogens. Imaging research has markers in various stages of development for quantifying relevant information about each of these mechanisms, and those that measure tumor oxygenation and predict for radioresistance are the most advanced. Positron-emission tomography (PET) measurement of oxygen 15 has yielded important information, particularly about brain tissue perfusion, metabolism, and function. Indirect markers of tumor hypoxia have exploited the covalent binding of bioreductive intermediates of azomycin-containing compounds whose uptakes are inversely proportional to intracellular oxygen concentrations. Pilot clinical studies with single-photon emission computed tomography (SPECT) and PET detection of radiolabeled markers to tumor hypoxia have been reported. Recently, other studies have attempted to exploit the reduction properties of both technetium and copper chelates for the selective deposition of radioactive metals in hypoxic tissues. A growing number of potentially useful isotopes are now available for labeling several novel chemicals that could have the appropriate specificity and sensitivity. Preclinical studies with "microSPECT" and "microPET" will be important to define the optimal radiodiagnostic(s) for measuring tissue oxygenation and for determining the time after their administration for optimal hypoxic signal acquisition. Radiolabeled markers of growth kinetics and intrinsic radiosensitivity of cells in solid tumors are also being developed. We conclude that
Ion-acoustic cnoidal waves in plasmas with warm ions and kappa distributed electrons and positrons
Kaladze, T.; Mahmood, S.
2014-03-15
Electrostatic ion-acoustic periodic (cnoidal) waves and solitons in unmagnetized electron-positron-ion (EPI) plasmas with warm ions and kappa distributed electrons and positrons are investigated. Using the reductive perturbation method, the Korteweg-de Vries (KdV) equation is derived with appropriate boundary conditions for periodic waves. The corresponding analytical and various numerical solutions are presented with Sagdeev potential approach. Differences between the results caused by the kappa and Maxwell distributions are emphasized. It is revealed that only hump (compressive) structures of the cnoidal waves and solitons are formed. It is shown that amplitudes of the cnoidal waves and solitons are reduced in an EPI plasma case in comparison with the ordinary electron-ion plasmas. The effects caused by the temperature variations of the warm ions are also discussed. It is obtained that the amplitude of the cnoidal waves and solitons decreases for a kappa distributed (nonthermal) electrons and positrons plasma case in comparison with the Maxwellian distributed (thermal) electrons and positrons EPI plasmas. The existence of kappa distributed particles leads to decreasing of ion-acoustic frequency up to thermal ions frequency.
Coupled ion acoustic and drift waves in magnetized superthermal electron-positron-ion plasmas
Adnan, Muhammad; Qamar, Anisa; Mahmood, S.
2014-09-15
Linear and nonlinear coupled drift-ion acoustic waves are investigated in a nonuniform magnetoplasma having kappa distributed electrons and positrons. In the linear regime, the role of kappa distribution and positron content on the dispersion relation has been highlighted; it is found that strong superthermality (low value of κ) and addition of positrons lowers the phase velocity via decreasing the fundamental scalelengths of the plasmas. In the nonlinear regime, first, coherent nonlinear structure in the form of dipoles and monopoles are obtained and the boundary conditions (boundedness) in the context of superthermality and positron concentrations are discussed. Second, in case of scalar nonlinearity, a Korteweg–de Vries-type equation is obtained, which admit solitary wave solution. It is found that both compressive and rarefactive solitons are formed in the present model. The present work may be useful to understand the low frequency electrostatic modes in inhomogeneous electron positron ion plasmas, which exist in astrophysical plasma situations such as those found in the pulsar magnetosphere.
Edwardson, C J; Coleman, P G; Paez, D J; Doylend, J K; Knights, A P
2013-03-29
Electron capture during forward bias and reemission at zero bias by divacancies in the depletion region of a silicon diode structure at room temperature have been studied for the first time using monoenergetic positrons. The positron response increases essentially linearly with electron current, as a result of increased positron trapping by negatively charged divacancies. The measurements indicate that ≤1% of the divacancies become negatively charged in the steady state at a forward bias of 1 V. Changes in the mean positron response when applying a square wave bias to the sample (1 V forward bias and 0 V, duty cycle 1:4, times at 0 V in the range 0.1-100 μs), were consistent with a rapid conversion of doubly to singly charged divacancies (in ∼10(1) ns), followed by slower defilling of the singly charged divacancies with a time constant of ∼10(1) μs. These ac measurements allow determination of the relative populations of singly and doubly charged divacancies. The results provide confirmation of consistency between the positron's response to the silicon divacancy and previously extracted capture and emission kinetics determined through charge transient measurements and assigned to the same defect. The possibility of combining these two, orthogonal techniques suggest a promising new and powerful approach to defect spectroscopy in which the structure and electrical properties of a defect may be determined in a single measurement.
Hashemzadeh, M.
2015-11-15
The effect of q-nonextensive parameter and saturation time on the electron density steepening in electron-positron-ion plasmas is studied by particle in cell method. Phase space diagrams show that the size of the holes, and consequently, the number of trapped particles strongly depends on the q-parameter and saturation time. Furthermore, the mechanism of the instability and exchange of energy between electron-positron and electric field is explained by the profiles of the energy density. Moreover, it is found that the q-parameter, saturation time, and electron and positron velocities affect the nonlinear evolution of the electron density which leads to the steepening of its structure. The q-nonextensive parameter or degree of nonextensivity is the relation between temperature gradient and potential energy of the system. Therefore, the deviation of q-parameter from unity indicates the degree of inhomogeneity of temperature or deviation from equilibrium. Finally, using the kinetic theory, a generalized q-dispersion relation is presented for electron-positron-ion plasma systems. It is found that the simulation results in the linear regime are in good agreement with the growth rate results obtained by the kinetic theory.
Aguilar, M; Aisa, D; Alvino, A; Ambrosi, G; Andeen, K; Arruda, L; Attig, N; Azzarello, P; Bachlechner, A; Barao, F; Barrau, A; Barrin, L; Bartoloni, A; Basara, L; Battarbee, M; Battiston, R; Bazo, J; Becker, U; Behlmann, M; Beischer, B; Berdugo, J; Bertucci, B; Bigongiari, G; Bindi, V; Bizzaglia, S; Bizzarri, M; Boella, G; de Boer, W; Bollweg, K; Bonnivard, V; Borgia, B; Borsini, S; Boschini, M J; Bourquin, M; Burger, J; Cadoux, F; Cai, X D; Capell, M; Caroff, S; Casaus, J; Cascioli, V; Castellini, G; Cernuda, I; Cervelli, F; Chae, M J; Chang, Y H; Chen, A I; Chen, H; Cheng, G M; Chen, H S; Cheng, L; Chikanian, A; Chou, H Y; Choumilov, E; Choutko, V; Chung, C H; Clark, C; Clavero, R; Coignet, G; Consolandi, C; Contin, A; Corti, C; Coste, B; Cui, Z; Dai, M; Delgado, C; Della Torre, S; Demirköz, M B; Derome, L; Di Falco, S; Di Masso, L; Dimiccoli, F; Díaz, C; von Doetinchem, P; Du, W J; Duranti, M; D'Urso, D; Eline, A; Eppling, F J; Eronen, T; Fan, Y Y; Farnesini, L; Feng, J; Fiandrini, E; Fiasson, A; Finch, E; Fisher, P; Galaktionov, Y; Gallucci, G; García, B; García-López, R; Gast, H; Gebauer, I; Gervasi, M; Ghelfi, A; Gillard, W; Giovacchini, F; Goglov, P; Gong, J; Goy, C; Grabski, V; Grandi, D; Graziani, M; Guandalini, C; Guerri, I; Guo, K H; Habiby, M; Haino, S; Han, K C; He, Z H; Heil, M; Hoffman, J; Hsieh, T H; Huang, Z C; Huh, C; Incagli, M; Ionica, M; Jang, W Y; Jinchi, H; Kanishev, K; Kim, G N; Kim, K S; Kirn, Th; Kossakowski, R; Kounina, O; Kounine, A; Koutsenko, V; Krafczyk, M S; Kunz, S; La Vacca, G; Laudi, E; Laurenti, G; Lazzizzera, I; Lebedev, A; Lee, H T; Lee, S C; Leluc, C; Li, H L; Li, J Q; Li, Q; Li, Q; Li, T X; Li, W; Li, Y; Li, Z H; Li, Z Y; Lim, S; Lin, C H; Lipari, P; Lippert, T; Liu, D; Liu, H; Lomtadze, T; Lu, M J; Lu, Y S; Luebelsmeyer, K; Luo, F; Luo, J Z; Lv, S S; Majka, R; Malinin, A; Mañá, C; Marín, J; Martin, T; Martínez, G; Masi, N; Maurin, D; Menchaca-Rocha, A; Meng, Q; Mo, D C; Morescalchi, L; Mott, P; Müller, M; Ni, J Q; Nikonov, N; Nozzoli, F; Nunes, P; Obermeier, A; Oliva, A; Orcinha, M; Palmonari, F; Palomares, C; Paniccia, M; Papi, A; Pedreschi, E; Pensotti, S; Pereira, R; Pilo, F; Piluso, A; Pizzolotto, C; Plyaskin, V; Pohl, M; Poireau, V; Postaci, E; Putze, A; Quadrani, L; Qi, X M; Rancoita, P G; Rapin, D; Ricol, J S; Rodríguez, I; Rosier-Lees, S; Rozhkov, A; Rozza, D; Sagdeev, R; Sandweiss, J; Saouter, P; Sbarra, C; Schael, S; Schmidt, S M; Schuckardt, D; Schulz von Dratzig, A; Schwering, G; Scolieri, G; Seo, E S; Shan, B S; Shan, Y H; Shi, J Y; Shi, X Y; Shi, Y M; Siedenburg, T; Son, D; Spada, F; Spinella, F; Sun, W; Sun, W H; Tacconi, M; Tang, C P; Tang, X W; Tang, Z C; Tao, L; Tescaro, D; Ting, Samuel C C; Ting, S M; Tomassetti, N; Torsti, J; Türkoğlu, C; Urban, T; Vagelli, V; Valente, E; Vannini, C; Valtonen, E; Vaurynovich, S; Vecchi, M; Velasco, M; Vialle, J P; Wang, L Q; Wang, Q L; Wang, R S; Wang, X; Wang, Z X; Weng, Z L; Whitman, K; Wienkenhöver, J; Wu, H; Xia, X; Xie, M; Xie, S; Xiong, R Q; Xin, G M; Xu, N S; Xu, W; Yan, Q; Yang, J; Yang, M; Ye, Q H; Yi, H; Yu, Y J; Yu, Z Q; Zeissler, S; Zhang, J H; Zhang, M T; Zhang, X B; Zhang, Z; Zheng, Z M; Zhuang, H L; Zhukov, V; Zichichi, A; Zimmermann, N; Zuccon, P; Zurbach, C
2014-09-19
Precision measurements by the Alpha Magnetic Spectrometer on the International Space Station of the primary cosmic-ray electron flux in the range 0.5 to 700 GeV and the positron flux in the range 0.5 to 500 GeV are presented. The electron flux and the positron flux each require a description beyond a single power-law spectrum. Both the electron flux and the positron flux change their behavior at ∼30 GeV but the fluxes are significantly different in their magnitude and energy dependence. Between 20 and 200 GeV the positron spectral index is significantly harder than the electron spectral index. The determination of the differing behavior of the spectral indices versus energy is a new observation and provides important information on the origins of cosmic-ray electrons and positrons.
Aguilar, M; Aisa, D; Alvino, A; Ambrosi, G; Andeen, K; Arruda, L; Attig, N; Azzarello, P; Bachlechner, A; Barao, F; Barrau, A; Barrin, L; Bartoloni, A; Basara, L; Battarbee, M; Battiston, R; Bazo, J; Becker, U; Behlmann, M; Beischer, B; Berdugo, J; Bertucci, B; Bigongiari, G; Bindi, V; Bizzaglia, S; Bizzarri, M; Boella, G; de Boer, W; Bollweg, K; Bonnivard, V; Borgia, B; Borsini, S; Boschini, M J; Bourquin, M; Burger, J; Cadoux, F; Cai, X D; Capell, M; Caroff, S; Casaus, J; Cascioli, V; Castellini, G; Cernuda, I; Cervelli, F; Chae, M J; Chang, Y H; Chen, A I; Chen, H; Cheng, G M; Chen, H S; Cheng, L; Chikanian, A; Chou, H Y; Choumilov, E; Choutko, V; Chung, C H; Clark, C; Clavero, R; Coignet, G; Consolandi, C; Contin, A; Corti, C; Coste, B; Cui, Z; Dai, M; Delgado, C; Della Torre, S; Demirköz, M B; Derome, L; Di Falco, S; Di Masso, L; Dimiccoli, F; Díaz, C; von Doetinchem, P; Du, W J; Duranti, M; D'Urso, D; Eline, A; Eppling, F J; Eronen, T; Fan, Y Y; Farnesini, L; Feng, J; Fiandrini, E; Fiasson, A; Finch, E; Fisher, P; Galaktionov, Y; Gallucci, G; García, B; García-López, R; Gast, H; Gebauer, I; Gervasi, M; Ghelfi, A; Gillard, W; Giovacchini, F; Goglov, P; Gong, J; Goy, C; Grabski, V; Grandi, D; Graziani, M; Guandalini, C; Guerri, I; Guo, K H; Habiby, M; Haino, S; Han, K C; He, Z H; Heil, M; Hoffman, J; Hsieh, T H; Huang, Z C; Huh, C; Incagli, M; Ionica, M; Jang, W Y; Jinchi, H; Kanishev, K; Kim, G N; Kim, K S; Kirn, Th; Kossakowski, R; Kounina, O; Kounine, A; Koutsenko, V; Krafczyk, M S; Kunz, S; La Vacca, G; Laudi, E; Laurenti, G; Lazzizzera, I; Lebedev, A; Lee, H T; Lee, S C; Leluc, C; Li, H L; Li, J Q; Li, Q; Li, Q; Li, T X; Li, W; Li, Y; Li, Z H; Li, Z Y; Lim, S; Lin, C H; Lipari, P; Lippert, T; Liu, D; Liu, H; Lomtadze, T; Lu, M J; Lu, Y S; Luebelsmeyer, K; Luo, F; Luo, J Z; Lv, S S; Majka, R; Malinin, A; Mañá, C; Marín, J; Martin, T; Martínez, G; Masi, N; Maurin, D; Menchaca-Rocha, A; Meng, Q; Mo, D C; Morescalchi, L; Mott, P; Müller, M; Ni, J Q; Nikonov, N; Nozzoli, F; Nunes, P; Obermeier, A; Oliva, A; Orcinha, M; Palmonari, F; Palomares, C; Paniccia, M; Papi, A; Pedreschi, E; Pensotti, S; Pereira, R; Pilo, F; Piluso, A; Pizzolotto, C; Plyaskin, V; Pohl, M; Poireau, V; Postaci, E; Putze, A; Quadrani, L; Qi, X M; Rancoita, P G; Rapin, D; Ricol, J S; Rodríguez, I; Rosier-Lees, S; Rozhkov, A; Rozza, D; Sagdeev, R; Sandweiss, J; Saouter, P; Sbarra, C; Schael, S; Schmidt, S M; Schuckardt, D; Schulz von Dratzig, A; Schwering, G; Scolieri, G; Seo, E S; Shan, B S; Shan, Y H; Shi, J Y; Shi, X Y; Shi, Y M; Siedenburg, T; Son, D; Spada, F; Spinella, F; Sun, W; Sun, W H; Tacconi, M; Tang, C P; Tang, X W; Tang, Z C; Tao, L; Tescaro, D; Ting, Samuel C C; Ting, S M; Tomassetti, N; Torsti, J; Türkoğlu, C; Urban, T; Vagelli, V; Valente, E; Vannini, C; Valtonen, E; Vaurynovich, S; Vecchi, M; Velasco, M; Vialle, J P; Wang, L Q; Wang, Q L; Wang, R S; Wang, X; Wang, Z X; Weng, Z L; Whitman, K; Wienkenhöver, J; Wu, H; Xia, X; Xie, M; Xie, S; Xiong, R Q; Xin, G M; Xu, N S; Xu, W; Yan, Q; Yang, J; Yang, M; Ye, Q H; Yi, H; Yu, Y J; Yu, Z Q; Zeissler, S; Zhang, J H; Zhang, M T; Zhang, X B; Zhang, Z; Zheng, Z M; Zhuang, H L; Zhukov, V; Zichichi, A; Zimmermann, N; Zuccon, P; Zurbach, C
2014-09-19
Precision measurements by the Alpha Magnetic Spectrometer on the International Space Station of the primary cosmic-ray electron flux in the range 0.5 to 700 GeV and the positron flux in the range 0.5 to 500 GeV are presented. The electron flux and the positron flux each require a description beyond a single power-law spectrum. Both the electron flux and the positron flux change their behavior at ∼30 GeV but the fluxes are significantly different in their magnitude and energy dependence. Between 20 and 200 GeV the positron spectral index is significantly harder than the electron spectral index. The determination of the differing behavior of the spectral indices versus energy is a new observation and provides important information on the origins of cosmic-ray electrons and positrons. PMID:25279617
A search for supersymmetric electrons with the Mark II detector at PEP (Positron Electron Project)
LeClaire, B.W.
1987-10-01
An experimental search for selectrons, the supersymmetric partner of the electron, has been performed at the PEP storage ring at SLAC using the Mark II detector. The experimental search done was based upon hypothetical reaction in e/sup +/e/sup -/ interactions at PEP center of mass energies of 29 GeV. In this reaction the selectrons, e-tilde, are assumed produced by the interaction of one of initial state electrons with a photon radiated from the other initial state electron. This latter electron is assumed to continue down the beam pipe undetected. The photon and electron then produce a selectron and a photino, ..gamma..-tilde, in the supersymmetric analog of Compton scattering. The photino is assumed to be the lightest supersymmetric particle, and as such, does not interact in the detector, thereby escaping detection very much like a neutrino. The selectron is assumed to immediately decay into an electron and photino. This electron is produced with large p perpendicular with respect to the beam pipe, since it must balance the transverse momentum carried off by the photinos. Thus, the experimental signature of the process is a single electron in the detector with a large unbalanced tranverse momentum. No events of this type were observed in the original search of 123 pb/sup -1/ of data, resulting in a cross section limit of less than 2.4 x 10/sup -2/ pb (at the 95% CL) within the detector acceptance. This cross section upper limit applies to any process which produces anomalous single electron events with missing transverse momentum. When interpreted as a supersymmetry search it results in a lower selectron mass limit of 22.2 GeV/c/sup 2/ for the case of massless photinos. Limits for non-zero mass photinos have been calculated. 87 refs., 67 figs., 17 tabs.
Maroof, R.; Ali, S.; Mushtaq, A.; Qamar, A.
2015-11-15
Linear properties of high and low frequency waves are studied in an electron-positron-ion (e-p-i) dense plasma with spin and relativity effects. In a low frequency regime, the magnetohydrodynamic (MHD) waves, namely, the magnetoacoustic and Alfven waves are presented in a magnetized plasma, in which the inertial ions are taken as spinless and non-degenerate, whereas the electrons and positrons are treated quantum mechanically due to their smaller mass. Quantum corrections associated with the spin magnetization and density correlations for electrons and positrons are re-considered and a generalized dispersion relation for the low frequency MHD waves is derived to account for relativistic degeneracy effects. On the basis of angles of propagation, the dispersion relations of different modes are discussed analytically in a degenerate relativistic plasma. Numerical results reveal that electron and positron relativistic degeneracy effects significantly modify the dispersive properties of MHD waves. Our present analysis should be useful for understanding the collective interactions in dense astrophysical compact objects, like, the white dwarfs and in atmosphere of neutron stars.
On the robustness of the localized spatiotemporal structures in electron-positron-ion plasmas
Mahajan, S.M.; Berezhiani, V.I. |; Miklaszewski, R.
1998-04-01
It is shown that, in an electron-positron plasma with a small fraction of ions, large-amplitude localized spatiotemporal structures (light bullets) can be readily generated and sustained. These light bullets are found to be exceptionally robust: they can emerge from a large variety of initial field distributions and are remarkably stable.
Tuning laser produced electron-positron jets for lab-astrophysics experiment
Chen, Hui; Fiuza, F.; Hazi, A.; Kemp, A.; Link, A.; Pollock, B.; Marley, E.; Nagel, S. R.; Park, J.; Schneider, M.; Shepherd, R.; Tommasini, R.; Wilks, S. C.; Williams, G. J.; Barnak, D.; Chang, P-Y.; Fiksel, G.; Glebov, V.; Meyerhofer, D. D.; Myatt, J. F.; Stoeckel, C.; Nakai, M.; Arikawa, Y.; Azechi, H.; Fujioka, S.; Hosoda, H.; Kojima, S.; Miyanga, N.; Morita, T.; Moritaka, T.; Nagai, T.; Namimoto, T.; Nishimura, H.; Ozaki, T.; Sakawa, Y.; Takabe, H.; Zhang, Z.
2015-02-23
This paper reviews the experiments on the laser produced electron-positron jets using large laser facilities worldwide. The goal of the experiments was to optimize the parameter of the pair jets for their potential applications in laboratory-astrophysical experiment. Results on tuning the pair jet’s energy, number, emittance and magnetic collimation will be presented.
NASA Astrophysics Data System (ADS)
Maroof, R.; Ali, S.; Mushtaq, A.; Qamar, A.
2015-11-01
Linear properties of high and low frequency waves are studied in an electron-positron-ion (e-p-i) dense plasma with spin and relativity effects. In a low frequency regime, the magnetohydrodynamic (MHD) waves, namely, the magnetoacoustic and Alfven waves are presented in a magnetized plasma, in which the inertial ions are taken as spinless and non-degenerate, whereas the electrons and positrons are treated quantum mechanically due to their smaller mass. Quantum corrections associated with the spin magnetization and density correlations for electrons and positrons are re-considered and a generalized dispersion relation for the low frequency MHD waves is derived to account for relativistic degeneracy effects. On the basis of angles of propagation, the dispersion relations of different modes are discussed analytically in a degenerate relativistic plasma. Numerical results reveal that electron and positron relativistic degeneracy effects significantly modify the dispersive properties of MHD waves. Our present analysis should be useful for understanding the collective interactions in dense astrophysical compact objects, like, the white dwarfs and in atmosphere of neutron stars.
NASA Astrophysics Data System (ADS)
Ali, S.; Ata-ur-Rahman
2014-04-01
The linear and nonlinear properties of the ion-acoustic (IA) waves are investigated in a relativistically degenerate magnetoplasma, whose constituents are the electrons, positrons, and ions. The electrons and positrons are assumed to obey the Fermi-Dirac statistics, whereas the cold ions are taken to be inertial and magnetized. In linear analysis, various limiting cases are discussed both analytically and numerically. However, for nonlinear studies, the well-known reductive perturbation technique is employed to derive the Zakharov-Kuznetsov and Zakharov-Kuznetsov Burgers equations in the presence of relativistically degenerate electrons and positrons. Furthermore, with the use of hyperbolic tangent method, the equations are simplified to admit the soliton and shock wave solutions. Numerically, it is shown that the amplitude, width, and phase speed associated with the localized IA solitons and shocks are significantly influenced by the various intrinsic plasma parameters relevant to our model. The present analysis can be useful for understanding the collective processes in dense astrophysical environments like neutron stars, where the electrons and positrons are expected to be relativistic and degenerate.
Misra, Amar P; Chowdhury, A Roy
2004-11-01
The theory of electromagnetic surface modes propagating along the planar interface between dusty electron-positron plasma and vacuum is reexamined by the conventional matching method of boundary conditions. It is shown that in a magnetoplasma the direct use of specular reflection method is not appropriate and the derivations for the TM-mode dispersion relation [Phys. Rev. E 61, 4357 (2000)] are incorrect.
Alam, M. S.; Uddin, M. J.; Mamun, A. A.; Masud, M. M.
2014-09-01
Positron-acoustic (PA) solitary waves (SWs) and double layers (DLs) in four-component plasmas consisting of immobile positive ions, mobile cold positrons, and superthermal (kappa distributed) hot positrons and electrons are investigated both numerically and analytically by deriving Korteweg–de Vries (K-dV), modified K-dV (mK-dV), and Gardner equations along with their DLs solutions using the reductive perturbation method. It is examined that depending on the plasma parameters, the K-dV SWs, Gardner SWs, and DLs support either compressive or rarefactive structures, whereas mK-dV SWs support only compressive structure. It is also found that the presence of superthermal (kappa distributed) hot positrons and hot electrons significantly modify the basic features of PA SWs as well as PA DLs. Besides, the critical number density ratio of hot positrons and cold positrons play an important role in the polarity of PA SWs and DLs. The implications of our results in different space as well as laboratory plasma environments are briefly discussed.
Electron and Photon Identification in the D0 Experiment
Abazov, Victor Mukhamedovich; et al.
2014-06-21
The electron and photon reconstruction and identification algorithms used by the D0 Collaboration at the Fermilab Tevatron collider are described. The determination of the electron energy scale and resolution is presented. Studies of the performance of the electron and photon reconstruction and identification are summarized.
Electron-cooled accumulation of 4 × 109 positrons for production and storage of antihydrogen atoms
NASA Astrophysics Data System (ADS)
Fitzakerley, D. W.; George, M. C.; Hessels, E. A.; Skinner, T. D. G.; Storry, C. H.; Weel, M.; Gabrielse, G.; Hamley, C. D.; Jones, N.; Marable, K.; Tardiff, E.; Grzonka, D.; Oelert, W.; Zielinski, M.; ATRAP Collaboration
2016-03-01
Four billion positrons (e+) are accumulated in a Penning-Ioffe trap apparatus at 1.2 K and <6 × 10-17 Torr. This is the largest number of positrons ever held in a Penning trap. The e+ are cooled by collisions with trapped electrons (e-) in this first demonstration of using e- for efficient loading of e+ into a Penning trap. The combined low temperature and vacuum pressure provide an environment suitable for antihydrogen (\\bar{{{H}}}) production, and long antimatter storage times, sufficient for high-precision tests of antimatter gravity and of CPT.
Quantum ion-acoustic double layers in unmagnetized dense electron-positron-ion plasmas
NASA Astrophysics Data System (ADS)
Khan, S. A.; Mahmood, S.; Ali, S.
2009-04-01
The existence of small amplitude quantum ion-acoustic double layers is studied in an unmagnetized dense electron-positron-ion plasma. For this purpose, the quantum hydrodynamic model is employed to derive a deformed Korteweg-de Vries (dKdV) equation. The steady state double layer solution of dKdV equation is obtained and its dependence on various parameters is discussed. It is found that only compressive double layers can exist in such plasmas. The analytical and numerical studies reveal that the quantum ion-acoustic double layer structures strongly depend on quantum diffraction effects and positron number density.
Obliquely propagating nonlinear structures in dense dissipative electron positron ion magnetoplasmas
NASA Astrophysics Data System (ADS)
Masood, W.; Rizvi, H.; Siddiq, M.
2012-02-01
Nonlinear electrostatic waves in dense dissipative magnetized electron-positron-ion (e-p-i) plasmas are investigated employing the quantum hydrodynamic model. In this regard, Zakharov Kuznetsov Burgers (ZKB) equation is derived in dense plasmas using the small amplitude perturbation expansion method. It is observed that obliqueness, positron concentration, kinematic viscosity, and the ambient magnetic field significantly alter the structure of nonlinear quantum ion acoustic waves in dense dissipative e-p-i magnetoplasmas. The present study may be useful to understand the nonlinear propagation characteristics of electrostatic shock structures in dense astrophysical systems where the quantum effects are expected to dominate.
Linear and nonlinear quantum ion-acoustic waves in dense magnetized electron-positron-ion plasmas
Khan, S. A.; Masood, W.
2008-06-15
The linear and nonlinear quantum ion-acoustic waves propagating obliquely in two dimensions in superdense, magnetized electron-positron-ion quantum plasma are investigated on the basis of quantum hydrodynamic model. It is found in linear analysis that the quantum corrections of diffraction are important in the very short wavelength regime that may be found in dense astrophysical plasmas. To investigate the solitary waves, the Zakharov-Kuznetsov equation is derived and the solution is presented in the small amplitude limit. By numerical analysis, it is found that the soliton structure of the ion acoustic wave depends upon quantum pressure, concentration of positrons, strength of magnetic field, and the propagation angle.
Linear and nonlinear quantum ion-acoustic waves in dense magnetized electron-positron-ion plasmas
NASA Astrophysics Data System (ADS)
Khan, S. A.; Masood, W.
2008-06-01
The linear and nonlinear quantum ion-acoustic waves propagating obliquely in two dimensions in superdense, magnetized electron-positron-ion quantum plasma are investigated on the basis of quantum hydrodynamic model. It is found in linear analysis that the quantum corrections of diffraction are important in the very short wavelength regime that may be found in dense astrophysical plasmas. To investigate the solitary waves, the Zakharov-Kuznetsov equation is derived and the solution is presented in the small amplitude limit. By numerical analysis, it is found that the soliton structure of the ion acoustic wave depends upon quantum pressure, concentration of positrons, strength of magnetic field, and the propagation angle.
Ali Shan, S.; El-Tantawy, S. A.; Moslem, W. M.
2013-08-15
Arbitrary amplitude ion-acoustic waves in an unmagnetized plasma consisting of cold positive ions, superthermal electrons, and positrons beam are reported. The basic set of fluid equations is reduced to an energy-balance like equation. The latter is numerically analyzed to examine the existence regions for solitary and shock waves. It is found that only solitary waves can propagate, however, the model cannot support shocks. The effects of superthermality and beam parameters (via, positrons concentration and streaming velocity) on the existence region, as well as solitary wave profile have been discussed.
Compressive and rarefactive dressed solitons in plasma with nonthermal electrons and positrons
NASA Astrophysics Data System (ADS)
Abdelwahed, H. G.; El-Shewy, E. K.; Zahran, M. A.; Elwakil, S. A.
2016-02-01
The study of dressed solitary ion waves in a collisionless unmagnetized plasma composed warm fluid of ion, nonthermal distributed positrons and electrons are discussed. Concerning nonlinear ion acoustic waves, a reductive perturbation method is applied to obtain the KdV equation in terms of first order potential. Our results exemplify that, if soliton amplitude enlarged, the shape of the wave sidetrack from KdV equation. In order to improve the soliton shape, the perturbed KdV equation is suggest. In particular, the effects of nonthermal positrons and ionic temperature on the electrostatic dressed rarefactive and compressive soliton structures are discussed.
Dissipationless electron transport in photon-dressed nanostructures.
Kibis, O V
2011-09-01
It is shown that the electron coupling to photons in field-dressed nanostructures can result in the ground electron-photon state with a nonzero electric current. Since the current is associated with the ground state, it flows without the Joule heating of the nanostructure and is nondissipative. Such a dissipationless electron transport can be realized in strongly coupled electron-photon systems with the broken time-reversal symmetry--particularly, in quantum rings and chiral nanostructures dressed by circularly polarized photons. PMID:21981519
Beam Tests of a Clearing Electrode for Electron Cloud Mitigation at KEKB Positron Ring
Suetsugu, Y.; Fukuma, H.; Shibata, K.; Pivi, M.; Wang, L.; /SLAC
2010-06-15
In order to mitigate the electron cloud instability in an intense positron ring, an electron clearing electrode with a very thin structure has been developed. The electrode was tested with a positron beam of the KEKB B-factory (KEKB). A drastic reduction in the electron density around the beam was demonstrated in a wiggler magnet with a dipole-type magnetic field of 0.78 T. The clearing electrode was then applied to a copper beam pipe with antechambers assuming an application of the electrode to a wiggler section in the Super KEKB. The beam pipe was installed at a magnetic-free region in the ring and tested with beam. No extra heating of the electrodes and feed-throughs were observed. A reduction in the electron density reasonable in a magnetic-free region was also obtained.
a Search for Low-Mass Short-Lived States Coupling to Positron-Electron
NASA Astrophysics Data System (ADS)
Phlips, Bernard Felix
Following the discovery of correlated positron -electron peaks in heavy ion experiments, the existence of a previously undetected particle coupling to e ^+e^- was postulated. A new experiment with improved sensitivity was suggested to detect this particle. Monoenergetic positrons would be accelerated onto electrons in a lithium target and the kinematics of the e^+e ^- scattering events measured by energy and position sensitive detectors. The experiment was carried out at Brookhaven National Laboratory where a 3 MV Dynamitron electrostatic accelerator was converted to a positron accelerator. The monoenergetic positrons were provided by a ^{22} Na source in conjunction with a thin single crystal tungsten moderator, and accelerated by the Dynamitron to a tunable energy between 1.0 and 2.5 MeV with keV resolution. The beam was transported through a new beam line to the target chamber where it could be focused down to 1 mm spot size. The energy of the interactions of the positrons with the lithium target was measured by plastic scintillators, and the position of the scattered particles was recorded by a set of four multi-wire proportional chambers capable of sub millimeter resolution. In a first experiment, the positron beam was scanned between 2150 and 2350 keV in 5 keV steps onto a 1.5 mg/cm ^2 lithium target with at least 60 000 coincidences recorded per energy point. The full kinematics of each positron-electron scattering event was reconstructed. The positron-nucleus scattering events were also detected and served as a normalization to eliminate all beam and target effects. A normalized e^+-e ^- scattering excitation function was derived, leading to an upper limit (90% CL) to the cross section for pointlike particles of sigma~ 1-5 mb. This translates to lower limits on the lifetime of tau>= 0.5 to 7 times10^{13} sec. In an extended run, data were acquired on a 2.5 mg/cm^2 lithium target from 1350 keV to 2350 keV in 3.5 keV steps with ~ 300 000 coincidences per
Observation of Magnetic Resonances in Electron Clouds in a Positron Storage Ring
Pivi, M.T.F.; Ng, J.S.T.; Cooper, F.; Kharakh, D.; King, F.; Kirby, R.E.; Kuekan, B.; Spencer, Cherrill M.; Raubenheimer, T.O.; Wang, L.F.; /SLAC
2011-08-24
The first experimental observation of magnetic resonances in electron clouds is reported. The resonance was observed as a modulation in cloud intensity for uncoated as well as TiN-coated aluminum surfaces in the positron storage ring of the PEP-II collider at SLAC. Electron clouds frequently arise in accelerators of positively charged particles, and severely impact the machines performance. The TiN coating was found to be an effective remedy, reducing the cloud intensity by three orders of magnitude.
Second-order Born approximation for the ionization of molecules by electron and positron impact
Dal Cappello, C.; Rezkallah, Z.; Houamer, S.; Charpentier, I.; Hervieux, P. A.; Ruiz-Lopez, M. F.; Dey, R.; Roy, A. C.
2011-09-15
Second-order Born approximation is applied to study the ionization of molecules. The initial and final states are described by single-center wave functions. For the initial state a Gaussian wave function is used while for the ejected electron it is a distorted wave. Results of the present model are compared with recent (e,2e) experiments on the water molecule. Preliminary results are also presented for the ionization of the thymine molecule by electrons and positrons.
An overview of the slow-positron beam facility at the photon factory, KEK
NASA Astrophysics Data System (ADS)
Kurihara, Toshikazu; Shirakawa, Akihiro; Enomoto, Atsushi; Shidara, Tetsuo; Kobayashi, Hitoshi; Nakahara, Kazuo
1995-01-01
The KEK slow-positron source is in the final stage of construction. The beam line comprises a 31 m long vacuum duct within an axial magnetic field and a following electrostatic guided section. In order to vary the energy of a positron beam dedicated to depth-profile measurements, a high voltage station capable of applying 60 kV has been installed in the beam transport system. The target assembly (a water-cooled tantalum rod of 5 radiation lengths and a moderator with multiple tungsten vanes) and the following straight section (8 m; used for positron storage) are under high voltage. The beam duct located downstream is at ground potential. Positron beams passing through this region have a high kinetic energy. A focusing triplet quadrupole lens and a moderator on the retarding electrode are located at the end of the magnetic transport. This beam line has 9 right-angle-curved ducts, comprising a radius of curvature of 40 cm. Positrons with a maximum energy of 60 keV are guided by bending magnets attached to the beam-transport ducts. A transport system to switch from magnetically guided to electrostatically guided has been installed. The design of the brightness-enhancement stage of the positron beam for positron re-emission microscopy is in progress. In a preliminary experiments at 2.0 GeV with a 2 kW primary beam, 4×10 6e +/s of slow positrons were observed by detecting annihilation γ-rays at the end of the magnetic beam-transport line. Further improvements are expected by careful surface and thermal treatments of the moderator.
