Rikio Watanabe

Investigation of space charge behavior in polyimide film during elevating temperature [spacecraft thermal blanket applications]

Spacecraft are covered by a, so-called, thermal blanket made of polyimide film to keep temperature stable in the spacecraft from drastic changes of temperature between -120 and 150/spl deg/C in the space environment. When the film is exposed to radioactive rays, like a high energy electron beam, under such a drastic change of temperature, the film may have degradation or suffered serious physical damage. To understand the interaction of electron beam irradiation on the polyimide film, we have observed the space charge formation process at room temperature using a pulsed electroacoustic method. In this paper, the decay process of space charge in electron beam irradiated polyimide film during elevating temperature was investigated, based on results obtained using simultaneous measurement of the pulsed electroacoustic method and thermally stimulated current.

Time-dependent charge distributions in polymer films under electron beam irradiation

The time-dependent charge distribution in polymer film under electron beam irradiation is studied by both experiment and numerical simulation. In the experiment, the distribution is measured with the piezoinduced pressure wave propagation method. In the simulation, the initial charge distribution is obtained by the Monte Carlo method of electron scattering, and the charge drift in the specimen is simulated by taking into account the Poisson equation, the charge continuity equation, Ohm’s law, and the radiation-induced conductivity. The results obtained show that the negative charge deposited in the polymer film, whose top and bottom surfaces are grounded, drifts toward both grounded electrodes and that twin peaks appear in the charge distribution. The radiation-induced conductivity plays an important role in determining the charge distribution in the polymer films under electron beam irradiation.

Effect of temperature and electron energy on volume resistivity of a polyimide film in a space environment

In this study, we develop a system for measuring the volume resistivity of a polyimide film in a simulated space environment and investigate the effect of sample temperature and incident electron beam energy on the volume resistivity of the film. The temperatures in the experiment range from 233 K to 353 K and are controlled by a temperature control system that uses Peltier devices. The incident electron energy is varied from 10 keV to 40 keV. The experimental results indicate that volume resistivity of the polyimide film decreases as its temperature increases in line with the Boltzmann model. The higher energy electrons penetrate deep into the experimental sample of spacecraft surface material and enhance conductivity, which results in a decrease in volume resistivity owing to radiation-induced conductivity (RIC).

Internal Charge Distributions in PTFE Film by Numerical and Experimental Analysis

The internal charge distributions in a PTFE film under electron irradiation of 20 keV and 30 keV obtained by numerical simulation and experiment are shown and compared. The numerical simulation is based on the Monte-Carlo methodology. Each electron inside the material is tracked three-dimensionally using the non-relativistic equations of motion. Collision processes between an electron and an atom consisting of PTFE (C2F4) are selected by Monte-Carlo strategy and the electron status after each collision is determined. Elastic and inelastic collision processes are both considered. The inelastic collision processes included are ionization, phonon interaction and trapping effect. The charge distribution inside the film is successfully obtained. The electric field and electric potential are also obtained. The computed results are validated through other Monte-Carlo simulation results and show good agreement except the higher positive charge due to inappropriate handling of ionization process in the present computation. The experiment utilizes an acoustic wave propagating through the specimen as a charge detector. The experimental results show the same features observed in the present computation results.

Space charge formation in glass materials after electron-beam irradiation

Charge distribution in various glass materials irradiated by electron beam was observed using PEA measurement system. Glass is used as a cover material for solar array panel of spacecraft. In space environment, the glass materials are sometimes charged up by irradiation of radioactive rays or plasma. The charging sometimes induced unexpected discharge accidents, which give serious damages to the spacecraft. Therefore, it is necessary to investigate the charge accumulation in glass materials irradiated by radioactive rays. In this experiment, we measured some kind of glasses with and without oxidized metal impurities. In the case of glass without impurity, almost no charge was observed after e-beam irradiation. On the other hand, negative or positive charge accumulations were observed in glass including oxidized metal impurities. The polarity of accumulated charge in samples irradiated by e-beam was related with the species of oxidized metal impurities.