Polyimides in the spacecraft equipment
Abstract—Charging of polymeric samples with grounded metal layer is studied by two main schemes of experiment. In the first scheme, a polymer film is irradiated with the low-energy electrons with energy of 20–40 keV under conditions of absence of grounded metal objects nearby. It is demonstrated that development of breakdown in the double electrical layer on the open surface of the polymer is impossible. In the second scheme, when a grounded metallic mask is placed on the surface of the polymer film in the irradiation zone, discharges are easily initiated and represent spark creeping discharges. A possible mechanism of their initiation is proposed.
Simulation of electron, ion and metastable excited atom motion and interactions in a low-current discharge between the flat electrodes of a gas- discharge device in argon-mercury mixture is fulfilled. Also influence of gas temperature on both densities and fluxes of particles has been investigated. Distributions of the particle densities along the discharge gap under different mixture temperatures are obtained. It has been demonstrated that the principal mechanism of mercury ion generation was the Penning ionization of mercury atoms by argon metastables, which contribution grows sharply with the mixture temperature due to mercury density increase. Calculations showed that both mercury and argon ion flow densities near the cathode where of the same order already under the relative mercury content of about 10-4 corresponding at the argon pressure 103 Pa to the mixture temperature 30 C. Because the mean path length of a mercury ion in the mixture between the resonant charge exchanges on parent gas atoms is much more than that of an argon ion, the energies of mercury ions exceed considerably the energies of argon ions, and they make the main contribution to the physical electrode sputtering. which reduces the service time of the gas- discharge device.
The fresh surfaces formation provided by materials destruction or cleavage often leads to surfaces charging and strong electric fields generation. These fields can create the high energy electrons beams and Bremsstrahlung radiation. For example the destruction of quartz and granite is accomplished by low intensity relativistic electron fluxes creation. However the adhesive tapes peeling is accomplished by significantly more intensive electron beams creation. These beams can provide hard irradiation of skin and other layers of biological tissues during the adhesive tapes separation. We will estimate this irradiation using the generalized diffusion model for non-relativistic electrons.
Experiments indicating acceleration of charged particles as a result of separation of solid surfaces are analyzed. As a possible mechanism of such acceleration, generation of surface charge on the separated surfaces of a cleaved ionic crystal is considered. The maximum electric field generated due to the charging of the separated surfaces and the energy of electrons accelerated in such a field are estimated. It is shown that, for the maximum attainable electric field, conditions are created for the generation of runaway electrons that, even at atmospheric pressure, electrons are accelerated to high energies, not experiencing collisions with gas particles.