Jao, C-S; Hau, L-N
2014-05-01
Electrostatic solitary waves (ESWs) and solitons are widely present in the solar system plasma environment. Many theoretical and numerical studies have been carried out to address the formation and structure of ESWs and solitons in electron-ion plasmas. Due to the inertia symmetry, the issue of whether solitons can exist in pair plasmas has been raised and has been discussed in a number of papers. Recently, we have shown that interlacing electron and positron holes in phase space associated with periodic positive and negative potentials may be generated by current-free electron and positron beams streaming in stationary electron-positron background plasmas [Jao and Hau, Phys. Rev. E 86, 056401 (2012)]. The question remains of whether pure electron or positron holes with positive or negative polarity may exist in neutral electron-positron plasmas. In this paper, we show the formation of electron (positron) holes associated with ESWs of positive (negative) potential based on the particle-in-cell simulations of bump-on-tail streaming instability in pair plasmas. The fluid theory shows that the coexistence of two unstable modes with different wavelengths is the essential condition for the generation of electrostatic solitons and hole structures in an electron-positron plasma. PMID:25353901
Bound-free electron-positron pair production in relativistic heavy-ion collisions
Senguel, M. Y.; Gueclue, M. C.; Fritzsche, S.
2009-10-15
The bound-free electron-positron pair production is considered for relativistic heavy ion collisions. In particular, cross sections are calculated for the pair production with the simultaneous capture of the electron into the 1s ground state of one of the ions and for energies that are relevant for the relativistic heavy ion collider and the large hadron colliders. In the framework of perturbation theory, we applied Monte Carlo integration techniques to compute the lowest-order Feynman diagrams amplitudes by using Darwin wave functions for the bound states of the electrons and Sommerfeld-Maue wave functions for the continuum states of the positrons. Calculations were performed especially for the collision of Au+Au at 100 GeV/nucleon and Pb+Pb at 3400 GeV/nucleon.
Interaction of two solitary waves in quantum electron-positron-ion plasma
NASA Astrophysics Data System (ADS)
Xu, Yan-Xia; Liu, Zong-Ming; Lin, Mai-Mai; Shi, Yu-Ren; Chen, Jian-Min; Duan, Wen-Shan
2011-05-01
The collision between two ion-acoustic solitary waves with arbitrary colliding angle θ in an unmagnetized, ultracold quantum three-component e-p-i plasma has been investigated. By using the extended Poincaré-Lighthill-Kuo (PLK) perturbation method, we obtain the KdV equations and the analytical phase shifts after the collision of two solitary waves in this three-component plasma. The effects of the quantum parameter H, the ratio of Fermi positron temperature to Fermi electron temperature σ, the ratio of Fermi positron number density to Fermi electron number density μ, and the ratio of Fermi ion temperature to Fermi electron temperature ρ on the phase shifts are studied. It is found that these parameters can significantly influence the phase shifts of the solitons.
Khorashadizadeh, S. M.; Rastbood, E.; Zeinaddini Meymand, H.; Niknam, A. R.
2013-08-15
The nonlinear coupling between circularly polarized electromagnetic (CPEM) waves and acoustic-like waves in a magnetoactive electron-positron-ion (e-p-i) plasma is studied, taking into account the relativistic motion of electrons and positrons. The possibility of modulational instability and its growth rate as well as the envelope soliton formation and its characteristics in such plasmas are investigated. It is found that the growth rate of modulation instability increases in the case that ω{sub c}/ω<1 (ω{sub c} and ω are the electron gyrofrequency and the CPEM wave frequency, respectively) and decreases in the case that ω{sub c}/ω>1. It is also shown that in a magnetoactive e-p-i plasma, the width of bright soliton increases/decreases in case of (ω{sub c}/ω)<1/(ω{sub c}/ω)>1 by increasing the magnetic field strength.
Interaction of two solitary waves in quantum electron-positron-ion plasma
Xu Yanxia; Lin Maimai; Shi Yuren; Duan Wenshan; Liu Zongming; Chen Jianmin
2011-05-15
The collision between two ion-acoustic solitary waves with arbitrary colliding angle {theta} in an unmagnetized, ultracold quantum three-component e-p-i plasma has been investigated. By using the extended Poincare-Lighthill-Kuo (PLK) perturbation method, we obtain the KdV equations and the analytical phase shifts after the collision of two solitary waves in this three-component plasma. The effects of the quantum parameter H, the ratio of Fermi positron temperature to Fermi electron temperature {sigma}, the ratio of Fermi positron number density to Fermi electron number density {mu}, and the ratio of Fermi ion temperature to Fermi electron temperature {rho} on the phase shifts are studied. It is found that these parameters can significantly influence the phase shifts of the solitons.
Ion-acoustic nonlinear periodic waves in electron-positron-ion plasma
Chawla, J. K.; Mishra, M. K.
2010-10-15
Ion-acoustic nonlinear periodic waves, namely, ion-acoustic cnoidal waves have been studied in electron-positron-ion plasma. Using reductive perturbation method and appropriate boundary condition for nonlinear periodic waves, the Korteweg-de Vries (KdV) equation is derived for the system. The cnoidal wave solution of the KdV equation is discussed in detail. It is found that the frequency of the cnoidal wave is a function of its amplitude. It is also found that the positron concentration modifies the properties of the ion-acoustic cnoidal waves. The existence regions for ion-acoustic cnoidal wave in the parameters space (p,{sigma}), where p and {sigma} are the positron concentration and temperature ratio of electron to positron, are discussed in detail. In the limiting case these ion-acoustic cnoidal waves reduce to the ion-acoustic soliton solutions. The effect of other parameters on the characteristics of the nonlinear periodic waves is also discussed.
NASA Astrophysics Data System (ADS)
Edwardson, C. J.; Coleman, P. G.; Paez, D. J.; Doylend, J. K.; Knights, A. P.
2013-03-01
Electron capture during forward bias and reemission at zero bias by divacancies in the depletion region of a silicon diode structure at room temperature have been studied for the first time using monoenergetic positrons. The positron response increases essentially linearly with electron current, as a result of increased positron trapping by negatively charged divacancies. The measurements indicate that ≤1% of the divacancies become negatively charged in the steady state at a forward bias of 1 V. Changes in the mean positron response when applying a square wave bias to the sample (1 V forward bias and 0 V, duty cycle 1∶4, times at 0 V in the range 0.1-100μs), were consistent with a rapid conversion of doubly to singly charged divacancies (in ˜101ns), followed by slower defilling of the singly charged divacancies with a time constant of ˜101μs. These ac measurements allow determination of the relative populations of singly and doubly charged divacancies. The results provide confirmation of consistency between the positron’s response to the silicon divacancy and previously extracted capture and emission kinetics determined through charge transient measurements and assigned to the same defect. The possibility of combining these two, orthogonal techniques suggest a promising new and powerful approach to defect spectroscopy in which the structure and electrical properties of a defect may be determined in a single measurement.
NASA Astrophysics Data System (ADS)
Ruan, Shi-Sen; Cheng, Ze
2013-07-01
In this paper, we study the head-on collision between two electron acoustic solitary waves (EASWs) in magnetized quantum electron-positron-ion plasma. Using the extended Poincaré-Lighthill-Kuo perturbation method, we obtain the Korteweg-de Vries equations, the phase shifts and the trajectories after the head-on collision of the two EASWs. It is found that the phase shifts are significantly affected by the values of the quantum parameter H, the ion to electron number density ratio δ, the electron cyclotron to electron plasma frequency ratio α and the obliqueness θ (propagation angle).
NASA Astrophysics Data System (ADS)
Medenwaldt, R.; Møller, S. P.; Uggerhøj, E.; Worm, T.; Elsener, K.; Sona, P.; Connell, S. H.; Sellschop, J. P. F.; Avakian, R. O.; Avetisian, A. E.; Taroian, S. P.
1995-10-01
Channeling radiation and energy loss for 150 GeV electrons and positrons incident on a 0.5 mm thick <100> diamond and a 0.6 mm thick <110> Si crystal have been measured — near axial and planar directions. It is found that yields from well channeled electrons are enhanced by a factor of two, and those for positrons are reduced by a factor of five, as compared to yields outside the channeling region. The experimental critical angle for channeling agrees very well with the Lindhard angle ψ1. For incidence along planes and close to axial directions, the overall picture of the radiation spectra for electrons and positrons is the same for the high-energy photons, where a strongly enhanced peak is found, as was first discovered in an earlier electron experiment. In diamond, the standard coherent bremsstrahlung has been measured close to the 110 planes but for 10 mrad and 50 mrad from the axis. These experimental results agree well with calculations using the Born approximation.
NASA Astrophysics Data System (ADS)
Tóth, Istvan; Nagy, Ladislau; Campeanu, Radu I.
2016-08-01
Triple differential cross sections are calculated for the ionization of NH3 by positron impact in coplanar and perpendicular geometrical arrangements. The cross sections are determined for symmetrically emerging particles with equal energies. The positron cross sections are compared with previously calculated electron cross sections for the same kinematical conditions.
NASA Astrophysics Data System (ADS)
Kirsebom, K.; Mikkelsen, U.; Uggerhøj, E.; Elsener, K.; Ballestrero, S.; Sona, P.; Connell, S. H.; Sellschop, J. P. F.; Vilakazi, Z. Z.
2001-04-01
A few years ago the CERN NA-43 collaboration installed an upgraded detector system which allows a detailed analysis of the particle motion before, during and after penetration of a crystal. Also, essentially perfect diamond crystals were produced by the collaborators from Schonland Research Centre. These facts have led to new and very detailed investigations of QED-processes in strong crystalline fields. Along axial directions the radiation emission is enhanced by more than two orders of magnitude. For incidence on a 0.7 mm thick diamond crystal of well-aligned 149 GeV electrons, 35% give rise to a high energy photon peak at ≃120 GeV. For 243 GeV electrons and ≃200 GeV photons, this number decreases to 25% - which may be an indication of quantum suppression. Different measurements of the photon multiplicities show that in most cases positrons and electrons emit equal number of photons. The dramatic radiation emission leads to a strong reduction in transverse energy and all electrons incident within the critical angle are captured to high lying channeling states and exit at channeling angles corresponding to their final energy - a completely new result for negatively charged particles. For the first time, we present an analysis where the photon is used as a `messenger' for the transverse energy of the electron during the formation time and we conclude that the more energetic photons are created closer to the string and emitted in the axial direction - in contrast to earlier calculations using the Dirac equation. The strongly enhanced radiation emission leads to angular cooling for electrons but angular heating for positrons and we show that at higher electron energies the cooling becomes stronger as expected from theory. For electrons, the radiative cooling gives rise to a capture of above-barrier particles into the channeled beam. The total radiative energy loss is shown as not to follow the γ2-law expected from classical electrodynamics, but turns over
Gamma-ray spectra of hexane (C6H14) in positron-electron annihilation process
NASA Astrophysics Data System (ADS)
Ma, Xiaoguang; Wang, Feng
2013-08-01
Theoretical gamma-ray spectra of molecule hexane have been calculated and compared with the experimental results in both gas (Iwata et al., 1997a) and liquid (Kerr et al., 1965) phases. The present study reveals that in gas phase not all valence electrons of hexane contribute the same degree in the electron-positron annihilation of hexane. The electrons which dominate the positron-electron annihilation of molecules are called positrophilic electrons. The positrophilic electrons are predominately found to involve the electrons on the lowest occupied valence orbital (LOVO) of a free molecule in gas phase. When hexane is confined in liquid phase, however, the intermolecular interactions ultimately eliminate the free molecular orientation and selectivity for the positrophilic electrons in the gas phase. As a result, the gamma-ray spectra of hexane become an "averaged" contribution from all valence electrons, which is again in agreement with liquid phase measurement. The roles of valence electrons in annihilation process for gas and liquid phases of hexane have been recognized for the first time in the present study.
Observational consequences of positron production by evaporating black holes
NASA Astrophysics Data System (ADS)
Okele, P. N.; Rees, M. J.
1980-01-01
The detectable effects of positrons emitted by the quantum evaporation of primordial black holes (PBHs) are discussed. The emission of electron-positron pairs, and of photons, gravitons, and neutrinos by evaporating PBHs is considered, taking the mass of the PBH into account. It is concluded that if the mass spectrum rises towards large masses, the 0.511 MeV annihilation radiation from the galactic center reported by Leventhal et al. could result from low energy positrons produced in this way.
Prototyping of the ILC Baseline Positron Target
Gronberg, J; Brooksby, C; Piggott, T; Abbott, R; Javedani, J; Cook, E
2012-02-29
The ILC positron system uses novel helical undulators to create a powerful photon beam from the main electron beam. This beam is passed through a titanium target to convert it into electron-positron pairs. The target is constructed as a 1 m diameter wheel spinning at 2000 RPM to smear the 1 ms ILC pulse train over 10 cm. A pulsed flux concentrating magnet is used to increase the positron capture efficiency. It is cooled to liquid nitrogen temperatures to maximize the flatness of the magnetic field over the 1 ms ILC pulse train. We report on prototyping effort on this system.
Low-Frequency Electrostatic Ion Surface Waves in Magnetized Electron-Positron Plasmas
NASA Astrophysics Data System (ADS)
Cho, Sang-Hoon; Lee, Hee J.
The dispersion relations of a surface ion wave propagating on the interface between a warm electron-positron plasma and vacuum when a static magnetic field is directed either normal to the interface (x-wave) or parallel to the wave vector (z-wave) are solved analytically, and the influence of the magnetic field on the ion surface wave is investigated in detail using some numerical work. It is shown that ion surface waves do not exist if the magnetic field is large enough to make the ion gyrofrequency greater than the ion plasma frequency. The attenuation constant of x-waves is more attenuated than that of z-waves and the x-wave is more attenuated as the parameter normalized ion gyrofrequency ζ increases toward 1, but this tendency is reversed for the z-wave. The z-wave does not exist for k2λD2< (ζ/(1-ζ))(p + 1) while the x-wave exists over the whole range of k, where the fractional number p is the ratio between the unperturbed positron and the electron number density. Additionally, we compare the ion surface wave properties of electron-positron plasma with conventional electron-ion plasma.
Sessler, A.M.
1995-04-01
Since the seminal work by Ginsburg, et at., the subject of giving the Next Linear Collider photon-photon capability, as well as electron-positron capability, has drawn much attention. A 1990 article by V.I. Teinov describes the situation at that time. In March 1994, the first workshop on this subject was held. This report briefly reviews the physics that can be achieved through the photon-photon channel and then focuses on the means of achieving such a collider. Also reviewed is the spectrum of backscattered Compton photons -- the best way of obtaining photons. We emphasize the spectrum actually obtained in a collider with both polarized electrons and photons (peaked at high energy and very different from a Compton spectrum). Luminosity is estimated for the presently considered colliders, and interaction and conversion-point geometries are described. Also specified are laser requirements (such as wavelength, peak power, and average power) and the lasers that might be employed. These include conventional and free-electron lasers. Finally, we describe the R&D necessary to make either of these approaches viable and explore the use of the SLC as a test bed for a photon-photon collider of very high energy.
Wang, Jian-Yong; Cheng, Xue-Ping; Tang, Xiao-Yan; Yang, Jian-Rong; Ren, Bo
2014-03-15
The oblique propagation of ion-acoustic soliton-cnoidal waves in a magnetized electron-positron-ion plasma with superthermal electrons is studied. Linear dispersion relations of the fast and slow ion-acoustic modes are discussed under the weak and strong magnetic field situations. By means of the reductive perturbation approach, Korteweg-de Vries equations governing ion-acoustic waves of fast and slow modes are derived, respectively. Explicit interacting soliton-cnoidal wave solutions are obtained by the generalized truncated Painlevé expansion. It is found that every peak of a cnoidal wave elastically interacts with a usual soliton except for some phase shifts. The influence of the electron superthermality, positron concentration, and magnetic field obliqueness on the soliton-cnoidal wave are investigated in detail.
NASA Astrophysics Data System (ADS)
Ahmad, Ali; Masood, W.
2015-10-01
> We investigate the low-frequency (by comparison with the ion Larmor frequency) electrostatic solitary structures in a spatially non-uniform electron-positron-ion (e-p-i) magnetoplasma with non-Maxwellian electrons. A linear dispersion relation for the obliquely propagating ion acoustic drift wave is derived and it is shown that the non-Maxwellian electron population modifies the dispersion characteristics of the wave under consideration. We also carry out a nonlinear analysis and derive the modified Zakharov-Kuznetsov (MZK) equation for the coupled drift acoustic wave in a non-uniform magnetized plasma. We highlight the differences between the MZK equation and its homogeneous counterpart. We also find the solution of the MZK equation using the tangent hyperbolic method. It is observed that the electron spectral index , positron concentration, and propagation angle alter the structure of the ion acoustic drift solitary waves. The results obtained in this paper may be beneficial to understanding the propagation characteristics of electrostatic drift solitary structures in the interstellar medium and in laboratory experiments where electron-positron plasmas have recently been created by impinging ultra-intense laser pulses on a solid density target at the Lawrence Livermore National Laboratory (LLNL).
Linear and nonlinear ion-acoustic waves in an unmagnetized electron-positron-ion quantum plasma
NASA Astrophysics Data System (ADS)
Ali, S.; Moslem, W. M.; Shukla, P. K.; Schlickeiser, R.
2007-08-01
The linear and nonlinear properties of the ion-acoustic waves (IAWs) are investigated by using the quantum hydrodynamic equations together with the Poisson equation in a three-component quantum electron-positron-ion plasma. For this purpose, a linear dispersion relation, a Korteweg-de Vries equation and an energy equation containing quantum corrections are derived. Computational investigations have been performed to examine the quantum mechanical effects on the linear and nonlinear waves. It is found that both the linear and nonlinear properties of the IAWs are significantly affected by the inclusion of the quantum corrections. The relevance of the present investigation to dense white dwarfs (where the electron-positron annihilation can be unimportant) is discussed.
Planar and non-planar ion acoustic shock waves in electron positron ion plasmas
NASA Astrophysics Data System (ADS)
Masood, Waqas; Jehan, Nusrat; Mirza, Arshad M.; Sakanaka, P. H.
2008-06-01
Ion acoustic shock waves (IASW's) are studied in an unmagnetized plasma consisting of electrons, positrons and adiabatically hot positive ions. This is done by deriving the Kortweg-deVries-Burger (KdVB) equation under the small amplitude perturbation expansion method. The dissipation is introduced by taking into account the kinematic viscosity among the plasma constituents. It is found that the strength of ion acoustic shock wave is maximum for spherical, intermediate for cylindrical, and minimum for planar geometry. It is observed that the positron concentration, ratio of ion to electron temperature, and the plasma kinematic viscosity significantly modifies the shock structure. Finally, it is found that the temporal evolution of the non-planar IASW's is quite different by comparison with the planar geometry. The relevance of the present study with regard to the dense astrophysical environments is also pointed out.
Cross section for production of low-energy electron-positron pairs by relativistic heavy ions
NASA Technical Reports Server (NTRS)
Eby, P. B.
1991-01-01
Starting with the lowest-order unscreened QED matrix element for electron-positron pair production by heavy charged particles, the paper calculates the cross section for this process differential in all independent variables and valid for all pair energies small compared to the incident particle energy. Integration over the possible emission angles of one of the pair members gives an expression that is valid for low-energy pairs that can be compared with previous work based on the Weizsaecker-Williams method. Integration over the possible angles of the other pair member then yields an expression identical to one derived by Racah. The high energy-transfer limit of the expression for the cross section integrated over electron and positron angles is found to be identical to that of Kelner in the unscreened case.
NASA Astrophysics Data System (ADS)
Diaz, Marco Aurelio; Ross, Douglas A.
2001-05-01
We present the contributions from all types of one-loop corrections to the scattering amplitude for the pair production of polarized charginos or neutralinos from polarized electron-positron annihilation. The contributions are classified in terms of ``prototypes'' distinguished by the number of particles inside the loops and their spins. The results are quoted in terms of the Veltman-Passarino functions in terms of general couplings and internal masses. The results can therefore be applied to any supersymmetric extension of the Standard Model or indeed to any polarized fermion pair production process in electron-positron annihilation. A FORTRAN program which encodes the results of the paper is available http://www.hep.phys.soton.ac.uk/hepwww/staff/D.Ross/chipackage/chipackage.html.
Head-tail instability caused by electron clouds in positron storage rings
Ohmi; Zimmermann
2000-10-30
In positron or proton storage rings with many closely spaced bunches, an electron cloud can build up in the vacuum chamber due to photoemission or secondary emission. We discuss the possibility of a single-bunch two-stream instability driven by this electron cloud. Depending on the strength of the beam-electron interaction, the chromaticity and the synchrotron oscillation frequency, this instability either resembles a linac beam breakup or a head-tail instability. We present computer simulations of the instabilities, and compare the simulation results with analytical estimates.
Head-tail instability caused by electron clouds in positron storage rings
Ohmi; Zimmermann
2000-10-30
In positron or proton storage rings with many closely spaced bunches, an electron cloud can build up in the vacuum chamber due to photoemission or secondary emission. We discuss the possibility of a single-bunch two-stream instability driven by this electron cloud. Depending on the strength of the beam-electron interaction, the chromaticity and the synchrotron oscillation frequency, this instability either resembles a linac beam breakup or a head-tail instability. We present computer simulations of the instabilities, and compare the simulation results with analytical estimates. PMID:11041936
{open_quotes}Heavy light bullets{close_quotes} in electron-positron plasma
Berezhiani, V.I.; Mahajan, S.M.
1995-03-01
The nonlinear propagation of circularly polarized electromagnetic waves with relativistically strong amplitudes in an unmagnetized hot electron-positron plasma with a small fraction of ions is investigated. The possibility of finding localized solutions in such a plasma is explored. It is shown that these plasmas support the propagation of {open_quotes}heavy light bullets{close_quotes}; nondiffracting and nondispersive electromagnetic (EM) pulses with large density bunching.
Electron Positron Proton Spectrometer for use at Laboratory for Laser Energetics
Ayers, S L
2010-04-07
The Electron Positron Proton Spectrometer (EPPS) is mounted in a TIM (Ten-Inch Manipulator) system on the Omega-60 or Omega-EP laser facilities at the University of Rochester, Laboratory for Laser Energetics (LLE), when in use, see Fig. 1. The Spectrometer assembly, shown in Fig. 2, is constructed of a steel box containing magnets, surrounded by Lead 6% Antimony shielding with SS threaded insert, sitting on an Aluminum 6061-T6 plate.
Prospects for the study of gluonic states at Beijing Electron- Positron Collider (BEPC)
Chanowitz, M.S.
1989-01-11
Progress in the study of gluonic states depends crucially on accumulating data samples of order 10/sup 8/ J//psi/ decays, in order to perform complete partial wave analyses of radiative and hadronic J//psi/ decays. This requirement is well matched to the capabilities of the Beijing Electron-Positron Collider, which has approached the necessary luminosity in its first two months of operation. 28 refs., 1 fig., 1 tab.
Theories of statistical equilibrium in electron-positron colliding-beam storage rings
Schonfeld, J.F.
1985-01-01
In this lecture I introduce you to some recent theoretical work that represents a significant and long overdue departure from the mainstream of ideas on the physics of colliding- beam storage rings. The goal of the work in question is to understand analytically - without recourse to computer simulation - the role that dissipation and noise play in the observed colliding-beam behavior of electron-positron storage rings.
Evaluation of bremsstrahlung contribution to photon transport in coupled photon-electron problems
NASA Astrophysics Data System (ADS)
Fernández, Jorge E.; Scot, Viviana; Di Giulio, Eugenio; Salvat, Francesc
2015-11-01
The most accurate description of the radiation field in x-ray spectrometry requires the modeling of coupled photon-electron transport. Compton scattering and the photoelectric effect actually produce electrons as secondary particles which contribute to the photon field through conversion mechanisms like bremsstrahlung (which produces a continuous photon energy spectrum) and inner-shell impact ionization (ISII) (which gives characteristic lines). The solution of the coupled problem is time consuming because the electrons interact continuously and therefore, the number of electron collisions to be considered is always very high. This complex problem is frequently simplified by neglecting the contributions of the secondary electrons. Recent works (Fernández et al., 2013; Fernández et al., 2014) have shown the possibility to include a separately computed coupled photon-electron contribution like ISII in a photon calculation for improving such a crude approximation while preserving the speed of the pure photon transport model. By means of a similar approach and the Monte Carlo code PENELOPE (coupled photon-electron Monte Carlo), the bremsstrahlung contribution is characterized in this work. The angular distribution of the photons due to bremsstrahlung can be safely considered as isotropic, with the point of emission located at the same place of the photon collision. A new photon kernel describing the bremsstrahlung contribution is introduced: it can be included in photon transport codes (deterministic or Monte Carlo) with a minimal effort. A data library to describe the energy dependence of the bremsstrahlung emission has been generated for all elements Z=1-92 in the energy range 1-150 keV. The bremsstrahlung energy distribution for an arbitrary energy is obtained by interpolating in the database. A comparison between a PENELOPE direct simulation and the interpolated distribution using the data base shows an almost perfect agreement. The use of the data base increases
Measurement of the hadronic cross section in electron-positron annihilation
Clearwater, S.
1983-11-01
This thesis describes the most precise measurement to date of the ratio R, the hadronic cross section in lowest order electron-positron annihilation to the cross section for muon pair production in lowest order electron-positron annihilation. This experiment is of interest because R is a fundamental parameter that tests in a model independent way the basic assumptions of strong interaction theories. According to the assumptions of one of these theories the value of R is determined simply from the electric charges, spin, and color assignments of the produced quark-pairs. The experiment was carried out with the MAgnetic Calorimeter using collisions of 14.5 GeV electrons and positrons at the 2200m circumference PEP storage ring at SLAC. The MAC detector is one of the best-suited collider detectors for measuring R due to its nearly complete coverage of the full angular range. The data for this experiment were accumulated between February 1982 and April 1983 corresponding to a total event sample of about 40,000 hadronic events. About 5% of the data were taken with 14 GeV beams and the rest of the data were taken with 14.5 GeV beams. A description of particle interactions and experimental considerations is given.
Oblique propagation of ion-acoustic solitary waves in a magnetized electron-positron-ion plasma
Ferdousi, M.; Sultana, S.; Mamun, A. A.
2015-03-15
The properties of obliquely propagating ion-acoustic solitary waves in the presence of ambient magnetic field have been investigated theoretically in an electron-positron-ion nonthermal plasma. The plasma nonthermality is introduced via the q-nonextensive distribution of electrons and positrons. The Korteweg-de Vries (K-dV) and modified K-dV (mK-dV) equations are derived by adopting reductive perturbation method. The solution of K-dV and modified K-dV equation, which describes the solitary wave characteristics in the long wavelength limit, is obtained by steady state approach. It is seen that the electron and positron nonextensivity and external magnetic field (obliqueness) have significant effects on the characteristics of solitary waves. A critical value of nonextensivity is found for which solitary structures transit from positive to negative potential. The findings of this investigation may be used in understanding the wave propagation in laboratory and space plasmas where static external magnetic field is present.
Nonlinear electromagnetic perturbations in a degenerate ultrarelativistic electron-positron plasma.
El-Taibany, W F; Mamun, A A
2012-02-01
Nonlinear propagation of fast and slow magnetosonic perturbation modes in an ultrarelativistic, ultracold, degenerate (extremely dense) electron positron (EP) plasma (containing ultrarelativistic, ultracold, degenerate electron and positron fluids) has been investigated by the reductive perturbation method. The Alfvén wave velocity is modified due to the presence of the enthalpy correction in the fluid equations of motion. The degenerate EP plasma system (under consideration) supports the Korteweg-de Vries (KdV) solitons, which are associated with either fast or slow magnetosonic perturbation modes. It is found that the ultrarelativistic model leads to compressive (rarefactive) electromagnetic solitons corresponding to the fast (slow) wave mode. There are certain critical angles, θ(c), at which no soliton solution is found corresponding to the fast wave mode. For the slow mode, the magnetic-field intensity affects both the soliton amplitude and width. It is also illustrated that the basic features of the electromagnetic solitary structures, which are found to exist in such a degenerate EP plasma, are significantly modified by the effects of enthalpy correction, electron and positron degeneracy, magnetic-field strength, and the relativistic effect. The applications of the results in a pair-plasma medium, which occurs in many astrophysical objects (e.g., pulsars, white dwarfs, and neutron stars) are briefly discussed. PMID:22463336
E166: Polarized Positrons & Polarimetry
Schuler, K.Peter; /DESY
2011-12-06
A proof-of-principle experiment has been carried out in the Final Focus Test Beam (FFTB) at Stanford Linear Accelerator Center (SLAC) to demonstrate production of polarized positrons in a manner suitable for implementation at the International Linear Collider (ILC). A helical undulator of 2.54 mm period and 1 -m length produced circularly polarized photons with a first harmonic endpoint energy of 8 MeV when traversed by a 46.6 GeV electron beam. The polarized photons were converted to polarized positrons in a 0.2-radiation-length tungsten target. The polarization of these positrons was measured using a Compton transmission polarimeter to have peak value in excess of 80%.
Ordered materials for organic electronics and photonics.
O'Neill, Mary; Kelly, Stephen M
2011-02-01
We present a critical review of semiconducting/light emitting, liquid crystalline materials and their use in electronic and photonic devices such as transistors, photovoltaics, OLEDs and lasers. We report that annealing from the mesophase improves the order and packing of organic semiconductors to produce state-of-the-art transistors. We discuss theoretical models which predict how charge transport and light emission is affected by the liquid crystalline phase. Organic photovoltaics and OLEDs require optimization of both charge transport and optical properties and we identify the various trade-offs involved for ordered materials. We report the crosslinking of reactive mesogens to give pixellated full-colour OLEDs and distributed bi-layer photovoltaics. We show how the molecular organization inherent to the mesophase can control the polarization of light-emitting devices and the gain in organic, thin-film lasers and can also provide distributed feedback in chiral nematic mirrorless lasers. We update progress on the surface alignment of liquid crystalline semiconductors to obtain monodomain devices without defects or devices with spatially varying properties. Finally the significance of all of these developments is assessed.
NASA Astrophysics Data System (ADS)
EL-Shamy, E. F.
2014-08-01
The solitary structures of multi-dimensional ion-acoustic solitary waves (IASWs) have been considered in magnetoplasmas consisting of electron-positron-ion with high-energy (superthermal) electrons and positrons are investigated. Using a reductive perturbation method, a nonlinear Zakharov-Kuznetsov equation is derived. The multi-dimensional instability of obliquely propagating (with respect to the external magnetic field) IASWs has been studied by the small-k (long wavelength plane wave) expansion perturbation method. The instability condition and the growth rate of the instability have been derived. It is shown that the instability criterion and their growth rate depend on the parameter measuring the superthermality, the ion gyrofrequency, the unperturbed positrons-to-ions density ratio, the direction cosine, and the ion-to-electron temperature ratio. Clearly, the study of our model under consideration is helpful for explaining the propagation and the instability of IASWs in space observations of magnetoplasmas with superthermal electrons and positrons.
EL-Shamy, E. F.
2014-08-15
The solitary structures of multi–dimensional ion-acoustic solitary waves (IASWs) have been considered in magnetoplasmas consisting of electron-positron-ion with high-energy (superthermal) electrons and positrons are investigated. Using a reductive perturbation method, a nonlinear Zakharov-Kuznetsov equation is derived. The multi-dimensional instability of obliquely propagating (with respect to the external magnetic field) IASWs has been studied by the small-k (long wavelength plane wave) expansion perturbation method. The instability condition and the growth rate of the instability have been derived. It is shown that the instability criterion and their growth rate depend on the parameter measuring the superthermality, the ion gyrofrequency, the unperturbed positrons-to-ions density ratio, the direction cosine, and the ion-to-electron temperature ratio. Clearly, the study of our model under consideration is helpful for explaining the propagation and the instability of IASWs in space observations of magnetoplasmas with superthermal electrons and positrons.
Electron transport through a quantum dot assisted by cavity photons.
Abdullah, Nzar Rauf; Tang, Chi-Shung; Manolescu, Andrei; Gudmundsson, Vidar
2013-11-20
We investigate transient transport of electrons through a single quantum dot controlled by a plunger gate. The dot is embedded in a finite wire with length Lx assumed to lie along the x-direction with a parabolic confinement in the y-direction. The quantum wire, originally with hard-wall confinement at its ends, ±Lx/2, is weakly coupled at t = 0 to left and right leads acting as external electron reservoirs. The central system, the dot and the finite wire, is strongly coupled to a single cavity photon mode. A non-Markovian density-matrix formalism is employed to take into account the full electron-photon interaction in the transient regime. In the absence of a photon cavity, a resonant current peak can be found by tuning the plunger-gate voltage to lift a many-body state of the system into the source-drain bias window. In the presence of an x-polarized photon field, additional side peaks can be found due to photon-assisted transport. By appropriately tuning the plunger-gate voltage, the electrons in the left lead are allowed to undergo coherent inelastic scattering to a two-photon state above the bias window if initially one photon was present in the cavity. However, this photon-assisted feature is suppressed in the case of a y-polarized photon field due to the anisotropy of our system caused by its geometry. PMID:24132041
Chang, H X; Qiao, B; Xu, Z; Xu, X R; Zhou, C T; Yan, X Q; Wu, S Z; Borghesi, M; Zepf, M; He, X T
2015-11-01
A scheme for enhanced quantum electrodynamics (QED) production of electron-positron-pair plasmas is proposed that uses two ultraintense lasers irradiating a thin solid foil from opposite sides. In the scheme, under a proper matching condition, in addition to the skin-depth emission of γ-ray photons and Breit-Wheeler creation of pairs on each side of the foil, a large number of high-energy electrons and photons from one side can propagate through it and interact with the laser on the other side, leading to much enhanced γ-ray emission and pair production. More importantly, the created pairs can be collected later and confined to the center by opposite laser radiation pressures when the foil becomes transparent, resulting in the formation of unprecedentedly overdense and high-energy pair plasmas. Two-dimensional QED particle-in-cell simulations show that electron-positron-pair plasmas with overcritical density 10(22) cm(-3) and a high energy of 100s of MeV are obtained with 10 PW lasers at intensities 10(23) W/cm(2), which are of key significance for laboratory astrophysics studies. PMID:26651802
NASA Astrophysics Data System (ADS)
Gast, Henning
2016-07-01
Precision measurements by the Alpha Magnetic Spectrometer on the International Space Station of the primary cosmic-ray electron flux in the range 0.5 to 700 GeV and the positron flux in the range 0.5 to 500 GeV are presented. The electron flux and the positron flux each require a description beyond a single power-law spectrum. Both the electron flux and the positron flux change their behavior at ˜30 GeV but the fluxes are significantly different in their magnitude and energy dependence. Between 20 and 200 GeV the positron spectral index is significantly harder than the electron spectral index. The results show, for the first time, that neither e+ nor e- can be described by a single power law above 27.2 and 52.3 GeV, respectively. The determination of the differing behavior of the spectral indices versus energy is a new observation and provides important information on the origins of cosmic-ray electrons and positrons. The dependence of the electron and positron fluxes on time will also be discussed.
Holtzapple, R. L.; Billing, M. G.; Campbell, R. C.; Dugan, G. F.; Flanagan, J.; McArdle, K. E.; Miller, M. I.; Palmer, M. A.; Ramirez, G. A.; Sonnad, K. G.; et al
2016-04-11
Electron cloud related emittance dilution and instabilities of bunch trains limit the performance of high intensity circular colliders. One of the key goals of the Cornell electron-positron storage ring Test Accelerator (CesrTA) research program is to improve our understanding of how the electron cloud alters the dynamics of bunches within the train. Single bunch beam diagnostics have been developed to measure the beam spectra, vertical beam size, two important dynamical effects of beams interacting with the electron cloud, for bunch trains on a turn-by-turn basis. Experiments have been performed at CesrTA to probe the interaction of the electron cloud withmore » stored positron bunch trains. The purpose of these experiments was to characterize the dependence of beam-electron cloud interactions on the machine parameters such as bunch spacing, vertical chromaticity, and bunch current. The beam dynamics of the stored beam, in the presence of the electron cloud, was quantified using: 1) a gated beam position monitor (BPM) and spectrum analyzer to measure the bunch-by-bunch frequency spectrum of the bunch trains, 2) an x-ray beam size monitor to record the bunch-by-bunch, turn-by-turn vertical size of each bunch within the trains. In this study we report on the observations from these experiments and analyze the effects of the electron cloud on the stability of bunches in a train under many different operational conditions.« less
NASA Astrophysics Data System (ADS)
Holtzapple, R. L.; Billing, M. G.; Campbell, R. C.; Dugan, G. F.; Flanagan, J.; McArdle, K. E.; Miller, M. I.; Palmer, M. A.; Ramirez, G. A.; Sonnad, K. G.; Totten, M. M.; Tucker, S. L.; Williams, H. A.
