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Notes: The characteristics of microchannel plates (MCPs) for detection of x rays have been investigated using synchrotron radiation in the energy ranges from 0.6 to 2.0 keV and from 5 to 20 keV. Microchannel plates are operated under the condition of an unsaturated pulse-height distribution mode. The current response curve of MCPs is measured continuously with x-ray energy variation for the first time. The experimental result of some discontinuous jumps in the response is obtained at the energies corresponding to the absorption edge of the MCP materials. In the low-energy range (hν〈2 keV), the dependence of the current response to the incident angle of x rays to the channel axis θ is measured to be proportional to cot θ, which is interpreted by the x-ray absorption near the surface of MCP channel wall. While, in the high-energy range (hν〉5 keV), a weak dependence on θ is observed, and is attributed mainly to the penetration of x rays through multiple channels.

Notes: Newly designed spectrometer arrays for ion-energy-spectrum observations are proposed and constructed in both end regions of the GAMMA 10 tandem mirror so as to obtain two dimensionally resolved radial profiles of end-loss-ion fluxes IELA, ion temperatures, and ion-confining potentials φc by the use of a single plasma discharge alone. Each spectrometer unit in the array has a specific structure with obliquely placed multiple grids with respect to the direction of the ambient plasma-confining magnetic fields. This structure is proposed to obtain precise ion-energy spectra without the disturbance of simultaneously incident energetic electrons into the array, since widely distributed "multigridded Faraday cup" signals have significant electron disturbances on ion spectra even if over a few tens of kV are applied to the electron-repeller grid. In tandem-mirror experiments, plasma-confining potentials produced by electron cyclotron heatings play one of the most critical roles in the improvement of simple-mirror confinement. Thus, diagnostics of these confining potentials using clear ion spectra are of essential importance. From these motivations, the spatial distribution details and relations of φc and IELA are investigated by the use of the novel ion spectrometers. Axisymmetric profiles of φc are found to have a good correlation with axisymmetric plugging distributions in IELA. These are consistently interpreted in terms of the Pastukhov theory of the relation of φc with IELA. Information on such specific spectrometer arrays would contribute to researchers in a wide variety of plasma devices, who employ analyzers for flux, temperature, and potential diagnostics under energetic plasma circumstances. © 2001 American Institute of Physics.

Notes: Charge-exchange (C–X) neutral particle measurements have been carried out in hot-ion-mode plasmas of the GAMMA 10 tandem mirror. In the present experiment, a microwave power of 40 kW in 28 GHz is injected toward a second harmonic ECR layer located in the vicinity of the ICR layer at the central region and the radial profiles of ion temperatures determined from the energy spectrum of the C–X neutrals by using a neutral particle energy analyzer (NPA) are investigated from the viewpoint of ion energy balance. At the onset of the ECRH pulse, a remarkable increase of C–X neutral flux with high energy (few keV to few tens keV) is observed with NPA and the resultant ion temperature on the plasma axis is found to increase from 2.5 to 5.0 keV at the electron line density of 3×1013 cm−2. Based on the measured plasma parameters, radial profiles of ion-energy losses due to classical processes are evaluated and ECRH in the central region is confirmed to reduce the energy loss due to electron drag significantly in the core-plasma region. © 1999 American Institute of Physics.

Notes: In the energy range from 1 keV down to a few hundred eV, a newly developed "ultralow-energy measurable'' pure-Ge detector for a pulse-height analysis and a current-mode observation has been characterized using synchrotron radiation monochromatized by a grasshopper monochromator at the Photon Factory of the National Laboratory for High Energy Physics (KEK). X-ray measurements in this low-energy region were previously tried out using several types of "windowless'' Si(Li) detectors. These detectors, however, had trouble, including temporal variations in the quantum efficiencies because of their detector-surface deteriorations due to various impurities in vacuum chambers. Our pure-Ge detector has a 4000-A(ring) thick polymer window metalized by a 1400-A(ring) thick Al supported by a 100-μm apart Si-ribbed structure. However, for this liquid-nitrogen-cooled detector with the special window, its actual energy-response data are not available at this time. Therefore, the investigations of its characteristics are reported particularly for the purpose of the reliable x-ray observations in such a low-energy regime. © 1995 American Institute of Physics.

