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  • 11
    Electronic Resource
    Electronic Resource
    Reply to "Comment on ‘A theory on the x-ray sensitivity of a silicon surface-barrier detector including a thermal charge-diffusion effect' '' [J. Appl. Phys. 72, 3363 (1992)] (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 1463-1464 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of thermal-diffusion charge on the x-ray energy response of silicon surface-barrier (SSB) detectors have generally been ignored; consequently, the SSB response has been believed to be analyzed using the thickness of the depletion layer alone. Our new theory on the SSB x-ray response [J. Appl. Phys. 72, 3363 (1992)] was prepared for addressing recent confusion on plasma x-ray analyses using SSB detectors [Rev. Sci. Instrum. 59, 1380 (1988); 61, 693 (1990); 63, 4850 (1992)]. This approach was made under the assumption of a dominant contribution of the diffusion-charge signal in the vicinity of the x-ray incident location because of the strong reduction of the x-ray produced charge within the thermal-diffusion length. In this report, the comparison between this approximation (having an approximated solution) and the exact numerical calculation (using an integral form) is carried out. Necessity and importance of such three-dimensional treatments for the data analyses as well as the design of multichannel semiconductor-array detectors developed for plasma x-ray tomography diagnostics are highlighted. Furthermore, for the total diffusing-charge amount, the calculated results from our theory and the values using the comment from Donolato agree well within the accuracy of 1%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354864
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  • 12
    Electronic Resource
    Electronic Resource
    X-ray tomography of hot electrons in the barrier region of the tandem mirror GAMMA 10 (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 1694-1699 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Tomographic reconstructions of x-ray emission from hot electrons have been carried out in the thermal barrier region of the GAMMA 10 plasmas. Here, the first application of two sets of the 50-channel microchannel plates have been performed using their detailed calibration data as a function of x-ray energy and incident angle [Rev. Sci. Instrum. 59, 256 (1988); 59, 2453 (1988); 60, 368 (1989)]. The x-ray reconstructed signals under standard thermal barrier operating conditions indicate a good axisymmetric radial profile peaked on the magnetic axis. This symmetric profile is important for preventing the formation of a local anisotropic electric field, which may cause particle confinement degradation, and its peaking profile is desirable for thermal barrier potential formation in the core plasma region. When we have relocated the second-harmonic electron cyclotron layers (ω=2Ωe) in two different ways (moving them out radially, or axially away from the midplane), tomographic reconstructions show hollow x-ray profiles in both cases. These may be formed due to the E×B rotations of the hot electrons produced near ω=2Ωe . These applications of x-ray tomography to two-dimensional radial profile observations along with the axial x-ray profile measurement give information that the production mechanism of these hot electrons is ascribed to second-harmonic electron cyclotron heating.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345639
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  • 13
    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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  • 14
    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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  • 15
    Electronic Resource
    Electronic Resource
    Quantum efficiency of gold photocathodes (2–8 keV) and EXAFS in its secondary electron yield and in the detection currents of a microchannel plate and a silicon surface barrier detector (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 2453-2456 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The quantum efficiency of gold photocathodes has been investigated by using synchrotron radiation from 2–8 keV; in particular its detailed structure near the M absorption edge region is obtained. The secondary electron conversion efficiency of gold has been calculated by using the mass absorption coefficient given by a relativistic Hartree-Slater model and by the semiempirical values of Henke et al., respectively. These data are compared with the published data at some discrete energies, and we add several new data points, especially for the gold M edge region (2–4 keV). X-ray absorption fine structure (EXAFS) has been observed in the secondary electron current of the gold photocathode as well as in the detection current responses of a microchannel plate and a silicon surface barrier detector.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139925
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  • 16
    Electronic Resource
    Electronic Resource
    Microwave absorption at the fundamental electron cyclotron resonance and potential formation in a tandem mirror (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 1815-1818 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Strong one-pass absorption of high-power microwaves is observed at the fundamental electron cyclotron resonance in an axisymmetric end mirror of the GAMMA 10 tandem mirror [Phys. Rev. Lett. 55, 939 (1985); Phys. Fluids 29, 2781 (1986)]. The radial profile of microwave power deposition is directly measured without the influence of wall reflection. It coincides with that of the axial flow of warm electrons driven by the fundamental heating as well as with that of the plasma potential at the resonance. This indicates that strong electron cyclotron heating largely affects the potential formation through driving an axial flow of warm electrons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866675
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  • 17
    Electronic Resource
    Electronic Resource
    Scaling study of potential in the end region of a tandem mirror based on end-loss electron measurement (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 866-871 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An empirical scaling for the potential difference between the plug potential ΦP and the floating potential ΦEP of an endplate is obtained in terms of end-loss electron temperatures. Results from the GAMMA 10 tandem mirror [Phys. Rev. Lett. 55, 939 (1985)] indicate that ΔΦ=ΦP−ΦEP scales much better with an effective temperature Teff≡(1−β)TeL+βTeH than with a single temperature TeL or TeH, where TeL and TeH are temperatures of the bulk and the high-energy tail components of the end-loss electrons and β denotes the flux fraction of the TeH component. Moreover, the observed scaling is consistent with a recently developed theoretical model [K. Kurihara et al., J. Phys. Soc. Jpn. 61, 3153 (1992)].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860937
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  • 18
    Electronic Resource
    Electronic Resource
    Production of hot electrons for axisymmetric thermal barrier formation in a tandem mirror (1986)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 2781-2784 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hot electrons have been produced by second harmonic electron-cyclotron resonance heating in axisymmetric end mirrors of the tandem mirror GAMMA10 [Phys. Rev. Lett. 55, 939 (1985)] with an on-axis density fraction reaching 80% and temperature of 25–50 keV, satisfying theoretically required conditions for the formation of thermal barriers. The successful control of the electron temperature may be attributed to the relativistic detuning of the second harmonic resonance for localized microwave power absorption. The time evolutions of relevant parameters are studied with extensive diagnostics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865473
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  • 19
    Electronic Resource
    Electronic Resource
    Newly developed matrix-type semiconductor detector for temporally and spatially resolved x-ray analyses ranging down to a few tens eV using a single plasma shot : 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. 633-636 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: For the purpose of the measurements of temporally and spatially resolved electron temperatures (Te) during a single plasma shot alone, we propose and fabricate a new matrix-type semiconductor x-ray detector. This detector is fabricated using the precise formation of thin dead layers (SiO2) with six different thicknesses (from 10 to 5000 Å) aligned in line on its surface compactly. Each "row" has seven channels for the measurements of plasma x-ray radial profiles so as to make x-ray tomographic reconstructions; namely, the compact-sized matrix detector having six rows and seven columns with a 5×5 mm2 active area for each matrix unit. These various SiO2 layers are proposed to be utilized as ultrathin "x-ray absorption filters" with different thicknesses, which are never obtained as "self-supporting material absorbers" because of their ultrathin properties. This novel idea enables us to analyze x-ray tomography data including in the Te region down to a few tens eV. The simultaneous comparison of each tomographically reconstructed data from each detector row provides the temporal evolution of energy-resolved x-ray or Te profiles using "the absorption method." The first application of this newly developed matrix detector is made to obtain Te profiles in the GAMMA 10 tandem mirror. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149522
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  • 20
    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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