2016-04-01
Electron cloud related emittance dilution and instabilities of bunch trains limit the performance of high intensity circular colliders. One of the key goals of the Cornell electron-positron storage ring Test Accelerator (CesrTA) research program is to improve our understanding of how the electron cloud alters the dynamics of bunches within the train. Single bunch beam diagnotics have been developed to measure the beam spectra, vertical beam size, two important dynamical effects of beams interacting with the electron cloud, for bunch trains on a turn-by-turn basis. Experiments have been performed at CesrTA to probe the interaction of the electron cloud with stored positron bunch trains. The purpose of these experiments was to characterize the dependence of beam-electron cloud interactions on the machine parameters such as bunch spacing, vertical chromaticity, and bunch current. The beam dynamics of the stored beam, in the presence of the electron cloud, was quantified using: 1) a gated beam position monitor (BPM) and spectrum analyzer to measure the bunch-by-bunch frequency spectrum of the bunch trains; 2) an x-ray beam size monitor to record the bunch-by-bunch, turn-by-turn vertical size of each bunch within the trains. In this paper we report on the observations from these experiments and analyze the effects of the electron cloud on the stability of bunches in a train under many different operational conditions.
Sessler, Andrew M.
1996-01-01
Since the seminal work by Ginsburg, et al., the subject of giving the Next Linear Collider photon-photon capability, as well as electron-positron capability, has drawn much attention [1]. A 1990 article by V.I. Telnov describes the situation at that time [2]. In March 1994, the first workshop on this subject was held [3]. This report briefly reviews the physics that can be achieved through the photon-photon channel and then focuses on the means of achieving such a collider. Also reviewed is the spectrum of backscattered Compton photons—the best way of obtaining photons. We emphasize the spectrum actually obtained in a collider with both polarized electrons and photons (peaked at high energy and very different from a Compton spectrum). Luminosity is estimated for the presently considered colliders, and interaction and conversion-point geometries are described. Also specified are laser requirements (such as wavelength, peak power, and average power) and the lasers that might be employed. These include conventional and free-electron lasers. Finally, we describe the R&D necessary to make either of these approaches viable and explore the use of the SLC as a test bed for a photon-photon collider of very high energy.
Measurement of electron-positron spectrum in high-energy cosmic rays in the PAMELA experiment
NASA Astrophysics Data System (ADS)
Karelin, A. V.; Adriani, O.; Barbarino, G. C.; Bazilevskaya, G. A.; Bellotti, R.; Boezio, M.; Bogomolov, E. A.; Bongi, M.; Bonvicini, V.; Bottai, S.; Bruno, A.; Cafagna, F.; Campana, D.; Carbone, R.; Carlson, P.; Casolino, M.; Castellini, G.; De Donato, C.; De Santis, C.; De Simone, N.; Di Felice, V.; Formato, V.; Galper, A. M.; Koldashov, S. V.; Koldobskiy, S. A.; Krutkov, S. Y.; Kvashnin, A. N.; Leonov, A. A.; Mayorov, A. G.; Malakhov, V. V.; Marcelli, L.; Martucci, M.; Menn, W.; Merge, M.; Mikhailov, V. V.; Mocchiutti, E.; Monaco, A.; Mori, N.; Munini, R.; Osteria, G.; Palma, F.; Panico, B.; Papini, P.; Pearce, M.; Picozza, P.; Ricci, M.; Ricciarini, S. B.; Sarkar, R.; Scotti, V.; Rossetto, L.; Simon, M.; Sparvoli, R.; Spillantini, P.; Vacchi, A.; Vannuccini, E.; Vasilyev, G. I.; Voronov, S. A.; Yurkin, Y. T.; Zampa, G.; Zampa, N.
2015-08-01
At present the existing data on the cosmic ray electron energy spectra in the high energy range are fragmented, and the situation is exacerbated by their small number. In the satellite PAMELA experiment measurements at high energies are carried out by the calorimeter. The experimental data accumulated for more than 8 years of measurements, with the information of the calorimeter, the neutron detector and the scintillation counters made it possible to obtain the total spectrum of high-energy electrons and positrons in energy range 0.3-3 TeV.
The gamma-ray spectra of halocarbons in positron-electron annihilation process
NASA Astrophysics Data System (ADS)
Ma, X. G.; Zhu, Y. H.; Liu, Y.
2015-10-01
The gamma-ray spectra of the positron annihilation process in methane CH4 and its fully substituent halocarbons CF4, CCl4, and CBr4 have been studied. The theoretical predictions of the inner valence electrons agree well with the experimental measurements for all these molecules. That the outermost s electrons in carbon or halogen atoms dominate the gamma-ray spectra has been confirmed for the first time. The positrophilic site has also been found in these molecules and understanding of annihilation processes in molecules has been enhanced.
Moortgat-Pick, G.; Abe, T.; Alexander, G.; Ananthanarayan, B.; Babich, A.A.; Bharadwaj, V.; Barber, D.; Bartl, A.; Brachmann, A.; Chen, S.; Clarke, J.; Clendenin, J.E.; Dainton, J.; Desch, K.; Diehl, M.; Dobos, B.; Dorland, T.; Eberl, H.; Ellis, John R.; Flottman, K.; Frass, H.; /CERN /Durham U., IPPP /Colorado U. /Tel-Aviv U. /Bangalore, Indian Inst. Sci. /Gomel State Tech. U. /SLAC /DESY /Vienna U. /Daresbury /Liverpool U. /Freiburg U. /Vienna, OAW /Wurzburg U. /Fermilab /Uppsala U. /Waseda U., RISE /Warsaw U. /Bonn U. /Aachen, Tech. Hochsch. /Cornell U., Phys. Dept.
2005-07-06
The proposed International Linear Collider (ILC) is well-suited for discovering physics beyond the Standard Model and for precisely unraveling the structure of the underlying physics. The physics return can be maximized by the use of polarized beams. This report shows the paramount role of polarized beams and summarizes the benefits obtained from polarizing the positron beam, as well as the electron beam. The physics case for this option is illustrated explicitly by analyzing reference reactions in different physics scenarios. The results show that positron polarization, combined with the clean experimental environment provided by the linear collider, allows to improve strongly the potential of searches for new particles and the identification of their dynamics, which opens the road to resolve shortcomings of the Standard Model. The report also presents an overview of possible designs for polarizing both beams at the ILC, as well as for measuring their polarization.
Moortgat-Pick, G.; Abe, T.; Alexander, G.; Ananthanarayan, B.; Babich, A.A.; Bharadwaj, V.; Barber, D.; Bartl, A.; Brachmann, A.; Chen, S.; Clarke, J.; Clendenin, J.E.; Dainton, J.; Desch, K.; Diehl, M.; Dobos, B.; Dorland, T.; Eberl, H.; Ellis, John R.; Flottman, K.; Frass, H.; /CERN /Durham U., IPPP /Colorado U. /Tel-Aviv U. /Bangalore, Indian Inst. Sci. /Gomel State Tech. U. /SLAC /DESY /Vienna U. /Daresbury /Liverpool U. /Freiburg U. /Vienna, OAW /Wurzburg U. /Fermilab /Uppsala U. /Waseda U., RISE /Warsaw U. /Bonn U. /Aachen, Tech. Hochsch. /Cornell U., Phys. Dept.
2005-07-01
The proposed International Linear Collider (ILC) is well-suited for discovering physics beyond the Standard Model and for precisely unraveling the structure of the underlying physics. The physics return can be maximized by the use of polarized beams. This report shows the paramount role of polarized beams and summarizes the benefits obtained from polarizing the positron beam, as well as the electron beam. The physics case for this option is illustrated explicitly by analyzing reference reactions in different physics scenarios. The results show that positron polarization, combined with the clean experimental environment provided by the linear collider, allows to improve strongly the potential of searches for new particles and the identification of their dynamics, which opens the road to resolve shortcomings of the Standard Model. The report also presents an overview of possible designs for polarizing both beams at the ILC, as well as for measuring their polarization.
Drift-Alfvén eigenmodes in inhomogeneous electron-positron-ion plasmas
NASA Astrophysics Data System (ADS)
Haque, Q.; Yamin, S.; Ahmad, Ali
2011-03-01
An analytical description of drift-Alfvén modes in nonuniform bounded magnetized electron-positron-ion plasmas is presented here. In the linear domain, linearized equations are solved by considering the Gaussian density profile in the radial direction. For this bounded plasma, the condition for the quantization of the modes is found. We note that the condition depends upon the density ratios of different plasma species. The full set of nonlinear equations is also solved, yielding stationary rotating solutions in terms of Bessel functions. We also note that the behavior of the nonlinear structures can be affected by the concentration of the positrons in the system. The importance of the present results with respect to astrophysical plasmas is pointed out.
NASA Astrophysics Data System (ADS)
Masood, W.; Mirza, Arshad M.
2012-12-01
Nonlinear equations governing the dynamics of finite amplitude drift-acoustic-waves are derived by taking into account sheared ion flow perpendicular to the ambient magnetic field in a quantum magnetoplasma comprised of electrons, positrons, and ions. It is shown that stationary solution of the nonlinear equations can be represented in the form of a counter-rotating vortex for a particular choice of the equilibrium profile. The counter rotating vortices are, however, observed to form on very short scales i.e., of the order of ion Larmor radius ρ i in quantum plasmas. It is observed that the scalelengths over which these structures form get modified in the presence of quantum statistical and Bohm potential terms as well as the positron concentration. The relevance of the present investigation with regard to dense astrophysical environments is also pointed out.
Ion-acoustic vortices in inhomogeneous and dissipative electron-positron-ion quantum magnetoplasmas
NASA Astrophysics Data System (ADS)
Masood, W.; Mirza, Arshad M.; Nargis, Shahida; Ayub, M.
2009-04-01
Linear and nonlinear properties of quantum ion-acoustic waves are studied in a nonuniform, dissipative quantum plasma (composed of electrons, positrons, and ions) with sheared ion flow parallel to the ambient magnetic field, using the quantum hydrodynamic model. It is shown that the shear ion flow parallel to the external magnetic field can drive the quantum ion-acoustic wave unstable provided ∣S∣ky>kz. Stationary solutions of the nonlinear equations that govern the quantum ion-acoustic waves are also obtained. It is found that electrostatic monopolar, dipolar, and vortex street-type solutions can appear in such a plasma. It is observed that the inclusion of positron, quantum statistical, and Bohm potential terms significantly modifies the scale lengths of these nonlinear structures. The relevance of the present investigation with regard to the dense astrophysical environments is also pointed out.
Two dimensional electromagnetic shock structures in dense electron-positron-ion magnetoplasmas
NASA Astrophysics Data System (ADS)
Masood, W.; Rizvi, H.; Hussain, S.
2011-04-01
Linear and nonlinear analysis of low frequency magnetoacoustic waves propagating at an angle θ with the ambient magnetic field are investigated in dense electron-positron-ion (e-p-i) plasmas using the quantum magnetohydrodynamic (QMHD) model. In this regard, a quantum Kadomtsev-Petviashvili-Burgers (KPB) equation is derived in the small amplitude limit. The stability of KPB equation is also presented. The variation of the nonlinear fast and slow magnetoacoustic shock waves with the positron concentration, kinematic viscosity, obliqueness parameter θ, and the magnetic field, are also investigated. It is observed that the aforementioned plasma parameters significantly modify the propagation characteristics of two dimensional nonlinear magnetoacoustic shock waves in dissipative quantum magnetoplasmas. The relevance of the present investigation with regard to dense astrophysical environments is also pointed out.
Dynamics of nonlinear ion-waves in Fermi-Dirac electron-positron-ion magnetoplasmas
NASA Astrophysics Data System (ADS)
Akbari-Moghanjoughi, M.
2011-06-01
Oblique propagation and head-on collisions of solitary structures is studied in a dense magnetized plasma comprised of relativistic ultra-cold electrons and positrons and positive dynamic ions using conventional extended multi-scales technique, in the ground of quantum hydrodynamics model. The variations of head-on collision phase-shift as well as the characteristic soliton amplitude and width is evaluated numerically in terms of other plasma parameters such as mass-density, normalized magnetic field strength, its angle with respect to the soliton propagation and the relative positron number-density. The relevance of current investigations, with appropriate plasma parameters for the astrophysical dense magnetized objects such as white-dwarfs, is addressed.
NASA Astrophysics Data System (ADS)
Ata-ur-Rahman, Ali, S.; Mirza, Arshad M.; Qamar, A.
2013-04-01
We have studied the propagation of ion acoustic shock waves involving planar and non-planar geometries in an unmagnetized plasma, whose constituents are non-degenerate ultra-cold ions, relativistically degenerate electrons, and positrons. By using the reductive perturbation technique, Korteweg-deVries Burger and modified Korteweg-deVries Burger equations are derived. It is shown that only compressive shock waves can propagate in such a plasma system. The effects of geometry, the ion kinematic viscosity, and the positron concentration are examined on the ion acoustic shock potential and electric field profiles. It is found that the properties of ion acoustic shock waves in a non-planar geometry significantly differ from those in planar geometry. The present study has relevance to the dense plasmas, produced in laboratory (e.g., super-intense laser-dense matter experiments) and in dense astrophysical objects.
Ata-ur-Rahman,; Qamar, A.; Ali, S.; Mirza, Arshad M.
2013-04-15
We have studied the propagation of ion acoustic shock waves involving planar and non-planar geometries in an unmagnetized plasma, whose constituents are non-degenerate ultra-cold ions, relativistically degenerate electrons, and positrons. By using the reductive perturbation technique, Korteweg-deVries Burger and modified Korteweg-deVries Burger equations are derived. It is shown that only compressive shock waves can propagate in such a plasma system. The effects of geometry, the ion kinematic viscosity, and the positron concentration are examined on the ion acoustic shock potential and electric field profiles. It is found that the properties of ion acoustic shock waves in a non-planar geometry significantly differ from those in planar geometry. The present study has relevance to the dense plasmas, produced in laboratory (e.g., super-intense laser-dense matter experiments) and in dense astrophysical objects.
A search for single electron production in electron positron annihilation at E = 29 GeV
Steele, T.R.
1989-09-01
This thesis presents experimental results from the ASP detector which took data on e{sup +}e{sup -} interactions in the PEP storage ring at SLAC. Its design was particularly suitable for searching for production of supersymmetric particles. The motivations for and phenomenology of Supersymmetry are discussed. In particular, the production of a single supersymmetric electron ( selectron'', {tilde e}) in combination with a supersymmetric photon ( photino'', {tilde {gamma}}) would result in events in which a single electron and no other particles are observed in the detector at an e{sup +}e{sup -} collider such as PEP, provided the masses of these particles are not too large. Such events would also result from the production of a single supersymmetric W-boson ( wino'', {tilde W}) in combination with a supersymmetric neutrino ( sneutrino'', {tilde {nu}}). These processes make it possible to search for electrons and winos with masses greater than the beam energy. Observation of these unusual events would distinctly indicate the production of new particles. The ASP detector was designed to be hermetic and to provide efficient event reconstruction for low multiplicity events. The detector is described and its performance is evaluated; it is found to be well-suited to this study. The data sample collected with the detector was thoroughly analyzed for evidence of single-electron events. The various possible background processes are considered and Monte Carlo calculations of the distributions from single selectron and single wino production are presented. Using this information an efficient off-line event selection process was developed, and it is described in detail. 82 refs., 41 figs., 4 tabs.
NASA Astrophysics Data System (ADS)
Reisfeld, Pore determination by positron annihilation lifetime spectroscopy R.; Saraidarov, T.; Jasinska, B.
2004-07-01
Porous glasses prepared by the sol-gel technique have a variety of applications when incorporated by photonic materials: tunable lasers, sensors, luminescence solar concentrators, semiconductor quantum dots, biological markers. The known methods of pore size determinations, the nitrogen adsorption and mercury porosimetry allow to determine the sizes of open pores. Positron annihilation lifetime spectroscopy (PALS) allows to determine pore sizes also of closed pores. As an example we have performed measurements of non-doped zirconia-silica-polyurethane (ZSUR) ormocer glasses and the same glasses doped with lead sulfide quantum dots. The pore radii range between 0.25-0.38 nm, total surface area 15.5-23.8 m 2/g.
High energy electrons, positrons and photonuclear reactions in petawatt laser-solid experiments
Cowan, T E; Hunt, A W; Johnson, J; Perry, M D; Fountain, W; Hatchett, S; Key, M H; Kuehl, T; Parnell, T; Pennington, D M; Phillips, T W; Roth, M; Takahashi, Y; Wilks, S C
1999-09-09
The Petawatt laser at LLNL has opened a new regime of high-energy laser-matter interactions in which the quiver motion of plasma electrons is fully relativistic with energies extending well above the threshold for nuclear processes. We have observed that, in addition to the large flux of several MeV electrons ponderomotively expelled from the ultra-intense laser focus, there is a high energy component of electrons extending to -100 MeV, apparently from relativistic self-focusing and plasma acceleration in the underdense pre-formed plasma. The generation of hard bremsstrahlung cascade as these electrons traverse the solid target material, and the resulting photo-nuclear reactions, nuclear fission, and positron-electron pair production are described.
Free-electron lasers: Echoes of photons past
NASA Astrophysics Data System (ADS)
Campbell, Lawrence T.; McNeil, Brian W. J.
2016-08-01
High-harmonic generation is an established method to significantly upshift laser photon energies. Now, researchers at the SLAC National Accelerator Laboratory have used echo concepts to generate coherent high-harmonic output from an electron-beam light source.
NASA Astrophysics Data System (ADS)
Calvez, Antoine; Essey, Warren; Fairbairn, Malcolm; Kusenko, Alexander; Loewenstein, Michael
2011-11-01
X-ray and γ-ray observations can help understand the origin of the electron and positron signals reported by ATIC, PAMELA, PPB-BETS, and Fermi. It remains unclear whether the observed high-energy electrons and positrons are produced by relic particles, or by some astrophysical sources. To distinguish between the two possibilities, one can compare the electron population in the local neighborhood with that in the dwarf spheroidal galaxies, which are not expected to host as many pulsars and other astrophysical sources. This can be accomplished using X-ray and γ-ray observations of dwarf spheroidal galaxies. Assuming the signal detected by Fermi and ATIC comes from dark matter and using the inferred dark matter profile of the Draco dwarf spheroidal galaxy as an example, we calculate the photon spectrum produced by electrons via inverse Compton scattering. Since little is known about the magnetic fields in dwarf spheroidal galaxies, we consider the propagation of charged particles with and without diffusion. Extending the analysis of Fermi collaboration for Draco, we find that for a halo mass ˜10 9 M ⊙, even in the absence of diffusion, the γ-ray signal would be above the upper limits. This conclusion is subject to uncertainties associated with the halo mass. If dwarf spheroidal galaxies host local magnetic fields, the diffusion of the electrons can result in a signal detectable by future X-ray telescopes.
Photon and electron Landau damping in quantum plasmas
NASA Astrophysics Data System (ADS)
Mendonça, J. T.; Serbeto, A.
2016-09-01
Using a quantum kinetic description, we establish a general expression for the dispersion relation of electron plasma waves in the presence of an arbitrary spectrum of electromagnetic waves. This includes both electron and photon Landau damping. The quantum kinetic description allows us to compare directly these two distinct processes, and to show that they are indeed quite similar. The present work also extends previous results on photon Landau damping onto the quantum domain.
NASA Astrophysics Data System (ADS)
Hafez, M. G.; Roy, N. C.; Talukder, M. R.; Hossain Ali, M.
2016-08-01
The characteristics of the nonlinear oblique propagation of ion acoustic solitary waves in unmagnetized plasmas consisting of Boltzmann positrons, trapped electrons and ions are investigated. The modified Kadomtsev-Petviashivili ( m K P ) equation is derived employing the reductive perturbation technique. The parametric effects on phase velocity, Sagdeev potential, amplitude and width of solitons, and electrostatic ion acoustic solitary structures are graphically presented with the relevant physical explanations. This study may be useful for the better understanding of physical phenomena concerned in plasmas in which the effects of trapped electrons control the dynamics of wave.
Williams, G.; Kourakis, I.
2013-12-15
Electrostatic solitary waves in plasmas are the focus of many current studies of localized electrostatic disturbances in both laboratory and astrophysical plasmas. Here, an investigation of the nonlinear dynamics of plasma evolving in two dimensions, in the presence of excess superthermal background electrons and positrons, is undertaken. We investigate the effect of a magnetic field on weakly nonlinear ion acoustic waves. Deviation from the Maxwellian distribution is effectively modelled by the kappa model. A linear dispersion relation is derived, and a decrease in frequency and phase speed in both parallel and perpendicular modes can be seen, when the proportion of positrons to electrons increases. We show that ion acoustic solitary waves can be generated during the nonlinear evolution of a plasma fluid, and their nonlinear propagation is governed by a Zakharov-Kuznetsov (ZK) type equation. A multiple scales perturbation technique is used to derive the ZK equation. The solitary wave structures are dependent on the relation between the system parameters, specifically the superthermality of the system, the proportion of positron content, magnetic field strength, and the difference between electron and positron temperature. The parametric effect of these on electrostatic shock structures is investigated. In particular, we find that stronger superthermality leads to narrower excitations with smaller potential amplitudes. Increased positron concentration also suppresses both the amplitude and the width of solitary wave structures. However, the structures are only weakly affected by temperature differentials between electrons and positrons in our model.
Proton form factors and two-photon exchange in elastic electron-proton scattering
Nikolenko, D. M.; Arrington, J.; Barkov, L. M.; Vries, H. de; Gauzshtein, V. V.; Golovin, R. A.; Gramolin, A. V.; Dmitriev, V. F.; Zhilich, V. N.; Zevakov, S. A.; Kaminsky, V. V.; Lazarenko, B. A.; Mishnev, S. I.; Muchnoi, N. Yu.; Neufeld, V. V.; Rachek, I. A.; Sadykov, R. Sh.; Stibunov, V. N.; Toporkov, D. K.; Holt, R. J.; and others
2015-05-15
Proton electromagnetic form factors are among the most important sources of information about the internal structure of the proton. Two different methods for measuring these form factors, the method proposed by Rosenbluth and the polarization-transfer method, yield contradictory results. It is assumed that this contradiction can be removed upon taking into account the hard part of the contribution of two-photon exchange to the cross section for elastic electron-proton scattering. This contribution can measured experimentally via a precision comparison of the cross sections for the elastic scattering of positrons and electrons on protons. Such a measurement, performed at the VEPP-3 storage ring in Novosibirsk at the beam energies of 1.6 and 1.0 GeV for positron (electron) scattering angles in the ranges of θ{sub e} = 15°–25° and 55°–75° in the first case and in the range of θ{sub e} = 65°–105° in the second case is described in the present article. Preliminary results of this experiment and their comparison with theoretical predictions are described.
An 8×8 Row-Column Summing Readout Electronics for Preclinical Positron Emission Tomography Scanners.
Shih, Y C; Sun, F W; Macdonald, L R; Otis, B P; Miyaoka, R S; McDougald, W; Lewellen, T K
2009-10-24
This work presents a row/column summing readout electronics for an 8×8 silicon photomultiplier array. The summation circuit greatly reduces the number of electronic channels, which is desirable for pursuing higher resolution positron emission tomography scanners. By using a degenerated common source topology in the summation circuit, more fan-in is possible and therefore a greater reduction in the number of electronic channels can be achieved. The timing signal is retrieved from a common anode, which allows the use of a single fast-sampling analog to digital converter (ADC) for the timing channel and slower, lower power ADCs for the 64 spatial channels. Preliminary results of one row summation of the 8×8 readout electronics exhibited FWHM energy resolution of 17.8% and 18.3% with and without multiplexing, respectively. The measured timing resolution is 2.9ns FWHM.
An 8×8 Row-Column Summing Readout Electronics for Preclinical Positron Emission Tomography Scanners
Shih, Y. C.; Sun, F. W.; MacDonald, L. R.; Otis, B. P.; Miyaoka, R. S.; McDougald, W.; Lewellen, T. K.
2010-01-01
This work presents a row/column summing readout electronics for an 8×8 silicon photomultiplier array. The summation circuit greatly reduces the number of electronic channels, which is desirable for pursuing higher resolution positron emission tomography scanners. By using a degenerated common source topology in the summation circuit, more fan-in is possible and therefore a greater reduction in the number of electronic channels can be achieved. The timing signal is retrieved from a common anode, which allows the use of a single fast-sampling analog to digital converter (ADC) for the timing channel and slower, lower power ADCs for the 64 spatial channels. Preliminary results of one row summation of the 8×8 readout electronics exhibited FWHM energy resolution of 17.8% and 18.3% with and without multiplexing, respectively. The measured timing resolution is 2.9ns FWHM. PMID:20729983
Admittance Test and Conceptual Study of a CW Positron Source for CEBAF
Golge, Serkan; Hyde, Charles E.; Freyberger, Arne
2009-09-02
A conceptual study of a Continuous Wave (CW) positron production is presented in this paper. The Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab (JLAB) operates with a CW electron beam with a well-defined emittance, time structure and energy spread. Positrons created via bremsstrahlung photons in a high-Z target emerge with a large emittance compared to incoming electron beam. An admittance study has been performed at CEBAF to estimate the maximum beam phase space area that can be transported in the LINAC and in the Arcs. A positron source is described utilizing the CEBAF injector electron beam, and directly injecting the positrons into the CEBAF LINAC.
Science and Technology of the TESLA Electron-Positron Linear Collider
NASA Astrophysics Data System (ADS)
Wagner, Albrecht
2002-07-01
Recent analyses of the long term future of particles physics in Asia, Europe, and the U.S.A. have led to the consensus that the next major facility to be built to unravel the secrets of the micro-cosmos is an electron-positron linear collider in the energy range of 500 to 1000 GeV. This collider should be constructed in an as timely fashion as possible to overlap with the Large Hadron Collider, under construction at CERN. Here, the scientific potential and the technological aspects of the TESLA projects, a superconducting collider with an integrated X-ray laser laboratory, are summarised.
Phase-mixing of electrostatic modes in a cold magnetized electron-positron plasma
Maity, Chandan; Chakrabarti, Nikhil
2013-08-15
In a fluid description, we study space-time evolution of electrostatic oscillations in a cold magnetized electron-positron plasma. Nonlinear results up to third order, obtained by employing a simple perturbation technique, indicate phase-mixing and thus breaking of excited oscillations, and provide an expression for the phase-mixing time. It is shown that an increase in the strength of ambient magnetic field results in an increase in the phase-mixing time. The results of our investigation will be of relevance to astrophysical environments as well as laboratory experiments.
Dipolar vortices and collisional instability in rotating electron-positron-ion plasmas
Haque, Q.
2011-11-15
Linear dispersion relation of electrostatic waves is derived for rotating electron-positron-ion (e-p-i) plasmas. The role of the rotational plasma frequency on drift wave through Coriolis force in the pulsar magnetosphere is discussed. This wave can couple with acoustic mode. In the nonlinear regime, stationary solution in the form of dipolar vortices is obtained. At the end we have also found the collisional instability in the presence of neutral-ion collisions for this rotating e-p-i plasma. The importance of the study with respect to astrophysical plasmas is also pointed out.
Nambu--Goldstone Dark Matter and Cosmic Ray Electron and Positron Excess
Ibe, Masahiro; Nakayama, Yu; Murayama, Hitoshi; Yanagida, Tsutomu T.; /Tokyo U. /Tokyo U., IPMU
2009-06-19
We propose a model of dark matter identified with a pseudo-Nambu-Goldstone boson in the dynamical supersymmetry breaking sector in a gauge mediation scenario. The dark matter particles annihilate via a below-threshold narrow resonance into a pair of R-axions each of which subsequently decays into a pair of light leptons. The Breit-Wigner enhancement explains the excess electron and positron fluxes reported in the recent cosmic ray experiments PAMELA, ATIC and PPB-BETS without postulating an overdensity in halo, and the limit on anti-proton flux from PAMELA is naturally evaded.
Nonplanar Ion-Acoustic Solitons in Electron-Positron-Ion Quantum Plasmas
NASA Astrophysics Data System (ADS)
Khan A., S.; Mahmood, S.; Arshad, Mirza M.
2009-04-01
The propagation of nonplanar quantum ion-acoustic solitary waves in a dense, unmagnetized electron-positronion (e-p-i) plasma are studied by using the Korteweg-de Vries (KdV) model. The quantum hydrodynamic (QHD) equations are used taking into account the quantum diffraction and quantum statistics corrections. The analytical and numerical solutions of KdV equation reveal that the nonplanar ion-acoustic solitons are modified significantly with quantum corrections and positron concentration, and behave differently in different geometries.
NASA Astrophysics Data System (ADS)
Akhtar, N.; El-Taibany, W. F.; Mahmood, S.; Behery, E. E.; Khan, S. A.; Ali, S.; Hussain, S.
2015-10-01
> . The magnetic field has no effect on the amplitude of the IASW, whereas the obliqueness angle of the wave propagation, the ion-to-electron temperature ratio and positron-to-ion density concentration ratio affect both the amplitude and the width of the solitary wave structures. The transverse instability analysis illustrates that the one soliton solution has a constant growth rate, and it suffers from instability in the transverse direction. The relevance of the present study to astrophysical space plasmas is also discussed.
Online beam energy measurement of Beijing electron positron collider II linear accelerator.
Wang, S; Iqbal, M; Liu, R; Chi, Y
2016-02-01
This paper describes online beam energy measurement of Beijing Electron Positron Collider upgraded version II linear accelerator (linac) adequately. It presents the calculation formula, gives the error analysis in detail, discusses the realization in practice, and makes some verification. The method mentioned here measures the beam energy by acquiring the horizontal beam position with three beam position monitors (BPMs), which eliminates the effect of orbit fluctuation, and is much better than the one using the single BPM. The error analysis indicates that this online measurement has further potential usage such as a part of beam energy feedback system. The reliability of this method is also discussed and demonstrated in this paper.
Online beam energy measurement of Beijing electron positron collider II linear accelerator
NASA Astrophysics Data System (ADS)
Wang, S.; Iqbal, M.; Liu, R.; Chi, Y.
2016-02-01
This paper describes online beam energy measurement of Beijing Electron Positron Collider upgraded version II linear accelerator (linac) adequately. It presents the calculation formula, gives the error analysis in detail, discusses the realization in practice, and makes some verification. The method mentioned here measures the beam energy by acquiring the horizontal beam position with three beam position monitors (BPMs), which eliminates the effect of orbit fluctuation, and is much better than the one using the single BPM. The error analysis indicates that this online measurement has further potential usage such as a part of beam energy feedback system. The reliability of this method is also discussed and demonstrated in this paper.
NASA Astrophysics Data System (ADS)
Lubberink, Mark; Lundqvist, Hans; Tolmachev, Vladimir
2002-02-01
We propose the use of the Auger electron and positron-emitting generator 134Ce/134La (half-lives 3.16 d and 6.45 min) for radionuclide therapy. It combines emission of high-energy beta particles with Auger electrons. The high-energy beta particles have similar energies as those emitted by 90Y. Many cancer patients receiving radionuclide therapy have both bulk tumours, which are best treated with high-energy beta particles, and single spread cells or micrometastasis, which are preferably treated with low-energy electrons such as Auger and conversion electrons. Furthermore, the positron-emitting 134La can be used to study kinetics and dosimetry using PET. Production and PET performance were investigated and theoretical dosimetry calculations were made. PET resolution, recovery and quantitative accuracy were slightly degraded for 134La compared to 18F. 134Ce/134La absorbed doses to single cells were higher than absorbed doses from 90Y and 111In. Absorbed doses to spheres representing bulk tumours were almost as high as for 90Y, and a factor 10 higher than for 111In. Whole-body absorbed doses, based on kinetics of the somatostatin analogue octreotide, were higher for 134Ce/134La than for 90Y because of the 134La annihilation photons. This initial study of the therapeutic possibilities of 134Ce/134La is encouraging and justifies further investigations.
Raman scattering of a photon with frequency doubling by a channelled positron
Kalashnikov, N P; Krokhin, O N
2014-12-31
We have analysed the possibility of appearance of anti-Stokes lines in the spectrum of Raman scattering of a photon by a 'quasi-bound' charged particle in the regime of planar (axial) channelling. It is shown that radiation may emerge at the frequency, which is a combination of the incident photon frequency ω{sub 0} and transition frequency ω{sub i} in the transverse quantised motion of a channelled particle: ω = ω{sub 0} ± 2γ{sup 2}ω{sub i}, where γ is the relativistic (Lorentz) factor of a channelled particle. (nonlinear optical phenomena)
Andreev, Pavel A; Iqbal, Z
2016-03-01
We consider the separate spin evolution of electrons and positrons in electron-positron and electron-positron-ion plasmas. We consider the oblique propagating longitudinal waves in these systems. Working in a regime of high-density n(0) ∼ 10(27) cm(-3) and high-magnetic-field B(0)=10(10) G, we report the presence of the spin-electron acoustic waves and their dispersion dependencies. In electron-positron plasmas, similarly to the electron-ion plasmas, we find one spin-electron acoustic wave (SEAW) at the propagation parallel or perpendicular to the external field and two spin-electron acoustic waves at the oblique propagation. At the parallel or perpendicular propagation of the longitudinal waves in electron-positron-ion plasmas, we find four branches: the Langmuir wave, the positron-acoustic wave, and a pair of waves having spin nature, they are the SEAW and the wave discovered in this paper, called the spin-electron-positron acoustic wave (SEPAW). At the oblique propagation we find eight longitudinal waves: the Langmuir wave, the Trivelpiece--Gould wave, a pair of positron-acoustic waves, a pair of SEAWs, and a pair of SEPAWs. Thus, for the first time, we report the existence of the second positron-acoustic wave existing at the oblique propagation and the existence of SEPAWs.
Tang, H.; Kulikov, A.V.; Clendenin, J.E.; Ecklund, S.D.; Miller, R.A.
1995-05-01
A baseline design for the NLC positron source based on the existing SLC positron system is described. The proposed NLC source consists of a dedicated S-band electron accelerator, a conventional positron production and capture system utilizing a high Z target and an adiabatic matching device, and an L-band positron linac. The invariant transverse acceptance of the capture system is 0.06 m{center_dot}rad, ensuring an adequate positron beam intensity for the NLC.
NASA Astrophysics Data System (ADS)
Rehman, Momin A.; Mishra, M. K.
2016-01-01
The ion-acoustic solitons in collisionless plasma consisting of warm adiabatic ions, isothermal positrons, and two temperature distribution of electrons have been studied. Using reductive perturbation method, Korteweg-de Vries (K-dV), the modified K-dV (m-KdV), and Gardner equations are derived for the system. The soliton solution of the Gardner equation is discussed in detail. It is found that for a given set of parameter values, there exists a critical value of β=Tc/Th, (ratio of cold to hot electron temperature) below which only rarefactive KdV solitons exist and above it compressive KdV solitons exist. At the critical value of β, both compressive and rarefactive m-KdV solitons co-exist. We have also investigated the soliton in the parametric regime where the KdV equation is not valid to study soliton solution. In this region, it is found that below the critical concentration the system supports rarefactive Gardner solitons and above it compressive Gardner solitons are found. The effects of temperature ratio of two-electron species, cold electron concentration, positron concentration on the characteristics of solitons are also discussed.
Oscillating two-stream instability in a magnetized electron-positron-ion plasma
NASA Astrophysics Data System (ADS)
Tinakiche, Nouara; Annou, R.
2015-04-01
Oscillating two-stream instability (OTSI) in a magnetized electron-ion plasma has been thoroughly studied, e.g., in ionospheric heating experiments [C. S. Liu and V. K. Tripathi, Interaction of Electromagnetic Waves With Electron Beams and Plasmas (World Scientific, 1994); V. K. Tripathi and P. V. Siva Rama Prasad, J. Plasma Phys. 41, 13 (1989); K. Ramachandran and V. K. Tripathi, IEEE Trans. Plasma Sci. 25, 423 (1997)]. In this paper, OTSI is investigated in a magnetized electron-positron-ion plasma. The dispersion relation of the process is established. The pump field threshold, along with the maximum growth rate of the instability is assessed using the Arecibo and HAARP parameters.
