Production of wavelength-selective, time-resolved, x-ray images of a neon plasma in the SPEED 2 plasma focus

The dynamics of pinching of a neon plasma in the SPEED 2 facility has been investigated by recording wavelength-selective, x-ray images of the plasma with good space and time resolution. A series of images of the plasma focus was obtained on the λ=1.21 nm and λ=1.35 nm emission lines of hydrogen-and helium-like ions at various stages of plasma compression. The stable nature of the discharge in a neon plasma was confirmed. It was established that at the final stage of pinching, the charge of the neon ions increases rapidly from +9 to +10, and when the pinch diameter is less than 1 mm, the plasma is completely ionized. Pis’ma Zh. Tekh. Fiz. 23, 53–59 (April 26, 1997)     

Spatial-temporal pulsations of an arc plasma pinch in a plasmatron channel

The results of an investigation of the pulsation characteristics of the arc column in a plasmatron, based on a statistical analysis of emission traces, are presented.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 35, No. 6, pp. 969–971, December, 1978.     

The electron pinch lifetime in high-current rod pinch diodes

In high-current coaxial diodes with rod anode (rod pinch diodes), the current of the magnetic self-insulation in the gap is approximately two times greater than the critical magnetic insulation current (J _S ≈2 J _C ). Based on this fact, a model is proposed according to which a quasistationary electron pinch state in such diodes is explained by a change in the gap magnetic insulation conditions caused by the pinch formation. This circumstance can be used to evaluate the pinch lifetime Δt. The Δt values calculated using the oscillograms measured on the Gamble I accelerator agree satisfactorily with the values experimentally determined in a coaxial rod pinch diode.     

Thermal loads of plasma focus chambers

The passage of current through the electrodes of a plasma focus chamber is analyzed taking into account the skin effect; the thermal load on the elliptical shaped electrodes is studied in the interaction with the current-plasma sheath, calculated within the two-dimensional ideal magnetohydrodynamic model. The heating of the anode of the plasma focus chamber by the discharge current is assessed under the limit modes of operation. Signs of the thermal action of plasma particles on the electrode surface are demonstrated.     

Neutron angular distribution in a plasma focus obtained using nuclear track detectors

The dense plasma focus (DPF) is a coaxial plasma gun in which a high-density, high-temperature plasma is obtained in a focused column for a few nanoseconds. When the filling gas is deuterium, neutrons can be obtained from fusion reactions. These are partially due to a beam of deuterons which are accelerated against the background hot plasma by large electric fields originating from plasma instabilities. Due to a beam-target effect, the angular distribution of the neutron emission is anisotropic, peaked in the forward direction along the axis of the gun. The purpose of this work is to illustrate the use of CR-39 nuclear track detectors as a diagnostic tool in the determination of the time-integrated neutron angular distribution. For the case studied in this work, neutron emission is found to have a 70% contribution from isotropic radiation and a 30% contribution from anisotropic radiation.     

M2高速钢中的M_2C碳化物

本文用扫描电镜研究了 M2 高速钢中的 M_2C 碳化物及其分解产物。在铸态下,M_2C呈“扇”状、片层状或长条状分布在晶界上。在热轧材中发现了两种混合碳化物颗粒:M_6C+MC 和M_6C+MC+M_2C。在冷拔加工时,混合碳化物易被拉裂。     

Using Mather-type plasma focus device for surface modification of AISI304 Steel

A 2.8 kJ plasma focus device with a nitrogen gas filling and a copper anode capsulated by aluminum was used to modify the surface of AISI304 steel substrate, in order to improve its properties. The treatment was carried out using a various number of nitrogen plasma focus shots at a pressure of 0.5 mbar and at two steel sample distances (20 and 40 mm) from the anode. The plasma diagnostics was made using the voltage and current curves recorded by a voltage divider, Rogowskii coil, accompanied with calculations using a five phase radiative Lee model (RADPF5.15a) to determine the temperature and plasma density.The surface hardness of AISI304 steel was increased by ∼175% after plasma treatment and the thickness of the treated layers was about 1-2 μm. Results show that the surface hardness is increased with increasing shot number and decreased with increasing distance from the anode. Changes in surface morphology and the elemental composition were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX).     

Monte Carlo simulation of neutron backscattering from concrete walls in the dense plasma focus laboratory of Bologna University

Between 2001 and 2003 a 3.2 kJ dense plasma focus (DPF) device has been built at the Montecuccolino Laboratory of the Department of Energy, Nuclear and Environmental Control Engineering (DIENCA) of the University of Bologna. A DPF is a pulsed device in which deuterium nuclear fusion reactions can be obtained through the pinching effects of electromagnetic fields upon a dense plasma. The empirical scale law that governs the total D-D neutron yield from a single pulse of a DPF predicts for this machine a figure of approximately 10(7) fast neutrons per shot. The aim of the present work is to evaluate the role of backscattering of neutrons from the concrete walls surrounding the Montecuccolino DPF in total neutron yield measurements. The evaluation is performed by MCNP-5 simulations that are aimed at estimating the neutron spectra at a few points of interest in the laboratory, where neutron detectors will be placed during the experimental campaigns. Spectral information from the simulations is essential because the response of detectors is influenced by neutron energy. Comparisons are made with the simple r(-2) law, which holds for a DPF in infinite vacuum. The results from the simulations will ultimately be used both in the design and optimisation of the neutron detectors and in their final calibration and placement inside the laboratory.     

