T. Tamano

EFFECTS OF NEUTRONS ON SEMICONDUCTOR X-RAY DETECTORS INCLUDING N-TYPE JOINT EUROPEAN TORUS AND P-TYPE GAMMA 10 TOMOGRAPHY DETECTORS

Characterization experiments have been carried out so as to investigate the effects of fusion-produced neutrons on the x-ray-energy responses of semiconductor detectors for x-ray tomography in the Joint European Torus (JET) tokamak (n-type silicon) and the GAMMA 10 tandem mirror (p-type silicon). Neutron effects on the x-ray-energy responses of these detectors are studied using synchrotron radiation from a 2.5 GeV positron storage ring at the Photon Factory. Changes in the material properties of the detectors have been investigated using an impedance analyzer to estimate neutron effects on x-ray-sensitive depletion thicknesses. A cyclotron accelerator is employed for well-calibrated neutron irradiation onto these plasma x-ray detectors; a fluence of 2–5×1013 neutrons/cm2 is utilized for simulating the effects of fusion-produced neutrons in JET. Modifications of the x-ray responses after neutron exposure due to fusion plasma shots in JET as well as cyclotron-produced neutron irradiations are found to have ...

A diagnostic method for both plasma ion and electron temperatures under simultaneous incidence of charge-exchange particles and x rays into a semiconductor detector array

An idea for using semiconductor detectors to simultaneously observe both plasma ion Ti and electron Te temperatures is proposed. The idea is also experimentally verified in tandem-mirror plasma shots. This method is developed on the basis of an alternative “positive” use of a semiconductor “dead layer” as an energy-analysis filter. Filtering dependence of charge-exchange neutral particles from plasmas on the thickness of a thin (on the order of nm thick) SiO2 layer is employed for analyzing Ti in the range from hundreds to thousands of eV. Even under the conditions of simultaneous incidence of such particles and x rays into semiconductor detectors, the different dependence on their penetration lengths and deposition depths in semiconductor materials makes it possible to distinguish particles (for Ti) from x rays (for Te). In this letter, proof-of-principle plasma experiments for the proposed idea are carried out to verify the availability of this concept of distinguishing and identifying each value of Ti ...

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

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 A) 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 tomogra...

Characterization of new semiconductor detectors for x-ray tomography in the ASDEX Upgrade Tokamak and its generalized physics interpretations

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; ...

Characterization of a semiconductor detector and its application for ion diagnostics using a novel ion energy spectrometer

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 n...

Development and characterization of semiconductor ion detectors for plasma diagnostics in the range over 0.3 keV

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...

New methods for semiconductor charge-diffusion-length measurements using synchrotron radiation

The extension of a new theory on the X-ray energy response of semiconductor detectors is carried out to characterize the X-ray response of a multichannel semiconductor detector fabricated on one silicon wafer. Recently, these multichannel detectors have been widely utilized for position-sensitive observations in various research fields, including synchrotron radiation research and fusion-plasma investigations. This article represents the verification of the physics essentials of a proposed theory on the X-ray response of semiconductor detectors. The three-dimensional charge-diffusion effects on the adjoining detector-channel signals are experimentally demonstrated at the Photon Factory for two types of multichannel detectors. These findings are conveniently applicable for measuring diffusion lengths for industrial requirements.

A new principle in plasma electron-temperature diagnostics using a semiconductor x-ray detector

Abstract Recently, the energy responses of widely utilized seraiconductor X-ray detectors employed in many plasma-confmement devices were found to show contradictory behavior against the predietion from the conventional X-ray-energy-response theory in textbooks employed over the last quarter of the century for the analyses of plasma electron tem-peratures T e. This problem gave serious confusion for plasma researchers, who were utilizing X-ray data from semiconductor detectors including widely utilized X-ray-tomography data. For solving this problem, we proposed a new theory on the X-ray-energy response using X-ray-produced three-dimensionally diffusing charges from a field-free-substrate region in a detector. This novel theory is verified by the detailed data on a semiconductor X-ray response using synchrotron radiation. On the basis of these significant new findings, a novel method for X-ray diagnostics is proposed for the pur-pose of developing novel Te measurements. The physics principle is essentiall...

Characterization and interpretation of the quantum efficiencies of multilayer semiconductor detectors using a new theory

On the basis of a new theory of semiconductor X-ray detector response, a new type of multilayer semiconductor detector was designed and developed for convenient energy analyses of intense incident X-ray flux in a cumulative-current mode. Another anticipated useful property of the developed detector is a drastic improvement in high-energy X-ray response ranging over several hundred eV. The formula for the quantum efficiency of multilayer semiconductor detectors and its physical interpretations are proposed and have been successfully verified by synchrotron radiation experiments at the Photon Factory. These detectors are useful for data analyses under strong radiation-field conditions, including fusion-plasma-emitting X-rays and energetic heavy-particle beams, without the use of high-bias applications.

X-ray diagnostics for investigating electron distribution functions and electron potential confinements

Abstract X-ray radiation from the GAMMA 10 tandem-mirror plasmas is investigated so as to interpret the electron-velocity-distribution functions as well as the formation mechanism of plasma-confining potentials from the X-ray data. In particular, plasma-electron behavior in the thermal-barrier and the plug regions are highlighted. Two different shapes of the distribution functions (i.e., relativistic Maxwellian electrons and plateau-shaped electrons bounded by an electron-confining potential) characterize the barrier and the plug plasmas, respectively. For the X-ray-data analyses, we employ a new theory on the X-ray response of semiconductor detectors. In particular, it is noted that the use of this theory modifies analysis results from the conventional X-ray-response theory in textbooks, which was employed over this quarter of the century for plasma-electron-temperature analyses.