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The sliding electrical contact (SEC) between rails and armature is a focus in electromagnetic rail launchers. The extreme conditions, such as high current density, high temperature, and high contact pressure, influence SEC performance. In this article, the segmented rails were used to study the effects of launch mass on SEC. Two groups of experiments, armatures with and without launch mass, were carried out. The mass difference of rail parts was measured, the macro- and micromorphology of rails surface were observed, and the driving current and muzzle voltage were obtained. Three conclusions are obtained: 1) the mass difference of rail parts in shooting with launch mass is greater than that without launch mass, due to the high temperature of armature contact surfaces; 2) because of the electron migration, the mass difference of the cathode rail is larger than the anode rail; and 3) the contact resistance between rails and armature without launch mass is lower than that with launch mass, result from the large contact area. Moreover, the current density and the temperature of the armature and rails were calculated. Results show that the temperature of surface of armature with launch mass is higher than that without launch mass. In a word, based on the results from experiments and simulations, the launch mass improves the sliding electric contact performance. [ABSTRACT FROM AUTHOR]

Armature ejecta, which erodes the insulator and reduces surface dielectric strength, has been considered as a threat to solid-armature launchers. Two series of experiments were carried out in a small caliber launcher (SCL) to investigate the sources of armature ejecta and degradation mechanisms of the insulator. In first series of experiment, the ejection of armature was imaged by a high-speed camera. The influence of linear current density on ejection was studied in second series of experiment. Mass difference of insulator samples was used to evaluate the output of armature ejecta. Insulation performance was judged from the surface flashover voltage. And the degradation mechanism resulted from armature ejecta was analyzed based on the process of surface flashover. Results show that the local breakdown at armature–rail interfaces is one of the sources of armature ejecta. The amount of ejecta on samples increased with linear current density. Average flashover voltages decreased when ejecta increased in Zone A (0–200 mm) and Zone B (200–600 mm). And there was little difference of average flashover voltages in Zone C (600–900 mm). The discharge channel of the post-shot sample was composed of arcs and ejecta. The distortion of the surface electric field and the shorten of creepage distance are degradation mechanisms of bore insulators in solid-armature launchers. [ABSTRACT FROM AUTHOR]

Muzzle arc is a general phenomenon when the armature leaves the muzzle, and it is also a reason for the complexity of intermediate ballistic of electromagnetic launchers. In this article, a 3-D model has been developed to investigate muzzle arc flow field in a smaller caliber launcher. The coupled interaction of electromagnetic, flow, and thermal fields is realized by the magnetohydrodynamic (MHD) theory in conjunction with a renormalization group (RNG) $k$ - $\varepsilon $ turbulence model. The arc boundary conditions, arc root radius, and time-dependent current density are reasonably set on the basis of the experimental data and physical process. Simulation results reveal the relationship between muzzle arc and muzzle voltage. The rising edge of muzzle voltage corresponds to the arc expansion stage. The falling edge corresponds to the muzzle breakdown stage. And the turning point from rising edge to falling edge is the moment of muzzle breakdown. The flat section corresponds to the arc extinguishing stage. The muzzle blowback is the consequence of the arc expansion which produces a compression wave moving toward the breech. The velocity of blowback flow decreases from 670 to 270 m/s during the arc expansion stage. Then, it increases to about 350 m/s and tends to be stable due to the muzzle breakdown. [ABSTRACT FROM AUTHOR]

The blowback caused by the separation of rail and armature at muzzle is an important factor for the degradation of bore insulator. A small caliber launcher was modified by the transparent material of polycarbonate for capturing the process of blowback in inner bore with a high-speed camera. Three groups of experiments with the same peak linear current density and various muzzle currents were carried out. Nesting insulator samples were used to reduce the measurement error in cutting samples after experiments. Insulation performance of postshot samples was conducted from surface morphology, surface flashover voltage, and partial surface conductivity. Results show that the effects of blowback are related to muzzle current. With the increases of muzzle current, the average flashover voltage of samples in the region of 300–600 mm (600–900 mm) decreases from 9.98 kV/cm (5.37 kV/cm) to 3.59 kV/cm (3.01 kV/cm). Moreover, the number of samples that the flashover voltage is less than 9 kV/cm (half value of the original samples) increases from 7 to 12, which indicates that the damage area caused by blowback is gradually expanding with the muzzle current. Correspondingly, the partial surface conductivity of samples in 300–900 mm region increases with muzzle current. The increase of surface conductivity should be the main reason for the sharply decrease of surface flashover voltage. [ABSTRACT FROM AUTHOR]

