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  • 1995-1999  (21)
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  • 1
    Electronic Resource
    Electronic Resource
    Conductivity and ion density of a plasma channel induced by a mildly relativistic electron beam from a gas-filled diode (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 1514-1521 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Conductivity and ion density of a plasma channel induced by a mildly relativistic electron beam (300 kV, ∼2 kA, 10–50 ns) have been experimentally investigated under various gas pressures. Pressures of filling gas (air) in this experiment ranged from 10 mTorr to 100 mTorr. The net currents of the beam-induced plasma channel were measured by four Rogowski coils located along the propagating region, while the electron beam currents were measured by a Faraday cup. The inductive plasma currents observed at the above pressure regimes have been characterized by magnetic decay time. Plasma-channel conductivity and ion density induced by the beam are measured along the propagating axial positions under various gas pressures. The numerical result of the ion density is also obtained at the charge neutralization time when the ion density is just the same as the electron beam density, and the digitizing experimental data of the beam current Ib(t) and voltage Vd(t) have been used. As expected, in both numerical and experimental results the ion density increases to a peak value of about 3.0×1011 cm−3 and 3.3×1011 cm−3, respectively, at 50 mTorr and slowly decreases for both cases as the gas pressure increases from 50 mTorr to 100 mTorr. Moreover, the results of ion density predicted by the theoretical model developed here are also found to be in remarkably good agreement with experimental and numerical results at pressure regimes from 10 mTorr to 100 mTorr. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872824
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  • 2
    Electronic Resource
    Electronic Resource
    Detection of fusion neutrons from a deuterium-proton mixed plasma in the GAMMA 10 Tandem Mirror (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 578-583 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Neutron diagnostics are applied to a deuterium plasma mixed with protons in the central cell of the GAMMA 10 tandem mirror [Inutake et al., Phys. Rev. Lett. 55, 939 (1985)]. The deuterium ions are heated with a slow ion cyclotron wave tuned to the fundamental deuterium resonance near the mid-plane of the central cell while the plasma is sustained with the fundamental resonance heating of protons in the minimum-B anchor cells. The measurement is based on in situ calibration to determine the transmission efficiency through machine walls and the counting efficiency of the detection system for neutrons emitted from 252Cf with energy close to that in the deuterium–deuterium (D–D) fusion reaction. The observation shows that the count rate of neutrons increases with diamagnetism, and this relation is accounted for in terms of fusion reaction between deuterium ions with a transverse temperature exceeding 10 keV. Discrepancies among ion temperatures determined with different diagnostics are mostly attributed to insufficient knowledge of the profiles of plasma parameters. The results indicate that the neutron measurement can be added as a powerful diagnostic tool for hot ions if combined with more detailed profile measurements. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871885
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  • 3
    Electronic Resource
    Electronic Resource
    Thickness dependence of the crystallization of Ba-ferrite films (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 1958-1964 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The crystallization of Ba-ferrite/sapphire(001) films of various thicknesses has been studied using synchrotron x-ray scattering, field emission scanning electron microscope, and atomic force microscope. In films thinner than 1000 Å, Ba-ferrite amorphous precursor was crystallized into perpendicular grains keeping the magnetically easy c-axis normal to the film plane during annealing to 750 °C. In films thicker than 1000 Å, however, acicular grains keeping the c-axis parallel to the film plane were grown on top of the perpendicular grains. The behavior of the saturation magnetization and the intrinsic coercivity was consistent with the thickness dependence of the crystallization. We attribute the thickness dependence of the crystallization to the substrate effect, which prefers the growth of the epitaxial, c-axis oriented perpendicular grains near the film/substrate interfacial area. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370993
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  • 4
    Electronic Resource
    Electronic Resource
