Science.gov

Sample records for large electron positron

  1. 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,

  2. 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.

  3. A new measurement of cosmic-ray electrons and positrons with the Large Area Telescope

    NASA Astrophysics Data System (ADS)

    Manfreda, Alberto; Fermi-LAT Collaboration

    2017-01-01

    We present an updated measurement of the cosmic-ray electron and positron spectrum between 7 GeV and 2 TeV, based on 7 years of data collected with the Fermi Large Area Telescope (LAT). The LAT is the first space-based instrument to directly explore the region above 1 TeV. At such high energies, the shape of the spectrum can provide useful information about the origin and propagation of cosmic-ray electrons in the nearby Galactic space. The best fit to the spectrum that we measure is given by a broken power-law, with the break located at 53 +/-8 GeV. Such break, however, is not significant when all the systematic uncertainties are taken into account. Above 50 GeV our data are well described by a single power law with a spectral index of 3.07 +/- 0.02 (stat + syst) +/- 0.06 (energy scale). An exponential cut-off lower than 1.7 TeV is excluded at 95% CL.

  4. Search for Cosmic-Ray Electron and Positron Anisotropies with Seven Years of Fermi Large Area Telescope Data.

    PubMed

    Abdollahi, S; Ackermann, M; Ajello, M; Albert, A; Atwood, W B; Baldini, L; Barbiellini, G; Bellazzini, R; Bissaldi, E; Bloom, E D; Bonino, R; Bottacini, E; Brandt, T J; Bruel, P; Buson, S; Caragiulo, M; Cavazzuti, E; Chekhtman, A; Ciprini, S; Costanza, F; Cuoco, A; Cutini, S; D'Ammando, F; de Palma, F; Desiante, R; Digel, S W; Di Lalla, N; Di Mauro, M; Di Venere, L; Donaggio, B; Drell, P S; Favuzzi, C; Focke, W B; Fukazawa, Y; Funk, S; Fusco, P; Gargano, F; Gasparrini, D; Giglietto, N; Giordano, F; Giroletti, M; Green, D; Guiriec, S; Harding, A K; Jogler, T; Jóhannesson, G; Kamae, T; Kuss, M; Larsson, S; Latronico, L; Li, J; Longo, F; Loparco, F; Lubrano, P; Magill, J D; Malyshev, D; Manfreda, A; Mazziotta, M N; Meehan, M; Michelson, P F; Mitthumsiri, W; Mizuno, T; Moiseev, A A; Monzani, M E; Morselli, A; Negro, M; Nuss, E; Ohsugi, T; Omodei, N; Paneque, D; Perkins, J S; Pesce-Rollins, M; Piron, F; Pivato, G; Principe, G; Rainò, S; Rando, R; Razzano, M; Reimer, A; Reimer, O; Sgrò, C; Simone, D; Siskind, E J; Spada, F; Spandre, G; Spinelli, P; Strong, A W; Tajima, H; Thayer, J B; Torres, D F; Troja, E; Vandenbroucke, J; Zaharijas, G; Zimmer, S

    2017-03-03

    The Large Area Telescope on board the Fermi Gamma-ray Space Telescope has collected the largest ever sample of high-energy cosmic-ray electron and positron events since the beginning of its operation. Potential anisotropies in the arrival directions of cosmic-ray electrons or positrons could be a signature of the presence of nearby sources. We use almost seven years of data with energies above 42 GeV processed with the Pass 8 reconstruction. The present data sample can probe dipole anisotropies down to a level of 10^{-3}. We take into account systematic effects that could mimic true anisotropies at this level. We present a detailed study of the event selection optimization of the cosmic-ray electrons and positrons to be used for anisotropy searches. Since no significant anisotropies have been detected on any angular scale, we present upper limits on the dipole anisotropy. The present constraints are among the strongest to date probing the presence of nearby young and middle-aged sources.

  5. Search for Cosmic-Ray Electron and Positron Anisotropies with Seven Years of Fermi Large Area Telescope Data

    NASA Astrophysics Data System (ADS)

    Abdollahi, S.; Ackermann, M.; Ajello, M.; Albert, A.; Atwood, W. B.; Baldini, L.; Barbiellini, G.; Bellazzini, R.; Bissaldi, E.; Bloom, E. D.; Bonino, R.; Bottacini, E.; Brandt, T. J.; Bruel, P.; Buson, S.; Caragiulo, M.; Cavazzuti, E.; Chekhtman, A.; Ciprini, S.; Costanza, F.; Cuoco, A.; Cutini, S.; D'Ammando, F.; de Palma, F.; Desiante, R.; Digel, S. W.; Di Lalla, N.; Di Mauro, M.; Di Venere, L.; Donaggio, B.; Drell, P. S.; Favuzzi, C.; Focke, W. B.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Giglietto, N.; Giordano, F.; Giroletti, M.; Green, D.; Guiriec, S.; Harding, A. K.; Jogler, T.; Jóhannesson, G.; Kamae, T.; Kuss, M.; Larsson, S.; Latronico, L.; Li, J.; Longo, F.; Loparco, F.; Lubrano, P.; Magill, J. D.; Malyshev, D.; Manfreda, A.; Mazziotta, M. N.; Meehan, M.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Moiseev, A. A.; Monzani, M. E.; Morselli, A.; Negro, M.; Nuss, E.; Ohsugi, T.; Omodei, N.; Paneque, D.; Perkins, J. S.; Pesce-Rollins, M.; Piron, F.; Pivato, G.; Principe, G.; Rainò, S.; Rando, R.; Razzano, M.; Reimer, A.; Reimer, O.; Sgrò, C.; Simone, D.; Siskind, E. J.; Spada, F.; Spandre, G.; Spinelli, P.; Strong, A. W.; Tajima, H.; Thayer, J. B.; Torres, D. F.; Troja, E.; Vandenbroucke, J.; Zaharijas, G.; Zimmer, S.; Fermi-LAT Collaboration

    2017-03-01

    The Large Area Telescope on board the Fermi Gamma-ray Space Telescope has collected the largest ever sample of high-energy cosmic-ray electron and positron events since the beginning of its operation. Potential anisotropies in the arrival directions of cosmic-ray electrons or positrons could be a signature of the presence of nearby sources. We use almost seven years of data with energies above 42 GeV processed with the Pass 8 reconstruction. The present data sample can probe dipole anisotropies down to a level of 10-3 . We take into account systematic effects that could mimic true anisotropies at this level. We present a detailed study of the event selection optimization of the cosmic-ray electrons and positrons to be used for anisotropy searches. Since no significant anisotropies have been detected on any angular scale, we present upper limits on the dipole anisotropy. The present constraints are among the strongest to date probing the presence of nearby young and middle-aged sources.

  6. Effects of ion-temperature on propagation of the large-amplitude ion-acoustic solitons in degenerate electron-positron-ion plasmas

    SciTech Connect

    Akbari-Moghanjoughi, M.

    2010-08-15

    Large-amplitude ion-acoustic solitary wave (IASW) propagation and matching criteria of existence of such waves are investigated in a degenerate dense electron-positron-ion plasma considering the ion-temperature as well as electron/positron degeneracy effects. It is shown that the ion-temperature effects play an important role in the existence criteria and allowed Mach-number range in such plasmas. Furthermore, a fundamental difference is remarked in the existence of supersonic IASW propagations between degenerate plasmas with nonrelativistic and ultrarelativistic electrons and positrons. Current study may be helpful in astrophysical as well as the laboratory inertial confinement fusion-research.

  7. Alternative positron-target design for electron-positron colliders

    SciTech Connect

    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.

  8. Positron annihilation induced Auger electron spectroscopy

    NASA Technical Reports Server (NTRS)

    Weiss, Alex; Koymen, A. R.; Mehl, David; Jensen, K. O.; Lei, Chun; Lee, K. H.

    1990-01-01

    Recently, Weiss et al. have demonstrated that it is possible to excite Auger transitions by annihilating core electrons using a low energy (less than 30eV) beam of positrons. This mechanism makes possible a new electron spectroscopy, Positron annihilation induced Auger Electron Spectroscopy (PAES). The probability of exciting an Auger transition is proportional to the overlap of the positron wavefunction with atomic core levels. Since the Auger electron energy provides a signature of the atomic species making the transition, PAES makes it possible to determine the overlap of the positron wavefunction with a particular element. PAES may therefore provide a means of detecting positron-atom complexes. Measurements of PAES intensities from clean and adsorbate covered Cu surfaces are presented which indicate that approx. 5 percent of positrons injected into CU at 25eV produce core annihilations that result in Auger transitions.

  9. 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.

  10. 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.

  11. Positron annihilation induced Auger electron emission

    SciTech Connect

    Weiss, A.; Jibaly, M.; Lei, Chun; Mehl, D.; Mayer, R.; Lynn, K.G.

    1988-01-01

    We report on measurements of Auger electron emission from Cu and Fe due to core hole excitations produced by the removal of core electrons by matter-antimatter annihilation. Estimates are developed of the probability of positrons annihilating with a 3p electron in these materials. Several important advantages of Positron annihilation induced Auger Electron Spectroscopy (PAES) for surface analysis are suggested. 10 refs., 2 figs.

  12. Nonplanar positron-acoustic Gardner solitary waves in electron-positron-ion plasmas with superthermal electrons and positrons

    NASA Astrophysics Data System (ADS)

    Uddin, M. J.; Alam, M. S.; Mamun, A. A.

    2015-02-01

    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.

  13. Nonplanar positron-acoustic Gardner solitary waves in electron-positron-ion plasmas with superthermal electrons and positrons

    SciTech Connect

    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.

  14. Electron capture from solids by positrons

    SciTech Connect

    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.

  15. Positron source position sensing detector and electronics

    DOEpatents

    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.

  16. Positron-acoustic shock waves associated with cold viscous positron fluid in superthermal electron-positron-ion plasmas

    SciTech Connect

    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.

  17. 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.

  18. Propagation of solitary waves in relativistic electron-positron-ion plasmas with kappa distributed electrons and positrons

    SciTech Connect

    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.

  19. The Clic Electron and Positron Polarized Sources

    NASA Astrophysics Data System (ADS)

    Rinolfi, L.

    2011-01-01

    The CLIC polarized electron source is based on a DC gun where the photocathode is illuminated by a laser beam. Each micro-bunch has a charge of 6 × 109 e-, a width of 100 ps and a repetition rate of 2 GHz. A peak current of 10 A in the micro-bunch is a challenge for the surface charge limit of the photo-cathode. Two options are feasible to generate the 2 GHz e- bunch train: 100 ps micro-bunches can be extracted from the photo-cathode either by a 2 GHz laser system or by generating a macro-bunch using a ~200 ns laser pulse and a subsequent RF bunching system to produce the appropriate micro-bunch structure. Recent results obtained by SLAC, for the latter case, are presented. The polarized positron source is based on a positron production scheme in which polarized photons are produced by a laser Compton scattering process. The resulting circularly-polarized gamma photons are sent onto a target, producing pairs of longitudinally polarized electrons and positrons. The Compton backscattering process occurs either in a Compton ring, where a 1 GeV electron beam interacts with circularly-polarized photons in an optical resonator or in a 1.8 GeV Compton Energy Recovery Linac (ERL) or in a 6 GeV Linac with several optical cavities. The undulator scheme is also studied. The nominal CLIC e+ bunch population is 6.7 × 109 particles per bunch at 200 MeV. The tradeoff between e+ yield and level of polarization is an important topic. The overall scheme for both polarized electron and positron beams is described.

  20. New generation electron-positron factories

    NASA Astrophysics Data System (ADS)

    Zobov, Mikhail

    2011-09-01

    In 2010 we celebrate 50 years since commissioning of the first particle storage ring ADA in Frascati (Italy) that also became the first electron-positron collider in 1964. After that date the particle colliders have increased their intensity, luminosity and energy by several orders of magnitude. Namely, because of the high stored beam currents and high rate of useful physics events (luminosity) the modern electron-positron colliders are called "factories". However, the fundamental physics has required luminosities by 1-2 orders of magnitudes higher with respect to those presently achieved. This task can be accomplished by designing a new generation of factories exploiting the potential of a new collision scheme based on the Crab Waist (CW) collision concept recently proposed and successfully tested at Frascati. In this paper we discuss the performance and limitations of the present generation electron-positron factories and give a brief overview of new ideas and collision schemes proposed for further collider luminosity increase. In more detail we describe the CW collision concept and the results of the crab waist collision tests in DAϕNE, the Italian ϕ-factory. Finally, we briefly describe most advanced projects of the next generation factories based on the CW concept: SuperB in Italy, SuperKEKB in Japan and SuperC-Tau in Russia.

  1. The impact of positrons beam on the propagation of super freak waves in electron-positron-ion plasmas

    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.

  2. 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.

  3. Positron annihilation lifetime spectroscopy at a superconducting electron accelerator

    NASA Astrophysics Data System (ADS)

    Wagner, A.; Anwand, W.; Attallah, A. G.; Dornberg, G.; Elsayed, M.; Enke, D.; Hussein, A. E. M.; Krause-Rehberg, R.; Liedke, M. O.; Potzger, K.; Trinh, T. T.

    2017-01-01

    The Helmholtz-Zentrum Dresden-Rossendorf operates a superconducting linear accelerator for electrons with energies up to 35 MeV and average beam currents up to 1.6 mA. The electron beam is employed for production of several secondary beams including X-rays from bremsstrahlung production, neutrons, and positrons. The secondary positron beam after moderation feeds the Monoenergetic Positron Source (MePS) where positron annihilation lifetime (PALS) and positron annihilation Doppler-broadening experiments in materials science are performed in parallel. The adjustable repetition rate of the continuous-wave electron beams allows matching of the pulse separation to the positron lifetime in the sample under study. The energy of the positron beam can be set between 0.5 keV and 20 keV to perform depth resolved defect spectroscopy and porosity studies especially for thin films.

  4. Electron-Positron Flows around Magnetars

    NASA Astrophysics Data System (ADS)

    Beloborodov, Andrei M.

    2013-11-01

    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 ± 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.

  5. ELECTRON-POSITRON FLOWS AROUND MAGNETARS

    SciTech Connect

    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.

  6. 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.

  7. Dynamics of the positron acoustic waves in electron-positron-ion magnetoplasmas

    NASA Astrophysics Data System (ADS)

    Ali, Rustam; Saha, Asit; Chatterjee, Prasanta

    2017-01-01

    Dynamics of the positron acoustic waves in electron-positron-ion (e-p-i) magnetoplasmas with κ-distributed hot electrons and positrons is investigated in the frameworks of the Kadomtsev-Petviashili (KP) and modified Kadomtsev-Petviashili (mKP) equations. Employing the reductive perturbation technique, the KP and mKP equations are derived. Using the bifurcation theory of planar dynamical systems, the positron acoustic solitary wave solutions, the kink and anti-kink wave solutions are obtained. Considering an external periodic perturbation in the electron-positron-ion magnetoplasmas, the perturbed KP and mKP equations are studied via some qualitative and quantitative approaches. To corroborate in the fact that the perturbed KP and mKP equations can indeed give rise to the quasiperiodic and chaotic motions, the phase plane plots, time series plots, and the Poincaré section are used. The quasiperiodic and developed chaos can be observed for the perturbed positron acoustic waves. The frequency (ω ) of the external periodic perturbation plays the role of the switching parameter in chaotic motions of the perturbed positron acoustic waves through quasiperiodic route to chaos. This work can be useful to understand the dynamics of nonlinear electromagnetic perturbations in space and laboratory plasmas consisting of κ-distributed hot electrons and positrons.

  8. Electrons and positrons from expanding supernova envelopes in dense clouds

    NASA Technical Reports Server (NTRS)

    Stephens, S. A.

    1985-01-01

    If antiprotons in cosmic rays are produced as secondary particles in sources, it is expected that positrons are also created by the same process. The interstellar spectra of positrons and electrons are calculated by taking into account such sources. Spectra are then compared with observations.

  9. 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.

  10. Nonlinear excitations for the positron acoustic shock waves in dissipative nonextensive electron-positron-ion plasmas

    NASA Astrophysics Data System (ADS)

    Saha, Asit

    2017-03-01

    Positron acoustic shock waves (PASHWs) in unmagnetized electron-positron-ion (e-p-i) plasmas consisting of mobile cold positrons, immobile positive ions, q-nonextensive distributed electrons, and hot positrons are studied. The cold positron kinematic viscosity is considered and the reductive perturbation technique is used to derive the Burgers equation. Applying traveling wave transformation, the Burgers equation is transformed to a one dimensional dynamical system. All possible vector fields corresponding to the dynamical system are presented. We have analyzed the dynamical system with the help of potential energy, which helps to identify the stability and instability of the equilibrium points. 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 PASHWs. Furthermore, fully nonlinear arbitrary amplitude positron acoustic waves are also studied applying the theory of planar dynamical systems. It is also observed that the fundamental features of the small amplitude and arbitrary amplitude PASHWs are significantly affected by the effect of the physical parameters q e , q h , μ e , μ h , σ , η , and U. This work can be useful to understand the qualitative changes in the dynamics of nonlinear small amplitude and fully nonlinear arbitrary amplitude PASHWs in solar wind, ionosphere, lower part of magnetosphere, and auroral acceleration regions.

  11. Preferential positron heating and acceleration by synchrotron maser instabilities in relativistic positron-electron-proton plasmas

    NASA Technical Reports Server (NTRS)

    Hoshino, Masahiro; Arons, Jonathan

    1991-01-01

    A new process of the preferential strong heating of positrons through the ion synchrotron maser instability in positron-electron-proton magnetized plasmas is investigated using particle-in-cell simulations. It is shown that the positrons form a nonthermal power-law-like energy distribution via their gyroresonant interaction with the extraordinary modes emitted by the ions. It is noted that this process may be of significance in connection with the shock excitation of nonthermal synchrotron radiation from astrophysical systems powered by relativistic outflows from compact central objects, e.g., supernova remnants powered by pulsars and jets from active galactic nuclei.

  12. The Calibration of the PEPPo Polarimeter for Electrons and Positrons

    SciTech Connect

    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.

  13. Progress toward positron-electron pair plasma experiments

    SciTech Connect

    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.

  14. Electron positron pair production at RHIC and LHC

    SciTech Connect

    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.

  15. Magnetoacoustic solitons in dense astrophysical electron-positron-ion plasmas

    NASA Astrophysics Data System (ADS)

    Hussain, S.; Mahmood, S.; Mushtaq, A.

    2013-08-01

    Nonlinear magnetoacoustic waves in dense electron-positron-ion plasmas are investigated by using three fluid quantum magnetohydrodynamic model. The quantum mechanical effects of electrons and positrons are taken into account due to their Fermionic nature (to obey Fermi statistics) and quantum diffraction effects (Bohm diffusion term) in the model. The reductive perturbation method is employed to derive the Korteweg-de Vries (KdV) equation for low amplitude magnetoacoustic soliton in dense electron-positron-ion plasmas. It is found that positron concentration has significant impact on the phase velocity of magnetoacoustic wave and on the formation of single pulse nonlinear structure. The numerical results are also illustrated by taking into account the plasma parameters of the outside layers of white dwarfs and neutron stars/pulsars.

  16. PEPPo: Using a Polarized Electron Beam to Produce Polarized Positrons

    SciTech Connect

    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.

  17. Positrons for Antihydrogen with ATRAP: efficient transfer of large positron numbers

    NASA Astrophysics Data System (ADS)

    Storry, Cody; Comeau, Daniel; Dror, Asaf; Fitzakerley, Daniel; George, Matthew; Hessels, Eric; Weel, Matthew

    2012-06-01

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

  18. Dipole configuration for confinement of positrons and electron-positron plasma

    NASA Astrophysics Data System (ADS)

    Stenson, E. V.; Saitoh, H.; Horn-Stanja, J.; Hergenhahn, U.; Paschkowski, N.; Sunn Pedersen, T.; Stoneking, M. R.; Dickmann, M.; Singer, M.; Vohburger, S.; Hugenschmidt, C.; Schweikhard, L.; Danielson, J. R.; Surko, C. M.

    2016-10-01

    Laboratory creation and confinement of electron-positron plasmas, which are expected to exhibit atypical plasma physics characteristics, would enable tests of many theory and simulation predictions (e.g., the stabilization of anomalous transport mechanisms). This is the goal of APEX/PAX (A Positron-Electron eXperiment/Positron Accumulation eXperiment). Following demonstration of efficient (38%) E ×B injection and subsequent confinement (τ = 3-5 ms) of cold positrons in a dipole magnetic field, the system is undergoing upgrades from a supported permanent magnet to a supported HTSC (high-temperature superconductor) coil, then to a levitated HTSC coil suitable for the simultaneous confinement of electrons and positrons. This contribution will report on the design and testing of the new systems and subsystems (e.g., for cooling, excitation, and levitation) and, if available, on results of upcoming experiments using a ``rotating wall'' to generate inward particle flux deeper into the confinement region. on behalf of the APEX/PAX team and collaborators.

  19. Enhanced electron-positron pair production by ultra intense laser irradiating a compound target

    NASA Astrophysics Data System (ADS)

    Liu, Jian-Xun; Ma, Yan-Yun; Yu, Tong-Pu; Zhao, Jun; Yang, Xiao-Hu; Gan, Long-Fei; Zhang, Guo-Bo; Zhao, Yuan; Zhang, Shi-Jie; Liu, Jin-Jin; Zhuo, Hong-Bin; Shao, Fu-Qiu; Kawata, Shigeo

    2016-12-01

    High-energy-density electron-positron pairs play an increasingly important role in many potential applications. Here, we propose a scheme for enhanced positron production by an ultra intense laser irradiating a gas-Al compound target via the multi-photon Breit-Wheeler (BW) process. The laser pulse first ionizes the gas and interacts with a near-critical-density plasma, forming an electron bubble behind the laser pulse. A great deal of electrons are trapped and accelerated in the bubble, while the laser front hole-bores the Al target and deforms its front surface. A part of the laser wave is thus reflected by the inner curved target surface and collides with the accelerated electron bunch. Finally, a large number of γ photons are emitted in the forward direction via the Compton back-scattering process and the BW process is initiated. Dense electron-positron pairs are produced with a maximum density of 6.02× {{10}27} m-3. Simulation results show that the positron generation is greatly enhanced in the compound target, where the positron yield is two orders of magnitude greater than that in only the solid slab case. The influences of the laser intensity, gas density and length on the positron beam quality are also discussed, which demonstrates the feasibility of the scheme in practice.

  20. Electron- and positron-proton elastic scattering in CLAS

    SciTech Connect

    Weinstein, L. B.

    2009-09-02

    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.

  1. Electron- and positron-proton elastic scattering in CLAS

    SciTech Connect

    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.

  2. Interpretation of AMS-02 electrons and positrons data

    SciTech Connect

    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.

  3. Dynamic behavior of ion acoustic waves in electron-positron-ion magnetoplasmas with superthermal electrons and positrons

    SciTech Connect

    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.

  4. Radiation damping induced electron trapping and positron creation

    NASA Astrophysics Data System (ADS)

    Gu, Yanjun; Klimo, Ondrej; Weber, Stefan; Korn, Georg

    2016-10-01

    High power laser facilities with intensities up to 1022 W /cm2 have been realized and the forthcoming installations are expected to reach 10 22 - 24 W /cm2 or even higher. At these intensities, the radiation effects and quantum electrodynamics description come into play. The emitted photon momentum becomes comparable to the momentum of the emitting electrons. In this work, we propose a regime of electron self-injection and trapping in the ultra-high intensity laser-plasma interaction. The electrons accumulated at the head of the laser pulse are injected into the pulse centre due to the strong longitudinal electrostatic field created by the high density shell. These electrons, which experience a restoring force provided by the emitted photons, can be confined in the laser pulse for a long time. The corresponding photons are produced in the region where the laser field is strong. High energy and well collimated positron bunches are produced. This regime may be beneficial for the potential experiments to be carried out on large laser facilities such as ELI. This work was supported by the project ELI: Extreme Light Infrastructure (CZ.02.1.01/0.0/0.0/15_008/0000162) from European Regional Development.

  5. Positron trapping at vacancies in electron-irradiated Si at low temperatures

    SciTech Connect

    Maekinen, J.; Corbel, C.; Hautojaervi, P.; Moser, P.; Pierre, F.

    1989-05-15

    Experimental results on positron trapping at vacancies in electron-irradiated silicon are presented. The positron lifetimes 273 +- 3 and 248 +- 2 ps in pure Si and heavily-phosphorus-doped Si ((P) = 10/sup 20/ cm/sup -3/) are assigned to a negative monovacancy V/sup -/ and a negative vacancy-phosphorus pair (V-P)/sup -/, respectively. In pure Si, positron trapping displays a strong negative temperature dependence, and the specific trapping rate reaches very large values (10/sup 17//sup --/10/sup 18/ s/sup -1/) at low temperatures. In Si:P the trapping rate is independent of temperature. These different temperature behaviors are attributed to different positron-trapping mechanisms, a cascade of one-phonon transitions in pure Si, and an Auger process in Si:P.

  6. Roles of superthermal electrons and positrons on positron-acoustic solitary waves and double layers in electron-positron-ion plasmas.

    PubMed

    Alam, M S; Uddin, M J; Masud, M M; Mamun, A A

    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.

  7. Arbitrary amplitude Langmuir solitons in a relativistic electron-positron plasma

    NASA Astrophysics Data System (ADS)

    Lazarus, I. J.; Bharuthram, R.; Singh, S. V.; Lakhina, G. S.

    2012-04-01

    The arbitrary amplitude Langmuir solitons are investigated in an unmagnetized, warm, relativistic plasma, consisting of electrons and positrons. Both the species are considered to have equal non-relativistic temperatures, but can have arbitrary relativistic drift speeds, and their dynamics are governed by fluid equations. Using the Sagdeev psuedo-potential approach, the effects of drift speed, Mach number, and thermal temperature on the amplitude and width of the Langmuir solitons are investigated. For the parameters considered, only rarefactive solitons are found. These solitons represent dip in electron density or electron holes in the configuration space. Existence domain of the Langmuir solitons is limited by the minimum and maximum Mach numbers for given parameters. An increase in the electron (positron) temperature leads to an increase in the Langmuir soliton amplitude and their half-widths. On the other hand, increasing the electron (positron) drift speeds results in decreasing soliton amplitudes and their half-widths. For some typical parameters corresponding to the pulsar magnetosphere, namely electron density ~106 cm-3 and electron thermal velocity of one-tenth of the velocity of light, the electric field of the Langmuir solitons can be of the order of (3-24)kV/m. The presence of such large amplitude electrostatic solitary structures may accelerate electrons and positrons and also produce fine structures of (1-5) microseconds in pulsar radio emissions.

  8. Simulation of tail distributions in electron-positron circular colliders

    SciTech Connect

    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.

  9. 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.

  10. Tuning laser produced electron-positron jets for lab-astrophysics experiment

    SciTech Connect

    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.

  11. Production of Highly Polarized Positrons Using Polarized Electrons at MeV Energies

    SciTech Connect

    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. 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.

  12. Monte carlo simulation of positron induced secondary electrons in thin carbon foils

    NASA Astrophysics Data System (ADS)

    Cai, L. H.; Yang, B.; Ling, C. C.; Beling, C. D.; Fung, S.

    2011-01-01

    Emission of secondary electrons induced by the passage of low energy positrons through thin carbon foils was studied by the Monte Carlo method. The positron and electron elastic cross sections were calculated by partial wave analysis. The inelastic positron-valence-electron was described by the energy loss function obtained from dielectric theory. The positron-core-electron interaction was modelled by the Gryzinski's excitation function. Positron transport inside the carbon foil was simulated in detail. Secondary electrons created by positrons and high energy secondary electrons through inelastic interactions were tracked through the foil. The positron transmission coefficient and secondary electron yielded in forward and backward geometry are calculated and dependences on positron energy and carbon foil thickness are discussed.

  13. Inelastic collisions of positrons with one-valence-electron targets

    NASA Technical Reports Server (NTRS)

    Abdel-Raouf, Mohamed Assad

    1990-01-01

    The total elastic and positronium formation cross sections of the inelastic collisions between positrons and various one-valence-electron atoms, (namely hydrogen, lithium, sodium, potassium and rubidium), and one-valence-electron ions, (namely hydrogen-like, lithium-like and alkaline-earth positive ions) are determined using an elaborate modified coupled-static approximation. Special attention is devoted to the behavior of the Ps cross sections at the energy regions lying above the Ps formation thresholds.

  14. Pumping Electron-Positron Pairs from a Well Potential

    PubMed Central

    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

  15. 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.

  16. 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.

  17. Electron and Positron Scattering from C3H6 Isomers

    NASA Astrophysics Data System (ADS)

    Makochekanwa, Casten; Sueoka, Osamu; Kimura, Mineo; Hoshino, Masamitsu; Tanaka, Takahiro; Kitajima, Masashi; Tanaka, Hiroshi

    2004-09-01

    Hydrocarbons play an important role in high temperature plasmas in Tokamak fusion devices in plasma processing and many other fields [1]. In this paper we report experiments for 0.4-1000 eV electron and 0.2-1000 eV positron total cross sections (TCS) measured using a linear time-of-flight apparatus [2], and electron differential cross sections (DCS) for elastic, vibrational and electronic excitations covering the ranges 1.5 to 100 eV and 15 deg to 130 deg, measured using the crossed beam and relative flow method [3]. The continuum multiple scattering (CMS) [4] calculations have also been performed for the theoretical analysis of the observed features in our cross sections. We observe the isomer effect in both electron and positron TCSs and DCSs. The presence of a dipole moment in propene molecules shows up in enhanced forward scattering in DCSs, leading to larger TCSs and integral cross sections compared to cyclopropane at energies less than 20 eV. However, both electron and positron TCSs for these two molecules nearly equal each other above 100 eV, i.e. the molecular size effect. [1] W. L. Moragn, Adv. At. Mol. Opt. Phys. 43, 79 (2000). [2] O. Sueoka, S. Mori and A. Hamada, J. Phys. B 27, 1453 (1994). [3] H. Tanaka, L. Boesten, D. Matsunaga and T. Kudo, J. Phys. B 21, 1255 (1988). [4] M. Kimura and H. Sato, Comments At. Mol. Phys. 26, 333 (1991).

  18. 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.

  19. 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.

  20. Correlations in laser-induced electron-positron pair creation

    SciTech Connect

    Krajewska, K.; Kaminski, J. Z.

    2011-09-15

    Probability rates of electron-positron pair creation in head-on laser-beam-proton collisions are investigated, using an exact treatment of the colliding proton as a finite-mass particle. We observe that the recoil effects become more important when passing from the perturbative multiphoton regime to the nonperturbative above-threshold regime of laser-matter coupling. Thus we concentrate on the latter case. In this regime, our detailed analysis shows that energy supplied by the colliding proton makes the process more effective, and that the electrons and positrons that are created during the collision are more energetic than in the case when the momentum transfer from the proton is neglected. A number of similarities to above-threshold atomic ionization are also illustrated.

  1. Nonlinear Electromagnetic Waves in a Degenerate Electron-Positron Plasma

    NASA Astrophysics Data System (ADS)

    El-Labany, S. K.; El-Taibany, W. F.; El-Samahy, A. E.; Hafez, A. M.; Atteya, A.

    2015-08-01

    Using the reductive perturbation technique (RPT), the nonlinear propagation of magnetosonic solitary waves in an ultracold, degenerate (extremely dense) electron-positron (EP) plasma (containing ultracold, degenerate electron, and positron fluids) is investigated. The set of basic equations is reduced to a Korteweg-de Vries (KdV) equation for the lowest-order perturbed magnetic field and to a KdV type equation for the higher-order perturbed magnetic field. The solutions of these evolution equations are obtained. For better accuracy and searching on new features, the new solutions are analyzed numerically based on compact objects (white dwarf) parameters. It is found that including the higher-order corrections results as a reduction (increment) of the fast (slow) electromagnetic wave amplitude but the wave width is increased in both cases. The ranges where the RPT can describe adequately the total magnetic field including different conditions are discussed.

  2. Langmuir rogue waves in electron-positron plasmas

    SciTech Connect

    Moslem, W. M.

    2011-03-15

    Progress in understanding the nonlinear Langmuir rogue waves which accompany collisionless electron-positron (e-p) plasmas is presented. The nonlinearity of the system results from the nonlinear coupling between small, but finite, amplitude Langmuir waves and quasistationary density perturbations in an e-p plasma. The nonlinear Schroedinger equation is derived for the Langmuir waves' electric field envelope, accounting for small, but finite, amplitude quasistationary plasma slow motion describing the Langmuir waves' ponderomotive force. Numerical calculations reveal that the rogue structures strongly depend on the electron/positron density and temperature, as well as the group velocity of the envelope wave. The present study might be helpful to understand the excitation of nonlinear rogue pulses in astrophysical environments, such as in active galactic nuclei, in pulsar magnetospheres, in neutron stars, etc.

  3. Collisionless Reconnection in an Electron-Positron Plasma

    SciTech Connect

    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.

  4. Polarized positrons and electrons at the linear collider

    NASA Astrophysics Data System (ADS)

    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.; Dreiner, H. K.; Eberl, H.; Ellis, J.; Flöttmann, K.; Fraas, H.; Franco-Sollova, F.; Franke, F.; Freitas, A.; Goodson, J.; Gray, J.; Han, A.; Heinemeyer, S.; Hesselbach, S.; Hirose, T.; Hohenwarter-Sodek, K.; Juste, A.; Kalinowski, J.; Kernreiter, T.; Kittel, O.; Kraml, S.; Langenfeld, U.; Majerotto, W.; Martinez, A.; Martyn, H.-U.; Mikhailichenko, A.; Milstene, C.; Menges, W.; Meyners, N.; Mönig, K.; Moffeit, K.; Moretti, S.; Nachtmann, O.; Nagel, F.; Nakanishi, T.; Nauenberg, U.; Nowak, H.; Omori, T.; Osland, P.; Pankov, A. A.; Paver, N.; Pitthan, R.; Pöschl, R.; Porod, W.; Proulx, J.; Richardson, P.; Riemann, S.; Rindani, S. D.; Rizzo, T. G.; Schälicke, A.; Schüler, P.; Schwanenberger, C.; Scott, D.; Sheppard, J.; Singh, R. K.; Sopczak, A.; Spiesberger, H.; Stahl, A.; Steiner, H.; Wagner, A.; Weber, A. M.; Weiglein, G.; Wilson, G. W.; Woods, M.; Zerwas, P.; Zhang, J.; Zomer, F.

    2008-05-01

    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.

  5. Threshold for Trapping Positrons in the Wake Driven by a Ultra-relativistic Electron Bunch

    SciTech Connect

    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.

  6. Bound-free electron-positron pair production in relativistic heavy-ion collisions

    NASA Astrophysics Data System (ADS)

    Şengül, M. Y.; Güçlü, M. C.; Fritzsche, S.

    2009-10-01

    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.

  7. Acceleration of positrons by a relativistic electron beam in the presence of quantum effects

    SciTech Connect

    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.

  8. Large-dimension configuration-interaction calculations of positron binding to the group-II atoms

    SciTech Connect

    Bromley, M. W. J.; Mitroy, J.

    2006-03-15

    The configuration-interaction (CI) method is applied to the calculation of the structures of a number of positron binding systems, including e{sup +}Be, e{sup +}Mg, e{sup +}Ca, and e{sup +}Sr. These calculations were carried out in orbital spaces containing about 200 electron and 200 positron orbitals up to l=12. Despite the very large dimensions, the binding energy and annihilation rate converge slowly with l, and the final values do contain an appreciable correction obtained by extrapolating the calculation to the l{yields}{infinity} limit. The binding energies were 0.00317 hartree for e{sup +}Be, 0.0170 hartree for e{sup +}Mg, 0.0189 hartree for e{sup +}Ca, and 0.0131 hartree for e{sup +}Sr.

  9. 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.

  10. Electron-positron pair equilibrium in strongly magnetized plasmas

    SciTech Connect

    Harding, A.K.

    1984-11-01

    Steady states of thermal electron-positron pair plasmas at mildly relativistic temperatures and in strong magnetic fields are investigated. The pair density in steady-state equilibrium, where pair production balances annihilation, is found as a function of temperature, magnetic field strength and source size, by a numerical calculation which includes pair production attenuation and Compton scattering of the photons. It is found that there is a maximum pair density for each value of temperature and field strength, and also a source size above which optically thin equilibrium states do not exist. (ESA)

  11. Optical distortions in electron/positron storage rings

    SciTech Connect

    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.

  12. Current Issues in Electron and Positron Transport Theory

    NASA Astrophysics Data System (ADS)

    Robson, Robert

    2007-10-01

    In this paper we review the current status of transport theory for low energy electrons or positrons in gases, in the context of both kinetic theory and fluid modelling. In particular, we focus on the following issues: (i) Muliterm vs two-term representation of the velocity distribution function in solution of Boltzmann's equation; (ii) the effect of non-conservative collisions (attachment, ionization, positron annihilation) on transport properties; (iii) the enduring electron- hydrogen vibrational cross section controversy and possible implications for the Boltzmann equation itself; (iv) closure of the fluid equations and the heat flux ansatz; and (v) correct use of swarm transport coefficients in fluid modelling of low temperature plasmas. Both hydrodynamic and non-hydrodynamic examples will be given, with attention focussed on the Franck-Hertz experiment, particularly the ``window'' of fields in which oscillations of transport properties are produced, and the way in which electric and magnetic fields combine to affect transport properties. In collaboration with co-authors Z. LJ. Petrovi'c, Institute of Physics Belgrade, and R.D. White, James Cook University.

  13. 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.

  14. DEPFET detectors for future electron-positron colliders

    NASA Astrophysics Data System (ADS)

    Marinas, C.

    2015-11-01

    The DEPFET Collaboration develops highly granular, ultra-thin pixel detectors for outstanding vertex reconstruction at future electron-positron collider experiments. A DEPFET sensor, by the integration of a field effect transistor on a fully depleted silicon bulk, provides simultaneous position sensitive detector capabilities and in pixel amplification. The characterization of the latest DEPFET prototypes has proven that a adequate signal-to-noise ratio and excellent single point resolution can be achieved for a sensor thickness of 50 micrometers. The close to final auxiliary ASICs have been produced and found to operate a DEPFET pixel detector of the latest generation with the required read-out speed. A complete detector concept is being developed for the Belle II experiment at the new Japanese super flavor factory. DEPFET is not only the technology of choice for the Belle II vertex detector, but also a prime candidate for the ILC. Therefore, in this contribution, the status of DEPFET R&D project is reviewed in the light of the requirements of the vertex detector at a future electron-positron collider.

  15. The effect of direct electron-positron pair production on relativistic feedback rates

    NASA Astrophysics Data System (ADS)

    Vodopiyanov, I. B.; Dwyer, J. R.; Cramer, E. S.; Lucia, R. J.; Rassoul, H. K.

    2015-01-01

    Runaway electron avalanches developing in thunderclouds in high electric field become self-sustaining due to relativistic feedback via the production of backward propagating positrons and backscattered X-rays. To date, only positrons created from pair production by gamma rays interacting with the air have been considered. In contrast, direct electron-positron pair production, also known as "trident process," occurs from the interaction of energetic runaway electrons with atomic nuclei, and so it does not require the generation of a gamma ray mediator. The positrons produced in this process contribute to relativistic feedback and become especially important when the feedback factor value approaches unity. Then the steady state flux of runaway electrons increases significantly. In certain cases, when the strong electrostatic field forms in a narrow area, the direct positrons become one of processes dominating relativistic feedback. Calculations of the direct positron production contribution to relativistic feedback are presented for different electric field configurations.

  16. Studies Of Oxidation And Thermal Reduction Of The Cu(100) Surface Using Positron Annihilation Induced Auger Electron Spectroscopy

    SciTech Connect

    Fazleev, N. G.; Nadesalingam, M. P.; Maddox, W.; Weiss, A. H.

    2011-06-01

    Positron annihilation induced Auger electron spectroscopy (PAES) measurements from the surface of an oxidized Cu(100) single crystal show a large increase in the intensity of the annihilation induced Cu M2,3VV Auger peak as the sample is subjected to a series of isochronal anneals in vacuum up to annealing temperature 300 deg. C. The PAES intensity then decreases monotonically as the annealing temperature is increased to {approx}550 deg. C. Experimental positron annihilation probabilities with Cu 3p and O 1s core electrons are estimated from the measured intensities of the positron annihilation induced Cu M{sub 2,3}VV and O KLL Auger transitions. PAES results are analyzed by performing calculations of positron surface states and annihilation probabilities of the surface-trapped positrons with relevant core electrons taking into account the charge redistribution at the surface and various surface structures associated with low and high oxygen coverages. The variations in atomic structure and chemical composition of the topmost layers of the oxidized Cu(100) surface are found to affect localization and spatial extent of the positron surface state wave function. The computed positron binding energy and annihilation characteristics reveal their sensitivity to charge transfer effects, atomic structure and chemical composition of the topmost layers of the oxidized Cu(100) surface. Theoretical positron annihilation probabilities with Cu 3p and O 1s core electrons computed for the oxidized Cu(100) surface are compared with experimental ones. The obtained results provide a demonstration of thermal reduction of the copper oxide surface after annealing at 300 deg. C followed by re-oxidation of the Cu(100) surface at higher annealing temperatures presumably due to diffusion of subsurface oxygen to the surface.

  17. The Effects of Surface Reconstruction and Electron-Positron Correlation on the Annihilation Characteristics of Positrons Trapped at Semiconductor Surfaces

    SciTech Connect

    Fazleev, N. G.; Jung, E.; Weiss, A. H.

    2009-03-10

    Experimental positron annihilation induced Auger electron spectroscopy (PAES) data from Ge(100) and Ge(111) surfaces display several strong Auger peaks corresponding to M{sub 4,5}N{sub 1}N{sub 2,3}, M{sub 2,3}M{sub 4,5}M{sub 4,5}, M{sub 2,3}M{sub 4,5}V, and M{sub 1}M{sub 4,5}M{sub 4,5} Auger transitions. The integrated peak intensities of Auger transitions have been used to obtain experimental annihilation probabilities for the Ge 3d and 3p core electrons. The experimental data were analyzed by performing theoretical studies of the effects of surface reconstructions and electron-positron correlations on image potential induced surface states and annihilation characteristics of positrons trapped at the reconstructed Ge(100) and Ge(111) surfaces. Calculations of positron surface states and annihilation characteristics have been performed for Ge(100) surface with (2x1), (2x2), and (4x2) reconstructions, and for Ge(111) surface with c(2x8) reconstruction. Estimates of the positron binding energy and annihilation characteristics reveal their sensitivity to the specific atomic structure of the topmost layers of the semiconductor and to the approximations used to describe electron-positron correlations. The results of these theoretical studies are compared with the ones obtained for the reconstructed Si(100)-(2x1) and Si(111)-(7x7) surfaces.

  18. Future directions in high energy electron-positron experimentation

    SciTech Connect

    Trilling, G.H.

    1988-09-01

    In this report, the possibilities of studying particle physics at the TeV scale with high energy electron-positron linear colliders are discussed. A status report on the SLC and the MARK II program is given to provide some insights on the feasibility of experiments at linear colliders. The technical issues in going from SLC to the development of TeV colliders are briefly discussed. Some of the elements of the e/sup +/e/sup -/ experimental environment which differentiate it from that in hadron colliders and give examples of processes particularly well suited to attack by e/sup +/e/sup -/ annihilation are summarized. Finally, some concluding remarks are given. 8 refs., 10 figs., 2 tabs.

  19. 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.

  20. Solitary and shock waves in magnetized electron-positron plasma

    SciTech Connect

    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.

  1. Langmuir oscillations in a nonthermal nonextensive electron-positron plasma

    NASA Astrophysics Data System (ADS)

    El-Taibany, W. F.; Zedan, N. A.

    2017-02-01

    The high-frequency Langmuir-type oscillations in a pure pair plasma are studied using Vlasov-Poisson's equations in the presence of hybrid nonthermal nonextensive distributed species. The characteristics of the Langmuir oscillations, Landau damping, and growing unstable modes in a nonthermal nonextensive electron-positron (EP) plasma are remarkably modified. It is found that the phase velocity of the Langmuir waves increases by decreasing (increasing) the value of nonextensive (nonthermal) parameter, q ( α). In particular, depending on the degree of nonthermality and nonextensivity, both damping and growing oscillations are predicted in the proposed EP plasma. It is seen that the Langmuir waves suffer from Landau damping in two different q regions. Furthermore, the mechanism that leads to unstable modes is established in the context of the nonthermal nonextensive formalism, yet the damping mechanism is the same developed by Landau. The present study is useful in the regions where such mixed distributions in space or laboratory plasmas exist.

  2. New fast beam profile monitor for electron-positron colliders

    SciTech Connect

    Bogomyagkov, A. V.; Gurko, V. F.; Zhuravlev, A. N.; Zubarev, P. V.; Kiselev, V. A.; Meshkov, O. I.; Muchnoi, N. Yu.; Selivanov, A. N.; Smaluk, V. V.; Khilchenko, A. D.

    2007-04-15

    A new fast beam profile monitor has been developed at the Budker Institute of Nuclear Physics. This monitor is based on the Hamamatsu multianode photomultiplier with 16 anode strips and provides turn-by-turn measurement of the transverse beam profile. The device is equipped with an internal memory, which has enough capacity to store 131 072 samples of the beam profile. The dynamic range of the beam profile monitor allows us to study turn-by-turn beam dynamics within the bunch charge range from 1 pC up to 10 nC. Using this instrument, we have investigated at the VEPP-4M electron-positron collider a number of beam dynamics effects which cannot be observed by other beam diagnostics tools.

  3. Oblique propagation of electrostatic waves in a magnetized electron-positron-ion plasma with superthermal electrons

    SciTech Connect

    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.

  4. Acoustic solitons in a magnetized quantum electron-positron-ion plasma with relativistic degenerate electrons and positrons pressure

    NASA Astrophysics Data System (ADS)

    Abdikian, A.; Mahmood, S.

    2016-12-01

    The obliquely nonlinear acoustic solitary propagation in a relativistically quantum magnetized electron-positron (e-p) plasma in the presence of the external magnetic field as well as the stationary ions for neutralizing the plasma background was studied. By considering the dynamic of the fluid e-p quantum and by using the quantum hydrodynamics model and the standard reductive perturbation technique, the Zakharov-Kuznetsov (ZK) equation is derived for small but finite amplitude waves and the solitary wave solution for the parameters relevant to dense astrophysical objects such as white dwarf stars is obtained. The numerical results show that the relativistic effects lead to propagate the electrostatic bell shape structures in quantum e-p plasmas like those in classical pair-ion or pair species for relativistic plasmas. It is also observed that by increasing the relativistic effects, the amplitude and width of the e-p acoustic solitary wave will decrease. In addition, the wave amplitude increases as positron density decreases in magnetized e-p plasmas. It is indicated that by increasing the strength of the magnetic field, the width of the soliton reduces and it becomes sharper. At the end, we have analytically and numerically shown that the pulse soliton solution of the ZK equation is unstable and have traced the dependence of the instability growth rate on electron density. It is found that by considering the relativistic pressure, the instability of the soliton pulse can be reduced. The results can be useful to study the obliquely nonlinear propagation of small amplitude localized structures in magnetized quantum e-p plasmas and be applicable to understand the particle and energy transport mechanism in compact stars such as white dwarfs, where the effects of relativistic electron degeneracy become important.

  5. High energy electrons, positrons and photonuclear reactions in petawatt laser-solid experiments

    SciTech Connect

    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.

  6. Ion acoustic solitons in dense magnetized plasmas with nonrelativistic and ultrarelativistic degenerate electrons and positrons

    SciTech Connect

    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.

