Ikuya Sakurai

Gas Slit Camera (GSC) onboard MAXI on ISS

The Gas Slit Camera (GSC) is an X-ray instrument on the MAXI (Monitor of All-sky X-ray Image) mission on the International Space Station. It is designed to scan the entire sky every 92-minute orbital period in the 2‐30 keV band and to achieve the highest sensitivity among the X-ray all-sky monitors ever flown so far. The GSC employs large-area position-sensitive proportional counters with the total detector area of 5350 cm 2 . The on-board data processor has functions to format telemetry data as well as to control the high voltage of the proportional counters to protect them from the particle irradiation. The paper describes the instruments, on-board data processing, telemetry data formats, and performance specifications expected from the ground calibration tests.

Performance of the GSC engineering counter for MAXI/ISS

We are developing Monitor of All Sky X-ray Image (MAXI) which will be mounted on the Japanese Experiment Module of the International Space Station. MAXI is an all-sky X-ray monitor which scans the sky in every 90 minutes. The sensitivity will be as high as 7 mCrab (5 (sigma) level) in one scan and 1 mCrab in one-week accumulation. The GSC (Gas Slit Camera) instrument consists of twelve one-dimensional position sensitive proportional counters using the Xe++CO2 gas and the carbon fiber anodes of 10micrometers diameter. The window size is 272 x 190 mm. The position is obtained by the charge division method. It is used to identify the source in the long rectangular field-of-view (1.5 x 80 degrees). Three cameras will be set to cover the 1.5 x 160 degrees arc. The position resolution is essentially important, which becomes better in the higher gas gain. We have tested gas mixtures of Xe+CO2with CO2 equals 0.2\%, 0.5\%, 1\%, 3%. The CO2 equals 0.5\% showed the most uniform gas gain, but has a little after pulses. We chose the Xe (99%) + CO2 (1%) combination for the flight counters. It can achieve the uniform gas gain in the cell and negligible after-pulse in high operating voltage. The engineering model of the counter (EM1) was build. We have tested the position resolution and the energy resolution across the counter. The position resolution and the energy resolution depend on the X-ray energy. On the basis of these results, together with the collimator response, we performed a realistic simulation.

DIOS: the diffuse intergalactic oxygen surveyor: status and prospects

DIOS (Diffuse Intergalactic Oxygen Surveyor) is a small scientific satellite with a main aim for the search of warm-hot intergalactic medium using redshifted OVII and OVIII lines. The instrument will consist of a 4-stage X-ray telescope and an array of TES microcalorimeters with 256 pixels, cooled with mechanical coolers. Hardware development of DIOS and the expected results are described. Survey observations over about 5° x 5° area will reveal new filamentary structures. DIOS will be proposed to the 3rd mission in JAXAs small satellite series in 2011, aiming for launch around 2016 if it will be selected.

Fine-pitch and thick-foil gas electron multipliers for cosmic x-ray polarimeters

We have produced various gas electron multiplier foils (GEMs) by using laser etching technique for cosmic X-ray polarimeters. The finest structure GEM we have fabricated has 30 μm-diameter holes on a 50 μm-pitch. The effective gain of the GEM reaches around 5000 at the voltage of 570 V between electrodes. The gain is slightly higher than that of the CERN standard GEM with 70 μm-diameter holes on a 140 μm-pitch. We have fabricated GEMs with thickness of 100 μm which has two times thicker than the standard GEM. The effective gain of the thick-foil GEM is 104 at the applied voltage of 350 V per 50 μm of thickness. The gain is about two orders higher than that of the standard GEM. The remarkable characteristic of the thick-foil GEM is that the effective gain at the beginning of micro-discharge is quite improved. For fabricating the thick-foil GEMs, we have employed new material, liquid crystal polymer (LCP) which has little moisture absorption rate, as an insulator layer instead of polyimide. One of the thick-foil GEM we have fabricated has 8 μm copper layer in the middle of the 100 μm-thick insulator layer. The metal layer in the middle of the foil works as a field-shaper in the multiplication channels, though it slightly decreases the effective gain.

Synthesis of metallic nanoparticles through X-ray radiolysis using synchrotron radiation

The potential to fabricate metallic nanoparticles directly on silicon substrates from liquid solutions is ideal for three-dimensional lithography systems, drug delivery materials, and sensing applications. Here, we report the successful synthesis of Au, Cu, and Fe nanoparticles from the corresponding liquid solutions [gold(I) trisodium disulphite, copper(II) sulfate, and potassium ferricyanide] by synchrotron (SR) X-ray irradiation. The deposition of gold nanoparticles in the gold(I) trisodium disulphite solution was performed by monochromatic X-ray exposure from synchrotron radiation. The use of ethanol as an additive enabled the nucleation and growth of Cu particles, while no Cu particles were produced in the copper sulfate solution without ethanol with polychromatic SR X-ray irradiation. Fe particles were generated by direct polychromatic SR X-ray irradiation. These results demonstrate the behavior of three-dimensional printers, enabling us to build composite material structures with metallic and plastic materials.