Oscillating two-stream instability in a magnetized electron-positron-ion plasma
Tinakiche, Nouara; Annou, R.
2015-04-15
Oscillating two-stream instability (OTSI) in a magnetized electron-ion plasma has been thoroughly studied, e.g., in ionospheric heating experiments [C. S. Liu and V. K. Tripathi, Interaction of Electromagnetic Waves With Electron Beams and Plasmas (World Scientific, 1994); V. K. Tripathi and P. V. Siva Rama Prasad, J. Plasma Phys. 41, 13 (1989); K. Ramachandran and V. K. Tripathi, IEEE Trans. Plasma Sci. 25, 423 (1997)]. In this paper, OTSI is investigated in a magnetized electron-positron-ion plasma. The dispersion relation of the process is established. The pump field threshold, along with the maximum growth rate of the instability is assessed using the Arecibo and HAARP parameters.
NASA Astrophysics Data System (ADS)
Hafez, M. G.; Roy, N. C.; Talukder, M. R.; Hossain Ali, M.
2016-09-01
This work investigates the oblique nonlinear propagation of ion acoustic (IA) shock waves for both weakly and highly relativistic plasmas composed of nonthermal electrons and positrons with relativistic thermal ions. The KdVB-like equation, involving dispersive, weakly transverse dispersive, nonlinearity and dissipative coefficients, is derived employing the well known reductive perturbation method. The integration of this equation is carried out by the {tanh} method taking the stable shock formation condition into account. The effects of nonthermal electrons and positrons, nonthermal electrons with isothermal positrons, isothermal electrons with nonthermal positrons, and isothermal electrons and positrons on oblique propagation of IA shock waves in weakly relativistic regime are described. Furthermore, the effects of plasma parameters on oblique propagation of IA shock waves in highly relativistic regime are discussed and compared with weakly relativistic case. It is seen that the plasma parameters within certain limits significantly modify the structures of the IA shock waves in both cases. The results may be useful for better understanding of the interactions of charged particles with extra-galactic jets as well as astrophysical compact objects.
New shower maximum trigger for electrons and photons at CDF
Amidei, D.; Burkett, K.; Gerdes, D.; Miao, C.; Wolinski, D.; Byrum, K.; Dawson, J.; Nodulman, L.; Wicklund, A.B.
1994-07-28
For the 1994 Tevatron collider run, CDF has upgraded the electron and photo trigger hardware to make use of shower position and size information from the central shower maximum detector. For electrons, the upgrade has resulted in a 50% reduction in backgrounds while retaining approximately 90% of the signal. The new trigger also eliminates the background to photon triggers from single-phototube spikes.
Infusing photonics to increase enrollment in electronics engineering technology
NASA Astrophysics Data System (ADS)
Panayiotou, Chrys A.; Seeber, Fred P.
2007-06-01
During the last 15 years most of the electronics engineering technology programs across the nation have experienced a constant decline in enrollment. Today's high school students do not seem to consider a career in electronics engineering appealing enough to commit to a field of study in desperate need of new students. They still associate electronics programs with the electronics section of a department store; televisions, stereo systems, DVD and VCR players, and other disposable electronics. While the downward trend continues across the nation, Indian River Community College (IRCC) has been able not only to stop it but to reverse it by attracting a new generation of students. By introducing high school students to new and emerging technologies, their perception of established degrees has changed and their interest has been stimulated. Photonics is one of those technologies capturing students' attention. IRCC, a partner college in the National Center for Optics and Photonics Education (OP-TEC), with the assistance of other colleges like Camden County College which already offers an Associate in Applied Science degree in Photonics, has created a Photonics specialization under the Electronics Engineering Technology program. The targeted marketing of this new specialization has led to an increase in enrollment of 50% in 2005, 80% in 2006, and for 2007 it is projected it to be over 100%. An interesting comparison can be made concerning enrollment at colleges with a full AAS program in photonics like Camden County College and IRCC which uses photonics as an enabling technology. This analysis could lead to a new approach in restructuring engineering technology degrees with the infusion of photonics throughout many technology fields. This presentation will discuss the plan of action that made possible this initiative at Indian River Community College and new program directions at Camden County College, Blackwood, New Jersey.
A photon position sensor consisting of single-electron circuits.
Kikombo, Andrew Kilinga; Tabe, Michiharu; Amemiya, Yoshihito
2009-10-01
This paper proposes a solid-state sensor that can detect the position of incident photons with a high spatial resolution. The sensor consists of a two-dimensional array of single-electron oscillators, each coupled to its neighbors through coupling capacitors. An incident photon triggers an excitatory circular wave of electron tunneling in the oscillator array. The wave propagates in all directions to reach the periphery of the array. By measuring the arrival time of the wave at the periphery, we can know the position of the incident photon. The tunneling wave's generation, propagation, arrival at the array periphery, and the determination of incident photon positions are demonstrated with the results of Monte Carlo based computer simulations.
Wave production in an ultrarelativistic electron-positron plasma. [in pulsar polar caps
NASA Technical Reports Server (NTRS)
Hardee, P. E.; Rose, W. K.
1978-01-01
In this paper we calculate the eigenmodes associated with an ultrarelativistic electron-positron beam traversing a low-energy electron-positron plasma under physical conditions that may exist along open magnetic field lines above pulsar polar caps. We assume that both beam and plasma are cold and charge neutral, and that magnetic field strength and particle density decrease as the cube of (1/R). In the superstrong magnetic fields near the stellar surface where cyclotron frequencies exceed plasma frequencies, electrostatic waves and associated transverse low-frequency waves are driven unstable by the two-stream type particle distribution. At larger distances above the stellar surface the slow beam cyclotron wave is driven unstable. At even greater radial distance (approximately when particle energy density exceeds magnetic energy density) both the Ordinary and Alfven modes become unstable. All of these instabilities can lead to generation of radiation. If the particle distribution as generated at the stellar surface, assumed to consist of two streams, is modified only by plasma effects, then electrostatic and associated transverse waves may only be unstable near the stellar surface. The beam cyclotron mode which is driven by a two-stream or an inverted particle distribution may be stable.
Bernardo, Giuseppe Di; Evoli, Carmelo; Gaggero, Daniele; Grasso, Dario; Maccione, Luca E-mail: carmelo.evoli@desy.de E-mail: dario.grasso@pi.infn.it
2013-03-01
A multichannel analysis of cosmic ray electron and positron spectra and of the diffuse synchrotron emission of the Galaxy is performed by using the DRAGON code. This study is aimed at probing the interstellar electron source spectrum down to E ∼< 1GeV and at constraining several propagation parameters. We find that above 4GeV the e{sup −} source spectrum is compatible with a power-law of index ∼ 2.5. Below 4GeV instead it must be significantly suppressed and the total lepton spectrum is dominated by secondary particles. The positron spectrum and fraction measured below a few GeV are consistently reproduced only within low reacceleration models. We also constrain the scale-height z{sub t} of the cosmic-ray distribution using three independent (and, in two cases, original) arguments, showing that values of z{sub t} ∼< 2kpc are excluded. This result may have strong implications for particle dark matter searches.
Nonplanar ion-acoustic two-soliton systems in quantum electron-positron-ion plasmas
NASA Astrophysics Data System (ADS)
Mandal, Pankaj Kumar; Ghorui, Malay Kumar; Saha, Asit; Chatterjee, Prasanta
2015-01-01
The basic features of planar and nonplanar time dependent ion-acoustic two-soliton systems have been studied in a three component unmagnetized, collisionless quantum plasma consisting of inertialess electrons and positrons. Using the reductive perturbation technique (RPT), we have derived the Korteweg-de Vries equation for our model. The effects of several parameters on the properties of ion-acoustic two-soliton systems in quantum electron-positron-ion plasmas have been discussed in planar and nonplanar geometries. It has been shown that the properties of ion-acoustic two-soliton systems are affected significantly due to cylindrical and spherical geometries. The amplitude of the cylindrical two-soliton system is smaller than that of the spherical two-soliton system for small values of | τ|. The propagation of ion-acoustic two-soliton systems is quite different from the propagation of ion-acoustic two-soliton systems in a nonplanar geometry. The present investigation may have relevance in the study of the propagation of ion-acoustic two-soliton systems in space and laboratory plasmas.
Imprints of Electron-Positron Winds on the Multiwavelength Afterglows of Gamma-ray Bursts
NASA Astrophysics Data System (ADS)
Geng, J. J.; Wu, X. F.; Huang, Y. F.; Li, L.; Dai, Z. G.
2016-07-01
Optical rebrightenings in the afterglows of some gamma-ray bursts (GRBs) are unexpected within the framework of the simple external shock model. While it has been suggested that the central engines of some GRBs are newly born magnetars, we aim to relate the behaviors of magnetars to the optical rebrightenings. A newly born magnetar will lose its rotational energy in the form of Poynting-flux, which may be converted into a wind of electron-positron pairs through some magnetic dissipation processes. As proposed by Dai, this wind will catch up with the GRB outflow and a long-lasting reverse shock (RS) would form. By applying this scenario to GRB afterglows, we find that the RS propagating back into the electron-positron wind can lead to an observable optical rebrightening and a simultaneous X-ray plateau (or X-ray shallow decay). In our study, we select four GRBs (i.e., GRB 080413B, GRB 090426, GRB 091029, and GRB 100814A), of which the optical afterglows are well observed and show clear rebrightenings. We find that they can be well interpreted. In our scenario, the spin-down timescale of the magnetar should be slightly smaller than the peak time of the rebrightening, which can provide a clue to the characteristics of the magnetar.
NASA Astrophysics Data System (ADS)
Habte, F.; Foudray, A. M. K.; Olcott, P. D.; Levin, C. S.
2007-07-01
We are studying two new detector technologies that directly measure the three-dimensional coordinates of 511 keV photon interactions for high-resolution positron emission tomography (PET) systems designed for small animal and breast imaging. These detectors are based on (1) lutetium oxyorthosilicate (LSO) scintillation crystal arrays coupled to position-sensitive avalanche photodiodes (PSAPD) and (2) cadmium zinc telluride (CZT). The detectors have excellent measured 511 keV photon energy resolutions (<=12% FWHM for LSO-PSAPD and <=3% for CZT) and good coincidence time resolutions (2 ns FWHM for LSO-PSAPD and 8 ns for CZT). The goal is to incorporate the detectors into systems that will achieve 1 mm3 spatial resolution (~1 mm3, uniform throughout the field of view (FOV)), with excellent contrast resolution as well. In order to realize 1 mm3 spatial resolution with high signal-to-noise ratio (SNR), it is necessary to significantly boost coincidence photon detection efficiency (referred to as photon sensitivity). To facilitate high photon sensitivity in the proposed PET system designs, the detector arrays are oriented 'edge-on' with respect to incoming 511 keV annihilation photons and arranged to form a compact FOV with detectors very close to, or in contact with, the subject tissues. In this paper, we used Monte Carlo simulation to study various factors that limit the photon sensitivity of a high-resolution PET system dedicated to small animal imaging. To optimize the photon sensitivity, we studied several possible system geometries for a fixed 8 cm transaxial and 8 cm axial FOV. We found that using rectangular-shaped detectors arranged into a cylindrical geometry does not yield the best photon sensitivity. This is due to the fact that forming rectangular-shaped detectors into a ring produces significant wedge-shaped inter-module gaps, through which Compton-scattered photons in the detector can escape. This effect limits the center point source photon sensitivity to
Habte, F; Foudray, A M K; Olcott, P D; Levin, C S
2007-07-01
We are studying two new detector technologies that directly measure the three-dimensional coordinates of 511 keV photon interactions for high-resolution positron emission tomography (PET) systems designed for small animal and breast imaging. These detectors are based on (1) lutetium oxyorthosilicate (LSO) scintillation crystal arrays coupled to position-sensitive avalanche photodiodes (PSAPD) and (2) cadmium zinc telluride (CZT). The detectors have excellent measured 511 keV photon energy resolutions (photon detection efficiency (referred to as photon sensitivity). To facilitate high photon sensitivity in the proposed PET system designs, the detector arrays are oriented 'edge-on' with respect to incoming 511 keV annihilation photons and arranged to form a compact FOV with detectors very close to, or in contact with, the subject tissues. In this paper, we used Monte Carlo simulation to study various factors that limit the photon sensitivity of a high-resolution PET system dedicated to small animal imaging. To optimize the photon sensitivity, we studied several possible system geometries for a fixed 8 cm transaxial and 8 cm axial FOV. We found that using rectangular-shaped detectors arranged into a cylindrical geometry does not yield the best photon sensitivity. This is due to the fact that forming rectangular-shaped detectors into a ring produces significant wedge-shaped inter-module gaps, through which Compton-scattered photons in the detector can escape. This effect limits the center point source
Foudray, A M K; Olcott, P D
2013-01-01
We are studying two new detector technologies that directly measure the three-dimensional coordinates of 511 keV photon interactions for high-resolution positron emission tomography (PET) systems designed for small animal and breast imaging. These detectors are based on (1) lutetium oxyorthosilicate (LSO) scintillation crystal arrays coupled to position-sensitive avalanche photodiodes (PSAPD) and (2) cadmium zinc telluride (CZT). The detectors have excellent measured 511 keV photon energy resolutions (≤12% FWHM for LSO-PSAPD and ≤3% for CZT) and good coincidence time resolutions (2 ns FWHM for LSO-PSAPD and 8 ns for CZT). The goal is to incorporate the detectors into systems that will achieve 1 mm3 spatial resolution (~1 mm3, uniform throughout the field of view (FOV)), with excellent contrast resolution as well. In order to realize 1 mm3 spatial resolution with high signal-to-noise ratio (SNR), it is necessary to significantly boost coincidence photon detection efficiency (referred to as photon sensitivity). To facilitate high photon sensitivity in the proposed PET system designs, the detector arrays are oriented ‘edge-on’ with respect to incoming 511 keV annihilation photons and arranged to form a compact FOV with detectors very close to, or in contact with, the subject tissues. In this paper, we used Monte Carlo simulation to study various factors that limit the photon sensitivity of a high-resolution PET system dedicated to small animal imaging. To optimize the photon sensitivity, we studied several possible system geometries for a fixed 8 cm transaxial and 8 cm axial FOV. We found that using rectangular-shaped detectors arranged into a cylindrical geometry does not yield the best photon sensitivity. This is due to the fact that forming rectangular-shaped detectors into a ring produces significant wedge-shaped inter-module gaps, through which Compton-scattered photons in the detector can escape. This effect limits the center point source photon
Habte, F; Foudray, A M K; Olcott, P D; Levin, C S
2007-07-01
We are studying two new detector technologies that directly measure the three-dimensional coordinates of 511 keV photon interactions for high-resolution positron emission tomography (PET) systems designed for small animal and breast imaging. These detectors are based on (1) lutetium oxyorthosilicate (LSO) scintillation crystal arrays coupled to position-sensitive avalanche photodiodes (PSAPD) and (2) cadmium zinc telluride (CZT). The detectors have excellent measured 511 keV photon energy resolutions (photon detection efficiency (referred to as photon sensitivity). To facilitate high photon sensitivity in the proposed PET system designs, the detector arrays are oriented 'edge-on' with respect to incoming 511 keV annihilation photons and arranged to form a compact FOV with detectors very close to, or in contact with, the subject tissues. In this paper, we used Monte Carlo simulation to study various factors that limit the photon sensitivity of a high-resolution PET system dedicated to small animal imaging. To optimize the photon sensitivity, we studied several possible system geometries for a fixed 8 cm transaxial and 8 cm axial FOV. We found that using rectangular-shaped detectors arranged into a cylindrical geometry does not yield the best photon sensitivity. This is due to the fact that forming rectangular-shaped detectors into a ring produces significant wedge-shaped inter-module gaps, through which Compton-scattered photons in the detector can escape. This effect limits the center point source
Kawanaka, Norita; Ioka, Kunihito; Nojiri, Mihoko M.
2010-02-20
We investigate the observed spectrum of cosmic ray electrons and positrons from astrophysical sources, especially pulsars, and the physical processes for making the spectrum spiky or smooth via continuous and multiple electron/positron injections. We find that (1) the average electron spectrum predicted from nearby pulsars is consistent with PAMELA, Fermi, and H.E.S.S. data. However, the ATIC/PPB-BETS peak around 500 GeV is hard to produce by the sum of multiple pulsar contributions and requires a single (or a few) energetic pulsar(s). (2) A continuous injection produces a broad peak and a high-energy tail above the peak, which can constrain the source duration ({approx}<10{sup 5} years with the current data). (3) The H.E.S.S. data in the TeV range suggest that young sources with age less than {approx}6 x 10{sup 4} years are less energetic than {approx}10{sup 48} erg. (4) We also expect a large dispersion in the TeV spectrum due to the small number of sources that may cause the high-energy cutoff inferred by H.E.S.S. and potentially provide a smoking gun for the astrophysical origin. These spectral diagnostics can be refined in the near future by the CALET experiments to discriminate different astrophysical and dark matter origins.
NASA Astrophysics Data System (ADS)
Kawanaka, Norita; Ioka, Kunihito; Nojiri, Mihoko M.
2010-02-01
We investigate the observed spectrum of cosmic ray electrons and positrons from astrophysical sources, especially pulsars, and the physical processes for making the spectrum spiky or smooth via continuous and multiple electron/positron injections. We find that (1) the average electron spectrum predicted from nearby pulsars is consistent with PAMELA, Fermi, and H.E.S.S. data. However, the ATIC/PPB-BETS peak around 500 GeV is hard to produce by the sum of multiple pulsar contributions and requires a single (or a few) energetic pulsar(s). (2) A continuous injection produces a broad peak and a high-energy tail above the peak, which can constrain the source duration (lsim105 years with the current data). (3) The H.E.S.S. data in the TeV range suggest that young sources with age less than ~6 × 104 years are less energetic than ~1048 erg. (4) We also expect a large dispersion in the TeV spectrum due to the small number of sources that may cause the high-energy cutoff inferred by H.E.S.S. and potentially provide a smoking gun for the astrophysical origin. These spectral diagnostics can be refined in the near future by the CALET experiments to discriminate different astrophysical and dark matter origins.
Assessing the effect of electron density in photon dose calculations
Seco, J.; Evans, P. M.
2006-02-15
Photon dose calculation algorithms (such as the pencil beam and collapsed cone, CC) model the attenuation of a primary photon beam in media other than water, by using pathlength scaling based on the relative mass density of the media to water. In this study, we assess if differences in the electron density between the water and media, with different atomic composition, can influence the accuracy of conventional photon dose calculations algorithms. A comparison is performed between an electron-density scaling method and the standard mass-density scaling method for (i) tissues present in the human body (such as bone, muscle, etc.), and for (ii) water-equivalent plastics, used in radiotherapy dosimetry and quality assurance. We demonstrate that the important material property that should be taken into account by photon dose algorithms is the electron density, and not the mass density. The mass-density scaling method is shown to overestimate, relative to electron-density predictions, the primary photon fluence for tissues in the human body and water-equivalent plastics, where 6%-7% and 10% differences were observed respectively for bone and air. However, in the case of patients, differences are expected to be smaller due to the large complexity of a treatment plan and of the patient anatomy and atomic composition and of the smaller thickness of bone/air that incident photon beams of a treatment plan may have to traverse. Differences have also been observed for conventional dose algorithms, such as CC, where an overestimate of the lung dose occurs, when irradiating lung tumors. The incorrect lung dose can be attributed to the incorrect modeling of the photon beam attenuation through the rib cage (thickness of 2-3 cm in bone upstream of the lung tumor) and through the lung and the oversimplified modeling of electron transport in convolution algorithms. In the present study, the overestimation of the primary photon fluence, using the mass-density scaling method, was shown
Observations of the ratio of low-energy cosmic-ray positrons and electrons during solar quiet times
NASA Technical Reports Server (NTRS)
Hurford, G. J.; Mewaldt, R. A.; Stone, E. C.; Vogt, R. E.
1974-01-01
Simultaneous observations of the quiet-time interplanetary positron and electron spectra between 0.16 and 1.6 MeV are reported. The measurements were made in selected time intervals between October 1, 1972 and February 1, 1973 with the Caltech Electron/Isotope Spectrometer on the IMP-7 satellite. The detector system consists of a stack of 11 silicon surface-barrier detectors surrounded by a plastic scintillator anti-coincidence cup. The method of e+ identification and possible background effects are discussed and upper limits to the 0.16 to 1.6 MeV quiet-time positron flux are reported. During this period positrons amounted to less than 20% of the total 0.16 to 1.6 MeV electron flux.
Directly tailoring photon-electron coupling for sensitive photoconductance
NASA Astrophysics Data System (ADS)
Huang, Zhiming; Zhou, Wei; Huang, Jingguo; Wu, Jing; Gao, Yanqing; Qu, Yue; Chu, Junhao
2016-03-01
The coupling between photons and electrons is at the heart of many fundamental phenomena in nature. Despite tremendous advances in controlling electrons by photons in engineered energy-band systems, control over their coupling is still widely lacking. Here we demonstrate an unprecedented ability to couple photon-electron interactions in real space, in which the incident electromagnetic wave directly tailors energy bands of solid to generate carriers for sensitive photoconductance. By spatially coherent manipulation of metal-wrapped material system through anti-symmetric electric field of the irradiated electromagnetic wave, electrons in the metals are injected and accumulated in the induced potential well (EIW) produced in the solid. Respective positive and negative electric conductances are easily observed in n-type and p-type semiconductors into which electrons flow down from the two metallic sides under light irradiation. The photoconductivity is further confirmed by sweeping the injected electrons out of the semiconductor before recombination applied by sufficiently strong electric fields. Our work opens up new perspectives for tailoring energy bands of solids and is especially relevant to develop high effective photon detection, spin injection, and energy harvesting in optoelectronics and electronics.
Directly tailoring photon-electron coupling for sensitive photoconductance
Huang, Zhiming; Zhou, Wei; Huang, Jingguo; Wu, Jing; Gao, Yanqing; Qu, Yue; Chu, Junhao
2016-01-01
The coupling between photons and electrons is at the heart of many fundamental phenomena in nature. Despite tremendous advances in controlling electrons by photons in engineered energy-band systems, control over their coupling is still widely lacking. Here we demonstrate an unprecedented ability to couple photon-electron interactions in real space, in which the incident electromagnetic wave directly tailors energy bands of solid to generate carriers for sensitive photoconductance. By spatially coherent manipulation of metal-wrapped material system through anti-symmetric electric field of the irradiated electromagnetic wave, electrons in the metals are injected and accumulated in the induced potential well (EIW) produced in the solid. Respective positive and negative electric conductances are easily observed in n-type and p-type semiconductors into which electrons flow down from the two metallic sides under light irradiation. The photoconductivity is further confirmed by sweeping the injected electrons out of the semiconductor before recombination applied by sufficiently strong electric fields. Our work opens up new perspectives for tailoring energy bands of solids and is especially relevant to develop high effective photon detection, spin injection, and energy harvesting in optoelectronics and electronics. PMID:26964883
Directly tailoring photon-electron coupling for sensitive photoconductance.
Huang, Zhiming; Zhou, Wei; Huang, Jingguo; Wu, Jing; Gao, Yanqing; Qu, Yue; Chu, Junhao
2016-01-01
The coupling between photons and electrons is at the heart of many fundamental phenomena in nature. Despite tremendous advances in controlling electrons by photons in engineered energy-band systems, control over their coupling is still widely lacking. Here we demonstrate an unprecedented ability to couple photon-electron interactions in real space, in which the incident electromagnetic wave directly tailors energy bands of solid to generate carriers for sensitive photoconductance. By spatially coherent manipulation of metal-wrapped material system through anti-symmetric electric field of the irradiated electromagnetic wave, electrons in the metals are injected and accumulated in the induced potential well (EIW) produced in the solid. Respective positive and negative electric conductances are easily observed in n-type and p-type semiconductors into which electrons flow down from the two metallic sides under light irradiation. The photoconductivity is further confirmed by sweeping the injected electrons out of the semiconductor before recombination applied by sufficiently strong electric fields. Our work opens up new perspectives for tailoring energy bands of solids and is especially relevant to develop high effective photon detection, spin injection, and energy harvesting in optoelectronics and electronics. PMID:26964883
NASA Astrophysics Data System (ADS)
Stem, Michelle R.
2016-05-01
The purpose of the present research was to investigate an intense violet shift displayed by a non-toxic, natural silicate material with a highly ordered nanostructure. The material displayed an unexpected, nonlinear 2:3 photon-phonon anti-Stokes upconversion while photonically, electronically, and thermally isolated. Conducted aphotonically and at ambient temperatures, the specimen upconverted a low-power, 650 nm constant wave red laser to an internally highly dispersed 433 nm violet wavelength. The strong dispersion was largely due to nearly total internal reflection of the laser. The upconversion had an efficiency of about 78 %, based on specimen volume, with no detectable thermal variance. The 2:3 anti-Stokes upconversion displayed by this material is likely the result of a previously unknown photon-phonon evanescence response that amplified the energy of a portion of the incident laser photons. Thus, a portion of the incident laser photons were upconverted, and the material converted another portion into an amplified energy that caused the upconversion. Internal micro-lasing appeared to be a means of photon-phonon evanescent energy redistribution, enabling dispersed photonic upconversion. Additional analyses also found an unexpectedly rhythmic photonic structure in spectrophotometric scans, polariscopic color changing, and previously undocumented ultraviolet responses.
Electron-positron momentum distributions associated with isolated silicon vacancies in 3C-SiC
Kawasuso, A.; Yoshikawa, M.; Itoh, H.; Chiba, T.; Higuchi, T.; Betsuyaku, K.; Redmann, F.; Krause-Rehberg, R.
2005-07-15
Two-dimensional angular correlation of annihilation radiation (2D-ACAR) and coincidence Doppler broadening (CDB) of annihilation radiation measurements have been performed on electron-irradiated n-type 3C-SiC in which isolated silicon vacancies are responsible for positron trapping. After irradiation, the intensity of the CDB spectrum increased and decreased in low- and high-momentum regions, respectively. These features were explained by a theoretical calculation considering silicon vacancies. The central region of the 2D-ACAR spectra became isotropic after irradiation, while the overall anisotropies extending within the Jones zone were conserved suggesting that isolated silicon vacancies have tetrahedral symmetry, as expected from a previous electron spin resonance study.
Bains, A. S.; Gill, T. S.; Misra, A. P.; Saini, N. S.
2010-01-15
The amplitude modulation of quantum ion-acoustic waves (QIAWs) along an external magnetic field is studied in a quantum electron-positron-ion (e-p-i) magnetoplasma. Reductive perturbation technique is used to derive the three-dimensional nonlinear Schroedinger equation which governs the slow modulation of QIAW packets. Accounting for the effects of the electron to ion number density ratio (mu), the normalized ion-cyclotron frequency (omega{sub c}) as well as the ratio (H) of the 'plasmonic energy density' to the Fermi energy, new regimes for the modulational instability of QIAWs are obtained and analyzed. In contrast to one-dimensional unmagnetized e-p-i plasmas, the instability growth rate is shown to suppress with increasing mu or decreasing the values of H. The predicted results could be important for understanding the salient features of modulated QIAW packets in dense astrophysical plasmas as well as to the next generation intense laser solid density plasma experiments.
Microwave Transmission Measurements of the Electron Cloud density In the Positron Ring of PEP-II
Pivi, Mauro T.F.; Krasnykh, Anatoly K.; Byrd, John; De Santis, Stefano; Sonnaad, Kiran G.; Caspers, Fritz; Kroyer, Tom
2008-06-18
Clouds of electrons in the vacuum chambers of accelerators of positively charged particle beams present a serious limitation for operation of these machines at high currents. Because of the size of these accelerators, it is difficult to probe the low energy electrons clouds over substantial lengths of the beam pipe. We applied a novel technique to directly measure the electron cloud density via the phase shift induced in a TE wave which is independently excited and transmitted over a straight section of the accelerator. The modulation in the wave transmission which appears to increase in depth when the clearing solenoids are switched off, seem to be directly correlated to the electron cloud density in the section. Furthermore, we expect a larger phase shift of a wave transmitted through magnetic dipole field regionsif the transmitted wave couples with the gyration motion of the electrons. We have used this technique to measure the average electron cloud density (ECD) specifically for the first time in magnetic field regions of a new 4-dipole chicane in the positron ring of the PEP-II collider at SLAC. In this paper we present and discuss the measurements taken in the Low Energy Ring (LER) between 2006 and 2008.
Microwave Transmission Measurements of the Electron Cloud Density In The Positron Ring of PEP-II
Pivi, M.T.F.; Krasnykh, A.K; Byrd, J.; Santis, S.De; Sonnad, K.G.; Caspers, F.; Kroyer, T.; /CERN
2008-07-03
Clouds of electrons in the vacuum chambers of accelerators of positively charged particle beams present a serious limitation for operation of these machines at high currents. Because of the size of these accelerators, it is difficult to probe the low energy electron clouds over substantial lengths of the beam pipe. We applied a novel technique to directly measure the electron cloud density via the phase shift induced in a TE wave which is independently excited and transmitted over a straight section of the accelerator. The modulation in the wave transmission which appear to increase in depth when the clearing solenoids are switched off, seem to be directly correlated to the electron cloud density in the section. Furthermore, we expect a larger phase shift of a wave transmitted through magnetic dipole field regions if the transmitted wave couples with the gyration motion of the electrons. We have used this technique to measure the average electron cloud density (ECD) specifically for the first time in magnetic field regions of a new 4-dipole chicane in the positron ring of the PEP-II collider at SLAC. In this paper we present and discuss the measurements taken in the Low Energy Ring (LER) between 2006 and 2008.
El-Labany, S. K.; Moslem, W. M.; El-Awady, E. I.
2010-06-15
Theoretical and numerical studies are performed for nonlinear Langmuir structures (soliton and shock) in a rotating weakly relativistic electron-positron magnetoplasma with background stationary positive ions. For this purpose, the reductive perturbation technique is employed to the weakly relativistic hydrodynamical electrons/positrons fluid equations and Poisson equation, obtaining extended Zakharov-Kuznetsov equation. The latter has been solved analytically. The features of the nonlinear excitations and their propagation conditions are investigated numerically. Our finding could elucidate the nonlinear electrostatic structures that propagate in astrophysical plasma situations where rotating, magnetized plasma can exist; such as polar cups region of pulsars, around active galactic nuclei, neutron stars, and white dwarfs.
Photon gating in four-dimensional ultrafast electron microscopy
Hassan, Mohammed T.; Liu, Haihua; Baskin, John Spencer; Zewail, Ahmed H.
2015-01-01
Ultrafast electron microscopy (UEM) is a pivotal tool for imaging of nanoscale structural dynamics with subparticle resolution on the time scale of atomic motion. Photon-induced near-field electron microscopy (PINEM), a key UEM technique, involves the detection of electrons that have gained energy from a femtosecond optical pulse via photon–electron coupling on nanostructures. PINEM has been applied in various fields of study, from materials science to biological imaging, exploiting the unique spatial, energy, and temporal characteristics of the PINEM electrons gained by interaction with a “single” light pulse. The further potential of photon-gated PINEM electrons in probing ultrafast dynamics of matter and the optical gating of electrons by invoking a “second” optical pulse has previously been proposed and examined theoretically in our group. Here, we experimentally demonstrate this photon-gating technique, and, through diffraction, visualize the phase transition dynamics in vanadium dioxide nanoparticles. With optical gating of PINEM electrons, imaging temporal resolution was improved by a factor of 3 or better, being limited only by the optical pulse widths. This work enables the combination of the high spatial resolution of electron microscopy and the ultrafast temporal response of the optical pulses, which provides a promising approach to attain the resolution of few femtoseconds and attoseconds in UEM. PMID:26438835
Observation of Polarized Positrons from an Undulator-Based Source
Alexander, G; Barley, J.; Batygin, Y.; Berridge, S.; Bharadwaj, V.; Bower, G.; Bugg, W.; Decker, F.-J.; Dollan, R.; Efremenko, Y.; Gharibyan, V.; Hast, C.; Iverson, R.; Kolanoski, H.; Kovermann, J.; Laihem, K.; Lohse, T.; McDonald, K.T.; Mikhailichenko, A.A.; Moortgat-Pick, G.A.; Pahl, P.; /Tel Aviv U. /Cornell U., Phys. Dept. /SLAC /Tennessee U. /Humboldt U., Berlin /DESY /Yerevan Phys. Inst. /Aachen, Tech. Hochsch. /DESY, Zeuthen /Princeton U. /Durham U. /Daresbury
2008-03-06
An experiment (E166) at the Stanford Linear Accelerator Center (SLAC) has demonstrated a scheme in which a multi-GeV electron beam passed through a helical undulator to generate multi-MeV, circularly polarized photons which were then converted in a thin target to produce positrons (and electrons) with longitudinal polarization above 80% at 6 MeV. The results are in agreement with Geant4 simulations that include the dominant polarization-dependent interactions of electrons, positrons and photons in matter.
An Electron/Photon/Relaxation Data Library for MCNP6
Hughes, III, H. Grady
2015-08-07
The capabilities of the MCNP6 Monte Carlo code in simulation of electron transport, photon transport, and atomic relaxation have recently been significantly expanded. The enhancements include not only the extension of existing data and methods to lower energies, but also the introduction of new categories of data and methods. Support of these new capabilities has required major additions to and redesign of the associated data tables. In this paper we present the first complete documentation of the contents and format of the new electron-photon-relaxation data library now available with the initial production release of MCNP6.
Electron/positron Excesses in the Cosmic Ray Spectrum and Possible Interpretations
NASA Astrophysics Data System (ADS)
Fan, Yi-Zhong; Zhang, Bing; Chang, Jin
2010-11-01
The data collected by ATIC, PPB-BETS, FERMI-LAT and HESS all indicate that there is an electron/positron excess in the cosmic ray energy spectrum above ~100 GeV, although different instrumental teams do not agree on the detailed spectral shape. PAMELA also reported clearly the excessive feature of the fraction of positron above several GeV, but with no excess in antiprotons. Here we review the observational status and theoretical models of this interesting observational feature. We pay special attention to various physical interpretations proposed in the literature, including modified supernova remnant models for the e± background, new astrophysical sources, and new physics (the dark matter models). We suggest that although most models can make a case to interpret the data, with the current observational constraints the dark matter interpretations, especially those invoking annihilation, require much more exotic assumptions than some other astrophysical interpretations. Future observations may present some "smoking-gun" observational tests to differentiate different models and to identify the correct interpretation of the phenomenon.
NASA Astrophysics Data System (ADS)
Masood, W.; Karim, S.; Shah, H. A.; Siddiq, M.
2009-11-01
Linear and nonlinear propagation characteristics of drift ion acoustic waves are investigated in an inhomogeneous electron-positron-ion (e-p-i) quantum magnetoplasma with neutrals in the background using the well known quantum hydrodynamic model. In this regard, Korteweg-de Vries-Burgers (KdVB) and Kadomtsev-Petviashvili-Burgers (KPB) equations are obtained. Furthermore, the solutions of KdVB and KPB equations are presented by using the tangent hyperbolic (tanh) method. The variation in the shock profile with the quantum Bohm potential, collision frequency, and the ratio of drift to shock velocity in the comoving frame, v*/u, is also investigated. It is found that increasing the positron concentration and collision frequency decreases the strength of the shock. It is also shown that when the localized structure propagates with velocity greater than the diamagnetic drift velocity (i.e., u >v*), the shock strength decreases. However, the shock strength is observed to increase when the localized structure propagates with velocity less than that of drift velocity (i.e., u
Standing electromagnetic solitons in hot ultra-relativistic electron-positron plasmas
Heidari, E.; Aslaninejad, M.; Eshraghi, H.; Rajaee, L.
2014-03-15
Using a one-dimensional self-consistent fluid model, we investigate standing relativistic bright solitons in hot electron-positron plasmas. The positron dynamics is taken into account. A set of nonlinear coupled differential equations describing the evolution of electromagnetic waves in fully relativistic two-fluid plasma is derived analytically and solved numerically. As a necessary condition for the existence of standing solitons the system should be relativistic. For the case of ultra-relativistic plasma, we investigate non-drifting bright solitary waves. Detailed discussions of the acceptable solutions are presented. New single hump non-trivial symmetric solutions for the scalar potential were found, and single and multi-nodal symmetric and anti-symmetric solutions for the vector potential are presented. It is shown that for a fixed value of the fluid velocity excited modes with more zeros in the profile of the vector potential show a higher magnitude for the scalar potential. An increase in the plasma fluid velocity also increases the magnitude of the scalar potential. Furthermore, the Hamiltonian and the first integral of the system are given.