As an important part of pulsed high-current launcher, insulator takes the functions of electrical insulation and support. Surveys were conducted after multishot to analysis matrix damage and insulation performance of insulator based on a medium-caliber and high linear current density launcher. Mechanical damage of matrix is mainly related to local current. The most serious damage located at zone of flattop and initial decline stage. In addition, serious damage may be caused by sprayed molten aluminum rather than high-temperature plasma. Metal contamination is dominated by local current and contact condition of rail–armature. There are more metal deposits on surface of high current and high muzzle voltage zones, and corresponding flashover voltages decrease significantly. Considering the effect of different damage forms and the operation conditions, the main damage form is matrix ablation located at the contact position of rail–insulator rather than the degradation of electrical insulation. Moreover, the main damage form of bore insulators is different for variety of caliber and linear current density launchers. Insulation damage may be considered mainly in small-caliber and low linear current density launcher, while mechanical damage may be considered mainly in large-caliber launcher and high linear current density launcher. [ABSTRACT FROM AUTHOR]

Surface modification of polytetrafluoroethylene (PTFE) is performed by nitrogen ion implantation for improving the PTFE surface flashover voltage in vacuum. In this paper, nitrogen ions are produced by an electron cyclotron resonance ion source. The properties of the samples are investigated with X-ray photoelectron spectroscopy, electrometer, microhardness tester, surface potential measurement, and surface flashover system. The Stopping and Range of Ions in Matter software is used to simulate the ion implantation. Experimental results show that the surface flashover voltage of treated samples improves remarkably and increases with the injection energy. After ion implantation, the content of fluorine in the treated samples decreases, and the content of oxygen increases. The surface conductivity increases from $1.15\times 10^{{-15}}$ to 1.36 10−13 S/m, the surface potential decreases faster, and the trap density and energy increase with the implantation energy. The process of electron avalanche and the accumulation of surface charges have been suppressed, thus hindering the development of flashover and improving the surface flashover voltage. [ABSTRACT FROM AUTHOR]

The light-emitting diode (LED) is the major source of nonlinearity in LED communication systems, which needs to be carefully handled to avoid significant performance degradation. Post-distortion is an effective and convenient way to compensate the nonlinear distortion at the receiver side. In this letter, we propose a soft-in-soft-out (SISO) post distorter, which works with an SISO decoder iteratively by exchanging log-likelihood ratios of the coded bits at the receiver. It is demonstrated that the proposed iterative technique can achieve a remarkable performance gain compared to the conventional post-distortion technique in the literature. [ABSTRACT FROM AUTHOR]

The light-emitting diode (LED) is the major source of nonlinearity in LED communications, and the nonlinearity needs to be effectively modeled and mitigated to avoid the degradation of communication performance. In indoor LED communications, multipath dispersion can lead to inter-symbol interference (ISI) at high data rates. In this paper, we jointly estimate the LED nonlinearity and ISI channel based on an orthogonal polynomial based technique. Then, frequency domain equalization and post-distortion are adopted to mitigate the ISI and nonlinearity. Simulation results are provided to demonstrate the effectiveness of the proposed technique. [ABSTRACT FROM AUTHOR]

Insulators between conductive rails assume a leading role in electrical insulation and support fixation. Failure of insulating materials during continuous repetitive launches has been found in experiments, the performance changes of insulators will directly affect efficiency and lifetime in repetitive electromagnetic launcher system. Many factors may influence the insulating performance because of complicated working condition, such as strong pulse stress and high temperature. A multishot minor-caliber launcher was designed for the study of the insulating performance. The length of the launcher is 890 mm with a caliber size of 10~\text mm \times 10 mm. C-shaped aluminum alloy armatures and glass-reinforced polymer insulator G10 are used. The muzzle speed is above 2 km/s. After the multishot experiments, the surface topography and surface resistivity of the insulators were measured by megger and digital microscope. The experimental and testing results show that the surface resistivity of G10 reduces gradually with the increase of experiment times, also the surface resistivity of different locations changes. Some pits and cracks appear at individual locations on the G10 surface, the phenomena of resin wear and fiber exposed are observed. Metal deposition is also found on the insulator surface by different types at different positions. Surface flashover voltage is measured after ablation. [ABSTRACT FROM AUTHOR]

The light-emitting diode (LED) is the major source of nonlinearity in LED communications, and the nonlinearity needs to be effectively modeled and thereby mitigated through predistortion or postdistortion to avoid degradation of communication performance. A memory polynomial is often used for LED nonlinearity modeling and mitigation in the literature. However, the estimation of memory polynomial coefficients suffers from numerical instability, resulting in inaccurate modeling and poor performance in nonlinearity mitigation. In this paper, we propose an orthogonal polynomial-based nonlinearity modeling and mitigation technique for LED communications with pulse amplitude modulation (PAM) signaling and show that the proposed technique significantly outperforms the conventional memory polynomial-based techniques. [ABSTRACT FROM PUBLISHER]