Hideki Koshiishi

Total dose orbital data by dosimeter onboard Tsubasa (MDS-1) satellite

The total dose data from a Tsubasa (MDS-1) satellite, flying in a highly eccentric orbit, is analyzed. The total dose is measured by the small dosimeter using RADFETs. The RADFETs have been calibrated with the Co60 gamma ray source, and 56 devices (denoted DOS-S) were mounted in several experimental modules in the satellite. The total dose data behind certain Aluminum shield domes have been analyzed initially. The total dose change is affected by electron flux in the thin shield. In thicker shield, electron and proton affect the total dose profile.

Magnetic fluctuations embedded in dipolarization inside geosynchronous orbit and their associated selective acceleration of O+ ions

We study magnetic fluctuations embedded in dipolarizations in the inner magnetosphere (a geocentric distance of ≤6.6 RE) and their associated ion flux changes, using the Engineering Test Satellite VIII and Active Magnetospheric Particle Tracer Explorers/CCE satellites. We select seven events of dipolarization that occur during the main phase of magnetic storms having a minimum value of the Dst index less than −40 nT. It is found that (1) all of the dipolarization events are accompanied by strong magnetic fluctuations with the major frequency close to the local O+ gyrofrequency; (2) the magnetic fluctuations appear with significant amplitude in the component nearly parallel to the local magnetic field; (3) the strong flux enhancement is seen in the energy range of 1–10 keV only for O+ ions. In terms of frequency and dominant components of the magnetic fluctuations, they are considered to be excited by the drift-driven electromagnetic ion cyclotron (EMIC) instability that is recently identified with the linear theory. We perform particle tracing for H+ and O+ ions in the electromagnetic fields modeled by the linear dispersion relation of the drift-driven EMIC instability. Results show that the O+ ions are accelerated to the energy range of 0.5–5 keV and undergo a significant modification of the spectral shape, while the H+ ions have no clear change of spectral shape, being consistent with the observations. We therefore suggest that the electromagnetic fluctuations associated with the dipolarizations can accelerate O+ ions locally and nonadiabatically in the inner magnetosphere. This selective acceleration of O+ ions may play a role in enhancing the O+ energy density in the storm time ring current.

CHROMOSPHERIC SUNSPOTS IN THE MILLIMETER RANGE AS OBSERVED BY THE NOBEYAMA RADIOHELIOGRAPH

We investigate the upper chromosphere and the transition region of the sunspot umbra using the radio brightness temperature at 34 GHz (corresponding to 8.8-mm observations) as observed by the Nobeyama Radioheliograph (NoRH). Radio free-free emission in the longer millimeter range is generated around the transition region, and its brightness temperature yields the regions temperature and density distribution. We use the NoRH data at 34 GHz by applying the Steer-CLEAN image synthesis. These data and the analysis method enable us to investigate the chromospheric structures in the longer millimeter range with high spatial resolution and sufficient visibilities. We also perform simultaneous observations of one sunspot using the NoRH and the Nobeyama 45-m telescope operating at 115 GHz. We determine that 115-GHz emission mainly originates from the lower chromosphere while 34-GHz emission mainly originates from the upper chromosphere and transition region. These observational results are consistent with the radio emission characteristics estimated from the current atmospheric models of the chromosphere. On the other hand, the observed brightness temperature of the umbral region is almost the same as that of the quiet region. This result is inconsistent with the current sunspot models, which predict a considerably higher brightness temperature of the sunspot umbra at 34 GHz. This inconsistency suggests that the temperature of the region at which the 34 GHz radio emission becomes optically thick should be lower than that predicted by the models.

MULTIWAVELENGTH OBSERVATION OF ELECTRON ACCELERATION IN THE 2006 DECEMBER 13 FLARE

We present a multiwavelength observation of a solar flare occurring on 2006 December 13 with Hinode, RHESSI, and the Nobeyama Radio Observatory to study the electron acceleration site and mechanism. The Solar Optical Telescope (SOT) on board Hinode observed elongated flare ribbons, and RHESSI observed double-footpoint hard X-ray (HXR) sources appearing in part of the ribbons. A photospheric vector magnetogram obtained from SOT reveals that the HXR sources are located at the region where horizontal magnetic fields change direction. The region is interpreted as the footpoint of magnetic separatrix. Microwave images taken with the Nobeyama Radioheliograph show a loop structure connecting the HXR sources. The brighter parts of the microwave intensity are located between the top and footpoints of the loop. We consider these observations as evidence of electron acceleration near the magnetic separatrix and injection parallel to the field line.