Photonic ADC: overcoming the bottleneck of electronic jitter.
Khilo, Anatol; Spector, Steven J; Grein, Matthew E; Nejadmalayeri, Amir H; Holzwarth, Charles W; Sander, Michelle Y; Dahlem, Marcus S; Peng, Michael Y; Geis, Michael W; DiLello, Nicole A; Yoon, Jung U; Motamedi, Ali; Orcutt, Jason S; Wang, Jade P; Sorace-Agaskar, Cheryl M; Popović, Miloš A; Sun, Jie; Zhou, Gui-Rong; Byun, Hyunil; Chen, Jian; Hoyt, Judy L; Smith, Henry I; Ram, Rajeev J; Perrott, Michael; Lyszczarz, Theodore M; Ippen, Erich P; Kärtner, Franz X
2012-02-13
Accurate conversion of wideband multi-GHz analog signals into the digital domain has long been a target of analog-to-digital converter (ADC) developers, driven by applications in radar systems, software radio, medical imaging, and communication systems. Aperture jitter has been a major bottleneck on the way towards higher speeds and better accuracy. Photonic ADCs, which perform sampling using ultra-stable optical pulse trains generated by mode-locked lasers, have been investigated for many years as a promising approach to overcome the jitter problem and bring ADC performance to new levels. This work demonstrates that the photonic approach can deliver on its promise by digitizing a 41 GHz signal with 7.0 effective bits using a photonic ADC built from discrete components. This accuracy corresponds to a timing jitter of 15 fs - a 4-5 times improvement over the performance of the best electronic ADCs which exist today. On the way towards an integrated photonic ADC, a silicon photonic chip with core photonic components was fabricated and used to digitize a 10 GHz signal with 3.5 effective bits. In these experiments, two wavelength channels were implemented, providing the overall sampling rate of 2.1 GSa/s. To show that photonic ADCs with larger channel counts are possible, a dual 20-channel silicon filter bank has been demonstrated.
Multimodal dyes: toward correlative two-photon and electron microscopy
NASA Astrophysics Data System (ADS)
Bolze, Frédéric; Ftouni, Hussein; Nicoud, Jean-François; Leoni, Piero; Schwab, Yannick; Rehspringer, Jean-Luc; Mafouana, Rodrigues R.
2013-03-01
Nowadays, many crucial biological questions involve the observation of biological samples at different scales. Thus, optical microscopy can be associated to magnetic nuclear imaging allowing access to data from the cellular to the organ level, or can be associated to electron microscopy to reach the sub cellular level. We will describe here the design, synthesis and characterization of new bimodal probes, which can be used as dye in two-photon excited microscopy (TPEM) and electron dense markers in scanning and transmission electron microscopy (EM). In a first part, we will describe new molecular dyes with small organic systems grafted on metal atoms (Pt, Au). Such systems show good twophoton induced fluorescence and two-photon images of HeLa cells will be presented. In a second part, we will present hybrid organic-inorganic fluorescent systems with diketopyrrolopyrole-based dye grafted on iron oxide-silica core shell nanoparticles by peptide bond. Such systems present high two-photon absorption cross sections and good fluorescence quantum yields. These nanoparticles are rapidly internalized in HeLa cells and high quality two-photon images were performed with low laser power. Then we will present our results on correlative light-electron microscopy were twophoton and electron microscopy (both scanning and transmission) images were obtained on the same biological sample.
The Panofsky ratio, and the response of the PIBETA calorimeter to photons and positrons
NASA Astrophysics Data System (ADS)
Slocum, Penelope Lee
1999-07-01
A precise measurement of the pion beta decay rate will allow accurate testing of the unitarity of the Cabbibo- Kobayashi-Maskawa quark mixing matrix, and of the Conserved Vector Current Hypothesis. The PIBETA collaboration intends to measure this decay rate with an accuracy of better than 0.5%, using a calorimeter comprised of 240 pure CsI crystals. Extensive calibrations of the CsI crystals have been done using cosmic muons. Further studies of the calorimeter response have been made using monoenergetic 70 MeV beam positions, and using the box spectrum of photons ranging in energy from 55-83 MeV from the single charge exchange reaction p- p-->p0n-->g gn . Finally, a measurement of the Panofsky Ratio, defined as the ratio of the rate of single charge exchange to that of radiative pion capture p-p-->gn in pionic hydrogen, has been made.
ON THE MORPHOLOGY OF THE ELECTRON-POSITRON ANNIHILATION EMISSION AS SEEN BY SPI/INTEGRAL
Bouchet, L.; Roques, J. P.; Jourdain, E.
2010-09-10
The 511 keV positron annihilation emission remains a mysterious component of the high energy emission of our Galaxy. Its study was one of the key scientific objectives of the SPI spectrometer on board the International Gamma-Ray Astrophysics Laboratory satellite. In fact, a lot of observing time has been dedicated to the Galactic disk with a particular emphasis on the central region. A crucial issue in such an analysis concerns the reduction technique used to treat this huge quantity of data, and more particularly the background modeling. Our method, after validation through a variety of tests, is based on detector pattern determination per {approx}6 month period, together with a normalization variable on a few hour timescale. The Galactic bulge is detected at a level of {approx}70{sigma}, allowing more detailed investigations. The main result is that the bulge morphology can be modeled with two axisymmetric Gaussians of 3.{sup 0}2 and 11.{sup 0}8 FWHM and respective fluxes of 2.5 and 5.4 x10{sup -4} photons cm{sup -2} s{sup -1}. We found a possible shift of the bulge center toward negative longitude at l = -0.{sup 0}6 {+-} 0.{sup 0}2. In addition to the bulge, a more extended structure is detected significantly with flux ranging from 1.7 to 2.9 x10{sup -3} photons cm{sup -2} s{sup -1} depending on its assumed geometry (pure disk or disk plus halo). The disk emission is also found to be symmetric within the limits of the statistical errors.
Electron-positron pair production in external electric fields varying both in space and time
NASA Astrophysics Data System (ADS)
Aleksandrov, I. A.; Plunien, G.; Shabaev, V. M.
2016-09-01
The Schwinger mechanism of electron-positron pair production in the presence of strong external electric fields is analyzed numerically for the case of one- and two-dimensional field configurations where the external field depends both on time and one spatial coordinate. In order to provide this analysis, a new efficient numerical approach is developed. The number of particles created is obtained numerically and also compared with the analytical results for several exactly solvable one-dimensional backgrounds. For the case of two-dimensional field configurations the effects of the spatial finiteness are examined, which confirms their importance and helps us to attest our approach further. The corresponding calculations are also performed for several more interesting and nontrivial combinations of temporal and spatial inhomogeneities. Finally, we discuss the case of a spatially periodic external field when the approach is particularly productive. The method employed is described in detail.
INTEGRAL/SPI Observations of Electron-Positron Annihilation Radiation from our Galaxy
NASA Technical Reports Server (NTRS)
Teegarden, B. J.; Watanabe, K.; Knoedlseder, J.; Jean, P.; Lonjou, V.; Weidenspointer, G.; Skinner, G.; Vedrenne, G.; Roques, J.-P.; Schanne, S.; Schoenfelder, V.
2005-01-01
The spectrometer on INTEGRAL (SPI) is a coded-aperture gamma-ray telescope with moderate angular resolution (3 deg) and superior energy resolution (2 keV at 511 kev). One of it's principal science goals is the detailed study of 511 keV electron-positron annihilation from our Galaxy. The origin of this radiation remains a mystery, however current morphological studies suggest an older stellar population. There has also been recent speculation on the possibility of the existence of light (< 100 MeV) dark matter particles whose annihilation or decay could produce the observed 511 keV emission. In this paper we summarize the current results from SPI, compare them with previous results and discuss their implication on possible models for the production of the annihilation radiation.
INTEGRAL/SPI Limits on Electron-Positron Annihilation Radiation from the Galactic Plane
NASA Technical Reports Server (NTRS)
Teegarden, B. J.; Watanabe, K.; Jean, P.; Knoedlseder, J.; Lonjou, V.; Roques, J. P.; Skinner, G. K.; vonBallmoos, P.; Weidenspointner, G.; Bazzano, A.
2005-01-01
The center of our Galaxy is a known strong source of electron-positron 511- keV annihilation radiation. Thus far, however, there have been no reliable detections of annihilation radiation outside of the central radian of our Galaxy. One of the primary objectives of the INTEGRAL (INTErnational Gamma-RAy Astrophysics Laboratory) mission, launched in Oct. 2002, is the detailed study of this radiation. The Spectrometer on INTEGRAL (SPI) is a high resolution coded-aperture gamma-ray telescope with an unprecedented combination of sensitivity, angular resolution and energy resolution. We report results from the first 10 months of observation. During this period a significant fraction of the observing time was spent in or near the Galactic Plane. No positive annihilation flux was detected outside of the central region (|l| greater than 40 degrees) of our Galaxy. In this paper we describe the observations and data analysis methods and give limits on the 511-keV flux.
Tau reconstruction methods at an electron-positron collider in the search for new physics
NASA Astrophysics Data System (ADS)
Li, Jinmian; Williams, Anthony G.
2016-04-01
By exploiting the relatively long lifetime of the tau lepton, we propose several novel methods for searching for new physics at an electron-positron collider. We consider processes that involve final states consisting of a tau lepton pair plus two missing particles. The mass and spin of the new physics particles can be measured in 3-prong tau decays. The tau polarization, which reflects the coupling to new physics, can be measured from the τ →π ν decay channel using the impact parameter distribution of the charged pion. We also discuss the corresponding backgrounds for these measurements, the next-to-leading order (NLO) effects, and the implications of finite detector resolution.
Enhanced Dark Matter Annihilation Rate for Positron and Electron Excesses from Q-Ball Decay
NASA Astrophysics Data System (ADS)
McDonald, John
2009-10-01
We show that Q-ball decay in Affleck-Dine baryogenesis models can account for dark matter when the annihilation cross section is sufficiently enhanced to explain the positron and electron excesses observed by PAMELA, ATIC, and PPB-BETS. For Affleck-Dine baryogenesis along a d=6 flat direction, the reheating temperature is approximately 30 GeV and the Q-ball decay temperature is in the range of 10-100 MeV. The lightest supersymmetric particles produced by Q-ball decay annihilate down to the observed dark matter density if the cross section is enhanced by a factor ˜103 relative to the thermal relic cross section.
Enhanced Dark Matter Annihilation Rate for Positron and Electron Excesses from Q-Ball Decay
McDonald, John
2009-10-09
We show that Q-ball decay in Affleck-Dine baryogenesis models can account for dark matter when the annihilation cross section is sufficiently enhanced to explain the positron and electron excesses observed by PAMELA, ATIC, and PPB-BETS. For Affleck-Dine baryogenesis along a d=6 flat direction, the reheating temperature is approximately 30 GeV and the Q-ball decay temperature is in the range of 10-100 MeV. The lightest supersymmetric particles produced by Q-ball decay annihilate down to the observed dark matter density if the cross section is enhanced by a factor approx10{sup 3} relative to the thermal relic cross section.
Cho; Lee; Kim
2000-04-01
Nonrelativistic electromagnetic surface waves propagating on the plane interface between dusty electron-positron plasma and vacuum are investigated by specular reflection procedure. In the presence of an applied magnetic field (B(0)=B(0)yinsertion mark) directed perpendicular to both the interface normal and the wave vector, transverse electromagnetic modes are studied in terms of the dispersion relation. The analytic modes are derived and discussed with the aid of some numerical analysis. The cold electromagnetic surface wave dispersion relation considering the effect of dust particle shows that possible modes appear only when the normalized frequency (omega;) and the wave vector (&Kmacr;) satisfy the condition Omega;
NASA Astrophysics Data System (ADS)
Hyodo, Tetsuo; Liu, Yan-Rui; Oka, Makoto; Sudoh, Kazutaka; Yasui, Shigehiro
2013-04-01
Structure and production of doubly charmed tetraquarks Tcc (cc ubardbar) are studied from the viewpoint of color configurations. Based on the diquark correlation, the tetraquark Tcc with I (JP) = 0 (1+) is considered to be stable against strong decay. We discuss that the mixing probability of color antitriplet and sextet cc components in Tcc is suppressed by 1 / mc2, so the two configurations are separately realized in the heavy quark limit. Utilizing the nonrelativistic QCD framework, we evaluate the production cross sections of Tcc in electron-positron collisions. The momentum dependence of the cross section of color antitriplet is found to be different from that of sextet, which can be used to discriminate the color structure of the Tcc states in experimental measurements.
Neutron dosimetry at a high-energy electron-positron collider
NASA Astrophysics Data System (ADS)
Bedogni, Roberto
Electron-positron colliders with energy of hundreds of MeV per beam have been employed for studies in the domain of nuclear and sub-nuclear physics. The typical structure of such a collider includes an LINAC, able to produce both types of particles, an accumulator ring and a main ring, whose diameter ranges from several tens to hundred meters and allows circulating particle currents of several amperes per beam. As a consequence of the interaction of the primary particles with targets, shutters, structures and barriers, a complex radiation environment is produced. This paper addresses the neutron dosimetry issues associated with the operation of such accelerators, referring in particular to the DAΦ NE complex, operative since 1997 at INFN-Frascati National Laboratory (Italy). Special attention is given to the active and passive techniques used for the spectrometric and dosimetric characterization of the workplace neutron fields, for radiation protection dosimetry purposes.
Polarization of the electron and positron produced in combined Coulomb and strong laser fields
Di Piazza, A.; Mueller, C.; Milstein, A. I.
2010-12-15
The process of e{sup +}e{sup -} production in the superposition of a Coulomb and a strong laser field is considered. The pair production rate integrated over the momentum and summed over the spin projections of one of the particles is derived exactly in the parameters of the laser field and in the Born approximation with respect to the Coulomb field. The case of a monochromatic circularly polarized laser field is considered in detail. A very compact analytical expression of the pair production rate and its dependence on the polarization of one of the created particles is obtained in the quasiclassical approximation for the experimentally relevant case of an undercritical laser field. As a result, the polarization of the created electron (positron) is derived.
Electron/Photon Verification Calculations Using MCNP4B
D. P. Gierga; K. J. Adams
1999-04-01
MCNP4BW was released in February 1997 with significant enhancements to electron/photon transport methods. These enhancements have been verified against a wide range of published electron/photon experiments, spanning high energy bremsstrahlung production to electron transmission and reflection. The impact of several MCNP tally options and physics parameters was explored in detail. The agreement between experiment and simulation was usually within two standard deviations of the experimental and calculational errors. Furthermore, sub-step artifacts for bremsstrahlung production were shown to be mitigated. A detailed suite of electron depth dose calculations in water is also presented. Areas for future code development have also been explored and include the dependence of cell and detector tallies on different bremsstrahlung angular models and alternative variance reduction splitting schemes for bremsstrahlung production.
Observations of cosmic-ray electrons and positrons using an imaging calorimeter
NASA Technical Reports Server (NTRS)
Golden, R. L.; Grimani, C.; Kimbell, B. L.; Stephens, S. A.; Stochaj, S. J.; Webber, W. R.; Basini, G.; Bongiorno, F.; Brancaccio, F. Massimo; Ricci, M.
1994-01-01
A ballon-borne magnet spectrometer system was flown for 5.5 hr at an altitude of more than 117,00 feet from Prince Albert, Saskatchewan (Canada), on 1989 September 5, when the Newark neutron monitor rate was 2952. The instrument was a modified version of the one used to observe antiprotons in 1979. The most significant modification was the addition of an imaging calorimeter, 7.33 radiation lengths thick. Inclusion of the calorimeter has significantly improved the ability to distinguish electrons and positrons from the other constituents of the cosmic rays. The absolute electron flux has been determined in the energy interval 1.3-26 GeV. The electron spectrum at the top of the atmosphere was found to be J(sub e-) = 177E(exp -(3.15+/-0.13)) electrons/ sq m/(sr s GeV) in the energy range 4.0-26 GeV. Below 4 GeV, the spectrum showed flattening, which is consistent with the effect of solar modulation. The e(+)/(e(+)+e(-)) ratio was found to be (0.11 +/- 0.03) in the energy range 5.2-13 GeV.
Comparison of positronium, positron and electron collisions with hydrogen at low velocities
NASA Astrophysics Data System (ADS)
Van Reeth, P.; Woods, Denton; Ward, S. J.; Humberston, J. W.
2016-06-01
Recent experimental findings indicate that at equal velocity electron and ortho-positronium scattering cross sections are similar over a wide range of velocities and targets where both elastic and inelastic processes can take place. We present a comparative study of positronium, positron and electron elastic scattering from atomic hydrogen in order to investigate if a similar behaviour occurs for this target at low velocities where inelastic channels are closed. We calculate elastic cross sections for the three projectiles using Kohn-type variational methods which allows us to make a detailed study of the differences and similarities. We find a qualitative similarity in the spin-weighted elastic integrated cross sections for positronium and electron scattering and a good agreement between the singlet integrated cross sections. However, this agreement does extend to the low velocity region and where the agreement is found in the integrated cross sections we show that it is not present in the individual partial waves cross sections. Interestingly, given the agreement we find in the singlet integrated cross section for electron and positronium scattering, when comparing the overall shapes of the corresponding singlet differential cross sections we find different angular and velocity dependencies.
Adjoint electron-photon transport Monte Carlo calculations with ITS
Lorence, L.J.; Kensek, R.P.; Halbleib, J.A.; Morel, J.E.
1995-02-01
A general adjoint coupled electron-photon Monte Carlo code for solving the Boltzmann-Fokker-Planck equation has recently been created. It is a modified version of ITS 3.0, a coupled electronphoton Monte Carlo code that has world-wide distribution. The applicability of the new code to radiation-interaction problems of the type found in space environments is demonstrated.
NASA Astrophysics Data System (ADS)
Varma, C. M.
1983-07-01
Electrons and positrons in the large magnetic fields at the surface of pulsars condense into rod shaped droplets. The conditions for stimulated annihilation in such droplets are examined. The motivation for this investigation are the observation of Leventhal et al. (1977) of very narrow gamma-ray lines emanating from the Crab Nebula.
NASA Technical Reports Server (NTRS)
Pellerin, C. J.; Hartman, R. C.
1975-01-01
Recently measured positron and negatron spectra are discussed with regard to the problem of solar modulation. At energies above 180 MeV, the spherically symmetric Fokker-Planck equation with a diffusion coefficient proportional to particle rigidity provides reasonable fits to both the positron and total electron data. At energies below 180 MeV, the data are consistent with a continuation of the same diffusion coefficient and a local source of negatrons or with a change in the diffusion coefficient to a constant value.
NASA Astrophysics Data System (ADS)
Banerjee, Gadadhar; Maitra, Sarit
2016-06-01
Sagdeev pseudopotential method is employed to study the arbitrary amplitude quantum ion-acoustic solitary waves in an unmagnetized electron-positron-ion plasma by using one dimensional quantum hydrodynamic model together with the Poisson equation. Sagdeev potential function is obtained in terms of electrostatic potential and analyzed with and without the effect of quantum diffraction parameter H. Effects of the parameter H on both the amplitude and width of the solitary waves have been observed. It is also observed that the positron density can affect the wave propagation.
Polarization of photons scattered by electrons in any spectral distribution
Chang, Zhe; Lin, Hai-Nan; Jiang, Yunguo
2014-01-01
On the basis of the quantum electrodynamics, we present a generic formalism of the polarization for beamed monochromatic photons scattered by electrons in any spectral distribution. The formulae reduce to the components of the Fano matrix when electrons are at rest. We mainly investigate the polarization in three scenarios, i.e., electrons at rest, isotropic electrons with a power-law spectrum, and thermal electrons. If the incident beam is polarized, the polarization is reduced significantly by isotropic electrons at large viewing angles; the degree of polarization caused by thermal electrons is about half of that caused by power-law electrons. If the incident bean is unpolarized, soft γ-rays can lead to about 15% polarization at viewing angles around π/4. For isotropic electrons, one remarkable feature is that the polarization as a function of the incident photon energy always peaks roughly at 1 MeV; this is valid for both the thermal and power-law cases. This feature can be used to distinguish the model of the inverse Compton scattering from that of the synchrotron radiation.
A positron-sensitive photon detector for the UV or X-ray range
NASA Astrophysics Data System (ADS)
Zutavern, F. J.; Schnatterly, S. E.; Källne, E.; Franck, C. P.; Aton, T.; Rife, J.
1980-05-01
This paper describes the conversion of a light sensitive self-scanning silicon photodiode array into a soft X-ray detector. We combine a photodiode array, a UHV compatible soft X-ray sensitive phosphor and read out electronics. The detector has been tested in the soft X-ray and UV regions. The results indicate a high quantum efficiency in the soft X-ray region.
Mesoscopic Physics of Electrons and Photons
NASA Astrophysics Data System (ADS)
Akkermans, Eric; Montambaux, Gilles
2001-12-01
Quantum mesoscopic physics covers a whole class in interference effects related to the propagation of waves in complex and random media. These effects are ubiquitous in physics, from the behaviour of electrons in metals and semiconductors to the propagation of electromagnetic waves in suspensions such as colloids, and quantum systems like cold atomic gases. A solid introduction to quantum mesoscopic physics, this book is a modern account of the problem of coherent wave propagation in random media. It provides a unified account of the basic theoretical tools and methods, highlighting the common aspects of the various optical and electronic phenomena involved and presenting a large number of experimental results. With over 200 figures, and exercises throughout, the book is ideal for graduate students in physics, electrical engineering, applied physics, acoustics and astrophysics. It will also be an interesting reference for researchers in this rapidly evolving field. Presents a large number of experimental results to give readers a broad overview of the field Self-contained, with all elementary presentations of the necessary basic theories in quantum mechanics and scattering theory Contains exercises throughout the book to help readers understand the concepts
Phase-mixing of Langmuir oscillations in cold electron-positron-ion plasmas
Maity, Chandan
2014-07-15
Space-time evolution of Langmuir oscillations in a cold homogeneous electron-positron-ion plasma has been analyzed by employing a straightforward perturbation expansion method, showing phase-mixing and, thus, wave-breaking of excited oscillations at arbitrary amplitudes. Within an assumption of infinitely massive ions, an approximate phase-mixing time is found to scale as ω{sub pe}t{sub mix}∼[(6/δ{sup 2})((2−α){sup 5/2}/(1−α))]{sup 1/3}, where “δ” and “α” (= n{sub 0i}/n{sub 0e}) are the amplitude of perturbation and the ratio of equilibrium ion density to equilibrium electron density, respectively, and ω{sub pe}∼√(4πn{sub 0e}e{sup 2}/m) is the electron plasma frequency. The results presented on phase-mixing of Langmuir modes in multispecies plasmas are expected to be relevant to laboratory and astrophysical environments.
Head on collision of multi-solitons in an electron-positron-ion plasma having superthermal electrons
Roy, Kaushik; Chatterjee, Prasanta Roychoudhury, Rajkumar
2014-10-15
The head-on collision and overtaking collision of four solitons in a plasma comprising superthermal electrons, cold ions, and Boltzmann distributed positrons are investigated using the extended Poincare-Lighthill-Kuo (PLK) together with Hirota's method. PLK method yields two separate Korteweg-de Vries (KdV) equations where solitons obtained from any KdV equation move along a direction opposite to that of solitons obtained from the other KdV equation, While Hirota's method gives multi-soliton solution for each KdV equation all of which move along the same direction where the fastest moving soliton eventually overtakes the other ones. We have considered here two soliton solutions obtained from Hirota's method. Phase shifts acquired by each soliton due to both head-on collision and overtaking collision are calculated analytically.
A single probe for imaging photons, electrons and physical forces.
Pilet, Nicolas; Lisunova, Yuliya; Lamattina, Fabio; Stevenson, Stephanie E; Pigozzi, Giancarlo; Paruch, Patrycja; Fink, Rainer H; Hug, Hans J; Quitmann, Christoph; Raabe, Joerg
2016-06-10
The combination of complementary measurement techniques has become a frequent approach to improve scientific knowledge. Pairing of the high lateral resolution scanning force microscopy (SFM) with the spectroscopic information accessible through scanning transmission soft x-ray microscopy (STXM) permits assessing physical and chemical material properties with high spatial resolution. We present progress from the NanoXAS instrument towards using an SFM probe as an x-ray detector for STXM measurements. Just by the variation of one parameter, the SFM probe can be utilised to detect either sample photo-emitted electrons or transmitted photons. This allows the use of a single probe to detect electrons, photons and physical forces of interest. We also show recent progress and demonstrate the current limitations of using a high aspect ratio coaxial SFM probe to detect photo-emitted electrons with very high lateral resolution. Novel probe designs are proposed to further progress in using an SFM probe as a STXM detector.
A single probe for imaging photons, electrons and physical forces
NASA Astrophysics Data System (ADS)
Pilet, Nicolas; Lisunova, Yuliya; Lamattina, Fabio; Stevenson, Stephanie E.; Pigozzi, Giancarlo; Paruch, Patrycja; Fink, Rainer H.; Hug, Hans J.; Quitmann, Christoph; Raabe, Joerg
2016-06-01
The combination of complementary measurement techniques has become a frequent approach to improve scientific knowledge. Pairing of the high lateral resolution scanning force microscopy (SFM) with the spectroscopic information accessible through scanning transmission soft x-ray microscopy (STXM) permits assessing physical and chemical material properties with high spatial resolution. We present progress from the NanoXAS instrument towards using an SFM probe as an x-ray detector for STXM measurements. Just by the variation of one parameter, the SFM probe can be utilised to detect either sample photo-emitted electrons or transmitted photons. This allows the use of a single probe to detect electrons, photons and physical forces of interest. We also show recent progress and demonstrate the current limitations of using a high aspect ratio coaxial SFM probe to detect photo-emitted electrons with very high lateral resolution. Novel probe designs are proposed to further progress in using an SFM probe as a STXM detector.
ENERGETIC PHOTON AND ELECTRON INTERACTIONS WITH POSITIVE IONS
Phaneuf, Ronald A.
2013-07-01
The objective of this research is a deeper understanding of the complex multi-electron interactions that govern inelastic processes involving positive ions in plasma environments, such as those occurring in stellar cares and atmospheres, x-ray lasers, thermonuclear fusion reactors and materials-processing discharges. In addition to precision data on ionic structure and transition probabilities, high resolution quantitative measurements of ionization test the theoretical methods that provide critical input to computer codes used for plasma modeling and photon opacity calculations. Steadily increasing computational power and a corresponding emphasis on simulations gives heightened relevance to precise and accurate benchmark data. Photons provide a highly selective probe of the internal electronic structure of atomic and molecular systems, and a powerful means to better understand more complex electron-ion interactions.
NASA Technical Reports Server (NTRS)
Derrickson, J. H.; Eby, P. B.; Moon, K. H.; Parnell, T. A.; King, D. T.; Gregory, J. C.; Takahashi, Y.; Ogata, T.
1995-01-01
Measurements of direct Coulomb electron-positron pair production have been made on the tracks of relativistic heavy ions in nuclear track emulsion. Tracks of 0(16) and S(32) at 200 GeV/nucleon were studied. The measured total cross sections and energy and emission angle distributions for the pair members are compared to theoretical predictions. The data are consistent with some recent calculations when knock-on electron contamination is accounted for.
Multidimensional electron-photon transport with standard discrete ordinates codes
Drumm, C.R.
1995-12-31
A method is described for generating electron cross sections that are compatible with standard discrete ordinates codes without modification. There are many advantages of using an established discrete ordinates solver, e.g. immediately available adjoint capability. Coupled electron-photon transport capability is needed for many applications, including the modeling of the response of electronics components to space and man-made radiation environments. The cross sections have been successfully used in the DORT, TWODANT and TORT discrete ordinates codes. The cross sections are shown to provide accurate and efficient solutions to certain multidimensional electronphoton transport problems.
FPGA-Based Front-End Electronics for Positron Emission Tomography
Haselman, Michael; DeWitt, Don; McDougald, Wendy; Lewellen, Thomas K.; Miyaoka, Robert; Hauck, Scott
2010-01-01
Modern Field Programmable Gate Arrays (FPGAs) are capable of performing complex discrete signal processing algorithms with clock rates above 100MHz. This combined with FPGA’s low expense, ease of use, and selected dedicated hardware make them an ideal technology for a data acquisition system for positron emission tomography (PET) scanners. Our laboratory is producing a high-resolution, small-animal PET scanner that utilizes FPGAs as the core of the front-end electronics. For this next generation scanner, functions that are typically performed in dedicated circuits, or offline, are being migrated to the FPGA. This will not only simplify the electronics, but the features of modern FPGAs can be utilizes to add significant signal processing power to produce higher resolution images. In this paper two such processes, sub-clock rate pulse timing and event localization, will be discussed in detail. We show that timing performed in the FPGA can achieve a resolution that is suitable for small-animal scanners, and will outperform the analog version given a low enough sampling period for the ADC. We will also show that the position of events in the scanner can be determined in real time using a statistical positioning based algorithm. PMID:21961085
Wave dispersion in a counterstreaming, cold, magnetized, electron-positron plasma.
Verdon, M W; Melrose, D B
2008-04-01
The dispersion equation is analyzed for waves in a strongly magnetized, electron-positron plasma in which counterstreaming electrons are cold in their respective rest frames. For propagation parallel to the magnetic field the dispersion equation factorizes into equations for two longitudinal modes and four transverse modes. Instabilities occur in both longitudinal and transverse modes, with the most notable being at low wave numbers where a longitudinal branch has purely imaginary frequency. For oblique propagation at small angles, the modes reconnect at points where the parallel modes intersect, either deviating away from each another, or being separated by a pair of complex modes. In addition, intrinsically oblique branches of the dispersion equation appear. The results are applied to an oscillating model for a pulsar magnetosphere, in which the oscillations are purely temporal with a frequency well below relevant wave frequencies, and in which the counterstreaming becomes highly relativistic. We assume that the medium may be treated as time stationary in treating the wave dispersion and wave growth. The wave properties, including the wave frequency, vary periodically with the phase of the oscillations. The fastest growing instability is when the counterstreaming is nonrelativistic or mildly relativistic. A given wave can experience bursts of growth over many oscillations. Mode coupling associated with the cyclotron resonance may be effective in generating the observed orthogonally polarized modes at phases of the oscillation where the (relativistic) cyclotron and wave frequencies are comparable. PMID:18517741
NASA Astrophysics Data System (ADS)
Bains, A. S.; Misra, A. P.; Saini, N. S.; Gill, T. S.
2010-01-01
The amplitude modulation of quantum ion-acoustic waves (QIAWs) along an external magnetic field is studied in a quantum electron-positron-ion (e-p-i) magnetoplasma. Reductive perturbation technique is used to derive the three-dimensional nonlinear Schrödinger equation which governs the slow modulation of QIAW packets. Accounting for the effects of the electron to ion number density ratio (μ), the normalized ion-cyclotron frequency (ωc) as well as the ratio (H) of the "plasmonic energy density" to the Fermi energy, new regimes for the modulational instability of QIAWs are obtained and analyzed. In contrast to one-dimensional unmagnetized e-p-i plasmas, the instability growth rate is shown to suppress with increasing μ or decreasing the values of H. The predicted results could be important for understanding the salient features of modulated QIAW packets in dense astrophysical plasmas as well as to the next generation intense laser solid density plasma experiments.
Justifying the Vacuum as an Electron-Positron Aggregation and Experimental Falsification
NASA Astrophysics Data System (ADS)
Guy Grantham, R.; Montgomery, Ian G.
2013-09-01
Historical aether models are placed in context with the electron-positron lattice (epola) model of space due to M. Simhony. A brief outline of the model as an aggregation state of matter, intermediate to the nuclear state and the atomic aggregation state, includes reference to its derivation of physical laws and fundamental constants. The broad application of the epola model is appraised for its validation against a range of physical laws, experiments and constants. Simhony declared a specific dependence for the stability of atomic matter upon speed through the epola, suggesting a test for falsification. This theme is further developed by the same logic to suggest practical experimental and theoretical tests of the epola model. A formula for the inverse fine structure constant of space, providing the accepted CODATA value, is derived from Simhony's explanation of the Bohr - de Broglie model of the ground state electron orbital of the hydrogen atom by including a term for speed through the Cosmos. A theoretical solution of the Michelson-Morley experiment is applied as evidence for the concept. The mechanism of motion through the epola is considered further for possible implications of speed including dependency of decay rates by radio nuclides and the results of former and ongoing experiments are considered.
Olofsson, Lennart; Karlsson, Magnus G.; Karlsson, Mikael
2005-10-15
In energy modulated electron therapy a large fraction of the segments will be arranged as abutting segments where inhomogeneities in segment matching regions must be kept as small as possible. Furthermore, the output variation between different segments should be minimized and must in all cases be well predicted. For electron therapy with add-on collimators, both the electron MLC (eMLC) and the photon MLC (xMLC) contribute to these effects when an xMLC tracking technique is utilized to reduce the x-ray induced leakage. Two add-on electron collimator geometries have been analyzed using Monte Carlo simulations: One isocentric eMLC geometry with an isocentric clearance of 35 cm and air or helium in the treatment head, and one conventional proximity geometry with a clearance of 5 cm and air in the treatment head. The electron fluence output for 22.5 MeV electrons is not significantly affected by the xMLC if the shielding margins are larger than 2-3 cm. For small field sizes and 9.6 MeV electrons, the isocentric design with helium in the treatment head or shielding margins larger than 3 cm is needed to avoid a reduced electron output. Dose inhomogeneity in the matching region of electron segments is, in general, small when collimator positions are adjusted to account for divergence in the field. The effect of xMLC tracking on the electron output can be made negligible while still obtaining a substantially reduced x-ray leakage contribution. Collimator scattering effects do not interfere significantly when abutting beam techniques are properly applied.
Validation of modulated electron radiotherapy delivered with photon multileaf collimation
NASA Astrophysics Data System (ADS)
Klein, Eric E.
There is a challenge in radiotherapy to treat shallow targets due to the inability to provide dose heterogeneity while simultaneously minimizing dose to distal critical organs. There is a niche for Modulated Electron Radiotherapy (MERT) to complement a photon IMRT program. Disease sites such as post-mastectomy chest wall, and subcutaneous lymphoma of the scalp, etc. are better suited for modulated electrons rather than photons, or perhaps a combination. Inherent collimation systems are not conducive for electron beam delivery (in lieu of extended applicators), nor do commercial treatment planning systems model electrons collimated without applicators. The purpose of this study is to evaluate modulation of electrons by inherent photon multileaf collimators, and calculated and optimized by means of Monte Carlo. Modulated electron radiotherapy (MERT) evaluation was conducted with a Trilogy 120 leaf MLC for 6-20 MeV. To provide a sharp penumbra, modulated beams were delivered with short SSDs (70-85cm). Segment widths (SW) ranging from 1 to 10cm were configured for delivery and planning, using BEAMnrc MC code with 109 particles, and DOSXYZnrc calculations. Calculations were set with: voxel size 0.2 x 0.2 x 0.1cm3, and photon/electron transport energy cutoffs of 0.01 MeV/0.521 MeV. Dosimetry was performed with film and micro chambers. Calculated and measured data were analyzed in MatLab. Once validation of static fields was successfully completed, modulated portals (segmented and dynamic) were configured for treatment and calculations. Optimization for target coverage and OAR sparing was achieved by choosing energies according to target depth, and SW according to spatial coverage. Intensity for each segment was optimized by MC methods. Beam sharpness (penumbra) degraded with: decreasing energy and SW, and increasing SSD. PDD decreased significantly with decreasing SW. We have demonstrated excellent calculation/measurement agreement (<3mm). Equal dose profiles were
Measurement of electron beam polarization from the energy asymmetry of Compton scattered photons
Field, R.C.; Woods, M.; Zhou, J.; Frey, R.; Arodzero, A.
1998-06-01
The authors describe a new method for precision measurement ({approximately} 1%) of the longitudinal polarization of high-energy electron beams. The method relies on measuring the energy asymmetry of Compton scattered photons which result from collisions between the electron beam and a polarized laser beam. The measurement takes place near the electron-positron interaction point at the SLAC Linear Collider (SLC). The detector described here (PGC) is a threshold gas Cherenkov device which follows a lead radiator. The Cherenkov threshold (14 MeV) is essential for eliminating enormous synchrotron radiation-induced backgrounds at the position of interest in the SLC. They also describe the calibration of the PGC energy response in a test beam and its performance as a working polarimeter for the SLC/SLD physics program. Preliminary results from the 1996 run indicate that PGC measurement with total error at or below the 1% level is indeed achievable, and hence serves as a valuable crosscheck of the polarization scale.