    Characterization of a semiconductor detector and its application for ion diagnostics using a novel ion energy spectrometer : Proceedings of the 12th topical conference on high temperature plasma diagnostics (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 857-860 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Semiconductor ion detectors are developed and characterized for the purpose of the use for high-output and wide-energy-sensitive upgraded ion diagnostics. In particular, the theoretical basis for the simulation of the semiconductor ion-energy response along with its experimental verification using monoenergetic ion beams is investigated. High-output-current semiconductor signals ranging from one to three orders of magnitude larger than those from widely employed commercially available silicon-surface-barrier detectors are attained in the ion-energy region above 0.2 keV. These data are found to be well fitted by the developed simulation results. In order to observe ion signals alone under the complicated condition of the simultaneous incidence of ions, electrons, and x rays, we develop an upgraded electrostatic ion-energy spectrometer, having specific structures with obliquely positioned multiple grids. The combination of the installation of such a low-ion-energy-sensitive semiconductor detector and this novel-structured ion spectrometer provides a new electrostatic large-output and low-energy-sensitive ion spectrometer having no signal disturbances from the other plasma species and giving no perturbations to ambient plasma-confining magnetic fields. Accordingly, this novel compact-sized electrostatic ion spectrometer using a single-channel semiconductor collector provides temporal-evolution data on ion-energy spectra during a single plasma shot alone; therefore, this spectrometer is usefully applicable to the opportunities of the observations of ion parameters in both divertor and hot-core regions. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149279
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  • 5
    Electronic Resource
    Electronic Resource
    Development and characterization of semiconductor ion detectors for plasma diagnostics in the range over 0.3 keV : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 324-327 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: For the purpose of plasma-ion-energy analyses in a wide-energy range from a few hundred eV to hundreds of keV, upgraded semiconductor detectors are newly fabricated and characterized using a test-ion-beam line from 0.3 to 12 keV. In particular, the detectable lowest-ion energy is drastically improved at least down to 0.3 keV; this energy is one to two orders-of-magnitude better than those for commercially available Si-surface-barrier diodes employed for previous plasma-ion diagnostics. A signal-to-noise ratio of two to three orders-of-magnitude better than that for usual metal-collector detectors is demonstrated for the compact-sized semiconductor along with the availability of the use under conditions of a good vacuum and a strong-magnetic field. Such characteristics are achieved due to the improving methods of the optimization of the thicknesses of a Si dead layer and a SiO2 layer, as well as the nitrogen-doping technique near the depletion layer along with minimizing impurity concentrations in Si. Such an upgraded capability of an extremely low-energy-ion detection with the low-noise characteristics enlarges research regimes of plasma-ion behavior using semiconductor detectors not only in the divertor regions of tokamaks but in wider spectra of open-field plasma devices including tandem mirrors. An application of the semiconductor ion detector for plasma-ion diagnostics is demonstrated in a specially designed ion-spectrometer structure. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147923
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  • 6
    Electronic Resource
    Electronic Resource
    Characterization of new semiconductor detectors for x-ray tomography in the ASDEX Upgrade Tokamak and its generalized physics interpretations : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 774-777 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The energy response of a new semiconductor detector in the ASDEX Upgrade Tokamak for plasma x-ray tomography studies is characterized using synchrotron radiation from a 2.5 GeV positron storage ring at the National Institute for High Energy Physics in Japan. This international collaborating research clarifies a fairly good agreement between the x-ray energy response data and our recently proposed theoretical predictions for such a semiconductor x-ray-detector response. The x-ray response for several positions on the active area of the detector unit is studied; a good uniformity observed guarantees that the detector can employ any sized and shaped collimator for the x-ray tomography regardless of any correction factor coming from the response nonuniformity on the detector active area. Operational conditions of the detector for the ASDEX Upgrade plasma diagnostics are optimized using its capacitance measurements as a function of an applied bias as well as the numerical evaluations of the detector response; these are also directly verified by the synchrotron-radiation experiments. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147913
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  • 7
    Electronic Resource
    Electronic Resource
