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  • 1
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    Inter‐Calibrated Measurements of Intense Whistlers by Arase and Van Allen Probes (2021)
    In:  Journal of Geophysical Research: Space Physics
    Details
    Publication Date: 2022-03-17
    Description: Measurements of electromagnetic waves in space plasmas are an important tool for our understanding of physical processes in this environment. Inter-calibration of data from different spacecraft missions is necessary for combining their measurements in empirical models or case studies. We show results collected during a close conjunction of the Van Allen Probes and Arase spacecraft. The inter-calibration is based on a fortuitous case of common observations of strong whistlers at frequencies between a few hundred hertz and 10 kHz, which are generated by the same lightning strokes and which propagate along very similar paths to the two spacecraft. Measured amplitudes of the magnetic field fluctuations are the same within ∼14% precision of our analysis, corresponding to 1.2 dB. Currently, archived electric field measurements show twice larger amplitudes on Arase compared to Van Allen Probes but they start to match within ∼33% precision (2.5 dB) once the newest results on the interface of the antennas to the surrounding plasma are included in the calibration procedures. Ray tracing simulations help us to build a consistent scenario of wave propagation to both spacecraft reflected by a successful inter-calibration of the polarization and propagation parameters obtained from multicomponent measurements. We succeed in linking the spacecraft observations to localizations of lightning return strokes by two different ground-based networks which independently verify the correctness of the Universal Time tags of waveform measurements by both spacecraft missions, with an uncertainty better than 10 ms.
    Language: English
    Type: info:eu-repo/semantics/article
    Format: application/pdf
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  • 2
    Electronic Resource
    Electronic Resource
    Spin fluctuations of La2−xSrxCu1−yZnyO4−δ (x=0.14, y=0.012) (abstract) : 37th annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6333-6333 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetism of high-Tc superconductors is still the subject of intensive investigation. Zn substitution for Cu together with removal of oxygen suppresses the superconductivity quickly. We prepared two crystals to perform a neutron scattering study of the spin fluctuations of La2−xSrxCu1−yZnyO4−δ. One is a Zn-doped and deoxygenated crystal La1.86Sr0.14Cu0.988Zn0.012O4−δ (#1) which does not show superconductivity above 1.5 K. The other is a Zn-doped crystal La1.86Sr0.14Cu0.988Zn0.012O4 (#2) which shows superconductivity below 16 K. The incommensurate spin excitations observed previously in superconducting samples1,2 containing no Zn remain in both samples. However, there is significant difference in the spectral weight χ‘(q,ω) at low temperatures between the non-superconducting and superconducting Zn-doped crystals. In crystal #1 the spectral weight at low temperatures is qualitatively similar to that of Zn-undoped non-superconducting samples.3 In crystal #2 the spectral weight at low temperatures is qualitatively similar to that of Zn-undoped superconducting samples.1,2 These results demonstrate that there is an intimate relationship between the magnetism and the superconductivity. We are in the process of further measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352638
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  • 3
    Electronic Resource
    Electronic Resource
    Electrostatic fluctuations in the Current Sustained Torus IV at Nagoya University (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 2449-2455 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A detailed experimental investigation of plasma fluctuation and its modification due to radial electric field effects, both its shear and curvature, has been carried out on the Current Sustained Torus IV at Nagoya University [Takamura et al., J. Plasma Fusion Res. 74, 38 (1998)] through measurement with an array of Langmuir probes. The observed statistical dispersion relation indicates a drift-wave-type turbulence. An examination of the radial electric field shear and curvature effects on the fluctuations as well as comparisons to theoretical predictions are presented. The decorrelation of turbulence is found to be influenced by the radial electric field shear in our experiment. A modification of the poloidal correlation length and the two-poloidal-point coherency due to the radial electric field has also been identified. Nonlinear analysis of quadratic mode coupling indicates that the radial electric field can affect the fluctuation amplitudes by modifying the coupling between different spectral components of the fluctuations. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874084
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  • 4
    Electronic Resource
    Electronic Resource
    Frequency dependence of tokamak plasma response to the externally applied rotating helical field (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 3288-3300 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The frequency dependence of the tokamak plasma response to the externally applied rotating helical field was investigated by measuring the radial profile of the perturbation field with small magnetic probes which were inserted in the plasma. The experimental results are discussed, directly comparing with the generally accepted linear theory, and taking into account the E×B drift and diamagnetic effect of the plasma. It was found that the experimental results are in good agreement with the simple linear analysis based on the single helicity approximation in a cylindrical geometry, except for the ergodic region, which comes from the overlapping of several sideband components of the perturbation. It is also found that the radial component of the perturbation field is still amplified inside the resonance surface (r〈rs), even when a partial shielding takes place at r(approximate)rs. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874194