Two-photon exchange and elastic electron-proton scattering
Peter Blunden; Wally Melnitchouk; John Tjon
2003-06-01
Two-photon exchange contributions to elastic electron-proton scattering cross sections are evaluated in a simple hadronic model including the finite size of the proton. The corrections are found to be small, but with a strong angular dependence at fixed Q{sup 2}. This is significant for the Rosenbluth technique for determining the ratio of electric and magnetic form factors of the proton, and partly reconciles the apparent discrepancy with the results of the polarization transfer technique.
Eslami, Parvin; Mottaghizadeh, Marzieh; Pakzad, Hamid Reza
2011-10-15
The propagation of ion acoustic waves (IAWs) in plasmas composed of ions and nonextensive electrons and positrons is investigated. By means of the reduction perturbation technique, a nonlinear Schroedinger equation is derived and the modulation instability (MI) of ion acoustic waves is analyzed in detail. The effects of different ranges of the nonextensive parameter q on the MI are studied. The growth rate of the MI is also given for different values of the q parameter. It is also found that the ratio of the electron temperature to positron temperature and the ratio of the positron density to electron density modify the nature of IAWs instability and the solitary structures.
TOPICAL REVIEW: RBE of low energy electrons and photons
NASA Astrophysics Data System (ADS)
Nikjoo, Hooshang; Lindborg, Lennart
2010-05-01
Relative biological effectiveness (RBE) compares the severity of damage induced by a radiation under test at a dose D relative to the reference radiation Dx for the same biological endpoint. RBE is an important parameter in estimation of risk from exposure to ionizing radiation (IR). The present work provides a review of the recently published data and the knowledge of the RBE of low energy electrons and photons. The review presents RBE values derived from experimental data and model calculations including cell inactivation, chromosome aberration, cell transformation, micronuclei formation and induction of double-strand breaks. Biophysical models, including physical features of radiation track, and microdosimetry parameters are presented, analysed and compared with experimental data. The biological effects of low energy electrons and photons are of particular interest in radiation biology as these are strongly absorbed in micrometer and sub-micrometer layers of tissue. RBE values not only depend on the electron and photon energies but also on the irradiation condition, cell type and experimental conditions.
Large-time evolution of an electron in photon bath
Kazakov, Kirill A.; Nikitin, Vladimir V.
2012-12-15
The problem of infrared divergence of the effective electromagnetic field produced by elementary charges is revisited using the model of an electron freely evolving in a photon bath. It is shown that for any finite travel time, the effective field of the electron is infrared-finite, and that at each order of perturbation theory the radiative contributions grow unboundedly with time. Using the Schwinger-Keldysh formalism, factorization of divergent contributions in multi-loop diagrams is proved, and summation of the resulting infinite series is performed. It is found that despite the unbounded growth of individual contributions to the effective field, their sum is bounded, tending to zero in the limit of infinite travel time. It is concluded that the physical meaning of infrared singularity in the effective field is the existence of a peculiar irreversible spreading of electric charges, caused by their interaction with the electromagnetic field. This spreading originates from the quantum electromagnetic fluctuations, rather than the electron-photon scattering, and exists in vacuum as well as at finite temperatures. It shows itself in a damping of the off-diagonal elements of the momentum-space density matrix of electron, but does not affect its momentum probability distribution. This effect is discussed in terms of thermalization of the electron state, and the asymptotic growth of its quantum entropy is determined. Relationship of the obtained results to the Bloch-Nordsieck theorem is established and considered from the standpoint of measurability of the electromagnetic field. The effect of irreversible spreading on the electron diffraction in the classic two-slit experiment is determined, and is shown to be detectable in principle by modern devices already at room temperature. - Highlights: Black-Right-Pointing-Pointer Infrared finiteness of the effective electromagnetic field of a free electron is proved. Black-Right-Pointing-Pointer Quantum radiative effects
Brein, Oliver; Figy, Terrance
2008-03-01
We present results of a calculation of the cross section for the production of a charged Higgs boson in association with an electron and a neutrino at electron-positron colliders (e{sup +}e{sup -}{yields}H{sup +}e{sup -}{nu}{sub e}, H{sup -}e{sup +}{nu}{sub e}). We study predictions for the cross section in the minimal supersymmetric standard model (MSSM) and the two Higgs doublet model (THDM), highlighting possible differences. The process is effectively loop-induced in both models. Hence, the cross section is expected to be strongly model-dependent. Most notably, due to the presence of superpartners, the MSSM amplitude contains Feynman graphs of pentagon-type, which are not present in the THDM. This is the first complete one-loop calculation of the cross section for this process in the THDM and the MSSM. For both models, so far, only approximate results with limited ranges of validity were available. Our main aim here is to clarify several open questions in the existing literature on this process. Specifically, we will discuss the validity of the heavy fermion loop approximation in both models, and of the fermion/sfermion loop approximation in the MSSM.
Laser-driven generation of high-quality ultra-relativistic positron beams
NASA Astrophysics Data System (ADS)
Sarri, G.
2015-04-01
An ultra-relativistic electron beam propagating through a high-Z solid triggers an electromagnetic cascade, whereby a large number of high-energy photons and electron-positron pairs are produced mainly via the bremsstrahlung and Bethe-Heitler processes, respectively. These mechanisms are routinely used to generate positron beams in conventional accelerators such as the electron-positron collider (LEP). Here we show that the application of similar physical mechanisms to a laser-driven electron source allows for the generation of high-quality positron beams in a much more compact and cheaper configuration. We anticipate that the application of these results to the next generation of lasers might open the pathway for the realization of an all-optical high-energy electron-positron collider.
NASA Astrophysics Data System (ADS)
Chrysler, M.; Chirayath, V.; McDonald, A.; Lim, Z.; Shastry, K.; Gladen, R.; Fairchild, A.; Koymen, A.; Weiss, A.
Positron annihilation induced Auger electron spectroscopy (PAES) was used to study the positron induced low energy electron spectra from HOPG and a sample composed of 6-8 layers of graphene grown on polycrystalline copper. A low energy (~2eV) beam of positrons was used to implant positrons into a surface localized state on the graphene and HOPG samples. Measurements of the energy spectra of the positron induced electrons obtained using a TOF spectrometer indicate the presence of an annihilation induced KLL C Auger peak (at ~263 eV) along with a narrow low energy secondary peak due to an Auger mediated positron sticking (AMPS) process. A broad spectral feature was also observed below ~15 eV which we believe may be due to a VVV C Auger transition not previously observed. The energy dependence of the integrated intensity of the AMPS peak was measured for a series of incident positron kinetic energies ranging from ~1.5 eV up to 11 eV from which the binding energy of the surface localized positron state on graphene and HOPG was estimated. The implication of our results regarding the applicability of AMPS and PAES to the study of graphene surfaces and interfaces will be discussed. This work was supported by NSF Grant No. DMR 1508719 and DMR 1338130.
Modulation of a compressional electromagnetic wave in a magnetized electron-positron quantum plasma.
Amin, M R
2015-09-01
Amplitude modulation of a compressional electromagnetic wave in a strongly magnetized electron-positron pair plasma is considered in the quantum magnetohydrodynamic regime. The important ingredients of this study are the inclusion of the external strong magnetic field, Fermi quantum degeneracy pressure, particle exchange potential, quantum diffraction effects via the Bohm potential, and dissipative effect due to collision of the charged carriers. A modified-nonlinear Schödinger equation is developed for the compressional magnetic field of the electromagnetic wave by employing the standard reductive perturbation technique. The linear and nonlinear dispersions of the electromagnetic wave are discussed in detail. For some parameter ranges, relevant to dense astrophysical objects such as the outer layers of white dwarfs, neutron stars, and magnetars, etc., it is found that the compressional electromagnetic wave is modulationally unstable and propagates as a dissipated electromagnetic wave. It is also found that the quantum effects due to the particle exchange potential and the Bohm potential are negligibly small in comparison to the effects of the Fermi quantum degeneracy pressure. The numerical results on the growth rate of the modulation instability is also presented.
Third-order transport coefficients for electron and positron swarms in gases
NASA Astrophysics Data System (ADS)
Simonovic, Ilija; Dujko, Sasa; White, Ronald; Petrovic, Zoran
2015-09-01
A multi term solution of the Boltzmann equation has been used to calculate third-order transport coefficients of charged particle swarms in neutral gases under the influence of electric and magnetic fields. The hierarchy resulting from a spherical harmonic decomposition of the Boltzmann equation in the hydrodynamic regime is solved numerically by representing the speed dependence of the phase-space distribution function in terms of an expansion in Sonine polynomials about a Maxwellian velocity distribution at an internally determined temperature. A group projector technique is employed to determine the structure and symmetries along individual elements of the skewness tensor when both electric and magnetic fields are present. Results are given for electron and positron swarms for certain model and real gases over a range of electric and magnetic field strengths. The results of the Boltzmann equation analysis are compared with those obtained by a Monte Carlo simulation technique. Various aspects in the behavior of skewness tensor elements are investigated, including the existence of correlation with low-order transport coefficients, sensitivity to post-ionization energy partitioning and errors of two-term approximation for solving Boltzmann's equation.
Propagation of ultra-intense electromagnetic waves through electron-positron-ion plasma
NASA Astrophysics Data System (ADS)
Rozina, Ch.; Tsintsadze, N. L.; Jamil, M.
2016-07-01
A kinetic approach is used to study the propagation of ultrarelativistic (amplitude) electromagnetic waves through electron-positron-ion plasma. For our purposes, we formulate a new plasma particle distribution function in the presence of ultrarelativistically intense circularly polarized electromagnetic (EM) waves. An effective dispersion relation of constant amplitude ultrarelativistic EM wave is derived, skin depth is calculated in particular, frequency regimes and has shown numerically that the penetration depth increases with the amplitude of ultra-intense electromagnetic waves, λ s k ˜ a /1 2 , i.e., plasma will be heated more in the region of skin depth. Next, we have found that the nonlinear interaction of ultrarelativistically intense EM waves of time and space varying amplitude leads to construct kinetic nonlinear Schrödinger equation (KNSE), containing both local and non-local nonlinear terms, where nonlocal nonlinear term appears due to density perturbations of plasma species. Taking the effects of the latter into consideration, nonlinear Landau damping is discussed for KNSE, damping rate is computed, and numerically ultrarelativistic EM waves are shown to decay exponentially. The present results should be helpful to understand the specific properties of the ultrarelativistic EM waves in astrophysical plasmas, e.g., pulsars, black holes, and neutron stars.
Fast magnetic reconnection in low-density electron-positron plasmas
Bessho, Naoki; Bhattacharjee, A.
2010-10-15
Two-dimensional particle-in-cell simulations have been performed to study magnetic reconnection in low-density electron-positron plasmas without a guide magnetic field. Impulsive reconnection rates become of the order of unity when the background density is much smaller than 10% of the density in the initial current layer. It is demonstrated that the outflow speed is less than the upstream Alfven speed, and that the time derivative of the density must be taken into account in the definition of the reconnection rate. The reconnection electric fields in the low-density regime become much larger than the ones in the high-density regime, and it is possible to accelerate the particles to high energies more efficiently. The inertial term in the generalized Ohm's law is the most dominant term that supports a large reconnection electric field. An effective collisionless resistivity is produced and tracks the extension of the diffusion region in the late stage of the reconnection dynamics, and significant broadening of the diffusion region is observed. Because of the broadening of the diffusion region, no secondary islands, which have been considered to play a role to limit the diffusion region, are generated during the extension of the diffusion region in the outflow direction.
Simulation of ultra-relativistic electrons and positrons channeling in crystals with MBN EXPLORER
Sushko, Gennady B.; Bezchastnov, Victor G.; Solov'yov, Ilia A.; Korol, Andrei V.; Greiner, Walter; Solov'yov, Andrey V.
2013-11-01
A newly developed code, implemented as a part of the MBN EXPLORER package (Solov'yov et al., 2012; (http://www.mbnexplorer.com/), 2012) [1,2] to simulate trajectories of an ultra-relativistic projectile in a crystalline medium, is presented. The motion of a projectile is treated classically by integrating the relativistic equations of motion with account for the interaction between the projectile and crystal atoms. The probabilistic element is introduced by a random choice of transverse coordinates and velocities of the projectile at the crystal entrance as well as by accounting for the random positions of the atoms due to thermal vibrations. The simulated trajectories are used for numerical analysis of the emitted radiation. Initial approbation and verification of the code have been carried out by simulating the trajectories and calculating the radiation emitted by ε=6.7 GeV and ε=855 MeV electrons and positrons in oriented Si(110) crystal and in amorphous silicon. The calculated spectra are compared with the experimental data and with predictions of the Bethe–Heitler theory for the amorphous environment.
Lopez, Rodrigo A.; Munoz, Victor; Asenjo, Felipe A.; Alejandro Valdivia, J.
2012-08-15
The nonlinear evolution of a circularly polarized electromagnetic wave in an electron-positron plasma propagating along a constant background magnetic field is considered, by studying its parametric decays. Relativistic effects, of the particle motion in the wave field and of the plasma temperature, are included to obtain the dispersion relation of the decays. The exact dispersion relation of the pump wave has been previously calculated within the context of a relativistic fluid theory and presents two branches: an electromagnetic and an Alfven one. We investigate the parametric decays for the pump wave in these two branches, including the anomalous dispersion zone of the Alfven branch where the group velocity is negative. We solve the nonlinear dispersion relation for different pump wave amplitudes and plasma temperatures, finding various resonant and nonresonant wave couplings. We are able to identify these couplings and study their behavior as we modify the plasma parameters. Some of these couplings are suppressed for larger amplitudes or temperatures. We also find two kinds of modulational instabilities, one involving two sideband daughter waves and another involving a forward-propagating electroacoustic mode and a sideband daughter wave.
White dwarf pulsars as possible cosmic ray electron-positron factories
NASA Astrophysics Data System (ADS)
Kashiyama, Kazumi; Ioka, Kunihito; Kawanaka, Norita
2011-01-01
We suggest that white dwarf (WD) pulsars can compete with neutron star (NS) pulsars for producing the excesses of cosmic ray electrons and positrons (e±) observed by the PAMELA, ATIC/PPB-BETS, Fermi, and H.E.S.S. experiments. A merger of two WDs leads to a rapidly spinning WD with a rotational energy (˜1050erg) comparable to the NS case. The birth rate (˜10-2-10-3/yr/galaxy) is also similar, providing the right energy budget for the cosmic ray e±. Applying the NS theory, we suggest that the WD pulsars can in principle produce e± up to ˜10TeV. In contrast to the NS model, the adiabatic and radiative energy losses of e± are negligible since their injection continues after the expansion of the pulsar wind nebula, and hence it is enough that a fraction ˜1% of WDs are magnetized (˜107-109G) as observed. The long activity also increases the number of nearby sources (˜100), which reduces the Poisson fluctuation in the flux. The WD pulsars could dominate the quickly cooling e± above TeV energy as a second spectral bump or even surpass the NS pulsars in the observing energy range ˜10GeV-1TeV, providing a background for the dark matter signals and a nice target for the future AMS-02, CALET, and CTA experiment.
TeV-scale stringy signatures at the electron-positron collider
NASA Astrophysics Data System (ADS)
Burikham, Piyabut
2006-03-01
We investigate the TeV-scale stringy signals of the four-fermion scattering at the electron-positron collider with the center-of-mass energy 500 1000 GeV. The nature of the stringy couplings leads to distinguishable asymmetries comparing to the other new physics models. Specifically, the stringy states in the four-fermion scattering at the leading-order corrections are of spin-1 and 2 with the chiral couplings inherited from the gauge bosons identified as the zeroth-mode string states. The angular left-right, forward-backward, center-edge asymmetries, and the corresponding polarized-beam asymmetries are investigated. The low-energy stringy corrections are compared to the ones induced by the Kaluza-Klein (KK) gravitons. The angular left-right asymmetry of the scattering with the final states of u and d-type quarks, namely c and b, shows significant deviations from the standard model values. The center-edge and forward-backward asymmetries for all final-states fermions also show significant deviations from the corresponding standard model values. The differences between the signatures induced by the stringy corrections and the KK gravitons are appreciable in both angular left-right and forward-backward asymmetries.
Ion acoustic shock waves in electron-positron-ion quantum plasma
NASA Astrophysics Data System (ADS)
Masood, W.; Mirza, Arshad M.; Hanif, M.
2008-07-01
Ion acoustic shock waves (IASWs) are studied in an unmagnetized quantum plasma consisting of electrons, positrons, and ions employing the quantum hydrodynamic (QHD) model. Nonlinear quantum IASWs are investigated by deriving the Korteweg-deVries-Burger equation under the small amplitude perturbation expansion method. The dissipation is introduced by taking into account the kinematic viscosity among the plasma constituents. It is found that the strength of the ion acoustic shock wave is maximum for spherical, intermediate for cylindrical, and minimum for planar geometry. The temporal evolution of the shock for a quantum e-p-i plasma in a spherical geometry is also investigated. It is found that the strength and the steepness of the quantum ion acoustic shock wave increases with decreasing stretched time coordinate (representing slow time scale) |τ|. It is also found that an increase in the quantum Bohm potential decreases the strength as well as the steepness of the shock. The temporal evolution of the quantum ion acoustic solitons in an e-p-i plasma for cylindrical and spherical geometries is also explored by substituting the dissipative coefficient C equal to zero. The relevance of the present study with regard to the dense astrophysical environments is also pointed out.
NASA Astrophysics Data System (ADS)
Rouhani, M. R.; Akbarian, A.; Mohammadi, Z.
2013-08-01
The behavior of quantum dust ion acoustic soliton and shocks in a plasma including inertialess quantum electrons and positrons, classical cold ions, and stationary negative dust grains are studied, using arbitrary amplitude approach. The effect of dissipation due to viscosity of ions is taken into account. The numerical analysis of Sagdeev potential for small value of quantum diffraction parameter (H) shows that for chosen plasma, only compressive solitons can exist and the existence domain of this type of solitons is decreased by increasing dust density (d). Additionally, the possibility of propagation of both subsonic and supersonic compressive solitons is investigated. It is shown that there is a critical dust density above which only supersonic solitons are observed. Moreover, increasing d leads to a reduction in the existence domain of compressive solitons and the possibility of propagation of rarefactive soliton is provided. So, rarefactive solitons are observed only due to the presence of dust particles in this model quantum plasma. Furthermore, numerical solution of governed equations for arbitrary amplitude shock waves has been investigated. It is shown that only compressive large amplitude shocks can propagate. Finally, the effects of plasma parameters on these structures are investigated. This research will be helpful in understanding the properties of dense astrophysical (i.e., white dwarfs and neutron stars) and laboratory dusty plasmas.
Rouhani, M. R.; Akbarian, A.; Mohammadi, Z.
2013-08-15
The behavior of quantum dust ion acoustic soliton and shocks in a plasma including inertialess quantum electrons and positrons, classical cold ions, and stationary negative dust grains are studied, using arbitrary amplitude approach. The effect of dissipation due to viscosity of ions is taken into account. The numerical analysis of Sagdeev potential for small value of quantum diffraction parameter (H) shows that for chosen plasma, only compressive solitons can exist and the existence domain of this type of solitons is decreased by increasing dust density (d). Additionally, the possibility of propagation of both subsonic and supersonic compressive solitons is investigated. It is shown that there is a critical dust density above which only supersonic solitons are observed. Moreover, increasing d leads to a reduction in the existence domain of compressive solitons and the possibility of propagation of rarefactive soliton is provided. So, rarefactive solitons are observed only due to the presence of dust particles in this model quantum plasma. Furthermore, numerical solution of governed equations for arbitrary amplitude shock waves has been investigated. It is shown that only compressive large amplitude shocks can propagate. Finally, the effects of plasma parameters on these structures are investigated. This research will be helpful in understanding the properties of dense astrophysical (i.e., white dwarfs and neutron stars) and laboratory dusty plasmas.
Testing sterile neutrino extensions of the Standard Model at the Circular Electron Positron Collider
NASA Astrophysics Data System (ADS)
Antusch, Stefan; Fischer, Oliver
2015-08-01
Extending the Standard Model with sterile (“right-handed”) neutrinos is one of the best motivated ways to account for the observed neutrino masses. We discuss the expected sensitivity of the Circular Electron Positron Collider (CEPC) for testing such extensions. An interesting scenario is given by symmetry protected seesaw models, which theoretically allow for sterile neutrino masses around the electroweak scale with up to order one mixings with the active (SM) neutrinos. When the masses of the sterile neutrinos are well above the electroweak scale, they affect precision data via effective non-unitarity of the leptonic mixing matrix in a model independent way. The expected improvement of the electroweak precision observables from the CEPC may allow to test mixings between active and sterile neutrinos down to ˜ 5 × 10-3 (using currently discussed CEPC performance parameters). For sterile neutrinos with masses around the electroweak scale, direct searches are possible. Such tests are given by the search for sterile neutrino decays at the Z pole, by deviations from the SM cross section for four leptons at and beyond the W threshold, and by Higgs boson production and decays. The expected sensitivities at the CEPC could reach down to mixings as small as ˜ 5 × 10-5.
Ion acoustic shock waves in electron-positron-ion quantum plasma
Masood, W.; Mirza, Arshad M.; Hanif, M.
2008-07-15
Ion acoustic shock waves (IASWs) are studied in an unmagnetized quantum plasma consisting of electrons, positrons, and ions employing the quantum hydrodynamic (QHD) model. Nonlinear quantum IASWs are investigated by deriving the Korteweg-deVries-Burger equation under the small amplitude perturbation expansion method. The dissipation is introduced by taking into account the kinematic viscosity among the plasma constituents. It is found that the strength of the ion acoustic shock wave is maximum for spherical, intermediate for cylindrical, and minimum for planar geometry. The temporal evolution of the shock for a quantum e-p-i plasma in a spherical geometry is also investigated. It is found that the strength and the steepness of the quantum ion acoustic shock wave increases with decreasing stretched time coordinate (representing slow time scale) |{tau}|. It is also found that an increase in the quantum Bohm potential decreases the strength as well as the steepness of the shock. The temporal evolution of the quantum ion acoustic solitons in an e-p-i plasma for cylindrical and spherical geometries is also explored by substituting the dissipative coefficient C equal to zero. The relevance of the present study with regard to the dense astrophysical environments is also pointed out.
Overview of laser-driven generation of electron-positron beams
NASA Astrophysics Data System (ADS)
Sarri, G.; Dieckmann, M. E.; Kourakis, I.; di Piazza, A.; Reville, B.; Keitel, C. H.; Zepf, M.
2015-08-01
Electron-positron (e-p) plasmas are widely thought to be emitted, in the form of ultra-relativistic winds or collimated jets, by some of the most energetic or powerful objects in the Universe, such as black-holes, pulsars, and quasars. These phenomena represent an unmatched astrophysical laboratory to test physics at its limit and, given their immense distance from Earth (some even farther than several billion light years), they also provide a unique window on the very early stages of our Universe. However, due to such gigantic distances, their properties are only inferred from the indirect interpretation of their radiative signatures and from matching numerical models: their generation mechanism and dynamics still pose complicated enigmas to the scientific community. Small-scale reproductions in the laboratory would represent a fundamental step towards a deeper understanding of this exotic state of matter. Here we present recent experimental results concerning the laser-driven production of ultra-relativistic e-p beams. In particular, we focus on the possibility of generating beams that present charge neutrality and that allow for collective effects in their dynamics, necessary ingredients for the testing pair-plasma physics in the laboratory. A brief discussion of the analytical and numerical modelling of the dynamics of these plasmas is also presented in order to provide a summary of the novel plasma physics that can be accessed with these objects. Finally, general considerations on the scalability of laboratory plasmas up to astrophysical scenarios are given.
Javan, N. Sepehri Homami, S. H. H.
2015-02-15
Self-guided nonlinear propagation of intense circularly-polarized electromagnetic waves in a hot electron-positron-ion magnetoplasma is studied. Using a relativistic fluid model, a nonlinear equation is derived, which describes the interaction of the electromagnetic wave with the plasma in the quasi-neutral approximation. Transverse Eigen modes, the nonlinear dispersion relation and the group velocity are obtained. Results show that the transverse profile in the case of magnetized plasma with cylindrical symmetry has a radially damping oscillatory form. Effect of applying external magnetic fields, existence of the electron-positron pairs, changing the amplitude of the electromagnetic wave, and its polarization on the nonlinear dispersion relation and Eigen modes are studied.
NASA Astrophysics Data System (ADS)
Uedono, Akira; Tsukada, Yusuke; Mikawa, Yutaka; Mochizuki, Tae; Fujisawa, Hideo; Ikeda, Hirotaka; Kurihara, Kaori; Fujito, Kenji; Terada, Shigeru; Ishibashi, Shoji; Chichibu, Shigefusa F.
2016-08-01
Defects in ammonothermal GaN have been studied using a monoenergetic positron beam. Through measurements of Doppler broadening spectra of the annihilation radiation, the major defect species was identified as a Ga vacancy coupled with impurities such as oxygen and/or hydrogen. Those defects were found to be stable even after annealing at 1000 °C. The shape parameter S for the Doppler broadening spectrum corresponding to positron annihilation at the surface was found to be decreased by illumination within energy ranges of 1.5-2.6 eV and 3.2-3.6 eV. This phenomenon is attributed to the suppression of recombinations between holes and electrons due to trapping centers, which can hold electrons for a long time, and a resultant accumulation of holes at the surface. Recovery of the S value required almost one day, but it was shortened by the annealing at 1000 °C.
Design of An 18 MW Beam Dump for 500 GeV Electron/Positron Beams at An ILC
Amann, John; Arnold, Ray; Seryi, Andrei; Walz, Dieter; Kulkarni, Kiran; Rai, Pravin; Satyamurthy, Polepalle; Tiwari, Vikar; Vincke, Heinz; /CERN
2012-07-05
This article presents a report on the progress made in designing 18 MW water based Beam Dumps for electrons or positrons for an International Linear Collider (ILC). Multi-dimensional technology issues have to be addressed for the successful design of the Beam Dump. They include calculations of power deposition by the high energy electron/positron beam bunch trains, computational fluid dynamic analysis of turbulent water flow, mechanical design, process flow analysis, hydrogen/oxygen recombiners, handling of radioactive 7Be and 3H, design of auxiliary equipment, provisions for accident scenarios, remote window exchanger, radiation shielding, etc. The progress made to date is summarized, the current status, and also the issues still to be addressed.
EL-Labany, S. K.; Khedr, D. M.; El-Shamy, E. F.; Sabry, R.
2013-01-15
In the present research paper, the effect of bounded nonplanar (cylindrical and spherical) geometry on the interaction between two nonplanar electrostatic solitary waves (NESWs) in electron-positron-ion plasmas has been studied. The extended Poincare-Lighthill-Kuo method is used to obtain nonplanar phase shifts after the interaction of the two NESWs. This study is a first attempt to investigate nonplanar phase shifts and trajectories for NESWs in a two-fluid plasma (a pair-plasma) consisting of electrons and positrons, as well as immobile background positive ions in nonplanar geometry. The change of phase shifts and trajectories for NESWs due to the effect of cylindrical geometry, spherical geometry, the physical processes (either isothermal or adiabatic), and the positions of two NESWs are discussed. The present investigation may be beneficial to understand the interaction between two NESWs that may occur in active galactic nuclei.
Ion-acoustic solitary waves in a dense pair-ion plasma containing degenerate electrons and positrons
NASA Astrophysics Data System (ADS)
Abdelsalam, U. M.; Moslem, W. M.; Shukla, P. K.
2008-05-01
Fully nonlinear propagation of ion-acoustic solitary waves in a collisionless dense/quantum electron-positron-ion plasma is investigated. The electrons and positrons are assumed to follow the Thomas-Fermi density distribution and the ions are described by the hydrodynamic equations. An energy balance-like equation involving a Sagdeev-type pseudo-potential is derived. Finite amplitude solutions are obtained numerically and their characteristics are discussed. The small-but finite-amplitude limit is also considered and an exact analytical solution is obtained. The present studies might be helpful to understand the excitation of nonlinear ion-acoustic solitary waves in a degenerate plasma such as in superdense white dwarfs.
NASA Astrophysics Data System (ADS)
Maekawa, M.; Kawasuso, A.
2013-06-01
A complementary study of vacancy defects in Si substrates by using scanning positron microscope (SPM) and electron beam induced current (EBIC) method were demonstrated for the same samples and in the same chamber. Both the S parameter and EBIC contrast were found to be enhanced in the regions containing vacancy defects introduced by ion implantation. That is, the SPM provides a criterion if the spatially resolved carrier recombination centres by the EBIC method are originating from vacancy defects or not.
Gevorgyan, N. E.; Dashyan, N. B.; Paremuzyan, R. G.; Stepanyan, S. G.
2010-01-01
We study the dependence of the sensitivity of response of the electromagnetic calorimeter of CLAS plant on the momenta of electrons and positrons. We made calculation of this dependence and elaborated a method for its employment in identification of e- and e+. We have shown that the new method of selection of e- and e+ improves the quality of identification by about 10%. We used the experimental data obtained with the plant CLAS of linear accelerator at Jefferson laboratory (USA).
Three-Jet Production in Electron-Positron Collisions at Next-to-Next-to-Leading Order Accuracy
NASA Astrophysics Data System (ADS)
Del Duca, Vittorio; Duhr, Claude; Kardos, Adam; Somogyi, Gábor; Trócsányi, Zoltán
2016-10-01
We introduce a completely local subtraction method for fully differential predictions at next-to-next-to-leading order (NNLO) accuracy for jet cross sections and use it to compute event shapes in three-jet production in electron-positron collisions. We validate our method on two event shapes, thrust and C parameter, which are already known in the literature at NNLO accuracy and compute for the first time oblateness and the energy-energy correlation at the same accuracy.
NASA Astrophysics Data System (ADS)
Rauch, B. F.
2014-05-01
The CALorimetric Electron Telescope (CALET) is an imaging calorimeter under construction for launch to the ISS in 2014 for a planned 5 year mission. CALET consists of a charge detection module (CHD) with two segmented planes of 1 cm thick plastic scintillator, an imaging calorimeter (IMC) with a total of 3 radiation lengths (X∘) of tungsten plates read out with 8 planes of interleaved scintillating fibers, and a total absorption calorimeter (TASC) with 27 X∘ of lead tungstate (PWO) logs. The primary objectives of the experiment are to measure the electron e+e energy spectra from 1 GeV to 20 TeV, to detect gamma-rays above 10 GeV, and to measure the energy spectra of nuclei from protons through iron up to 1000 TeV. In this paper we describe how the geomagnetic field at the 51.6° inclination orbit of the ISS can be used to allow CALET to measure the distinct electron and positron fluxes. The positron fraction has been seen to rise above ˜10 GeV by previous experiments (HEAT, AMS-01), and more recently to continue to increase to higher energies (˜80 GeV for PAMELA, ˜200 GeV for Fermi and ˜350 GeV with the best statistics for AMS-02). Utilizing the geomagnetic cutoff, CALET will be able to distinguish electrons and positrons in the ˜3-20 GeV energy range where the positron fraction turns upward to complement existing high statistics measurements.
Zhang Jiefang; Wang Yueyue; Wu Lei
2009-06-15
The propagation of ion acoustic waves in plasmas composed of ions, positrons, and nonthermally distributed electrons is investigated. By means of the reduction perturbation technique, a nonlinear Schroedinger equation is derived and the modulation instability of ion acoustic wave is analyzed, where the nonthermal parameter is found to be of significant importance. Furthermore, analytical expressions for the bright and dark solitons are obtained, and the interaction of multiple solitons is discussed.
NASA Technical Reports Server (NTRS)
Hughes, E. B.; Beron, B. L.; Carrington, R. L.; Ford, R. L.; Hofstadter, R.; Liberman, A. D.; Martin, T. W.; Oneill, L. H.; Simpson, J. W.; Hilger, E.
1976-01-01
An experiment was conducted to measure gamma ray pairs produced in the electron-positron reaction in the region of psi(3684) resonance. The apparatus consisted of two identical spectrometers mounted in a collinear configuration about the beam interaction region. Graphs are presented for the coplanarity angle between reconstructed gamma ray directions, for the scattering and energy deposition of gamma rays in the two crystals used, and for the observed rate of annihilation reactions as a function of center of mass energy.
Controlling Photons, Qubits and their Interactions in Superconducting Electronic Circuits
NASA Astrophysics Data System (ADS)
Wallraff, Andreas
2009-03-01
A combination of ideas from atomic physics, quantum optics and solid state physics allows us to investigate the fundamental interaction of matter and light on the level of single quanta in electronic circuits. In an approach known as circuit quantum electrodynamics, we coherently couple individual photons stored in a high quality microwave frequency resonator to a fully controllable superconducting two-level system (qubit) realized in a macroscopic electronic circuit [1]. In particular, we have recently observed the simultaneous interaction of one, two and three photons with a single qubit. In these experiments, we have probed the quantum nonlinearity of the qubit/light interaction governed by the Jaynes-Cummings hamiltonian, clearly demonstrating the quantization of the radiation field in the on-chip cavity. We have also performed quantum optics experiments with no photons at all. In this situation, i.e. in pure vacuum, we have resolved the renormalization of the qubit transition frequency - known as the Lamb shift - due to its non-resonant interaction with the cavity vacuum fluctuations [3].[4pt] [1] A. Wallraff et al., Nature (London) 431, 162 (2004)[0pt] [2] J. Fink et al., Nature (London) 454, 315 (2008)[0pt] [3] A. Fragner et al., Science 322, 1357 (2008)
Radial Moment Calculations of Coupled Electron-Photon Beams
FRANKE,BRIAN C.; LARSEN,EDWARD W.
2000-07-19
The authors consider the steady-state transport of normally incident pencil beams of radiation in slabs of material. A method has been developed for determining the exact radial moments of 3-D beams of radiation as a function of depth into the slab, by solving systems of 1-D transport equations. They implement these radial moment equations in the ONEBFP discrete ordinates code and simulate energy-dependent, coupled electron-photon beams using CEPXS-generated cross sections. Modified P{sub N} synthetic acceleration is employed to speed up the iterative convergence of the 1-D charged particle calculations. For high-energy photon beams, a hybrid Monte Carlo/discrete ordinates method is examined. They demonstrate the efficiency of the calculations and make comparisons with 3-D Monte Carlo calculations. Thus, by solving 1-D transport equations, they obtain realistic multidimensional information concerning the broadening of electron-photon beams. This information is relevant to fields such as industrial radiography, medical imaging, radiation oncology, particle accelerators, and lasers.
Fine-grid calculations for stellar electron and positron capture rates on Fe isotopes
Nabi, Jameel-Un; Tawfik, Abdel Nasser
2013-03-15
The acquisition of precise and reliable nuclear data is a prerequisite to success for stellar evolution and nucleosynthesis studies. Core-collapse simulators find it challenging to generate an explosion from the collapse of the core of massive stars. It is believed that a better understanding of the microphysics of core-collapse can lead to successful results. The weak interaction processes are able to trigger the collapse and control the lepton-to-baryon ratio (Y{sub e}) of the corematerial. It is suggested that the temporal variation of Y{sub e} within the core of a massive star has a pivotal role to play in the stellar evolution and a fine-tuning of this parameter at various stages of presupernova evolution is the key to generate an explosion. During the presupernova evolution of massive stars, isotopes of iron, mainly {sup 54-56}Fe, are considered to be key players in controlling Y{sub e} ratio via electron capture on these nuclides. Recently an improved microscopic calculation of weak-interaction-mediated rates for iron isotopes was introduced using the proton-neutron quasiparticle random-phase-approximation (pn-QRPA) theory. The pn-QRPA theory allows a microscopic state-by-state calculation of stellar capture rates which greatly increases the reliability of calculated rates. The results were suggestive of some fine-tuning of the Y{sub e} ratio during various phases of stellar evolution. Here we present for the first time the fine-grid calculation of the electron and positron capture rates on {sup 54-56}Fe. The sensitivity of the pn-QRPA calculated capture rates to the deformation parameter is also studied in this work. Core-collapse simulators may find this calculation suitable for interpolation purposes and for necessary incorporation in the stellar evolution codes.
