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  • 1
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    Note: A pulsed laser ion source for linear induction accelerators (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-01-13
    Description: We have developed a high-current laser ion source for induction accelerators. A copper target was irradiated by a frequency-quadrupled Nd:YAG laser (266 nm) with relatively low intensities of 10 8 W/cm 2 . The laser-produced plasma supplied a large number of Cu + ions (∼10 12 ions/pulse) during several microseconds. Emission spectra of the plasma were observed and the calculated electron temperature was about 1 eV. An induction voltage adder extracted high-current ion beams over 0.5 A/cm 2 from a plasma-prefilled gap. The normalized beam emittance measured by a pepper-pot method was smaller than 1 π mm mrad.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    Magnetic reconnection driven by Gekko XII lasers with a Helmholtz capacitor-coil target (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-03-26
    Description: We demonstrate a novel plasma device for magnetic reconnection, driven by Gekko XII lasers irradiating a double-turn Helmholtz capacitor-coil target. Optical probing revealed an accumulated plasma plume near the magnetic reconnection outflow. The background electron density and magnetic field were measured to be approximately 10 18  cm −3 and 60 T by using Nomarski interferometry and the Faraday effect, respectively. In contrast with experiments on magnetic reconnection constructed by the Biermann battery effect, which produced high beta values, our beta value was much lower than one, which greatly extends the parameter regime of laser-driven magnetic reconnection and reveals its potential in astrophysical plasma applications.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 3
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    Size effects on negative thermal expansion in cubic ScF3 (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-07-16
    Description: Scandium trifluoride (ScF 3 ), adopting a cubic ReO 3 -type structure at ambient pressure, undergoes a pronounced negative thermal expansion (NTE) over a wide range of temperatures (10 K–1100 K). Here, we report the size effects on the NTE properties of ScF 3 . The magnitude of NTE is reduced with diminishing the crystal size. As revealed by the specific heat measurement, the low-energy phonon vibrations which account for the NTE behavior are stiffened as the crystal size decreases. With decreasing the crystal size, the peaks in high-energy X-ray pair distribution function (PDF) become broad, which cannot be illuminated by local symmetry breaking. Instead, the broadened PDF peaks are strongly indicative of enhanced atomic displacements which are suggested to be responsible for the stiffening of NTE-related lattice vibrations. The present study suggests that the NTE properties of ReO 3 -type and other open-framework materials can be effectively adjusted by controlling the crystal size.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 4
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    A novel approach to correct the coded aperture misalignment for fast neutron imaging (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-01-01
    Description: Aperture alignment is crucial for the diagnosis of neutron imaging because it has significant impact on the coding imaging and the understanding of the neutron source. In our previous studies on the neutron imaging system with coded aperture for large field of view, “residual watermark,” certain extra information that overlies reconstructed image and has nothing to do with the source is discovered if the peak normalization is employed in genetic algorithms (GA) to reconstruct the source image. Some studies on basic properties of residual watermark indicate that the residual watermark can characterize coded aperture and can thus be used to determine the location of coded aperture relative to the system axis. In this paper, we have further analyzed the essential conditions for the existence of residual watermark and the requirements of the reconstruction algorithm for the emergence of residual watermark. A gamma coded imaging experiment has been performed to verify the existence of residual watermark. Based on the residual watermark, a correction method for the aperture misalignment has been studied. A multiple linear regression model of the position of coded aperture axis, the position of residual watermark center, and the gray barycenter of neutron source with twenty training samples has been set up. Using the regression model and verification samples, we have found the position of the coded aperture axis relative to the system axis with an accuracy of approximately 20 μ m. Conclusively, a novel approach has been established to correct the coded aperture misalignment for fast neutron coded imaging.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 5
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    Strong magnetic fields generated with a simple open-ended coil irradiated by high power laser pulses (2015)
    American Institute of Physics (AIP)
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    Publication Date: 2015-12-30
    Description: A simple scheme to produce strong magnetic fields due to cold electron flow in an open-ended coil heated by high power laser pulses is proposed. It differs from previous generation of magnetic fields driven by fast electron current in a capacitor-coil target [S. Fujioka et al ., Sci. Rep. 3 , 1170 (2013)]. The fields in our experiments are measured by B-dot detectors and proton radiography, respectively. A 205 T strong magnetic field at the center of the coil target is generated in the free space at Iλ 2 of 6.85 × 10 14  W cm −2   μ m 2 , where I is the laser intensity, and λ is the laser wavelength. The magnetic field strength is proportional to Iλ 2 . Compared with the capacitor-coil target, the generation mechanism of the magnetic field is straightforward and the coil is easy to be fabricated.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 6
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    Magnetic nature of surface and exchange bias effect in NiO nanosheets (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-09-21