Notes: Current response characteristics of microchannel plates (MCPs) x-ray detectors have been measured in a wide energy range from 0.6 to 82 keV using synchrotron radiation. In the current response curve with continuous photon energy, some discontinuities have been observed to correspond to absorption edges of elements which are the constituents of MCP glass and electrode materials (Si, Pb, Ba, and Fe). The dependence of the MCP response on the incident angle of x rays to the channel axis, θ, is also investigated. The characteristics change from the cot θ dependence for soft x rays (hν〈4 keV) to the sec θ one for hard x rays (hν〉60 keV). These results could provide guidelines on the design of x-ray diagnostic instruments using MCPs.

Notes: The characteristics of microchannel plates (MCPs) for detection of x rays have been investigated using synchrotron radiation in the energy range from 1.8 to 8 keV. The current response curve of MCPs is measured with approximately continuous x-ray energy variation, which is added to the previous data [T. Kondoh et al., Rev. Sci. Instrum. 59, 252 (1988)]. It is confirmed that there is a minimum in the current response at the x-ray energy of about 4 keV. The precise current response curve has been completed for the wide x-ray energy range from 0.6 to 20 keV. A transition in the incident angle dependence of current response is found from the feature based on single cylindrical photocathode model for soft x rays to that based on multiple channel activation due to the penetration of x rays through channel walls for hard x rays. In the current response of MCPs the structure similar to that in EXAFS is observed near the Si K edge.

Notes: The characteristics of microchannel plates (MCPs) for x-ray detection have been investigated with continuous x-ray energy variation using synchrotron radiation in the XUV and soft x-ray region (from 60 to 600 eV). The current response data have shown x-ray absorption fine structure (EXAFS or XANES) near the oxygen K absorption edge as well as a jump structure near the silicon L edge; these structures are explained by the surface composition of channel walls (SiO2). The data show that the surface layer of a microchannel is essential for x-ray detection by MCPs in this energy range. The precise current response curve has been completed for the wide x-ray energy range from 0.06 to 82 keV combined with the previously reported data [Kondoh et al., Rev. Sci. Instrum. 59, 252 (1988); Cho et al., ibid. 59, 2453 (1988); Yamaguchi et al., ibid. 60, 368, 2307 (1989)].

Notes: Using undulator radiation from 2 to 8 keV, quantum efficiencies [QE(E)] of gold photocathodes, microchannel plates (MCP), and silicon surface barrier (SSB) detectors have been investigated. For the gold photocathodes, the detailed structure of QE(E) near the M absorption edges has been presented. Also, the secondary electron conversion efficiency of gold has been calculated using the mass absorption coefficient given by a relativistic Hartree–Slater model and by the semiempirical values of Henke et al., respectively. Extended 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 an MCP and of an SSB detector. Furthermore, the new findings adding to our recent paper1 have been summarized as follows: (i) EXAFS above the Si-K edge in the MCP response depends on photon incident angles, and (ii) a little upshift of the starting point energy of EXAFS in the MCP response is observed. These detailed characteristics and their interpretation are described in the following: (i) The current responses of the MCP are obtained as a function of the incident x-ray energy for θ=13° (the bias angle of the MCP), and 40° by using a gold-monitor current. Here, θ denotes the incident angle of the photons to the channel. The data for θ=40° show a smaller jump near the Si-K edge as compared with the data for θ=13°.This is explained as follows: The incident photons for θ=13° are irradiated to and absorbed in the MCP ingredient of SiO2, while photons for θ=40° are incident to the electrode region. (The depth of the electrode coating is more than 10 μm from the MCP surface, while the photons are absorbed at less than 8 μm from the surface for θ=40°.) Thus, the data for θ=40° strongly reflect the characteristics of the electrode, but not of SiO2. The data for several values of θ consistently indicate that the height of this jump becomes smaller with increasing θ. (ii) The observed upshift of the starting point energy of EXAFS in the MCP response presents a contrast to EXAFS in the SSB detector response, in which upshift is not observed. This upshift is ascribed to the molecular structure of SiO2 (the chemical shift); that is, some valence electrons are removed from the Si atoms due to the oxidation (i.e., SiO2). Thus, the screening effects of the valence electrons on the core electron-nucleus attraction are reduced. This results in the shift of binding energy towards the higher-energy side. On the other hand, EXAFS in the SSB detector response reflects the characteristics of Si.

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.