NASA Astrophysics Data System (ADS)
Hosseinpour, M.; Mohammadi, M. A.; Biabani, S.; Biabani
2013-10-01
Collisionless magnetic reconnection via tearing instability in non-relativistic electron-positron (pair) plasma with an anisotropic pressure is investigated. The equilibrium magnetic field is considered to be sheared force-free, and a set of linearized collisionless Magnetohydrodynamics equations describes the evolution of reconnection dynamics. A linear analytical analysis, based on scaling, demonstrates that in such a pair plasma, breaking the frozen in flow constraint for field lines can be mainly provided by the non-gyrotropic pressure of electrons and positrons (rather than the particle bulk inertia) when the current sheet width is smaller than the particle Larmor radius (Δx < r L ). This condition is satisfied when β > d 2 (d = c/ω p is the particle skin-depth with the electron/positron frequency ω p and β = 8πP (0)/B 0 2 << 1). Meanwhile, on top of the Lorentz force and in the absence of the reconnection facilitating mechanism of the Hall effect, non-scalar pressure force can accelerate bulk plasma into the diffusion region at the scale lengths of the order of dx. Therefore, the respective regime of tearing instability proceeds much faster compared with the case of an isotropic pressure with a new dimensionless growth rate of (γτ A ) ~ d.
NASA Astrophysics Data System (ADS)
Malik, Hitendra K.; Malik, Rakhee; Malik
2014-08-01
An electron-positron pair plasma having dust impurity and density non-uniformity is studied for its unperturbed state and evolution of solitary structures under the effect of either positively charged or negatively charged dust grains. Zeroth-order equations are solved to examine the unperturbed state of the plasma via unperturbed potential φ0, drift velocities of the electrons and positrons (v e0 and v p0), and plasma (positron) density gradient n p0η. It is observed that the dust distribution affects the gradient n p0η significantly, which increases very sharply with a small increment in the dust density gradient n d0η. With relation to the solitary structures, a modified form of Korteweg-deVries equation (mKdV equation) is realized in the said plasma, which reveals that a tailing structure is associated with the soliton (sech2 structure). This tail is less prominent in the present pair plasma, contrary to the observation made in ordinary plasmas having only ions and electrons. The dust impurity is found to influence the solitary structure much significantly and its presence suppresses the rarefactive solitons, which are generally observed in multi-component species plasmas.
Multidimensional electron-photon transport with standard discrete ordinates codes
Drumm, C.R.
1997-04-01
A method is described for generating electron cross sections that are comparable with standard discrete ordinates codes without modification. There are many advantages of using an established discrete ordinates solver, e.g. immediately available adjoint capability. Coupled electron-photon transport capability is needed for many applications, including the modeling of the response of electronics components to space and man-made radiation environments. The cross sections have been successfully used in the DORT, TWODANT and TORT discrete ordinates codes. The cross sections are shown to provide accurate and efficient solutions to certain multidimensional electron-photon transport problems. The key to the method is a simultaneous solution of the continuous-slowing-down (CSD) portion and elastic-scattering portion of the scattering source by the Goudsmit-Saunderson theory. The resulting multigroup-Legendre cross sections are much smaller than the true scattering cross sections that they represent. Under certain conditions, the cross sections are guaranteed positive and converge with a low-order Legendre expansion.
Multidimensional electron-photon transport with standard discrete ordinates codes
Drumm, C.R.
1997-09-01
A method is described for generating electron cross sections that are compatible with standard discrete ordinates codes without modification. There are many advantages to using an established discrete ordinates solver, e.g., immediately available adjoint capability. Coupled electron-photon transport capability is needed for many applications, including the modeling of the response of electronics components to space and synthetic radiation environments. The cross sections have been successfully used in the DORT, TWODANT, and TORT discrete ordinates codes. The cross sections are shown to provide accurate and efficient solutions to certain multidimensional electron-photon transport problems. The key to the method is a simultaneous solution of the continuous-slowing-down and elastic-scattering portions of the scattering source by the Goudsmit-Saunderson theory. The resulting multigroup-Legendre cross sections are much smaller than the true scattering cross sections that they represent. Under certain conditions, the cross sections are guaranteed positive and converge with a low-order Legendre expansion.
Characterization of electron contamination in megavoltage photon beams
Medina, Antonio Lopez; Teijeiro, Antonio; Garcia, Juan; Esperon, Jorge; Terron, J. Antonio; Ruiz, Diego P.; Carrion, Maria C.
2005-05-01
The purpose of the present study is to characterize electron contamination in photon beams in different clinical situations. Variations with field size, beam modifier (tray, shaping block) and source-surface distance (SSD) were studied. Percentage depth dose measurements with and without a purging magnet and replacing the air by helium were performed to identify the two electron sources that are clearly differentiated: air and treatment head. Previous analytical methods were used to fit the measured data, exploring the validity of these models. Electrons generated in the treatment head are more energetic and more important for larger field sizes, shorter SSD, and greater depths. This difference is much more noticeable for the 18 MV beam than for the 6 MV beam. If a tray is used as beam modifier, electron contamination increases, but the energy of these electrons is similar to that of electrons coming from the treatment head. Electron contamination could be fitted to a modified exponential curve. For machine modeling in a treatment planning system, setting SSD at 90 cm for input data could reduce errors for most isocentric treatments, because they will be delivered for SSD ranging from 80 to 100 cm. For very small field sizes, air-generated electrons must be considered independently, because of their different energetic spectrum and dosimetric influence.
NASA Astrophysics Data System (ADS)
Janek Strååt, Sara; Andreassen, Björn; Jonsson, Cathrine; Noz, Marilyn E.; Maguire, Gerald Q., Jr.; Näfstadius, Peder; Näslund, Ingemar; Schoenahl, Frederic; Brahme, Anders
2013-08-01
The purpose of this study was to investigate in vivo verification of radiation treatment with high energy photon beams using PET/CT to image the induced positron activity. The measurements of the positron activation induced in a preoperative rectal cancer patient and a prostate cancer patient following 50 MV photon treatments are presented. A total dose of 5 and 8 Gy, respectively, were delivered to the tumors. Imaging was performed with a 64-slice PET/CT scanner for 30 min, starting 7 min after the end of the treatment. The CT volume from the PET/CT and the treatment planning CT were coregistered by matching anatomical reference points in the patient. The treatment delivery was imaged in vivo based on the distribution of the induced positron emitters produced by photonuclear reactions in tissue mapped on to the associated dose distribution of the treatment plan. The results showed that spatial distribution of induced activity in both patients agreed well with the delivered beam portals of the treatment plans in the entrance subcutaneous fat regions but less so in blood and oxygen rich soft tissues. For the preoperative rectal cancer patient however, a 2 ± (0.5) cm misalignment was observed in the cranial-caudal direction of the patient between the induced activity distribution and treatment plan, indicating a beam patient setup error. No misalignment of this kind was seen in the prostate cancer patient. However, due to a fast patient setup error in the PET/CT scanner a slight mis-position of the patient in the PET/CT was observed in all three planes, resulting in a deformed activity distribution compared to the treatment plan. The present study indicates that the induced positron emitters by high energy photon beams can be measured quite accurately using PET imaging of subcutaneous fat to allow portal verification of the delivered treatment beams. Measurement of the induced activity in the patient 7 min after receiving 5 Gy involved count rates which were about
NASA Astrophysics Data System (ADS)
Yuyang, Huang; Yanqiong, Lu; Yanyan, Zhu; Yuxia, Li; Wen, Deng
2009-09-01
Microdefects and 3d electrons in B2-FeAl alloys with different chemical composition, single crystal of Fe and cold-rolled Fe has been studied by positron lifetime and coincidence Doppler broadening spectroscopy. The coincidence Doppler broadening spectrum of the single crystal of Fe shows the highest 3d electron signal in the spectra of all tested samples. The 3d electron signal in the spectrum of Fe50Al50 alloy is much lower than that of the cold-rolled Fe. This indicates that some of the 3d electrons of Fe atoms and 3p electrons of Al atoms in B2-FeAl alloy are localized to form strong covalent bonds, thus decreasing the probability of positron annihilation with 3d electrons of Fe atoms. With the increase of Al content in B2-FeAl alloys, the 3d electron signal in the spectrum of the alloy decreases, while the open volume of defect increases.
Positron sensing of distribution of defects in depth materials
NASA Astrophysics Data System (ADS)
Kupchishin, A. I.; Kupchishin, A. A.; Voronova, N. A.; Kirdyashkin, V. I.
2016-02-01
It was developed a non-destructive method of positron sensing, which allows to determine the distribution of defects in the depth of the material. From the analysis we can conclude that the angular distribution curves of annihilation photons (well as and on the characteristics in experiments on the lifetime, 3γ - angular correlation, Doppler effect) is influenced by three main factors: a) The distribution of defects in the depth of the material, their dimensions as well as parameters of the interaction of positrons with defects. With increasing the concentration of defects the intensity Jγ(a, ξ) varies more; b) Modification of the energy spectrum of slow positrons due to the influence of defects, wherein the spectrum of positrons becomes softer, and the average energy of the positron annihilation is reduced; c) Deformation of the momentum distribution of the electrons in the region of defect. The energy spectrum of electrons is also becomes softer, and the average energy of the electrons (on which positrons annihilate) is less. The experimentally were measured spectra of photons in the zone of annihilation and were calculated the distribution of defects in depth for a number of metals.
Waves and Instabilities in AN Electron-Positron Plasma in AN Ultra-Strong Magnetic Field.
NASA Astrophysics Data System (ADS)
Pulsifer, Peter Emery
1987-09-01
Magnetic fields of up to 10^{13 } Gauss have been observed in pulsars. At these ultrastrong fields, the energy between Landau levels is comparable to the electron rest-mass, and the cyclotron radius is comparable to the Compton wavelength. To study the electromagnetic properties of an electron or positron gas in such ultrastrong fields, the polarization tensor Pi_{mu nu} is calculated. This response function is simply related to other functions like the dielectric and diamagnetic tensors. A dispersion relation is found involving Pi_{munu }, whose solution determines the frequency -wavenumber relation for propagating electromagnetic waves in the system. Damping of these waves is determined by the imaginary part of Pi_{mu nu}. A relativistic quantum-kinetic (Wigner function) technique is used. A relativistic treatment is needed partly because of the high magnetic field and partly because of the assumed high electron densities (of order 10 ^{29} cm^{ -3}). The quantum analog to the Vlasov equation is derived and linearized about a zero-temperature Fermi equilibrium, an approximation scheme equivalent to the random-phase-approximation (RPA). An integral equation is found for the four-current, which then determines the polarization tensor. The resulting dispersion is evaluated for propagation parallel to the magnetic field. In this case, solutions have one of three possible polarizations: longitudinal, right-circular and left-circular. Many acoustic-like waves are seen, arising from logarithmic peaks in Pi . The longitudinal plasmon oscillation, always undamped, is discussed. Generalizations of the cyclotron frequency and the whistler mode are considered. A previously unreported propagating wave, with frequency slightly above the pair-production energy, is discovered at all polarizations. Wave propagation and damping are analyzed in terms of two-body processes. Cutoffs and discontinuities in phase velocities of waves are noted and discussed in terms of the different
Vorster, Michael J.; Moraal, Harm
2014-06-20
Charged particles propagating through a structured magnetic field are subject to drift motion. The primary aim of the present paper is therefore to investigate the effects of gradient, curvature, and neutral sheet drift on the evolution of the electron and positron spectra in a pulsar wind nebula, where the drift motion is a direct result of the magnetic field having an Archimedean spiral structure. In order to investigate the evolution of the spectra, the steady-state, axisymmetric Fokker-Planck transport equation is solved numerically using a finite-difference scheme. Apart from drift motion, the transport processes of convection and diffusion, along with the energy loss processes of adiabatic cooling and synchrotron radiation, are also included in the model. It is found that drift, particularly neutral sheet drift, can lead to a quantitative difference in the evolution of the electron and positron spectra. This difference may be of importance when interpreting the positron excess observed by PAMELA and AMS-02 near Earth.
Grasso, D.; Profumo, S.; Strong, A.W.; Baldini, L.; Bellazzini, R.; Bloom, E.D.; Bregeon, J.; Di Bernardo, G.; Gaggero, D.; Giglietto, N.; Kamae, T.; Latronico, L.; Longo, F.; Mazziotta, M.N.; Moiseev, A.A.; Morselli, A.; Ormes, J.F.; Pesce-Rollins, M.; Pohl, M.; Razzano, M.; Sgro, C.
2009-05-15
The Fermi-LAT experiment recently reported high precision measurements of the spectrum of cosmic-ray electrons-plus-positrons (CRE) between 20 GeV and 1 TeV. The spectrum shows no prominent spectral features, and is significantly harder than that inferred from several previous experiments. Here we discuss several interpretations of the Fermi results based either on a single large scale Galactic CRE component or by invoking additional electron-positron primary sources, e.g. nearby pulsars or particle Dark Matter annihilation. We show that while the reported Fermi-LAT data alone can be interpreted in terms of a single component scenario, when combined with other complementary experimental results, specifically the CRE spectrum measured by H.E.S.S. and especially the positron fraction reported by PAMELA between 1 and 100 GeV, that class of models fails to provide a consistent interpretation. Rather, we find that several combinations of parameters, involving both the pulsar and dark matter scenarios, allow a consistent description of those results. We also briefly discuss the possibility of discriminating between the pulsar and dark matter interpretations by looking for a possible anisotropy in the CRE flux.
NASA Astrophysics Data System (ADS)
Rahman, Ata-ur-; Kerr, Michael Mc; El-Taibany, Wael F.; Kourakis, Ioannis; Qamar, A.
2015-02-01
A semirelativistic fluid model is employed to describe the nonlinear amplitude modulation of low-frequency (ionic scale) electrostatic waves in an unmagnetized electron-positron-ion plasma. Electrons and positrons are assumed to be degenerated and inertialess, whereas ions are warm and classical. A multiscale perturbation method is used to derive a nonlinear Schrödinger equation for the envelope amplitude, based on which the occurrence of modulational instability is investigated in detail. Various types of localized ion acoustic excitations are shown to exist, in the form of either bright type envelope solitons (envelope pulses) or dark-type envelope solitons (voids, holes). The plasma configurational parameters (namely, the relativistic degeneracy parameter, the positron concentration, and the ionic temperature) are shown to affect the conditions for modulational instability significantly, in fact modifying the associated threshold as well as the instability growth rate. In particular, the relativistic degeneracy parameter leads to an enhancement of the modulational instability mechanism. Furthermore, the effect of different relevant plasma parameters on the characteristics (amplitude, width) of these envelope solitary structures is also presented in detail. Finally, the occurrence of extreme amplitude excitation (rogue waves) is also discussed briefly. Our results aim at elucidating the formation and dynamics of nonlinear electrostatic excitations in superdense astrophysical regimes.
Rahman, Ata-ur-; Kerr, Michael Mc Kourakis, Ioannis; El-Taibany, Wael F.; Qamar, A.
2015-02-15
A semirelativistic fluid model is employed to describe the nonlinear amplitude modulation of low-frequency (ionic scale) electrostatic waves in an unmagnetized electron-positron-ion plasma. Electrons and positrons are assumed to be degenerated and inertialess, whereas ions are warm and classical. A multiscale perturbation method is used to derive a nonlinear Schrödinger equation for the envelope amplitude, based on which the occurrence of modulational instability is investigated in detail. Various types of localized ion acoustic excitations are shown to exist, in the form of either bright type envelope solitons (envelope pulses) or dark-type envelope solitons (voids, holes). The plasma configurational parameters (namely, the relativistic degeneracy parameter, the positron concentration, and the ionic temperature) are shown to affect the conditions for modulational instability significantly, in fact modifying the associated threshold as well as the instability growth rate. In particular, the relativistic degeneracy parameter leads to an enhancement of the modulational instability mechanism. Furthermore, the effect of different relevant plasma parameters on the characteristics (amplitude, width) of these envelope solitary structures is also presented in detail. Finally, the occurrence of extreme amplitude excitation (rogue waves) is also discussed briefly. Our results aim at elucidating the formation and dynamics of nonlinear electrostatic excitations in superdense astrophysical regimes.
Electronic/photonic interfaces for ultrafast data processing.
Overberg, Mark E.; Geib, Kent Martin; Serkland, Darwin Keith; Hsu, Alan Yuan-Chun; Keeler, Gordon Arthur; Finnegan, Patrick Sean
2008-09-01
This report summarizes a 3-month program that explored the potential areas of impact for electronic/photonic integration technologies, as applied to next-generation data processing systems operating within 100+ Gb/s optical networks. The study included a technology review that targeted three key functions of data processing systems, namely receive/demultiplexing/clock recovery, data processing, and transmit/multiplexing. Various technical approaches were described and evaluated. In addition, we initiated the development of high-speed photodetectors and hybrid integration processes, two key elements of an ultrafast data processor. Relevant experimental results are described herein.
Counting statistics of photons produced by electronic shot noise.
Beenakker, C W; Schomerus, H
2001-01-22
A theory is presented for the photodetection statistics of radiation produced by current fluctuations in a phase-coherent conductor. Deviations are found from the Poisson statistics that would result from a classical current. For detection in a narrow frequency interval delta omega, the photocount distribution has the negative-binomial form of blackbody radiation if e delta omega is less than the mean current I in the conductor. When electronic localization sets in, I drops below e delta omega and a different type of super-Poissonian photon statistics results. PMID:11177916
Optical XOR circuit using combined technology of photonics and electronics
NASA Astrophysics Data System (ADS)
Takiguchi, Koichi
2013-12-01
I propose and demonstrate a novel and simple optical exclusive OR circuit for binary signals, which is composed of a balanced photo-detector and a Mach-Zehnder intensity modulator. Two input optical signals into the photo-detector produce an electrical signal to drive the modulator. The modulator outputs an optical exclusive OR signal of the two input optical signals. I report the configuration, operating principle, and primary experimental results using 10 Gbit/s binary signals to demonstrate that the exclusive OR circuit operates properly. The proposed simple circuit is suitable for the future hybrid integration of photonics and electronics.
LDRD project 151362 : low energy electron-photon transport.
Kensek, Ronald Patrick; Hjalmarson, Harold Paul; Magyar, Rudolph J.; Bondi, Robert James; Crawford, Martin James
2013-09-01
At sufficiently high energies, the wavelengths of electrons and photons are short enough to only interact with one atom at time, leading to the popular %E2%80%9Cindependent-atom approximation%E2%80%9D. We attempted to incorporate atomic structure in the generation of cross sections (which embody the modeled physics) to improve transport at lower energies. We document our successes and failures. This was a three-year LDRD project. The core team consisted of a radiation-transport expert, a solid-state physicist, and two DFT experts.
Artificial honeycomb lattices for electrons, atoms and photons.
Polini, Marco; Guinea, Francisco; Lewenstein, Maciej; Manoharan, Hari C; Pellegrini, Vittorio
2013-09-01
Artificial honeycomb lattices offer a tunable platform for studying massless Dirac quasiparticles and their topological and correlated phases. Here we review recent progress in the design and fabrication of such synthetic structures focusing on nanopatterning of two-dimensional electron gases in semiconductors, molecule-by-molecule assembly by scanning probe methods and optical trapping of ultracold atoms in crystals of light. We also discuss photonic crystals with Dirac cone dispersion and topologically protected edge states. We emphasize how the interplay between single-particle band-structure engineering and cooperative effects leads to spectacular manifestations in tunnelling and optical spectroscopies.
Chatterjee, Debjani; Misra, A P
2015-12-01
The nonlinear theory of amplitude modulation of electrostatic wave envelopes in a collisionless electron-positron (EP) pair plasma is studied by using a set of Vlasov-Poisson equations in the context of Tsallis' q-nonextensive statistics. In particular, the previous linear theory of Langmuir oscillations in EP plasmas [Saberian and Esfandyari-Kalejahi, Phys. Rev. E 87, 053112 (2013)] is rectified and modified. Applying the multiple scale technique (MST), it is shown that the evolution of electrostatic wave envelopes is governed by a nonlinear Schrödinger (NLS) equation with a nonlocal nonlinear term ∝P∫|ϕ(ξ',τ)|(2)dξ'ϕ/(ξ-ξ') [where P denotes the Cauchy principal value, ϕ is the small-amplitude electrostatic (complex) potential, and ξ and τ are the stretched coordinates in MST], which appears due to the wave-particle resonance. It is found that a subregion 1/3
The extent of non-thermal particle acceleration in relativistic, electron-positron reconnection
Werner, Greg; Guo, Fan
2015-07-21
Reconnection is studied as an explanation for high-energy flares from the Crab Nebula. The production of synchrotron emission >100 MeV challenges classical models of acceleration. 3D simulation shows that reconnection, converting magnetic energy to kinetic energy, can accelerate beyond γ_{rad}. The power-law index and high-energy cutoff are important for understanding the radiation spectrum dN/dγ = f(γ) ∝ γ^{-α}. α and cutoff were measured vs. L and σ, where L is system (simulation) size and σ is upstream magnetization (σ = B^{2}/4πnmc^{2}). α can affect the high-energy cutoff. In conclusion, for collisionless relativistic reconnection in electron-positron plasma, without guide field, n_{b}/n_{d}=0.1: (1) relativistic magnetic reconnection yields power-law particle spectra, (2) the power law index decreases as σ increases, approaching ≈1.2. (3) the power law is cut off at an energy related to acceleration within a single current layer, which is proportional to the current layer length (for small systems, that length is the system length, yielding γ_{c2} ≈ 0.1 L/ρ_{0}; for large systems, the layer length is limited by secondary tearing instability, yielding γ_{c1} ≈ 4σ; the transition from small to large is around L/ρ_{0} = 40σ.). (4) although the large-system energy cutoff is proportional to the average energy per particle, it is significantly higher than the average energy per particle.
White dwarf pulsars as possible cosmic ray electron-positron factories
Kashiyama, Kazumi; Ioka, Kunihito; Kawanaka, Norita
2011-01-15
We suggest that white dwarf (WD) pulsars can compete with neutron star (NS) pulsars for producing the excesses of cosmic ray electrons and positrons (e{sup {+-}}) observed by the PAMELA, ATIC/PPB-BETS, Fermi, and H.E.S.S. experiments. A merger of two WDs leads to a rapidly spinning WD with a rotational energy ({approx}10{sup 50} erg) comparable to the NS case. The birth rate ({approx}10{sup -2}-10{sup -3}/yr/galaxy) is also similar, providing the right energy budget for the cosmic ray e{sup {+-}}. Applying the NS theory, we suggest that the WD pulsars can in principle produce e{sup {+-}} up to {approx}10 TeV. In contrast to the NS model, the adiabatic and radiative energy losses of e{sup {+-}} are negligible since their injection continues after the expansion of the pulsar wind nebula, and hence it is enough that a fraction {approx}1% of WDs are magnetized ({approx}10{sup 7}-10{sup 9} G) as observed. The long activity also increases the number of nearby sources ({approx}100), which reduces the Poisson fluctuation in the flux. The WD pulsars could dominate the quickly cooling e{sup {+-}} above TeV energy as a second spectral bump or even surpass the NS pulsars in the observing energy range {approx}10 GeV-1 TeV, providing a background for the dark matter signals and a nice target for the future AMS-02, CALET, and CTA experiment.
Chatterjee, Debjani; Misra, A P
2015-12-01
The nonlinear theory of amplitude modulation of electrostatic wave envelopes in a collisionless electron-positron (EP) pair plasma is studied by using a set of Vlasov-Poisson equations in the context of Tsallis' q-nonextensive statistics. In particular, the previous linear theory of Langmuir oscillations in EP plasmas [Saberian and Esfandyari-Kalejahi, Phys. Rev. E 87, 053112 (2013)] is rectified and modified. Applying the multiple scale technique (MST), it is shown that the evolution of electrostatic wave envelopes is governed by a nonlinear Schrödinger (NLS) equation with a nonlocal nonlinear term ∝P∫|ϕ(ξ',τ)|(2)dξ'ϕ/(ξ-ξ') [where P denotes the Cauchy principal value, ϕ is the small-amplitude electrostatic (complex) potential, and ξ and τ are the stretched coordinates in MST], which appears due to the wave-particle resonance. It is found that a subregion 1/3
NASA Astrophysics Data System (ADS)
Chatterjee, Debjani; Misra, A. P.
2015-12-01
The nonlinear theory of amplitude modulation of electrostatic wave envelopes in a collisionless electron-positron (EP) pair plasma is studied by using a set of Vlasov-Poisson equations in the context of Tsallis' q -nonextensive statistics. In particular, the previous linear theory of Langmuir oscillations in EP plasmas [Saberian and Esfandyari-Kalejahi, Phys. Rev. E 87, 053112 (2013), 10.1103/PhysRevE.87.053112] is rectified and modified. Applying the multiple scale technique (MST), it is shown that the evolution of electrostatic wave envelopes is governed by a nonlinear Schrödinger (NLS) equation with a nonlocal nonlinear term ∝P ∫|ϕ (ξ',τ ) |2d ξ'ϕ /(ξ -ξ') [where P denotes the Cauchy principal value, ϕ is the small-amplitude electrostatic (complex) potential, and ξ and τ are the stretched coordinates in MST], which appears due to the wave-particle resonance. It is found that a subregion 1 /3
NASA Astrophysics Data System (ADS)
Emadi, E.; Zahed, H.
2016-08-01
The behavior of linear and nonlinear dust ion acoustic (DIA) solitary waves in an unmagnetized quantum dusty plasma, including inertialess electrons and positrons, ions, and mobile negative dust grains, are studied. Reductive perturbation and Sagdeev pseudopotential methods are employed for small and large amplitude DIA solitary waves, respectively. A minimum value of the Mach number obtained for the existence of solitary waves using the analytical expression of the Sagdeev potential. It is observed that the variation on the values of the plasma parameters such as different values of Mach number M, ion to electron Fermi temperature ratio σ, and quantum diffraction parameter H can lead to the creation of compressive solitary waves.
Tang, Z.; Chiba, T.; Nagai, Y.; Inoue, K.; Toyama, T.; Hasegawa, M.
2014-04-28
A compact ensemble of high density nitrogen-vacancy (NV) centers in diamond is essential to sense various external fields with a high precision at the nanoscale. Here, defects in type IIa and type Ib diamonds induced by 28 MeV electron irradiation at 77 K were studied by combining the positron annihilation spectroscopy and first-principles calculations. It is shown that the electron irradiation at 77 K can significantly enhance the NV center formation by directly converting 24% vacancies into the NV centers, indicating that it is an efficient way to produce the high density NV centers in the type Ib diamond.
Plemmons, Dayne A; Flannigan, David J
2016-05-26
In femtosecond ultrafast electron microscopy (UEM) experiments, the initial excitation period is composed of spatiotemporal overlap of the temporally commensurate pump photon pulse and probe photoelectron packet. Generation of evanescent near-fields at the nanostructure specimens produces a dispersion relation that enables coupling of the photons (ℏω = 2.4 eV, for example) and freely propagating electrons (200 keV, for example) in the near-field. Typically, this manifests as discrete peaks occurring at integer multiples (n) of the photon energy in the low-loss/gain region of electron-energy spectra (i.e., at 200 keV ± nℏω eV). Here, we examine the UEM imaging resolution implications of the strong inelastic near-field interactions between the photons employed in optical excitation and the probe photoelectrons. We find that the additional photoinduced energy dispersion occurring when swift electrons pass through intense evanescent near-fields results in a discrete chromatic aberration that limits the spatial resolving power to several angstroms during the excitation period. PMID:27111530
A Guide to Electronic Multipoles in Photon Scattering and Absorption
NASA Astrophysics Data System (ADS)
Lovesey, Stephen William; Balcar, Ewald
2013-02-01
The practice of replacing matrix elements in atomic calculations by those of convenient operators with strong physical appeal has a long history, and in condensed matter physics it is perhaps best known through use of operator equivalents in electron resonance by Elliott and Stevens. Likewise, electronic multipoles, created with irreducible spherical-tensors, to represent charge-like and magnetic-like quantities are widespread in modern physics. Examples in recent headlines include a magnetic charge (a monopole), an anapole (a dipole) and a triakontadipole (a magnetic-like atomic multipole of rank 5). In this communication, we aim to guide the reader through use of atomic, spherical multipoles in photon scattering, and resonant Bragg diffraction and dichroic signals in particular. Applications to copper oxide CuO and neptunium dioxide (NpO2) are described. In keeping with it being a simple guide, there is sparse use in the communication of algebra and expressions are gathered from the published literature and not derived, even when central to the exposition. An exception is a thorough grounding, contained in an Appendix, for an appropriate version of the photon scattering length based on quantum electrodynamics. A theme of the guide is application of symmetry in scattering, in particular constraints imposed on results by symmetry in crystals. To this end, a second Appendix catalogues constraints on multipoles imposed by symmetry in crystal point-groups.
Inexpensive electronics and software for photon statistics and correlation spectroscopy
Gamari, Benjamin D.; Zhang, Dianwen; Buckman, Richard E.; Milas, Peker; Denker, John S.; Chen, Hui; Li, Hongmin; Goldner, Lori S.
2016-01-01
Single-molecule-sensitive microscopy and spectroscopy are transforming biophysics and materials science laboratories. Techniques such as fluorescence correlation spectroscopy (FCS) and single-molecule sensitive fluorescence resonance energy transfer (FRET) are now commonly available in research laboratories but are as yet infrequently available in teaching laboratories. We describe inexpensive electronics and open-source software that bridges this gap, making state-of-the-art research capabilities accessible to undergraduates interested in biophysics. We include a discussion of the intensity correlation function relevant to FCS and how it can be determined from photon arrival times. We demonstrate the system with a measurement of the hydrodynamic radius of a protein using FCS that is suitable for the undergraduate teaching laboratory. The FPGA-based electronics, which are easy to construct, are suitable for more advanced measurements as well, and several applications are described. As implemented, the system has 8 ns timing resolution, can control up to four laser sources, and can collect information from as many as four photon-counting detectors. PMID:26924846
Inexpensive electronics and software for photon statistics and correlation spectroscopy
NASA Astrophysics Data System (ADS)
Gamari, Benjamin D.; Zhang, Dianwen; Buckman, Richard E.; Milas, Peker; Denker, John S.; Chen, Hui; Li, Hongmin; Goldner, Lori S.
2014-07-01
Single-molecule-sensitive microscopy and spectroscopy are transforming biophysics and materials science laboratories. Techniques such as fluorescence correlation spectroscopy (FCS) and single-molecule sensitive fluorescence resonance energy transfer (FRET) are now commonly available in research laboratories but are as yet infrequently available in teaching laboratories. We describe inexpensive electronics and open-source software that bridges this gap, making state-of-the-art research capabilities accessible to undergraduates interested in biophysics. We include a discussion of the intensity correlation function relevant to FCS and how it can be determined from photon arrival times. We demonstrate the system with a measurement of the hydrodynamic radius of a protein using FCS that is suitable for the undergraduate teaching laboratory. The FPGA-based electronics, which are easy to construct, are suitable for more advanced measurements as well, and several applications are described. As implemented, the system has 8 ns timing resolution, can control up to four laser sources, and can collect information from as many as four photon-counting detectors.
NASA Astrophysics Data System (ADS)
Akins, Charles G.; Gauthier, Richard; Kracklauer, A. F.; Macken, John A.; Meulenberg, Andrew; Rangacharyulu, Chary; Roychoudhuri, Chandrasekhar; van der Mark, Martin B.; Williamson, John G.
2015-09-01
Platform: What physical attributes separate EM waves, of the enormous band of radio to visible to x-ray, from the high energy narrow band of gamma-ray? From radio to visible to x-ray, telescopes are designed based upon the optical imaging theory; which is an extension of the Huygens-Fresnel diffraction integral. Do we understand the physical properties of gamma rays that defy us to manipulate them similarly? One demonstrated unique property of gamma rays is that they can be converted to elementary particles (electron and positron pair); or a particle-antiparticle pair can be converted into gamma rays. Thus, EM waves and elementary particles, being inter-convertible; we cannot expect to understand the deeper nature of light without succeeding to find structural inter-relationship between photons and particles. This topic is directly relevant to develop a deeper understanding of the nature of light; which will, in turn, help our engineers to invent better optical instruments.
Comptonization of thermal photons by relativistic electron beams
NASA Technical Reports Server (NTRS)
Daugherty, Joseph K.; Harding, Alice K.
1989-01-01
This paper presents a numerical calculation of gamma-ray emission produced by Compton scattering of relativistic electron beams on background thermal radiation, which includes spatial dependence of electron energy losses and cyclotron resonance scattering in a strong magnetic field. In the first version, the scattering is described by the fully relativistic Klein-Nishina cross section, but the magnetic field is neglected. In the second version, the scattering is described by the magnetic resonant cross section in the Thomson limit. It is found that when the magnetic field is not included, electron energy losses are important only at higher neutron star surface temperatures (T about 3,000,000 K). In the presence of a strong magnetic field, (10 to the 12th G), resonant scattering greatly increases electron energy losses, making scattering very efficient even at lower surface temperatures. Resulting photon and electron spectra for both cases ae discussed in relation to models for pulsar X-ray and gamma-ray emission.
A search for single electron production in electron-positron annihilation at E = 29 GeV
Steele, T.R.
1989-01-01
This thesis presents experimental results from the ASP detector which took data on e{sup +}e{sup {minus}} interactions in the PEP storage ring at SLAC. Its design was particularly suitable for searching for production of supersymmetric particles. The motivations for and phenomenology of Supersymmetry are discussed. In particular, the production of a single supersymmetric electron ( selectron,' {tilde e}) in combination with a supersymmetric photon ( photino,' {tilde {gamma}}) would result in events in which a single electron and no other particles are observed in the detector at an e{sup +}e{sup {minus}} collider such as PEP, provided the masses of these particles are not too large. Such events would also result from the production of a single supersymmetric W-boson ( wino', {tilde W}) in combination with a supersymmetric neutrino ( sneutrino,' {tilde {nu}}). These process make it possible to search for selectrons and winos with masses greater than the beam energy. Observation of these unusual events would distinctly indicate the production of new particles. The ASP detector was designed to be hermetic and to provide efficient event reconstruction for low multiplicity events. The detector is described and its performance is evaluated; it is found to be well-suited to this study. No evidence for single-electron events was observed, allowing limits (95% CL) to be set on the supersymmetric particle masses.
Photon-Photon Collisions -- Past and Future
Brodsky, Stanley J.; /SLAC
2005-12-02
I give a brief review of the history of photon-photon physics and a survey of its potential at future electron-positron colliders. Exclusive hadron production processes in photon-photon and electron-photon collisions provide important tests of QCD at the amplitude level, particularly as measures of hadron distribution amplitudes. There are also important high energy {gamma}{gamma} and e{gamma} tests of quantum chromodynamics, including the production of jets in photon-photon collisions, deeply virtual Compton scattering on a photon target, and leading-twist single-spin asymmetries for a photon polarized normal to a production plane. Since photons couple directly to all fundamental fields carrying the electromagnetic current including leptons, quarks, W's and supersymmetric particles, high energy {gamma}{gamma} collisions will provide a comprehensive laboratory for Higgs production and exploring virtually every aspect of the Standard Model and its extensions. High energy back-scattered laser beams will thus greatly extend the range of physics of the International Linear Collider.
Visualizing surface plasmons with photons, photoelectrons, and electrons.