    Photoelectron spectroscopy for plasma x-ray measurements : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 565-567 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new x-ray spectrometer using the principle of a photoelectron spectroscopy method is developed for the purpose of the observations of plasma-electron temperatures in the range of a hundred of eV. X-ray photoelectron spectroscopy is a widely utilized method for surface-physics analyses; here, we employ a parallel-plate energy analyzer. This new type spectrometer is calibrated using synchrotron radiation from a 2.5 GeV positron storage ring at the Photon Factory (KEK). Theoretical calculations for photoelectron spectra from plasmas with various electron temperatures are carried out using the calibration data. This spectrometer is set up at the central cell of the GAMMA 10 tandem mirror for the measurements of potential-confined electron temperatures. Experimentally observed spectra are compared with the calculated spectra as well as the data from the other x-ray detection method. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146286
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  • 8
    Electronic Resource
    Electronic Resource
    A newly developed multilayer semiconductor x-ray detector for the observations of wide energy-range x rays : Proceedings of the 5th international conference on synchrotron radiation instrumentation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 2311-2313 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: For the purpose of the developments of wide-energy-range-sensitive x-ray detectors, we have designed and fabricated a new-type multilayer semiconductor x-ray detector. This new-type detector has been characterized using synchrotron radiation from a 2.5-GeV positron storage ring at the Photon Factory of the National Laboratory for High Energy Physics (KEK). This new detector is essentially composed of four layers of commercially available photodiodes. Each photodiode is made from a 300-μm thick, and a 10×10-mm square-shaped wafer. For the common affiliation of these individual photodiodes, the quantum efficiency normalized by the photon energy η/E begins to decrease at 8 keV, and then η/E decreases down to 26% at 20 keV. On the other hand, for our newly designed detector a flat response even in the 10–20-keV energy regime (beam line 15C at the Photon Factory) is observed, and even at 100 keV η/E〈30% is still anticipated. This new x-ray detector has various advantages: (i) A compact, and (ii) outgas-free detector for a high-vacuum use, along with (iii) a high degree of immunity to ambient magnetic fields. Furthermore, (iv) the combination of the x-ray signal outputs from each detector layer provides information on the x-ray emitting electron energies. These properties are quite suitable for the use of the fusion-oriented plasma x-ray diagnostics under intense-magnetic field and high-vacuum conditions so as to interpret wide-band x-ray emitting electron-velocity distribution functions from the x-ray data. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145673
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  • 9
    Electronic Resource
    Electronic Resource
    Experimental verification of the three-dimensional diffusion effect of x-ray-produced charges in semiconductor x-ray detectors on the quantum-efficiency enhancement : Proceedings of the 5th international conference on synchrotron radiation instrumentation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 2300-2302 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: One of the characteristic physical principles of our recently proposed theory on the x-ray-energy response of a semiconductor x-ray detector is the effect of the three-dimensional diffusion of x-ray-produced charges in a semiconductor field-free substrate region. It is found and reported that the quantum efficiency of a semiconductor x-ray detector is enhanced when this phenomenon is taken into account, and the data on the x-ray-energy response of the semiconductor detector using monochromatized synchrotron radiation at the Photon Factory are actually well fitted by the theory. In addition, we measure the diffusion length L of the detector using a precisely collimated x-ray narrow beam and a multichannel detector array setting on a μm-order position-controllable stage. The verification of the consistency between this observed value of L and the predicted value of L from our theory on the quantum efficiency, has been achieved. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145669
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  • 10
    Electronic Resource
    Electronic Resource
    A differential-spectrum ion-energy analyzer with electrostatic slanted grids (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 4928-4936 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A novel end-loss ion-energy spectrometer is designed for plasma-ion diagnostics in open-ended plasma-confinement devices. This analyzer significantly upgrades a previous slanted grid end-loss analyzer (SELA) to essentially eliminate secondary-electron current, and to provide a differential-spectrum mode of operation, in addition to the usual integral-spectrum operation of gridded ion-energy analyzers. The upgraded SELA does not perturb the ambient magnetic field due to its electrostatic operation. Either the differential or integral spectra are obtained by a time sweep of grid voltages, collecting the ion current on a single-channel plate. Because the angular alignment of the SELA is not critical, it can be used as a spatially scannable diagnostic of ion-energy distributions and plasma potentials. It is characterized using computer simulations of ion trajectories, monoenergetic ion beams, and end-loss plasma from the world's largest tandem mirror—GAMMA 10. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146177
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