  7. The VEPP-2000 electron-positron collider: First experiments

    SciTech Connect

    Berkaev, D. E. Shwartz, D. B.; Shatunov, P. Yu.; Rogovskii, Yu. A.; Romanov, A. L.; Koop, I. A.; Shatunov, Yu. M.; Zemlyanskii, I. M.; Lysenko, A. P.; Perevedentsev, E. A.; Stankevich, A. S.; Senchenko, A. I.; Khazin, B. I.; Anisenkov, A. V.; Gayazov, S. E.; Kozyrev, A. N.; Ryzhenenkov, A. E.; Shemyakin, D. N.; Epshtein, L. B.; Serednyakov, S. I.; and others

    2011-08-15

    In 2007, at the Institute of Nuclear Physics (Novosibirsk), the construction of the VEPP-2000 electron-positron collider was completed. The first electron beam was injected into the accelerator structure with turned-off solenoids of the final focus. This mode was used to tune all subsystems of the facility and to train the vacuum chamber using synchrotron radiation at electron currents of up to 150 mA. The VEPP-2000 structure with small beta functions and partially turned-on solenoids was used for the first testing of the 'round beams' scheme at an energy of 508 MeV. Beam-beam effects were studied in strong-weak and strong-strong modes. Measurements of the beam sizes in both cases showed a dependence corresponding to model predictions for round colliding beams. Using a modernized SND (spherical neutral detector), the first energy calibration of the VEPP-2000 collider was performed by measuring the excitation curve of the phimeson resonance; the phi-meson mass is known with high accuracy from previous experiments at VEEP-2M. In October 2009, a KMD-3 (cryogenic magnetic detector) was installed at the VEPP-2000 facility, and the physics program with both the SND and LMD-3 particle detectors was started in the energy range of 1-1.9 GeV. This first experimental season was completed in summer 2010 with precision energy calibration by resonant depolarization.

  8. Positron annihilation study for cadmium (electronic structure and enhancement effect)

    NASA Astrophysics Data System (ADS)

    Hamid, A.

    2003-12-01

    The three dimensional electron density in momentum space ρ(p) and in wave vector space n(k) was reconstructed for cadmium (Cd). The measurements were performed using the two dimensional angular correlation of annihilation radiation (2D-ACAR) technique. Enhanced contributions in the spectra were observed around 5.5 mrad, discussed in terms of a Kahana-like enhancement effect. From another viewpoint, Fermi radii were analyzed in the (λM K), (ALM) and (AHK) planes, and they showed a maximum deviation of about 4% from the free electron Fermi radius. Moreover, comparisons to a radio-frequency size effect (RFSE) experiment and theoretical band structure calculations (using augmented plane wave (APW), linear combination of atomic orbital (LCAO) and linear muffin tin orbital (LMTO) methods) were examined. The results showed a qualitative agreement with both APW and LCAO calculations. However, a favorable agreement with the APW method was determined via Fermi surface dimensions. The differences of bands' occupation of n(k) between the current work and the APW method were argued in view of positron wave function in Cd.

  9. Beam-Beam Study on the Upgrade of Beijing Electron Positron Collider

    SciTech Connect

    Wang, S.; Cai, Y.; /SLAC

    2006-02-10

    It is an important issue to study the beam-beam interaction in the design and performance of such a high luminosity collider as BEPCII, the upgrade of Beijing Electron Positron Collider. The weak-strong simulation is generally used during the design of a collider. For performance a large scale tune scan, the weak-strong simulation studies on beam-beam interaction were done, and the geometry effects were taken into account. The strong-strong simulation studies were done for investigating the luminosity goal and the dependence of the luminosity on the beam parameters.

  10. 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.

  11. Detection of Ga vacancies in electron irradiated GaAs by positrons

    SciTech Connect

    Hautojaervi, P.; Moser, P.; Stucky, M.; Corbel, C.; Plazaola, F.

    1986-03-24

    Positron lifetime measurements have been used to study the recovery of electron irradiated GaAs between 77 and 800 K. Below room temperature positrons are trapped by vacancies in Ga sublattices. The Ga vacancies recover between 200 and 350 K.

  12. Properties of the electron cloud in a high-energy positron and electron storage ring

    DOE PAGES

    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

  13. Properties of the electron cloud in a high-energy positron and electron storage ring

    SciTech Connect

    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.

  14. Wakefields generated by collisional neutrinos in neutral-electron-positron-ion plasma

    SciTech Connect

    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.

  15. Studies of slow-positron production using low-energy primary electron beams.

    SciTech Connect

    Lessner, E.

    1999-04-20

    Slow-positron beams produced from negative-work-function solid-state moderators have found numerous applications in condensed matter physics. There are potential advantages in using low-energy primary electron beams for positron production, including reduced radiation damage to single-crystal moderators and reduced activation of nearby components. We present numerical calculations of positron yields and other beam parameters for various target-moderator configurations using the Argonne Wakefield Accelerator (AWA) [1] and Advanced Photon Source (APS) [2] electron linacs [3] as examples of sources for the primary electron beams. The status of experiments at these facilities is reviewed.

  16. Stable confinement of electron plasma and initial results on positron injection in RT-1

    NASA Astrophysics Data System (ADS)

    Saitoh, H.; Yoshida, Z.; Morikawa, J.; Yano, Y.; Kasaoka, N.; Sakamoto, W.; Nogami, T.

    2013-03-01

    The Ring Trap 1 (RT-1) device is a dipole field configuration generated by a levitated superconducting magnet. It offers very interesting opportunities for research on the fundamental properties on non-neutral plasmas, such as self-organization of charged particles in the strongly positive and negative charged particles on magnetic surfaces. When strong positron sources will be available in the future, the dipole field configuration will be potentially applicable to the formation of an electron-positron plasma. We have realized stable, long trap of toroidal pure electron plasma in RT-1; Magnetic levitation of the superconducting magnet resulted in more than 300s of confinement for electron plasma of ˜ 1011 m-3. Aiming for the confinement of positrons as a next step, we started a positron injection experiment. For the formation of positron plasma in the closed magnetic surfaces, one of the key issues to be solved is the efficient injection method of positron across closed magnetic surfaces. In contrast to linear configurations, toroidal configurations have the advantage that they are capable of trapping high energy positrons in the dipole field configuration and consider the possibility of direct trapping of positrons emitted from a 22Na source.

  17. Third order transport coefficients for electrons and positrons in gases

    NASA Astrophysics Data System (ADS)

    Dujko, Sasa; Simonovic, Ilija; White, Ronald; Petrovic, Zoran

    2016-09-01

    Third order transport coefficients (the skewness tensor) of the electron and positron swarms, in atomic and molecular gases, are investigated. The knowledge of the skewness tensor is necessary for the conversion of the hydrodynamic transport coefficients to the arrival time and steady-state Townsend transport data as well as for the determination of the deviations of the spatial density profiles from an ideal Gaussian. In this work, we investigate the structure and symmetries along individual elements of the skewness tensor by the group projector method. Individual components of the skewness tensor are calculated using a Monte Carlo simulation technique and multi term theory for solving the Boltzmann equation. Results obtained by these two methods are in excellent agreement. We extend previous studies by considering the sensitivity of the skewness components to explicit and implicit effects of non-conservative collisions, post-ionization energy partitioning, and inelastic collisions. The errors of the two term approximation for solving the Boltzmann equation are highlighted. We also investigate the influence of a magnetic field on the skewness tensor in varying configurations of electric and magnetic fields. Among many interesting points, we have observed a strong correlation between the skewness and diffusion.

  18. 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.

  19. Calculation of the positron annihilation rate in PsH with the positronic extension of the explicitly correlated nuclear-electronic orbital method.

    PubMed

    Pak, Michael V; Chakraborty, Arindam; Hammes-Schiffer, Sharon

    2009-04-23

    The nuclear-electronic orbital explicitly correlated Hartree-Fock (NEO-XCHF) method is modified and extended to study electron-positron quantum systems. The NEO-XCHF method is more computationally efficient than the explicitly correlated methods previously applied to positron systems because only the electron-positron dynamical correlation is treated explicitly in NEO-XCHF. As a result, the form of the wave function is much simpler with fewer parameters, and the variational optimization of the molecular orbital parameters is performed through an iterative scheme rather than a stochastic optimization. The NEO-XCHF approach is used to calculate the positron annihilation rate for positronium hydride (PsH). The resulting annihilation rate for PsH is within 20% of the most accurate values available and is calculated at a fraction of the computational cost. These results suggest that qualitatively accurate positron annihilation rates can be calculated treating only electron-positron correlation explicitly, leading to significant computational savings by neglecting electron-electron dynamical correlation. Thus, the NEO-XCHF approach could potentially enable the calculation of qualitatively accurate positron annihilation rates for larger positron systems.

  20. Time of flight spectrometer for background-free positron annihilation induced Auger electron spectroscopy.

    PubMed

    Mukherjee, S; Shastry, K; Anto, C V; Joglekar, P V; Nadesalingam, M P; Xie, S; Jiang, N; Weiss, A H

    2016-03-01

    We describe a novel spectrometer designed for positron annihilation induced Auger electron spectroscopy employing a time-of-flight spectrometer. The spectrometer's new configuration enables us to implant monoenergetic positrons with kinetic energies as low as 1.5 eV on the sample while simultaneously allowing for the detection of electrons emitted from the sample surface at kinetic energies ranging from ∼500 eV to 0 eV. The spectrometer's unique characteristics made it possible to perform (a) first experiments demonstrating the direct transition of a positron from an unbound scattering state to a bound surface state and (b) the first experiments demonstrating that Auger electron spectra can be obtained down to 0 eV without the beam induced secondary electron background obscuring the low energy part of the spectra. Data are presented which show alternative means of estimating positron surface state binding energy and background-free Auger spectra.

  1. 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.

  2. Neutrino emissivity from electron-positron annihilation in hot matter in a strong magnetic field

    SciTech Connect

    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.

  3. Antiproton, positron, and electron imaging with a microchannel plate/phosphor detector

    SciTech Connect

    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.

  4. 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

  5. Calculation of Positron Binding Energies and Electron-Positron Annihilation Rates for Atomic Systems with the Reduced Explicitly Correlated Hartree-Fock Method in the Nuclear-Electronic Orbital Framework.

    PubMed

    Brorsen, Kurt R; Pak, Michael V; Hammes-Schiffer, Sharon

    2017-01-19

    Although the binding of a positron to a neutral atom has not been directly observed experimentally, high-level theoretical methods have predicted that a positron will bind to a neutral atom. In the present study, the binding energies of a positron to lithium, sodium, beryllium, and magnesium, as well as the electron-positron annihilation rates for these systems, are calculated using the reduced explicitly correlated Hartree-Fock (RXCHF) method within the nuclear-electronic orbital (NEO) framework. Due to the lack of explicit electron-positron correlation, NEO Hartree-Fock and full configuration interaction calculations with reasonable electronic and positronic basis sets do not predict positron binding to any of these atoms. In contrast, the RXCHF calculations predict positron binding energies and electron-positron annihilation rates in qualitative agreement with previous highly accurate but computationally expensive stochastic variational method calculations. These results illustrate that the RXCHF method can successfully describe the binding of a positron to a neutral species with no dipole moment. Moreover, the RXCHF method will be computationally tractable for calculating positron binding to molecular systems. The RXCHF approach offers a balance of accuracy and computational tractability for studying these types of positronic systems.

  6. Electromagnetic cascade in high-energy electron, positron, and photon interactions with intense laser pulses

    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.

  7. Positron-electron autocorrelation function study of E-center in silicon

    NASA Astrophysics Data System (ADS)

    Ho, K. F.; Ching, H. M.; Beling, C. D.; Fung, S.; Ng, K. P.; Biasini, M.; Ferro, G.; Gong, M.

    2003-11-01

    Two-dimensional angular correlation of annihilation radiation (2D-ACAR) spectra have been taken for 1019cm-3 phosphorus-doped Si in the as-grown state after having been subjected to 1.8 MeV electron fluences of 1×1018 and 2×1018 cm-2. Positron annihilation lifetime spectroscopy confirms, in accordance with previous works, that positrons are saturation trapping into (VSi:P) pair defect (E-center) monovacancy sites in the electron irradiated samples. In the as-grown case, the positron-electron autocorrelation functions along the [111] and [1-10] directions, obtained through Fourier transformation of the 2D-ACAR data, reveal zero-crossings that deviate only slightly from the lattice points, in a manner consistent with positron-electron correlation effects. Conversely, in the spectra of the irradiated samples, the zero-crossing points are observed to move outward further by between 0.15 and 0.50 Å. This displacement is associated with positron annihilation with electrons in localized orbitals at the defect site. An attempt is made to extract just the component of the defect's positron-electron autocorrelation function that relates to the localized defect orbitals. In doing this features are found that correspond to the expected atomic positions at the vacancy defect site suggesting that this real-space function may provide a convenient means for obtaining a mapping of localized orbitals. The observed approximate separability of positron and electron wave-function autocorrelates leads to an estimate of 0.22 eV for the positron binding energy to the E-center.

  8. Electronic correlations in vanadium revealed by electron-positron annihilation measurements

    NASA Astrophysics Data System (ADS)

    Weber, Josef Andreas; Benea, Diana; Appelt, Wilhelm H.; Ceeh, Hubert; Kreuzpaintner, Wolfgang; Leitner, Michael; Vollhardt, Dieter; Hugenschmidt, Christoph; Chioncel, Liviu

    2017-02-01

    The electronic structure of vanadium measured by angular correlation of electron-positron annihilation radiation (ACAR) is compared with the predictions of the combined density functional and dynamical mean-field theory (DMFT). Reconstructing the momentum density from five two-dimensional projections we were able to determine the full Fermi surface and found excellent agreement with the DMFT calculations. In particular, we show that the local, dynamic self-energy corrections contribute to the anisotropy of the momentum density and need to be included to explain the experimental results.

  9. Computer simulation of electron-positron pair production by channeling radiation in amorphous converter

    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-.

  10. 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.

  11. Enhancement of electron-positron pair creation due to transient excitation of field-induced bound states

    NASA Astrophysics Data System (ADS)

    Jiang, M.; Lv, Q. Z.; Sheng, Z. M.; Grobe, R.; Su, Q.

    2013-04-01

    We study the creation of electron-positron pairs induced by two spatially separated electric fields that vary periodically in time. The results are based on large-scale computer simulations of the time-dependent Dirac equation in reduced spatial dimensions. When the separation of the fields is very large, the pair creation is caused by multiphoton transitions and mainly determined by the frequency of the fields. However, for small spatial separations a coherence effect can be observed that can enhance or reduce the particle yield compared to the case of two infinitely separated fields. If the travel time for a created electron or positron between both field locations becomes comparable to the period of the oscillating fields, we observe peaks in the energy spectrum which can be explained in terms of field-induced transient bound states.

  12. The scaling of electron and positron generation in intense laser-solid interactionsa)

    NASA Astrophysics Data System (ADS)

    Chen, Hui; Link, A.; Sentoku, Y.; Audebert, P.; Fiuza, F.; Hazi, A.; Heeter, R. F.; Hill, M.; Hobbs, L.; Kemp, A. J.; Kemp, G. E.; Kerr, S.; Meyerhofer, D. D.; Myatt, J.; Nagel, S. R.; Park, J.; Tommasini, R.; Williams, G. J.

    2015-05-01

    This paper presents experimental scalings of the electrons and positrons produced by intense laser-target interactions at relativistic laser intensities (1018-1020 W cm-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 (≈EL2) 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.

  13. The scaling of electron and positron generation in intense laser-solid interactions

    SciTech Connect

    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.

  14. Simultaneous confinement of low-energy electrons and positrons in a compact magnetic mirror trap

    NASA Astrophysics Data System (ADS)

    Higaki, H.; Kaga, C.; Fukushima, K.; Okamoto, H.; Nagata, Y.; Kanai, Y.; Yamazaki, Y.

    2017-02-01

    More than 107 electrons and 105 positrons with energy less than a few eV were confined simultaneously for the first time in a compact magnetic mirror trap with plugging potentials. The exponential decay time constant of the confined positrons exceeded 70 ms at the beginning of the simultaneous confinement. Particle simulations in the early stages of the mixing process were also conducted. The results obtained in the experiments and simulations suggested that an improved setup would make it possible to investigate the unexplored field of low-energy electron–positron plasmas experimentally.

  15. Nonlinear waves in electron-positron-ion plasmas including charge separation

    NASA Astrophysics Data System (ADS)

    Mugemana, A.; Moolla, S.; Lazarus, I. J.

    2017-02-01

    Nonlinear low-frequency electrostatic waves in a magnetized, three-component plasma consisting of hot electrons, hot positrons and warm ions have been investigated. The electrons and positrons are assumed to have Boltzmann density distributions while the motion of the ions are governed by fluid equations. The system is closed with the Poisson equation. This set of equations is numerically solved for the electric field. The effects of the driving electric field, ion temperature, positron density, ion drift, Mach number and propagation angle are investigated. It is shown that depending on the driving electric field, ion temperature, positron density, ion drift, Mach number and propagation angle, the numerical solutions exhibit waveforms that are sinusoidal, sawtooth and spiky. The introduction of the Poisson equation increased the Mach number required to generate the waveforms but the driving electric field E 0 was reduced. The results are compared with satellite observations.

  16. Reduced explicitly correlated Hartree-Fock approach within the nuclear-electronic orbital framework: applications to positronic molecular systems.

    PubMed

    Sirjoosingh, Andrew; Pak, Michael V; Swalina, Chet; Hammes-Schiffer, Sharon

    2013-07-21

    In the application of the nuclear-electronic orbital (NEO) method to positronic systems, all electrons and the positron are treated quantum mechanically on the same level. Explicit electron-positron correlation can be included using Gaussian-type geminal functions within the variational self-consistent-field procedure. In this paper, we apply the recently developed reduced explicitly correlated Hartree-Fock (RXCHF) approach to positronic molecular systems. In the application of RXCHF to positronic systems, only a single electronic orbital is explicitly correlated to the positronic orbital. We apply NEO-RXCHF to three systems: positron-lithium, lithium positride, and positron-lithium hydride. For all three of these systems, the RXCHF approach provides accurate two-photon annihilation rates, average contact densities, electronic and positronic single-particle densities, and electron-positron contact densities. Moreover, the RXCHF approach is significantly more accurate than the original XCHF approach, in which all electronic orbitals are explicitly correlated to the positronic orbital in the same manner, because the RXCHF wavefunction is optimized to produce a highly accurate description of the short-ranged electron-positron interaction that dictates the annihilation rates and other local properties. Furthermore, RXCHF methods that neglect or approximate the electronic exchange interactions between the geminal-coupled electronic orbital and the regular electronic orbitals lead to virtually identical annihilation rates and densities as the fully antisymmetric RXCHF method but offer substantial advantages in computational tractability. Thus, NEO-RXCHF is a promising, computationally practical approach for studying larger positron-containing systems.

  17. 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.

  18. Scaling the Yield of Laser-Driven Electron-Positron Jets to Laboratory Astrophysical Applications

    NASA Astrophysics Data System (ADS)

    Chen, Hui; Fiuza, F.; Link, A.; Hazi, A.; Hill, M.; Hoarty, D.; James, S.; Kerr, S.; Meyerhofer, D. D.; Myatt, J.; Park, J.; Sentoku, Y.; Williams, G. J.

    2015-05-01

    We report new experimental results obtained on three different laser facilities that show directed laser-driven relativistic electron-positron jets with up to 30 times larger yields than previously obtained and a quadratic (˜EL2 ) dependence of the positron yield on the laser energy. This favorable scaling stems from a combination of higher energy electrons due to increased laser intensity and the recirculation of MeV electrons in the mm-thick target. Based on this scaling, first principles simulations predict the possibility of using such electron-positron jets, produced at upcoming high-energy laser facilities, to probe the physics of relativistic collisionless shocks in the laboratory.

  19. 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.

  20. Environmental assessment for the proposed B-Factory (Asymmetric Electron Positron Collider)

    SciTech Connect

    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.

  1. Resonance method to produce a polarisation asymmetry in electron-positron storage rings

    SciTech Connect

    Toner, W.T.

    1988-01-01

    Pulsed solenoids of a few tens of ampere turns, operated in synchronism with the ..gamma..(g-2/2) 'th harmonic of the orbit period, can be used to prevent a stored electron beam from becoming polarised through the emission of synchrotron radiation. With such low fields it is easy to arrange that only some of the stored bunches are affected. This makes it possible to produce collisions between counter-rotating electrons and positrons stored in a single ring in which the electron and positron polarisations are not equal and opposite. 8 refs.

  2. Photon induced positron annihilation spectroscopy: A nondestructive method for assay of defects in large engineering materials

    NASA Astrophysics Data System (ADS)

    Pujari, P. K.; Sudarshan, K.; Tripathi, R.; Dutta, D.; Maheshwari, P.; Sharma, S. K.; Srivastava, D.; Krause-Rehberg, R.; Butterling, M.; Anwand, W.; Wagner, A.

    2012-01-01

    This paper describes a new methodology for volumetric assay of defects in large engineering materials nondestructively. It utilizes high energy photons produced by nuclear reaction to create positrons in situ whose fate is followed using conventional positron spectroscopic techniques. The photon induced positron annihilation (PIPA) spectroscopy system has been set-up using a Folded Tandem Ion Accelerator (FOTIA). Possibility of using prompt γ-rays produced in nuclear reactions 27Al( 1H,γ) 28Si and 19F( 1H,αγ) 16O has been examined. The reaction 19F( 1H,αγ) 16O is seen to provide higher photon flux (and positron yield) and measurements have been carried out in large samples of metals and polymers. We could establish good sensitivity of the technique as well as reproducibility in a number of measurements. This technique has been used to carry out defect studies in cold worked zircaloy-2 plates. The measured S-parameter, indicative of defect concentration, was seen to correlate well with the measured residual stress using X-ray technique. The results were validated by γ-induced positron annihilation lifetime measurements at ELBE LINAC based GiPS facility.

  3. Calculations of the Probability of Positron Trapping by a Vacancy in a Metal and the Estimation of the Vacancy Contribution to the Work Function of Electrons and Positrons

    NASA Astrophysics Data System (ADS)

    Babich, A. V.; Pogosov, V. V.; Reva, V. I.

    2016-03-01

    The probabilities of the localization of positrons in monovacancies of Al and Cu have been calculated as functions of the energy and temperature. The vacancy was simulated by a void with a radius equal to the radius of the Wigner—Seitz cell in the model of stable jellium. Using the Fermi—Dirac golden rule for transitions, the formula for the rate of positron trapping by a vacancy has been derived as the function of the positron energy. For the thermalized positrons, the rate of localization near the triple point proved to be, on the order of magnitude, close to the rate of annihilation. Within the framework of our previously proposed models, the contribution of vacancies to the work function of electrons and positrons has been demonstrated based on the example of Al. The physical situations where the vacancy effect can manifest have been considered.

  4. 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

  5. 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

  6. 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

  7. Electromagnetic envelope solitons in ultrarelativistic inhomogeneous electron-positron-ion plasma

    SciTech Connect

    Du, Hong-E; Cheng, Li-Hong; Yu, Zi-Fa; Xue, Ju-Kui

    2014-08-15

    The nonlinear interaction of ultra-intense short laser beam and homogeneous/inhomogeneous electron-positron-ion (e-p-i) plasma is investigated. It is found that soliton solutions can exist in both homogeneous and inhomogeneous e-p-i plasma. The influence of the positron density, the phase velocity, the inhomogeneity nature, and the Hamiltonian of the system on the soliton structure is investigated. The evolution of envelope solitons in homogeneous e-p-i plasma is analyzed analytically by using a two-time-scale method and confirmed by numerical simulations. However, the soliton solutions can exist in inhomogeneous e-p-i plasma only when the positron density is high enough. Furthermore, the phase diagram for existing envelope soliton in positron density and phase velocity of the wave plane is obtained.

  8. 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.

  9. Nonlinear density excitations in electron-positron-ion plasmas with trapping in a quantizing magnetic field

    NASA Astrophysics Data System (ADS)

    Iqbal, M. J.; Masood, W.; Shah, H. A.; Tsintsadze, N. L.

    2017-01-01

    In the present work, we have investigated the effect of trapping as a microscopic phenomenon on the formation of solitary structures in the presence of a quantizing magnetic field in an electron-positron-ion (e-p-i) plasma having degenerate electrons and positrons, whereas ions are taken to be classical and cold. We have found that positron concentration, quantizing magnetic field, and finite electron temperature effects not only affect the linear dispersion characteristics of the electrostatic waves under consideration but also have a significant bearing on the propagation of solitary structures in the nonlinear regime. Importantly, the system under consideration has been found to allow the formation of compressive solitary structures only. The work presented here may be beneficial to understand the propagation of nonlinear electrostatic structures in dense astrophysical environments and in intense-laser plasma interactions.

  10. Nonlinear ion-acoustic structures in dusty plasma with superthermal electrons and positrons

    SciTech Connect

    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.

  11. On a plasma having nonextensive electrons and positrons: Rogue and solitary wave propagation

    SciTech Connect

    El-Awady, E. I.; Moslem, W. M.

    2011-08-15

    Generation of nonlinear ion-acoustic waves in a plasma having nonextensive electrons and positrons has been studied. Two wave modes existing in such plasma are considered, namely solitary and rogue waves. The reductive perturbation method is used to obtain a Korteweg-de Vries equation describing the system. The latter admits solitary wave pulses, while the dynamics of the modulationally unstable wave packets described by the Korteweg-de Vries equation gives rise to the formation of rogue excitation that is described by a nonlinear Schroedinger equation. The dependence of both solitary and rogue waves profiles on the nonextensive parameter, positron-to-ion concentration ratio, electron-to-positron temperature ratio, and ion-to-electron temperature ratio are investigated numerically. The results from this work are expected to contribute to the in-depth understanding of the nonlinear excitations that may appear in nonextensive astrophysical plasma environments, such as galactic clusters, interstellar medium, etc.

  12. Local electron-electron interaction strength in ferromagnetic nickel determined by spin-polarized positron annihilation.

    PubMed

    Ceeh, Hubert; Weber, Josef Andreas; Weber, Josef Andreass; Böni, Peter; Leitner, Michael; Benea, Diana; Chioncel, Liviu; Ebert, Hubert; Minár, Jan; Vollhardt, Dieter; Hugenschmidt, Christoph

    2016-02-16

    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.

  13. Local electron-electron interaction strength in ferromagnetic nickel determined by spin-polarized positron annihilation

    PubMed Central

    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

  14. γ-Ray spectra and enhancement factors for positron annihilation with core electrons.

    PubMed

    Green, D G; Gribakin, G F

    2015-03-06

    Many-body theory is developed to calculate the γ spectra for positron annihilation in noble-gas atoms. Inclusion of electron-positron correlation effects and core annihilation gives spectra in excellent agreement with experiment [K. Iwata et al., Phys. Rev. Lett. 79, 39 (1997)]. The calculated correlation enhancement factors γ_{nl} for individual electron orbitals nl are found to scale with the ionization energy I_{nl} (in eV), as γ_{nl}=1+sqrt[A/I_{nl}]+(B/I_{nl})^{β}, where A≈40  eV, B≈24  eV, and β≈2.3.

  15. Positron annihilation studies of the electronic structure and fermiology of the high-{Tc} superconductors

    SciTech Connect

    Smedskjaer, L.C.; Bansil, A.

    1992-09-01

    We discuss the application of the positron annihilation angular correlation (ACAR) spectroscopy for investigating the electronic structure and Fermiology of the high-T{sub c} superconductors, with focus on the YBa{sub 2}Cu{sub 3}O{sub 7} system where most of the experimental and theoretical work has to date been concentrated. Comparisons between measured 2D-ACAR positron spectra and band theory predictions show a remarkable agreement (for the normal state), indicating that the electronic structure and Fermi surface of this material is described reasonably by the conventional picture.

  16. Positron annihilation studies of the electronic structure and fermiology of the high-[Tc] superconductors

    SciTech Connect

    Smedskjaer, L.C. ); Bansil, A. . Dept. of Physics)

    1992-09-01

    We discuss the application of the positron annihilation angular correlation (ACAR) spectroscopy for investigating the electronic structure and Fermiology of the high-T[sub c] superconductors, with focus on the YBa[sub 2]Cu[sub 3]O[sub 7] system where most of the experimental and theoretical work has to date been concentrated. Comparisons between measured 2D-ACAR positron spectra and band theory predictions show a remarkable agreement (for the normal state), indicating that the electronic structure and Fermi surface of this material is described reasonably by the conventional picture.

  17. 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.

  18. Electron and positron scattering on rubidium at 200 eV

    SciTech Connect

    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].

  19. Visible and dark matter genesis and cosmic positron and electron excesses

    SciTech Connect

    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.

  20. Photons, Electrons and Positrons Transport in 3D by Monte Carlo Techniques

    SciTech Connect

    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.

  1. Positron Acceleration by Plasma Wakefields Driven by a Hollow Electron Beam

    NASA Astrophysics Data System (ADS)

    Jain, Neeraj; Antonsen, T. M.; Palastro, J. P.

    2015-11-01

    A scheme for positron plasma wakefield acceleration using hollow or donut-shaped electron driver beams is studied. An annular-shaped, electron-free region forms around the hollow driver beam, creating a favorable region (longitudinal field is accelerating and transverse field is focusing) for positron acceleration. For Facility for Advanced Accelerator Experimental Tests (FACET)-like parameters, the hollow beam driver produces accelerating gradients on the order of 10 GV /m . The accelerating gradient increases linearly with the total charge in the driver beam. Simulations show acceleration of a 23-GeV positron beam to 35.4 GeV with a maximum energy spread of 0.4% and very small emittance over a plasma length of 140 cm is possible.

  2. Ion-acoustic solitary waves in a positron beam plasma with electron trapping and nonextensivity effects

    NASA Astrophysics Data System (ADS)

    Ali Shan, S.; -Ur-Rehman, Aman; Mushtaq, A.

    2017-03-01

    Ion-acoustic solitary waves (IASWs) are investigated in a plasma having a cold positron beam fluid, electrons following a vortex-like distribution with entropic index q, and dynamic ions. Using a standard procedure, a pseudo-potential energy equation is derived. The presence of nonextensive q - distributed trapped electrons and cold positron beam has been shown to influence the small amplitude soliton structure quite significantly. From the analysis of our results, it is shown that compressive IASWs are supported in this plasma model. As the real plasma situations are observed with plasma species having a relative flow, our present analysis should be beneficial for comprehending the electrostatic solitary structures observed in fusion plasma devices and positron winds observed in astrophysical plasmas.

  3. Ion acoustic shock waves in plasmas with warm ions and kappa distributed electrons and positrons

    SciTech Connect

    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.

  4. A new equation in two dimensional fast magnetoacoustic shock waves in electron-positron-ion plasmas

    SciTech Connect

    Masood, W.; Jehan, Nusrat; Mirza, Arshad M.

    2010-03-15

    Nonlinear properties of the two dimensional fast magnetoacoustic waves are studied in a three-component plasma comprising of electrons, positrons, and ions. In this regard, Kadomtsev-Petviashvili-Burger (KPB) equation is derived using the small amplitude perturbation expansion method. Under the condition that the electron and positron inertia are ignored, Burger-Kadomtsev-Petviashvili (Burger-KP) for a fast magnetoacoustic wave is derived for the first time, to the best of author's knowledge. The solutions of both KPB and Burger-KP equations are obtained using the tangent hyperbolic method. The effects of positron concentration, kinematic viscosity, and plasma beta are explored both for the KPB and the Burger-KP shock waves and the differences between the two are highlighted. The present investigation may have relevance in the study of nonlinear electromagnetic shock waves both in laboratory and astrophysical plasmas.

  5. Ion-acoustic cnoidal waves in plasmas with warm ions and kappa distributed electrons and positrons

    NASA Astrophysics Data System (ADS)

    Kaladze, T.; Mahmood, S.

    2014-03-01

    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.

  6. Positron-impact ionization, positronium formation, and electronic excitation cross sections for diatomic molecules

    SciTech Connect

    Marler, J. P.; Surko, C. M.

    2005-12-15

    Absolute measurements are presented for the positron-impact cross sections for positronium formation, direct ionization, and total ionization of the diatomic molecules N{sub 2}, CO, and O{sub 2}, in the range of energies from threshold to 90 eV. Cross sections for the electronic excitation of the a {sup 1}{pi} and a{sup '} {sup 1}{sigma} state in N{sub 2} and the A {sup 1}{pi} state in CO near threshold are also presented. The experiment uses a cold, trap-based positron beam and the technique of studying positron scattering in a strong magnetic field. In O{sub 2}, a feature previously seen in the total ionization cross section is observed in both the positronium formation and total ionization cross sections. The possible origin of this feature and its relationship to positron-induced dissociation is discussed. In N{sub 2}, the near-threshold electronic excitation cross section is larger than that for positronium formation. This likely explains the relatively high efficiency of this molecule when used for buffer-gas positron trapping.

  7. Evidence for a significant mixture of electron/positron pairs in FRII jets constrained by cocoon dynamics

    NASA Astrophysics Data System (ADS)

    Kawakatu, Nozomu; Kino, Motoki; Takahara, Fumio

    2016-03-01

    We examine the plasma composition of relativistic jets in four Fanaroff-Riley type II (FRII) radio galaxies by analysing the total cocoon pressure in terms of partial pressures of thermal and non-thermal electrons/positrons and protons. The total cocoon pressure is determined by cocoon dynamics via comparison of theoretical model with the observed cocoon shape. By inserting the observed number density of non-thermal electrons/positrons and the upper limit of thermal electron/positron number density into the equation of state, the number density of protons is constrained. We apply this method to four FRII radio galaxies (Cygnus A, 3C 219, 3C 223 and 3C 284), for which the total cocoon pressures have been already evaluated. We find that the positron-free plasma comprising protons and electrons is ruled out, when we consider plausible particle distribution functions. In other words, the mixture of positrons is required for all four FRII radio galaxies; the number density ratio of electrons/positrons to protons is larger than 2. Thus, we find that the plasma composition is independent of the jet power and the size of cocoons. We also investigate the additional contribution of thermal electrons/positrons and protons on the cocoon dynamics. When thermal electrons/positrons are absent, the cocoon is supported by the electron/proton plasma pressure, while both electron/positron pressure supported and electron/proton plasma pressure supported cocoons are allowed if the number density of thermal electrons/positrons is about 10 times larger than that of non-thermal ones.

  8. Electron and Positron Fluxes in Primary Cosmic Rays Measured with the Alpha Magnetic Spectrometer on the International Space Station

    NASA Astrophysics Data System (ADS)

    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.; von Dratzig, A. Schulz; 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.; Türkoǧlu, 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.; AMS Collaboration

    2014-09-01

    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 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.

  9. Electron and positron fluxes in primary cosmic rays measured with the alpha magnetic spectrometer on the international space station.

    PubMed

    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.

  10. Effect of q-nonextensive parameter and saturation time on electron density steepening in electron-positron-ion plasmas

    SciTech Connect

    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.

  11. Effect of q-nonextensive parameter and saturation time on electron density steepening in electron-positron-ion plasmas

    NASA Astrophysics Data System (ADS)

    Hashemzadeh, M.

    2015-11-01

    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.

  12. Development of an Electron-Positron Source for Positron Annihilation Lifetime Spectroscopy

    DTIC Science & Technology

    2009-12-19

    coherent processes were sponsored by the NSF Quasi- monoenergetic MeV electron spectra emitted by an SiO2 plasma with (red) and without...adhering to the target surface. Aspects of this work that were directed toward neutron production were sponsored by the NRL. High-order

  13. Linear electrostatic waves in two-temperature electron-positron plasmas

    NASA Astrophysics Data System (ADS)

    Lazarus, I. J.; Bharuthram, R.; Singh, S. V.; Pillay, S. R.; Lakhina, G. S.; Lakhina

    2012-12-01

    Linear electrostatic waves in a magnetized four-component, two-temperature electron-positron plasma are investigated, with the hot species having the Boltzmann density distribution and the dynamics of cooler species governed by fluid equations with finite temperatures. A linear dispersion relation for electrostatic waves is derived for the model and analyzed for different wave modes. Analysis of the dispersion relation for perpendicular wave propagation yields a cyclotron mode with contributions from both cooler and hot species, which in the absence of hot species goes over to the upper hybrid mode of cooler species. For parallel propagation, both electron-acoustic and electron plasma modes are obtained, whereas for a single-temperature electron-positron plasma, only electron plasma mode can exist. Dispersion characteristics of these modes at different propagation angles are studied numerically.

  14. Measurement of the spectra of low energy electrons resulting from Auger transitions induced by the annihilation of low energy positrons implanted at The Ag (100) surface

    NASA Astrophysics Data System (ADS)

    Shastry, Karthik; Joglekar, Prasad; Weiss, A. H.; Fazleev, N. G.

    2013-04-01

    A few percent of positrons bound to a solid surface annihilate with core electrons resulting in highly excited atoms containing core holes. These core holes may be filled in an auto-ionizing process in which a less tightly bound electron drops into the hole and the energy difference transferred to an outgoing "Auger electron." Because the core holes are created by annihilation and not impact it is possible to use very low energy positron beams to obtain annihilation induced Auger signals. The Auger signals so obtained have little or none of the large impact induced secondary electron background that interferes with measurements of the low energy Auger spectra obtained using the much higher incident energies necessary when using electron or photon beams. Here we present the results of measurements of the energy spectrum of low energy electrons emitted as a result of Positron Annihilation Induce Auger Electron Emission [1] from a clean Ag (100) surface. The measurements were performed using the University of Texas Arlington Time of Flight Positron Annihilation induced Auger Electron Spectrometer (T-O-F-PAES) System [2]. A strong double peak was observed at ˜35eV corresponding to the N2VV and N3VV Auger transitions in agreement with previous PAES studies [3].

  15. Solitons and shocks in dense astrophysical magnetoplasmas with relativistic degenerate electrons and positrons

    SciTech Connect

    Ali, S.; Ata-ur-Rahman

    2014-04-15

    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.

  16. Magnetohydrodynamic waves with relativistic electrons and positrons in degenerate spin-1/2 astrophysical plasmas

    SciTech Connect

    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.

  17. Electron-positron pair production in the Aharonov-Bohm potential

    SciTech Connect

    Skarzhinsky, V.D. |; Audretsch, J.; Jasper, U.

    1996-02-01

    In the framework of QED we evaluate the cross section for electron-positron pair production by a single photon in the presence of the external Aharonov-Bohm potential in first order of perturbation theory. We analyze energy, angular, and polarization distributions at different energy regines: near the threshold and at high photon energies. {copyright} {ital 1996 The American Physical Society.}

  18. Roles of superthermal electrons and positrons on positron-acoustic solitary waves and double layers in electron–positron–ion plasmas

    SciTech Connect

    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.

  19. J-PET detector system for studies of the electron-positron annihilations

    NASA Astrophysics Data System (ADS)

    Pawlik-Niedźwiecka, M.; Khreptak, O.; Gajos, A.; Wieczorek, A.; Alfs, D.; Bednarski, T.; Białas, P.; Curceanu, C.; Czerwiński, E.; Dulski, K.; Głowacz, B.; Gupta-Sharma, N.; Gorgol, M.; Hiesmayr, B. C.; Jasińska, B.; Kamińska, D.; Korcyl, G.; Kowalski, P.; Krzmień, W.; Krawczyk, N.; Kubicz, E.; Mohammed, M.; Niedźwiecki, Sz.; Raczyński, L.; Rudy, Z.; Silarski, M.; Wiślicki, W.; Zgardzińska, B.; Zieliński, M.; Moskal, P.

    2016-11-01

    Jagiellonian Positron Emission Tomograph (J-PET) has been recently constructed at the Jagiellonian University as a prototype of a cost-effective scanner for the metabolic imaging of the whole human body. J-PET detector is optimized for the measurement of momentum and polarization of photons from the electron-positron annihilations. It is built out of strips of plastic scintillators, forming three cylindrical layers. As detector of gamma quanta it will be used for studies of discrete symmetries and multiparticle entanglement of photons originating from the decays of ortho-positronium atoms.

  20. On the fully nonlinear acoustic waves in a plasma with positrons beam impact and superthermal electrons

    SciTech Connect

    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.

  1. Novel time-of-flight spectrometer for the analysis of positron annihilation induced Auger electrons

    SciTech Connect

    Hugenschmidt, Christoph; Legl, Stefan

    2006-10-15

    Positron annihilation induced Auger-electron spectroscopy (PAES) has several advantages over conventional Auger-electron spectroscopy such as extremely high surface sensitivity and outstanding signal-to-noise ratio at the Auger-transition energy. In order to benefit from these prominent features a low-energy positron beam of high intensity is required for surface sensitive PAES studies. In addition, an electron energy analyzer is required, which efficiently detects the Auger electrons with acceptable energy resolution. For this reason a novel time-of-flight (TOF) spectrometer has been developed at the intense positron source NEPOMUC that allows PAES studies within short measurement time. This TOF-PAES setup combines a trochoidal filter and a flight tube in a Faraday cage in order to achieve an improved energy resolution of about 1 eV at high electron energies up to E{approx_equal}1000 eV. The electron flight time is the time between the annihilation radiation at the sample and when the electron hits a microchannel plate detector at the end of the flight tube.

  2. Novel time-of-flight spectrometer for the analysis of positron annihilation induced Auger electrons

    NASA Astrophysics Data System (ADS)

    Hugenschmidt, Christoph; Legl, Stefan

    2006-10-01

    Positron annihilation induced Auger-electron spectroscopy (PAES) has several advantages over conventional Auger-electron spectroscopy such as extremely high surface sensitivity and outstanding signal-to-noise ratio at the Auger-transition energy. In order to benefit from these prominent features a low-energy positron beam of high intensity is required for surface sensitive PAES studies. In addition, an electron energy analyzer is required, which efficiently detects the Auger electrons with acceptable energy resolution. For this reason a novel time-of-flight (TOF) spectrometer has been developed at the intense positron source NEPOMUC that allows PAES studies within short measurement time. This TOF-PAES setup combines a trochoidal filter and a flight tube in a Faraday cage in order to achieve an improved energy resolution of about 1eV at high electron energies up to E ≈1000eV. The electron flight time is the time between the annihilation radiation at the sample and when the electron hits a microchannel plate detector at the end of the flight tube.

  3. Second-order Born approximation for the ionization of molecules by electron and positron impact

    SciTech Connect

    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.

  4. Observation of Magnetic Resonances in Electron Clouds in a Positron Storage Ring

    SciTech Connect

    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.

  5. 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.

  6. 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).

  7. Double scattering production of two positron-electron pairs in ultraperipheral heavy-ion collisions

    NASA Astrophysics Data System (ADS)

    Kłusek-Gawenda, Mariola; Szczurek, Antoni

    2016-12-01

    We present first measurable predictions for electromagnetic (two-photon) double scattering production of two positron-electron pairs in ultraperipheral heavy-ion collisions at LHC. Measurable cross sections are obtained with realistic cuts on electron/positron (pseudo)rapidities and transverse momenta for the ALICE and ATLAS or CMS experiments. The predictions for total and differential cross sections are presented. We show also two-dimensional distributions in rapidities of the opposite-sign (from the same or different subcollisions) and of the same-sign (e+e+ or e-e-) electrons and in rapidity distance between them. Expected number of events are presented and discussed. Our calculations strongly suggest that relevant measurements with the help of ATLAS, CMS and ALICE detectors are possible in a near future. We show and compare energy dependence of the cross sections for one-pair and two-pair production.

  8. Positron lifetime studies on 8 MeV electron-irradiated n-type 6H silicon carbide

    NASA Astrophysics Data System (ADS)

    Lam, C. H.; Lam, T. W.; Ling, C. C.; Fung, S.; Beling, C. D.; De-Sheng, Hang; Huimin, Weng

    2004-11-01

    The positron lifetime technique was employed to study vacancy-type defects in 8 MeV electron-irradiated n-type 6H silicon carbide. A long-lifetime component having a characteristic lifetime of 223-232 ps was observed in the irradiated sample and was attributed to the VCVSi divacancy. Other positron traps, which dominated at low temperatures, were observed to compete with the VCVSi for trapping positrons. A positron trapping model involving a positron shallow trap, a negatively charged monovacancy and the VCVSi divacancy was found to give a good description of the temperature-dependent positron lifetime data of the 1200 °C annealed sample. The identity of the monovacancy could not be unambiguously determined, but its lifetime was found to be in the range 160-172 ps.

  9. Linear tearing modes in an electron-positron plasma

    NASA Astrophysics Data System (ADS)

    Guiliang, SONG; Huishan, CAI

    2017-04-01

    The general dispersion of tearing modes due to the effects of electron inertia and resistivity in pair plasmas is derived analytically, and is discussed in two cases: \\bigtriangleup \\prime \\gg 1 and \\bigtriangleup \\prime \\ll 1, where {{Δ }}\\prime is the instability criterion of the tearing mode. It is found that the conditions under which either resistivity or electron inertia dominates depend strongly on the limit of {{Δ }}\\prime considered.

  10. The possibilities of simultaneous detection of gamma rays, cosmic-ray electrons and positrons on the GAMMA-400 space observatory

    NASA Astrophysics Data System (ADS)

    Galper, A. M.; Aptekar, R. L.; Arkhangelskaya, I. V.; Boezio, M.; Bonvicini, V.; Dolgoshein, B. A.; Farber, M. O.; Fradkin, M. I.; Gecha, V. Ya.; Kachanov, V. A.; Kaplin, V. A.; Mazets, E. P.; Menshenin, A. L.; Picozza, P.; Prilutskii, O. F.; Rodin, V. G.; Runtso, M. F.; Spillantini, P.; Suchkov, S. I.; Topchiev, N. P.; Vacchi, A.; Yurkin, Yu. T.; Zampa, N.; Zverev, V. G.

    2011-02-01

    The GAMMA-400 space observatory will provide precise measurements of gamma rays, electrons, and positrons in the energy range 0.1-3000 GeV. The good angular and energy resolutions, as well as identification capabilities (angular resolution ~0.01°, energy resolution ~1%, and proton rejection factor ~106) will allow us to study the main galactic and extragalactic sources, diffuse gamma-ray background, gamma-ray bursts, and to measure electron and positron fluxes. The peculiar characteristics of the experiment is simultaneous detection of gamma rays and cosmic-ray electrons and positrons, which can be connected with annihilation or decay of dark matter particles.

  11. Insight into the electron-positron correlations in metals through the looking glass

    NASA Astrophysics Data System (ADS)

    Rubaszek, Anna

    2016-05-01

    A semi-empirical analysis of the positron annihilation experimental spectra indicates for a strong sensitivity of the two-particle electron-positron (e-p) enhancement factor to the l=s, p, d, f character of the initial electronic state [1,2]. The essential discrepancy between the models consists in the dependence of the relevant correlation functions on the energy of the annihilating electron. The present contribution contains a theoretical study of the e-p enhancement factors for s, p, d and f states as a function of the electron energy. The slope of the resulting characteristics is directly related to the degree of localisation of the s, p, d and f electrons in the electron density of states. This effect occurs especially for d electrons in transition metals, in favour to the approach of Ref. [1]. The energy dependence of the two-particle correlation functions is also a source of controversy between various theoretical approaches. The energy dependent enhancement factors describe properly the positron interaction with delocalised s and p electrons, but this approach overestimates the high momentum components of the e-p momentum densities, dominated by the localised d and f states. On the contrary, the calculations that employ the energy averaged enhancement factors match better with experiment for localised d and f electrons, but they hardly reproduce experimental spectra for nearly-free electron populations. An attempt to visit two sides of the looking glass is made in the theory of the present work. The model combines the properties of both approaches. The resulting e-p momentum densities and enhancement factors are in good agreement with the experimental data for simple, noble and transition metals, both in the low and high momentum region.

  12. Nonlinear dust-acoustic structures in space plasmas with superthermal electrons, positrons, and ions

    NASA Astrophysics Data System (ADS)

    Saberian, E.; Esfandyari-Kalejahi, A.; Afsari-Ghazi, M.