El-Khoury, P Z; Abellan, P; Gong, Y; Hage, F S; Cottom, J; Joly, A G; Brydson, R; Ramasse, Q M; Hess, W P
2016-06-21
Both photons and electrons may be used to excite surface plasmon polaritons, the collective charge density fluctuations at the surface of metal nanostructures. By virtue of their nanoscopic and dissipative nature, a detailed characterization of surface plasmon (SP) eigenmodes in real space-time ultimately requires joint nanometer spatial and femtosecond temporal resolution. The latter realization has driven significant developments in the past few years, aimed at interrogating both localized and propagating SP modes. In this mini-review, we briefly highlight different techniques employed by our own groups to visualize the enhanced electric fields associated with SPs. Specifically, we discuss recent hyperspectral optical microscopy, tip-enhanced Raman nano-spectroscopy, nonlinear photoemission electron microscopy, as well as correlated scanning transmission electron microscopy-electron energy loss spectroscopy measurements targeting prototypical plasmonic nanostructures and constructs. Through selected practical examples from our own laboratories, we examine the information content in multidimensional images recorded by taking advantage of each of the aforementioned techniques. In effect, we illustrate how SPs can be visualized at the ultimate limits of space and time. PMID:27067797
Chelkowski, Szczepan; Bandrauk, André D; Corkum, Paul B
2014-12-31
We investigate photon-momentum sharing between an electron and an ion following different photoionization regimes. We find very different partitioning of the photon momentum in one-photon ionization (the photoelectric effect) as compared to multiphoton processes. In the photoelectric effect, the electron acquires a momentum that is much greater than the single photon momentum ℏω/c [up to (8/5) ℏω/c] whereas in the strong-field ionization regime, the photoelectron only acquires the momentum corresponding to the photons absorbed above the field-free ionization threshold plus a momentum corresponding to a fraction (3/10) of the ionization potential Ip. In both cases, due to the smallness of the electron-ion mass ratio, the ion takes nearly the entire momentum of all absorbed N photons (via the electron-ion center of mass). Additionally, the ion takes, as a recoil, the photoelectron momentum resulting from mutual electron-ion interaction in the electromagnetic field. Consequently, the momentum partitioning of the photofragments is very different in both regimes. This suggests that there is a rich, unexplored physics to be studied between these two limits which can be generated with current ultrafast laser technology. PMID:25615323
Chelkowski, Szczepan; Bandrauk, André D; Corkum, Paul B
2014-12-31
We investigate photon-momentum sharing between an electron and an ion following different photoionization regimes. We find very different partitioning of the photon momentum in one-photon ionization (the photoelectric effect) as compared to multiphoton processes. In the photoelectric effect, the electron acquires a momentum that is much greater than the single photon momentum ℏω/c [up to (8/5) ℏω/c] whereas in the strong-field ionization regime, the photoelectron only acquires the momentum corresponding to the photons absorbed above the field-free ionization threshold plus a momentum corresponding to a fraction (3/10) of the ionization potential Ip. In both cases, due to the smallness of the electron-ion mass ratio, the ion takes nearly the entire momentum of all absorbed N photons (via the electron-ion center of mass). Additionally, the ion takes, as a recoil, the photoelectron momentum resulting from mutual electron-ion interaction in the electromagnetic field. Consequently, the momentum partitioning of the photofragments is very different in both regimes. This suggests that there is a rich, unexplored physics to be studied between these two limits which can be generated with current ultrafast laser technology.
Mechanics of flexible electronics and photonics based on inorganic micro- and nanomaterials
NASA Astrophysics Data System (ADS)
Lu, Nanshu; Yang, Shixuan; Qiao, Shutao
2014-06-01
Flexible electronics and photonics are providing revolutionary solutions for communication, energy, and health care. While some of the organic electronic and photonic materials are intrinsically deformable and low cost to manufacture, their performance and chemical stabilities are yet to match conventional inorganic semiconductors. Strategies for high performance flexible electronics and photonics must overcome challenges associated with the intrinsic stiffness and brittleness of inorganic materials. This paper discusses recent modeling and experimental advancement in the bendability and stretchability of inorganic electronics and photonics. Examples include the discovery of multiple neutral axes in multilayer structures and the comparison between freestanding and polymer-bonded serpentine ribbons.
Kim, Changjae; Nam, Ki Yeun; Park, Jin Woo; Lee, Ho Jun
2016-01-01
Zolpidem is a non-benzodiazepine drug that has selectivity for the gamma-aminobutyric acid (GABA) receptors. We experienced paradoxical effect of zolpidem in a 48-year-old male patient with hypoxic-ischemic brain injury after cardiac arrest. The patient was in stupor and could not communicate. His Glasgow Coma Scale (GCS) was E2M4V2 and Rancho Los Amigos (RLA) was grade III to IV. Zolpidem was prescribed to induce sedation but paradoxically, he became alert (GCS 15, RLA VII) and was able to communicate. The arousal lasted for 2 hours repeatedly following each administration of the medication. While he was alert, electroencephalogram showed the reversal of slow wave into beta range fast activity and F-18 flumazenil positron emission tomography (PET) showed increased GABAergic receptor activity in both frontoparietotemporal cortices. Single photon emission computed tomography (SPECT) also showed increased cerebral perfusion and reversal of cerebellar diaschisis. PMID:26949686
Rauf Abdullah, Nzar; Tang, Chi-Shung; Manolescu, Andrei; Gudmundsson, Vidar
2016-09-21
We investigate theoretically the balance of the static magnetic and the dynamical photon forces in the electron transport through a quantum dot in a photon cavity with a single photon mode. The quantum dot system is connected to external leads and the total system is exposed to a static perpendicular magnetic field. We explore the transport characteristics through the system by tuning the ratio, [Formula: see text], between the photon energy, [Formula: see text], and the cyclotron energy, [Formula: see text]. Enhancement in the electron transport with increasing electron-photon coupling is observed when [Formula: see text]. In this case the photon field dominates and stretches the electron charge distribution in the quantum dot, extending it towards the contact area for the leads. Suppression in the electron transport is found when [Formula: see text], as the external magnetic field causes circular confinement of the charge density around the dot.
Rauf Abdullah, Nzar; Tang, Chi-Shung; Manolescu, Andrei; Gudmundsson, Vidar
2016-09-21
We investigate theoretically the balance of the static magnetic and the dynamical photon forces in the electron transport through a quantum dot in a photon cavity with a single photon mode. The quantum dot system is connected to external leads and the total system is exposed to a static perpendicular magnetic field. We explore the transport characteristics through the system by tuning the ratio, [Formula: see text], between the photon energy, [Formula: see text], and the cyclotron energy, [Formula: see text]. Enhancement in the electron transport with increasing electron-photon coupling is observed when [Formula: see text]. In this case the photon field dominates and stretches the electron charge distribution in the quantum dot, extending it towards the contact area for the leads. Suppression in the electron transport is found when [Formula: see text], as the external magnetic field causes circular confinement of the charge density around the dot. PMID:27420809
Jackman, T.M.
1987-01-01
A theoretical investigation of the interaction potential between the helium atom and the antihydrogen atom was performed for the purpose of determining the feasibility of antihydrogen atom containment. The interaction potential showed an energy barrier to collapse of this system. A variational estimate of the height of this energy barrier and estimates of lifetime with respect to electron-positron annihilation were determined by the Variational Monte Carlo method. This calculation allowed for an improvement over an SCF result through the inclusion of explicit correlation factors in the trial wave function. An estimate of the correlation energy of this system was determined by the Green's Function Monte Carlo (GFMC) method.
Hertzbach, S.S.; Kofler, R.R.
1993-12-31
The High Energy Physics group at the University of Massachusetts has continued its` program of experimental studies of electron-positron interactions at the Stanford Linear Accelerator Center (SLAC). The group activities have included: analysis of data taken between 1982 and 1990 with the TPC detector at the PEP facility, continuing data collection and data analysis using the SLC/SLD facility, planning for the newly approved B-factory at SLAC, and participation in design studies for future high energy linear colliders. This report will briefly summarize these activities.
Ultrafast terahertz electrodynamics of photonic and electronic nanostructures
NASA Astrophysics Data System (ADS)
Luo, Liang
This thesis summarizes my work on using ultrafast laser pulses to study Terahertz (THz) electrodynamics of photonic and electronic nanostructures and microstructures. Ultrafast time-resolved (optical, NIR, MIR, THz) pump-probe spectroscopy setup has been successfully built, which enables me to perform a series of relevant experiments. Firstly, a novel high efficiency and compact THz wave emitter based on split-ring-resonators has been developed and characterized. The emitter can be pumped at any wavelength by tailoring the magnetic resonance and could generate gapless THz waves covering the entire THz band. Secondly, two kinds of new photonic structures for THz wave manipulation have been successfully designed and characterized. One is based on the 1D and 2D photo-imprinted diffractive elements. The other is based on the photoexcited double-split-ring-resonator metamaterials. Both structures are flexible and can modulate THz waves with large tunability. Thirdly, the dark excitons in semiconducting single-walled carbon nanotubes are studied by optical pump and THz probe spectroscopy, which provides the first insights into the THz responses of nonequilibrium excitonic correlations and dynamics from the dark ground states in carbon nanotubes. Next, several on-going projects are briefly presented such as the study of ultrafast THz dynamics of Dirac fermions in topological insulator Bi_{2}Se_{3} with Mid-infrared excitation. Finally, the thesis ends with a summary of the completed experiments and an outlook of the future plan.
NASA Astrophysics Data System (ADS)
Misra, A. P.; Bhowmik, C.; Shukla, P. K.
2009-07-01
The theoretical study of modulational instability (MI) and localized envelope excitations of finite amplitude ion-acoustic waves (IAWs) is revisited in an unmagnetized quantum electron-positron-ion plasma. For this purpose, a one-dimensional nonlinear Schrödinger equation, which governs the slow modulation of IAW packets, is derived by using the standard reductive perturbations technique. Two parameters, defining the ratio of the electron to ion number density (μ) and the quantum coupling parameter (H) describing the ratio of the "plasmonic energy density" to the Fermi energy density, are shown to play crucial roles in determining the modulational stability/MI domains, as well as for the existence of both bright and dark envelope solitons. It is found that the stability region increases (decreases) with increasing μ(H ), whereas the MI region for the IAW mode shifts to larger (smaller) wave number k as the value of μ(H ) increases. Moreover, the parameter H is shown to suppress the MI growth rate of the IAWs. The present results may be relevant to dense astrophysical plasmas (e.g., white dwarfs, where the electron-positron annihilation can be important, and where the particle density is of the order of 1034-1035 m-3) as well as to the next generation intense laser solid density plasma experiments.
PREFACE: XXV International Conference on Photonic, Electronic and Atomic Collisions
NASA Astrophysics Data System (ADS)
Becker, Uwe; Moshammer, Robert; Mokler, Paul; Ullrich, Joachim
2007-07-01
The XXVth ICPEAC in Freiburg marked a notable anniversary in collision physics: half a century ago the first conference in the series of International Conferences on the Physics of Electronic and Atomic Collisions (ICPEAC) was held in New York (1958). Since then, the development of electronic and atomic collision physics has seen tremendous progress. Starting during a time, when this field was regarded as somehow out-of-date, certainly not being in the main stream compared to particle and high-energy physics, it has expanded in a rather exceptional and unforeseen way. Over the years the original scope on electronic, atomic and heavy-ion collision physics was extended substantially to include upcoming expanding fields like synchrotron-radiation and strong-field laser-based atomic and molecular physics giving rise to a change of name to 'Photonic', Electronic and Atomic Collisions (ICPEAC) being used for the first time for the ICPEAC in Santa Fee in 2001. Nowadays, the ICPEAC has opened its agenda even more widely to other fields of atomic and molecular physics, such as interactions with clusters, bio-molecules and surfaces, to cold collisions, coherent control, femto- and attosecond physics and, with the Freiburg conference, to the application of free-electron lasers in the vacuum ultraviolet and soft x-ray regime, a field of potentially huge future impact in essentially all areas of science. In this larger context the XXVth ICPEAC in Freiburg with more than 800 participants set new standards. Representatives from all fields of Atomic, Molecular and Photon-based science came together and had very fruitful, inter-disciplinary discussions. This new forum of collision-based AMP physics will serve as a showcase example of future conferences, bridging not only the gap between different fields of collision physics but also, equally important, between different continents and cultures. The next ICPEAC is going to take place in Kalamazoo in North America, the one after that
Virtual photon structure functions and the parton content of the electron
Drees, M. ); Godbole, R.M. )
1994-09-01
We point out that in processes involving the parton content of the photon the usual effective photon approximation should be modified. The reason is that the parton content of virtual photons is logarithmically suppressed compared to real photons. We describe this suppression using several simple, physically motivated [ital Ansa]$[ital uml---tze]. Although the parton content of the electron in general no longer factorizes into an electron flux function and a photon structure function, it can still be expressed as a single integral. Numerical examples are given for the [ital e][sup +][ital e][sup [minus
NASA Astrophysics Data System (ADS)
Farsaei, Ahmadreza; Wang, Yun; Molavi, Reza; Jayatilleka, Hasitha; Caverley, Michael; Beikahmadi, Mohammad; Masnadi Shirazi, Amir Hossein; Jaeger, Nicolas; Chrostowski, Lukas; Mirabbasi, Shahriar
2016-08-01
Photonic networks form the backbone for data communications. In particular, in current and future wireless communication systems, photonic networks are becoming increasingly popular for data distribution between the central office and the remote antenna units at base stations. As wireless-photonic systems become in increasing demand, low-cost implementation of such systems will be desirable. This paper describes how integrated photonics and electronics, on silicon, can be used to design such systems. Various building blocks of such silicon-photonics systems are reviewed. The emphasis is on a 60 GHz wireless system which could be suitable for the emerging 5th-generation (5G) cellular networks. The implementation discussed here uses digital baseband optical transmission as opposed to the radio-over-fibre approach.
Progress Towards a Laser Produced Relativistic Electron-Positron Pair Plasma
NASA Astrophysics Data System (ADS)
Chen, Hui; Bonlie, J.; Cauble, R.; Fiuza, F.; Goldstein, W.; Hazi, A.; Keane, C.; Link, A.; Marley, E.; Nagel, S. R.; Park, J.; Shepherd, R.; Williams, G. J.; Meyerhofer, D. D.; Fiksel, G.; Barnak, D.; Chang, P. Y.; Nakai, M.; Arikawa, Y.; Azechi, H.; Fujioka, S.; Kojima, S.; Miyanaga, N.; Morita, T.; Nagai, T.; Nishimura, H.; Ozaki, T.; Sakawa, Y.; Takabe, H.; Zhang, Z.; Kerr, S.; Fedosejevs, R.; Sentoku, Y.; Hill, M. P.; Hoarty, D. J.; Hobbs, L. M. R.; James, S. F.
2016-03-01
A set of experiments has been performed exploring unique characteristics of pair jets and plasmas at several energetic short-pulse laser facilities including Titan at Livermore and OMEGA EP in Rochester, as well as the Osaka LFEX and AWE Orion lasers. New results are summarized, including positron beam emittance, scaling of pair production vs. laser energy, and initial results on the pair jet collimation using electromagnetic fields.
Photon-Electron Interactions in Graphene-Based Heterojunctions
NASA Astrophysics Data System (ADS)
Liu, Fangze
Graphene, a single layer of carbon atoms arranged in honeycomb lattice, has been one of the most attractive materials for fundamental and applied research in the past decade. Its unique electronic, optical, thermal, chemical and mechanical properties have lead to the discovery of new physics and many promising applications. In particular, research on photon-electron interaction in graphene-based heterojunctions has revealed a new route to design photoactive devices. In this thesis, I present our work on the synthesis of graphene by chemical vapor deposition (CVD) and the study of graphene-based optoelectronic devices. In addition to the conventional synthesis of graphene on copper (Cu) foils, we also present the CVD synthesis of graphene on a new substrate: palladium (Pd). Especially, we performed detailed study of the nucleation, evolution and morphology of graphene growth on Pd substrate. It helps us to understand the growth reaction mechanism and achieve controllable synthesis of graphene from single layer to multiple layers with different morphologies. We then studied the broadband and ultrasensitive photocurrent and photovoltage response of graphene/silicon (Si) Schottky diodes. For the same architecture, we identified a new photoconductive mode with ultra high photoconductive gain, namely "quantum carrier reinvestment (QCR)". A gain exceeding 107 A/W was demonstrated. The underlying physics of photon-electron interactions in these junctions were studied by a combination of optical characterization tools including Raman spectroscopy, UV-Vis spectroscopy and scanning optical microscopy. The results obtained have been discussed in the framework of the unique electronic band structure, density states, and mobility of graphene, along with the manner in witch photoexcited carrier behave under various externally tuned parameters. We also systematically studied the optimization of performance of graphene/Si and thin transparent graphite/Si junction solar cells and
Aaltonen, T.; Abulencia, A.; Adelman, J.; Affolder, Anthony Allen; Akimoto, T.; Albrow, Michael G.; Amerio, S.; Amidei, Dante E.; Anastassov, A.; Anikeev, K.; Annovi, A. /Taiwan, Inst. Phys. /Argonne /Barcelona, IFAE /Baylor U. /INFN, Bologna /Bologna U. /Brandeis U. /UC, Davis /UCLA /UC, San Diego /UC, Santa Barbara
2007-07-01
We report the results of a search for a narrow resonance in electron-positron events in the invariant mass range of 150-950 GeV/c{sup 2} using 1.3 fb{sup -1} of p{bar p} collision data at {radical}s=1.96 TeV collected by the CDF II detector at Fermilab. No significant evidence of such a resonance is observed and we interpret the results to exclude the standard model-like Z{prime} with a mass below 923 GeV/c{sup 2} and the Randall-Sundrum graviton with a mass below 807 GeV/c{sup 2} for k/{bar M}{sub pl} = 0.1, both at the 95% confidence level. Combining with di-photon data excludes the Randall-Sundrum graviton for masses below 889 GeV/c{sup 2} for k/{bar M}{sub pl} = 0.1
Scott, D J; Clarke, J A; Baynham, D E; Bayliss, V; Bradshaw, T; Burton, G; Brummitt, A; Carr, S; Lintern, A; Rochford, J; Taylor, O; Ivanyushenkov, Y
2011-10-21
The first demonstration of a full-scale working undulator module suitable for future TeV-scale positron-electron linear collider positron sources is presented. Generating sufficient positrons is an important challenge for these colliders, and using polarized e(+) would enhance the machine's capabilities. In an undulator-based source polarized positrons are generated in a metallic target via pair production initiated by circularly polarized photons produced in a helical undulator. We show how the undulator design is developed by considering impedance effects on the electron beam, modeling and constructing short prototypes before the successful fabrication, and testing of a final module.
Undulator Production of Polarized Positrons
William M. Bugg
2008-08-27
E-166 at SLAC has demonstrated the feasibilty of production of polarized positrons for the International Linear Collider using a helical undulator to produce polarized photons which are converted in a thin target to polarized positrons. The success of the experim ent has resulted in the choice of this technique for the baseline design of ILC.
Study of four-lepton final states in electron-positron interactions at 29 GeV
Petradza, A.
1989-08-01
This thesis presents a study of electron-positron scattering to four light leptons. The motivations behind it are twofold. Firstly, the study is a test of the theory of electron-positron interactions to 4th order in the fine structure constant {alpha}. A deviation from the theory could indicate the existence of a heavy new particle. Secondly, a measurement of these processes may prove useful in the understanding of other QED-type reactions. The method for simulating the four-lepton processes by the Monte Carlo event generator of Berends, Daverveldt and Kleiss is described. Theoretical predictions are compared to data from the Mark II and HRS experiments at the PEP storage ring. The observed events consist of four leptons at large angles. Data for all three e{sup +}e{sup -}e{sup +}e{sup -}, e{sup +}e{sup -}{mu}{sup +}{mu}{sup -} and {mu}{sup +}{mu}{sup -}{mu}{sup +}{mu}{sup -} processes are well described by the QED Monte Carlo calculation. The various kinematical distributions are in good agreement with QED to order {alpha}{sup 4}. 18 refs., 64 figs., 19 tabs.
NASA Astrophysics Data System (ADS)
Wiktor, Julia; Jomard, Gérald; Torrent, Marc; Barthe, Marie-France; Bertolus, Marjorie
2016-05-01
We performed calculations of momentum distributions of annihilating electron-positron pairs in various fully relaxed vacancy defects in SiC. We used self-consistent two-component density functional theory schemes to find the electronic and positronic densities and wave functions in the considered systems. Using the one-dimensional momentum distributions (Doppler-broadened annihilation radiation line shapes) we calculated the line-shape parameters S and W . We emphasize the effect of the experimental resolution and the choice of the integration ranges for the S and W parameters on the distributions of the points corresponding to different defects in the S (W ) plot. We performed calculation for two polytypes of SiC, 3 C , and 6 H and showed that for silicon vacancies and clusters containing this defect there were no significant differences between the Doppler spectra. The results of the Doppler spectra calculations were compared with experimental data obtained for n -type 6 H -SiC samples irradiated with 4-MeV Au ions. We observed a good general agreement between the measured and calculated points.
NASA Astrophysics Data System (ADS)
Zhou, X. X.; Wang, X. J.; Huang, D. H.; Jia, H. Y.
2016-11-01
Monte Carlo simulations are performed to study the correlation between the ground cosmic ray intensity and near-earth thunderstorms electric field at YBJ (located at YangBaJing, Tibet, China, 4300 m a. s. l.). The variations of the secondary cosmic ray intensity are found to be highly dependent on the strength and polarity of the electric field. In negative fields and in positive fields greater than 600 V/cm, the total number of ground comic ray positrons and electrons increases with increasing electric field strength. And these values increase more obviously when involving a shower with lower primary energy or a higher zenith angle. While in positive fields ranging from 0 to 600 V/cm, the total number of ground comic ray positrons and electrons declines and the amplitude is up to 3.1% for vertical showers. A decrease of intensity occurs in inclined showers within the range of 0-500 V/cm, which is accompanied by smaller amplitudes. In this paper, the intensity changes are analyzed, especially concerning those decreasing phenomena in positive electric fields. Our simulation results could be helpful in understanding the decreases observed in some ground-based experiments (such as the Carpet air shower array and ARGO-YBJ), and also be useful in understanding the acceleration mechanisms of secondary charged particles caused by an atmospheric electric field.
Anisotropic Electron-Photon and Electron-Phonon Interactions in Black Phosphorus.
Ling, Xi; Huang, Shengxi; Hasdeo, Eddwi H; Liang, Liangbo; Parkin, William M; Tatsumi, Yuki; Nugraha, Ahmad R T; Puretzky, Alexander A; Das, Paul Masih; Sumpter, Bobby G; Geohegan, David B; Kong, Jing; Saito, Riichiro; Drndic, Marija; Meunier, Vincent; Dresselhaus, Mildred S
2016-04-13
Orthorhombic black phosphorus (BP) and other layered materials, such as gallium telluride (GaTe) and tin selenide (SnSe), stand out among two-dimensional (2D) materials owing to their anisotropic in-plane structure. This anisotropy adds a new dimension to the properties of 2D materials and stimulates the development of angle-resolved photonics and electronics. However, understanding the effect of anisotropy has remained unsatisfactory to date, as shown by a number of inconsistencies in the recent literature. We use angle-resolved absorption and Raman spectroscopies to investigate the role of anisotropy on the electron-photon and electron-phonon interactions in BP. We highlight, both experimentally and theoretically, a nontrivial dependence between anisotropy and flake thickness and photon and phonon energies. We show that once understood, the anisotropic optical absorption appears to be a reliable and simple way to identify the crystalline orientation of BP, which cannot be determined from Raman spectroscopy without the explicit consideration of excitation wavelength and flake thickness, as commonly used previously.
Anisotropic Electron-Photon and Electron-Phonon Interactions in Black Phosphorus
Ling, Xi; Huang, Shengxi; Hasdeo, Eddwi; Liang, Liangbo; Parkin, William; Tatsumi, Yuki; Nugraha, Ahmad; Puretzky, Alexander A; Das, Paul; Sumpter, Bobby G; et al
2016-03-10
Orthorhombic black phosphorus (BP) and other layered materials, such as gallium telluride (GaTe) and tin selenide (SnSe), stand out among two-dimensional (2D) materials owing to their anisotropic in-plane structure. This anisotropy adds a new dimension to the properties of 2D materials and stimulates the development of angle-resolved photonics and electronics. However, understanding the effect of anisotropy has remained unsatisfactory to-date, as shown by a number of inconsistencies in the recent literatures. We use angle-resolved absorption and Raman spectroscopies to investigate the role of anisotropy on the electron-photon and electron-phonon interactions in BP. We highlight a non-trivial dependence between anisotropies andmore » flake thickness, photon and phonon energies. We show that once understood, the anisotropic optical absorption appears to be a reliable and simple way to identify the crystalline orientation of BP, which cannot be determined from Raman spectroscopy without the explicit consideration of excitation wavelength and flake thickness, as commonly used previously.« less
Status of the Advanced Photon Source (APS) linear accelerator
White, M.; Arnold, N.; Berg, W.; Cours, A.; Fuja, R.; Grelick, A.; Ko, K.; Qian, Y.; Russell, T.; Sereno, N.
1994-09-01
A 2856-MHz S-band, electron-positron linear accelerator (linac) has been constructed at the Advanced Photon Source (APS). It is the source of particles and the injector for the other APS accelerators, and linac commissioning is well underway. The linac is operated 24 hours per day to support linac beam studies and rf conditioning, as well as positron accumulator ring and synchrotron commissioning studies. The design goal for accelerated positron current is 8-mA, and has been met. Maximum positron energy to date is 420-MeV, approaching the design goal of 450-MeV. The linac design and its performance are discussed.
Leuenberger, Michael N; Flatté, Michael E; Awschalom, D D
2005-03-18
We propose a teleportation scheme that relies only on single-photon measurements and Faraday rotation, for teleportation of many-qubit entangled states stored in the electron spins of a quantum dot system. The interaction between a photon and the two electron spins, via Faraday rotation in microcavities, establishes Greenberger-Horne-Zeilinger entanglement in the spin-photon-spin system. The appropriate single-qubit measurements, and the communication of two classical bits, produce teleportation. This scheme provides the essential link between spintronic and photonic quantum information devices by permitting quantum information to be exchanged between them.
Asayama, T.; Fujita, T.; Kiyama, H.; Oiwa, A.; Tarucha, S.
2011-12-23
We propose an experimental scheme of photon-spin quantum interface using a semiconductor double quantum dot. A polarized electron spin is excited by a circularly polarized photon. We detect the spin state applying Pauli spin blockade which is often employed to detect orientation of a single electron spin in double quantum dots.
Teaching Electron--Positron--Photon Interactions with Hands-on Feynman Diagrams
ERIC Educational Resources Information Center
Kontokostas, George; Kalkanis, George
2013-01-01
Feynman diagrams are introduced in many physics textbooks, such as those by Alonso and Finn and Serway, and their use in physics education has been discussed by various authors. They have an appealing simplicity and can give insight into events in the microworld. Yet students often do not understand their significance and often cannot combine the…
Teaching Electron--Positron--Photon Interactions with Hands-on Feynman Diagrams
NASA Astrophysics Data System (ADS)
Kontokostas, George; Kalkanis, George
2013-04-01
Feynman diagrams are introduced in many physics textbooks, such as those by Alonso and Finn 1 and Serway,2 and their use in physics education has been discussed by various authors.3-5 They have an appealing simplicity and can give insight into events in the microworld. Yet students often do not understand their significance and often cannot combine the basic units of interaction—points where the world lines of two fermions and one boson meet—to construct diagrams for observed processes.
Review of two-photon exchange in electron scattering
J. Arrington, P. G. Blunden, W. Melnitchouk
2011-10-01
We review the role of two-photon exchange (TPE) in electron-hadron scattering, focusing in particular on hadronic frameworks suitable for describing the low and moderate Q^2 region relevant to most experimental studies. We discuss the effects of TPE on the extraction of nucleon form factors and their role in the resolution of the proton electric to magnetic form factor ratio puzzle. The implications of TPE on various other observables, including neutron form factors, electroproduction of resonances and pions, and nuclear form factors, are summarized. Measurements seeking to directly identify TPE effects, such as through the angular dependence of polarization measurements, nonlinear epsilon contributions to the cross sections, and via e+p to e-p cross section ratios, are also outlined. In the weak sector, we describe the role of TPE and gamma-Z interference in parity-violating electron scattering, and assess their impact on the extraction of the strange form factors of the nucleon and the weak charge of the proton.
NASA Astrophysics Data System (ADS)
Meyyappan, Meyya
2009-10-01
This year marks the 20th volume of Nanotechnology, the first journal dedicated to the emerging field of nanotechnology, pre-empting the US National Nanotechnology Initiative (NNI) by ten years. Throughout the evolution and revolution of nanomaterials and devices, Nanotechnology has been at the forefront. The journal's first article on nanoelectronics reported research on electronic transport through three- dimensionally confined semiconductor quantum dots by Professor Mark Reed, now Editor-in-Chief, and his colleagues at the time at Texas Instruments in Dallas (Reed M A, Randall J N and Luscombe J H 1990 Nanotechnology 1 63-6). In the first decade of the journal, papers on nanoelectronics were scarce and primarily reported research on resonant tunnelling devices, transport in quantum dots and other III-V devices. With the ability to produce single-walled carbon nanotubes (SWCNTs) and semiconducting nanowires on patterned substrates using CVD and similar techniques, nanoscale electronics and photonics flourished. A pioneering contribution by Collins et al (Collins P G, Bando H and Zettl A 1998 Nanotechnology 9 153-7) discussed conductivity measurements on SWCNTs using scanning tunnelling microscopy. In the same issue, Fritzsche et al (Fritzsche W, Böhm Unger E and Köhler J M 1998 Nanotechnology 9 177-3) discussed making electrical contacts to a single molecule, another early contribution in molecular electronics. There have been numerous interesting and trend-setting articles. My personal favourite is an article from Hewlett-Packard researchers Greg Snider, Phil Kuekes and Stan Williams (2004 Nanotechnology 15 881-91) discussing an approach to building a defect-tolerant computer out of defective configurable FETs and switches. The construction of defect-free materials, devices and components may well begin to pose an obstacle to nanotechnology, so this pioneering article exhibits extraordinary foresight in attempting to construct a useful machine from defective
Electron and positron scattering from CF 3I molecules below 600 eV: a comparison with CF 3H
NASA Astrophysics Data System (ADS)
Kawada, Michihito K.; Sueoka, Osamu; Kimura, Mineo
2000-11-01
The total cross-sections (TCSs) for electron and positron scattering from CF 3I molecules have been studied experimentally. A theoretical analysis based on the continuum multiple-scattering (CMS) method has been performed to understand the origin of resonances and the elastic cross-sections. The present TCS for electron scattering is found to be larger by about 20% than that of T. Underwood-Lemons, D.C. Winkler, J.A. Tossel, J.H. Moore [J. Chem. Phys. 100 (1994) 9117] although the general shape agrees well in the entire energy studied. The difference in the cross-sections for CF 3I and CF 3H is explained by the sizes and the dipole moments of these molecules.
Fan, Q.; Bodek, A. |
1996-12-01
We describe the application of a new methods for the determination of charge and track parameters for electrons and positrons in both central (pseudo-rapidity 0 < |{eta}| < 1.2) and forward (pseudo- rapidity 1.2 < |{eta}| < 2.3) regions at CDF. The method uses the shower centroid position in the calorimeter in combination with a track in the inner silicon vertex detector. The use of the central tracking chamber is not required. A comparison of the shower centroid in the calorimeter, with the extrapolated silicon vertex detector track determines the electron sign. This technique has been used to measure the W asymmetry in CDF in regions beyond the pseudo-rapidity coverage of the central tracking chamber. Application to other Physics analyses in current collider experiments at the Tevatron and in future high luminosity experiments at the LHC are discussed. 5 refs., 5 figs., 1 tab.
Photon-activated electron hopping in a single-electron trap enhanced by Josephson radiation
NASA Astrophysics Data System (ADS)
Lotkhov, S. V.; Jalali-Jafari, B.; Zorin, A. B.
2016-04-01
Using a Josephson junction interferometer (DC SQUID) as a microwave source for irradiating a single-electron trap, both devices fabricated on the same chip, we study the process of photon-assisted tunneling as an effective mechanism of single photon detection. High sensitivity down to a very small oscillation amplitude v J ˜ 10 nV ≪ E act ≲ h f J and down to low photon absorption rates Γph ˜ (1-50) Hz, as well as a clear threshold type of operation with an activation energy Eact ˜ 400 μeV, is demonstrated for the trap with respect to the microwave photons of frequency fJ ˜ (100-200) GHz. Tunable generation is demonstrated with respect to the power and frequency of the microwave signal produced by the SQUID source biased within the subgap voltage range. A much weaker effect is observed at the higher junction voltages along the quasiparticle branch of the I-V curve; this response mostly appears due to the recombination phonons.
Positron lifetime spectrometer using a DC positron beam
Xu, Jun; Moxom, Jeremy
2003-10-21
An entrance grid is positioned in the incident beam path of a DC beam positron lifetime spectrometer. The electrical potential difference between the sample and the entrance grid provides simultaneous acceleration of both the primary positrons and the secondary electrons. The result is a reduction in the time spread induced by the energy distribution of the secondary electrons. In addition, the sample, sample holder, entrance grid, and entrance face of the multichannel plate electron detector assembly are made parallel to each other, and are arranged at a tilt angle to the axis of the positron beam to effectively separate the path of the secondary electrons from the path of the incident positrons.
Guo, Jinghua
2008-09-22
The applications of resonant soft X-ray emission spectroscopy on a variety of carbon systems have yielded characteristic fingerprints. With high-resolution monochromatized synchrotron radiation excitation, resonant inelastic X-ray scattering has emerged as a new source of information about electronic structure and excitation dynamics. Photon-in/photon-out soft-X-ray spectroscopy is used to study the electronic properties of fundamental materials, nanostructure, and complex hydrides and will offer potential in-depth understanding of chemisorption and/or physisorption mechanisms of hydrogen adsorption/desorption capacity and kinetics.
NASA Astrophysics Data System (ADS)
Simhony, Menahem
2003-04-01
Scientists would not believe that the appearance and disappearance of rabbits in a magic box means their creation and annihilation by energy signals. However the belief in MEE made the results of the Anderson Experiment (1932) be accepted as creation and annihilation of particles out of and into energy, though never since was there a single electron created or annihilated in empy space, even now with muli TeV energies, and though phenomena obtain simple physical explanations as due to the epola structure of space,1, while the MEE fails. E.g., MEE yields the 2.82 fm value for the "classical electron radius" while scattering of fast electron beams proves (since the 1980's) that the electron radius must be below 0.1fm, and the value obtained then in the epola model is 0.094fm. Thus the density of matter in the electron is 3 10^17 kg/m^3, as in all stable nuclear particles known on earth. Another crush of MEE is the physically impossible direct transfer of kinetic energy from a several eV photon to a free electron of 511,000 eV MEE, as in Einstein's 1905 interpretation of the photo-electric effect. The solution is that the acting particle is an epola electron or positron that momentarily carries the photon energy and is thus able to transfer it to a nuclear particle of comparable mass. See:1.M.Simhony, Invitation to the Natural Physics of Matter, Space, and Radiation, World Scientific, 1994, ISBN 981-02-1649-1. Website: www.word1.co.il/physics
NASA Astrophysics Data System (ADS)
Vos, Etienne; Boezio, Mirko; Di Felice, Valeria; Potgieter, Marius; Munini, Riccardo
2016-07-01
Over the course of the recent solar minimum of cycle 23/24, the PAMELA mission measured simultaneous electron and positron intensities over the energy range of interest to heliospheric modulation. Drift theory predicts that for an A < 0 cycle, such as during the recent minimum of cycle 23/24, positively charged cosmic rays (CRs) will drift toward Earth mostly along the wavy heliospheric current sheet (HCS), while negatively charged CRs drift inwards mainly over the heliospheric polar regions. During such polarity cycles, electrons elude the full impact that the wavy HCS has on CR modulation. This results in electrons experiencing notably less modulation compared to protons (of the same rigidity) or positrons over the same time period; a phenomenon known as charge-sign dependent modulation. For this study, a 3D modulation model is applied to simultaneous electron, positron and proton measurements from PAMELA by reproducing the energy spectra of these CR particles at different times throughout the recent solar minimum. Since electrons and positrons undergo identical diffusion, simultaneous measurements of these CRs enable us to determine reasonably accurate diffusion coefficients as well as to study and reproduce the effects of drifts using a model that includes all the relevant modulation processes. With the availability of Voyager 1 measurements from beyond the heliopause, it has also become possible to determine the shape of the electron very local interstellar spectrum more accurately.
NASA Astrophysics Data System (ADS)
Petrovic, Zoran; Marjanovic, Srdjan
2015-05-01
The only existing explanation of the rotating wall positron trap operating in the low space charge limit (swarm) [ref] is based on momentum transfer collisions to represent the collisions of positrons in gas and to facilitate the effective narrowing of the profile and heating/cooling succession. The collisions are represented through a viscous term of a simple transport equation. In that model effective viscosity term is used to fit the observed data with no attention paid to the magnitude of the term compared to the measured or theoretically predicted values. We apply a well tested Monte Carlo technique whereby all interactions may be described by exact experimental or theoretical cross sections. We separate effects due to inelastic processes with small and large energy losses (i.e. on vibrational or rotational excitation versus electronic excitation). It turns out that large energy loss processes are essential in narrowing the profile but also that low energy loss processes define thermalization to the room temperature or lower and allow cooling of the ensemble. Heating was necessary to allow narrowing of the profile but the particles have to return to the thermal equilibrium with low fields.