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Temporally and spatially resolved X-ray analyses are carried out by using novel matrix-type X-ray semiconductor detector arrays in the GAMMA 10 tandem mirror. The detector array has seven “matrix columns” for the measurements of plasma X-ray profiles so as to make X-ray tomographic reconstructions. Further, six “matrix rows” having various dead layer thicknesses are fabricated as “unbreakable ultra-thin X-ray absorption filters” for simultaneous analyses of six different X-ray energy ranges. The characteristics of the detector array make it possible to obtain spatially resolved plasma electron temperatures down to a few tens of eV and investigate various magnetohydrodynamic activities during a single-plasma discharge alone. Several applications including investigations of electron energy confinement during a period with central-cell electron cyclotron heatings are made with the novel position sensitive semiconductor arrays. [Copyright &y& Elsevier]

Effects of neutron irradiation on X-ray energy responses of silicon semiconductor detectors have been investigated. Neutron irradiation experiments were carried out for n-type photodiode arrays utilized in the Joint European Torus (JET) using deuterium (D) beam-injection into a tritium (T) target for a well-calibrated deuterium–tritium (D–T) fusion neutron production at the Fusion Neutronics Source (FNS) facility of Japan Atomic Energy Research Institute. X-ray energy responses of these detectors are characterized before and after irradiation by the use of synchrotron radiation from a 2.5 GeV positron storage ring at the Photon Factory of High Energy Accelerator Research Organization (KEK). A recovery of the degraded X-ray energy response after the neutron irradiation has been found at fluences beyond around 1013 neutrons/cm2. A further novel finding is followed as a “re-degradation” by a neutron irradiation level over about 1014 neutrons/cm2. This “non-linear response” may be physically interpreted in terms of a type inversion from n- to p-type silicon in the detectors. Long-term observations of X-ray energy responses of the detectors after neutron irradiation have also been made in order to clarify the “annealing effect”. [Copyright &y& Elsevier]

The first results of simultaneous observations of temporally and spatially resolved electron temperatures (T[sub e]) in both circularly shaped central-cell and elliptically shaped anchor regions are reported in the GAMMA 10 tandem mirror. A data set is provided using a novel matrix-type x-ray semiconductor detector. The detector has seven “matrix columns” for the measurement of plasma x-ray profiles along with six “matrix rows” for simultaneous analyses of six different x-ray-energy ranges by the fabrication of six different thicknesses of SiO[sub 2] semiconductor surface layers from 1 to 495 nm as ultrathin and unbreakable “x-ray absorption filters.” Such a matrix idea enables us to analyze x-ray tomography data in the T[sub e] region down to a few tens of eV. Simultaneous application of the x-ray detectors in the central-cell and the anchor region gives information on not only detailed electron behavior in each region but also the mutually communicating relation between the two regions: The role of the anchor-region plasmas in magnetohydrodynamic plasma stabilization in the central-cell plasmas is confirmed by the data from these detailed simultaneous electron observations. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Current response characteristics of mirochannel 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 ( hv < 4 keV) to the sec θ one for hard x rays ( hv > 60 keV ). These results could provide guidelines on the design of x-ray diagnostic instruments using MCPs. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 (SiO[sub 2]). 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)]. [ABSTRACT FROM AUTHOR]

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 (hv < 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 (hv > 5 keV), a weak dependence on θ is observed, and is attributed mainly to the penetration of x rays through multiple channels. [ABSTRACT FROM AUTHOR]

The quantum efficiency of an ultralow-energy-sensitive pure-Ge (ULE Ge) detector is investigated using synchrotron radiation from the storage ring at AIST especially for x-ray pulse-height analyses (PHAs), down to a few hundred eV. Several types of x-ray diagnostics such as x-ray PHA, x-ray absorption methods, and x-ray tomography using the ULE Ge detector, a NaI(Tl) detector, as well as a microchannel-plate tomography system are employed for investigating electron distribution functions and electron temperature profiles with preliminary central electron-cyclotron heating in the central cell of the GAMMA 10 tandem mirror. These measurements play an important role in studying an essential physics scaling of the electron temperature as a function of electron confining potential in tandem mirror plasmas. [ABSTRACT FROM AUTHOR]

Our proposed “matrix-type” semiconductor detectors are applied for studying the relaxation of ion anisotropic distribution functions having several keV in the central cell of the tandem mirror GAMMA 10. The matrix-type detector array consists of compactly produced six “rows” having different thicknesses of thin dead layers (SiO2) on its surface. Each row has seven channel units (“columns”) for measuring radiation profiles in the radial direction of plasmas. These various SiO2 layers are, thus, employed as “unbreakable ultrathin radiation–absorption filters” having various thicknesses to analyze x-ray energies and distinguish x rays from neutral particles simultaneously. Development of these detectors along with high power gyrotrons allow us to investigate energy transport analyses between ion-cyclotron heated hot ions and electron-cyclotron heated electrons. An application of the matrix-type detectors reveals detailed behavior of electron and ion relaxation from the perpendicular to parallel ion energies in the central cell. [ABSTRACT FROM AUTHOR]

Experimental verification of the effects of radially sheared electric-field (or potential) formation in plasmas is one of the most critical issues to understand the physics basis for plasma confinement improvements. In the GAMMA 10 tandem mirror, recent experimental results show shear formation effects on the suppression of not only coherent drift waves but turbulence-like fluctuations without any coherent phasing relation during the ion-confining potential formation period. Contours of the central-cell soft x-ray brightness show spatially and temporally fluctuated structures during a weak sheared period by the use of the 50 channel microchannel plate system. A new x-ray tomography system is developed for analyzing temporally and spatially resolved plasma behavior in the presence or absence of these shear formation effects in GAMMA 10. The system consists of two 48-channel silicon semiconductor detector arrays with different viewing angles. X-ray energy responses of the new detector arrays along with response uniformity of detector channels have been characterized using synchrotron radiation at the Photon Factory. [ABSTRACT FROM AUTHOR]

Reports on the first experimental verification of the three-dimensional diffusion effect of x-ray-produced charges in semiconductor x-ray detectors on the quantum-efficiency enhancement. Description of the positron storage ring, monochromator, and detectors used in the experiments; Relation between the x-ray-beam position and the multichannel-detector location.

Investigates the detection characteristics of an ultralow-energy measurable pure-germanium detector in the hundreds-eV photon-energy region. Description of the experimental setup; Output current from each detector; X-ray response for high-energy x rays; Detection-efficiency data.

Describes the design and fabrication of a new-type multilayer semiconductor x-ray detector for the purpose of the development of wide-energy-range-sensitive x-rays. Characterization of the multilayer detector; Application for a plasma-electron temperature detector.

Investigates the x-ray energy responses of silicon semiconductor detectors using synchronous radiation from a positron storage ring at the Photon Factory. Study of the fundamental physics mechanism of the output signals; Technique for obtaining the principles of the future designs of plasma x-ray detectors.

Develops a new x-ray spectrometer using the principle of a photoelectron spectroscopy for the purpose of the observations of plasma-electron temperatures in the range of a hundred eV. Application of the spectrometer for surface-physics analyses; Employment of a parallel-plate energy analyzer.