Compact, lightweight spectrometer for energetic particles

We have developed an energetic particle spectrometer called a standard dose monitor (SDOM) that can discriminate and analyze the energy of electrons, protons, and alphas. SDOMs unique characteristics include a large G-factor, a wide energy range, and the ability to simultaneously identify and analyze the energy of multiple particle types. We plan to use this instrument to update current space radiation environment models.

Compact Energetic Light Particle Detector and Spectrometer

We have developed a megaelectron-volt class energetic charged-particle spectrometer based on a novel configuration and processing algorithm. The National Space Development Agency of Japan has undertaken a program to develop a particle monitor capable of discriminating and measuring protons in the range from 0.9 to 150 MeV, electrons in the range from 0.5 to >10 MeV and alpha particles >8 MeV, all within a single sensor called the standard dose monitor. The goal is to utilize sensors with nearly identical design and performance on several simultaneous missions to develop a clearer understanding of particle energies and their variability as a function of solar activity, latitude, and altitude. To date, four flight model sensors have been delivered. The sensors are designed to detect accurately the higher-energy particles and high count rates present during active solar periods. In addition, this sensor exhibits extremely efficient discrimination between low-energy electrons and protons. The sensors have been calibrated over nearly their entire particle-energy range. The design is described and calibration data are compared with the results of a Monte Carlo sensor performance model.

HELIUM ISOTOPES IN THE RADIATION BELTS OBTAINED BY HIT ONBOARD TSUBASA

The helium isotopes were observed by Heavy Ion Telescope (HIT) onboard the TSUBASA satellite from March, 2002 to September, 2003 in the geostationary transfer orbit. The mass resolution of the HIT instrument is ~ 0.25 amu in energy range 20÷43 MeV/nucleon for helium isotopes. Helium data in the quiet periods were analyzed to obtain the spatial and temporal variation of fluxes of helium isotopes, 3He and 4He. From this analysis, the enhancement of 3He flux as compared with 4He one in low L-value was found. Both of the helium fluxes strongly fluctuated in their L-distributions in each period.

Development of semiconductor sensor as a use for pulsed electro-acoustic method

In this report, we study of fundamental research for a high positional resolution of pulse electro-acoustic (PEA) method. Positional resolution of PEA method depends on a pulse width of the applied pulse voltage and a traveling time of the acoustic signal through a piezo electric sensor. Our laboratory tried to develop a thin sensor using the polyvinylidene fluoride (PVDF). Consequently, we succeeded in developing a measuring device with a position resolution of ca. 2.5 μm using thin PVDF sensor which is 1 ßm thick. However, since PVDF is polymer material, which is difficult to form a film thinner than under 1 ßm. So, we focused on a depletion layer in semiconductor as a sensor material for further improvement of the sensor. The depletion layer is formed at the contact interface with the semiconductor and the metal. Which have space charge distribution inside, and it distribution is similar to an electric dipole. So we expect to apply the depletion layer for sensor. In this report, we tried to measure the space charge distribution of the depletion layer which is formed by contact a silicon substrate to an aluminum electrode. As a result, we succeeded in measuring the space charge distribution of depletion layer.

Studies of correction methods for influences from space environment on observation of radiation dose in space

Observation of radiation dose in space by using semiconductor devices is advantageous in terms of compactness, small power consumption, and structural simplicity. However, data sets obtained by these devices tend to have errors due to annealing effect and temperature variation, leading ambiguities in evaluations and models of space radiation environment used in spacecraft design. These errors can be briefly corrected by data processing. The correction makes temporal variation of radiation dose rate more clear and total radiation dose more accurate.

Space Weather Mission of SmartSat Program

The SmartSat Program is a collaborative program of government agency (NICT,JAXA) and private sector (MHI) in Japan to develop small satellite about 200 Kg. The space weather experiment of the SmartSat consists of Wide Field CME Imager (WCI), Space Environment Data Acquisition Equipment (SEDA), and mission processor (MP). Both of the instruments will be principal components of the L5 mission. WCI is a imager to track CME as far as earth orbit. CME brightness near earth orbit is expected 1E‐15 solar brightness or 1/200 of zodiacal light brightness. To observe such a extreme faint target, we are developing wide field of view camera with very high sensitivity and large dynamic range. These highly challenging experiment and demonstration will be implemented in SmartSat program.