    Description: The Mesoporous NiO nanosheets with an average thickness of ∼30 nm have been synthesized by annealing Ni(OH) 2 precursors. Magnetic measurements show that the NiO nanosheets can be considered as a core-shell type magnetic structure, in which the surface shell layer behaves as a coexistence of two-dimensional diluted antiferromagnetic (2D DAFF) and spin glass (SG) behaviors; the core retains its original bulk antiferromagnetic (AFM) phase. Field-cooled hysteresis loop measurements confirm the presence of exchange bias (EB) effect in the NiO nanosheets. The temperature dependence of the exchange bias field indicates that the observed EB effect originates from an interface exchange coupling interaction between the AFM core and the 2D DAFF shell layer. A phenomenological AFM-DAFF-SG magnetic structure model is proposed to interpret the magnetic properties of these NiO nanosheets.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 7
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    Argon ion beam induced surface pattern formation on Si (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-01-20
    Description: The development of self-organized surface patterns on Si due to noble gas ion irradiation has been studied extensively in the past. In particular, Ar ions are commonly used and the pattern formation was analyzed as function of ion incidence angle, ion fluence, and ion energies between 250 eV and 140 keV. Very few results exist for the energy regime between 1.5 keV and 10 keV and it appears that pattern formation is completely absent for these ion energies. In this work, we present experimental data on pattern formation for Ar ion irradiation between 1 keV and 10 keV and ion incidence angles between 50° and 75°. We confirm the absence of patterns at least for ion fluences up to 10 18 ions/cm 2 . Using the crater function formalism and Monte Carlo simulations, we calculate curvature coefficients of linear continuum models of pattern formation, taking into account contribution due to ion erosion and recoil redistribution. The calculations consider the recently introduced curvature dependence of the erosion crater function as well as the dynamic behavior of the thickness of the ion irradiated layer. Only when taking into account these additional contributions to the linear theory, our simulations clearly show that that pattern formation is strongly suppressed between about 1.5 keV and 10 keV, most pronounced at 3 keV. Furthermore, our simulations are now able to predict whether or not parallel oriented ripple patterns are formed, and in case of ripple formation the corresponding critical angles for the whole experimentally studied energies range between 250 eV and 140 keV.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 8
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    Guiding and collimating fast electron beam by the quasi-static electromagnetic field array (2014)
    American Institute of Physics (AIP)
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    Publication Date: 2014-10-28
    Description: A guidance and collimation scheme for fast electron beam in a traverse periodic quasi-static electromagnetic field array is proposed with the semi-analytic method and the particle-in-cell simulation. The sheath electric fields on the surfaces of nanowires and the magnetic fields around the nanowires form a traverse periodic quasi-static electromagnetic field array. Therefore, most of the fast electrons are confined at the nanowire surfaces and transport forward. More importantly, due to the divergent property of the beams, the magnitudes of the generated fields decrease with the target depth. The lateral momenta of the electrons convert into the forward momenta through Lorenz force, and they cannot recover their initial values. Therefore, the fast electrons can be guided and collimated efficiently in the gaps between the nanowires. In our particle-in-cell simulations, the observed guiding efficiency exceeds 80% compared with the reference target.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
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  • 9
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    Note: Design and initial results of a multi-pulsed intense electron beam source (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-06-20
    Description: A multi-pulsed intense electron beam source is introduced, including the design and the initial experimental results. The source can generate a burst of three pulses of intense electron beams with energy of 2–3 MeV and beam intensities of around 2.5 kA. An inductive adder is chosen to generate the pulsed diode voltages and a dispenser cathode is chosen to emit electron beams. The test results indicate that the design of the source is reliable. The multi-pulsed diode voltage is up to 2.5 MV and the beam intensities are more than 2 kA at the exit of the source with small variation.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 10
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    Broadband optical scattering in coupled silicon nanocylinders (2014)
    American Institute of Physics (AIP)
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    Publication Date: 2014-07-01
    Description: In this work, we demonstrate the broadband scattering of light waves incident on coupled silicon nanocylinders. First, it is shown that both electric and magnetic resonances are observed in a single silicon nanocylinder. By using two silicon nanocylinders, we next construct a silicon nanodimer. Thereafter, the original electric and magnetic resonances of the single nanocylinder shift and form hybrid resonant modes in the dimer; meanwhile, a new magnetic resonant mode emerges at a longer wavelength. Consequently, the silicon nanodimer exhibits a broadband scattering response that originates from optically magnetic interactions between dimeric silicon nanocylinders. Furthermore, the scattering bandwidth further increases upon using a silicon nanotrimer. This broadband optical response in silicon nanocylinders is demonstrated via their scattering spectra, and the magnetic interaction is verified by examining the spatial distributions of electromagnetic fields and the retrieved permittivity and permeability of the nanocylinders system. This theoretical finding may provide an approach to realize silicon-based broadband nanoantennas and nanosensors.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
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