    2017-01-01

    Some features of nonlinear dust-acoustic (DA) structures are investigated in a space plasma consisting of superthermal electrons, positrons, and positive ions in the presence of negatively charged dust grains with finite-temperature by employing a pseudo-potential technique in a hydrodynamic model. For this purpose, it is assumed that the electrons, positrons, and ions obey a kappa-like (κ) distribution in the background of adiabatic dust population. In the linear analysis, it is found that the dispersion relation yield two positive DA branches, i.e., the slow and fast DA waves. The upper branch (fast DA waves) corresponds to the case in which both (negatively charged) dust particles and (positively charged) ion species oscillate in phase with electrons and positrons. On the other hand, the lower branch (slow DA waves) corresponds to the case in which only dust particles oscillate in phase with electrons and positrons, while ion species are in antiphase with them. On the other hand, the fully nonlinear analysis shows that the existence domain of solitons and their characteristics depend strongly on the dust charge, ion charge, dust temperature, and the spectral index κ. It is found that the minimum/maximum Mach number increases as the spectral index κ increases. Also, it is found that only solitons with negative polarity can propagate and that their amplitudes increase as the parameter κ increases. Furthermore, the domain of Mach number shifts to the lower values, when the value of the dust charge Z d increases. Moreover, it is found that the Mach number increases with an increase in the dust temperature. Our analysis confirms that, in space plasmas with highly charged dusts, the presence of superthermal particles (electrons, positrons, and ions) may facilitate the formation of DA solitary waves. Particularly, in two cases of hydrogen ions H+ ( Z i = 1) and doubly ionized Helium atoms He2+ ( Z i = 2), the mentioned results are the same. Additionally, the

  13. Toward tests of QED and CPT with improved electron and positron g-factor measurements

    NASA Astrophysics Data System (ADS)

    Novitski, Elise; Dorr, Joshua; Fogwell Hoogerheide, Shannon; Gabrielse, Gerald

    2013-05-01

    We describe progress toward improved measurements of the electron and positron g-factors using quantum jump spectroscopy between the lowest quantum states of either particle trapped in a 100 mK cylindrical Penning trap. In a new apparatus--designed for improved stability and a better geometry for cavity-assisted sideband cooling--we have trapped a single electron, driven and observed single cyclotron transitions, and trapped positrons in a loading trap. This should enable measurements of both g-factors with better than the 0.28 ppt precision of the best electron value (the most precise measurement of a fundamental property of an elementary particle), thereby improving the positron value by a factor of more than 15., These measurements, in combination with QED theory relating the electron g-factor to α, will improve on the most precise determination of α, the fine structure constant. The comparison of this value with an independent measurement of α is the most precise test of QED. The comparison of the e- and e+ g-factors will improve upon the best test of CPT symmetry in a lepton system. This work is supported by the NSF

  14. Magnetic field induced by strong transverse plasmons in ultra-relativistic electron-positron plasmas

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Li, X. Q.; Liu, S. Q.

    2012-08-01

    Context. We investigated the generation of localized magnetic fields in an ultra-relativistic non-isothermal electron-positron plasma by strong electromagnetic plasmons. Aims: The results obtained can be used to explain the origin of small-scale magnetic fields in the internal shock region of gamma-ray bursts with ultra-relativistic electron positron plasmas. Methods: The generation of magnetic fields was investigated with kinetic Vlasov Maxwell equations. Results: The self-generated magnetic field will collapse for modulation instability, leading to spatially highly intermittent magnetic fluxes, whose characteristic scale is much larger than relativistic plasma skin depth, which in turn is conducive to the generation of the long-life small-scale magnetic fields in the internal shock region of gamma-ray bursts.

  15. 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.

  16. Fast magnetic reconnection in low-density electron-positron plasmas

    SciTech Connect

    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.

  17. Dust ion acoustic solitary structures in presence of nonthermally distributed electrons and positrons

    NASA Astrophysics Data System (ADS)

    Paul, Ashesh; Bandyopadhyay, Anup; Das, K. P.

    2017-01-01

    The purpose of this paper is to extend the recent work of Paul and Bandyopadhyay [Astrophys. Space Sci. 361, 172 (2016)] on the existence of different dust ion acoustic solitary structures in an unmagnetized collisionless dusty plasma consisting of negatively charged static dust grains, adiabatic warm ions, nonthermal electrons, and isothermal positrons in a more generalized form by considering nonthermal positrons instead of isothermal positrons. The present system supports both positive and negative potential double layers, coexistence of solitary waves of both polarities, and positive potential supersolitons. The qualitative and quantitative changes in existence domains of different solitary structures, which occur in the presence of nonthermal positrons, have been presented in comparison with the results of Paul and Bandyopadhyay [Astrophys. Space Sci. 361, 172 (2016)]. The formation of supersoliton structures and their limitations has been analyzed with the help of phase portraits of the dynamical system corresponding to the dust ion acoustic solitary structures. Phase portrait analysis clearly indicates a smooth transition between solitons and supersolitons.

  18. AMS-02 positron excess: New bounds on dark matter models and hint for primary electron spectrum hardening

    NASA Astrophysics Data System (ADS)

    Feng, Lei; Yang, Rui-Zhi; He, Hao-Ning; Dong, Tie-Kuang; Fan, Yi-Zhong; Chang, Jin

    2014-01-01

    The data collected by ATIC, CREAM and PAMELA all display remarkable cosmic ray nuclei spectrum hardening above the magnetic rigidity ∼240 GV. One natural speculation is that the primary electron spectrum also gets hardened (possibly at ∼80 GV) and the hardening partly accounts for the electron/positron total spectrum excess discovered by ATIC, HESS and Fermi-LAT. If it is the case, the increasing behavior of the subsequent positron-to-electron ratio will get flattened and the spectrum hardening should be taken into account in the joint fit of the electron/positron data otherwise the inferred parameters will be biased. Our joint fits of the latest AMS-02 positron fraction data together with the PAMELA/Fermi-LAT electron/positron spectrum data suggest that the primary electron spectrum hardening is needed in most though not all modelings. The bounds on dark matter models have also been investigated. In the presence of spectrum hardening of primary electrons, the amount of dark-matter-originated electron/positron pairs needed in the modeling is smaller. Even with such a modification, the annihilation channel χχ→μ+μ- has been tightly constrained by the Fermi-LAT Galactic diffuse emission data. The decay channel χ→μ+μ- is found to be viable.

  19. RELATIVISTIC POSITRON-ELECTRON-ION SHEAR FLOWS AND APPLICATION TO GAMMA-RAY BURSTS

    SciTech Connect

    Liang, Edison; Fu, Wen; Smith, Ian; Roustazadeh, Parisa; Boettcher, Markus

    2013-12-20

    We present particle-in-cell simulation results of relativistic shear flows for hybrid positron-electron-ion plasmas and compare to those for pure e {sup +} e {sup –} and pure e {sup –} ion plasmas. Among the three types of relativistic shear flows, we find that only hybrid shear flow is able to energize the electrons to form a high-energy spectral peak plus a hard power law tail. Such electron spectra are needed to model the observational properties of gamma-ray bursts.

  20. Degradation of electron-irradiated polyethylene studied by positron annihilation lifetime spectroscopy

    NASA Astrophysics Data System (ADS)

    Onodera, K.; Oka, T.; Kino, Y.; Sekine, T.

    2017-01-01

    Degradation of electron beam irradiated high-density polyethylene was studied by positron annihilation lifetime spectroscopy (PALS), micro-FT-IR, and gel fraction measurements. The obtained results indicated that ortho-positronium intensity is influenced not only by the irradiation but also the post oxidation, which illustrates that PALS may be a promising tool to monitor/evaluate the degradation of polyethylene induced by irradiation and long-term storage.

  1. Theories of statistical equilibrium in electron-positron colliding-beam storage rings

    SciTech Connect

    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.

  2. Electroweak measurements in electron-positron collisions at W-boson-pair energies at LEP

    NASA Astrophysics Data System (ADS)

    ALEPH Collaboration; DELPHI Collaboration; L3 Collaboration; OPAL Collaboration; LEP Electroweak Working Group 1

    2013-11-01

    Electroweak measurements performed with data taken at the electron-positron collider LEP at CERN from 1995 to 2000 are reported. The combined data set considered in this report corresponds to a total luminosity of about 3 fb-1 collected by the four LEP experiments ALEPH, DELPHI, L3 and OPAL, at centre-of-mass energies ranging from 130 GeV to 209 GeV.

  3. Electron Positron Proton Spectrometer for use at Laboratory for Laser Energetics

    SciTech Connect

    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.

  4. Oblique propagation of ion-acoustic solitary waves in a magnetized electron-positron-ion plasma

    SciTech Connect

    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.

  5. Measurement of the hadronic cross section in electron-positron annihilation

    SciTech Connect

    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.

  6. Nonlinear electromagnetic perturbations in a degenerate ultrarelativistic electron-positron plasma.

    PubMed

    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.

  7. On thermalization of electron-positron-photon plasma

    SciTech Connect

    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.

  8. Nonlinear Korteweg-de Vries equation for soliton propagation in relativistic electron-positron-ion plasma with thermal ions

    SciTech Connect

    Saeed, R.; Shah, Asif; Noaman-ul-Haq, Muhammad

    2010-10-15

    The nonlinear propagation of ion-acoustic solitons in relativistic electron-positron-ion plasma comprising of Boltzmannian electrons, positrons, and relativistic thermal ions has been examined. The Korteweg-de Vries equation has been derived by reductive perturbation technique. The effect of various plasma parameters on amplitude and structure of solitary wave is investigated. The pert graphical view of the results has been presented for illustration. It is observed that increase in the relativistic streaming factor causes the soliton amplitude to thrive and its width shrinks. The soliton amplitude and width decline as the ion to electron temperature ratio is increased. The increase in positron concentration results in reduction of soliton amplitude. The soliton amplitude enhances as the electron to positron temperature ratio is increased. Our results may have relevance in the understanding of astrophysical plasmas.

  9. Nonlinear Korteweg-de Vries equation for soliton propagation in relativistic electron-positron-ion plasma with thermal ions

    NASA Astrophysics Data System (ADS)

    Saeed, R.; Shah, Asif; Noaman-Ul-Haq, Muhammad

    2010-10-01

    The nonlinear propagation of ion-acoustic solitons in relativistic electron-positron-ion plasma comprising of Boltzmannian electrons, positrons, and relativistic thermal ions has been examined. The Korteweg-de Vries equation has been derived by reductive perturbation technique. The effect of various plasma parameters on amplitude and structure of solitary wave is investigated. The pert graphical view of the results has been presented for illustration. It is observed that increase in the relativistic streaming factor causes the soliton amplitude to thrive and its width shrinks. The soliton amplitude and width decline as the ion to electron temperature ratio is increased. The increase in positron concentration results in reduction of soliton amplitude. The soliton amplitude enhances as the electron to positron temperature ratio is increased. Our results may have relevance in the understanding of astrophysical plasmas.

  10. Multi-dimensional instability of obliquely propagating ion acoustic solitary waves in electron-positron-ion superthermal magnetoplasmas

    SciTech Connect

    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.

  11. The extent of non-thermal particle acceleration in relativistic, electron-positron reconnection

    SciTech Connect

    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 γrad. The power-law index and high-energy cutoff are important for understanding the radiation spectrum dN/dγ = f(γ) ∝ γ. α and cutoff were measured vs. L and σ, where L is system (simulation) size and σ is upstream magnetization (σ = B2/4πnmc2). α can affect the high-energy cutoff. In conclusion, for collisionless relativistic reconnection in electron-positron plasma, without guide field, nb/nd=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 γc2 ≈ 0.1 L/ρ0; for large systems, the layer length is limited by secondary tearing instability, yielding γc1 ≈ 4σ; the transition from small to large is around L/ρ0 = 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.

  12. Arbitrary amplitude dust ion acoustic solitons and double layers in the presence of nonthermal positrons and electrons

    NASA Astrophysics Data System (ADS)

    Banerjee, Gadadhar; Maitra, Sarit

    2016-12-01

    Existence of arbitrary amplitude solitons and double layers have been studied in collisionless unmagnetized multicomponent dusty plasmas with nonthermally distributed positrons and electrons by using Sagdeev's pseudopotential method. The linear dispersion relation is obtained for dust ion acoustic wave mode. The present model supports the coexistence of positive potential solitary waves and negative potential solitary waves and double layers. The criterion for the existence of solitary waves and double layers is derived in terms of Mach number limit. The effects of ion temperature and nonthermality of electrons and positrons are studied. Also the effects of positron and dust concentration on the wave propagation are observed.

  13. Methods of optical diagnostics of electron-positron beams and interaction between plasma and high-current electron beam

    NASA Astrophysics Data System (ADS)

    Vyacheslavov, L. N.; Ivantsivskii, M. V.; Meshkov, O. I.; Popov, S. S.; Smaluk, V. V.

    2012-03-01

    Optical diagnostics is widely used, both in plasma-physics experiments and in measuring parameters of electron and positron beams in accelerators. In doing so, the approaches with the same methodological base are often applied, which is explained by similarity of certain properties of objects under study despite the fact that these fields of physics are absolutely specific and require using the specialized techniques. The possibility of close contacts and cooperation among scientists concerned with similar problems in different fields of physics contributes to the fruitful exchange of ideas and helps to overcome these problems. It is especially characteristic of the Budker Institute of Nuclear Physics, Siberian Branch of Russian Academy of Sciences, which is famous for pioneering works in the field of electron-positron colliders and controlled thermonuclear fusion. The first part of this paper presents a review of optical diagnostics of the stationary beam parameters in cyclic accelerators of electrons and positrons. The only techniques considered are those that became the recognized tools at colliders and storage rings of the latest generation, without which the routine operation of the facility is difficult to imagine. The second part of the paper describes optical diagnostics used in experiments of heating the plasma by a high-current electron beam.

  14. Evidence of Positron Annihilation at Electronic Excitation Threshold for N2 ^*

    NASA Astrophysics Data System (ADS)

    Miller, E. G.; Edwards, J. J.; Kauppila, W. E.; Stein, T. S.; Surdutovich, E.

    2006-05-01

    We are investigating Positronium (Ps) formation for < 20 eV positrons interacting with N2 in a gas scattering cell. The technique [1] of Ps annihilation ratio spectroscopy (PsARS) is used to obtain the ratios of coincidence signals for two of the three gamma rays (S3γ) in the photon energy window 300 to 460 keV resulting from ortho-Ps decay to that for two 511 keV gamma rays (S2γ) arising from para-Ps decay and other processes. By comparing these ratios of S3 γ/S2γ for N2 to those for Ar it is found that N2 exhibits strikingly anomalous behavior near and below the Ps formation threshold. Typically, this ratio remains constant within 2 eV above the Ps threshold. For N2, this ratio decreases to zero at the threshold and an S2 γ signal remains for an energy of ˜0.3 eV below. Since N2 has an electronic excitation threshold for positron impact that opens up at ˜0.3 eV below the Ps threshold, the present results strongly suggest that the incident positron is electronically exciting N2 and then binding to the excited N2 in a temporary resonance-like state from which the bound positron annihilates with a molecular electron. ^*Research supported by NSF Grant PHY 99-88093.[1] W.E. Kauppila, E.G. Miller, H. F.M. Mohamed, K. Pipinos, T. S. Stein, and E. Surdutovich, Phys. Rev. Lett. 93, 113401 (2004).

  15. Observation of Electron Cloud Instabilities and Emittance Dilution at the Cornell Electron-Positron Storage Ring Test Accelerator

    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.

  16. Observation of electron cloud instabilities and emittance dilution at the Cornell electron-positron Storage ring Test Accelerator

    SciTech Connect

    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.

    2016-04-11

    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 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 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.

  17. Observation of electron cloud instabilities and emittance dilution at the Cornell electron-positron Storage ring Test Accelerator

    DOE PAGES

    Holtzapple, R. L.; Billing, M. G.; Campbell, R. C.; ...

    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

  18. Experiment with a crystal-assisted positron source using 6 and 10 GeV electrons

    NASA Astrophysics Data System (ADS)

    Artru, X.; Baier, V.; Beloborodov, K.; Bochek, G.; Bogdanov, A.; Bozhenok, A.; Bukin, A.; Burdin, S.; Chehab, R.; Chevallier, M.; Cizeron, R.; Dauvergne, D.; Dimova, T.; Drozdetsky, A.; Druzhinin, V.; Dubrovin, M.; Gatignon, L.; Golubev, V.; Jejcic, A.; Keppler, P.; Kirsch, R.; Kulibaba, V.; Lautesse, Ph.; Major, J.; Maslov, N.; Poizat, J.-C.; Potylitsin, A.; Remillieux, J.; Serednyakov, S.; Shary, V.; Strakhovenko, V.; Sylvia, C.; Vnukov, I.

    2003-01-01

    Axially oriented crystals, penetrated by high-energy electrons, are powerful photon sources and, hence, intense positron sources. Such kinds of positron sources have been studied experimentally at CERN, with the tertiary electron beam of the SPS having an energy of 6 and 10 GeV. Four and eight millimeters thick tungsten crystals and a compound target made of a 4 mm crystal followed by a 4 mm amorphous disk were used with an orientation along the <1 1 1> axis. The positrons were detected by a drift chamber, partially immersed in a magnetic field. The reconstructed trajectories allowed the determination of their energy and angular spectra. Significant enhancements were observed for the crystal source when compared to the amorphous one. The gain was about 3 for the 4 mm target and about 2 for the 8 mm and the compound targets. These preliminary results are described after short presentations of the experimental set-up and of the method of track reconstruction.

  19. 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.

  20. Cosmic ray electrons and positrons from supernova explosions of massive stars.

    PubMed

    Biermann, P L; Becker, J K; Meli, A; Rhode, W; Seo, E S; Stanev, T

    2009-08-07

    We attribute the recently discovered cosmic ray electron and cosmic ray positron excess components and their cutoffs to the acceleration in the supernova shock in the polar cap of exploding Wolf-Rayet and red supergiant stars. Considering a spherical surface at some radius around such a star, the magnetic field is radial in the polar cap as opposed to most of 4pi (the full solid angle), where the magnetic field is nearly tangential. This difference yields a flatter spectrum, and also an enhanced positron injection for the cosmic rays accelerated in the polar cap. This reasoning naturally explains the observations. Precise spectral measurements will be the test, as this predicts a simple E;{-2} spectrum for the new components in the source, steepened to E;{-3} in observations with an E;{-4} cutoff.

  1. Revealing Fundamental Interactions: the Role of Polarized Positrons and Electrons at the Linear Collider

    SciTech Connect

    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.

  2. The Role of polarized positrons and electrons in revealing fundamental interactions at the linear collider

    SciTech Connect

    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.

  3. Planar and nonplanar ion acoustic shock waves in relativistic degenerate astrophysical electron-positron-ion plasmas

    SciTech Connect

    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.

  4. Hunting for glueballs in electron-positron annihilation

    SciTech Connect

    Stanley Brodsky; Alfred Scharff Goldhaber; Jungil Lee

    2003-05-01

    We calculate the cross section for the exclusive production of J{sup PC} = 0{sup ++} glueballs G{sub 0} in association with the J/{psi} in e{sup +}e{sup -} annihilation using the pQCD factorization formalism. The required long-distance matrix element for the glueball is bounded by CUSB data from a search for resonances in radiative {Upsilon} decay. The cross section for e{sup +}e{sup -} {yields} J/{psi} + G{sub 0} at {radical}s = 10.6 GeV is similar to exclusive charmonium-pair production e{sup +}e{sup -} {yields} J/{psi} + h for h = {eta}{sub c} and {chi}{sub c0}, and is larger by a factor 2 than that for h = {eta}{sub c}(2S). As the subprocesses {gamma}* {yields} (c {bar c}) (c {bar c}) and {gamma}* {yields} (c {bar c}) (g g) are of the same nominal order in perturbative QCD, it is possible that some portion of the anomalously large signal observed by Belle in e{sup +}e{sup -} {yields} J/{psi} X may actually be due to the production of charmonium-glueball J/{psi} G{sub J} pairs.

  5. A search for supersymmetric electrons with the Mark II detector at PEP (Positron Electron Project)

    SciTech Connect

    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.

  6. Study of four-lepton final states in electron-positron interactions at 29 GeV

    SciTech Connect

    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.

  7. Magnetorotational instability of weakly ionized and magnetized electron-positron-ion plasma

    NASA Astrophysics Data System (ADS)

    Mehdian, H.; Hajisharifi, K.; Azadnia, F.; Tajik-Nezhad, S.

    2016-10-01

    The magnetorotational instability in a differential rotating weakly ionized and magnetized plasma consisting of electron, positron, ion, and neutral particles has been investigated by using the multi-fluid model. Satisfying the current neutrality and homogeneity of the system in the equilibrium state by assuming the same unperturbed angular velocity for charge species and neutrals, the general local dispersion relation (DR) has been derived by taking into account the collision effects. By analytical examination of the obtained DR in the arbitrary and high frequency regimes, the instability conditions have been found in which the presence of light positive species (positrons) plays an important role in the instability criteria. Moreover, numerical investigation shows the broadening of instability range as well as increasing the maximum growth rate of instability (especially for the small number density ratio of light to heavy positive species) in the presence of positrons. The obtained results of the present investigation will greatly contribute to the understanding of the particles' dynamics as well as dissipation mechanism in some astrophysical environments, such as the region of accretion disks surrounding the central of black holes and protoplanetary disks.

  8. 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.

  9. On-ground detection of an electron-positron annihilation line from thunderclouds.

    PubMed

    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.

  10. Positron 2D-ACAR experiments and electron-positron momentum density in YBa{sub 2}Cu{sub 3}O{sub 7-x}

    SciTech Connect

    Smedskjaer, L.C.; Welp, U.; Fang, Y.; Bailey, K.G.; Bansil, A.

    1991-12-01

    We discuss positron annihilation (2D-ACAR) measurements in the C- projection on an untwinned metallic single crystal of YBa{sub 2}Cu{sub 3}O{sub 7-x} as a function of temperature, for five temperatures ranging from 30K to 300K. The measured 2D-ACAR intensities are interpreted in terms of the electron-positron momentum density obtained within the KKR-band theory framework. The temperature dependence of the 2D-ACAR spectra is used to extract a ``background corrected`` experimental spectrum which is in remarkable accord with the corresponding band theory predictions, and displays in particular clear signatures of the electron ridge Fermi surface.

  11. Positron 2D-ACAR experiments and electron-positron momentum density in YBa sub 2 Cu sub 3 O sub 7-x

    SciTech Connect

    Smedskjaer, L.C.; Welp, U.; Fang, Y.; Bailey, K.G. ); Bansil, A. . Dept. of Physics)

    1991-12-01

    We discuss positron annihilation (2D-ACAR) measurements in the C- projection on an untwinned metallic single crystal of YBa{sub 2}Cu{sub 3}O{sub 7-x} as a function of temperature, for five temperatures ranging from 30K to 300K. The measured 2D-ACAR intensities are interpreted in terms of the electron-positron momentum density obtained within the KKR-band theory framework. The temperature dependence of the 2D-ACAR spectra is used to extract a background corrected'' experimental spectrum which is in remarkable accord with the corresponding band theory predictions, and displays in particular clear signatures of the electron ridge Fermi surface.

  12. Towards a Resolution of the Proton Form Factor Problem: New Electron and Positron Scattering Data

    SciTech Connect

    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.

  13. Towards a Resolution of the Proton Form Factor Problem: New Electron and Positron Scattering Data

    NASA Astrophysics Data System (ADS)

    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.; CLAS Collaboration

    2015-02-01

    There is a significant discrepancy between the values of the proton electric form factor, GEp, extracted using unpolarized and polarized electron scattering. Calculations predict that small two-photon exchange (TPE) contributions can significantly affect the extraction of GEp 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 (ɛ ) and momentum transfer (Q2) simultaneously, as well as to cancel luminosity-related systematic errors. The cross section ratio increases with decreasing ɛ 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 Δ intermediate states, which have been shown to resolve the discrepancy up to 2 - 3 GeV2 .

  14. Towards a Resolution of the Proton Form Factor Problem: New Electron and Positron Scattering Data

    DOE PAGES

    Adikaram, D.; Rimal, D.; Weinstein, L. B.; ...

    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

  15. Towards a resolution of the proton form factor problem: new electron and positron scattering data.

    PubMed

    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).

  16. Positron and electron scattering by glycine and alanine: Shape resonances and methylation effect

    NASA Astrophysics Data System (ADS)

    Nunes, Fernanda B.; Bettega, Márcio H. F.; Sanchez, Sergio d'Almeida

    2016-12-01

    We report integral cross sections (ICSs) for both positron and electron scattering by glycine and alanine amino acids. These molecules differ only by a methyl group. We computed the scattering cross sections using the Schwinger multichannel method for both glycine and alanine in different levels of approximation for both projectiles. The alanine ICSs are greater in magnitude than the glycine ICSs for both positron and electron scattering, probably due to the larger size of the molecule. In electron scattering calculations, we found two resonances for each molecule. Glycine presents one at 1.8 eV, and another centered at around 8.5 eV, in the static-exchange plus polarization (SEP) approximation. The ICS for alanine shows one resonance at 2.5 eV and another at around 9.5 eV, also in SEP approximation. The results are in good agreement with most of the data present in the literature. The comparison of the electron scattering ICSs for both molecules indicates that the methylation of glycine destabilizes the resonances, shifting them to higher energies.

  17. An 8×8 Row-Column Summing Readout Electronics for Preclinical Positron Emission Tomography Scanners

    PubMed Central

    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

  18. Electron irradiated liquid encapsulated Czochralski grown undoped gallium antimonide studied by positron lifetime spectroscopy and photoluminescence

    NASA Astrophysics Data System (ADS)

    Ma, S. K.; Lui, M. K.; Ling, C. C.; Fung, S.; Beling, C. D.; Li, K. F.; Cheah, K. W.; Gong, M.; Hang, H. S.; Weng, H. M.

    2004-09-01

    Electron irradiated undoped liquid encapsulated Czochralski (LEC) grown GaSb samples were studied by positron lifetime spectroscopy (PLS) and photoluminescence (PL). In addition to the 315 ps component reported in the previous studies, another defect with a lifetime of 280 ps was also identified in the present electron irradiated samples. The bulk lifetime of the GaSb material was found to be 258 ps. The VGa,280 ps and the VGa,315 ps defects were associated with two independent Ga vacancy related defects having different microstructures. The well known 777 meV PL signal (usually band A) was also observed in the electron irradiated undoped GaSb samples. The band A intensity decreases with increasing electron irradiation dosage and it disappears after the 300 °C annealing regardless of the irradiation dosage. The origin of the band A signal is also discussed.

  19. Electron Cloud in the Wigglers of the Positron Damping Ring of the International Linear Collider

    SciTech Connect

    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.

  20. 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.

  1. Production of {omega}{pi}{sup 0} pairs in electron-positron annihilation

    SciTech Connect

    Arbuzov, A. B.; Kuraev, E. A.; Volkov, M. K.

    2011-04-15

    The process of electron-positron annihilation into a pair of {pi}{sup 0} and {omega} mesons is considered in the framework of the SU(2)xSU(2) Nambu-Jona-Lasinio model. Contributions of intermediate photons, {rho}(770) and {rho}{sup '}(1450) vector mesons are taken into account. It is shown that the bulk of the cross section at energies below 2 GeV is provided by the process with intermediate {rho}{sup '}(1450) state. The contribution due to single photon and {rho}(770) exchange is in agreement with the vector meson dominance model. Numerical results are compared with experimental data.

  2. Phase-mixing of electrostatic modes in a cold magnetized electron-positron plasma

    SciTech Connect

    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.

  3. MAGNETIC FIELD GENERATION AND PARTICLE ENERGIZATION AT RELATIVISTIC SHEAR BOUNDARIES IN COLLISIONLESS ELECTRON-POSITRON PLASMAS

    SciTech Connect

    Liang, Edison; Smith, Ian; Boettcher, Markus E-mail: iansmith@rice.edu

    2013-04-01

    Using particle-in-cell simulations, we study the kinetic physics of relativistic shear flow in collisionless electron-positron (e+e-) plasmas. We find efficient magnetic field generation and particle energization at the shear boundary, driven by streaming instabilities across the shear interface and sustained by the shear flow. Nonthermal, anisotropic high-energy particles are accelerated across field lines to produce a power-law tail turning over just below the shear Lorentz factor. These results have important implications for the dissipation and radiation of jets in blazars and gamma-ray bursts.

  4. Comoving acceleration of overdense electron-positron plasma by colliding ultra-intense laser pulses

    SciTech Connect

    Liang, Edison

    2006-06-15

    Particle-in-cell (PIC) simulation results of sustained acceleration of electron-positron (e+e-) plasmas by comoving electromagnetic (EM) pulses are presented. When a thin slab of overdense e+e- plasma is irradiated with linear-polarized ultra-intense short laser pulses from both sides, the pulses are transmitted when the plasma is compressed to thinner than {approx}2 relativistic skin depths. A fraction of the plasma is then captured and efficiently accelerated by self-induced JxB forces. For 1 {mu}m laser and 10{sup 21} W cm{sup -2} intensity, the maximum energy exceeds GeV in a picosecond.

  5. Shock formation in magnetised electron-positron plasmas: mechanism and timing

    NASA Astrophysics Data System (ADS)

    Stockem Novo, A.; Bret, A.; Sinha, U.

    2016-10-01

    The shock formation process in electron-positron pair plasmas is investigated in the presence of an ambient perpendicular magnetic field. In initially unmagnetised plasmas, which are dominated by the Weibel or filamentation instability, the shock formation time is a multiple of the saturation time of the linear instability. While in weakly magnetised plasmas the mechanism is still the same, higher magnetisations induce synchrotron maser modes such that the shock formation is dominated by magnetic reflection. As a consequence the formation times are reduced. The focus is on the detailed picture of the particle kinetics, in which the transition between Weibel and magneto-hydrodynamic shocks can be clearly identified.

  6. Theoretical calculation of electron-positron momentum density in YBa 2Cu 3O 7-δ

    NASA Astrophysics Data System (ADS)

    Massidda, S.

    1990-07-01

    We present calculations of the electron-positron momentum density for the high- Tc superconductor YBa 2Cu 3O 7-δ for δ=0 and for the insulating parent compound YBa 2Cu 3O 6, based on first-principle electronic structure calculations performed within the local density approximation (LDA) using the full potential linearized augmented plane wave (FLAPW) method. Our results indicate a small overlap of the positron wave function with the CuO 2 plane electrons and, as a consequence, relatively small signals due to the related Fermi surfaces. By contrast, the present calculations show, after the folding of Umklapp terms according to Lock, Crisp and West, clear Fermi surface breaks arising from the Cu-O chain bands. No general agreement with existing experiments allows a clear definition of Fermi surface structures in the latter. A comparison of the calculated momentum with the experimental two-dimensional angular correlation of annihilation radiation (2D-ACAR) recently measured in Geneva shows an overall agreement for the insulating compound, despite the spurious LDA metallic state, and possibly suggests the importance of O vacancies in experiments performed on non-stoichiometric YBa 2Cu 3O 7-δ samples.

  7. Positron Annihilation Induced Auger Electron Spectroscopy of Inner Shell Transitions Using Time-Of Technique

    NASA Astrophysics Data System (ADS)

    Xie, Shuping; Jiang, Neng; Weiss, A. H.

    2003-03-01

    Positron annihilation induced Auger electron spectroscopy (PAES) has been shown to have unique advantages over conventional electron collision induced Auger techniques, including the ability to eliminate the secondary electron background and selectively probe the top-most atomic layer on the sample surface. Here we report on the development of a new time-of-flight (TOF) spectrometer which combines features high efficiency magnetic transport and parrallel energy measurment with high resolution by using an innovative timing method. The new TOF-PAES system, was used to make the first quantitative comparative measurements of the Auger intensities associated with the annihilation of positrons with the deep core levels (1s) of S KLL (180eV), C KLL (270eV), N KLL (360eV), and O KLL (510eV). Experimental results of Auger probabilities at outer core level (3s, 3P) of Cu M2,3VV (60eV), M1VV (105eV) are compared with the theoretical value of Jensen and Weiss. Quantitatively study the surface adsorbate process on Cu is performed and concentration changes of surface components are obtained. These results demonstrate that TOF-PAES can be used to obtain quantitative,top-layer specific, information from chemically important elements including those with relatively deep core levels (e.g. C and O).

  8. Rich eight-branch spectrum of the oblique propagating longitudinal waves in partially spin-polarized electron-positron-ion plasmas.

    PubMed

    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.

  9. Intense source of slow positrons

    NASA Astrophysics Data System (ADS)

    Perez, P.; Rosowsky, A.

    2004-10-01

    We describe a novel design for an intense source of slow positrons based on pair production with a beam of electrons from a 10 MeV accelerator hitting a thin target at a low incidence angle. The positrons are collected with a set of coils adapted to the large production angle. The collection system is designed to inject the positrons into a Greaves-Surko trap (Phys. Rev. A 46 (1992) 5696). Such a source could be the basis for a series of experiments in fundamental and applied research and would also be a prototype source for industrial applications, which concern the field of defect characterization in the nanometer scale.

  10. Ion-acoustic Gardner Solitons in electron-positron-ion plasma with two-electron temperature distributions

    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.

  11. Positron-proton to electron-proton elastic cross section ratios from CLAS

    NASA Astrophysics Data System (ADS)

    Adikaram, Dasuni; Rimal, Dipak; Weinstein, Larry; Raue, Brian

    2014-03-01

    There is a significant discrepancy between the ratio of the electromagnetic form factors of the proton measured by the Rosenbluth and the polarization transfer technique. The most likely explanation of this discrepancy is the inclusion of two-photon exchange (TPE) amplitude contributions to the elastic electron-proton cross section. The CLAS TPE experiment measured the TPE contribution in the wide range of Q2 and ɛ range using a comparison of positron-proton to electron-proton elastic cross sections (R = σ (e+ p) / σ (e- p)). Preliminary results will be presented, along with the estimations of systematic uncertainties. A detailed comparison of new results with previous R measurements and theoretical calculations will be presented. Implications of the CLAS TPE measurements on the elastic electron-proton cross section will be also discussed.

  12. 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.

  13. Oscillating two-stream instability in a magnetized electron-positron-ion plasma

    SciTech Connect

    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.

  14. Oblique propagation of ion acoustic shock waves in weakly and highly relativistic plasmas with nonthermal electrons and positrons

    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.

  15. A coincidence study of electron and positron impact ionization of Ar (3p) at 1 keV

    NASA Astrophysics Data System (ADS)

    Campeanu, Radu I.; Walters, James H. R.; Whelan, Colm T.

    2015-10-01

    Distorted-wave calculations of the triple differential cross section (TDCS) are presented for electron and positron impact ionization of Ar(3p) in coplanar asymmetric geometry at an impact energy of 1 keV and are compared with a recent experiment. The experiment indicates that the positron TDCS is generally larger than the equivalent electron TDCS. It is shown that the magnitude of the TDCS is extremely sensitive to the energy of the ejected electron and that only when the cross section is averaged over energy do we get a reasonable agreement with experiment.

  16. A coincidence study of electron and positron impact ionization of Ar (3p) at 1 keV

    NASA Astrophysics Data System (ADS)

    Campeanu, Radu I.; Walters, James H. R.; Whelan, Colm T.

    2015-10-01

    Distorted-wave calculations of the triple differential cross section (TDCS) are presented for electron and positron impact ionization of Ar(3 p) in coplanar asymmetric geometry at an impact energy of 1 keV and are compared with a recent experiment. The experiment indicates that the positron TDCS is generally larger than the equivalent electron TDCS. It is shown that the magnitude of the TDCS is extremely sensitive to the energy of the ejected electron and that only when the cross section is averaged over energy do we get a reasonable agreement with experiment.

  17. Positron-electron correlation-polarization potentials for the calculation of positron collisions with atoms and molecules*

    NASA Astrophysics Data System (ADS)

    Franz, Jan

    2017-02-01

    We present correlation-polarization potentials for the calculation of scattering cross sections of positrons with atoms and molecules. The potentials are constructed from a short-range correlation term and a long-range polarization term. For the short-range correlation term we present four different potentials that are derived from multi-component density functionals. For the long-range polarization term we employ a multi-term expansion. Quantum scattering calculations are presented for low energy collisions of positrons with two atomic targets (argon and krypton) and two molecular targets (nitrogen and methane). For collision energies below the threshold for Positronium formation our calculations of scattering cross sections are in good agreement with recent data sets from experiments and theory. Contribution to the Topical Issue "Low-Energy Interactions related to Atmospheric and Extreme Conditions", edited by S. Ptasinska, M. Smialek-Telega, A. Milosavljevic and B. Sivaraman.

  18. Dipole anisotropy in cosmic electrons and positrons: inspection on local sources

    NASA Astrophysics Data System (ADS)

    Manconi, S.; Di Mauro, M.; Donato, F.

    2017-01-01

    The cosmic electrons and positrons have been measured with unprecedented statistics up to several hundreds GeV, thus permitting to explore the role that close single sources can have in shaping the flux at different energies. In the present analysis, we consider electrons and positrons in cosmic rays to be produced by spallations of hadron fluxes with the interstellar medium, by a smooth Supernova Remnant (SNR) population, by all the ATNF catalog pulsars, and by few discrete, local SNRs. We test several source models on the e++e‑ and e+ AMS-02 flux data. For the configurations compatible with the data, we compute the dipole anisotropy in e++e‑, e+, e+/e‑ from single sources. Our study includes a dedicated analysis to the Vela SNR. We show that Fermi-LAT present data on dipole anisotropy of e++e‑ start to explore some of the models for the Vela SNR selected by AMS-02 flux data. We also investigate how the observed anisotropy could result from a combination of local sources. Our analysis shows that the search of anisotropy in the lepton fluxes up to TeV energies can be an interesting tool for the inspection of properties of close SNRs, complementary to the high precision flux data.

  19. Cosmic ray electron and positron excesses from a fourth generation heavy Majorana neutrino

    SciTech Connect

    Masina, Isabella; Sannino, Francesco E-mail: sannino@cp3-origins.net

    2011-08-01

    Unexpected features in the energy spectra of cosmic rays electrons and positrons have been recently observed by PAMELA and Fermi-LAT satellite experiments, opening to the exciting possibility of an indirect manifestation of new physics. A TeV-scale fourth lepton family is a natural extension of the Standard Model leptonic sector (also linked to the hierarchy problem in Minimal Walking Technicolor models). The heavy Majorana neutrino of this setup mixes with Standard Model charged leptons through a weak charged current interaction. Here, we first study analytically the energy spectrum of the electrons and positrons originated in the heavy Majorana neutrino decay modes, also including polarization effects. We then compare the prediction of this model with the experimental data, exploiting both the standard direct method and our recently proposed Sum Rules method. We find that the decay modes involving the tau and/or the muon charged leptons as primary decay products fit well the PAMELA and Fermi-LAT lepton excesses while there is tension with respect to the antiproton to proton fraction constrained by PAMELA.

  20. Cosmic ray electrons, positrons and the synchrotron emission of the Galaxy: consistent analysis and implications

    SciTech Connect

    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.

  1. Coherent electron-positron pair production in ultra-peripheral AuAu collisions at STAR

    NASA Astrophysics Data System (ADS)

    Rehbein, Matthew; STAR Collaboration

    2016-09-01

    The focus of this study is coherent photoproduction of electron-positron pairs in 200 GeV ultraperipheral AuAu collisions detected by STAR, with an integrated luminosity of 1.9 inverse nanobarns. Because hadronic interactions are suppressed in ultra-peripheral collisions, these events provide an opportunity to study purely electromagnetic interaction in the non-perturbative regime. This presentation will provide a description of the techniques used to select exclusive electron-positron events, as well as the resulting kinematic distributions for pair invariant mass greater than 0.35 GeV, pair transverse momentum less than 0.1 GeV, and absolute value of pair pseudorapidity less than 0.8. Efficiency correction techniques will also be discussed. In previous measurements at the same energy at STAR, the shape of the transverse momentum distribution could not be fully described by the equivalent photon approximation (EPA). Measurements at the LHC indicate that the cross section is reduced by approximately 25 percent compared to the EPA. This study ultimately seeks to examine these effects in more detail at RHIC energies. Partial funding provided by DOE Grant #DE-FG02-96ER40991.

  2. Creation of electron-positron pairs at excited Landau levels by neutrino in a strong magnetic field

    NASA Astrophysics Data System (ADS)

    Kuznetsov, A. V.; Rumyantsev, D. A.; Savin, V. N.

    2014-10-01

    The process of neutrino production of electron-positron pairs in a magnetic field of arbitrary strength, where electrons and positrons can be created in the states corresponding to excited Landau levels, is analyzed. The mean value of the neutrino energy loss due to the process ν → νe-e+ is calculated. The result can be applied for calculating the efficiency of the electron-positron plasma production by neutrinos in the conditions of the Kerr black hole accretion disk considered by experts as the most possible source of a short cosmological gamma burst. The presented research can also be useful for further development of the calculation technique for an analysis of quantum processes in external active medium, and in part in the conditions of moderately strong magnetic field, when taking account of the ground Landau level appears to be insufficient.

  3. Detection efficiency calculation for photons, electrons and positrons in a well detector. Part I: Analytical model

    NASA Astrophysics Data System (ADS)

    Pommé, S.

    2009-06-01

    An analytical model is presented to calculate the total detection efficiency of a well-type radiation detector for photons, electrons and positrons emitted from a radioactive source at an arbitrary position inside the well. The model is well suited to treat a typical set-up with a point source or cylindrical source and vial inside a NaI well detector, with or without lead shield surrounding it. It allows for fast absolute or relative total efficiency calibrations for a wide variety of geometrical configurations and also provides accurate input for the calculation of coincidence summing effects. Depending on its accuracy, it may even be applied in 4π-γ counting, a primary standardisation method for activity. Besides an accurate account of photon interactions, precautions are taken to simulate the special case of 511 keV annihilation quanta and to include realistic approximations for the range of (conversion) electrons and β -- and β +-particles.

  4. Scattering of Low Energy Electrons and Positrons from Hydrogenic Systems and Applications

    NASA Technical Reports Server (NTRS)

    Bhatia, Anand K.

    2007-01-01

    While the electron scatters from the target, the target no longer stays in its original form. One of the first methods to take into account the distortion of the target at low incident energies is the method of polarized orbitals. In this method the wave function for the process is written using the first-order perturbation theory and the equation for the scattering function is derived from the Schradinger equation. This method has been very successful in calculating the phase shifts and therefore the cross sections at various energies. The total wave function can be used to calculate photoionization cross sections. The disadvantage of this approach is that the method is not variational and therefore does not provide bounds on the phase shifts. These difficulties can be overcome by using the Feshbach projection operator formalism. This approach has been employed for the scattering of electrons and positrons from targets. Results of various calculations will be discussed.

  5. A search for single electron production in electron positron annihilation at E = 29 GeV

    SciTech Connect

    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.

  6. Thermal and optical excitation of trapped electrons in high-density polyethylene (HDPE) studied through positron annihilation

    NASA Astrophysics Data System (ADS)

    Nahid, F.; Zhang, J. D.; Yu, T. F.; Ling, C. C.; Fung, S.; Beling, C. D.

    2011-04-01

    Positronium (Ps) formation in high-density polyethylene (HDPE) has been studied below the glass transition temperature. The formation probability increases with positron irradiation time due to an increasing number of inter-track trapped electrons becoming available for positron capture. The temperature variation of the saturated Ps level is discussed in different models. The quenching of trapped electrons by light has been studied and the optical de-trapping cross-section for different photon energies has been estimated over the visible region.

  7. Standing electromagnetic solitons in hot ultra-relativistic electron-positron plasmas

    SciTech Connect

    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.

  8. First-principles calculations of momentum distributions of annihilating electron-positron pairs in defects in UO2

    NASA Astrophysics Data System (ADS)

    Wiktor, Julia; Jomard, Gérald; Torrent, Marc; Bertolus, Marjorie

    2017-01-01

    We performed first-principles calculations of the momentum distributions of annihilating electron-positron pairs in vacancies in uranium dioxide. Full atomic relaxation effects (due to both electronic and positronic forces) were taken into account and self-consistent two-component density functional theory schemes were used. We present one-dimensional momentum distributions (Doppler-broadened annihilation radiation line shapes) along with line-shape parameters S and W. We studied the effect of the charge state of the defect on the Doppler spectra. The effect of krypton incorporation in the vacancy was also considered and it was shown that it should be possible to observe the fission gas incorporation in defects in UO2 using positron annihilation spectroscopy. We suggest that the Doppler broadening measurements can be especially useful for studying impurities and dopants in UO2 and of mixed actinide oxides.

  9. Enhanced Dark Matter Annihilation Rate for Positron and Electron Excesses from Q-Ball Decay

    SciTech Connect

    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.

