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  • Articles: DFG German National Licenses  (21)
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  • Articles: DFG German National Licenses  (21)
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  • 1
    Electronic Resource
    Electronic Resource
    Antimatter plasmas and antihydrogen : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1528-1543 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent successes in confining antimatter in the form of positron and antiproton plasmas have created new scientific and technological opportunities. Plasma techniques have been the cornerstone of experimental work in this area, and this is likely to be true for the foreseeable future. Work by a number of groups on trapping antimatter plasmas is summarized, and an overview of the promises and challenges in this field is presented. Topics relating to positron plasmas include the use of positrons to study the unique properties of electron–positron plasmas, the interaction between positrons and ordinary matter, and the laboratory modeling of positron-annihilation processes in interstellar media. The availability of cold, trapped antiprotons and positrons makes possible the production of neutral antimatter in the form of antihydrogen. This is expected to enable precise comparisons of the properties of matter and antimatter, including tests of fundamental symmetries and the measurement of the interaction of antimatter with gravity. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872284
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  • 2
    Electronic Resource
    Electronic Resource
    Modes of spheroidal ion plasmas at the Brillouin limit (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 749-758 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The confinement properties and collective modes of single-component plasmas are investigated in a quadrupole Penning trap. Brillouin-density pure ion plasmas are generated by electron-beam ionization of a low-pressure gas. Large, spheroidal, steady-state plasmas are produced, extending out to contact one or more of the trap electrodes. With the density fixed at the Brillouin limit by the high ion production rate, the electrode potentials determine the plasma shape. The frequencies of azimuthally propagating cyclotron and diocotron modes are found to vary significantly with the plasma aspect ratio. For oblate plasmas, the frequencies are in good agreement with a simple fluid model. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871809
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  • 3
    Electronic Resource
    Electronic Resource
    An electron–positron beam–plasma instability (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 4982-4994 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using a new technique to generate cold electron beams, an electron-beam positron-plasma experiment was performed in a previously unexplored range of energies. An electron beam, formed from a thermalized room-temperature electron plasma, is transmitted through a positron plasma stored in a quadrupole Penning trap geometry. The transit-time instability, which is excited by the beam, was previously studied using a hot-cathode electron gun. The large beam energies produced by the cathode did not permit an investigation of the instability in the interesting range of energies near its onset. Using a new 0.1 eV energy width electron beam, we have reinvestigated the system. The experimental data are compared with the results of a theoretical model, also described in this paper. The theory employs a linearized cold fluid and Vlasov approach to model the plasma and beam dynamics, respectively. The data and predictions are in good agreement over the broad range of energies and beam currents studied. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1407284
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  • 4
    Electronic Resource
    Electronic Resource
    Low-order longitudinal modes of single-component plasmas (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2880-2894 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The low-order modes of spheroidal, pure electron plasmas have been studied experimentally, both in a cylindrical electrode structure and in a quadrupole trap. Comparison is made between measurements of mode frequencies, recent analytical theories, and numerical simulations. Effects considered include trap anharmonicity, image charges, and temperature. Quantitative agreement is obtained between the predictions and these measurements for spheroidal plasmas in the quadrupole trap. In many experiments on single-component plasmas, including antimatter plasmas, the standard diagnostic techniques used to measure the density and temperature are not appropriate. A new method is presented for determining the size, shape, average density, and temperature of a plasma confined in a Penning trap from measurements of the mode frequencies. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871188
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  • 5
    Electronic Resource
    Electronic Resource
    Creation and uses of positron plasmasf| (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 1439-1446 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Advances in positron trapping techniques have led to room-temperature plasmas of 107 positrons with lifetimes of 103 s. Improvements in plasma manipulation and diagnostic methods make possible a variety of new experiments, including studies just being initiated of electron–positron plasmas. The large numbers of confined positrons have also opened up a new area of positron annihilation research, in which the annihilation cross sections for positrons with a variety of molecules have been measured, as well as the energy spread of the resulting gamma rays. Such measurements are of interest for fundamental physics and for the modeling of astrophysical plasmas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870693
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  • 6
    Electronic Resource
    Electronic Resource
    Creation of a monoenergetic pulsed positron beam (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 1944-1946 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have developed a versatile, pulsed source of cold (ΔE=0.018 eV), low-energy positrons (E(approximate)0–9 eV). Multiple pulses of 105 positrons, each 10 μs in duration, are extracted from a thermalized, room temperature positron plasma stored in a Penning trap. The frequency, duration, and amplitude of the pulses can be varied over a wide range. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.118787
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  • 7
    Electronic Resource
    Electronic Resource
    Use of positrons to study transport in tokamak plasmas (invited) (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 1862-1867 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: It now appears feasible to deposit positrons (e+) in a tokamak plasma by injecting bursts of neutral positronium atoms (e+e−), which are then ionized by the plasma. The annihilation time of these positrons in the plasma is long compared with typical particle containment times. Thus the subsequent transport of the positrons can be studied by monitoring the time dependence of the annihilation, gamma radiation produced when the positrons strike a limiter. This paper discusses the design of such an experiment, the kinds of data which can be obtained, and the physics questions which this experiment might address. This diagnostic technique could also be useful in studying transport in other magnetic confinement devices such as reversed-field pinches and magnetic mirrors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139154
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  • 8
    Electronic Resource
    Electronic Resource
    Low-frequency density fluctuations in a tokamak plasma (1985)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 2857-2867 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: CO2 laser scattering and correlation techniques are used to study low-frequency density fluctuations in plasmas in the Alcator C tokamak. Using crossed-beam correlation techniques, these fluctuations are found to have largest amplitudes near the plasma edge. In discharges with mean plasma densities n¯(approximately-greater-than)2×1014 cm−3, the normalized fluctuation amplitude is ñ/n(approximately-equal-to)0.5 and peaks at the limiter radius; however, at lower plasma densities, ñ/n peaks in the plasma interior at a normalized minor radius r/a(approximately-equal-to)0.75 (where a is the limiter radius). The radial and poloidal wave vectors of the fluctuations are comparable, with mean wavenumbers k¯∼20 cm−1. At any given k, the observed frequency spectrum is broad. For plasma densities n¯(approximately-less-than)1.5×1014 cm−3, the poloidal group propagation velocity vθ of the fluctuations is measured to be approximately 2×105 cm/sec in the electron diamagnetic drift direction, while at plasma densities n¯(approximately-greater-than)2×1014 cm−3, vθ(approximately-equal-to)9×104 cm/sec in the ion diamagnetic drift direction. The nature of these fluctuations is also studied in discharges exhibiting a boundary-layer instability (i.e., "marfes'').
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865206
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  • 9
    Electronic Resource
    Electronic Resource
    Spectrum and propagation of lower-hybrid waves in a tokamak plasma (1985)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 2622-2624 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Waveguide-launched lower-hybrid waves are studied using CO2 laser scattering techniques. These experiments provide the first direct experimental confirmation that the spectrum of the wavelengths inside, but near the edge of, the tokamak plasma is similar to predictions of linear theory for the launched spectrum and varies with waveguide phasing. The spectrum observed farther into the plasma is dominated by longer wavelengths and is much less dependent on phasing. An explanation of these results is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865220
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  • 10
    Electronic Resource
    Electronic Resource
    Use of the positron as a plasma particle (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 1372-1375 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The use of positrons in laboratory plasma physics experiments is considered. Recent progress in this area is discussed, including the creation of a single-component positron plasma in the laboratory. Specific applications of such antimatter plasmas are also discussed, with emphasis on areas where existing plasma physics technology and that currently under development are likely to produce results in the next few years.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859558
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