Electric breakdown of a thin film of polypropylene is accompanied by emission of the electromagnetic radiation pulse of about 400 ns duration with a spectrum consisting of three main frequencies. A ...relationship between the electric resistance of the breakdown channel and observed radiation spectrum is explained.
An explanation is proposed for the difference of the electric-strength properties of polymers in dc and ac electric fields. The energy release upon the recombination of electrons and holes injected ...into a polymer dielectric is considered as a factor accelerating the processes of electric aging of these dielectrics in an ac electric field. It is shown that the nonradiative relaxation of electron excited states, which causes the bond scission in macromolecules and the formation of free radicals, leads to the formation of deep electron traps in the polymer dielectric; as a result, the macromolecule ionization in an electric field is accelerated due to the transition of electrons into these traps. In the solid-state plasma, screening effect, which decreases the molecule ionization potential, appears. As a result, the macromolecule ionization rate, i.e., the rate of charge carrier formation, increases, which leads to a decrease in the lifetime of a polymer dielectric in an ac electric field as compared to the polymer lifetime in a dc electric field.
We describe a method for producing high power, coherent x-ray pulses from a free electron laser with femtosecond scale periodic temporal modulation of the polarization vector. This approach relies on ...the generation of a temporal intensity modulation after self seeding either by modulating the seed intensity or the beam current. After generating a coherent temporally modulateds-polarization pulse, the electron beam is delayed by half a modulation period and sent into a short orthogonally oriented undulator, serving as ap-polarization afterburner. We provide simulations of three configurations for realizing this polarization switching, namely, enhanced self seeding with an intensity modulation generated by 2 color self seeding, enhanced self seeding of a current modulated bunch, and regular self seeding of a current modulated bunch. Start to end simulations for the Linac Coherent Light Source-II are provided for the latter.
In this article we present the results of time-of-flight mass spectrometry of volatile products formed during the electrical breakdown of polyethylene terephthalate and polypropylene polymer films in ...high vacuum. During the breakdown of films, all the substance emitted from the breakdown channel is a gas of low-molecular products of destruction of macromolecules. The breakdown mass spectra do not contain lines of carbon molecules, the presence of which could indicate carbonation of the channel. To explain the formation of charge carriers, the ionization mechanism of destruction of macromolecules in an electric field is used without the involvement of impact ionization. The final stage of electrical breakdown (the flow of a high-density conduction current) occurs when the critical concentration of traps and electrons ≈10
24
m
–3
is reached.
Photonic structures operating in the terahertz (THz) spectral region enable the essential characteristics of confinement, modal control, and electric field shielding for very high gradient ...accelerators based on wakefields in dielectrics. We report here an experimental investigation of THz wakefield modes in a three-dimensional photonic woodpile structure. Selective control in exciting or suppressing of wakefield modes with a nonzero transverse wave vector is demonstrated by using drive beams of varying transverse ellipticity. Additionally, we show that the wakefield spectrum is insensitive to the offset position of strongly elliptical beams. These results are consistent with analytic theory and three-dimensional simulations and illustrate a key advantage of wakefield systems with Cartesian symmetry: the suppression of transverse wakes by elliptical beams.
An explanation of the difference in the electric strengths of polymers in AC and DC electric fields has been suggested. Energy release due to the recombination of electrons and holes injected into a ...polymer dielectric is considered as a factor enhancing electrical aging of these dielectrics in AC electric field. It has been shown that nonradiative relaxation of excited electron states causes bond breaking in macromolecules with the formation of free radicals. Since the ionization energy of free radicals is lower than that of parent molecules, the charge accumulation rate in a polymer dielectric grows. As a result, its lifetime in AC electric field is shorter than in DC field.
Dielectric properties of polyvinylidene fluoride based thin films and electrospun mats have been studied. Frequency dependences of samples capacity and tangent of dielectric losses have been ...obtained. The influence of trifluoroethylene presence in copolymer on dielectric properties has been investigated. Efficiency of using deposited contacts instead of pressed contacts was considered.
It is shown that the method for the growth of conducting polyaniline nanotubes, based on the direct polymerization of aniline on the surface of channels in track membranes, can be used to produce ...nanotubes with a given conductivity. An island-type film with a channel resistance of ~10
19
Ω is formed during the initial stage of polymerization (up to 2 min). As the polymerization duration increases to 3 min, the channel resistance falls by more than 10 orders of magnitude. This is attributed to the formation of a continuous film on the channel surface, i.e., a nanotube is formed. With the polymerization duration increasing further, the channel (nanotube) resistance gradually decreases to ~10
19
Ω at 10 min. The conductivity of polyaniline during the formation of a hollow nanotube is estimated to be 0.01–0.04 S/cm. If the nanotube is completely filled with polyaniline, the conductivity increases to ~0.2 S/cm.
PDF