  10. Observation of exclusive electron-positron production in hadron-hadron collisions.

    PubMed

    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; Freeman, J C; Furic, I; Gallinaro, M; Galyardt, J; Garcia, J E; Garberson, F; Garfinkel, A F; Gay, C; Gerberich, H; Gerdes, D; Giagu, S; Giannetti, P; Gibson, A; Gibson, K; Gimmell, J L; Ginsburg, C; Giokaris, N; Giordani, M; Giromini, P; Giunta, M; Giurgiu, G; Glagolev, V; Glenzinski, D; Gold, M; Goldschmidt, N; Goldstein, J; Gomez, G; Gomez-Ceballos, G; Goncharov, M; González, O; Gorelov, I; Goshaw, A T; Goulianos, K; Gresele, A; Griffiths, M; Grinstein, S; Grosso-Pilcher, C; Grundler, U; da Costa, J Guimaraes; Gunay-Unalan, Z; Haber, C; Hahn, K; Hahn, S R; Halkiadakis, E; Hamilton, A; Han, B-Y; Han, J Y; Handler, R; Happacher, F; Hara, K; Hare, M; Harper, S; Harr, R F; Harris, R M; Hartz, M; Hatakeyama, K; Hauser, J; Heijboer, A; Heinemann, B; Heinrich, J; Henderson, C; Herndon, M; Heuser, J; Hidas, D; Hill, C S; Hirschbuehl, D; Hocker, A; Holloway, A; Hou, S; Houlden, M; Hsu, S-C; Huffman, B T; Hughes, R E; Husemann, U; Huston, J; Incandela, J; Introzzi, G; Iori, M; Ishizawa, Y; Ivanov, A; Iyutin, B; James, E; Jang, D; Jayatilaka, B; Jeans, D; Jensen, H; Jeon, E J; Jindariani, S; Jones, M; Joo, K K; Jun, S Y; Jung, J E; Junk, T R; Kamon, T; Karchin, P E; Kato, Y; Kemp, Y; Kephart, R; Kerzel, U; Khotilovich, V; Kilminster, B; Kim, D H; Kim, H S; Kim, J E; Kim, M J; Kim, S B; Kim, S H; Kim, Y K; Kimura, N; Kirsch, L; Klimenko, S; Klute, M; Knuteson, B; Ko, B R; Kondo, K; Kong, D J; Konigsberg, J; Korytov, A; Kotwal, A V; Kovalev, A; Kraan, A C; Kraus, J; Kravchenko, I; Kreps, M; Kroll, J; Krumnack, N; Kruse, M; Krutelyov, V; Kubo, T; Kuhlmann, S E; Kuhr, T; Kusakabe, Y; Kwang, S; Laasanen, A T; Lai, S; Lami, S; Lammel, S; Lancaster, M; Lander, R L; Lannon, K; Lath, A; Latino, G; Lazzizzera, I; Lecompte, T; Lee, J; Lee, J; Lee, Y J; Lee, S W; Lefèvre, R; Leonardo, N; Leone, S; Levy, S; Lewis, J D; Lin, C; Lin, C S; Lindgren, M; Lipeles, E; Lister, A; Litvintsev, D O; Liu, T; Lockyer, N S; Loginov, A; Loreti, M; Loverre, P; Lu, R-S; Lucchesi, D; Lujan, P; Lukens, P; Lungu, G; Lyons, L; Lys, J; Lysak, R; Lytken, E; Mack, P; Macqueen, D; Madrak, R; Maeshima, K; Makhoul, K; Maki, T; Maksimovic, P; Malde, S; Manca, G; Margaroli, F; Marginean, R; Marino, C; Marino, C P; Martin, A; Martin, M; Martin, V; Martínez, M; Maruyama, T; Mastrandrea, P; Masubuchi, T; Matsunaga, H; Mattson, M E; Mazini, R; Mazzanti, P; McFarland, K S; McIntyre, P; McNulty, R; Mehta, A; Mehtala, P; Menzemer, S; Menzione, A; Merkel, P; Mesropian, C; Messina, A; Miao, T; Miladinovic, N; Miles, J; Miller, R; Mills, C; Milnik, M; Mitra, A; Mitselmakher, G; Miyamoto, A; Moed, S; Moggi, N; Mohr, B; Moore, R; Morello, M; Fernandez, P Movilla; Mülmenstädt, J; Mukherjee, A; Muller, Th; Mumford, R; Murat, P; Nachtman, J; Nagano, A; Naganoma, J; Nakano, I; Napier, A; Necula, V; Neu, C; Neubauer, M S; Nielsen, J; Nigmanov, T; Nodulman, L; Norniella, O; Nurse, E; Oh, S H; Oh, Y D; Oksuzian, I; Okusawa, T; Oldeman, R; Orava, R; Osterberg, K; Pagliarone, C; Palencia, E; Papadimitriou, V; Paramonov, A A; Parks, B; Pashapour, S; Patrick, J; Pauletta, G; Paulini, M; Paus, C; Pellett, D E; Penzo, A; Phillips, T J; Piacentino, G; Piedra, J; Pinera, L; Pinfold, J; Pitts, K; Plager, C; Pondrom, L; Portell, X; Poukhov, O; Pounder, N; Prakoshyn, F; Pronko, A; Proudfoot, J; Ptohos, F; Punzi, G; Pursley, J; Rademacker, J; Rahaman, A; Ranjan, N; Rappoccio, S; Reisert, B; Rekovic, V; Renton, P; Rescigno, M; Richter, S; Rimondi, F; Ristori, L; Robson, A; Rodrigo, T; Rogers, E; Rolli, S; Roser, R; Rossi, M; Rossin, R; Ruiz, A; Russ, J; Rusu, V; Saarikko, H; Sabik, S; Safonov, A; Sakumoto, W K; Salamanna, G; Saltó, O; Saltzberg, D; Sánchez, C; Santi, L; Sarkar, S; Sartori, L; Sato, K; Savard, P; Savoy-Navarro, A; Scheidle, T; Schlabach, P; Schmidt, E E; Schmidt, M P; Schmitt, M; Schwarz, T; Scodellaro, L; Scott, A L; Scribano, A; Scuri, F; Sedov, A; Seidel, S; Seiya, Y; Semenov, A; Sexton-Kennedy, L; Sfyrla, A; Shapiro, M D; Shears, T; Shepard, P F; Sherman, D; Shimojima, M; Shochet, M; Shon, Y; Shreyber, I; Sidoti, A; Sinervo, P; Sisakyan, A; Sjolin, J; Slaughter, A J; Slaunwhite, J; Sliwa, K; Smith, J R; Snider, F D; Snihur, R; Soderberg, M; Soha, A; Somalwar, S; Sorin, V; Spalding, J; Spinella, F; Spreitzer, T; Squillacioti, P; Stanitzki, M; Staveris-Polykalas, A; Denis, R St; Stelzer, B; Stelzer-Chilton, O; Stentz, D; Strologas, J; Stuart, D; Suh, J S; Sukhanov, A; Sun, H; Suzuki, T; Taffard, A; Takashima, R; Takeuchi, Y; Takikawa, K; Tanaka, M; Tanaka, R; Tecchio, M; Teng, P K; Terashi, K; Thom, J; Thompson, A S; Thomson, E; Tipton, P; Tiwari, V; Tkaczyk, S; Toback, D; Tokar, S; Tollefson, K; Tomura, T; Tonelli, D; Torre, S; Torretta, D; Tourneur, S; Trischuk, W; Tsuchiya, R; Tsuno, S; Turini, N; Ukegawa, F; Unverhau, T; Uozumi, S; Usynin, D; Vallecorsa, S; van Remortel, N; Varganov, A; Vataga, E; Vázquez, F; Velev, G; Veramendi, G; Veszpremi, V; Vidal, R; Vila, I; Vilar, R; Vine, T; Vollrath, I; Volobouev, I; Volpi, G; Würthwein, F; Wagner, P; Wagner, R G; Wagner, R L; Wagner, J; Wagner, W; Wallny, R; 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.

  11. Gamma-ray bursts: Modeling electron-positron pair plasmas in cataclysmic astrophysical phenomena

    NASA Astrophysics Data System (ADS)

    Salmonson, Jay David

    Despite three decades of intense scientific scrutiny, gamma-ray bursts have remained one of astronomy's biggest unsolved mysteries. Recent observational breakthroughs have allowed us to learn much about these big, brief, brilliant bangs seen from across the cosmos, but their origin remains a mystery. In this work we study three progenitor models: a neutron star binary system near its last stable orbit, a charged black hole, and the collapse of a globular star cluster. All of these scenarios result in a common theme; the relativistic expansion of a super- heated electron-positron-photon plasma. Thus we study the evolution of, and emission from, this plasma as it might result from these three progenitors using numerical general relativistic hydrodynamic simulations. This emission is then compared with that of gamma-ray bursts to test the feasibility of each of these models as a gamma-ray burst progenitor.

  12. Ion acoustic solitary waves in plasmas with nonextensive electrons, Boltzmann positrons and relativistic thermal ions

    NASA Astrophysics Data System (ADS)

    Hafez, M. G.; Talukder, M. R.

    2015-09-01

    This work investigates the theoretical and numerical studies on nonlinear propagation of ion acoustic solitary waves (IASWs) in an unmagnetized plasma consisting of nonextensive electrons, Boltzmann positrons and relativistic thermal ions. The Korteweg-de Vries (KdV) equation is derived by using the well known reductive perturbation method. This equation admits the soliton like solitary wave solution. The effects of phase velocity, amplitude of soliton, width of soliton and electrostatic nonlinear propagation of weakly relativistic ion-acoustic solitary waves have been discussed with graphical representation found in the variation of the plasma parameters. The obtained results can be helpful in understanding the features of small but finite amplitude localized relativistic ion-acoustic waves for an unmagnetized three component plasma system in astrophysical compact objects.

  13. Investigation into electron cloud effects in the International Linear Collider positron damping ring

    SciTech Connect

    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.

    2014-03-01

    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

  14. 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.

  15. 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.

  16. Interaction of nonthermal muon beam with electron-positron-photon plasma: A thermal field theory approach

    SciTech Connect

    Noorian, Zainab; Eslami, Parvin; Javidan, Kurosh

    2013-11-15

    Interaction of a muon beam with hot dense QED plasma is investigated. Plasma system contains electrons and positrons with Fermi-Dirac distribution and Bose-Einstein distributed photons while the beam particles have nonthermal distribution. The energy loss of the beam particles during the interaction with plasma is calculated to complete leading order of interaction in terms of the QED coupling constant using thermal field theory approach. The screening effects of the plasma are computed consistently using resummation of perturbation theory with hard thermal loop approximation according to the Braaten-Pisarski method. Time evolution of the plasma characteristics and also plasma identifications during the interaction are investigated. Effects of the nonthermal parameter of the beam distribution on the energy exchange and the evolution of plasma-beam system are also explained.

  17. Moments of event shapes in electron-positron annihilation at next-to-next-to-leading order

    SciTech Connect

    Weinzierl, Stefan

    2009-11-01

    This article gives the perturbative next-to-next-to-leading order results for the moments of the most commonly used event shape variables associated to three-jet events in electron-positron annihilation: thrust, heavy jet mass, wide jet broadening, total jet broadening, C parameter and the Durham three-to-two-jet transition variable.

  18. Simultaneous Creation of Electron-Positron Pairs and Photons in Robertson-Walker Universes with Statically Bounded Expansion

    NASA Astrophysics Data System (ADS)

    Lotze, K.-H.

    We present, based upon quantum electrodynamics in Robertson-Walker flat universes, a thorough analysis of the creation of mutually interacting electron-positron pairs and photons from vacuum. Therefore we discuss at least qualitatively all processes contributing to the number densities of created particles up to the second order in the coupling constant. For two particular expansion laws with Minkowskian in respectively in and out regions, we obtain exact solutions to the Dirac equation and investigate in detail the process of simultaneous creation of electron-positron pairs and photons and the related attenuation effect for fermionic particles. This is done for electrons and positrons which have nonrelativistic momenta at Compton time in rapidly expanding universes. The results are compared with the zeroth-order creation of electron-positron pairs. Despite being smaller by a factor of roughly e02 /4π ≈ 1 /137, the interacting-particle creation is important mainly as a source of photons even in conformally flat universes.

  19. Interpretation of recent positron-electron measurements between 20 and 800 MeV. [interplanetary cosmic ray solar modulation

    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.

  20. Excitation of Electronic States of Ar, H{sub 2}, and N{sub 2} by Positron Impact

    SciTech Connect

    Sullivan, J. P.; Marler, J. P.; Gilbert, S. J.; Buckman, S. J.; Surko, C. M.

    2001-08-13

    We have measured the first state-resolved, absolute cross sections for positron excitation of electronic states of an atom or molecule using a high resolution ({Delta}E{approx}25 meV FWHM) beam of positrons from a Penning-Malmberg trap. We present cross sections for the excitation of the low-lying levels of Ar, H{sub 2}, and N{sub 2} for incident positron energies between threshold and 30eV. For Ar and H{sub 2}, comparison can be made with theoretical calculations, and, in the case of H{sub 2}, the results resolve a significant discrepancy between the only two available calculations.

  1. Phase-mixing of Langmuir oscillations in cold electron-positron-ion plasmas

    SciTech Connect

    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.

  2. Head on collision of multi-solitons in an electron-positron-ion plasma having superthermal electrons

    SciTech Connect

    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.

  3. Direct Production of Electron-Positron Pairs by 200-GeV/Nucleon Oxygen and Sulfur Ions in Nuclear Emulsion

    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.

  4. Wave dispersion in a counterstreaming, cold, magnetized, electron-positron plasma.

    PubMed

    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.

  5. PIC simulations of the MagnetoRotational instability in electron-positron plasmas

    NASA Astrophysics Data System (ADS)

    Inchingolo, Giannandrea; Grismayer, Thomas; Loureiro, Nuno F.; Fonseca, Ricardo A.; Silva, Luis O.

    2016-10-01

    The magnetorotational instability (MRI) is a crucial mechanism of angular momentum transport in a variety of astrophysical scenarios, as e-e+ plasmas accretion disks nearness neutron stars and black holes. The MRI has been widely studied using MHD models and simulations, in order to understand the behavior of astrophysical fluids in a state of differential rotation. When the timescale for electron and ion collisions is longer than the inflow time in the disk, the plasma is macroscopically collisionless and MHD breaks down. This is the case of the limit of weak magnetic field, i.e., as the ratio of the ion cyclotron frequency to orbital frequency becomes small. Leveraging on the recent addition of the shearing co-rotating frames equations of motion and Maxwell's equations modules in our PIC code OSIRIS 3.0, we intend to present our recent results of the analysis of MRI in electron-positron plasma in the limit of weak magnetic field. We will recall the theoretical 1D linear model of Krolik et Zweibel that describes the behavior of MRI in the limit of weak magnetic field and use it to support our results. Moving to 2D simulations, the analysis of MRI via PIC code permits to investigate also how MRI will act in comparison with other Kinetic instabilities, like mirror instability.

  6. 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.

  7. FPGA-Based Front-End Electronics for Positron Emission Tomography.

    PubMed

    Haselman, Michael; Dewitt, Don; McDougald, Wendy; Lewellen, Thomas K; Miyaoka, Robert; Hauck, Scott

    2009-02-22

    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.

  8. The electron-cloud instability in the arcs of the PEP-II positron ring

    SciTech Connect

    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.

  9. Higher-order nonlinear equations for the electron-acoustic waves in a nonextensive electron-positron-ion plasma

    NASA Astrophysics Data System (ADS)

    Rafat, A.; Rahman, M. M.; Alam, M. S.; Mamun, A. A.

    2015-07-01

    A precise theoretical investigation has been made on electron-acoustic (EA) Gardner solitons (GSs) and double layers (DLs) in a four-component plasma system consisting of nonextensive hot electrons and positrons, inertial cold electrons, and immobile positive ions. The well-known reductive perturbation method has been used to derive the Korteweg-de Vries (K-dV), modified K-dV (mK-dV), and Gardner equations along with their solitary wave as well as double layer solutions. It has been found that depending on the plasma parameters, the K-dV solitons and GSs are either compressive or rarefactive, whereas the mK-dV solitons are only compressive, and Gardner DLs are only rarefactive. The analytical comparison among the K-dV solitons, mK-dV solitons, and GSs are also investigated. It has been identified that the basic properties of such EA solitons and EA DLs are significantly modified due to the effects of nonextensivity and other plasma parameters related to plasma particle number densities and to temperature of different plasma species. The results of our present investigation can be helpful for understanding the nonlinear electrostatic structures associated with EA waves in various interstellar space plasma environments and cosmological scenarios (viz. quark-gluon plasma, protoneutron stars, stellar polytropes, hadronic matter, dark-matter halos, etc.)

  10. Applications and advances of positron beam spectroscopy

    SciTech Connect

    Howell, R., LLNL

    1998-03-18

    Over 50 scientists from DOE-DP, DOE-ER, the national laboratories, academia and industry attended a workshop held on November 5-7, 1997 at Lawrence Livermore National Laboratory. Workshop participants were charged to address two questions: Is there a need for a national center for materials analysis using positron techniques and can the capabilities at Lawrence Livermore National Laboratory serve this need. To demonstrate the need for a national center, the workshop participants discussed the technical advantages enabled by high positron currents and advanced measurement techniques, the role that these techniques would play in materials analysis and the demand for the data. Livermore now leads the world in materials analysis capabilities by positrons due to developments in response to demands of stockpile stewardship. The Livermore facilities now include the world`s highest current beam of keV positrons, a scanning pulsed positron microprobe under development capable of three dimensional maps of defect size and concentration, an MeV positron beam for defect analysis of large samples, and electron momentum spectroscopy by positrons. It was concluded that the positron microprobe under development at LLNL and other new instruments that would be relocated at LLNL at the high current keV source are an exciting step forward in providing results for the positron technique. These new data will impact a wide variety of applications.

  11. Operating instructions for ORELA (Oak Ridge Electron Linear Accelerator) positron beam line

    SciTech Connect

    Donohue, D.L.; Hulett, L.D. Jr.; Lewis, T.A.

    1990-11-01

    This report will contain details of the construction and operation of the positron beam line. Special procedures which are performed on a less frequent basis will also be described. Appendices will contain operating instructions for experiments which make use of the positron beam and are connected to the beam line. Finally, a review of safety-related considerations will be presented.

  12. Motion and energy dissipation of secondary electrons, positrons and hadrons correlated with terrestrial gamma-ray flashes

    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.

  13. Pumped helium system for cooling positron and electron traps to 1.2 K

    NASA Astrophysics Data System (ADS)

    Wrubel, J.; Gabrielse, G.; Kolthammer, W. S.; Larochelle, P.; McConnell, R.; Richerme, P.; Grzonka, D.; Oelert, W.; Sefzick, T.; Zielinski, M.; Borbely, J. S.; George, M. C.; Hessels, E. A.; Storry, C. H.; Weel, M.; Müllers, A.; Walz, J.; Speck, A.

    2011-06-01

    Extremely precise tests of fundamental particle symmetries should be possible via laser spectroscopy of trapped antihydrogen ( H¯) atoms. H¯ atoms that can be trapped must have an energy in temperature units that is below 0.5 K—the energy depth of the deepest magnetic traps that can currently be constructed with high currents and superconducting technology. The number of atoms in a Boltzmann distribution with energies lower than this trap depth depends sharply upon the temperature of the thermal distribution. For example, ten times more atoms with energies low enough to be trapped are in a thermal distribution at a temperature of 1.2 K than for a temperature of 4.2 K. To date, H¯ atoms have only been produced within traps whose electrode temperature is 4.2 K or higher. A lower temperature apparatus is desirable if usable numbers of atoms that can be trapped are to eventually be produced. This report is about the pumped helium apparatus that cooled the trap electrodes of an H¯ apparatus to 1.2 K for the first time. Significant apparatus challenges include the need to cool a 0.8 m stack of 37 trap electrodes separated by only a mm from the substantial mass of a 4.2 K Ioffe trap and the substantial mass of a 4.2 K solenoid. Access to the interior of the cold electrodes must be maintained for antiprotons, positrons, electrons and lasers.

  14. Modulation and filamentation instability of ultrarelativistic electromagnetic waves in electron-positron-ion plasma

    NASA Astrophysics Data System (ADS)

    Rozina, Ch.; Tsintsade, N. L.; Maryam, N.; Komal, S.

    2016-11-01

    In this study, we have analytically investigated the effects of nonlinear Landau damping on the temporal growth rate of modulation and filamentation instabilities. Here, the nonlocal nonlinear Landau damping phenomena is appearing due to the nonlinear interaction between ultrarelativistic electromagnetic (UREM) wave (having wave vector normal to the beam) and electron-positron-ion plasma. We found that the ultrarelativistic ponderomotive force is linear, while usually it is nonlinear in relativistic case. We construct three dimensional kinetic nonlinear Schrödinger equation for a slowly varying spatio and temporal amplitude of UREM waves. The equations are then Fourier analyzed to obtain dispersion relation, which admit both modulation and filamentation instabilities. It is shown that nonlinear Landau damping is the main source of modulation instability, for a particular condition taking into account later one the maximum growth rate of modulation instability obtained as a function of amplitude of UREM waves and is displayed graphically. Further, it is shown that for an oscillating density profile, plane wave of uniform intensity becomes unstable and gets filamented. Growth rate of stationary state filament is found to be a function of amplitude of UREM waves and is emphasized that the maximum value of growth rate of filamentation instability is further increased in the presence of nonlinear Landau damping term. Finally, the growth rate of non stationary state filamentation instability is calculated and is shown that the characteristic growth length increases both with perpendicular wave vector and the amplitude of UREM waves.

  15. Parametric decays in relativistic magnetized electron-positron plasmas with relativistic temperatures

    SciTech Connect

    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.

  16. Simulation of ultra-relativistic electrons and positrons channeling in crystals with MBN EXPLORER

    NASA Astrophysics Data System (ADS)

    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.

  17. Radial Electron Momentum Densities of Colloidal CdSe Nanocrystals Determined by Positron Beam Analysis

    SciTech Connect

    Denison, A B; Meulenberg, R; Eijt, S W H; Van Veen, A; Mijnarends, P E; Barbiellini, B; Bansil, A; Fischer, C; Weber, M H; Lynn, K G

    2003-07-31

    We present depth-resolved positron 2D angular correlation of annihilation radiation (2DACAR) experiments on CdSe quantum dots in the diameter range from 2.5 to 6 nm, deposited as micrometer thin layers. The average radial distribution of the valence electron momentum density (EMD) of CdSe quantum dots has been extracted, which reveals a systematic dependence upon particle size. The quantum confinement related changes and their size scaling observable at the Jones zone momentum of {approx}0.8 a.u. seem to agree with the previous coincidence Doppler study. In addition, the average radial EMD shows an increase in the low-momentum range (<0.6 a.u.) and a reduction in the high-momentum range (>1.6 a.u.) with respect to that measured on a bulk CdSe single crystal. Possible origins of these are described. First-principles calculations based on the Korringa-Kohn-Rostoker (KKR) method were performed to gain a better insight.

  18. Semiclassical picture for electron-positron photoproduction in strong laser fields

    NASA Astrophysics Data System (ADS)

    Meuren, Sebastian; Keitel, Christoph H.; Di Piazza, Antonino

    2016-04-01

    The nonlinear Breit-Wheeler process is studied in the presence of strong and short laser pulses. We show that for a relativistically intense plane-wave laser field many features of the momentum distribution of the produced electron-positron pair like its extension, region of highest probability and carrier-envelope phase effects can be explained from the classical evolution of the created particles in the background field. To this end an intuitive semiclassical picture based on the local constant-crossed field approximation applied on the probability-amplitude level is established and compared with the standard approach used in QED-PIC codes. The main difference is the substructure of the spectrum, which results from interference effects between macroscopically separated formation regions. In order to compare the predictions of the semiclassical approach with exact calculations, a very fast numerical scheme is introduced. It renders the calculation of the fully differential spectrum on a grid which resolves all interference fringes feasible. Finally, the difference between classical and quantum absorption of laser four-momentum in the process is pointed out and the dominance of the former is proven. As a self-consistent treatment of the quantum absorption is not feasible within existing QED-PIC approaches, our results provide reliable error estimates relevant for regimes where the laser depletion due to a developing QED cascade becomes significant.

  19. Simulation of ultra-relativistic electrons and positrons channeling in crystals with MBN EXPLORER

    SciTech Connect

    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.

  20. The beam energy feedback system for Beijing electron positron collider II linac.

    PubMed

    Wang, S; Iqbal, M; Chi, Y; Liu, R; Huang, X

    2017-03-01

    A beam-energy feedback system has been developed for the injection linac to meet the beam quality needed for the Beijing electron positron collider II storage ring. This paper describes the implementation and commissioning of this system in detail. The system consists of an energy measurement unit, application software, and an actuator unit. A non-intersecting beam energy monitor was developed to allow real-time online energy adjustment. The beam energy adjustment is achieved by adjusting the output microwave phase of the RF power source station. The phase control mechanism has also been modified, and a new control method taking the return difference of the phase shifter into account is used to improve the system's performance. This system achieves the design aim and can adjust the beam center energy with a rate of 2 Hz. With the energy feedback system, the stability of the injection rate is better; the fluctuation range is reduced from 20 mA/min to 10 mA/min, while the stability of the beam center energy is maintained within ±0.1%.

  1. Dynamics of laser beams in inhomogeneous electron-positron-ion plasmas

    NASA Astrophysics Data System (ADS)

    Cheng, Li-Hong; Tang, Rong-An; Du, Hong-E.; Xue, Ju-Kui

    2015-07-01

    Nonlinear interaction of laser and electron-positron-ion plasmas is investigated by invoking the variational principle and numerical simulation, in terms of a nonlinear Schrödinger equation with inhomogeneities effect. It is shown that the plasma inhomogeneity has great influence on the laser beam dynamics. The laser beam can be self-trapped, focused, or defocused depending on the inhomogeneity character. The linearly decreasing axial plasma density makes the laser beam defocus, while the linearly increasing axial plasma density results in self-trapping of the beam. The self-focusing of the trapped beam is found in a high-density region. For the Gaussian types of density distribution, the beam field submits nonlinearly oscillating regime. The results provide an efficient way to manipulate the dynamics of laser beam propagating in plasma. Project supported by the National Natural Science Foundation of China (Grant Nos. 11274255 and 11305132), the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20136203110001), the Natural Science Foundation of Gansu Province, China (Grant No. 2011GS04358), and the Creation of Science and Technology of Northwest Normal University, China (Grant Nos. NWNU-KJCXGC-03-48 and NWNU-LKQN-12-12).

  2. Positron annihilation study of defects in electron-irradiated single crystal zinc oxide

    NASA Astrophysics Data System (ADS)

    To, C. K.; Yang, B.; Beling, C. D.; Fung, S.; Ling, C. C.; Gong, M.

    2011-01-01

    Pressurized melt grown zinc oxide (ZnO) single crystals purchased from Cermet Inc. were irradiated by 2MeV electrons with fluence of 6x1017cm-2. Isochronal annealing from 100°C-800°C was performed on the crystals under argon and air ambience. Variable Energy Doppler Broadening Spectroscopy (VEDBS) was carried out on both the as-grown and the irradiated samples at each annealing step. The migration, agglomeration and annealing of grown-in and irradiated-introduced defects were studied. It was observed that the grown-in vacancy-type defects concentration decreased at 300°C and 600 °C. For the irradiated sample annealed in argon, the positron trapping vacancy-type defect concentration decreased at 300°C and 600°C. Further annealing the as-grown and irradiated samples in argon increased the S parameter further. For the irradiated sample annealed in air, the vacancy-type defect concentration decreases at 300°C and 700°C.

  3. 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.

  4. Pair creation induced by transitions between electronic and positronic bound states

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Lv, Q. Z.; Li, Y. T.; Grobe, R.; Su, Q.

    2015-05-01

    We study the creation process of electron-positron pairs from the quantum electrodynamical vacuum under very strong electric fields by solving the quantum field theoretical Dirac equation on a space-time grid. We investigate the role of bound-bound state mixing in such a process, which can be studied if the external force can be modeled by a combination of a potential barrier and a potential well. By increasing the magnitude of the two potentials, discrete states that originate from the positive and negative energy continua can become quasidegenerate in the mass gap region (between -mc 2 and mc 2). We show that this bound-bound state mixing is quite different from the usual bound-continuum state mixing where the particles are created until the Pauli exclusion principle inhibits this process. In the case of bound-bound mixing the particle number exhibits a characteristic oscillatory behavior that in principle can last forever. These findings can be modeled by an effective two-state model.

  5. Observation of Exclusive Electron-Positron Production in Hadron-Hadron Collisions

    SciTech Connect

    Abulencia, A.; Adelman, J.; Affolder, T.; Akimoto, T.; Albrow, M.G.; Ambrose, D.; Amerio, S.; Amidei, D.; Anastassov, A.; Anikeev, K.; Annovi, A.

    2006-11-01

    We present the first observation of exclusive e{sup +}e{sup -} production in hadron-hadron collisions, using p{bar p} collision data at {radical}s = 1.96 TeV taken by the Run II Collider Detector at Fermilab, and corresponding to an integrated luminosity of 532 pb{sup -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{sub 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 p{bar p} {yields} p + e{sup +}e{sup -} + {bar p} through two-photon exchange. The measured cross section is 1.6{sub -0.3}{sup +0.5}(stat) {+-} 0.3(syst) pb. This agrees with the theoretical prediction of 1.71 {+-} 0.01 pb.

  6. Modulation of a compressional electromagnetic wave in a magnetized electron-positron quantum plasma

    NASA Astrophysics Data System (ADS)

    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.

  7. Nonlinear dispersion and transverse profile of intense electromagnetic waves, propagating through electron-positron-ion hot magnetoplasma

    SciTech Connect

    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.

  8. Positronium formation as a three-body reaction. I. The second-order positron-electron interaction amplitude

    NASA Astrophysics Data System (ADS)

    Bolorizadeh, M. A.; Brunger, M. J.; Maddern, T.; Ghanbari Adivi, E.

    2007-03-01

    We derive the exact analytic form for the second-order positron-electron interaction term in the Faddeev three-body approach which is applicable in the nonrelativistic high energy region. Although there is no nonintegrable singularity in the six-dimensional integral form of this amplitude, here the basic difficulty arises from the presence of complex nonintegral exponents in the components included in the integrand. Consequently, three brunch cuts must be handled simultaneously. However, by using an integral representation of the gamma function, these brunch cuts are removed from the integrand. Expanding the radial parts of the initial and final wave functions further reduces the second-order positron-electron interaction term to a one-variable integral in terms of Bessel functions of the third kind. The different final closed expressions are ultimately derived in terms of the generalized hypergeometric functions for different regions of the scattering angle.

  9. The interaction of two nonplanar solitary waves in electron-positron-ion plasmas: An application in active galactic nuclei

    SciTech Connect

    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.

  10. Kinetic Phenomena in Transport of Electrons and Positrons in Gases caused by the Properties of Scattering Cross Sections

    NASA Astrophysics Data System (ADS)

    Petrović, Zoran Lj; Marjanović, Srdan; Dujko, Saša; Banković, Ana; Šašić, Olivera; Bošnjaković, Danko; Stojanović, Vladimir; Malović, Gordana; Buckman, Stephen; Garcia, Gustavo; White, Ron; Sullivan, James; Brunger, Michael

    2014-04-01

    Collisions of electrons, atoms, molecules, photons and ions are the basic processes in plasmas and ionized gases in general. This is especially valid for low temperature collisional plasmas. Kinetic phenomena in transport are very sensitivitive to the shape of the cross sections and may at the same time affect the macroscopic applications. We will show how transport theory or simulation codes, phenomenology, kinetic phenomena and transport data may be used to improve our knowledge of the cross sections, our understanding of the plasma models, application of the swarm physics in ionized gases and similar applications to model and improve gas filled traps of positrons. Swarm techniques could also be a starting point in applying atomic and molecular data in models of electron or positron therapy/diagnostics in radiation related medicine.

  11. Design of An 18 MW Beam Dump for 500 GeV Electron/Positron Beams at An ILC

    SciTech Connect

    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.

  12. Dense electron-positron plasmas and bursts of gamma-rays from laser-generated quantum electrodynamic plasmas

    SciTech Connect

    Ridgers, C. P.; Bell, A. R.; Brady, C. S.; Bennett, K.; Arber, T. D.; Duclous, R.; Kirk, J. G.

    2013-05-15

    In simulations of a 12.5 PW laser (focussed intensity I=4×10{sup 23}Wcm{sup −2}) striking a solid aluminum target, 10% of the laser energy is converted to gamma-rays. A dense electron-positron plasma is generated with a maximum density of 10{sup 26}m{sup −3}, seven orders of magnitude denser than pure e{sup −} e{sup +} plasmas generated with 1PW lasers. When the laser power is increased to 320 PW (I=10{sup 25}Wcm{sup −2}), 40% of the laser energy is converted to gamma-ray photons and 10% to electron-positron pairs. In both cases, there is strong feedback between the QED emission processes and the plasma physics, the defining feature of the new “QED-plasma” regime reached in these interactions.

  13. Modulation instability of ion acoustic waves, solitons, and their interactions in nonthermal electron-positron-ion plasmas

    SciTech Connect

    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.

  14. Improvement of the technique of identification of electrons and positrons with use of electromagnetic calorimeter of the CLAS detector

    SciTech Connect

    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).

  15. Fine-grid calculations for stellar electron and positron capture rates on Fe isotopes

    SciTech Connect

    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.

  16. Generation of overdense and high-energy electron-positron-pair plasmas by irradiation of a thin foil with two ultraintense lasers.

    PubMed

    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.

  17. Hydrodynamic and kinetic models for spin-1/2 electron-positron quantum plasmas: Annihilation interaction, helicity conservation, and wave dispersion in magnetized plasmas

    SciTech Connect

    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.

  18. Recent Developments in the Design of the NLC Positron Source

    SciTech Connect

    Kotseroglou, T.; Bharadwaj, V.; Clendenin, J.E.; Ecklund, S,; Frisch, J.; Krejcik, P,; Kukikov, A.V.; Liu, J.; Maruyama, T.; Millage, K.K.; Mulhollan, G.; Nelson, W.R.; Schultz, D.C.; Sheppard, J.C.; Turner, J.; Van Bibber, K.; Flottmann, K.; Namito, Y.

    1999-11-05

    Recent developments in the design of the Next Linear Collider (NLC) positron source based on updated beam parameters are described. The unpolarized NLC positron source [1,2] consists of a dedicated 6.2 GeV S-band electron accelerator, a high-Z positron production target, a capture system and an L-band positron linac. The 1998 failure of the SLC target, which is currently under investigation, may lead to a variation of the target design. Progress towards a polarized positron source is also presented. A moderately polarized positron beam colliding with a highly polarized electron beam results in an effective polarization large enough to explore new physics at NLC. One of the schemes towards a polarized positron source incorporates a polarized electron source, a 50 MeV electron accelerator, a thin target for positron production and a new capture system optimized for high-energy, small angular-divergence positrons. The yield for such a process, checked using the EGS4 code, is of the order of 10{sup -3}. The EGS4 code has being enhanced to include the effect of polarization in bremsstrahlung and pair-production process.

  19. The effect of drift on the evolution of the electron/positron spectra in an axisymmetric pulsar wind nebula

    SciTech Connect

    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.

  20. Amplitude modulation of quantum-ion-acoustic wavepackets in electron-positron-ion plasmas: Modulational instability, envelope modes, extreme waves

    SciTech Connect

    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.

  1. Positron annihilation study for enhanced nitrogen-vacancy center formation in diamond by electron irradiation at 77 K

    SciTech Connect

    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.

  2. Positron-molecule bound states and positive ion production

    NASA Technical Reports Server (NTRS)

    Leventhal, M.; Passner, A.; Surko, C. M.

    1990-01-01

    The interaction was studied of low energy positrons with large molecules such as alkanes. These data provide evidencce for the existence of long lived resonances and bound states of positrons with neutral molecules. The formation process and the nature of these resonances are discussed. The positive ions produced when a positron annihilates with an electron in one of these resonances were observed and this positive ion formation process is discussed. A review is presented of the current state of the understanding of these positron-molecule resonances and the resulting positive ion formation. A number of outstanding issues in this area is also discussed.

  3. Admittance Test and Conceptual Study of a CW Positron Source for CEBAF

    SciTech Connect

    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.

  4. Large electron screening effect in different environments

    SciTech Connect

    Cvetinović, Aleksandra Lipoglavšek, Matej; Markelj, Sabina; Vesić, Jelena

    2015-10-15

    Electron screening effect was studied in the {sup 1}H({sup 7}Li,α){sup 4}He, {sup 1}H({sup 11}B,α){sup 4}He and {sup 1}H({sup 19}F,αγ){sup 16}O reactions in inverse kinematics on different hydrogen implanted targets. Results show large electron screening potentials strongly dependent on the proton number Z of the projectile.

  5. Large electron screening effect in different environments

    NASA Astrophysics Data System (ADS)

    Cvetinović, Aleksandra; Lipoglavsek, Matej; Markelj, Sabina; Vesić, Jelena

    2016-05-01

    Electron screening effect was studied on different hydrogen containing targets with the 7Li, 11B and 19F ion beams. Results show large electron screening potentials strongly dependent on the proton number Z of the projectile. The largest ever measured screening potential with the value about a factor of 50 above the calculations from the model in adiabatic limit was observed in the graphite target containing hydrogen as an impurity.

  6. Positrons in surface physics

    NASA Astrophysics Data System (ADS)

    Hugenschmidt, Christoph

    2016-12-01

    Within the last decade powerful methods have been developed to study surfaces using bright low-energy positron beams. These novel analysis tools exploit the unique properties of positron interaction with surfaces, which comprise the absence of exchange interaction, repulsive crystal potential and positron trapping in delocalized surface states at low energies. By applying reflection high-energy positron diffraction (RHEPD) one can benefit from the phenomenon of total reflection below a critical angle that is not present in electron surface diffraction. Therefore, RHEPD allows the determination of the atom positions of (reconstructed) surfaces with outstanding accuracy. The main advantages of positron annihilation induced Auger-electron spectroscopy (PAES) are the missing secondary electron background in the energy region of Auger-transitions and its topmost layer sensitivity for elemental analysis. In order to enable the investigation of the electron polarization at surfaces low-energy spin-polarized positrons are used to probe the outermost electrons of the surface. Furthermore, in fundamental research the preparation of well defined surfaces tailored for the production of bound leptonic systems plays an outstanding role. In this report, it is envisaged to cover both the fundamental aspects of positron surface interaction and the present status of surface studies using modern positron beam techniques.

  7. Fast Magnetic Reconnection and Particle Acceleration in Relativistic Low-density Electron-Positron Plasmas without Guide Field

    NASA Astrophysics Data System (ADS)

    Bessho, Naoki; Bhattacharjee, A.

    2012-05-01

    Magnetic reconnection and particle acceleration in relativistic Harris sheets in low-density electron-positron plasmas with no guide field have been studied by means of two-dimensional particle-in-cell simulations. Reconnection rates are of the order of one when the background density in a Harris sheet is of the order of 1% of the density in the current sheet, which is consistent with previous results in the non-relativistic regime. It has been demonstrated that the increase of the Lorentz factors of accelerated particles significantly enhances the collisionless resistivity needed to sustain a large reconnection electric field. It is shown analytically and numerically that the energy spectrum of accelerated particles near the X-line is the product of a power law and an exponential function of energy, γ-1/4exp (- aγ1/2), where γ is the Lorentz factor and a is a constant. However, in the low-density regime, while the most energetic particles are produced near X-lines, many more particles are energized within magnetic islands. Particles are energized in contracting islands by multiple reflection, but the mechanism is different from Fermi acceleration in magnetic islands for magnetized particles in the presence of a guide field. In magnetic islands, strong core fields are generated and plasma beta values are reduced. As a consequence, the fire-hose instability condition is not satisfied in most of the island region, and island contraction and particle acceleration can continue. In island coalescence, reconnection between two islands can accelerate some particles, however, many particles are decelerated and cooled, which is contrary to what has been discussed in the literature on particle acceleration due to reconnection in non-relativistic hydrogen plasmas.

  8. The contribution of Fermi gamma-ray pulsars to the local flux of cosmic-ray electrons and positrons

    SciTech Connect

    Gendelev, Leo; Profumo, Stefano; Dormody, Michael E-mail: profumo@scipp.ucsc.edu

    2010-02-01

    We analyze the contribution of gamma-ray pulsars from the first Fermi-Large Area Telescope (LAT) catalogue to the local flux of cosmic-ray electrons and positrons (e{sup +}e{sup −}). We present new distance estimates for all Fermi gamma-ray pulsars, based on the measured gamma-ray flux and pulse shape. We then estimate the contribution of gamma-ray pulsars to the local e{sup +}e{sup −} flux, in the context of a simple model for the pulsar e{sup +}e{sup −} emission. We find that 10 of the Fermi pulsars potentially contribute significantly to the measured e{sup +}e{sup −} flux in the energy range between 100 GeV and 1 TeV. Of the 10 pulsars, 2 are old EGRET gamma-ray pulsars, 2 pulsars were discovered with radio ephemerides, and 6 were discovered with the Fermi pulsar blind-search campaign. We argue that known radio pulsars fall in regions of parameter space where the e{sup +}e{sup −} contribution is predicted to be typically much smaller than from those regions where Fermi-LAT pulsars exist. However, comparing the Fermi gamma-ray flux sensitivity to the regions of pulsar parameter space where a significant e{sup +}e{sup −} contribution is predicted, we find that a few known radio pulsars that have not yet been detected by Fermi can also significantly contribute to the local e{sup +}e{sup −} flux if a) they are closer than 2 kpc, and if b) they have a characteristic age on the order of one mega-year.

  9. Direct measurements of two photon exchange on lepton-proton elastic scattering using simultaneous electron-positron beams in CLAS

    NASA Astrophysics Data System (ADS)

    Adikaram, Dasuni Kalhari

    The electric (GE) and magnetic ( GM) form factors of the proton are fundamental observables which characterize its charge and magnetization distributions. There are two methods to measure the proton form factors: the Rosenbluth separation method and the polarization transfer technique. However, the ratio of the electric and magnetic form factors measured by those methods significantly disagree at momentum transfer Q2 > 1 GeV2. The most likely explanation of this discrepancy is the inclusion of two-photon exchange (TPE) amplitude contributions to the elastic electron-proton cross section which significantly changes the extraction of GE from the Rosenbluth separation measurement. The Jefferson Lab CLAS TPE experiment determined the TPE contribution by measuring the ratio of positron-proton to electron-proton elastic scattering cross sections. The primary electron beam was used to create an intense bremsstrahlung photon beam. Some of the photons were then converted to a mixed e+/ e- beam which then interacted with a liquid hydrogen target. The e+p and e-p events were detected by the CLAS (CEBAF Large Acceptance Spectrometer). The elastic cross section ratios ((sigma( e+p)/(sigma(e -p)) were measured over a wide range of virtual photon polarization epsilon and Q2. The cross section ratios displayed a strong epsilon dependence at Q2 = 1.45 GeV2. There is no significant Q2 dependence observed at epsilon = 0.45. The results are consistent with a recent measurement at the VEPP-3 lepton storage ring in Novosibirsk and with the hadronic calculation by Blunders, Melnitchouk and Tjon. The hadronic calculation resolves the disagreement between the Rosenbluth separation and polarization transfer extractions of GE/GM at Q2 up to 2 -- 3 GeV2. Applying the GLAS TPE correction to the Rosenbluth cross section measurements significantly decreases the extracted value of GE and brings it into good agreement with the polarization transfer measurement at Q2˜1.75 GeV2. Thus, these

  10. Systematic comparison of positron- and electron-impact excitation of the {nu}{sub 3} vibrational mode of CF{sub 4}

    SciTech Connect

    Marler, J. P.; Surko, C. M.

    2005-12-15

    Absolute measurements are presented for the excitation of the {nu}{sub 3} vibrational mode in CF{sub 4} by positron and electron impact from 0.1 to 2 eV. To minimize systematic differences, these measurements were made using the same trap-based electron or positron beam, associated experimental apparatus, and procedures. Unlike other vibrational excitation cross sections studied to date, the near-threshold cross section for the {nu}{sub 3} vibrational mode in CF{sub 4} is similar, both in magnitude and shape, for positrons and electrons. Comparison of the cross sections with an analytic Born dipole model yields good agreement, while comparison of this model with other measured positron-impact vibrational cross sections indicates that the contribution of this long-range dipole coupling varies widely. The maximum value of the cross section in CF{sub 4} is the largest of any positron-impact vibrational excitation cross section measured to date. This provides a likely explanation of the observation that CF{sub 4} is very effective when used as a buffer gas to cool positron gases and plasmas.

  11. Higher-Order Effects in the Elastic Scattering of Electrons and Positrons from LEAD-208 and CARBON-12

    NASA Astrophysics Data System (ADS)

    Linzey, Andrew Joseph

    Here we report on a precise study of the ratio of elastic scattering cross sections of electrons and positrons from ^{12}C and ^{208}Pb, in an effort to observe and quantify deviations from the predictions of a phase shift calculation of the scattering from a static charge density. Any deviations observed can be attributed to higher-order processes sensitive to the sign of the charge of the scattered particle. The beam energies were ~450 MeV and the angular ranges covered were 26-37^circ for ^{12}C and 26-53^ circ for ^{208}Pb. No deviations were observed within the uncertainties of the measurement.

  12. Investigation of the production of electron-positron pairs in nucleon-nucleon interactions with the HADES detector

    SciTech Connect

    Lapidus, K. O.

    2010-06-15

    The inclusive production of electron-positron pairs in proton-proton and deuteron-proton collisions at a beam kinetic energy of 1.25 GeV per nucleon was studied with the HADES (High Acceptance Dielectron Spectrometer) detector. The main objective of the deuteron-proton experiment was to investigate pair production in quasifree neutron-proton collisions. In the invariant-mass region M > 140 MeV/c{sup 2}, the invariant-mass spectrum determined in this channel shows a significant enhancement of the pair yield in relation to that in the case of proton-proton collisions.

  13. Soliton and Shock Profiles in Electron-positron-ion Degenerate Plasmas for Both Nonrelativistic and Ultra-Relativistic Limits

    NASA Astrophysics Data System (ADS)

    Haider, Md. Masum

    2016-12-01

    An attempt has been taken to find a general equation for degenerate pressure of Chandrasekhar and constants, by using which one can study nonrelativistic as well as ultra-relativistic cases instead of two different equations and constants. Using the general equation, ion-acoustic solitary and shock waves have been studied and compared, numerically and graphically, the two cases in same situation of electron-positron-ion plasmas. Korteweg-de Vries (KdV) and KdV-Barger equations have been derived as well as their solution to study the soliton and shock profiles, respectively.

  14. 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.

  15. Progress towards a laser produced relativistic electron-positron pair plasma

    SciTech Connect

    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

    Here, 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.

  16. Progress towards a laser produced relativistic electron-positron pair plasma

    DOE PAGES

    Chen, Hui; Bonlie, J.; Cauble, R.; ...

    2016-04-01

    Here, 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.

  17. A method to detect positron anisotropies with Pamela data

    NASA Astrophysics Data System (ADS)

    Panico, B.; 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.; Giaccari, U.; Karelin, A. V.; Koldashov, S. V.; Koldobskiy, S.; Krutkov, S. Y.; Kvashnin, A. N.; Leonov, A.; Malakhov, V.; Marcelli, L.; Martucci, M.; Mayorov, A. G.; Menn, W.; Merge, M.; Mikhailov, V. V.; Mocchiutti, E.; Monaco, A.; Mori, N.; Munini, R.; Osteria, G.; Palma, F.; Papini, P.; Pearce, M.; Picozza, P.; Pizzolotto, C.; Ricci, M.; Ricciarini, S. B.; Sarkar, R.; Scotti, V.; Simon, M.; Sparvoli, R.; Spillantini, P.; Stozhkov, Y. I.; Vacchi, A.; Vannuccini, E.; Vasilyev, G. I.; Voronov, S. A.; Yurkin, Y. T.; Zampa, G.; Zampa, N.; Zverev, V. G.

    2014-11-01

    The PAMELA experiment is collecting data since 2006; its results indicate the presence of a large flux of positron with respect to electrons in the CR spectrum above 10 GeV. This excess might also be originated in objects such as pulsars and microquasars or through dark matter annihilation. Here the electrons and positrons events collected by PAMELA have been analized searching for anisotropies. The analysis is performed at different angular scales and results will be presented at the conference.

  18. Measurement of Electron Clouds in Large Accelerators by Microwave Dispersion

    SciTech Connect

    De Santis, S.; Byrd, J.M.; Caspers, F.; Krasnykh, A.; Kroyer, T.; Pivi, M.T.F.; Sonnad, K.G.; /LBL, Berkeley

    2008-03-19

    Clouds of low energy electrons in the vacuum beam pipes of accelerators of positively charged particle beams present a serious limitation for operation at high currents. Furthermore, it is difficult to probe their density over substantial lengths of the beam pipe. We have developed a novel technique to directly measure the electron cloud density via the phase shift induced in a TE wave transmitted over a section of the accelerator and used it to measure the average electron cloud density over a 50 m section in the positron ring of the PEP-II collider at the Stanford Linear Accelerator Center.

  19. Measurement of electron clouds in large accelerators by microwave dispersion.

    PubMed

    De Santis, S; Byrd, J M; Caspers, F; Krasnykh, A; Kroyer, T; Pivi, M T F; Sonnad, K G

    2008-03-07

    Clouds of low energy electrons in the vacuum beam pipes of accelerators of positively charged particle beams present a serious limitation for operation at high currents. Furthermore, it is difficult to probe their density over substantial lengths of the beam pipe. We have developed a novel technique to directly measure the electron cloud density via the phase shift induced in a TE wave transmitted over a section of the accelerator and used it to measure the average electron cloud density over a 50 m section in the positron ring of the PEP-II collider at the Stanford Linear Accelerator Center.

  20. Dense GeV electron-positron pairs generated by lasers in near-critical-density plasmas.

    PubMed

    Zhu, Xing-Long; Yu, Tong-Pu; Sheng, Zheng-Ming; Yin, Yan; Turcu, Ion Cristian Edmond; Pukhov, Alexander

    2016-12-14

    Pair production can be triggered by high-intensity lasers via the Breit-Wheeler process. However, the straightforward laser-laser colliding for copious numbers of pair creation requires light intensities several orders of magnitude higher than possible with the ongoing laser facilities. Despite the numerous proposed approaches, creating high-energy-density pair plasmas in laboratories is still challenging. Here we present an all-optical scheme for overdense pair production by two counter-propagating lasers irradiating near-critical-density plasmas at only ∼10(22) W cm(-2). In this scheme, bright γ-rays are generated by radiation-trapped electrons oscillating in the laser fields. The dense γ-photons then collide with the focused counter-propagating lasers to initiate the multi-photon Breit-Wheeler process. Particle-in-cell simulations indicate that one may generate a high-yield (1.05 × 10(11)) overdense (4 × 10(22) cm(-3)) GeV positron beam using 10 PW scale lasers. Such a bright pair source has many practical applications and could be basis for future compact high-luminosity electron-positron colliders.

  1. Gamma Spectra Resulting From the Annihilation of Positrons with Electrons in Single, Selected Core Levels of Cu, Ag and Au

    SciTech Connect

    Kim, S; Eshed, A; Goktepeli, S; Sterne, P A; Koymen, A R; Chen, W C; Weiss, A H

    2005-07-25

    The {gamma}-ray energy spectra due to positron annihilation with the 3p core-level of Cu, the 4p core-level of Ag, and 5p core level of Au were obtained separately from the total annihilation spectrum by measuring the energies of {gamma}-rays time coincident with Auger electrons emitted as a result of filling the core-hole left by annihilation. The results of these measurements are compared to the total annihilation spectra and with LDA based theoretical calculations. A comparison of area normalized momentum distributions with the individual cores extracted from the Doppler measurements shows good qualitative agreement, however, in all three spectra, the calculated values of the momentum density appears to fall below the measured values as the momentum increases. The discrepancies between theory and experiment are well outside the statistical uncertainties of the experiment and become more pronounced with increasing Z going down the column from Cu to Ag to Au. The comparison with the experimental results clearly indicates that the calculations are not predicting the correct ratio of high momentum to low momentum spectral weight and suggest the need to improve the treatment of many body electron-positron correlation effects in annihilation as they pertain to core levels.