Space charge effects in a self-magnetically insulated pinch diode

Space charge effects in a self-magnetically insulated pinch diode have been studied numerically using the electromagnetic time-independent BFCPIC code (Particle-In-Cell code based on Boundary-Fitted Coordinates). The influence of the eigenfields on the electromagnetic system and in particular on the focusing properties will be discussed in detail. In the case of a bipolar flow of electrons and ions about 77% of the electrons reach the anode near the rotational axis. Due to accumulating space charge a potential hill is established in a region close to the rotational axis. The corresponding radial electric field slows down the electrons, causing them to lose most of their kinetic energy, before they are accelerated almost perpendicular to the anode. The angle between the normal to the anode and the current density of the electrons lies between 15 and 30° which is confirmed by experimental results from Maron [Phys. Rev. Lett. 45 (1980) 1849]. It will be demonstrated that the focusing properties of the pinch diode are influenced by this effect dramatically: As a consequence of the large electric field near the axis the ions from the lower region of the diode are defocused as experimentally observed by Goldstein et al. [Phys. Rev. Lett. 40 (1978) 1504].     

Image focus volume enhancement in shape from focus systems

Three-dimensional object reconstructions is an active research area in digital imaging. In shape from focus approach, erroneous focus measurements result in inaccuracy in the depth map reconstruction of 2D object. Conventionally, to enhance the image focus volume, focus values are aggregated within a window, which is a linear filtering approach. Owing to the inherent limitation of linear process, optimal results may not be obtained. In order to overcome this limitation, a non-linear filtering approach is proposed to enhance the image focus volume for accurate depth estimation. The noisy focus values are restored in two steps. First, noisy focus values are detected using min–max operators. In order to increase the dynamic range between the minimum and the maximum focus values within the window, an appropriate power law function is designed. In second step, only the noisy measurements are replaced with the estimated ones. A refined depth map is obtained from the updated focus volume. This process continues until the difference between the previous and the current depth maps becomes very small. The performance of the proposed non-linear filtering approach is obtained for various synthetic and real objects. The results highlight the depth map estimates of the proposed approach more accurate while preserving object edges. Comparative analysis demonstrates the effectiveness of the proposed approach.     

Maoris in focus

Abstract

The virtually simultaneous announcement of the invention of photography in Paris and London in January 1839 marks the “official” birthday of the new technology. The reception given to this announcement in the course of that year, and the subsequent diffusion of knowledge and practice of the technology, show significant differences from country to country. These differences in impact and the rate of take-up may have depended on such factors as the country's proximity to the key events, its level of intellectual openness and general economic development, as well as the ex~stence of key individuals — businessmen and scientists — willing to experiment in the untried processes out of sheer curiosity or for personal gain.     

硼对M2高速钢凝固组织的影响

研究了微量硼对Ｍ２高速钢的凝固组织以及热处理过程中共晶碳化物团球化的影响及其机理。发现,硼促进层片状Ｍ２Ｃ碳化物的形成;促进共晶碳化物的偏析,使碳化物量增加,层片变粗;促进共晶碳化物在高温加热时的断网和团球化,在高速钢中硼主要偏聚在晶界共晶碳化物上。     

A review of shape and size considerations in pinch grips

In handgrip-related studies, it has been theorised that modifying the design of object shapes and sizes to accommodate the hand can reduce risks of cumulative trauma disorders (CTDs). However, there appears to be a lack of theoretical groundwork to support this premise in the area of pinch grip research. Therefore, this article aims to provide a review of shape and size considerations in pinch grips. The literature reviews were first conducted individually on shape, size and pinch grip factors, followed by the development of a literature summary based on the theoretical connections among shape, size and pinch grips. Though further studies are still required, this review has provided fundamental knowledge on possible theoretical connections among shape, size and pinch grip factors. These preliminary efforts shed light on potential mechanisms that explain how shape and size can influence pinch grips towards preventing CTDs and maximising the human performance.     

New perspective on nano-porous gallium nitride formation on p-type silicon with plasma focus device

For the first time, the formation of nano-porous (NP) gallium nitride (GaN) on p-type silicon (Si) (100) substrate with the plasma focus device was observed. Four and six main plasma focus shots with GaN as the target on the Si substrate were applied. Subsequently, two shots of nitrogen plasma without the GaN target were applied to both of the Si surfaces. Then the substrates were gone through a 1050°C nitrogen treatment by a thermal chemical vapor deposition (TCVD) device. Field emission scanning electron microscopy and atomic force microscopy indicated NP structures on the surface of the substrates. With the increase in the amount of shots, thicker and rougher NP structures were formed. Additionally, X-ray diffraction shows GaN polycrystalline formation on the surface with the energy-dispersive X-ray spectroscopy, indicating that there was nitrogen deficiency on the Si substrates.     

An improved design of Faraday cup detector to reduce the escape of secondary electrons in plasma focus device by COMSOL

Faraday cup (FC) is a beamline diagnostic which is used to measure the total charge of pulsed beams. The reliable operation of an FC depends on its ability to recapture the ejected electrons when energetic particles strike with interior cup(IC) of an FC. In this paper COMSOL multi-physics software is used to investigate the performance of two new proposed FCs. The FC with A = 40 mm and B = 98 mm had better efficiency in contrast with traditional FC geometries.     

An improved design of Faraday cup detector to reduce the escape of secondary electrons in plasma focus device by COMSOL

Faraday cup (FC) is a beamline diagnostic which is used to measure the total charge of pulsed beams. The reliable operation of an FC depends on its ability to recapture the ejected electrons when energetic particles strike with interior cup(IC) of an FC. In this paper COMSOL multi-physics software is used to investigate the performance of two new proposed FCs. The FC with A = 40 mm and B = 98 mm had better efficiency in contrast with traditional FC geometries.