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  • 5
    Electronic Resource
    Electronic Resource
    High current H− ion production in cesium seeded large ion sources : Proceedings of the 5th international conference on ion sources (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 1195-1197 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The characteristics of a large negative-ion source with external filter is investigated for the neutral-beam injection system in a large helical device. The magnetic cusp field is set up at almost the same strength as that in our well optimized 1/3 ion source with rod-type magnetic filter. An H− ion current of 5.2 A is extracted from the ion source with Cs seeding. The H− current corresponds to 19.7 mA/cm2, and the value is comparable to the current density obtained using the 1/3 scaled ion source with a rod-type magnetic filter at the same extraction voltage. In low operating pressure, the ion source with the external filter has a better performance on the extraction of H− ions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145055
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  • 6
    Electronic Resource
    Electronic Resource
    Effects of hydrogen addition on C44 and ultrasonic attenuation of vanadium single crystals (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 4337-4342 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Examination was made of ultrasonic attenuation α44 and elastic constant C44 of vanadium single crystals with hydrogen between 4.2 and 220 K, as a function of temperature, hydrogen concentration, frequency, and rates of cooling and heating. Attenuation in the V–H α phase at 210 K increased in proportion to the square of hydrogen concentration, while C44 was linear. At a cooling rate of 3.0 K/min, attenuation of the specimen with 1000 at. ppm H increased below the critical solution temperature and showed a peak. At 0.1 K/min, discontinuous decrease was observed at the temperature. During isothermal annealing below this temperature, attenuation at the higher cooling rate decreased with time in two stages and approached the value for the lower cooling rate. The results are discussed based on ultrasonic double refraction due to the volume array of hydrogens and hydride particles formed under the influence of C44-mode ultrasonic waves. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363390
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  • 7
    Electronic Resource
    Electronic Resource
    Observation of CH2 radical and comparison with CH3 radical in a rf methane discharge (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 1292-1294 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Methylene radical (CH2) in a rf methane discharge was detected using threshold ionization mass spectrometry. The absolute density of CH2 radical (∼109 cm−3) for the discharge in 10 mTorr CH4 with 10 W rf power was two orders of magnitude less than the density of methyl radical (CH3). The CH2 density in the afterglow of a pulsed rf discharge turned out to decay on a time scale (≤10 ms) much shorter than the decay time of CH3 radical (∼100 ms). The observed rapid loss of CH2 radical was attributed to a large sticking coefficient and the resultant surface loss, in addition to gas phase losses due to the CH2 reactions with CH3 and CH4.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101636
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  • 8
    Electronic Resource
    Electronic Resource
    Mass spectroscopic investigation of the CH3 radicals in a methane rf discharge (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 1507-1509 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Neutral CH3 radicals in a capacitively coupled rf discharge in methane have been detected with a quadrupole mass spectrometer utilizing a threshold ionization technique. The absolute density of CH3 radicals was measured at pressures from 0.5 to 20 mTorr, together with the ionic composition of the methane plasma. The principal ionic species were CH+5 and C2H+5 , except in the low-pressure region, suggesting the importance of ion-molecule reactions in the plasma. The lifetime of CH3 radicals in the afterglow of pulsed rf discharges was measured and explained in terms of the recombination reaction CH3 +CH3 →C2 H6.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101336
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  • 9
    Electronic Resource
    Electronic Resource
    Spatial distribution of CH3 and CH2 radicals in a methane rf discharge (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 2616-2618 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spatial distributions of neutral radicals CH3 and CH2 in a capacitively coupled rf glow discharge of methane were measured by threshold ionization mass spectrometry. A strong asymmetry of the density profile was found for the CH2 radical in the high-pressure (∼100 mTorr) discharge. In addition, comprehensive measurements of electron energy distribution, ionic composition, and radical sticking coefficient were made to use as inputs to theoretical modeling of radicals in the methane plasma. The model predictions agree substantially with the measured radical distributions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.103264
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  • 10
    Electronic Resource
    Electronic Resource
    A 14 cm×36 cm volume negative ion source producing multi-ampere H− ion beams : International conference on ion sources (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 499-501 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A large volume negative ion source, which has a newly devised magnetic filter called a PG filter, was designed and tested. The PG filter produces a uniform magnetic filter field over a large extraction area of 14×36 cm2 by flowing a high current through the plasma grid itself. By optimizing the filter strength, we succeeded to produce 3.4-A 75-keV negative hydrogen ion beams for 50 ms from 253 apertures of 11.3 mm diam with an average current H− density of 13 mA/cm2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141233
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