Observational response of MAXI onboard ISS

The current status is reported of the development of Monitor of All-sky X-ray Image and the measurement of its observational response. MAXI is a scanning X-ray camera to be attached to the Japanese Experiment Module of the International Space Station in 2008. MAXI is mainly composed of two kinds of instruments, GSC which is sensitive to the 2 - 30 keV photons, and SSC to the 0.5 - 10 keV ones. As an X-ray all-sky monitor, MAXI has an unprecedented sensitivity of 7 mCrab in one orbit scan, and 1 mCrab in one week. Using the engineering mode of the proportional counter and of the collimator for GSC, the observational response of GSC is extensively measured. The acceptable performances are obtained as a whole for both the collimator and the counter. The engineering models of the other part of MAXI are also constructed and the measurement of their performance is ongoing.

Development of cosmic x-ray polarimeter

We present a performance study of a cosmic X-ray polarimeter which is based on the photoelectric effect in gas, and sensitive to a few to 30 keV range. In our polarimeter, the key device would be the 50 μm pitch Gas Electron Multiplier (GEM). We have evaluated the modulation factor using highly polarized X-ray, provided by a synchrotron accelerator. In the analysis, we selected events by the eccentricity of the charge cloud of the photoelectron track. As a result, we obtained the relationship between the selection criteria for the eccentricity and the modulation factors; for example, when we selected the events which have their eccentricity of > 0.95, the polarimeter exhibited with the modulation factor of 0.32. In addition, we estimated the Minimum Detectable Polarization degree (MDP) of Crab Nebula with our polarimeter and found 10 ksec observation is enough to detect the polarization, if we adopt suitable X-ray mirrors.

Spectroscopic Studies on Impurity Transport of Core and Edge Plasmas in LHD

Spectroscopic diagnostics have been extensively developed for studies of impurity and neutral particle transports at core and edge plasmas in LHD. Diagnostics of core plasmas are similar to a tokamak case, i.e., Zeff from visible bremsstrahlung, K-x-ray measurements from x-ray spectroscopy using Si(Li) detectors and a compact crystal spectrometer, and high-Z impurity diagnostics from VUV spectroscopy using a flat-field EUV spectrometer. A combination of impurity pellet injection and visible bremsstrahlung is an active tool for determination of the diffusion coefficient D and convective velocity V. Using this tool the spatial structures of D and V are obtained and discussed with a neoclassical effect. On the other hand, the spectroscopic method for edge diagnostics is considerably different from the tokamak case because of the existence of a thick ergodic layer in addition to the x-points necessarily included into the diagnostic chord view. In order to break this negative situation, Zeeman and polarization spectroscopy are adopted to LHD edge plasmas. As a result, 2-dimensional emission contours of HeI and Hα are successfully obtained. Laser absorption spectroscopy is tried to measure hydrogen neutrals directly. Radial profiles of edge impurities are also measured with a mirror-assembled 3 m VUV spectrometer. Recent results of and progress in LHD spectroscopy are briefly reviewed.

Monitor of All-sky X-ray Image (MAXI)

Monitor of All-sky X-ray Image (MAXI) is the first astrophysical payload which will be mounted on the Japanese Experiment Module (JEM) Exposed Facility of International Space Station (ISS) in 2008. It is designed for monitoring all-sky in the X-ray band by scanning with slat collimators and slit apertures. Its angular resolution and scanning period are 1arc degree and 90 minutes, respectively. MAXI employs two types of X-ray camera. One is Gas slit Camera (GSC), the detectors of which are one-dimensional position sensitive proportional counters. Its position resolution is 1.0 mm along carbon anode wires. GSC covers the 2.0-30keV energy band. The other camera is Solid-state Slit Camera (SSC). We employ a pair of SSCs, each of which consists of sixteen CCD chips. Each CCD has 1024x1024 pixels, and each pixel is 24x24 micrometers. The CCDs are to be operated at -60 degree using Peltier coolers. SSC covers an energy range of 0.5-10.0keV. PDR is finished in September 2001. CDR will be performed in September 2003. The continuous Ethernet down link will enables us to alert the astronomers in all over the world to the appearance of X-ray transients, novae, bursts, flares etc. MAXI cannot only monitor Galactic and extra-galactic variable X-ray sources, but also this mission can produce simultaneous observations for variable sources such as BL Lac objects with various institutes. In this paper we will report on the current status of the MAXI mission. pp. 2771–2774 c ©2003 by Universal Academy Press, Inc.

The X-ray CCD camera of the MAXI experiment on the ISS/JEM

Abstract Monitor of All-sky X-ray Image (MAXI), is the X-ray observatory on the Japanese experimental module (JEM) Exposed Facility (EF) on the International Space Station (ISS). MAXI is a slit scanning camera which consists of two kinds of X-ray detectors: one is a one-dimensional position-sensitive proportional counter with a total area of ∼5000 cm 2 , the Gas Slit Camera (GSC), and the other is an X-ray CCD array with a total area of ∼200 cm 2 , the Solid-state Slit Camera (SSC). The GSC subtends a field of view with an angular dimension of 1°×180° while the SSC subtends a field of view with an angular dimension of 1° times a little less than 180°. In the course of one station orbit, MAXI can scan almost the entire sky with a precision of 1° and with an X-ray energy range of 0.5–30 keV. We have developed the engineering model of CCD chips and the analogue electronics for the SSC. The energy resolution of EM CCD for Mn Kα has a full-width at half-maximum of ≃182 eV. Readout noise is ≃11 e − rms.