  2. Effect of near-earth thunderstorms electric field on the intensity of ground cosmic ray positrons/electrons in Tibet

    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.

  3. Dense GeV electron-positron pairs generated by lasers in near-critical-density plasmas

    NASA Astrophysics Data System (ADS)

    Zhu, Xing-Long; Yu, Tong-Pu; Sheng, Zheng-Ming; Yin, Yan; Turcu, Ion Cristian Edmond; Pukhov, Alexander

    2016-12-01

    Pair production can be triggered by high-intensity lasers via the Breit-Wheeler process. However, the straightforward laser-laser colliding for copious numbers of pair creation requires light intensities several orders of magnitude higher than possible with the ongoing laser facilities. Despite the numerous proposed approaches, creating high-energy-density pair plasmas in laboratories is still challenging. Here we present an all-optical scheme for overdense pair production by two counter-propagating lasers irradiating near-critical-density plasmas at only ~1022 W cm-2. In this scheme, bright γ-rays are generated by radiation-trapped electrons oscillating in the laser fields. The dense γ-photons then collide with the focused counter-propagating lasers to initiate the multi-photon Breit-Wheeler process. Particle-in-cell simulations indicate that one may generate a high-yield (1.05 × 1011) overdense (4 × 1022 cm-3) GeV positron beam using 10 PW scale lasers. Such a bright pair source has many practical applications and could be basis for future compact high-luminosity electron-positron colliders.

  4. Depolarization due to beam-beam interaction in electron-positron linear colliders

    SciTech Connect

    Yokoya, K. ); Chen, P. )

    1989-05-05

    We investigate two major mechanisms which induce depolarization of electron beams during beam-beam interaction in linear colliders. These are the classical spin precession under the collective field of the oncoming beam, and the spin-flip effect from beamstrahlung. Analytic formulas are derived for estimating these depolarization effects. As examples, we estimate the depolarization in the Stanford Linear Collider (SLC) and a possible future TeV linear collider (TLC). The effects are found to be negligibly small for SLC and not very large for TLC.

  5. Positron lifetime spectrometer using a DC positron beam

    DOEpatents

    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.

  6. Total and differential cross sections of C3H8 and C3F8 by electron and positron impacts

    NASA Astrophysics Data System (ADS)

    Sueoka, Osamu; Kitajima, Masashi; Sakamoto, Y.; Suzuki, T.; Samukawa, S.; Sueoka, Osamu; Hamada, Akira; Kimura, Mineo

    1998-10-01

    Total and differential elastic cross sections in e-/e+ + C3H8 and C3F8 scattering have been investigated experimentally and theoretically. The differential cross section measurement by electron impact has been carried out from 2 eV to 100 eV, while the total cross section measurement by electron and positron has been for 0.7 eV to 600 eV. The theoretical study has been performed by using the continuum multiple-scattering method. The present total cross sections are found to agree reasonably well with those by Wayne State Univ. group, and theoretical rationale for origins of shape resonances are provided.

  7. 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.

  8. Studies of Oxidation of the Cu(100) Surface Using Low Energy Positrons

    SciTech Connect

    Fazleev, N. G.; Maddox, W. B.; Nadesalingam, M.; Rajeshwar, K.; Weiss, A. H.

    2009-03-10

    Changes in the surface of an oxidized Cu(100) single crystal resulting from vacuum annealing have been investigated using positron annihilation induced Auger electron spectroscopy (PAES). PAES measurements show a large increase in the intensity of the positron annihilation induced Cu M{sub 2,3}VV Auger peak as the sample is subjected to a series of isochronal anneals in vacuum up to annealing temperature 300 deg. C. The intensity then decreases monotonically as the annealing temperature is increased to {approx}600 deg. C. Experimental PAES results are analyzed by performing calculations of positron surface states and annihilation probabilities of surface-trapped positrons with relevant core electrons taking into account the charge redistribution at the surface, surface reconstructions, and electron-positron correlations effects. Possible explanation for the observed behavior of the intensity of positron annihilation induced Cu M{sub 2,3}VV Auger peak with changes of the annealing temperature is proposed.

  9. Modelling drifts in solar modulation using simultaneous electron and positron measurements from PAMELA during the solar minimum of Cycle 23/24

    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.

  10. Positron Annihilation in the Bipositronium Ps2

    SciTech Connect

    Bailey, David H.; Frolov, Alexei M.

    2005-07-01

    The electron-positron-pair annihilation in the bipositronium PS2 is considered. In particular, the two-, three-, one- and zero-photon annihilation rates are determined to high accuracy. The corresponding analytical expressions are also presented. Also, a large number of bound state properties have been determined for this system.

  11. Nonlinear structures of the Korteweg-de Vries and modified Korteweg-de Vries equations in non-Maxwellian electron-positron-ion plasma: Solitons collision and rogue waves

    SciTech Connect

    El-Tantawy, S. A.; Moslem, W. M.

    2014-05-15

    Solitons (small-amplitude long-lived waves) collision and rogue waves (large-amplitude short-lived waves) in non-Maxwellian electron-positron-ion plasma have been investigated. For the solitons collision, the extended Poincaré-Lighthill-Kuo perturbation method is used to derive the coupled Korteweg-de Vries (KdV) equations with the quadratic nonlinearities and their corresponding phase shifts. The calculations reveal that both positive and negative polarity solitons can propagate in the present model. At critical value of plasma parameters, the coefficients of the quadratic nonlinearities disappear. Therefore, the coupled modified KdV (mKdV) equations with cubic nonlinearities and their corresponding phase shifts have been derived. The effects of the electron-to-positron temperature ratio, the ion-to-electron temperature ratio, the positron-to-ion concentration, and the nonextensive parameter on the colliding solitons profiles and their corresponding phase shifts are examined. Moreover, generation of ion-acoustic rogue waves from small-amplitude initial perturbations in plasmas is studied in the framework of the mKdV equation. The properties of the ion-acoustic rogue waves are examined within a nonlinear Schrödinger equation (NLSE) that has been derived from the mKdV equation. The dependence of the rogue wave profile on the relevant physical parameters has been investigated. Furthermore, it is found that the NLSE that has been derived from the KdV equation cannot support the propagation of rogue waves.

  12. PROSPECTS FOR DETECTION OF SYNCHROTRON EMISSION FROM SECONDARY ELECTRONS AND POSITRONS IN STARLESS CORES: APPLICATION TO G0.216+0.016

    SciTech Connect

    Jones, D. I.

    2014-09-01

    We investigate the diffusion of cosmic rays into molecular cloud complexes. Using the cosmic-ray diffusion formalism of Protheroe et al., we examine how cosmic rays diffuse into clouds exhibiting different density structures, including a smoothed step-function, as well as Gaussian and inverse-r density distributions, which are well known to trace the structure of star-forming regions. These density distributions were modeled as an approximation to the Galactic center cloud G0.216+0.016, a recently discovered massive dust clump that exhibits limited signs of massive star formation and thus may be the best region in the Galaxy to observe synchrotron emission from secondary electrons and positrons. Examination of the resulting synchrotron emission, produced by the interaction of cosmic-ray protons interacting with ambient molecular matter producing secondary electrons and positrons reveals that, due to projection effects, limb-brightened morphology results in all cases. However, we find that the Gaussian and inverse-r density distributions show much broader flux density distributions than step-function distributions. Significantly, some of the compact (compared to the 2.''2 resolution, 5.3 GHz Karl G. Jansky Very Large Array (JVLA) observations) sources show non-thermal emission, which may potentially be explained by the density structure and the lack of diffusion of cosmic rays into the cloud. We find that we can match the 5.3 and 20 GHz flux densities of the non-thermal source JVLA 1 and 6 from Rodríguez and Zapata with a local cosmic-ray flux density, a diffusion coefficient suppression factor of χ = 0.1-0.01 for a coefficient of 3 × 10{sup 27} cm{sup –2} s{sup –1}, and a magnetic field strength of 470 μG.

  13. Positrons for linear colliders

    SciTech Connect

    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)

  14. Positron microscopy

    SciTech Connect

    Hulett, L.D. Jr.; Xu, J.

    1995-02-01

    The negative work function property that some materials have for positrons make possible the development of positron reemission microscopy (PRM). Because of the low energies with which the positrons are emitted, some unique applications, such as the imaging of defects, can be made. The history of the concept of PRM, and its present state of development will be reviewed. The potential of positron microprobe techniques will be discussed also.

  15. Positron microprobe at LLNL

    SciTech Connect

    Asoka, P; Howell, R; Stoeffl, W

    1998-11-01

    The electron linac based positron source at Lawrence Livermore National Laboratory (LLNL) provides the world's highest current beam of keV positrons. We are building a positron microprobe that will produce a pulsed, focused positron beam for 3-dimensional scans of defect size and concentration with sub-micron resolution. The widely spaced and intense positron packets from the tungsten moderator at the end of the 100 MeV LLNL linac are captured and trapped in a magnetic bottle. The positrons are then released in 1 ns bunches at a 20 MHz repetition rate. With a three-stage re-moderation we will compress the cm-sized original beam to a 1 micro-meter diameter final spot on the target. The buncher will compress the arrival time of positrons on the target to less than 100 ps. A detector array with up to 60 BaF2 crystals in paired coincidence will measure the annihilation radiation with high efficiency and low background. The energy of the positrons can be varied from less than 1 keV up to 50 keV.

  16. High current pulsed positron microprobe

    SciTech Connect

    Howell, R.H.; Stoeffl, W.; Kumar, A.; Sterne, P.A.; Cowan, T.E.; Hartley, J.

    1997-05-01

    We are developing a low energy, microscopically focused, pulsed positron beam for defect analysis by positron lifetime spectroscopy to provide a new defect analysis capability at the 10{sup 10} e{sup +}s{sup -l} beam at the Lawrence Livermore National Laboratory electron linac. When completed, the pulsed positron microprobe will enable defect specific, 3-dimensional maps of defect concentrations with sub-micron resolution of defect location. By coupling these data with first principles calculations of defect specific positron lifetimes and positron implantation profiles we will both map the identity and concentration of defect distributions.

  17. Matrix Isolation Spectroscopy Applied to Positron Moderatioin in Cryogenic Solids

    DTIC Science & Technology

    2011-07-01

    nanoseconds. Positrons that reach a free surface of the moderator before annihilating with an electron may escape into vacuum where they can be...0324. 3 • The positron (e+) is the antiparticle to the electron (e-). • Positrons are stable, but annihilate with electrons to produce γ-rays...Current Positron Applications • 2-γ decay exploited in Positron Emission Tomography (PET) scanners. • Positrons localize & annihilate preferentially at

  18. Propagation of localized structures in relativistic magnetized electron-positron plasmas using particle-in-cell simulations

    SciTech Connect

    López, Rodrigo A.; Muñoz, Víctor; Viñas, Adolfo F.; Valdivia, Juan A.

    2015-09-15

    We use a particle-in-cell simulation to study the propagation of localized structures in a magnetized electron-positron plasma with relativistic finite temperature. We use as initial condition for the simulation an envelope soliton solution of the nonlinear Schrödinger equation, derived from the relativistic two fluid equations in the strongly magnetized limit. This envelope soliton turns out not to be a stable solution for the simulation and splits in two localized structures propagating in opposite directions. However, these two localized structures exhibit a soliton-like behavior, as they keep their profile after they collide with each other due to the periodic boundary conditions. We also observe the formation of localized structures in the evolution of a spatially uniform circularly polarized Alfvén wave. In both cases, the localized structures propagate with an amplitude independent velocity.

  19. Report of Snowmass 2001 working group E2: Electron - positron colliders from the phi to the Z

    SciTech Connect

    Zhen-guo Zhao et al.

    2002-12-23

    We report on the status and plans of experiments now running or proposed for electron-positron colliders at energies between the {phi} and the Z. The e{sup +}e{sup -}B and charm factories we considered were PEP-II/BABAR, KEKB/Belle, superKEK, SuperBABAR, and CESR-c/CLEO-c. We reviewed the programs at the {phi} factory at Frascati and the proposed PEP-N facility at Stanford Linear Accelerator Center. We studied the prospects for B physics with a dedicated linear collider Z factory, associated with the TESLA high energy linear collider. In all cases, we compared the physics reach of these facilities with that of alternative experiments at hadron colliders or fixed target facilities.

  20. Pulsar Wind Nebulae as a source of the observed electron and positron excess at high energy: The case of Vela-X

    NASA Astrophysics Data System (ADS)

    Della Torre, S.; Gervasi, M.; Rancoita, P. G.; Rozza, D.; Treves, A.

    2015-12-01

    We investigate, in terms of production from pulsars and their nebulae, the cosmic ray positron and electron fluxes above ∼10 GeV, observed by the AMS-02 experiment up to 1 TeV. We concentrate on the Vela-X case. Starting from the gamma-ray photon spectrum of the source, generated via synchrotron and inverse Compton processes, we estimated the electron and positron injection spectra. Several features are fixed from observations of Vela-X and unknown parameters are borrowed from the Crab nebula. The particle spectra produced in the pulsar wind nebula are then propagated up to the Solar System, using a diffusion model. Differently from previous works, the omnidirectional intensity excess for electrons and positrons is obtained as a difference between the AMS-02 data and the corresponding local interstellar spectrum. An equal amount of electron and positron excess is observed and we interpreted this excess (above ∼100 GeV in the AMS-02 data) as a supply coming from Vela-X. The particle contribution is consistent with models predicting the gamma-ray emission at the source. The input of a few more young pulsars is also allowed, while below ∼100 GeV more aged pulsars could be the main contributors.

  1. Van de Graaff based positron source production

    NASA Astrophysics Data System (ADS)

    Lund, Kasey Roy

    The anti-matter counterpart to the electron, the positron, can be used for a myriad of different scientific research projects to include materials research, energy storage, and deep space flight propulsion. Currently there is a demand for large numbers of positrons to aid in these mentioned research projects. There are different methods of producing and harvesting positrons but all require radioactive sources or large facilities. Positron beams produced by relatively small accelerators are attractive because they are easily shut down, and small accelerators are readily available. A 4MV Van de Graaff accelerator was used to induce the nuclear reaction 12C(d,n)13N in order to produce an intense beam of positrons. 13N is an isotope of nitrogen that decays with a 10 minute half life into 13C, a positron, and an electron neutrino. This radioactive gas is frozen onto a cryogenic freezer where it is then channeled to form an antimatter beam. The beam is then guided using axial magnetic fields into a superconducting magnet with a field strength up to 7 Tesla where it will be stored in a newly designed Micro-Penning-Malmberg trap. Several source geometries have been experimented on and found that a maximum antimatter beam with a positron flux of greater than 0.55x10 6 e+s-1 was achieved. This beam was produced using a solid rare gas moderator composed of krypton. Due to geometric restrictions on this set up, only 0.1-1.0% of the antimatter was being frozen to the desired locations. Simulations and preliminary experiments suggest that a new geometry, currently under testing, will produce a beam of 107 e+s-1 or more.

  2. High intensity positron beam and angular correlation experiments at Livermore

    SciTech Connect

    Howell, R.H.; Rosenberg, I.J.; Meyer, P.; Fluss, M.J.

    1985-03-01

    A positron beam apparatus that produces a variable energy positron beam with sufficient intensity to perform new positron experiments in an ultrahigh vacuum environment has been installed at the Lawrence Livermore 100 MeV electron linac. We have installed two large area position sensitive gamma-ray detectors to measure angular correlations in two dimensions and a separate highly collimated detector to measure positronium energy distributions by time-of-flight velocity determination. Data from measurements on single crystals of Cu will be described.

  3. NLC Positron Target Heating(LCC-0065)

    SciTech Connect

    Schultz, D

    2003-10-07

    The NLC requires an intense beam with a large number of positrons. These positrons are produced by a high energy electron beam impinging on a solid tungsten-rhenium alloy target. The particle shower that develops in the solid target deposits significant energy in the material, leading to target stresses and potentially to target damage. The stresses can be analyzed once the magnitude and extent of the energy deposition is known. This note details the modeling of the energy deposition using EGS, performed for the NLC and the SLC targets and for possible NLC targets made of copper or nickel instead of WRe.

  4. Studies of positron electron pair production in {sup 238}U + {sup 232}Th

    SciTech Connect

    Ahmad, I.; Back, B.B.; Betts, R.R.

    1995-08-01

    Following the non-observation of sharp sum-energy lines in our earlier {sup 238}U + {sup 181}Ta measurements, it was decided to pursue measurements of the {sup 238}U + {sup 232}Th system which, in the previously published work, showed the most striking evidence for near-equal-energy back-to-back pairs leading to sharp sum-energy lines. Following the refurbishing of the APEX silicon arrays and extensive tests of the rotating target wheel assembly, a major positron run took place in November 1994. Rolled 1-mg/cm{sub 2} {sup 232}Th targets were bombarded with 5.95-MeV/u {sup 238}U. The target rotation allowed up to 2 pnA of beam to be used without serious deterioration of the targets. Over 300,000 pairs were accumulated, representing an order-of-magnitude improvement in statistics over the previously published results. Preliminary analysis shows no evidence for the sharp lines at a cross section level orders of magnitude below those previously reported. The analysis of these data is currently being completed in preparation for publication.

  5. Position-resolved Positron Annihilation Lifetime Spectroscopy

    NASA Astrophysics Data System (ADS)

    Wagner, A.; Butterling, M.; Fiedler, F.; Fritz, F.; Kempe, M.; Cowan, T. E.

    2013-06-01

    A new method which allows for position-resolved positron lifetime spectroscopy studies in extended volume samples is presented. In addition to the existing technique of in-situ production of positrons inside large (cm3) bulk samples using high-energy photons up to 16 MeV from bremsstrahlung production, granular position-sensitive photon detectors have been employed. A beam of intense bremsstrahlung is provided by the superconducting electron linear accelerator ELBE (Electron Linear Accelerator with high Brilliance and low Emittance) which delivers electron bunches of less than 10 ps temporal width and an adjustable bunch separation of multiples of 38 ns, average beam currents of 1 mA, and energies up to 40 MeV. Since the generation of bremsstrahlung and the transport to the sample preserves the sharp timing of the electron beam, positrons generated inside the entire sample volume by pair production feature a sharp start time stamp for positron annihilation lifetime studies with high timing resolutions and high signal to background ratios due to the coincident detection of two annihilation photons. Two commercially available detectors from a high-resolution medial positron-emission tomography system are being employed with 169 individual Lu2SiO5:Ce scintillation crystals, each. In first experiments, a positron-lifetime gated image of a planar Si/SiO2 (pieces of 12.5 mm × 25 mm size) sample and a 3-D structured metal in Teflon target could be obtained proving the feasibility of a three dimensional lifetime-gated tomographic system.

  6. A large hadron electron collider at CERN

    SciTech Connect

    Abelleira Fernandez, J. L.

    2015-04-06

    This document provides a brief overview of the recently published report on the design of the Large Hadron Electron Collider (LHeC), which comprises its physics programme, accelerator physics, technology and main detector concepts. The LHeC exploits and develops challenging, though principally existing, accelerator and detector technologies. This summary is complemented by brief illustrations of some of the highlights of the physics programme, which relies on a vastly extended kinematic range, luminosity and unprecedented precision in deep inelastic scattering. Illustrations are provided regarding high precision QCD, new physics (Higgs, SUSY) and eletron-ion physics. The LHeC is designed to run synchronously with the LHC in the twenties and to achieve an integrated luminosity of O(100)fb–1. It will become the cleanest high resolution microscope of mankind and will substantially extend as well as complement the investigation of the physics of the TeV energy scale, which has been enabled by the LHC.

  7. A large hadron electron collider at CERN

    DOE PAGES

    Abelleira Fernandez, J. L.

    2015-04-06

    This document provides a brief overview of the recently published report on the design of the Large Hadron Electron Collider (LHeC), which comprises its physics programme, accelerator physics, technology and main detector concepts. The LHeC exploits and develops challenging, though principally existing, accelerator and detector technologies. This summary is complemented by brief illustrations of some of the highlights of the physics programme, which relies on a vastly extended kinematic range, luminosity and unprecedented precision in deep inelastic scattering. Illustrations are provided regarding high precision QCD, new physics (Higgs, SUSY) and eletron-ion physics. The LHeC is designed to run synchronously withmore » the LHC in the twenties and to achieve an integrated luminosity of O(100)fb–1. It will become the cleanest high resolution microscope of mankind and will substantially extend as well as complement the investigation of the physics of the TeV energy scale, which has been enabled by the LHC.« less

  8. Particle physics. Positrons ride the wave

    SciTech Connect

    Piot, Philippe

    2015-08-26

    Here, experiments reveal that positrons — the antimatter equivalents of electrons — can be rapidly accelerated using a plasma wave. The findings pave the way to high-energy electron–positron particle colliders.

  9. High Power Polarized Positron Source

    NASA Astrophysics Data System (ADS)

    Mikhailichenko, Alexander

    2009-09-01

    We discuss the basics of polarized positron production by low energy polarized electrons. Efficiency of conversion ˜0.1-1% might be interesting for the Continuous Electron Beam Accelerator Facility (CEBAF) and the International Linear Collider (ILC).

  10. Energy of atomic shakeoff electrons from positron decay of 37K

    NASA Astrophysics Data System (ADS)

    Behr, John; Fenker, Benjamin; Gorelov, Alexandre; Anholm, Melissa; Behling, Spencer; Mehlman, Michael; Melconian, Dan; Ashery, Danny; Gwinner, Gerald

    2015-10-01

    We have measured the low-energy atomic shakeoff electron spectrum from the β+ decay of 37K. We collect atomic electrons emitted from laser-cooled 37K using a nearly uniform electric field at low magnetic field into a position-sensitive microchannel plate. A coincidence with energetic β+s removes background. The differential position information translates to a differential electron energy spectrum. The energy spectrum from 1-100 eV is reproduced well by an analytic calculation for hydrogenic wavefunctions [Levinger PR 90 11 (1953)] using potassium quantum defects. Less than one percent of the electrons have energies higher than the 25 eV threshold for double DNA strand breaks, so relative biological effectiveness would not be altered by including these electrons. The average energy carried off by these electrons (a few eV) is smaller than expected from simple Thomas-Fermi estimates (65eV). Supported by NSERC, NRC through TRIUMF, U.S. D.O.E., State of Texas, Israel Science Foundation

  11. Unthermalized positrons in gamma ray burst sources

    NASA Technical Reports Server (NTRS)

    Tkaczyk, W.; Karakula, S.

    1992-01-01

    The spectra of the broadening 0.511 MeV annihilation line produced by high temperatures was calculated in the case of unthermalized plasma; i.e., T sub e(+) is not = T sub e(-). The flattening in the spectrum of the annihilation lines for large differences of electron and positron temperatures is a strong indication that the observed features of the hard tailed spectrum of the gamma bursts can be well described by annihilation of unthermalized positrons. It is proposed that the charge separation occurring in Eddington limited accretion onto a neutron star or the one photon pair production in strong magnetic fields as a mechanism for the production of unthermalized positrons in the sources of gamma bursts. From the best fit of experimental spectra by the model, the parameters of sources for which the regions with different plasma temperatures can exist is evaluated.

  12. PROBING THE PULSAR ORIGIN OF THE ANOMALOUS POSITRON FRACTION WITH AMS-02 AND ATMOSPHERIC CHERENKOV TELESCOPES

    SciTech Connect

    Linden, Tim; Profumo, Stefano

    2013-07-20

    Recent observations by PAMELA, Fermi-LAT, and AMS-02 have conclusively indicated a rise in the cosmic-ray positron fraction above 10 GeV, a feature which is impossible to mimic under the paradigm of secondary positron production with self-consistent Galactic cosmic-ray propagation models. A leading explanation for the positron fraction rise is an additional source of electron-positron pairs, for example one or more mature, energetic, and relatively nearby pulsars. We point out that any one of two well-known nearby pulsars, Geminga and Monogem, can satisfactorily provide enough positrons to reproduce AMS-02 observations. A smoking-gun signature of this scenario is an anisotropy in the arrival direction of the cosmic-ray electrons and positrons, which may be detectable by existing, or future, telescopes. The predicted anisotropy level is, at present, consistent with limits from Fermi-LAT and AMS-02. We argue that the large collecting area of atmospheric Cherenkov telescopes (ACTs) makes them optimal tools for detecting such an anisotropy. Specifically, we show that much of the proton and {gamma}-ray background which affects measurements of the cosmic-ray electron-positron spectrum with ACTs may be controlled in the search for anisotropies. We conclude that observations using archival ACT data could already constrain or substantiate the pulsar origin of the positron anomaly, while upcoming instruments (such as the Cherenkov Telescope Array) will provide strong constraints on the source of the rising positron fraction.

  13. The threshold laws for electron-atom and positron-atom impact ionization

    NASA Technical Reports Server (NTRS)

    Temkin, A.

    1983-01-01

    The Coulomb-dipole theory is employed to derive a threshold law for the lowest energy needed for the separation of three particles from one another. The study focuses on an electron impinging on a neutral atom, and the dipole is formed between an inner electron and the nucleus. The analytical dependence of the transition matrix element on energy is reduced to lowest order to obtain the threshold law, with the inner electron providing a shield for the nucleus. Experimental results using the LAMPF accelerator to produce a high energy beam of H- ions, which are then exposed to an optical laser beam to detach the negative H- ion, are discussed. The threshold level is found to be confined to the region defined by the upper bound of the inverse square of the Coulomb-dipole region. Difficulties in exact experimental confirmation of the threshold are considered.

  14. Nonlinear Korteweg-de Vries-Burger equation for ion acoustic shock waves in a weakly relativistic electron-positron-ion plasma with thermal ions

    NASA Astrophysics Data System (ADS)

    Saeed, R.; Shah, Asif

    2010-03-01

    The nonlinear propagation of ion acoustic waves in electron-positron-ion plasma comprising of Boltzmannian electrons, positrons, and relativistic thermal ions has been examined. The Korteweg-de Vries-Burger equation has been derived by reductive perturbation technique, and its shock like solution is determined analytically through tangent hyperbolic method. The effect of various plasma parameters on strength and structure of shock wave is investigated. The pert graphical view of the results has been presented for illustration. It is observed that strength and steepness of the shock wave enervate with an increase in the ion temperature, relativistic streaming factor, positron concentrations, electron temperature and they accrue with an increase in coefficient of kinematic viscosity. The convective, dispersive, and dissipative properties of the plasma are also discussed. It is determined that the electron temperature has remarkable influence on the propagation and structure of nonlinear wave in such relativistic plasmas. The numerical analysis has been done based on the typical numerical data from a pulsar magnetosphere.

  15. Study of Submonolayer Films of GOLD/COPPER(100) and PALLADIUM/COPPER(100) Using Positron Annihilation Induced Auger Electron Spectroscopy

    NASA Astrophysics Data System (ADS)

    Lee, Keunho

    Positron Annihilation induced Auger Electron Spectroscopy (PAES), Electron induced Auger Electron Spectroscopy (EAES), and Low Energy Electron Diffraction (LEED) have been used to study the surface composition, surface alloying and overlayer formation of ultrathin films of Au and Pd on Cu(100). This is the first systematic application of PAES to the study of the surface properties of ultrathin layers of metals on metal substrates. Temperature induced changes in the top layer surface compositions in Au/Cu(100) and Pd/Cu(100) are directly observed using PAES, while EAES spectra indicate only minor changes. The surface alloying of the Au/Cu(100) and Pd/Cu(100) systems are demonstrated using PAES in conjunction with LEED. The PAES intensity measurements also provide evidence for positron trapping at surface defects such as steps, kinks and isolated adatoms. The PAES intensity was found to be strongly dependent on surface defects introduced by ion sputtering. The surface defect dependence of the PAES intensity is interpreted in terms of the surface atomic diffusion and positron trapping at surface defects in Au/Cu(100) and Pd/Cu(100). In both systems the shapes of the PAES intensity versus coverage curves for submonolayer coverages at 173K are quite distinct indicating differences in overlayer growth and diffusion behavior of Au and Pd adatoms on the Cu(100) surface. PAES intensities for both Au and Pd are saturated at 1 monolayer demonstrating the extreme surface selectivity of PAES.

  16. Nonlinear Korteweg-de Vries-Burger equation for ion acoustic shock waves in a weakly relativistic electron-positron-ion plasma with thermal ions

    SciTech Connect

    Saeed, R.; Shah, Asif

    2010-03-15

    The nonlinear propagation of ion acoustic waves in electron-positron-ion plasma comprising of Boltzmannian electrons, positrons, and relativistic thermal ions has been examined. The Korteweg-de Vries-Burger equation has been derived by reductive perturbation technique, and its shock like solution is determined analytically through tangent hyperbolic method. The effect of various plasma parameters on strength and structure of shock wave is investigated. The pert graphical view of the results has been presented for illustration. It is observed that strength and steepness of the shock wave enervate with an increase in the ion temperature, relativistic streaming factor, positron concentrations, electron temperature and they accrue with an increase in coefficient of kinematic viscosity. The convective, dispersive, and dissipative properties of the plasma are also discussed. It is determined that the electron temperature has remarkable influence on the propagation and structure of nonlinear wave in such relativistic plasmas. The numerical analysis has been done based on the typical numerical data from a pulsar magnetosphere.

  17. Modeling and Simulation of Longitudinal Dynamics for Low Energy Ring_High Energy Ring at the Positron-Electron Project

    SciTech Connect

    Rivetta, Claudio; Mastorides, T.; Fox, J.D.; Teytelman, D.; Van Winkle, D.; /SLAC

    2007-03-06

    A time domain dynamic modeling and simulation tool for beam-cavity interactions in the Low Energy Ring (LER) and High Energy Ring (HER) at the Positron-Electron Project (PEP-II) is presented. Dynamic simulation results for PEP-II are compared to measurements of the actual machine. The motivation for this tool is to explore the stability margins and performance limits of PEP-II radio-frequency (RF) systems at future higher currents and upgraded RF configurations. It also serves as a test bed for new control algorithms and can define the ultimate limits of the low-level RF (LLRF) architecture. The time domain program captures the dynamic behavior of the beam-cavity-LLRF interaction based on a reduced model. The ring current is represented by macrobunches. Multiple RF stations in the ring are represented via one or two macrocavities. Each macrocavity captures the overall behavior of all the 2 or 4 cavity RF stations. Station models include nonlinear elements in the klystron and signal processing. This enables modeling the principal longitudinal impedance control loops interacting via the longitudinal beam model. The dynamics of the simulation model are validated by comparing the measured growth rates for the LER with simulation results. The simulated behavior of the LER at increased operation currents is presented via low-mode instability growth rates. Different control strategies are compared and the effects of both the imperfections in the LLRF signal processing and the nonlinear drivers and klystrons are explored.

  18. Kinetic transverse dispersion relation for relativistic magnetized electron-positron plasmas with Maxwell-Jüttner velocity distribution functions

    SciTech Connect

    López, Rodrigo A.; Moya, Pablo S.; Muñoz, Víctor; Viñas, Adolfo F.; Valdivia, J. Alejandro

    2014-09-15

    We use a kinetic treatment to study the linear transverse dispersion relation for a magnetized isotropic relativistic electron-positron plasma with finite relativistic temperature. The explicit linear dispersion relation for electromagnetic waves propagating along a constant background magnetic field is presented, including an analytical continuation to the whole complex frequency plane for the case of Maxwell-Jüttner velocity distribution functions. This dispersion relation is studied numerically for various temperatures. For left-handed solutions, the system presents two branches, the electromagnetic ordinary mode and the Alfvén mode. In the low frequency regime, the Alfvén branch has two dispersive zones, the normal zone (where ∂ω/∂k > 0) and an anomalous zone (where ∂ω/∂k < 0). We find that in the anomalous zone of the Alfvén branch, the electromagnetic waves are damped, and there is a maximum wave number for which the Alfvén branch is suppressed. We also study the dependence of the Alfvén velocity and effective plasma frequency with the temperature. We complemented the analytical and numerical approaches with relativistic full particle simulations, which consistently agree with the analytical results.

  19. Impacts of B-factory measurements on determination of fragmentation functions from electron-positron annihilation data

    NASA Astrophysics Data System (ADS)

    Hirai, M.; Kawamura, H.; Kumano, S.; Saito, K.

    2016-11-01

    Fragmentation functions are determined for the pion and kaon by global analyses of charged-hadron production data in electron-positron annihilation. Accurate measurements were reported by the Belle and BaBar collaborations for the fragmentation functions at the center-of-mass energies of 10.52 and 10.54 GeV, respectively, at the KEK and SLAC B factories, whereas other available ee measurements were mostly done at higher energies, mainly at the Z mass of 91.2 GeV. There is a possibility that gluon fragmentation functions, as well as quark fragmentation functions, are accurately determined by scaling violation. We report our global analysis of the fragmentation functions especially to show impacts of the B-factory measurements on the fragmentation function determination. Our results indicate that the fragmentation functions are determined more accurately not only by the scaling violation but also by the high-statistical nature of the Belle and BaBar data. However, there are some tensions between the Belle and BaBar data in comparison with previous measurements. We also explain how the flavor dependence of quark fragmentation functions and the gluon function are separated by using measurements at different Q values. In particular, the electric and weak charges are different depending on the quark type, so that a light-quark flavor separation also became possible in principle due to the precise data at both √s ≃10.5 and 91.2 GeV.

  20. Nonlinear theory of ionic sound waves in a hot quantum-degenerate electron-positron-ion plasma

    SciTech Connect

    Dubinov, A. E. Sazonkin, M. A.

    2010-11-15

    A collisionless nonmagnetized e-p-i plasma consisting of quantum-degenerate gases of ions, electrons, and positrons at nonzero temperatures is considered. The dispersion equation for isothermal ionic sound waves is derived and analyzed, and an exact expression is obtained for the linear velocity of ionic sound. Analysis of the dispersion equation has made it possible to determine the ranges of parameters in which nonlinear solutions in the form of solitons should be sought. A nonlinear theory of isothermal ionic sound waves is developed and used for obtaining and analyzing the exact solution to the system of initial equations. Analysis has been carried out by the method of the Bernoulli pseudopotential. The ranges of phase velocities of periodic ionic sound waves and soliton velocities are determined. It is shown that in the plasma under investigation, these ranges do not overlap and that the soliton velocity cannot be lower than the linear velocity of ionic sound. The profiles of physical quantities in a periodic wave and in a soliton are constructed, as well as the dependences of the velocity of sound and the critical velocity on the ionic concentration in the plasma. It is shown that these velocities increase with the ion concentration.

  1. Measurement of the Total Cross Section and Energy - Correlations for Electron-Positron Annihilation Into Hadrons at 29 GEV.

    NASA Astrophysics Data System (ADS)

    Heltsley, Brian Keith

    This work describes measurements of the total cross section and the energy-energy correlation cross section for hadronic events produced in electron-positron annihilation at a center-of-mass energy of 29 GeV. The performance of the MAC detector at PEP, featuring total absorption calorimetry and charged particle tracking over nearly the full solid angle, is examined and found to meet the original design requirements. The unique and optimal features of MAC are fully exploited to reduce the systematics involved in both measurements, resulting in significant quantitative tests of the theory of quantum chromodynamics. Special attention is focussed on radiative corrections to the total cross section, which constitute a critical component of the acceptance determination, and for the first time the effects of higher order than (alpha)('3) QED processes are included. The total cross section measurement yields R = 3.91 with a total error of (+OR-)2.7%, an accuracy not previously attained by other experiments. For the energy-energy correlation cross section, the consequences of combining pure quantum chromodynamics with contrasting fragmentation models are explored and compared with the data, and result in different values for the strong coupling constant, (alpha)(,s) (TURNEQ) 0.13 (+OR-) 0.02 for incoherent jet formation and 0.24 (+OR-) 0.04 in the string model.

  2. Electron momentum distribution and singlet-singlet annihilation in the organic anthracene molecular crystals using positron 2D-ACAR and fluorescence spectroscopy.

    PubMed

    Selvakumar, Sellaiyan; Sivaji, Krishnan; Arulchakkaravarthi, Arjunan; Sankar, Sambasivam

    2014-08-14

    We present the mapping of electron momentum distribution (EMD) in a single crystal of anthracene by two-dimensional angular correlation of positron annihilation radiation (2D-ACAR). The projected EMD is explained on the basis of the crystallographic features of the material. The EMD spectra provide information about the positron states and their behavior and also about the hindrance of the positronium (Ps) formation in this material. The EMD has exhibited evidence for the absence of free volume defects. The characteristic EMD features regarding the delocalized electronic states are explained. Further, scintillation characteristics such as fluorescence and time-correlated single photon counting have also been studied. The emission peaks are attributed to vibrational bands of fluorescence emission from the singlet excitons and lifetime components are observed to be due to singlet fission and the singlet-singlet excitons annihilation.

  3. Modified Ion-Acoustic Shock Waves and Double Layers in a Degenerate Electron-Positron-Ion Plasma in Presence of Heavy Negative Ions

    NASA Astrophysics Data System (ADS)

    Hossen, M. A.; Hossen, M. R.; Mamun, A. A.

    2014-12-01

    A general theory for nonlinear propagation of one dimensional modified ion-acoustic waves in an unmagnetized electron-positron-ion (e-p-i) degenerate plasma is investigated. This plasma system is assumed to contain relativistic electron and positron fluids, non-degenerate viscous positive ions, and negatively charged static heavy ions. The modified Burgers and Gardner equations have been derived by employing the reductive perturbation method and analyzed in order to identify the basic features (polarity, width, speed, etc.) of shock and double layer (DL) structures. It is observed that the basic features of these shock and DL structures obtained from this analysis are significantly different from those obtained from the analysis of standard Gardner or Burgers equations. The implications of these results in space and interstellar compact objects (viz. non-rotating white dwarfs, neutron stars, etc.) are also briefly mentioned.

  4. Electron Lenses for the Large Hadron Collider

    SciTech Connect

    Stancari, Giulio; Valishev, Alexander; Bruce, Roderik; Redaelli, Stefano; Rossi, Adriana; Salvachua, Belen

    2014-07-01

    Electron lenses are pulsed, magnetically confined electron beams whose current-density profile is shaped to obtain the desired effect on the circulating beam. Electron lenses were used in the Fermilab Tevatron collider for bunch-by-bunch compensation of long-range beam-beam tune shifts, for removal of uncaptured particles in the abort gap, for preliminary experiments on head-on beam-beam compensation, and for the demonstration of halo scraping with hollow electron beams. Electron lenses for beam-beam compensation are being commissioned in RHIC at BNL. Within the US LHC Accelerator Research Program and the European HiLumi LHC Design Study, hollow electron beam collimation was studied as an option to complement the collimation system for the LHC upgrades. This project is moving towards a technical design in 2014, with the goal to build the devices in 2015-2017, after resuming LHC operations and re-assessing needs and requirements at 6.5 TeV. Because of their electric charge and the absence of materials close to the proton beam, electron lenses may also provide an alternative to wires for long-range beam-beam compensation in LHC luminosity upgrade scenarios with small crossing angles.

  5. c-Axis projected electron-positron momentum density in YBa{sub 2}Cu{sub 3}O{sub 7}

    SciTech Connect

    Bansil, A.; Mijnarends, P.E.; Smedskjaer, L.C.

    1990-11-01

    The authors present the theoretical c-axis projected electron-positron momentum density N{sub 2{gamma}}(P{sub x},p{sub y}) in YBa{sub 2}Cu{sub 3}O{sub 7} based on the local density approximation (LDA) framework along various lines in momentum space. The calculations use the Korringa-Kohn-Rostoker (KKR) band structure formalism. The anisotropic distribution defined by taking cuts through the calculated spectra along different lines in the (p{sub x},p{sub y}) plane possesses complex structures which arise from both Fermi surface effects and the anisotropy of the smoothly varying underlying background from filled bands; the maximum size of the anisotropy is about 10% of N{sub 2{gamma}}(0,0). The theoretically predicted N{sub 2{gamma}}(p{sub x},{sub y}) distribution is compared with the measured 2D-ACAR spectrum. The considerations suggest that in interpreting the 2D-ACAR data on YBa{sub 2}Cu{sub 3}O{sub 7} in terms of a band theory LDA picture, a substantial, largely isotropic, background should be subtracted from both the 2D-ACAR`s and the associated LCW-folded spectra.

  6. MC-PEPTITA: A Monte Carlo model for Photon, Electron and Positron Tracking In Terrestrial Atmosphere—Application for a terrestrial gamma ray flash

    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.

  7. Bulk Materials Analysis Using High-Energy Positron Beams

    SciTech Connect

    Glade, S C; Asoka-Kumar, P; Nieh, T G; Sterne, P A; Wirth, B D; Dauskardt, R H; Flores, K M; Suh, D; Odette, G R

    2002-11-11

    This article reviews some recent materials analysis results using high-energy positron beams at Lawrence Livermore National Laboratory. We are combining positron lifetime and orbital electron momentum spectroscopic methods to provide electron number densities and electron momentum distributions around positron annihilation sites. Topics covered include: correlation of positron annihilation characteristics with structural and mechanical properties of bulk metallic glasses, compositional studies of embrittling features in nuclear reactor pressure vessel steel, pore characterization in Zeolites, and positron annihilation characteristics in alkali halides.

  8. Time Dependence of the Electron and Positron Components of the Cosmic Radiation Measured by the PAMELA Experiment between July 2006 and December 2015

    NASA Astrophysics Data System (ADS)

    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.; Carlson, P.; Casolino, M.; Castellini, G.; De Santis, C.; Di Felice, V.; Galper, A. M.; Karelin, A. V.; Koldashov, S. V.; Koldobskiy, S. A.; Krutkov, S. Y.; Kvashnin, A. N.; Leonov, A.; Malakhov, V.; Marcelli, L.; Martucci, M.; Mayorov, A. G.; Menn, W.; Mergé, M.; Mikhailov, V. V.; Mocchiutti, E.; Monaco, A.; Mori, N.; Munini, R.; Osteria, G.; Panico, B.; Papini, P.; Pearce, M.; Picozza, P.; Ricci, M.; Ricciarini, S. B.; Simon, M.; Sparvoli, R.; Spillantini, P.; Stozhkov, Y. I.; Vacchi, A.; Vannuccini, E.; Vasilyev, G. I.; Voronov, S. A.; Yurkin, Y. T.; Zampa, G.; Zampa, N.; Potgieter, M. S.; Vos, E. E.

    2016-06-01

    Cosmic-ray electrons and positrons are a unique probe of the propagation of cosmic rays as well as of the nature and distribution of particle sources in our Galaxy. Recent measurements of these particles are challenging our basic understanding of the mechanisms of production, acceleration, and propagation of cosmic rays. Particularly striking are the differences between the low energy results collected by the space-borne PAMELA and AMS-02 experiments and older measurements pointing to sign-charge dependence of the solar modulation of cosmic-ray spectra. The PAMELA experiment has been measuring the time variation of the positron and electron intensity at Earth from July 2006 to December 2015 covering the period for the minimum of solar cycle 23 (2006-2009) until the middle of the maximum of solar cycle 24, through the polarity reversal of the heliospheric magnetic field which took place between 2013 and 2014. The positron to electron ratio measured in this time period clearly shows a sign-charge dependence of the solar modulation introduced by particle drifts. These results provide the first clear and continuous observation of how drift effects on solar modulation have unfolded with time from solar minimum to solar maximum and their dependence on the particle rigidity and the cyclic polarity of the solar magnetic field.

  9. Time Dependence of the Electron and Positron Components of the Cosmic Radiation Measured by the PAMELA Experiment between July 2006 and December 2015.

    PubMed

    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; Carlson, P; Casolino, M; Castellini, G; De Santis, C; Di Felice, V; Galper, A M; Karelin, A V; Koldashov, S V; Koldobskiy, S A; Krutkov, S Y; Kvashnin, A N; Leonov, A; Malakhov, V; Marcelli, L; Martucci, M; Mayorov, A G; Menn, W; Mergé, M; Mikhailov, V V; Mocchiutti, E; Monaco, A; Mori, N; Munini, R; Osteria, G; Panico, B; Papini, P; Pearce, M; Picozza, P; Ricci, M; Ricciarini, S B; Simon, M; Sparvoli, R; Spillantini, P; Stozhkov, Y I; Vacchi, A; Vannuccini, E; Vasilyev, G I; Voronov, S A; Yurkin, Y T; Zampa, G; Zampa, N; Potgieter, M S; Vos, E E

    2016-06-17

    Cosmic-ray electrons and positrons are a unique probe of the propagation of cosmic rays as well as of the nature and distribution of particle sources in our Galaxy. Recent measurements of these particles are challenging our basic understanding of the mechanisms of production, acceleration, and propagation of cosmic rays. Particularly striking are the differences between the low energy results collected by the space-borne PAMELA and AMS-02 experiments and older measurements pointing to sign-charge dependence of the solar modulation of cosmic-ray spectra. The PAMELA experiment has been measuring the time variation of the positron and electron intensity at Earth from July 2006 to December 2015 covering the period for the minimum of solar cycle 23 (2006-2009) until the middle of the maximum of solar cycle 24, through the polarity reversal of the heliospheric magnetic field which took place between 2013 and 2014. The positron to electron ratio measured in this time period clearly shows a sign-charge dependence of the solar modulation introduced by particle drifts. These results provide the first clear and continuous observation of how drift effects on solar modulation have unfolded with time from solar minimum to solar maximum and their dependence on the particle rigidity and the cyclic polarity of the solar magnetic field.

  10. X-ray and TeV Gamma-Ray Emission from Parallel Electron-Positron or Electron-Proton Beams in BL Lac Objects

    NASA Astrophysics Data System (ADS)

    Krawczynski, Henric

    2007-04-01

    In this contribution we discuss models of the X-rays and TeV gamma-ray emission from BL Lac objects based on parallel electron-positron or electron-proton beams that form close to the central black hole owing to the strong electric fields generated by the accretion disk and possibly also by the black hole itself. Fitting the energy spectrum of the BL Lac object Mrk 501, we obtain tight constrains on the beam properties. Launching a sufficiently energetic beam requires rather strong magnetic fields close to the black hole 100-1000 G. However, the model fits imply that the magnetic field in the emission region is only 0.02 G. Thus, the particles are accelerated close to the black hole and propagate a considerable distance before instabilities trigger the dissipation of energy through synchrotron and self-Compton emission. We discuss various approaches to generate enough power to drive the jet and, at the same time, to accelerate particles to 20 TeV energies. Although the parallel beam model has its own problems, it explains some of the long-standing problems that plague models based on Fermi type particle acceleration, like the presence of a very high minimum Lorentz factor of accelerated particles. We conclude with a brief discussion of the implications of the model for the difference between the processes of jet formation in BL Lac type objects and in quasars.

  11. X-Ray and TeV Gamma-Ray Emission from Parallel Electron-Positron or Electron-Proton Beams in BL Lacertae Objects

    NASA Astrophysics Data System (ADS)

    Krawczynski, H.

    2007-04-01

    In this paper we discuss models of the X-ray and TeV γ-ray emission from BL Lac objects based on parallel electron-positron or electron-proton beams that form close to the central black hole, due to the strong electric fields generated by the accretion disk and possibly also by the black hole itself. Fitting the energy spectrum of the BL Lac object Mrk 501, we obtain tight constraints on the beam properties. Launching a sufficiently energetic beam requires rather strong magnetic fields close to the black hole (~100-1000 G). However, the model fits imply that the magnetic field in the emission region is only ~0.02 G. Thus, the particles are accelerated close to the black hole and propagate a considerable distance before instabilities trigger the dissipation of energy through synchrotron and self-Compton emission. We discuss various approaches to generate enough power to drive the jet and, at the same time, to accelerate particles to ~20 TeV energies. Although the parallel beam model has its own problems, it explains some of the long-standing problems that plague models based on Fermi-type particle acceleration, such as the presence of a very high minimum Lorentz factor of accelerated particles. We conclude with a brief discussion of the implications of the model for the difference between the processes of jet formation in BL Lac-type objects and those in quasars.

  12. The prognostic value of interim positron emission tomography scans combined with immunohistochemical data in diffuse large B-cell lymphoma.

    PubMed

    Fields, Paul A; Mikhaeel, George; Hutchings, Martin; van der Walt, Jon; Nunan, Tom; Schey, Steve A

    2005-12-01

    The treatment of hematologic malignancies is moving towards risk-stratified directed therapy, whereby treatment is based on the disease's biological characteristics and response to treatment. We investigated whether BCL2 and BCL6 status could add to the prognostic information yielded by an interim positron emission tomography (PET) scan in the ability to predict outcome. Negative interim scans and BCL2-negative status correlated with continuing remission (p<0.005) at a median follow up of 24 months.

  13. Foil support structure for large electron guns

    SciTech Connect

    Brucker, J.P.; Rose, E.A.

    1993-08-01

    This paper describes a novel support structure for a vacuum diode used to pump a gaseous laser with an electron beam. Conventional support structures are designed to hold a foil flat and rigid. This new structure takes advantage of the significantly greater strength of metals in pure tension, utilizing curved shapes for both foil and support structure. The shape of the foil is comparable to the skin of a balloon, and the shape of the support structures is comparable to the cables of a suspension bridge. This design allows a significant reduction in foil thickness and support structure mass, resulting in a lower electron-beam loss between diode and laser gas. In addition, the foil is pre-formed in the support structure at pressures higher than operating pressure. Therefore, the foil is operated far from the yield point. Increased reliability is anticipated.

  14. Nonthermal electron-positron pairs and cold matter in the central engines of active galactic nuclei

    NASA Technical Reports Server (NTRS)

    Zdziarski, Andrzej A.

    1992-01-01

    The nonthermal e(+/-) pair model of the central engine of active galactic nuclei (AGNs) is discussed. The model assumes that nonthermal e(+/-) pairs are accelerated to highly relativistic energies in a compact region close to the central black hole and in the vicinity of some cold matter. The model has a small number of free parameters and explains a large body of AGN observations from EUV to soft gamma-rays. In particular, the model explains the existence of the UV bump, the soft X-rays excess, the canonical hard X-ray power law, the spectral hardening above about 10 keV, and some of the variability patterns in the soft and hard X-rays. In addition, the model explains the spectral steepening above about 50 keV seen in NGC 4151.

  15. The SPRITE and POS-SPRITE user report: An extensible calculation of particle, positron and electron implantation in solids

    SciTech Connect

    Ritley, K.A.; Ghosh, V.J.; Lynn, K.G.; McKewown, M.; Welch, D.O.

    1997-10-20

    SPRITE (Simulation of Particle Reemission, Implantation and Transmission--Extensible) is a Fortran computer program designed to model the transport of a stream of energetic particles as they scatter through a solid or multilayer. SPRITE is intended to be a user-friendly and easily-extensible engine for performing basic transport calculations, and SPRITE incorporates such physics as is required to simulate the transport process, but specifically omits the details of the scattering mechanisms. PSPRITE is a Fortran computer program, built around the SPRITE transport engine and incorporating physical information necessary for modeling the implantation and thermalization of a stream of positrons or electrons with a solid. This document is intended to be the primary source of information and the only operations manual for SPRITE and the POS-SPRITE family of programs. This information includes the mode of operation of SPRITE, the format of the required and optional file types, as well as information about the output and results of the calculation. Information about installing and running these programs on a variety of computer systems will not be addressed in this report. Such information is rapidly expanding as these programs are adapted to run on different platforms, and thus the user can expect such information to be contained with the source code distribution set. Detailed information about the calculations of the structure of the POS-SPRITE programs are provided in this report, but detailed benchmark comparisons between the output of these calculations and experimental data are an active topic of research, and they refer the reader to the published literature for this information.

  16. Detailed microscopic calculation of stellar electron and positron capture rates on 24Mg for O+Ne+Mg core simulations

    NASA Astrophysics Data System (ADS)

    Nabi, Jameel-Un

    2008-09-01

    A few white dwarfs, located in binary systems, may acquire sufficiently high mass-accretion rates resulting in the burning of carbon and oxygen under nondegenerate conditions forming an O+Ne+Mg core. These O+Ne+Mg cores are gravitationally less bound than more massive progenitor stars and can release more energy due to the nuclear burning. They are also amongst the probable candidates for low entropy r-process sites. Recent observations of subluminous Type II-P supernovae (e.g. 2005cs, 2003gd, 1999br and 1997D) were able to rekindle the interest in 8-10 Modot which develop O+Ne+Mg cores. Microscopic calculations of capture rates on 24Mg, which may contribute significantly to the collapse of O+Ne+Mg cores, using the shell model and the proton-neutron quasiparticle random-phase approximation (pn-QRPA) theory, were performed earlier and comparisons made. Simulators, however, may require these capture rates on a fine scale. For the first time, a detailed microscopic calculation of the electron and positron capture rates on 24Mg on an extensive temperature-density scale is presented here. This type of scale is more appropriate for interpolation purposes and of greater utility for simulation codes. The calculations are done using the pn-QRPA theory using a separable interaction. The deformation parameter, believed to be a key parameter in QRPA calculations, is adopted from experimental data to increase the reliability of the QRPA results further. The resulting calculated rates are up to a factor of 14 or more enhanced as compared to shell model rates and may lead to some interesting scenarios for core collapse simulators.

  17. Simulation of planar channeling-radiation spectra of relativistic electrons and positrons channeled in a diamond-structure or tungsten single crystal (classical approach)

    NASA Astrophysics Data System (ADS)

    Azadegan, B.; Wagner, W.

    2015-01-01

    We present a Mathematica package for simulation of spectral-angular distributions and energy spectra of planar channeling radiation of relativistic electrons and positrons channeled along major crystallographic planes of a diamond-structure or tungsten single crystal. The program is based on the classical theory of channeling radiation which has been successfully applied to study planar channeling of light charged particles at energies higher than 100 MeV. Continuous potentials for different planes of diamond, Si, Ge and W single crystals are calculated using the Doyle-Turner approximation to the atomic scattering factor and taking thermal vibrations of the crystal atoms into account. Numerical methods are applied to solve the classical one-dimensional equation of motion. The code is designed to calculate the trajectories, velocities and accelerations of electrons (positrons) channeled by the planar continuous potential. In the framework of classical electrodynamics, these data allow realistic simulations of spectral-angular distributions and energy spectra of planar channeling radiation. Since the generated output is quantitative, the results of calculation may be useful, e.g., for setup configuration and crystal alignment in channeling experiments, for the study of the dependence of channeling radiation on the input parameters of particle beams with respect to the crystal orientation, but also for the simulation of positron production by means of pair creation what is mandatory for the design of efficient positron sources necessary in high-energy and collider physics. Although the classical theory of channeling is well established for long time, there is no adequate library program for simulation of channeling radiation up to now, which is commonly available, sufficiently simple and effective to employ and, therefore, of benefit as for special investigations as for a quick overview of basic features of this type of radiation.

  18. Hard photon processes in electron-positron annihilation at 29 GeV

    SciTech Connect

    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)%.

  19. Spin polarized low-energy positron source

    NASA Astrophysics Data System (ADS)

    Petrov, V. N.; Samarin, S. N.; Sudarshan, K.; Pravica, L.; Guagliardo, P.; Williams, J. F.

    2015-06-01

    This paper presents an investigation of spin polarization of positrons from a source based on the decay of 22Na isotopes. Positrons are moderated by transmission through a tungsten film and electrostatically focussed and transported through a 90 deg deflector to produce a slow positron beam with polarization vector normal to the linear momentum. The polarization of the beam was determined to be about 10% by comparison with polarized electron scattering asymmetries from a thin Fe film on W(110) at 10-10 Torr. Low energy electron emission from Fe layer on W(100) surfaces under positron impact is explored. It is shown that the intensity asymmetry of the electron emission as a function of the incident positron energy can be used to estimate the polarization of the positron beam. Also several materials with long mean free paths for spin relaxation are considered as possible moderators with increased polarization of the emergent positrons.

  20. Laser crystallization for large-area electronics

    NASA Astrophysics Data System (ADS)

    Sameshima, Toshiyuki

    2009-07-01

    Laser crystallization is reviewed for the purpose of fabrication of polycrystalline silicon thin film transistors (poly-Si TFTs). Laser-induced rapid heating is important for formation of crystalline films with a low thermal budget. Reduction of electrically active defects located at grain boundaries is essential for improving electrical properties of poly-Si films and achieving poly-Si TFTs with high performances. The internal film stress is attractive to increase the carrier mobility. Recent developments in laser crystallization methods with pulsed and continuous-wave lasers are also reviewed. Control of heat flow results in crystalline grain growth in the lateral direction, which is important for fabrication of large crystalline grains. We also report an annealing method using a high-power infrared semiconductor laser. High-power lasers will be attractive for rapid formation of crystalline films over a large area and activation of silicon with impurity atoms.

  1. Applications and advances of positron beam spectroscopy: appendix a

    SciTech Connect

    Howell, R. H., LLNL

    1997-11-05

    Over 50 scientists from DOE-DP, DOE-ER, the national laboratories, academia and industry attended a workshop held on November 5-7, 1997 at Lawrence Livermore National Laboratory jointly sponsored by the DOE-Division of Materials Science, The Materials Research Institute at LLNL and the University of California Presidents Office. Workshop participants were charged to address two questions: Is there a need for a national center for materials analysis using positron techniques and can the capabilities at Lawrence Livermore National Laboratory serve this need. To demonstrate the need for a national center the workshop participants discussed the technical advantages enabled by high positron currents and advanced measurement techniques, the role that these techniques will play in materials analysis and the demand for the data. There were general discussions lead by review talks on positron analysis techniques, and their applications to problems in semiconductors, polymers and composites, metals and engineering materials, surface analysis and advanced techniques. These were followed by focus sessions on positron analysis opportunities in these same areas. Livermore now leads the world in materials analysis capabilities by positrons due to developments in response to demands of science based stockpile stewardship. There was a detailed discussion of the LLNL capabilities and a tour of the facilities. The Livermore facilities now include the worlds highest current beam of keV positrons, a scanning pulsed positron microprobe under development capable of three dimensional maps of defect size and concentration, an MeV positron beam for defect analysis of large samples, and electron momentum spectroscopy by positrons. This document is a supplement to the written summary report. It contains a complete schedule, list of attendees and the vuegraphs for the presentations in the review and focus sessions.

  2. The Japanese Positron Factory

    NASA Astrophysics Data System (ADS)

    Okada, S.; Sunaga, H.; Kaneko, H.; Takizawa, H.; Kawasuso, A.; Yotsumoto, K.; Tanaka, R.

    1999-06-01

    The Positron Factory has been planned at Japan Atomic Energy Research Institute (JAERI). The factory is expected to produce linac-based monoenergetic positron beams having world-highest intensities of more than 1010e+/sec, which will be applied for R&D of materials science, biotechnology and basic physics & chemistry. In this article, results of the design studies are demonstrated for the following essential components of the facilities: 1) Conceptual design of a high-power electron linac with 100 MeV in beam energy and 100 kW in averaged beam power, 2) Performance tests of the RF window in the high-power klystron and of the electron beam window, 3) Development of a self-driven rotating electron-to-positron converter and the performance tests, 4) Proposal of multi-channel beam generation system for monoenergetic positrons, with a series of moderator assemblies based on a newly developed Monte Carlo simulation and the demonstrative experiment, 5) Proposal of highly efficient moderator structures, 6) Conceptual design of a local shield to suppress the surrounding radiation and activation levels.

  3. Positron program at the Idaho Accelerator Center

    SciTech Connect

    Stancari, Giulio

    2009-09-02

    Positron physics is an important part of the research activities at the Idaho Accelerator Center (IAC). With positron annihilation spectroscopy, maps of nanodefects in materials have been obtained. For this purpose, positrons are generated by radioactive decay, photoactivation, or pair production. Preliminary tests of positron sources in the MeV range based on electron linacs have also been carried out at the IAC, and an expansion of this program is planned. A similar positron beam at Jefferson Lab would greatly improve our knowledge of the inner structure of the proton. In this paper, research with positrons at the IAC is reviewed. After a description of the Center's facilities, results from positron annihilation spectroscopy are discussed, together with future plans for testing a prototype positron source for CEBAF.

  4. Capture and polarization of positrons in a proposed NLC polarized positron source

    SciTech Connect

    Batygin, Yuri K

    2003-05-28

    A proposed NLC polarized positron source utilizes a 150 GeV electron beam passing through a helical undulator. The resulting flux of polarized photons is converted in a thin positron production target. Spin polarized positrons are captured using a high field flux concentrator followed by an accelerator section immersed in a solenoidal field. Positron tracking through the accelerating and focusing systems is done together with integration of spin precession. Optimization of the collection system is performed to insure high positron yield into the 6-dimensional acceptance of the subsequent pre-damping ring while keeping the high value of positron beam polarization.

  5. Production, PET performance and dosimetric considerations of 134Ce/134La, an Auger electron and positron-emitting generator for radionuclide therapy.

    PubMed

    Lubberink, Mark; Lundqvist, Hans; Tolmachev, Vladimir

    2002-02-21

    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.

  6. Positron Physics

    NASA Technical Reports Server (NTRS)

    Drachman, Richard J.

    2003-01-01

    I will give a review of the history of low-energy positron physics, experimental and theoretical, concentrating on the type of work pioneered by John Humberston and the positronics group at University College. This subject became a legitimate subfield of atomic physics under the enthusiastic direction of the late Sir Harrie Massey, and it attracted a diverse following throughout the world. At first purely theoretical, the subject has now expanded to include high brightness beams of low-energy positrons, positronium beams, and, lately, experiments involving anti-hydrogen atoms. The theory requires a certain type of persistence in its practitioners, as well as an eagerness to try new mathematical and numerical techniques. I will conclude with a short summary of some of the most interesting recent advances.

  7. Dense electron-positron plasmas and gamma-ray bursts generation by counter-propagating quantum electrodynamics-strong laser interaction with solid targets

    NASA Astrophysics Data System (ADS)

    Luo, Wen; Zhu, Yi-Bo; Zhuo, Hong-Bin; Ma, Yan-Yun; Song, Ying-Ming; Zhu, Zhi-Chao; Wang, Xiao-Dong; Li, Xing-Huo; Turcu, I. C. E.; Chen, Min

    2015-06-01

    We use quantum electrodynamics (QED) particle-in-cell simulations to investigate and compare the generation of dense electron-positron plasmas and intense γ-ray bursts in the case of counter-propagating laser solid interaction (two-side irradiation) and single laser solid interaction (one-side irradiation). In the case of counter-propagating linearly polarized laser pulses irradiating a thin aluminum foil with each pulse peak power of 12.5 PW (I = 4 × 1023 W/cm2), we calculate that about 20% of the laser energy is converted into a burst of γ-rays with flux exceeding 1014 s.-1 This would be one of the most intense γ-ray sources among those currently available in laboratories. The γ-ray conversion efficiency in the case of two-side irradiation is three times higher than in the case of one-side irradiation using a single 12.5 PW laser. Dense electron-positron plasma with a maximum density of 6 × 1027 m-3 are generated simultaneously during the two-side irradiation which is eightfold denser compared to the one-side irradiation. The enhancement of the effects in the case of counter-propagating lasers are the results of the symmetrical compression of the foil target and the formation of electric potential and standing wave around the target. Realizing experimentally the proposed counter-propagating QED-strong laser-solid interaction to produce dense electron-positron pairs and prolific γ-rays will be made possible by the Extreme Light Infrastructure-Nuclear Physics facility under construction.

  8. Dense electron-positron plasmas and gamma-ray bursts generation by counter-propagating quantum electrodynamics-strong laser interaction with solid targets

    SciTech Connect

    Luo, Wen; Zhu, Yi-Bo; Song, Ying-Ming; Zhu, Zhi-Chao; Wang, Xiao-Dong; Zhuo, Hong-Bin; Ma, Yan-Yun; Li, Xing-Huo; Turcu, I. C. E.; Chen, Min

    2015-06-15

    We use quantum electrodynamics (QED) particle-in-cell simulations to investigate and compare the generation of dense electron-positron plasmas and intense γ-ray bursts in the case of counter-propagating laser solid interaction (two-side irradiation) and single laser solid interaction (one-side irradiation). In the case of counter-propagating linearly polarized laser pulses irradiating a thin aluminum foil with each pulse peak power of 12.5 PW (I = 4 × 10{sup 23 }W/cm{sup 2}), we calculate that about 20% of the laser energy is converted into a burst of γ-rays with flux exceeding 10{sup 14 }s.{sup −1} This would be one of the most intense γ-ray sources among those currently available in laboratories. The γ-ray conversion efficiency in the case of two-side irradiation is three times higher than in the case of one-side irradiation using a single 12.5 PW laser. Dense electron-positron plasma with a maximum density of 6 × 10{sup 27 }m{sup −3} are generated simultaneously during the two-side irradiation which is eightfold denser compared to the one-side irradiation. The enhancement of the effects in the case of counter-propagating lasers are the results of the symmetrical compression of the foil target and the formation of electric potential and standing wave around the target. Realizing experimentally the proposed counter-propagating QED-strong laser-solid interaction to produce dense electron-positron pairs and prolific γ-rays will be made possible by the Extreme Light Infrastructure-Nuclear Physics facility under construction.

  9. Prediction of Central Nervous System Relapse of Diffuse Large B-Cell Lymphoma Using Pretherapeutic [18F]2-Fluoro-2-Deoxyglucose (FDG) Positron Emission Tomography/Computed Tomography

    PubMed Central

    Song, Yoo Sung; Lee, Won Woo; Lee, Jong Seok; Kim, Sang Eun

    2015-01-01

    Abstract Central nervous system (CNS) relapse of diffuse large B-cell lymphoma (DLBCL) is a rare complication, but has a poor prognosis with unknown pathophysiology. Recent trials of CNS prophylaxis have shown to be ineffective, despite patient's selection using several known clinical risk factors. In this study, the authors evaluated the value of pretreatment [18F]2-Fluoro-2-deoxyglucose positron emission tomography in predicting CNS relapse in DLBCL patients. The authors analyzed 180 pathologically confirmed DLBCL patients, retrospectively. Patients underwent [18F]2-Fluoro-2-deoxyglucose positron emission tomography/computed tomography before first line rituximab to cyclophosphamide, doxorubicin, vincristine, and prednisone therapy. Clinical characteristics were evaluated and total lesion glycolysis (TLG) with a threshold margin of 50% was calculated. Among age, sex, Ann Arbor stage, International Prognostic Index, revised International Prognostic Index, high serum lactate dehydrogenase level, presence of B symptoms, bulky disease (≥10 cm), extranodal lesion involvement, bone marrow involvement, high metabolic tumor volume ( >450 mL), and high TLG50 (>2000), the high TLG50 was the only significant prognostic factor for predicting CNS relapse in a multivariate analysis (P = 0.04). Kaplan–Meir survival analysis between high TLG50 (>2000) and low TLG50 (≤2000) groups revealed significantly different mean progression free survival (PFS) of 1317.2 ± 134.3 days and 1968.6 ± 18.3 days, respectively (P < 0.001). High TLG50 on [18F]2-Fluoro-2-deoxyglucose positron emission tomography/computed tomography is the most significant predictor of CNS relapse in un-treated DLBCL patients. PMID:26554808

  10. Observation of the electron ridge Fermi surface in YBa{sub 2}Cu{sub 3}O{sub 7-x} by positron annihilation

    SciTech Connect

    Smedskjaer, L.C.; Fang, Y.; Bailey, K.G.; Welp, U.; Bansil, A.

    1991-04-01

    Positron annihilation (two-dimensional-angular-correlation) experiments on an untwinned single crystal of metallic YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} sample are reported in the c-projection. The measurements were carried out at room temperature and involved 94 Mcounts. An analysis of the spectra reveals clearly for the first time the presence of the electron ridge Fermi surface associated with the one-dimensional chain bands, and orthorhombic anisotropies in momentum density in good agreement with the band theory predictions.

  11. Positron Injector Accelerator and RF System for the ILC

    SciTech Connect

    Wang, J.W.; Adolphsen, C.; Bharadwaj, V.; Bowden, G.; Jongewaard, E.; Li, Z.; Miller, R.; Sheppard, J.C.; /SLAC

    2007-03-28

    Due to the extremely high energy deposition from positrons, electrons, photons and neutrons behind the positron target, and because a solenoid is required to focus the large emittance positron beam, the 1.3 GHz preaccelerator has to use normal conducting structures up to energy of 400 MeV. There are many challenges in the design of the normal-conducting portion of the ILC positron injector system such as obtaining high positron yield with required emittance, achieving adequate cooling with the high RF and particle loss heating, and sustaining high accelerator gradients during millisecond-long pulses in a strong magnetic field. Considering issues of feasibility, reliability and cost savings for the ILC, the proposed design for the positron injector contains both standing-wave (SW) and traveling-wave (TW) L-band accelerator structures. A short version of the new type of the SW section is under fabrication and testing. An updated status report is given. This paper also covers acceleration vs. deceleration for pre-accelerator sections, SW vs. TW structures, as well as longitudinal matching from target to linac and linac to damping ring.

  12. Positron transport and thermalization - the plasma-gas interface

    NASA Astrophysics Data System (ADS)

    Marler, Joan

    2008-11-01

    Low energy positrons are now used in many fields including atomic physics, material science and medicine [1]. Plasma physics is providing new tools for this research, including Penning-Malmberg buffer-gas traps to accumulate positrons and the use of rotating electric fields (the ``rotating wall'' technique) to compress positrons radially and create tailored beams [1]. These devices (now available commercially), which rely in key instances on positron-neutral interactions, are a convenient way to create plasmas and beams for a variety of applications. A deeper understanding of the relevant cooling and loss mechanisms is required to take full advantage of this technology. This talk focuses on a recent study of positrons in such a tenuous gaseous environment in the presence of an applied electric field [2]. Energy-resolved collision cross sections and a Monte Carlo code modified to include positrionium (Ps) formation are used to obtain transport coefficients and the thermalization and Ps-formation rates. A markedly different type of negative differential conductivity is observed (i.e., not seen in electron systems), due to the non-conservative nature of the Ps-formation process. It is particularly prominent in gases with large, highly energy dependent Ps-formation cross sections. The relevance of these calculations to other positron applications will also be discussed, including a currently planned study of positrons in gaseous water. It is hoped that these calculations will inspire a new generation of positron transport experiments.*Work done in collaboration with Z.Lj. Petrovi'c, A. Bankovi'c, M. Suvakov, G. Malovi'c, S. Dujko, S.J. Buckman. 1. C. M. Surko and R. G. Greaves, Phys. Plasmas 11, 2333-2348 (2004).2. A. Bankovi'c, J. P. Marler, M. Suvakov, G. Malovi'c, and Z. Lj. Petrovi'c, Nucl. Instrum. and Meth. in Phys. Res. B 266, 462-465 (2008).

  13. Slow positron beam generator for lifetime studies

    NASA Technical Reports Server (NTRS)

    Singh, Jag J. (Inventor); Eftekhari, Abe (Inventor); St.clair, Terry L. (Inventor)

    1991-01-01

    A slow positron beam generator uses a conductive source residing between two test films. Moderator pieces are placed next to the test film on the opposite side of the conductive source. A voltage potential is applied between the moderator pieces and the conductive source. Incident energetic positrons: (1) are emitted from the conductive source; (2) are passed through test film; and (3) isotropically strike moderator pieces before diffusing out of the moderator pieces as slow positrons, respectively. The slow positrons diffusing out of moderator pieces are attracted to the conductive source which is held at an appropriate potential below the moderator pieces. The slow positrons have to pass through the test films before reaching the conductive source. A voltage is adjusted so that the potential difference between the moderator pieces and the conductive source forces the positrons to stop in the test films. Measurable annihilation radiation is emitted from the test film when positrons annihilate (combine) with electrons in the test film.

  14. High intensity positron program at LLNL

    SciTech Connect

    Asoka-Kumar, P.; Howell, R.H.; Stoeffl, W.

    1998-09-23

    Lawrence Livermore National Laboratory (LLNL) is the home of the world's highest current beam of keV positrons. The potential for establishing a national center for materials analysis using positron annihilation techniques around this capability is being actively pursued. The high LLNL beam current will enable investigations in several new areas. We are developing a positron microprobe that will produce a pulsed, focused positron beam for 3-dimensional scans of defect size and concentration with submicron resolution. Below we summarize the important design features of this microprobe. Several experimental end stations will be available that can utilize the high current beam with a time distribution determined by the electron linac pulse structure, quasi-continuous, or bunched at 20 MHz, and can operate in an electrostatic or (and) magnetostatic environment. Some of the planned early experiments are: two-dimensional angular correlation of annihilation radiation of thin films and buried interfaces, positron diffraction holography, positron induced desorption, and positron induced Auger spectra.

  15. Total cross sections of electron and positron collisions with C3F8 and C3H8 molecules and differential elastic and vibrational excitation cross sections by electron impact on these molecules

    NASA Astrophysics Data System (ADS)

    Tanaka, Hiroshi; Tachibana, Yoshio; Kitajima, Masashi; Sueoka, Osamu; Takaki, Hideki; Hamada, Akira; Kimura, Mineo

    1999-03-01

    Total cross sections for electron (e-) and positron (e+) scattering from C3H8 and C3F8 have been measured from 0.8 to 600 eV and 0.7 to 600 eV, respectively. We have also investigated differential elastic cross sections by electron impact from 2.0 to 200 eV, and compared them with the present theoretical results. For e- scattering from C3H8, the cross sections are found to be larger by a factor of 2 than those of e+ scattering below 20-30 eV. They show a large peak at 8 eV due to a shape resonance and a shoulderlike structure in the region of 20-40 eV. For e- scattering from C3F8, the cross sections are again larger by at least a factor of 2 than those of e+ scattering below 50 eV, and they have two peaks at 4 and 8 eV, followed by a broad peak in the region of 20-40 eV. Some small structures overlie the broad hump. Both e- and e+ impact cross sections for C3H8 and C3F8 quickly approach each other beyond 200 eV. From the differential cross section study, we have been able to provide more detailed information on shape resonances, and also we have carried out some analysis of resonances in vibrational excitation results. In general, the total and integrated elastic cross sections are in good qualitative and quantitative agreement.

  16. Cross sections for ionization of K, L and M shells of atoms by impact of electrons and positrons with energies up to 1 GeV: Analytical formulas

    SciTech Connect

    Bote, David; Salvat, Francesc Jablonski, Aleksander

    2009-11-15

    Analytical formulas are presented for the easy calculation of cross sections for ionization of K, L and M shells of neutral atoms by impact of electrons and positrons with kinetic energies up to 1 GeV. Each formula contains a number of parameters that are characteristic of the element, the active electron shell and the projectile particle. The values of these parameters were determined by fitting the cross section values in an extensive database that was calculated recently by means of a composite algorithm that combines the distorted-wave and plane-wave Born approximations. Tables of parameter values are given for all elements, from hydrogen (Z=1) to einsteinium (Z=99). The proposed analytical expressions yield ionization cross sections that agree with those in the numerical database to within about 1%, except for projectiles with near-threshold energies.

  17. Electron capture and positron decay of /sup 206/Fr and /sup 208/Fr and the energy levels of /sup 206/Rn and /sup 208/Rn

    SciTech Connect

    Ritchie, B.G.; Avignone, F.T. III; Carter, H.K.; Mlekodaj, R.L.; Spejewski, E.H.

    1981-04-01

    The isotopes /sup 206/Fr and /sup 208/Fr were produced by the reactions Ir(/sup 20/Ne,xn)/sup 206,208/Fr and mass separated on-line. The electron-capture and positron decays to /sup 206/Rn and /sup 208/Rn were studied by collecting ..gamma.. ray and internal conversion electron singles spectra as a function of decay time as well as ..gamma..-..gamma.., ..gamma..-e/sup -/, and ..gamma..-x ray coincidence spectra. The energies and many of the spins were determined for 18 excited, even parity states in /sup 208/Rn and for 10 excited, even parity states in /sup 206/Rn. These nuclei appear to be excellent candidates for interpretation in terms of a weak coupling shell model. The energy levels were also compared to the predictions of the interacting boson approximation model.

  18. Propagation and Generation of Electromagnetic Waves at Proton Gyrofrequencies in a Relativistic Electron-Positron Plasma. II. Excitation of Electromagnetic Waves

    NASA Astrophysics Data System (ADS)

    Zheleznyakov, V. V.; Bespalov, P. A.

    2016-04-01

    In part I of this work [1], we study the dispersion characteristics of low-frequency waves in a relativistic electron-positron plasma. In part II, we examine the electromagnetic wave instability in this plasma caused by an admixture of nonrelativistic protons with energy comparable with the energy of relativistic low-mass particles. The instability occurs in the frequency band between the fundamental harmonic of proton gyrofrequency and the fundamental harmonic of relativistic electron gyrofrequency. The results can be used for the interpretation of known observations of the pulsar emissions obtained with a high time and frequency resolution. The considered instability can probably be the initial stage of the microwave radio emission nanoshots typical of the pulsar in the Crab Nebula.

  19. Cosmic-ray Positrons from Millisecond Pulsars

    NASA Astrophysics Data System (ADS)

    Venter, C.; Kopp, A.; Harding, A. K.; Gonthier, P. L.; Büsching, I.

    2015-07-01

    Observations by the Fermi Large Area Telescope of γ-ray millisecond pulsar (MSP) light curves imply copious pair production in their magnetospheres, and not exclusively in those of younger pulsars. Such pair cascades may be a primary source of Galactic electrons and positrons, contributing to the observed enhancement in positron flux above ∼10 GeV. Fermi has also uncovered many new MSPs, impacting Galactic stellar population models. We investigate the contribution of Galactic MSPs to the flux of terrestrial cosmic-ray electrons and positrons. Our population synthesis code predicts the source properties of present-day MSPs. We simulate their pair spectra invoking an offset-dipole magnetic field. We also consider positrons and electrons that have been further accelerated to energies of several TeV by strong intrabinary shocks in black widow (BW) and redback (RB) systems. Since MSPs are not surrounded by pulsar wind nebulae or supernova shells, we assume that the pairs freely escape and undergo losses only in the intergalactic medium. We compute the transported pair spectra at Earth, following their diffusion and energy loss through the Galaxy. The predicted particle flux increases for non-zero offsets of the magnetic polar caps. Pair cascades from the magnetospheres of MSPs are only modest contributors around a few tens of GeV to the lepton fluxes measured by the Alpha Magnetic Spectrometer, PAMELA, and Fermi, after which this component cuts off. The contribution by BWs and RBs may, however, reach levels of a few tens of percent at tens of TeV, depending on model parameters.

  20. COSMIC-RAY POSITRONS FROM MILLISECOND PULSARS

    SciTech Connect

    Venter, C.; Kopp, A.; Büsching, I.; Harding, A. K.; Gonthier, P. L.

    2015-07-10

    Observations by the Fermi Large Area Telescope of γ-ray millisecond pulsar (MSP) light curves imply copious pair production in their magnetospheres, and not exclusively in those of younger pulsars. Such pair cascades may be a primary source of Galactic electrons and positrons, contributing to the observed enhancement in positron flux above ∼10 GeV. Fermi has also uncovered many new MSPs, impacting Galactic stellar population models. We investigate the contribution of Galactic MSPs to the flux of terrestrial cosmic-ray electrons and positrons. Our population synthesis code predicts the source properties of present-day MSPs. We simulate their pair spectra invoking an offset-dipole magnetic field. We also consider positrons and electrons that have been further accelerated to energies of several TeV by strong intrabinary shocks in black widow (BW) and redback (RB) systems. Since MSPs are not surrounded by pulsar wind nebulae or supernova shells, we assume that the pairs freely escape and undergo losses only in the intergalactic medium. We compute the transported pair spectra at Earth, following their diffusion and energy loss through the Galaxy. The predicted particle flux increases for non-zero offsets of the magnetic polar caps. Pair cascades from the magnetospheres of MSPs are only modest contributors around a few tens of GeV to the lepton fluxes measured by the Alpha Magnetic Spectrometer, PAMELA, and Fermi, after which this component cuts off. The contribution by BWs and RBs may, however, reach levels of a few tens of percent at tens of TeV, depending on model parameters.

  1. Elastic and inelastic scattering of positrons in gases and solids

    NASA Technical Reports Server (NTRS)

    Mcgowan, J. W.

    1972-01-01

    Three apparatuses were designed and built: The first, which is now operative, was designed to study the details of positron thermalization in solids and the subsequent emission of the low energy positrons from moderating foils; The second apparatus now under test is a positron bottle similar in design to an electron trap. It was built to store positrons at a fixed energy and to look at the number of stored positrons (storage time) as a function of a scattering gas in the vacuum chamber. The third apparatus is a crossed beam apparatus where positron-, alkali scattering will be studied. Much of the apparatus is now under test with electrons.

  2. Positron microanalysis with high intensity beams

    SciTech Connect

    Hulett, L.D. Jr.; Donohue, D.L.

    1990-01-01

    One of the more common applications for a high intensity slow positron facility will be microanalysis of solid materials. In the first section of this paper some examples are given of procedures that can be developed. Since most of the attendees of this workshop are experts in positron spectroscopy, comprehensive descriptions will be omitted. With the exception of positron emission microscopy, most of the procedures will be based on those already in common use with broad beams. The utility of the methods have all been demonstrated, but material scientists use very few of them because positron microbeams are not generally available. A high intensity positron facility will make microbeams easier to obtain and partially alleviate this situation. All microanalysis techniques listed below will have a common requirement, which is the ability to locate the microscopic detail or area of interest and to focus the positron beam exclusively on it. The last section of this paper is a suggestion of how a high intensity positron facility might be designed so as to have this capability built in. The method will involve locating the specimen by scanning it with the microbeam of positrons and inducing a secondary electron image that will immediately reveal whether or not the positron beam is striking the proper portion of the specimen. This scanning positron microscope' will be a somewhat prosaic analog of the conventional SEM. It will, however, be an indispensable utility that will enhance the practicality of positron microanalysis techniques. 6 refs., 1 fig.

  3. Modelling Positron Interactions with Matter

    NASA Astrophysics Data System (ADS)

    Garcia, G.; Petrovic, Z.; White, R.; Buckman, S.

    2011-05-01

    In this work we link fundamental measurements of positron interactions with biomolecules, with the development of computer codes for positron transport and track structure calculations. We model positron transport in a medium from a knowledge of the fundamental scattering cross section for the atoms and molecules comprising the medium, combined with a transport analysis based on statistical mechanics and Monte-Carlo techniques. The accurate knowledge of the scattering is most important at low energies, a few tens of electron volts or less. The ultimate goal of this work is to do this in soft condensed matter, with a view to ultimately developing a dosimetry model for Positron Emission Tomography (PET). The high-energy positrons first emitted by a radionuclide in PET may well be described by standard formulas for energy loss of charged particles in matter, but it is incorrect to extrapolate these formulas to low energies. Likewise, using electron cross-sections to model positron transport at these low energies has been shown to be in serious error due to the effects of positronium formation. Work was supported by the Australian Research Council, the Serbian Government, and the Ministerio de Ciencia e Innovación, Spain.

  4. Electron cyclotron emission diagnostics on the large helical device

    NASA Astrophysics Data System (ADS)

    Nagayama, Y.; Kawahata, K.; England, A.; Ito, Y.; Bretz, N.; McCarthy, M.; Taylor, G.; Doane, J.; Ikezi, H.; Edlington, T.; Tomas, J.

    1999-01-01

    The electron cyclotron emission (ECE) diagnostic system is installed on the large helical device (LHD). The system includes the following instruments: a heterodyne radiometer, a Michelson spectrometer, and a grating polychromator. A 63.5 mm corrugated waveguide system is fully utilized. Large collection optics and notch filters at the frequency of the LHD electron cyclotron heating (ECH) were developed for this system. In addition to these filters, the rectangular waveguide notch filters, the ECE measurement with the radiometer has been successfully performed during the ECH.

  5. In vivo quantitative imaging of photoassimilate transport dynamics and allocation in large plants using a commercial positron emission tomography (PET) scanner

    DOE PAGES

    Karve, Abhijit A.; Alexoff, David; Kim, Dohyun; ...

    2015-11-09

    Although important aspects of whole-plant carbon allocation in crop plants (e.g., to grain) occur late in development when the plants are large, techniques to study carbon transport and allocation processes have not been adapted for large plants. Positron emission tomography (PET), developed for dynamic imaging in medicine, has been applied in plant studies to measure the transport and allocation patterns of carbohydrates, nutrients, and phytohormones labeled with positron-emitting radioisotopes. However, the cost of PET and its limitation to smaller plants has restricted its use in plant biology. Here we describe the adaptation and optimization of a commercial clinical PET scannermore » to measure transport dynamics and allocation patterns of 11C-photoassimilates in large crops. Based on measurements of a phantom, we optimized instrument settings, including use of 3-D mode and attenuation correction to maximize the accuracy of measurements. To demonstrate the utility of PET, we measured 11C-photoassimilate transport and allocation in Sorghum bicolor, an important staple crop, at vegetative and reproductive stages (40 and 70 days after planting; DAP). The 11C-photoassimilate transport speed did not change over the two developmental stages. However, within a stem, transport speeds were reduced across nodes, likely due to higher 11C-photoassimilate unloading in the nodes. Photosynthesis in leaves and the amount of 11C that was exported to the rest of the plant decreased as plants matured. In young plants, exported 11C was allocated mostly (88 %) to the roots and stem, but in flowering plants (70 DAP) the majority of the exported 11C (64 %) was allocated to the apex. Our results show that commercial PET scanners can be used reliably to measure whole-plant C-allocation in large plants nondestructively including, importantly, allocation to roots in soil. This capability revealed extreme changes in carbon allocation in sorghum plants, as they advanced to maturity

  6. In vivo quantitative imaging of photoassimilate transport dynamics and allocation in large plants using a commercial positron emission tomography (PET) scanner

    SciTech Connect

    Karve, Abhijit A.; Alexoff, David; Kim, Dohyun; Schueller, Michael J.; Ferrieri, Richard A.; Babst, Benjamin A.

    2015-11-09

    Although important aspects of whole-plant carbon allocation in crop plants (e.g., to grain) occur late in development when the plants are large, techniques to study carbon transport and allocation processes have not been adapted for large plants. Positron emission tomography (PET), developed for dynamic imaging in medicine, has been applied in plant studies to measure the transport and allocation patterns of carbohydrates, nutrients, and phytohormones labeled with positron-emitting radioisotopes. However, the cost of PET and its limitation to smaller plants has restricted its use in plant biology. Here we describe the adaptation and optimization of a commercial clinical PET scanner to measure transport dynamics and allocation patterns of 11C-photoassimilates in large crops. Based on measurements of a phantom, we optimized instrument settings, including use of 3-D mode and attenuation correction to maximize the accuracy of measurements. To demonstrate the utility of PET, we measured 11C-photoassimilate transport and allocation in Sorghum bicolor, an important staple crop, at vegetative and reproductive stages (40 and 70 days after planting; DAP). The 11C-photoassimilate transport speed did not change over the two developmental stages. However, within a stem, transport speeds were reduced across nodes, likely due to higher 11C-photoassimilate unloading in the nodes. Photosynthesis in leaves and the amount of 11C that was exported to the rest of the plant decreased as plants matured. In young plants, exported 11C was allocated mostly (88 %) to the roots and stem, but in flowering plants (70 DAP) the majority of the exported 11C (64 %) was allocated to the apex. Our results show that commercial PET scanners can be used reliably to measure whole-plant C-allocation in large plants nondestructively including, importantly, allocation to roots in soil. This capability revealed extreme changes in

  7. Electron and Positron Scattering from Chlorine Molecules in the Energy Region from 0.8 ev to 600 eV

    NASA Astrophysics Data System (ADS)

    Kimura, Mineo

    2002-10-01

    ELECTRON AND POSITRON SCATTERING FROM CHLORINE MOLECULES IN THE ENERGY REGION FROM 0.8 eV TO 600 eV C. Makochekanwa, H. Kawate, O. Sueoka and M. Kimura Graduate School of Science and Engineering, Yamaguchi University, Ube, Yamaguchi 755-8611, Japan Total scattering cross sections for chlorine molecules by electron impact are determined experimentally for the impact energies from 0.8 eV to 600 eV. Elastic scattering cross sections are also determined theoretically. The results above 23 eV are the first report on these processes. The present results are in good accord in the energy-dependence with the previous measurements, although the absolute magnitude is found to be about 30% smaller than that of Gulley et al. [J. Phys. B31, 2971 (1998)]. Strong sharp peaks around 7.8 eV and 12 eV are observed and well separated, and the one at 7.8 eV is attributed to dissociative electron attachment, while the one at 12 eV is speculated to be due to ion-pair formation through direct dissociation. The present elastic cross sections are found to show the similar shape to the TCS although the magnitude is smaller by a few % below 30 eV to a factor of two at 100 eV. Small-scale experimental study is also carried out for determining total and positronium formation cross sections by positron impact as well to carry out the comparative study.

  8. Development of large area, pico-second resolution photo-detectors and associated readout electronics

    SciTech Connect

    Grabas, H.; Oberla, E.; Attenkoffer, K.; Bogdan, M.; Frisch, H. J.; Genat, J. F.; May, E. N.; Varner, G. S.; Wetstein, M.

    2011-07-01

    The Large Area Pico-second Photo-detectors described in this contribution incorporate a photo-cathode and a borosilicate glass capillary Micro-Channel Plate (MCP) pair functionalized by atomic layer deposition (ALD) of separate resistive and electron secondary emitters materials. They may be used for biomedical imaging purposes, a remarkable opportunity to apply technologies developed in HEP having the potential to make major advances in the medical world, in particular for Positron Emission Tomography (PET). If daisy-chained and coupled to fast transmission lines read at both ends, they could be implemented in very large dimensions. Initial testing with matched pairs of small glass capillary test has demonstrated gains of the order of 105 to 106. Compared to other fast imaging devices, these photo-detectors are expected to provide timing resolutions in the 10-100 ps range, and two-dimension position in the sub-millimeter range. A 6-channel readout ASIC has been designed in 130 nm CMOS technology and tested. As a result, fast analog sampling up to 17 GS/s has been obtained, the intrinsic analog bandwidth being presently under evaluation. The digitization in parallel of several cells in two microseconds allows getting off-chip digital data read at a maximum rate of 40 MHz. Digital Signal Processing of the sampled waveforms is expected achieving the timing and space resolutions obtained with digital oscilloscopes. (authors)

  9. Beam rotation and shear in a large electron beam diode

    SciTech Connect

    Mansfield, C.R.; Oona, H.; Shurter, R.P.

    1990-01-01

    The time averaged electron beam current distribution of one of the electron guns of the Large Aperture Module (LAM) of the Aurora laser was measured as part of a larger set of experiments designed to study the electron beam transport to and energy deposition in the LAM laser chamber. The LAM laser chamber has a 1-m {times} 1-m aperture and is pumped from two sides along a 2-m length. A 10 ga. stainless steel sheet was placed inside the laser chamber and served multiple purposes. First, it was used to convert high energy electrons into X-rays in order to make radiograms of the electron beam. Second, the sheet was used as a Faraday cup to measure the total beam current. Third, individual Faraday cups were mounted on the plate to sample the time history of the electron beam at various positions. Each of the LAM electron gun diodes produces a beam of 750 kV electrons with a total current of about 500 kA which is relatively uniform over the cathode area of 1 m {times} 2 m. An applied magnetic field of about 1300 Gauss is used to prevent pinch of the beam during beam transport.

  10. Auger mediated positron sticking on graphene and highly oriented pyrolytic graphite

    NASA Astrophysics Data System (ADS)

    Chirayath, V. A.; Chrysler, M.; McDonald, A.; Lim, Z.; Shastry, K.; Gladen, R.; Fairchild, A.; Koymen, A.; Weiss, A.

    Positron annihilation induced Auger electron spectroscopy (PAES) measurements on 6-8 layers graphene grown on polycrystalline copper and the measurements on a highly oriented pyrolytic graphite (HOPG) sample have indicated the presence of a bound surface state for positrons. Measurements carried out with positrons of kinetic energies lower than the electron work function for graphene or HOPG have shown emission of low energy electrons possible only through the Auger mediated positron sticking (AMPS) process. In this process the positron makes a transition from a positive energy scattering state to a bound surface state. The transition energy is coupled to a valence electron which may then have enough energy to get ejected from the sample surface. The positrons which are bound to surface state are highly localized in a direction perpendicular to surface and delocalized parallel to it which makes this process highly surface sensitive and can thus be used for characterizing graphene or graphite surfaces for open volume defects and surface impurities. The measurements have also shown an extremely large low energy tail for the C KVV Auger transition at 263eV indicative of another physical process for low energy emission. This work was supported by NSF Grant No. DMR 1508719 and DMR 1338130.

  11. Electron drift in a large scale solid xenon

    SciTech Connect

    Yoo, J.; Jaskierny, W. F.

    2015-08-21

    A study of charge drift in a large scale optically transparent solid xenon is reported. A pulsed high power xenon light source is used to liberate electrons from a photocathode. The drift speeds of the electrons are measured using a 8.7 cm long electrode in both the liquid and solid phase of xenon. In the liquid phase (163 K), the drift speed is 0.193 ± 0.003 cm/μs while the drift speed in the solid phase (157 K) is 0.397 ± 0.006 cm/μs at 900 V/cm over 8.0 cm of uniform electric fields. Furthermore, it is demonstrated that a factor two faster electron drift speed in solid phase xenon compared to that in liquid in a large scale solid xenon.

  12. Improving CASINO performance for models with large number of electrons

    SciTech Connect

    Anton, L; Alfe, D; Hood, R Q; Tanqueray, D

    2009-05-13

    Quantum Monte Carlo calculations have at their core algorithms based on statistical ensembles of multidimensional random walkers which are straightforward to use on parallel computers. Nevertheless some computations have reached the limit of the memory resources for models with more than 1000 electrons because of the need to store a large amount of electronic orbitals related data. Besides that, for systems with large number of electrons, it is interesting to study if the evolution of one configuration of random walkers can be done faster in parallel. We present a comparative study of two ways to solve these problems: (1) distributed orbital data done with MPI or Unix inter-process communication tools, (2) second level parallelism for configuration computation.

  13. Electron drift in a large scale solid xenon

    DOE PAGES

    Yoo, J.; Jaskierny, W. F.

    2015-08-21

    A study of charge drift in a large scale optically transparent solid xenon is reported. A pulsed high power xenon light source is used to liberate electrons from a photocathode. The drift speeds of the electrons are measured using a 8.7 cm long electrode in both the liquid and solid phase of xenon. In the liquid phase (163 K), the drift speed is 0.193 ± 0.003 cm/μs while the drift speed in the solid phase (157 K) is 0.397 ± 0.006 cm/μs at 900 V/cm over 8.0 cm of uniform electric fields. Furthermore, it is demonstrated that a factor twomore » faster electron drift speed in solid phase xenon compared to that in liquid in a large scale solid xenon.« less

  14. Direct Observation of the Surface Segregation of Cu in Pd by Time-Resolved Positron-Annihilation-Induced Auger Electron Spectroscopy

    SciTech Connect

    Mayer, J.; Hugenschmidt, C.; Schreckenbach, K.

    2010-11-12

    Density functional theory calculations predict the surface segregation of Cu in the second atomic layer of Pd which has not been unambiguously confirmed by experiment so far. We report measurements on Pd surfaces covered with three and six monolayers of Cu using element selective positron-annihilation-induced Auger electron spectroscopy (PAES) which is sensitive to the topmost atomic layer. Moreover, time-resolved PAES, which was applied for the first time, enables the investigation of the dynamics of surface atoms and hence the observation of the segregation process. The time constant for segregation was experimentally determined to {tau}=1.38(0.21) h, and the final segregated configuration was found to be consistent with calculations. Time-dependent PAES is demonstrated to be a novel element selective technique applicable for the investigation of, e.g., heterogeneous catalysis, corrosion, or surface alloying.

  15. Particle-in-cell simulation for parametric decays of a circularly polarized Alfvén wave in relativistic thermal electron-positron plasma

    SciTech Connect

    López, Rodrigo A. Muñoz, Víctor; Viñas, Adolfo F.; Alejandro Valdivia, J.

    2014-03-15

    Parametric decays of a left-handed circularly polarized Alfvén wave propagating along a constant background magnetic field in a relativistic thermal electron-positron plasma are studied by means of a one dimensional relativistic particle-in-cell simulation. Relativistic effects are included in the Lorentz equation for the momentum of the particles and in their thermal motion, by considering a Maxwell-Jüttner velocity distribution function for the initial condition. In the linear stage of the simulation, we find many instabilities that match the predictions of relativistic fluid theory. In general, the growth rates of the instabilities increase as the pump wave amplitude is increased, and decrease with a raise in the plasma temperatures. We have confirmed that for very high temperatures the Alfvén branch is suppressed, consistent with analytical calculations.

  16. Search for new physics in high-mass electron-positron events in pp[over] collisions at square root s = 1.96 TeV.

    PubMed

    Aaltonen, T; Abulencia, A; Adelman, J; Affolder, T; Akimoto, T; Albrow, M G; Amerio, S; Amidei, D; Anastassov, A; Anikeev, K; Annovi, A; Antos, J; Aoki, M; Apollinari, G; Arisawa, T; Artikov, A; Ashmanskas, W; Attal, A; Aurisano, 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; Beauchemin, P-H; Bedeschi, F; Behari, S; Bellettini, G; Bellinger, J; Belloni, A; Benjamin, D; Beretvas, A; Beringer, J; Berry, T; Bhatti, A; Binkley, M; Bisello, D; Bizjak, I; 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; Burkett, K; Busetto, G; Bussey, P; Buzatu, A; Byrum, K L; Cabrera, S; Campanelli, M; Campbell, M; Canelli, F; Canepa, A; Carrillo, S; Carlsmith, D; Carosi, R; Carron, S; Casal, B; 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; Cilijak, 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; Cuenca Almenar, C; Cuevas, J; Culbertson, R; Cully, J C; DaRonco, S; Datta, M; D'Auria, S; Davies, T; Dagenhart, D; de Barbaro, P; De Cecco, S; Deisher, A; De Lentdecker, G; De Lorenzo, G; Dell'Orso, M; Delli Paoli, F; Demortier, L; Deng, J; Deninno, M; De Pedis, D; Derwent, P F; Di Giovanni, G P; Dionisi, C; Di Ruzza, B; Dittmann, J R; D'Onofrio, M; Dörr, C; Donati, S; 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; Forrest, R; Forrester, S; Franklin, M; Freeman, J C; Furic, I; Gallinaro, M; Galyardt, J; Garcia, J E; Garberson, F; Garfinkel, A F; Gay, C; Gerberich, H; Gerdes, D; Giagu, S; Giannetti, P; Gibson, K; Gimmell, J L; Ginsburg, C; Giokaris, N; Giordani, M; Giromini, P; Giunta, M; Giurgiu, G; Glagolev, V; Glenzinski, D; Gold, M; Goldschmidt, N; Goldstein, J; Golossanov, A; Gomez, G; Gomez-Ceballos, G; Goncharov, M; González, O; Gorelov, I; Goshaw, A T; Goulianos, K; Gresele, A; Grinstein, S; Grosso-Pilcher, C; Grundler, U; Guimaraes da Costa, J; Gunay-Unalan, Z; Haber, C; Hahn, K; Hahn, S R; Halkiadakis, E; Hamilton, A; Han, B-Y; Han, J Y; Handler, R; Happacher, F; Hara, K; Hare, D; Hare, M; Harper, S; Harr, R F; Harris, R M; Hartz, M; Hatakeyama, K; Hauser, J; Hays, C; Heck, M; Heijboer, A; Heinemann, B; Heinrich, J; Henderson, C; Herndon, M; Heuser, J; Hidas, D; Hill, C S; Hirschbuehl, D; Hocker, A; Holloway, A; Hou, S; Houlden, M; Hsu, S-C; Huffman, B T; Hughes, R E; Husemann, U; Huston, J; Incandela, J; Introzzi, G; Iori, M; Ivanov, A; Iyutin, B; James, E; Jang, D; Jayatilaka, B; Jeans, D; Jeon, E J; Jindariani, S; Johnson, W; Jones, M; Joo, K K; Jun, S Y; Jung, J E; Junk, T R; Kamon, T; Karchin, P E; Kato, Y; Kemp, Y; Kephart, R; Kerzel, U; Khotilovich, V; Kilminster, B; Kim, D H; Kim, H S; Kim, J E; Kim, M J; Kim, S B; Kim, S H; Kim, Y K; Kimura, N; Kirsch, L; Klimenko, S; Klute, M; Knuteson, B; Ko, B R; Kondo, K; Kong, D J; Konigsberg, J; Korytov, A; Kotwal, A V; Kraan, A C; Kraus, J; Kreps, M; Kroll, J; Krumnack, N; Kruse, M; Krutelyov, V; Kubo, T; Kuhlmann, S E; Kuhr, T; Kulkarni, N P; Kusakabe, Y; Kwang, S; Laasanen, A T; Lai, S; Lami, S; Lammel, S; Lancaster, M; Lander, R L; Lannon, K; Lath, A; Latino, G; Lazzizzera, I; Lecompte, T; Lee, J; Lee, J; Lee, Y J; Lee, S W; Lefèvre, R; Leonardo, N; Leone, S; Levy, S; Lewis, J D; Lin, C; Lin, C S; Lindgren, M; Lipeles, E; Lister, A; Litvintsev, D O; Liu, T; Lockyer, N S; Loginov, A; Loreti, M; Lu, R-S; Lucchesi, D; Lujan, P; Lukens, P; Lungu, G; Lyons, L; Lys, J; Lysak, R; Lytken, E; Mack, P; Macqueen, D; Madrak, R; Maeshima, K; Makhoul, K; Maki, T; Maksimovic, P; Malde, S; Malik, S; Manca, G; Manousakis, A; Margaroli, F; Marginean, R; Marino, C; Marino, C P; Martin, A; Martin, M; Martin, V; Martínez, M; Martínez-Ballarín, R; Maruyama, T; Mastrandrea, P; Masubuchi, T; Matsunaga, H; Mattson, M E; Mazini, R; Mazzanti, P; McFarland, K S; McIntyre, P; McNulty, R; Mehta, A; Mehtala, P; Menzemer, S; Menzione, A; Merkel, P; Mesropian, C; Messina, A; Miao, T; Miladinovic, N; Miles, J; Miller, R; Mills, C; Milnik, M; Mitra, A; Mitselmakher, G; Miyamoto, A; Moed, S; Moggi, N; Mohr, B; Moon, C S; Moore, R; Morello, M; Fernandez, P Movilla; Mülmenstädt, J; Mukherjee, A; Muller, Th; Mumford, R; Murat, P; Mussini, M; Nachtman, J; Nagano, A; Naganoma, J; Nakamura, K; Nakano, I; Napier, A; Necula, V; Neu, C; Neubauer, M S; Nielsen, J; Nodulman, L; Norniella, O; Nurse, E; Oh, S H; Oh, Y D; Oksuzian, I; Okusawa, T; Oldeman, R; Orava, R; Osterberg, K; Pagliarone, C; Palencia, E; Papadimitriou, V; Papaikonomou, A; Paramonov, A A; Parks, B; Pashapour, S; Patrick, J; Pauletta, G; Paulini, M; Paus, C; Pellett, D E; Penzo, A; Phillips, T J; Piacentino, G; Piedra, J; Pinera, L; Pitts, K; Plager, C; Pondrom, L; Portell, X; Poukhov, O; Pounder, N; Prakoshyn, F; Pronko, A; Proudfoot, J; Ptohos, F; Punzi, G; Pursley, J; Rademacker, J; Rahaman, A; Ramakrishnan, V; Ranjan, N; Redondo, I; Reisert, B; Rekovic, V; Renton, P; Rescigno, M; Richter, S; Rimondi, F; Ristori, L; Robson, A; Rodrigo, T; Rogers, E; Rolli, S; Roser, R; Rossi, M; Rossin, R; Roy, P; Ruiz, A; Russ, J; Rusu, V; Saarikko, H; Safonov, A; Sakumoto, W K; Salamanna, G; Saltó, O; Santi, L; Sarkar, S; Sartori, L; Sato, K; Savard, P; Savoy-Navarro, A; Scheidle, T; Schlabach, P; Schmidt, E E; Schmidt, M P; Schmitt, M; Schwarz, T; Scodellaro, L; Scott, A L; Scribano, A; Scuri, F; Sedov, A; Seidel, S; Seiya, Y; Semenov, A; Sexton-Kennedy, L; Sfyrla, A; Shalhout, S Z; Shapiro, M D; Shears, T; Shepard, P F; Sherman, D; Shimojima, M; Shochet, M; Shon, Y; Shreyber, I; Sidoti, A; Sinervo, P; Sisakyan, A; Slaughter, A J; Slaunwhite, J; Sliwa, K; Smith, J R; Snider, F D; Snihur, R; Soderberg, M; Soha, A; Somalwar, S; Sorin, V; Spalding, J; Spinella, F; Spreitzer, T; Squillacioti, P; Stanitzki, M; Staveris-Polykalas, A; St Denis, R; Stelzer, B; Stelzer-Chilton, O; Stentz, D; Strologas, J; Stuart, D; Suh, J S; Sukhanov, A; Sun, H; Suslov, I; Suzuki, T; Taffard, A; Takashima, R; Takeuchi, Y; Tanaka, R; Tecchio, M; Teng, P K; Terashi, K; Thom, J; Thompson, A S; Thomson, E; Tipton, P; Tiwari, V; Tkaczyk, S; Toback, D; Tokar, S; Tollefson, K; Tomura, T; Tonelli, D; Torre, S; Torretta, D; Tourneur, S; Trischuk, W; Tsuno, S; Tu, Y; Turini, N; Ukegawa, F; Uozumi, S; Vallecorsa, S; van Remortel, N; Varganov, A; Vataga, E; Vazquez, F; Velev, G; Vellidis, C; Veramendi, G; Veszpremi, V; Vidal, M; Vidal, R; Vila, I; Vilar, R; Vine, T; Vogel, M; Vollrath, I; Volobouev, I; Volpi, G; Würthwein, F; Wagner, P; Wagner, R G; Wagner, R L; Wagner, J; Wagner, W; Wallny, R; Wang, S M; Warburton, A; Waters, D; Weinberger, M; 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

    2007-10-26

    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(2) using 1.3 fb(-1) of pp[over] collision data at square root 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' with a mass below 923 GeV/c(2) and the Randall-Sundrum graviton with a mass below 807 GeV/c(2) for k/M[over](pl) = 0.1, both at the 95% confidence level. Combining with diphoton data excludes the Randall-Sundrum graviton for masses below 889 GeV/c(2) for k/M[over](pl) = 0.1.

  17. Enhanced production of low-mass electron-positron pairs in 40-AGeV Pb-Au collisions at the CERN SPS.

    PubMed

    Adamová, D; Agakichiev, G; Appelshäuser, H; Belaga, V; Braun-Munzinger, P; Cherlin, A; Damjanović, S; Dietel, T; Dietrich, L; Drees, A; Esumi, S I; Filimonov, K; Fomenko, K; Fraenkel, Z; Garabatos, C; Glässel, P; Hering, G; Holeczek, J; Kushpil, V; Lenkeit, B; Maas, A; Marín, A; Milosević, J; Milov, A; Miśkowiec, D; Panebrattsev, Yu; Petchenova, O; Petrácek, V; Pfeiffer, A; Rak, J; Ravinovich, I; Rehak, P; Richter, M; Sako, H; Schmitz, W; Sedykh, S; Seipp, W; Sharma, A; Shimansky, S; Slívová, J; Specht, H J; Stachel, J; Sumbera, M; Tilsner, H; Tserruya, I; Wessels, J P; Wienold, T; Windelband, B; Wurm, J P; Xie, W; Yurevich, S; Yurevich, V

    2003-07-25

    We report on first measurements of low-mass electron-positron pairs in Pb-Au collisions at the CERN SPS beam energy of 40 AGeV. The observed pair yield integrated over the range of invariant masses 0.2e(+)e(-) annihilation with a modified rho propagator. They may be linked to chiral symmetry restoration and support the notion that the in-medium modifications of the rho are more driven by baryon density than by temperature.

  18. Dislocation Substructure in the Cold-Rolled Ni-20 Mass Pct Cr Alloy Analyzed by X-ray Diffraction, Positron Annihilation Lifetime, and Transmission Electron Microscopy

    NASA Astrophysics Data System (ADS)

    Yonemura, Mitsuharu; Inoue, Koji

    2016-12-01

    The systematic change in the dislocation density and characteristics that develop under cold rolling as a simulated deformation was studied in order to examine the fundamental behavior of dislocations in terms of the dislocation substructure formation. In particular, the dislocation density was quantified by X-ray line profile analysis (XLPA), which is effective for quantifying the dislocation density and character; positron annihilation lifetime (PAL), which is sensitive to vacancy-type lattice defects; the Bailey-Hirsch equation from the hardness (Hv); and transmission electron microscopy (TEM). The strain dependency of the dislocation density analyzed by XLPA, PAL, TEM, and Hv showed a similar tendency with an increase in the dislocation. In particular, the dislocation density by XLPA had good agreement with the results of TEM at low strain levels and with PAL at high strain levels. As a result, a combination of these techniques successfully showed the behavior of the dislocation substructure.

  19. Positron confinement in embedded lithium nanoclusters

    NASA Astrophysics Data System (ADS)

    van Huis, M. A.; van Veen, A.; Schut, H.; Falub, C. V.; Eijt, S. W.; Mijnarends, P. E.; Kuriplach, J.

    2002-02-01

    Quantum confinement of positrons in nanoclusters offers the opportunity to obtain detailed information on the electronic structure of nanoclusters by application of positron annihilation spectroscopy techniques. In this work, positron confinement is investigated in lithium nanoclusters embedded in monocrystalline MgO. These nanoclusters were created by means of ion implantation and subsequent annealing. It was found from the results of Doppler broadening positron beam analysis that approximately 92% of the implanted positrons annihilate in lithium nanoclusters rather than in the embedding MgO, while the local fraction of lithium at the implantation depth is only 1.3 at. %. The results of two-dimensional angular correlation of annihilation radiation confirm the presence of crystalline bulk lithium. The confinement of positrons is ascribed to the difference in positron affinity between lithium and MgO. The nanocluster acts as a potential well for positrons, where the depth of the potential well is equal to the difference in the positron affinities of lithium and MgO. These affinities were calculated using the linear muffin-tin orbital atomic sphere approximation method. This yields a positronic potential step at the MgO||Li interface of 1.8 eV using the generalized gradient approximation and 2.8 eV using the insulator model.

  20. Positron collisions with alkali-metal atoms

    NASA Technical Reports Server (NTRS)

    Gien, T. T.

    1990-01-01

    The total cross sections for positron and electron collisions with potassium, sodium, lithium and rubidium are calculated, employing the modified Glauber approximation. The Modified Glauber cross sections for positron collision with potassium and sodium at low intermediate energies are found to agree reasonably well with existing experimental data.

  1. A novel design for a variable energy positron lifetime spectrometer

    NASA Astrophysics Data System (ADS)

    Chen, D.; Zhang, J. D.; Cheng, C. C.; Beling, C. D.; Fung, S.

    2008-10-01

    We present computer simulations of a new design of a variable energy positron lifetime beam that uses for a start signal the secondary electron emission from a 25-nm thick carbon foil (C-foil) located in front of the sample. A needle of ˜30 μm diameter is positioned on-axis right behind the foil, creating a radial electric field that deflects the secondary electrons radially outward so as to miss the sample and to hit the micro-channel plate (MCP) detector placed down beam. The MCP signal provides the start signal for the positron lifetime spectrometer. A grid can be further introduced between the sample holder and the MCP to yield a cleaner signal by preventing the positrons with large transmitted scattering angle from hitting the MCP. The cylindrical symmetry of this design reduces the experimental complexity and offers good timing resolution. We show that the design is robust against the transmitted energy and angle of the secondary electrons and positrons.

  2. THEMIS Observations of the Magnetopause Electron Diffusion Region: Large Amplitude Waves and Heated Electrons

    NASA Technical Reports Server (NTRS)

    Tang, Xiangwei; Cattell, Cynthia; Dombeck, John; Dai, Lei; Wilson, Lynn B. III; Breneman, Aaron; Hupack, Adam

    2013-01-01

    We present the first observations of large amplitude waves in a well-defined electron diffusion region based on the criteria described by Scudder et al at the subsolar magnetopause using data from one Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite. These waves identified as whistler mode waves, electrostatic solitary waves, lower hybrid waves, and electrostatic electron cyclotron waves, are observed in the same 12 s waveform capture and in association with signatures of active magnetic reconnection. The large amplitude waves in the electron diffusion region are coincident with abrupt increases in electron parallel temperature suggesting strong wave heating. The whistler mode waves, which are at the electron scale and which enable us to probe electron dynamics in the diffusion region were analyzed in detail. The energetic electrons (approx. 30 keV) within the electron diffusion region have anisotropic distributions with T(sub e(right angle))/T(sub e(parallel)) > 1 that may provide the free energy for the whistler mode waves. The energetic anisotropic electrons may be produced during the reconnection process. The whistler mode waves propagate away from the center of the "X-line" along magnetic field lines, suggesting that the electron diffusion region is a possible source region of the whistler mode waves.

  3. Bound states of the positron with nitrile species with a configuration interaction multi-component molecular orbital approach.

    PubMed

    Tachikawa, Masanori; Kita, Yukiumi; Buenker, Robert J

    2011-02-21

    Characteristic features of the positron binding structure of some nitrile (-CN functional group) species such as acetonitrile, cyanoacetylene, acrylonitrile, and propionitrile are discussed with the configuration interaction scheme of multi-component molecular orbital calculations. This method can take the electron-positron correlation contribution into account through single electronic-single positronic excitation configurations. Our PA value of acetonitrile with the electronic 6-31++G(2df,2pd) and positronic [15s15p3d2f1g] basis set is calculated as 4.96 mhartree, which agrees to within 25% with the recent experimental value of 6.6 mhartree by Danielson et al. [Phys. Rev. Lett., 2010, 104, 233201]. Our PA values of acrylonitrile and propionitrile (5.70 and 6.04 mhartree) are the largest among these species, which is consistent with the relatively large dipole moments of the latter two systems.

  4. Semiconductor-based, large-area, flexible, electronic devices

    DOEpatents

    Goyal, Amit

    2011-03-15

    Novel articles and methods to fabricate the same resulting in flexible, large-area, triaxially textured, single-crystal or single-crystal-like, semiconductor-based, electronic devices are disclosed. Potential applications of resulting articles are in areas of photovoltaic devices, flat-panel displays, thermophotovoltaic devices, ferroelectric devices, light emitting diode devices, computer hard disc drive devices, magnetoresistance based devices, photoluminescence based devices, non-volatile memory devices, dielectric devices, thermoelectric devices and quantum dot laser devices.

  5. Radiation Belt Electron Dynamics Driven by Large-Amplitude Whistlers

    NASA Technical Reports Server (NTRS)

    Khazanov, G. V.; Tel'nikhin, A. A.; Kronberg, T. K.

    2013-01-01

    Acceleration of radiation belt electrons driven by oblique large-amplitude whistler waves is studied. We show analytically and numerically that this is a stochastic process; the intensity of which depends on the wave power modified by Bessel functions. The type of this dependence is determined by the character of the nonlinear interaction due to coupling between action and phase. The results show that physically significant quantities have a relatively weak dependence on the wave power.

  6. Gravure printing of graphene for large-area flexible electronics.

    PubMed

    Secor, Ethan B; Lim, Sooman; Zhang, Heng; Frisbie, C Daniel; Francis, Lorraine F; Hersam, Mark C

    2014-07-09

    Gravure printing of graphene is demonstrated for the rapid production of conductive patterns on flexible substrates. Development of suitable inks and printing parameters enables the fabrication of patterns with a resolution down to 30 μm. A mild annealing step yields conductive lines with high reliability and uniformity, providing an efficient method for the integration of graphene into large-area printed and flexible electronics.

  7. Deriving large electron temperatures and small electron densities with the Cassini Langmuir probe at Saturn

    NASA Astrophysics Data System (ADS)

    Garnier, Philippe; Wahlund, Jan-Erik; Holmberg, Mika; Lewis, Geraint; Schippers, Patricia; Rochel Grimald, Sandrine; Gurnett, Donald; Coates, Andrew; Dandouras, Iannis; Waite, Hunter

    2014-05-01

    The Langmuir Probes (LPs) are commonly used to investigate the cold plasma characteristics in planetary ionospheres/magnetospheres. The LPs performances are limited to low temperatures (i.e. below 5-10 eV at Saturn) and large densities (above several particles/cm3). A strong sensitivity of the Cassini LP measurements to energetic electrons (hundreds eV) may however be observed at Saturn in the L Shell range L=6-10 RS. These electrons impact the surface of the probe and generate a detectable current of secondary electrons. We investigate the influence of such electrons on the current-voltage (I-V) characteristics (for negative potentials), and manage to reproduce the observations with a reasonable precision through empirical and theoretical methods. Conversely, the modelling allows us to derive useful information about the energetic electrons from the LP observations : some information about their pitch angle anisotropy (if combined with the data from a single CAPS ELS anode), as well as an estimate of the electron temperature (in the range 100-300 eV) and of the electron density (above 0.1 particles/cm3). This enlarges the LP measurements capabilities when the influence of the energetic electrons is large (essentially near L=6-10 RS at Saturn). We finally show that a significant influence of the energetic electrons (larger than the contribution of thermal ions) is also expected in various plasma environments of the Solar System, such as at Jupiter (i.e near Ganymede, Europa, Callisto and Io), or even at Earth (in the plasmasheet, the magnetosheath or in plasma cavities). Large electron temperatures and small electron densities could potentially be derived in these environments, which may be of interest for Langmuir Probes in the Earth magnetosphere or onboard the future JUICE mission at Jupiter.

  8. Physics perspectives at JLab with a polarized positron beam

    SciTech Connect

    Voutier, Eric J.-M.

    2014-06-01

    Polarized positron beams are in some respect mandatory complements to polarized electron beams. The advent of the PEPPo concept for polarized positron production opens the possibility for the developement at the Jefferson Laboratory of a continuous polarized positron beam. The benefits of such a beam for hadronic structure studies are discussed, together with the technical and technological challenges to face.

  9. High-yield positron systems for linear colliders

    SciTech Connect

    Clendenin, J.E.

    1989-04-01

    Linear colliders, such as the SLC, are among those accelerators for which a high-yield positron source operating at the repetition rate of the accelerator is desired. The SLC, having electron energies up to 50 GeV, presents the possibility of generating positron bunches with useful charge even exceeding that of the initial electron bunch. The exact positron yield to be obtained depends on the particular capture, transport and damping system employed. Using 31 GeV electrons impinging on a W-type converter phase-space at the target to the acceptance of the capture rf section, the SLC source is capable of producing, for every electron, up to two positrons within the acceptance of the positron damping ring. The design of this source and the performance of the positron system as built are described. Also, future prospects and limitations for high-yield positron systems are discussed. 11 refs., 5 figs., 3 tabs.

  10. Positron acceleration in plasma bubble wakefield driven by an ultraintense laser

    SciTech Connect

    Hou, Ya-Juan; Wan, Feng; Sang, Hai-Bo Xie, Bai-Song

    2016-01-15

    The dynamics of positrons accelerating in electron-positron-ion plasma bubble fields driven by an ultraintense laser is investigated. The bubble wakefield is obtained theoretically when laser pulses are propagating in the electron-positron-ion plasma. To restrict the positrons transversely, an electron beam is injected. Acceleration regions and non-acceleration ones of positrons are obtained by the numerical simulation. It is found that the ponderomotive force causes the fluctuation of the positrons momenta, which results in the trapping of them at a lower ion density. The energy gaining of the accelerated positrons is demonstrated, which is helpful for practical applications.

  11. Measurement of the total spectrum of electrons and positrons in the energy range of 300–1500 GeV in the PAMELA experiment with the aid of a sampling calorimeter and a neutron detector

    SciTech Connect

    Karelin, A. V. Voronov, S. A.; Galper, A. M.; Koldobskiy, S. A.; Collaboration: on behalf of the PAMELA Collaboration

    2015-03-15

    A method based on the use of a sampling calorimeter was developed for measuring the total energy spectrum of electrons and positrons from high-energy cosmic rays in the PAMELA satellite-borne experiment. This made it possible to extend the range of energies accessible to measurements by the magnetic system of the PAMELA spectrometer. Themethod involves a procedure for selecting electrons on the basis of features of a secondary-particle shower in the calorimeter. The results obtained by measuring the total spectrum of cosmic-ray electrons and positrons in the energy range of 300–1500 GeV by the method in question are presented on the basis of data accumulated over a period spanning 2006 and 2013.

  12. Measurement of the total spectrum of electrons and positrons in the energy range of 300-1500 GeV in the PAMELA experiment with the aid of a sampling calorimeter and a neutron detector

    NASA Astrophysics Data System (ADS)

    Karelin, A. V.; Voronov, S. A.; Galper, A. M.; Koldobskiy, S. A.

    2015-03-01

    A method based on the use of a sampling calorimeter was developed for measuring the total energy spectrum of electrons and positrons from high-energy cosmic rays in the PAMELA satellite-borne experiment. This made it possible to extend the range of energies accessible to measurements by the magnetic system of the PAMELA spectrometer. Themethod involves a procedure for selecting electrons on the basis of features of a secondary-particle shower in the calorimeter. The results obtained by measuring the total spectrum of cosmic-ray electrons and positrons in the energy range of 300-1500 GeV by the method in question are presented on the basis of data accumulated over a period spanning 2006 and 2013.

  13. Polarization radiation of vortex electrons with large orbital angular momentum

    NASA Astrophysics Data System (ADS)

    Ivanov, Igor P.; Karlovets, Dmitry V.

    2013-10-01

    Vortex electrons—freely propagating electrons whose wave functions have helical wave fronts—could become a novel tool in the physics of electromagnetic radiation. They carry a nonzero intrinsic orbital angular momentum (OAM) ℓ with respect to the propagation axis and, for ℓ≫1, a large OAM-induced magnetic moment μ≈ℓμB (μB is the Bohr magneton), which influences the radiation of electromagnetic waves. Here, we consider in detail the OAM-induced effects caused by such electrons in two forms of polarization radiation, namely, in Cherenkov radiation and transition radiation. Thanks to the large ℓ, we can neglect quantum or spin-induced effects, which are of the order of ℏω/Ee≪1, but retain the magnetic moment contribution ℓℏω/Ee≲1, which makes the quasiclassical approach to polarization radiation applicable. We discuss the magnetic moment contribution to polarization radiation, which has never been experimentally observed, and study how its visibility depends on the kinematical parameters and the medium permittivity. In particular, it is shown that this contribution can, in principle, be detected in azimuthally nonsymmetrical problems, for example when vortex electrons obliquely cross a metallic screen (transition radiation) or move near it (diffraction radiation). We predict a left-right angular asymmetry of the transition radiation (in the plane where the charge radiation distributions would stay symmetric), which appears due to an effective interference between the charge radiation field and the magnetic moment contribution. Numerical values of this asymmetry for vortex electrons with Ee=300 keV and ℓ=100-1000 are 0.1%-1%, and we argue that this effect could be detected with existing technology. The finite conductivity of the target and frequency dispersion play crucial roles in these predictions.

  14. Prototyping of the ILC Baseline Positron Target

    SciTech Connect

    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.

  15. Analysis Of Electronic Medication Orders With Large Overdoses

    PubMed Central

    Kirkendall, E.S.; Kouril, M.; Minich, T.; Spooner, SA.

    2014-01-01

    Summary Background Users of electronic health record (EHR) systems frequently prescribe doses outside recommended dose ranges, and tend to ignore the alerts that result. Since some of these dosing errors are the result of system design flaws, analysis of large overdoses can lead to the discovery of needed system changes. Objectives To develop database techniques for detecting and extracting large overdose orders from our EHR. To identify and characterize users’ responses to these large overdoses. To identify possible causes of large-overdose errors and to mitigate them. Methods We constructed a data mart of medication-order and dosing-alert data from a quaternary pediatric hospital from June 2011 to May 2013. The data mart was used along with a test version of the EHR to explain how orders were processed and alerts were generated for large (>500%) and extreme (>10,000%) overdoses. User response was characterized by the dosing alert salience rate, which expresses the proportion of time users take corrective action. Results We constructed an advanced analytic framework based on workflow analysis and order simulation, and evaluated all 5,402,504 medication orders placed within the 2 year timeframe as well as 2,232,492 dose alerts associated with some of the orders. 8% of orders generated a visible alert, with ¼ of these related to overdosing. Alerts presented to trainees had higher salience rates than those presented to senior colleagues. Salience rates were low, varying between 4–10%, and were lower with larger overdoses. Extreme overdoses fell into eight causal categories, each with a system design mitigation. Conclusions Novel analytic systems are required to accurately understand prescriber behavior and interactions with medication-dosing CDS. We described a novel analytic system that can detect apparent large overdoses (≥500%) and explain the sociotechnical factors that drove the error. Some of these large overdoses can be mitigated by system changes. EHR

  16. The Buffer-Gas Positron Accumulator and Resonances in Positron-Molecule Interactions

    NASA Technical Reports Server (NTRS)

    Surko, C.M.

    2007-01-01

    This is a personal account of the development of our buffer-gas positron trap and the new generation of cold beams that these traps enabled. Dick Drachman provided much appreciated advice to us from the time we started the project. The physics underlying trap operation is related to resonances (or apparent resonances) in positron-molecule interactions. Amusingly, experiments enabled by the trap allowed us to understand these processes. The positron-resonance "box score" to date is one resounding "yes," namely vibrational Feshbach resonances in positron annihilation on hydrocarbons; a "probably" for positron-impact electronic excitation of CO and NZ;an d a "maybe" for vibrational excitation of selected molecules. Two of these processes enabled the efficient operation of the trap, and one almost killed it in infancy. We conclude with a brief overview of further applications of the trapping technology discussed here, such as "massive" positron storage and beams with meV energy resolution.

  17. Prognostic significance of metabolic tumor burden by positron emission tomography/computed tomography in patients with relapsed/refractory diffuse large B-cell lymphoma

    PubMed Central

    Tateishi, Ukihide; Tatsumi, Mitsuaki; Terauchi, Takashi; Ando, Kiyoshi; Niitsu, Nozomi; Kim, Won Seog; Suh, Cheolwon; Ogura, Michinori; Tobinai, Kensei

    2015-01-01

    The aim of the present study was to investigate the feasibility of measuring metabolic tumor burden using [F-18] fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) in patients with relapsed or refractory diffuse large B-cell lymphoma (DLBCL) treated with bendamustine–rituximab. Because the standardized uptake value is a critical parameter of tumor characterization, we carried out a phantom study of 18F-FDG PET/CT to ensure quality control for 28 machines in the 24 institutions (Japan, 17 institutions; Korea, 7 institutions) participating in our clinical study. Fifty-five patients with relapsed or refractory DLBCL were enrolled. The 18F-FDG PET/CT was acquired before treatment, after two cycles, and after the last treatment cycle. Treatment response was assessed after two cycles and after the last cycle using the Lugano classification. Using this classification, remission was complete in 15 patients (27%) and incomplete in 40 patients (73%) after two cycles of therapy, and remission was complete in 32 patients (58%) and incomplete in 23 patients (42%) after the last treatment cycle. The percentage change in all PET/CT parameters except for the area under the curve of the cumulative standardized uptake value–volume histogram was significantly greater in complete response patients than in non-complete response patients after two cycles and the last cycle. The Cox proportional hazard model and best subset selection method revealed that the percentage change of the sum of total lesion glycolysis after the last cycle (relative risk, 5.24; P = 0.003) was an independent predictor of progression-free survival. The percent change of sum of total lesion glycolysis, calculated from PET/CT, can be used to quantify the response to treatment and can predict progression-free survival after the last treatment cycle in patients with relapsed or refractory DLBCL treated with bendamustine–rituximab. PMID:25495273

  18. Improvements in Monte Carlo Simulation of Large Electron Fields

    SciTech Connect

    Faddegon, Bruce A.; Perl, Joseph; Asai, Makoto; /SLAC

    2007-11-28

    Two Monte Carlo systems, EGSnrc and Geant4, were used to calculate dose distributions in large electron fields used in radiotherapy. Source and geometry parameters were adjusted to match calculated results with measurement. Both codes were capable of accurately reproducing the measured dose distributions of the 6 electron beams available on the accelerator. Depth penetration was matched to 0.1 cm. Depth dose curves generally agreed to 2% in the build-up region, although there is an additional 2-3% experimental uncertainty in this region. Dose profiles matched to 2% at the depth of maximum dose in the central region of the beam, out to the point of the profile where the dose begins to fall rapidly. A 3%/3mm match was obtained outside the central region except for the 6 MeV beam, where dose differences reached 5%. The discrepancy observed in the bremsstrahlung tail in published results that used EGS4 is no longer evident. The different systems required different source energies, incident beam angles, thicknesses of the exit window and primary foils, and distance between the primary and secondary foil. These results underscore the requirement for an experimental benchmark of electron scatter for beam energies and foils relevant to radiotherapy.

  19. Nanomaterials processing toward large-scale flexible/stretchable electronics

    NASA Astrophysics Data System (ADS)

    Takahashi, Toshitake

    In recent years, there has been tremendous progress in large-scale mechanically flexible electronics, where electrical components are fabricated on non-crystalline substrates such as plastics and glass. These devices are currently serving as the basis for various applications such as flat-panel displays, smart cards, and wearable electronics. In this thesis, a promising approach using chemically synthesized nanomaterials is explored to overcome various obstacles current technology faces in this field. Here, we use chemically synthesized semiconducting nanowires (NWs) including group IV (Si, Ge), III-V (InAs) and II-IV (CdS, CdSe) NWs, and semiconductor-enriched SWNTs (99 % purity), and developed reliable, controllable, and more importantly uniform assembly methods on 4-inch wafer-scale flexible substrates in the form of either parallel NW arrays or SWNT random networks, which act as the active components in thin film transistors (TFTs). Thusly obtained TFTs composed of nanomaterials show respectable electrical and optical properties such as 1) cut-off frequency, ft ~ 1 GHz and maximum frequency of oscillation, fmax ~ 1.8 GHz from InAs parallel NW array TFTs with channel length of ~ 1.5 μm, 2) photodetectors covering visible wavelengths (500-700 nm) using compositionally graded CdSxSe1-x (0 < x < 1) parallel NW arrays, and 3) carrier mobility of ~ 20 cm2/Vs, which is an order of magnitude larger than conventional TFT materials such as a-Si and organic semiconductors, without sacrificing current on/off ratio (Ion/Ioff ~ 104) from SWNT network TFTs. The capability to uniformly assemble nanomaterials over large-scale flexible substrates enables us to use them for more sophisticated applications. Artificial electronic skin (e-skin) is demonstrated by laminating pressure sensitive rubber on top of nanomaterial-based active matrix backplanes. Furthermore, an x-ray imaging device is also achieved by combining organic photodiodes with this backplane technology.

  20. Design of the large hadron electron collider interaction region

    NASA Astrophysics Data System (ADS)

    Cruz-Alaniz, E.; Newton, D.; Tomás, R.; Korostelev, M.

    2015-11-01

    The large hadron electron collider (LHeC) is a proposed upgrade of the Large Hadron Collider (LHC) within the high luminosity LHC (HL-LHC) project, to provide electron-nucleon collisions and explore a new regime of energy and luminosity for deep inelastic scattering. The design of an interaction region for any collider is always a challenging task given that the beams are brought into crossing with the smallest beam sizes in a region where there are tight detector constraints. In this case integrating the LHeC into the existing HL-LHC lattice, to allow simultaneous proton-proton and electron-proton collisions, increases the difficulty of the task. A nominal design was presented in the the LHeC conceptual design report in 2012 featuring an optical configuration that focuses one of the proton beams of the LHC to β*=10 cm in the LHeC interaction point to reach the desired luminosity of L =1033 cm-2 s-1 . This value is achieved with the aid of a new inner triplet of quadrupoles at a distance L*=10 m from the interaction point. However the chromatic beta beating was found intolerable regarding machine protection issues. An advanced chromatic correction scheme was required. This paper explores the feasibility of the extension of a novel optical technique called the achromatic telescopic squeezing scheme and the flexibility of the interaction region design, in order to find the optimal solution that would produce the highest luminosity while controlling the chromaticity, minimizing the synchrotron radiation power and maintaining the dynamic aperture required for stability.

  1. Positron beam studies of transients in semiconductors

    NASA Astrophysics Data System (ADS)

    Beling, C. D.; Ling, C. C.; Cheung, C. K.; Naik, P. S.; Zhang, J. D.; Fung, S.

    2006-02-01

    Vacancy-sensing positron deep level transient spectroscopy (PDLTS) is a positron beam-based technique that seeks to provide information on the electronic ionization levels of vacancy defects probed by the positron through the monitoring of thermal transients. The experimental discoveries leading to the concept of vacancy-sensing PDLTS are first reviewed. The major problem associated with this technique is discussed, namely the strong electric fields establish in the near surface region of the sample during the thermal transient which tend to sweep positrons into the contact with negligible defect trapping. New simulations are presented which suggest that under certain conditions a sufficient fraction of positrons may be trapped into ionizing defects rendering PDLTS technique workable. Some suggestions are made for techniques that might avoid the problematic electric field problem, such as optical-PDLTS where deep levels are populated using light and the use of high forward bias currents for trap filling.

  2. Design Issues for the ILC Positron Source

    SciTech Connect

    Bharadwaj, V.; Batygin, Yu.K.; Pitthan, R.; Schultz, D.C.; Sheppard, J.; Vincke, H.; Wang, J.W.; Gronberg, J.; Stein, W.; /LLNL, Livermore

    2006-02-15

    A positron source for the International Linear Collider (ILC) can be designed using either a multi-GeV electron beam or a multi-MeV photon beam impinging on a metal target. The major design issues are: choice of drive beam and its generation, choice of target material, the target station, positron capture section, target vault and beam transport to the ILC positron damping ring complex. This paper lists the ILC positron source requirements and their implications for the design of the positron source. A conceptual design for the ILC is expected to be finished in the next two years. With emphasis on this timescale, source design issues and possible solutions are discussed.

  3. Search for new physics in high mass electron-positron events in p anti-p collisions at s**(1/2) = 1.96-TeV

    SciTech Connect

    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

  4. The 3K Blackbody Radiation, 'Stored' & 'Frozen' Light, 'Viscous Optical Molasses' as Effects of the Electron Positron Lattice (EPOLA) Structure of Our "Vacuum" Space

    NASA Astrophysics Data System (ADS)

    Simhony, Menahem

    2002-05-01

    In the EPOLA model of space [1] the mysterious 3K blackbody radiation of the sky is due to random thermal vibrations of the electrons and positrons, bound in the epola. They also cause the zero-point motion of helium atoms, a Brownian Motion analog. The temperature T of our epola region is therefore 3K. In space regions with more hot stars, more nuclear activity, T is higher and they may create the mystery of gray matter. Epola regions below 3K are observed as mysterious dark matter. The gray and dark matter regions are considered to constitute 90 percent of the mass of the universe. The 1997 Nobel Prize winners' "Optical Molasses" at micro-K T's are also explained by the epola model, as well as the 'stored', 'frozen' light effects, observed in 1999-2001. References: 1. M.Simhony, Invitation to the Natural Physics of Matter, Space, and Radiation, World Scientific, 1994 (292 pp), ISBN 981-02-1649-1. See the website: www.word1.co.il/physics .

  5. General relativistic ray-tracing algorithm for the determination of the electron-positron energy deposition rate from neutrino pair annihilation around rotating neutron and quark stars

    NASA Astrophysics Data System (ADS)

    Kovács, Z.; Harko, T.

    2011-11-01

    We present a full general relativistic numerical code for estimating the energy-momentum deposition rate (EMDR) from neutrino pair annihilation (?). The source of the neutrinos is assumed to be a neutrino-cooled accretion disc around neutron and quark stars. We calculate the neutrino trajectories by using a ray-tracing algorithm with the general relativistic Hamilton's equations for neutrinos and derive the spatial distribution of the EMDR due to the annihilations of neutrinos and antineutrinos around rotating neutron and quark stars. We obtain the EMDR for several classes of rotating neutron stars, described by different equations of state of the neutron matter, and for quark stars, described by the Massachusetts Institute of Technology (MIT) bag model equation of state and in the colour-flavour-locked (CFL) phase. The distribution of the total annihilation rate of the neutrino-antineutrino pairs around rotating neutron and quark stars is studied for isothermal discs and accretion discs in thermodynamical equilibrium. We demonstrate both the differences in the equations of state for neutron and quark matter and rotation with the general relativistic effects significantly modify the EMDR of the electrons and positrons generated by the neutrino-antineutrino pair annihilation around compact stellar objects, as measured at infinity.

  6. The Influence of Energetic Electrons on the Cassini Langmuir Probe at Saturn : Deriving Large Electron Temperatures and Small Electron Densities

    NASA Astrophysics Data System (ADS)

    Garnier, P.; Wahlund, J.; Holmberg, M.; Lewis, G.; Schippers, P.; Thomsen, M. F.; Rochel Grimald, S.; Gurnett, D. A.; Coates, A. J.; Dandouras, I. S.; Waite, J. H.

    2013-12-01

    The Langmuir probes (LPs) are commonly used to investigate the cold plasma characteristics in planetary ionospheres/magnetospheres. The LPs performances are limited to low temperatures (i.e. below 5-10 eV at Saturn) and large densities (above several particles/cm3). A strong sensitivity of the Cassini LP measurements to energetic electrons (hundreds eV) may however be observed at Saturn in the L Shell range L=6-10 RS. These electrons impact the surface of the probe and generate a detectable current of secondary electrons. We investigated the influence of such electrons on the current-voltage (I-V) characteristics (for negative potentials), showing that both the DC level and slope of the I-V curve are modified. The influence of energetic electrons may be interpreted in terms of the critical and anticritical temperatures concept that is important for spacecraft charging studies. Estimations of the maximum secondary yield value for the LP surface are obtained without using laboratory measurements. Empirical and theoretical methods were developed to reproduce the influence of the energetic electrons with a reasonable precision. Conversely, this modelling allows us to derive useful information about the energetic electrons from the LP observations : some information about their pitch angle anisotropy (if combined with the data from a single CAPS ELS anode), as well as an estimate of the electron temperature (in the range 100-300 eV) and of the electron density (above 0.1 particles/cm3). This enlarges the LP measurements capabilities when the influence of the energetic electrons is large (essentially near L=6-10 RS at Saturn). The understanding of this influence may be used for other missions using Langmuir probes, such as the future missions JUICE at Jupiter, BepiColombo at Mercury, or even the probes in the Earth magnetosphere.

  7. Electron cyclotron beam measurement system in the Large Helical Device

    SciTech Connect

    Kamio, S. Takahashi, H.; Kubo, S.; Shimozuma, T.; Yoshimura, Y.; Igami, H.; Ito, S.; Kobayashi, S.; Mizuno, Y.; Okada, K.; Osakabe, M.; Mutoh, T.

    2014-11-15

    In order to evaluate the electron cyclotron (EC) heating power inside the Large Helical Device vacuum vessel and to investigate the physics of the interaction between the EC beam and the plasma, a direct measurement system for the EC beam transmitted through the plasma column was developed. The system consists of an EC beam target plate, which is made of isotropic graphite and faces against the EC beam through the plasma, and an IR camera for measuring the target plate temperature increase by the transmitted EC beam. This system is applicable to the high magnetic field (up to 2.75 T) and plasma density (up to 0.8 × 10{sup 19} m{sup −3}). This system successfully evaluated the transmitted EC beam profile and the refraction.

  8. Compact dewar and electronics for large-format infrared detectors

    NASA Astrophysics Data System (ADS)

    Manissadjian, A.; Magli, S.; Mallet, E.; Cassaigne, P.

    2011-06-01

    Infrared systems cameras trend is to require higher performance (thanks to higher resolution) and in parallel higher compactness for easier integration in systems. The latest developments at SOFRADIR / France on HgCdTe (Mercury Cadmium Telluride / MCT) cooled IR staring detectors do show constant improvements regarding detector performances and compactness, by reducing the pixel pitch and optimizing their encapsulation. Among the latest introduced detectors, the 15μm pixel pitch JUPITER HD-TV format (1280×1024) has to deal with challenging specifications regarding dewar compactness, low power consumption and reliability. Initially introduced four years ago in a large dewar with a more than 2kg split Stirling cooler compressor, it is now available in a new versatile compact dewar that is vacuum-maintenance-free over typical 18 years mission profiles, and that can be integrated with the different available Stirling coolers: K548 microcooler for light solution (less than 0.7 kg), K549 or LSF9548 for split cooler and/or higher reliability solution. The IDDCAs are also required with simplified electrical interface enabling to shorten the system development time and to standardize the electronic boards definition with smaller volumes. Sofradir is therefore introducing MEGALINK, the new compact Command & Control Electronics compatible with most of the Sofradir IDDCAs. MEGALINK provides all necessary input biases and clocks to the FPAs, and digitizes and multiplexes the video outputs to provide a 14 bit output signal through a cameralink interface, in a surface smaller than a business card.

  9. DIFFUSE EMISSION MEASUREMENT WITH THE SPECTROMETER ON INTEGRAL AS AN INDIRECT PROBE OF COSMIC-RAY ELECTRONS AND POSITRONS

    SciTech Connect

    Bouchet, Laurent; Jourdain, Elisabeth; Roques, Jean-Pierre; Strong, Andrew W.; Porter, Troy A.; Moskalenko, Igor V.

    2011-09-20

    Significant advances have been made in the understanding of the diffuse Galactic hard X-ray continuum emission using data from the INTEGRAL observatory. The diffuse hard power-law component seen with the SPectrometer on INTEGRAL (SPI) has been identified with inverse-Compton emission from relativistic (GeV) electrons on the cosmic microwave background and Galactic interstellar radiation field. In the present analysis, SPI data from 2003 to 2009, with a total exposure time of {approx}10{sup 8} s, are used to derive the Galactic ridge hard X-ray spatial distribution and spectrum between 20 keV and 2.4 MeV. Both are consistent with predictions from the GALPROP code. The good agreement between measured and predicted emission from keV to GeV energies suggests that the correct production mechanisms have been identified. We discuss the potential of the SPI data to provide an indirect probe of the interstellar cosmic-ray electron distribution, in particular for energies below a few GeV.

  10. Detecting positron-atom bound states through resonant annihilation.

    PubMed

    Dzuba, V A; Flambaum, V V; Gribakin, G F

    2010-11-12

    A method is proposed for detecting positron-atom bound states by observing enhanced positron annihilation due to electronic Feshbach resonances at electron-volt energies. The method is applicable to a range of open-shell transition-metal atoms which are likely to bind the positron: Fe, Co, Ni, Tc, Ru, Rh, Sn, Sb, Ta, W, Os, Ir, and Pt. Estimates of their binding energies are provided.

  11. Precise measurement of the left-right cross section asymmetry in Z boson production by electron-positron collisions

    SciTech Connect

    Frey, R.E.; SLD Collaboration

    1994-03-01

    A precise measurement of the left-right cross section asymmetry (A{sub LR}) for Z boson production by e{sup +}e{sup {minus}} collisions has been attained at the Slac Linear Collider with the SLD detector. We describe this measurement for the 1993 data run, emphasizing the significant improvements in polarized beam operation which took place for this run, where the luminosity-weighted electron beam polarization averaged 62.6 {plus_minus} 1.2 %. Preliminary 1993 results for A{sub LR} are presented. When combined with the (less precise) 1992 result, the preliminary result for the effective weak mixing angle is sin{sup 2} {theta}{sub W {sup eff}} = 0.2290 {plus_minus} 0.0010.

  12. Mw Dependence of Ionospheric Electron Enhancement Immediately Before Large Earthquakes

    NASA Astrophysics Data System (ADS)

    Heki, K.; He, L.

    2015-12-01

    Ionospheric electrons were reported to have increased ~40 minutes before the 2011 Tohoku-oki (Mw9.0) earthquake, Japan, by observing total electron content (TEC) with GNSS receivers [e.g. Heki and Enomoto, 2013]. They further demonstrated that similar TEC enhancements preceded all the recent earthquakes with Mw of 8.5 or more. Their reality has been repeatedly questioned due mainly to the ambiguity in the derivation of the reference TEC curves from which anomalies are defined [e.g. Masci et al., 2015]. Here we propose a numerical approach, based on Akaike's Information Criterion, to detect positive breaks (sudden increase of TEC rate) in the vertical TEC time series without using reference curves. We demonstrate that such breaks are detected 20-80 minutes before the ten recent large earthquakes with Mw7.8-9.2. The amounts of breaks were found to depend on the background absolute VTEC and Mw, i.e. Break (TECU/h)=4.74Mw+0.13VTEC-39.86, with the standard deviation of ~1.2 TECU/h. We can convert this equation to Mw = (Break-0.13VTEC+39.86)/4.74, which can tell us the Mw of impending earthquakes with uncertainty of ~0.25. The precursor times were longer for larger earthquakes, ranging from ~80 minutes for the largest (2004 Sumatra-Andaman) to ~21 minutes for the smallest (2015 Nepal). The precursors of intraplate earthquakes (e.g. 2012 Indian Ocean) started significantly earlier than interplate ones. We performed the same analyses during periods without earthquakes, and found that positive breaks comparable to that before the 2011 Tohoku-oki earthquake occur once in 20 hours. They originate from small amplitude Large-scale Travelling Ionospheric Disturbances (LSTID), which are excited in the auroral oval and move southward with the velocity of internal gravity waves. This probability is small enough to rule out the fortuity of these breaks, but large enough to make it a challenge to apply preseismic TEC enhancements for short-term earthquake prediction.

  13. Predictive Significance of a New Prognostic Score for Patients With Diffuse Large B-Cell Lymphoma in the Interim-Positron Emission Tomography Findings.

    PubMed

    Kong, Yu; Qu, Lili; Li, Yuekai; Liu, Dai; Lv, Xuemin; Han, Jiankui

    2016-02-01

    We hypothesized that the objective treatment response of patients with diffuse large B-cell lymphoma (DLBCL) was affected by many factors such as pathophysiological, biological, and pharmaceutical mechanisms. This retrospective study aimed to evaluate the predictive significance of clinical prognostic factors and interim fluorine-18-fluorodeoxyglucose (F-FDG) positron emission tomography/computed tomography (PET/CT), and to find a new prognostic predictor significantly associated with DLBCL patients' outcome. A total of 105 adult patients with DLBCL were reviewed. Each patient underwent an interim F-FDG PET/CT scan after the second chemotherapy cycle. The visual method based on the Deauville 5-point scale was used to evaluate the interim-PET/CT scans. The relationships among the prognostic factors, the 3-year progression-free survival (PFS) rate and overall survival (OS) rate were analyzed with Kaplan-Meier plots. The predictive value of the newly constructed prognostic score was analyzed with multivariate analysis (Cox proportional hazard regression model). The visual analysis showed statistically significant differences in both PFS and OS between the patients with a negative interim-PET/CT and those with a positive interim-PET/CT. Advanced age, advanced stage, and DLBCL subtype were also significantly associated with outcome. A new prognostic score that composed of the above 4 factors was obtained. New prognostic score stratified patients into 4 risk groups with 3-year PFS of 98.5%, 73.9%, 11.1%, and 0%, and 3-year OS of 100%, 91.3%, 55.6%, and 0% (P < 0.001 for PFS and OS). Multivariate analysis showed that the new prognostic score had the greatest ability to predict relapse (P < 0.001) and death (P < 0.001). In DLBCL patients, interim F-FDG PET/CT can provide significant independent prognostic information. Our work illustrates that the new prognostic score has the strongest potential for accurately prognostication, for stratification in clinical

  14. Positron-attachment to small molecules: Vibrational enhancement of positron affinities with configuration interaction level of multi-component molecular orbital approach

    SciTech Connect

    Tachikawa, Masanori

    2015-12-31

    To theoretically demonstrate the binding of a positron to small polarized molecules, we have calculated the vibrational averaged positron affinity (PA) values along the local vibrational contribution with the configuration interaction level of multi-component molecular orbital method. This method can take the electron-positron correlation contribution into account through single electronic - single positronic excitation configurations. The PA values are enhanced by including the local vibrational contribution from vertical PA values due to the anharmonicity of the potential.

  15. Search for the electron-positron decay of axions and axionlike particles at a nuclear power reactor at Bugey

    NASA Astrophysics Data System (ADS)

    Altmann, M.; Declais, Y.; Feilitzsch, F. V.; Hagner, C.; Kajfasz, E.; Oberauer, L.

    1995-06-01

    A search for the decay of isoscalar penetrating particles into an e + e-pair has been performed at the nuclear power reactor Bugey 5, situated close to Lyon (France). The detector set-up, consisting of an arrangement of large-area multiwire proportional chambers, and the data analysis are described. No excess of decay events over background has been observed. For standard axions, therefrom, stringent upper limits for the branching ratio < Γ a / Γ {/M γ}, averaged over the entire reactor gamma spectrum of magnetic multipolarity, have been obtained. Analysis in terms of the decay χ→ e ++ e - of a more general axionlike boson χ yields new constraints for the decay constant f χ which enhance existing laboratory limits considerably.

  16. Electron turbulence and transport in large magnetic islands

    NASA Astrophysics Data System (ADS)

    Morton, Lucas

    2016-10-01

    Magnetic islands, observed in both reversed-field pinches (RFPs) and tokamaks, often display unexpected turbulence and transport characteristics. For the first time in an RFP, the high repetition rate Thomson scattering diagnostic on MST has captured a 2D image of the rotating electron temperature structure of a magnetic island in a single discharge. MHD modeling using edge magnetic signals implies a 16 cm wide m,n =1,6 tearing mode island which completely overlaps a 5.5 cm n =7 island (12 cm between island centers). The 3D field is partially chaotic, but still reflective of the n =6 island structure. The measured temperature structure matches the shape and location of the n =6 partially chaotic (or `remnant') island. Contrary to the usual assumption that islands have flat internal temperature, the electron temperature is peaked inside the remnant magnetic island due to ohmic heating. The temperature peaking implies a local effective perpendicular conductivity 10-40 m2/s inside the remnant island. This agrees quantitatively with an effective perpendicular conductivity of 16 m2/s estimated using the magnetic diffusion coefficient (evaluated at the electron mean free path) calculated from the modeled chaotic field. Statistical analysis of measurement ensembles with lower time resolution implies that remnant island heating is common in MST discharges. To investigate the role of turbulence near a magnetic island, the 2D structure of long-wavelength density turbulence has been mapped around a large applied static m,n =2,1 L-mode island in the DIII-D tokamak. The turbulence exhibits intriguing spatial structure. Fluctuations are enhanced several-fold (compared to the no-island case) on the inboard side of the X-point, but not on the outboard side of the X-point and are also reduced near the O-point. This work is supported by the NSF and US DOE under DE-FC02-04ER54698, and DE-FG02-89ER53296.

  17. Comparison of three-jet and radiative two-jet events in electron-positron annihilation at 29 GeV

    SciTech Connect

    Sheldon, P.D.

    1986-11-01

    By comparing 3-jet (e/sup +/e/sup -/ ..-->.. q anti q g) and radiative 2-jet (e/sup +/e/sup -/ ..-->.. q anti q ..gamma..) events from electron-positron annihilation, we have studied the local and global effects of the presence of a hard bremsstrahlung gluon in hadronic events. Detector and event selection efficiencies and biases affect these two kinds of events almost equally because they have very similar kinematics and topologies. Accurate comparisons of q anti q g and q anti q ..gamma.. events can therefore be made. Globally, we observe a depletion of hadrons in q anti q g events relative to q anti q ..gamma.. events on the opposite side of the event plane from the gluon, in the angular region between the q and anti q jets. This depletion is shown to be in agreement with the predictions of Quantum Chromodynamics (QCD). The existence of this effect demonstrates that the presence of a gluon significantly alters the color forces and hence the fragmentation process in hadronic events. We also use these q anti q ..gamma.. and q anti q g events to compare low energy (4.5 GeV) gluon and quark jets. Our data indicate that gluon jets have softer x/sub p/ distributions than quark jets, while the transverse momentum distributions of these two types of jets are identical within our errors. Although we are unable to determine if the multiplicities of gluon (n/sub /) and quark (n/sub q/) jets are different, the ratio n/sub g//n/sub q/ = 9/4 predicted asymptotically in QCD would not be consistent with our data.

  18. Large Scale Electronic Structure Calculations using Quantum Chemistry Methods

    NASA Astrophysics Data System (ADS)

    Scuseria, Gustavo E.

    1998-03-01

    This talk will address our recent efforts in developing fast, linear scaling electronic structure methods for large scale applications. Of special importance is our fast multipole method( M. C. Strain, G. E. Scuseria, and M. J. Frisch, Science 271), 51 (1996). (FMM) for achieving linear scaling for the quantum Coulomb problem (GvFMM), the traditional bottleneck in quantum chemistry calculations based on Gaussian orbitals. Fast quadratures(R. E. Stratmann, G. E. Scuseria, and M. J. Frisch, Chem. Phys. Lett. 257), 213 (1996). combined with methods that avoid the Hamiltonian diagonalization( J. M. Millam and G. E. Scuseria, J. Chem. Phys. 106), 5569 (1997) have resulted in density functional theory (DFT) programs that can be applied to systems containing many hundreds of atoms and ---depending on computational resources or level of theory-- to many thousands of atoms.( A. D. Daniels, J. M. Millam and G. E. Scuseria, J. Chem. Phys. 107), 425 (1997). Three solutions for the diagonalization bottleneck will be analyzed and compared: a conjugate gradient density matrix search (CGDMS), a Hamiltonian polynomial expansion of the density matrix, and a pseudo-diagonalization method. Besides DFT, our near-field exchange method( J. C. Burant, G. E. Scuseria, and M. J. Frisch, J. Chem. Phys. 105), 8969 (1996). for linear scaling Hartree-Fock calculations will be discussed. Based on these improved capabilities, we have also developed programs to obtain vibrational frequencies (via analytic energy second derivatives) and excitation energies (through time-dependent DFT) of large molecules like porphyn or C_70. Our GvFMM has been extended to periodic systems( K. N. Kudin and G. E. Scuseria, Chem. Phys. Lett., in press.) and progress towards a Gaussian-based DFT and HF program for polymers and solids will be reported. Last, we will discuss our progress on a Laplace-transformed \\cal O(N^2) second-order pertubation theory (MP2) method.

  19. Auxiliary basis expansions for large-scale electronic structure calculations.

    PubMed

    Jung, Yousung; Sodt, Alex; Gill, Peter M W; Head-Gordon, Martin

    2005-05-10

    One way to reduce the computational cost of electronic structure calculations is to use auxiliary basis expansions to approximate four-center integrals in terms of two- and three-center integrals, usually by using the variationally optimum Coulomb metric to determine the expansion coefficients. However, the long-range decay behavior of the auxiliary basis expansion coefficients has not been characterized. We find that this decay can be surprisingly slow. Numerical experiments on linear alkanes and a toy model both show that the decay can be as slow as 1/r in the distance between the auxiliary function and the fitted charge distribution. The Coulomb metric fitting equations also involve divergent matrix elements for extended systems treated with periodic boundary conditions. An attenuated Coulomb metric that is short-range can eliminate these oddities without substantially degrading calculated relative energies. The sparsity of the fit coefficients is assessed on simple hydrocarbon molecules and shows quite early onset of linear growth in the number of significant coefficients with system size using the attenuated Coulomb metric. Hence it is possible to design linear scaling auxiliary basis methods without additional approximations to treat large systems.

  20. Positron states and annihilation characteristics of surface-trapped positrons at the oxidized Cu(110) surface

    NASA Astrophysics Data System (ADS)

    Fazleev, N. G.; Olenga, Antoine; Weiss, A. H.

    2013-03-01

    The process by which oxide layers are formed on metal surfaces is still not well understood. In this work we present the results of theoretical studies of positron states and annihilation characteristics of surface-trapped positrons at the oxidized Cu(110) surface. An ab-initio investigation of stability and associated electronic properties of different adsorption phases of oxygen on Cu(110) has been performed on the basis of density functional theory and using DMOl3 code. The changes in the positron work function and the surface dipole moment when oxygen atoms occupy on-surface and sub-surface sites have been attributed to charge redistribution within the first two layers, buckling effects within each layer and interlayer expansion. The computed positron binding energy, positron surface state wave function, and annihilation probabilities of surface trapped positrons with relevant core electrons demonstrate their sensitivity to oxygen coverage, elemental content, atomic structure of the topmost layers of surfaces, and charge transfer effects. Theoretical results are compared with experimental data obtained from studies of oxidized transition metal surfaces using positron annihilation induced Auger electron spectroscopy. This work was supported in part by the National Science Foundation Grant DMR-0907679.

  1. Positron-rubidium scattering

    NASA Technical Reports Server (NTRS)

    Mceachran, R. P.; Horbatsch, M.; Stauffer, A. D.

    1990-01-01

    A 5-state close-coupling calculation (5s-5p-4d-6s-6p) was carried out for positron-Rb scattering in the energy range 3.7 to 28.0 eV. In contrast to the results of similar close-coupling calculations for positron-Na and positron-K scattering the (effective) total integrated cross section has an energy dependence which is contrary to recent experimental measurements.

  2. Effects of process parameters on the defects in graphene oxide-polyaniline composites investigated by positron annihilation spectroscopy.

    PubMed

    Rana, Utpal; Nambissan, P M G; Malik, Sudip; Chakrabarti, Kuntal

    2014-02-21

    Graphene oxide (GO)-polyaniline (PANI) composites were prepared with different relative abundance of PANI and GO by in situ polymerization of aniline in the presence of GO and ammonium persulphate at different temperatures. In the process, GO also got reduced to graphene. Positron lifetimes and coincidence Doppler broadening of the electron-positron annihilation gamma ray spectra originating from the composite samples were measured and the results are reported. The positron lifetimes indicated the presence of very large size defects in the form of vacancy clusters within the samples. Another interesting observation was the increase of relative intensity of the defect specific positron lifetime component when an increase in relative abundance of PANI led to increased reduction of GO to graphene. The reduction also shrank the volume occupied by GO and the free volume thereby released added to the overall defect concentration, resulting in a simultaneous increase of the intensity of the positron lifetime component. The variation of the positron lifetime and its intensity with the synthesis temperature suggested an optimum temperature suitable for the process. The above observations are corroborated by other experimental investigations like electron microscopy, X-ray diffraction and electrical conductivity.

  3. Positron annihilation studies of organic superconductivity

    SciTech Connect

    Yen, H.L.; Lou, Y.; Ali, E.H.

    1994-09-01

    The positron lifetimes of two organic superconductors, {kappa}-(ET){sub 2}Cu(NCS){sub 2} and {kappa}-(ET){sub 2}Cu[N(CN){sub 2}]Br, are measured as a function of temperature across {Tc}. A drop of positron lifetime below {Tc} is observed. Positron-electron momentum densities are measured by using 2D-ACAR to search for the Fermi surface in {kappa}-(ET){sub 2}Cu[N(CN){sub 2}]Br. Positron density distributions and positron-electron overlaps are calculated by using the orthogonalized linear combination atomic orbital (OLCAO) method to interprete the temperature dependence due to the local charge transfer which is inferred to relate to the superconducting transition. 2D-ACAR results in {kappa}-(ET){sub 2}Cu[N(CN){sub 2}]Br are compared with theoretical band calculations based on a first-principles local density approximation. Importance of performing accurate band calculations for the interpretation of positron annihilation data is emphasized.

  4. Spontaneous and induced radiation by electrons/positrons in natural and photonic crystals. Volume free electron lasers (VFELs): From microwave and optical to X-ray range

    NASA Astrophysics Data System (ADS)

    Baryshevsky, V. G.

    2015-07-01

    Spontaneous and induced radiation produced by relativistic particles passing through natural and photonic crystals has enhanced capabilities for achieving the radiation sources operating in different wavelength ranges. Use of a non-one-dimensional distributed feedback, arising through Bragg diffraction in spatially periodic systems (natural and artificial (electromagnetic, photonic) crystals), establishes the foundation for the development of volume free electron lasers/masers (VFELs/VFEMs) as well as high-energy charged particle accelerators. The analysis of basic principles of VFEL theory demonstrates the promising potential of VFELs as the basis for the development of high-power microwave and optical sources.

  5. A General Quantum Mechanical Method to Predict Positron Spectroscopy

    DTIC Science & Technology

    2007-06-01

    70 6.2.3 Positronic Systems for Modeling and Experiment 71 Appendix A. Electron-Positron Annihilation Observables from NEO-HF and NEO-MP2...spectroscopy (PAS) experiments are widely used to study materials defects, including point defects in semiconductors and voids in composite materials...addition to traditional PAS techniques, experiments involving VFRs are also discussed. In Section 2.2, methods for modeling positron interaction with

  6. Modulation of a quantum positron acoustic wave

    NASA Astrophysics Data System (ADS)

    Amin, M. R.

    2015-09-01

    Amplitude modulation of a positron acoustic wave is considered in a four-component electron-positron plasma in the quantum magnetohydrodynamic regime. The important ingredients of this study are the inclusion of the particle exchange-correlation potential, quantum diffraction effects via the Bohm potential, and dissipative effect due to viscosity in the momentum balance equation of the charged carriers. A modified nonlinear Schrödinger equation is derived for the evolution of the slowly varying amplitude of the quantum positron acoustic wave by employing the standard reductive perturbation technique. Detailed analysis of the linear and nonlinear dispersions of the quantum positron acoustic wave is presented. For a typical parameter range, relevant to some dense astrophysical objects, it is found that the quantum positron acoustic wave is modulationally unstable above a certain critical wavenumber. Effects of the exchange-correlation potential and the Bohm potential in the wave dynamics are also studied. It is found that the quantum effect due to the particle exchange-correlation potential is significant in comparison to the effect due to the Bohm potential for smaller values of the carrier wavenumber. However, for comparatively larger values of the carrier wavenumber, the Bohm potential effect overtakes the effect of the exchange-correlation potential. It is found that the critical wavenumber for the modulation instability depends on the ratio of the equilibrium hot electron number density and the cold positron number density and on the ratio of the equilibrium hot positron number density and the cold positron number density. A numerical result on the growth rate of the modulation instability is also presented.

  7. Large-time evolution of an electron in photon bath

    SciTech Connect

    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

  8. Trapped positrons observed by PAMELA experiment

    NASA Astrophysics Data System (ADS)

    Mikhailov, V. V.; Adriani, O.; Barbarino, G.; Bazilevskaya, G. A.; Bellotti, R.; Boezio, M.; Bogomolov, E. A.; Bongi, M.; Bonvicini, V.; Bottai, S.; Bruno, A.; Cafagna, F. S.; Campana, D.; Carbone, R.; Carlson, P.; Casolino, M.; Castellini, G.; Consiglio, L.; De Santis, C.; De Simone, N.; Di Felice, V.; Galper, A. M.; Karelin, A. V.; Koldashov, S. V.; Koldobsky, S.; Krutkov, S. Yu; Kvashnin, A. N.; Leonov, A. A.; Malakhov, V. V.; Marcelli, L.; Martucci, M.; Mayorov, A. G.; Menn, W.; Merge, M.; Mocchiutti, E.; Monaco, A.; Mori, N.; Munini, R.; Osteria, G.; Papini, P.; Palma, F.; Panico, B.; Pearce, M.; Picozza, P.; Ricci, M.; Ricciarini, S. B.; Sarkar, R.; Scotti, V.; Simon, M.; Sparvoli, R.; Spillantini, P.; Stozhkov, Yu I.; Vacchi, A.; Vannuccini, E.; Vasiliev, G. I.; Voronov, S. A.; Yurkin, Yu T.; Zampa, G.; Zampa, N.

    2016-02-01

    Measurements of electron and positron spatial distributions in energy range from 80 MeV to several GeV below the geomagnetic cutoff rigidity were carried out using the PAMELA magnetic spectrometer. The instrument is installed on board the Resurs-DK satellite which was launched June 15th 2006 on an elliptical orbit with the inclination 70 degrees and the altitude 350-600 km. The procedure of trajectories calculations in the geomagnetic filed gives a way to separate stably trapped and short lived albedo components produced in interactions of cosmic ray protons with the residual atmosphere. The work presents spatial distributions of trapped, quasitrapped and short-lived albedo electrons and positrons in the near Earth space. Electron to positron ratio points out on different production mechanism of trapped and quasitrapped particles.

  9. What is the fate of runaway positrons in tokamaks?

    DOE PAGES

    Liu, Jian; Qin, Hong; Fisch, Nathaniel J.; ...

    2014-06-19

    In this study, massive runaway positrons are generated by runaway electrons in tokamaks. The fate of these positrons encodes valuable information about the runaway dynamics. The phase space dynamics of a runaway position is investigated using a Lagrangian that incorporates the tokamak geometry, loop voltage, radiation and collisional effects. It is found numerically that runaway positrons will drift out of the plasma to annihilate on the first wall, with an in-plasma annihilation possibility less than 0.1%. The dynamics of runaway positrons provides signatures that can be observed as diagnostic tools.

  10. Search for a positron anisotropy with PAMELA experiment

    NASA Astrophysics Data System (ADS)

    Panico, B.; 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.; Carlson, P.; Casolino, M.; Castellini, G.; De Donato, C.; De Santis, C.; De Simone, N.; Di Felice, V.; Formato, V.; Galper, A. M.; Giaccari, U.; Karelin, A. V.; Koldashov, S. V.; Koldobskiy, S.; Krutkov, S. Y.; Kvashnin, A. N.; Leonov, A.; Malakhov, V.; Marcelli, L.; Martucci, M.; Mayorov, A. G.; Menn, W.; Mergé, M.; Mikhailov, V. V.; Mocchiutti, E.; Monaco, A.; Mori, N.; Munini, R.; Osteria, G.; Palma, F.; Pearce, M.; Picozza, P.; Ricci, M.; Ricciarini, S. B.; Sarkar, R.; Scotti, V.; Simon, M.; Sparvoli, R.; Spillantini, P.; Stozhkov, Y. I.; Vacchi, A.; Vannuccini, E.; Vasilyev, G. I.; Voronov, S. A.; Yurkin, Y. T.; Zampa, G.; Zampa, N.

    2015-09-01

    The PAMELA experiment has been collecting data since 2006; its results indicate a rise in the positron fraction with respect to the sum of electrons and positrons in the cosmic-ray (CR) spectrum above 10 GeV. This excess can be due to additional sources, as SNRs or pulsars, which can lead to an anisotropy in the local CR positron, detectable from current experiments. We report on the analysis on spatial distributions of positron events collected by PAMELA, taking into account also the geomagnetic field effects. No significant deviation from the isotropy has been observed.

  11. Surfaces of colloidal PbSe nanocrystals probed by thin-film positron annihilation spectroscopy

    SciTech Connect

    Chai, L.; Schut, H.; Schaarenburg, L. C. van; Eijt, S. W. H.; Al-Sawai, W.; Barbiellini, B.; Bansil, A.; Gao, Y.; Houtepen, A. J.; Mijnarends, P. E.; Huis, M. A. van; Ravelli, L.; Egger, W.; Kaprzyk, S.

    2013-08-01

    Positron annihilation lifetime spectroscopy and positron-electron momentum density (PEMD) studies on multilayers of PbSe nanocrystals (NCs), supported by transmission electron microscopy, show that positrons are strongly trapped at NC surfaces, where they provide insight into the surface composition and electronic structure of PbSe NCs. Our analysis indicates abundant annihilation of positrons with Se electrons at the NC surfaces and with O electrons of the oleic ligands bound to Pb ad-atoms at the NC surfaces, which demonstrates that positrons can be used as a sensitive probe to investigate the surface physics and chemistry of nanocrystals inside multilayers. Ab initio electronic structure calculations provide detailed insight in the valence and semi-core electron contributions to the positron-electron momentum density of PbSe. Both lifetime and PEMD are found to correlate with changes in the particle morphology characteristic of partial ligand removal.

  12. High-field capture section for SLC positron source

    SciTech Connect

    Hoag, H.A.; Deruyter, H.; Kramer, J.; Yao, C.G.

    1986-05-01

    The positron source for SLC is being installed at the two-thirds point on the SLAC linac. Electron bunches at 33 GeV impinge upon a Tantalum/Tungsten target, producing showers of positrons with energies extending from approximately 2 to 20 MeV, with most positrons at the low end of this range. Positrons with low energies and finite transverse momenta slip phase during the processes of reacceleration and reinjection into the SLC system, increasing the energy spread and reducing the overall yield of the positron source. This reduction in yield has to be minimized by ''capturing'' the positrons with a high-field accelerator section placed as soon after the target as possible. The design, fabrication and RF testing of this accelerator section are described.

  13. A Simple Estimate of the Mass of the Positron.

    ERIC Educational Resources Information Center

    Jones, Goronwy Tudor

    1993-01-01

    Discusses a small part of the final state of a high-energy neutrino interaction: a head-on collision of a positron and a stationary electron. Provides a bubble chamber picture and describes the resulting particle effects. Uses momentum to determine the mass of the positron. (MVL)

  14. Positron transport: The plasma-gas interface

    SciTech Connect

    Marler, J. P.; Petrovic, Z. Lj.; Bankovic, A.; Dujko, S.; Suvakov, M.; Malovic, G.; Buckman, S. J.

    2009-05-15

    Motivated by an increasing number of applications, new techniques in the analysis of electron transport have been developed over the past 30 years or so, but similar methods had yet to be applied to positrons. Recently, an in-depth look at positron transport in pure argon gas has been performed using a recently established comprehensive set of cross sections and well-established Monte Carlo simulations. The key novelty as compared to electron transport is the effect of positronium formation which changes the number of particles and has a strong energy dependence. This coupled with spatial separation by energy of the positron swarm leads to counterintuitive behavior of some of the transport coefficients. Finally new results in how the presence of an applied magnetic field affects the transport coefficients are presented.

  15. Large area electron beam pumped krypton fluoride laser amplifier

    SciTech Connect

    Sethian, J.D.; Obenschain, S.P.; Gerber, K.A.; Pawley, C.J.; Serlin, V.; Sullivan, C.A.; Webster, W.; Deniz, A.V.; Lehecka, T.; McGeoch, M.W.; Altes, R.A.; Corcoran, P.A.; Smith, I.D.; Barr, O.C.

    1997-06-01

    Nike is a recently completed multi-kilojoule krypton fluoride (KrF) laser that has been built to study the physics of direct drive inertial confinement fusion. This paper describes in detail both the pulsed power and optical performance of the largest amplifier in the Nike laser, the 60 cm amplifier. This is a double pass, double sided, electron beam-pumped system that amplifies the laser beam from an input of 50 J to an output of up to 5 kJ. It has an optical aperture of 60 cm {times} 60 cm and a gain length of 200 cm. The two electron beams are 60 cm high {times} 200 cm wide, have a voltage of 640 kV, a current of 540 kA, and a flat top power pulse duration of 250 ns. A 2 kG magnetic field is used to guide the beams and prevent self-pinching. Each electron beam is produced by its own Marx/pulse forming line system. The amplifier has been fully integrated into the Nike system and is used on a daily basis for laser-target experiments. {copyright} {ital 1997 American Institute of Physics.}

  16. Engineering tradeoffs in miniaturization of electronics for very large detectors

    SciTech Connect

    Larsen, R.S.

    1987-10-01

    The trend toward Application-Specific Integrated Circuits and similar systems-on-a-chip-technologies is fueling a new wave of innovation in detector electronics, just in time to address some of the problems being introduced by detectors which will approach a million channels of electronics. The cost-effectiveness of these technologies can be easily demonstrated, and the trend of the past twenty years of achieving more powerful electronics at a lower per-channel cost should receive a major impetus. The investment required in the new technologies will reshape the work force of most laboratories, by providing more and better tools, and by requiring training or retraining of significant numbers of personnel. The need for new instrumentation standards will arise at new levels in the detectors of the future. The laboratories must also invest heavily in integrating various computer aided engineering and computer aided design tools into a smoothly functioning system. They must also establish a new and different kind of working relationship with vendors and suppliers of both basic devices as well as standard packaged products. This paper discusses three concepts.

  17. Positron diffusion in Si

    SciTech Connect

    Nielsen, B.; Lynn, K.G.; Vehanen, A.; Schultz, P.J.

    1985-06-01

    Positron diffusion in Si(100) and Si(111) has been studied using a variable energy positron beam. The positron diffusion coefficient is found to be D/sub +/ = 2.7 +- 0.3 cm/sup 2//sec using a Makhov-type positron implantation profile, which is demonstrated to fit the data more reliably than the more commonly applied exponential profile. The diffusion related parameter, E/sub 0/, which results from the exponential profile, is found to be 4.2 +- 0.2 keV, significantly longer than previously reported values. A drastic reduction in E/sub 0/ is found after annealing the sample at 1300 K, showing that previously reported low values of E/sub 0/ are probably associated with the thermal history of the sample.

  18. Monoenergetic positron beam at the reactor based positron source at FRM-II

    NASA Astrophysics Data System (ADS)

    Hugenschmidt, C.; Kögel, G.; Repper, R.; Schreckenbach, K.; Sperr, P.; Straßer, B.; Triftshäuser, W.

    2002-05-01

    The principle of the in-pile positron source at the Munich research reactor FRM-II is based on absorption of high energy prompt γ-rays from thermal neutron capture in 113Cd. For this purpose, a cadmium cap is placed inside the tip of the inclined beam tube SR-11 in the moderator tank of the reactor, where an undisturbed thermal neutron flux up to 2×10 14n cm-2 s-1 is expected. Inside the cadmium cap a structure of platinum foils is placed for converting high energy γ-radiation into positron-electron pairs. Due to the negative positron work function, moderation in annealed platinum leads to emission of monoenergetic positrons. Therefore, platinum will also be used as moderator, since its moderation property seems to yield long-term stability under reactor conditions and it is much easier to handle than tungsten. Model calculations were performed with SIMION-7.0w to optimise geometry and potential of Pt-foils and electrical lenses. It could be shown that the potentials between the Pt-foils must be chosen in the range of 1-10 V to extract moderated positrons. After successive acceleration to 5 keV by four electrical lenses the beam is magnetically guided in a solenoid field of 7.5 mT resulting in a beam diameter of about 25 mm. An intensity of about 10 10 slow positrons per second is expected in the primary positron beam. Outside of the reactor shield a W(1 0 0) single crystal remoderation stage will lead to an improvement of the positron beam brilliance before the positrons are guided to the experimental facilities.

  19. Large electronic sputtering yield of nanodimensional Au thin films: Dominant role of thermal conductivity and electron phonon coupling factor

    NASA Astrophysics Data System (ADS)

    Singh, Udai B.; Pannu, Compesh; Agarwal, Dinesh C.; Ojha, Sunil; Khan, Saif A.; Ghosh, Santanu; Avasthi, Devesh K.

    2017-03-01

    Detailed experiments and theoretical calculations on electronic sputtering of Au thin films (5-200 nm) on a quartz substrate are performed, revealing unusually large electronic sputtering, dependent on the thickness of the films. The dependence of electronic thermal conductivity (κe), electron-phonon coupling factor (g), and lattice thermal conductivity (κa) on the effective electron mean free path is taken into account in the thermal spike calculation for nanodimensional systems to elucidate the combined effect of the thickness and grain size on the electronic sputtering yield. The thermal spike simulation with refined parameters for nanodimensional systems gives a better explanation of the electronic sputtering process with a very good correlation between the experimental and theoretical yields than that of the thermal spike model with bulk parameters.

  20. Large space systems technology electronics: Data and power distribution

    NASA Astrophysics Data System (ADS)

    Dunbar, W. G.

    1980-02-01

    The development of hardware technology and manufacturing techniques required to meet space platform and antenna system needs in the 1980s is discussed. Preliminary designs for manned and automatically assembled space power system cables, connectors, and grounding and bonding materials and techniques are reviewed. Connector concepts, grounding design requirements, and bonding requirements are discussed. The problem of particulate debris contamination for large structure spacecraft is addressed.

  1. Large space systems technology electronics: Data and power distribution

    NASA Technical Reports Server (NTRS)

    Dunbar, W. G.

    1980-01-01

    The development of hardware technology and manufacturing techniques required to meet space platform and antenna system needs in the 1980s is discussed. Preliminary designs for manned and automatically assembled space power system cables, connectors, and grounding and bonding materials and techniques are reviewed. Connector concepts, grounding design requirements, and bonding requirements are discussed. The problem of particulate debris contamination for large structure spacecraft is addressed.

  2. Development of a Positron Source for JLab at the IAC

    SciTech Connect

    Forest, Tony

    2013-10-12

    We report on the research performed towards the development of a positron sour for Jefferson Lab's (JLab) Continuous Electron Beam Accelerator Facility (CEBAF) in Newport News, VA. The first year of work was used to benchmark the predictions of our current simulation with positron production efficiency measurements at the IAC. The second year used the benchmarked simulation to design a beam line configuration which optimized positron production efficiency while minimizing radioactive waste as well as design and construct a positron converter target. The final year quantified the performance of the positron source. This joint research and development project brought together the experiences of both electron accelerator facilities. Our intention is to use the project as a spring board towards developing a program of accelerator based research and education which will train students to meet the needs of both facilities as well as provide a pool of trained scientists.

  3. A low energy positron accumulator for the plasma confinement in a compact magnetic mirror trap

    SciTech Connect

    Higaki, Hiroyuki Kaga, Chikato; Nagayasu, Katsushi; Okamoto, Hiromi; Nagata, Yugo; Kanai, Yasuyuki; Yamazaki, Yasunori

    2015-06-29

    A low energy positron accumulator was constructed at RIKEN for the purpose of confining an electron-positron plasma. The use of 5 mCi {sup 22}Na RI source with a standard solid Ne moderator and N{sub 2} buffer gas cooling resulted in a low energy positron yield of ∼ 3 × 10{sup 5} e+/s. So far, 2 × 10{sup 6} positrons have been accumulated in 120s.

  4. Advanced Instrumentation for Positron Emission Tomography [PET

    DOE R&D Accomplishments Database

    Derenzo, S. E.; Budinger, T. F.

    1985-04-01

    This paper summarizes the physical processes and medical science goals that underlay modern instrumentation design for Positron Emission Tomography. The paper discusses design factors such as detector material, crystalphototube coupling, shielding geometry, sampling motion, electronics design, time-of-flight, and the interrelationships with quantitative accuracy, spatial resolution, temporal resolution, maximum data rates, and cost.

  5. Advanced instrumentation for Positron Emission Tomography

    SciTech Connect

    Derenzo, S.E.; Budinger, T.F.

    1985-04-01

    This paper summarizes the physical processes and medical science goals that underly modern instrumentation design for Positron Emission Tomography. The paper discusses design factors such as detector material, crystalphototube coupling, shielding geometry, sampling motion, electronics design, time-of-flight, and the interrelationships with quantitative accuracy, spatial resolution, temporal resolution, maximum data rates, and cost. 71 refs., 3 figs., 3 tabs.

  6. On the localization of positrons in metal vacancies

    NASA Astrophysics Data System (ADS)

    Babich, A. V.; Pogosov, V. V.; Reva, V. I.

    2015-11-01

    The probability of localization of positrons in single vacancies of Al, Cu, and Zn as a function of temperature has been calculated. Vacancy has been simulated by a cavity with a radius of the Wigner-Seitz cell in the stabilized jellium model. A formula for the rate of trapping of a positron by a vacancy as a function of the positron energy has been obtained using the "golden" rule for transitions under the assumption that the positron energy is spent on excitation of electron-hole pairs. The temperature dependence of the localization rate has been calculated for thermalized positrons. It has been found that, in the vicinity of the triple point, the localization rate is close in order of magnitude to the annihilation rate. Based on the results reported in our previous publications devoted to the evaluation of the influence of vacancies on the work function of free positrons, it has been assumed that, near the surface of the metal, there are vacancies charged by positrons. In the approximation of a two-dimensional superlattice, the near-surface vacancy barrier has been estimated. The experimentally revealed shift of the energy distribution of re-emitted positrons has been assumed to be caused by the reflection of low-energy positrons from the vacancy barrier back into the bulk of the metal where they annihilate.

  7. Apparatus for photon activation positron annihilation analysis

    DOEpatents

    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.

  8. Towards laboratory produced relativistic electron–positron pair plasmas

    SciTech Connect

    Chen, Hui; Meyerhofer, D. D.; Wilks, S. C.; Cauble, R.; Dollar, F.; Falk, K.; Gregori, G.; Hazi, A.; Moses, E. I.; Murphy, C. D.; Myatt, J.; Park, J.; Seely, J.; Shepherd, R.; Spitkovsky, A.; Stoeckl, C.; Szabo, C. I.; Tommasini, R.; Zulick, C.; Beiersdorfer, P.

    2011-12-01

    We review recent experimental results on the path to producing electron–positron pair plasmas using lasers. 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 past 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 1016 cm-3 and 1013 cm-3, respectively. With the increasing performance of high-energy ultra-short laser pulses, we expect that a high-density, up to 1018 cm-3, relativistic pair-plasma is achievable, a novel regime of laboratory-produced hot dense matter.

  9. Formation of a high intensity low energy positron string

    NASA Astrophysics Data System (ADS)

    Donets, E. D.; Donets, E. E.; Syresin, E. M.; Itahashi, T.; Dubinov, A. E.

    2004-05-01

    The possibility of a high intensity low energy positron beam production is discussed. The proposed Positron String Trap (PST) is based on the principles and technology of the Electron String Ion Source (ESIS) developed in JINR during the last decade. A linear version of ESIS has been used successfully for the production of intense highly charged ion beams of various elements. Now the Tubular Electron String Ion Source (TESIS) concept is under study and this opens really new promising possibilities in physics and technology. In this report, we discuss the application of the tubular-type trap for the storage of positrons cooled to the cryogenic temperatures of 0.05 meV. It is intended that the positron flux at the energy of 1-5 eV, produced by the external source, is injected into the Tubular Positron Trap which has a similar construction as the TESIS. Then the low energy positrons are captured in the PST Penning trap and are cooled down because of their synchrotron radiation in the strong (5-10 T) applied magnetic field. It is expected that the proposed PST should permit storing and cooling to cryogenic temperature of up to 5×109 positrons. The accumulated cooled positrons can be used further for various physics applications, for example, antihydrogen production.

  10. Defects in metals. [Positron annihilation spectroscopy

    SciTech Connect

    Siegel, R.W.

    1982-06-01

    The application of positron annihilation spectroscopy (PAS) to the study of defects in metals has led to increased knowledge on lattice-defect properties during the past decade in two areas: the determination of atomic defect properties, particularly those of monovacancies, and the monitoring and characterization of vacancy-like microstructure development during post-irradiation and post-quench annealing. The study of defects in metals by PAS is reviewed within the context of the other available techniques for defect studies. The strengths and weaknesses of PAS as a method for the characterization of defect microstructures are considered. The additional possibilities for using the positron as a localized probe of the atomic and electronic structures of atomic defects are discussed, based upon theoretical calculations of the annihilation characteristics of defect-trapped positrons and experimental observations. Finally, the present status and future potential of PAS as a tool for the study of defects in metals is considered. 71 references, 9 figures.

  11. Anti-hydrogen production with positron beam ion trap

    SciTech Connect

    Itahashi, Takahisa

    2008-08-08

    In low-energy antiproton physics, it is advantageous to be able to manipulate anti-particles as freely as normal particles. A robust production and storage system for high-quality positrons and antiprotons would be a substantial advance for the development of anti-matter science. The idea of electron beam ion trap could be applied for storage of anti-particle when the electron beam could be replaced by the positron beam. The bright positron beam would be brought about using synchrotron radiation source with a superconducting wiggler. The new scheme for production of anti-particles is proposed by using new accelerator technologies.

  12. Positron annihilation in TiBe/sub 2/

    SciTech Connect

    Manuel, A.A.; Hoffmann, L.; Singh, A.K.; Jarlborg, T.; Peter, M.; Smith, J.L.; Fisk, Z.; Pecora, L.M.; Ehrlich, A.C.

    1988-01-01

    We report positron annihilation measurements on TiBe/sub 2/. Calculations using LMTO band structure method are also presented. The good agreement with the experimental data leads to the conclusion that the unusual magnetic properties of this compound can be well explained in terms of its electronic structure. A reconstruction of the electron-positron momentum distribution from calculated and measured 2D-ACPAR is discussed. 10 refs., 3 figs.

  13. Positron Interactions with Atoms and Ions

    NASA Technical Reports Server (NTRS)

    Bhatia, Anand K.

    2012-01-01

    Dirac, in 1928, combining the ideas of quantum mechanics and the ideas of relativity invented the well-known relativistic wave equation. In his formulation, he predicted an antiparticle of the electron of spin n-bar/2. He thought that this particle must be a proton. Dirac published his interpretation in a paper 'A theory of electrons and protons.' It was shown later by the mathematician Hermann Weyl that the Dirac theory was completely symmetric between negative and positive particles and the positive particle must have the same mass as that of the electron. In his J. Robert Oppenheimer Memorial Prize Acceptance Speech, Dirac notes that 'Blackett was really the first person to obtain hard evidence for the existence of a positron but he was afraid to publish it. He wanted confirmation, he was really over cautious.' Positron, produced by the collision of cosmic rays in a cloud chamber, was detected experimentally by Anderson in 1932. His paper was published in Physical Review in 1933. The concept of the positron and its detection were the important discoveries of the 20th century. I have tried to discuss various processes involving interactions of positrons with atoms and ions. This includes scattering, bound states and resonances. It has not been possible to include the enormous work which has been carried out during the last 40 or 50 years in theory and measurements.

  14. Relativistic Electron Microburst Induced by Large Amplitude EMIC Rising-tone Emissions

    NASA Astrophysics Data System (ADS)

    Kubota, Y.; Omura, Y.

    2015-12-01

    We study dynamics of radiation belt electrons interacting with large amplitude EMIC rising-tone emissions by performing test particle simulations. Engebretson et al. [JGR, 2015] reported observation of large amplitude EMIC rising-tone emissions outside the plasmasphere and depletion of radiation belt electrons in response to these emissions. We make the two kinds of wave models; one is in low-density region based on the observation and the other is in the plasmasphere. To reproduce the large wave amplitude we include the convective wave growth, which are neglected through propagation of EMIC model waves in the previous studies [Omura and Zhao, JGR, 2012, 2013; Kubota et al., JGR, 2015]. Furthermore, we also include Landau damping in setting up the model waves. Comparing with a wave model ignoring the convective wave growth, it is found that the large wave amplitude contributes to rapid electron precipitation. Some of relativistic electrons change their equatorial pitch angles more than 15 degrees in a time scale of 0.1 s, precipitated into the atmosphere. We set up the EMIC model waves in a local longitude and distribute test electrons throughout all longitudinal direction initially. The electrons moving eastward encounter the localized EMIC waves and some of resonant electrons are precipitated into the atmosphere. We obtain distribution of radiation belt electrons with respect to their equatorial pitch angle and kinetic energy. We find that the frequency variation expands the resonant electron range of pitch angles and energies. For comparison with observation of precipitated electrons, we monitor fluxes of electrons lost into the atmosphere in a narrow longitudinal range. Furthermore, we find echo of electron depletion due to eastward drift around the Earth. Energy ranges of efficient precipitation are different depending on the regions of interaction inside and outside of the plasmapause. Inside the plasmapause, electrons with energy > 0.5 MeV are precipitated

  15. Theoretical calculation of positron affinities of solute clusters in aluminum alloys

    NASA Astrophysics Data System (ADS)

    Mizuno, Masataka; Araki, Hideki; Shirai, Yasuharu

    2016-01-01

    We have performed theoretical calculations of positron states for solute clusters in aluminum alloys to estimate the positron affinity of solute clusters. Positron states of solute clusters in aluminum alloys were calculated under the electronic structures obtained by first- principles molecular orbital calculations using Al158-X13 clusters. We defined the positron affinity of the solute clusters by the difference in the lowest potential sensed by positrons between the solute clusters and Al bulk. With increasing atomic number of 3d metals, the annihilation fraction of the solute clusters rapidly increases at Mn and shows a maximum at Ni. A similar trend is observed for 4d metals. The localization of positron at the solute clusters mainly arises from charge transfer from Al matrix to solute clusters. The positron affinity defined in this work well represents the localization of positron at the solute clusters in aluminum alloys.

  16. Conceptual design of an intense positron source based on an LIA

    NASA Astrophysics Data System (ADS)

    Long, Ji-Dong; Yang, Zhen; Dong, Pan; Shi, Jin-Shui

    2012-04-01

    Accelerator based positron sources are widely used due to their high intensity. Most of these accelerators are RF accelerators. An LIA (linear induction accelerator) is a kind of high current pulsed accelerator used for radiography. A conceptual design of an intense pulsed positron source based on an LIA is presented in the paper. One advantage of an LIA is its pulsed power being higher than conventional accelerators, which means a higher amount of primary electrons for positron generations per pulse. Another advantage of an LIA is that it is very suitable to decelerate the positron bunch generated by bremsstrahlung pair process due to its ability to adjustably shape the voltage pulse. By implementing LIA cavities to decelerate the positron bunch before it is moderated, the positron yield could be greatly increased. These features may make the LIA based positron source become a high intensity pulsed positron source.

  17. Positron studies of defected metals, metallic surfaces

    SciTech Connect

    Bansil, A.

    1991-01-01

    Specific problems proposed under this project included the treatment of electronic structure and momentum density in various disordered and defected systems. Since 1987, when the new high-temperature superconductors were discovered, the project focused extensively on questions concerning the electronic structure and Fermiology of high-[Tc] superconductors, in particular, (i) momentum density and positron experiments, (ii) angle-resolved photoemission intensities, (iii) effects of disorder and substitutions in the high-[Tc]'s.

  18. Theoretical analysis of reflection high-energy electron diffraction (RHEED) and reflection high-energy positron diffraction (RHEPD) intensity oscillations expected for the perfect layer-by-layer growth.

    PubMed

    Mitura, Zbigniew

    2015-09-01

    Predictions from two theoretical models, allowing one to determine the phase of intensity oscillations, are compared for reflected beams of electrons and positrons. Namely, results of the precise dynamical calculations are compared with results obtained using a simplified approach. Within the simplified model, changes in the specularly reflected beam intensity, expected to occur during the deposition of new atoms, are described with the help of interfering waves and the effect of refraction, and respective approximate analytical formulas are employed to determine the phase of the oscillations. It is found that the simplified model is very useful for understanding the physics ruling the appearance of intensity oscillations. However, it seems that the model with the realistic potential is more suitable for carrying out interpretations of experimental data.

  19. Multiple-ionization of xenon atoms by positron impact

    NASA Technical Reports Server (NTRS)

    Kruse, Georg; Quermann, Andreas; Raith, Wilhelm; Sinapius, Guenther

    1990-01-01

    Previously the cross sections were measured for positronium formation and single ionization by positron impact for He and H2. With the same apparatus, slightly modified, the single and multiple ionization of xenon is now investigated. The principle of the method is the detection of ion and positron in time correlation which allows the discrimination of positronium formation (whereby the positron vanishes) and the destinction of single, double and triple impact ionization (which lead to different ion flight times from the gas target to the ion detector). By using secondary electrons from the positron moderator, similar measurements were performed on electron impact ionization. By comparing with literature values for electron multiple ionization cross sections, the detection-probability ratios were determined for the differently charged ions.

  20. Positron sources for Linear Colliders

    SciTech Connect

    Gai Wei; Liu Wanming

    2009-09-02

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