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The behavior of the transient heat flux produced by a three-electrode capillary discharge generator working at a repetitive mode is presented in this paper. The radial distribution profiles of plasma temperature, electron density, and thermal load are obtained by the optical emission spectrometry and correction algorithm. Experiments with different capillary diameters and charging voltages are carried out, and the relation between the discharge characteristics and the geometry parameters of the capillary is measured. A maximum transient thermal load of 1.42 GW·m−2 is obtained with 10 Hz, which can meet the thermal load amplitude requirement of Type-I edge localized mode heat flux in the ITER-like Tokamak. [ABSTRACT FROM AUTHOR]

The formation of precursor plasma and ablation dynamics of Al thin liner explosion are investigated in this manuscript. The size of 12 mm in diameter, 10 μm in thickness Al liners are exploded on the Qin-1 facility (about 450 ns, 450 kA). An axial laser shadowgraphy and interferometry platform is set up to observe the plasma dynamics inside the liner. To solve the problem that the inside plasma density of the liner cannot be absolutely calibrated due to the lack of a zero plasma density area, we have established a CW laser interference system using a streak camera which can trace the interference lines over time. Low-density (10−7−10−6 g cm−3) precursor plasma is generated from the interior wall and flows towards the center with a velocity of about 150–200 km s−1, thus forming a column with high electron density by accumulation. Simultaneously, a high-density plasma layer flows toward the center at about 10 km s−1. The electron density of the central plasma column rises up rapidly after the precursor reaches the center and achieves 2.5 × 1018 cm−3 at 280 ns after the current starts. To fully understand the process, we have used the resistive magnetohydrodynamic code FLASH to realize a simulation to study interior precursor dynamics. We compared these simulation results with our experiments. Finally, we measured the voltage for the whole process and derived the inductance change and effective current radius. We compared the simulated current density distribution with the experimental result which proves that a considerable amount of current flows through the center plasma column, making the effective radius of current become smaller over time. [ABSTRACT FROM AUTHOR]

We investigate the evolution of the species from both the target and the air, and the plasma parameter distribution of the nanosecond laser-produced plasmas in atmospheric air. The technique used is spatially resolved optical emission spectroscopy. It is argued that the N II from the air, which is distributed over a wider region than the target species in the early stages of the discharge, is primarily formed by the shock wave. The ionized species have a larger expansion velocity than the excited atoms in the first ∼100 ns, providing direct evidence for space-charge effects. The electron density decreases with the distance from the target surface in the early stages of the discharge, and both the electron density and the excited temperature variation in the axial direction are found to become insignificant at later stages. [ABSTRACT FROM AUTHOR]

Nanosecond laser produced brass plasmas are studied at the ambient pressures of 10−3, 20, 100 and 500 Pa. Spatial and temporal dynamics of the plasmas are captured by fast photography and optical emission spectroscopy (OES). The phenomena of plasma free expansion, splitting, sharpening, and instability are observed, respectively. At different pressures and incident laser fluences, the plasma lengths are found to be in good agreement with the drag force model, and the plasma stopping distance are interpreted with the Dyer's model. By spatially resolved OES, we confirm that the excited target ions (Zn+, and Cu+) play a growing important role on the emission near plasma front with the increase of the ambient pressure. It also demonstrates that at the late time of 300 ns, there is no significant variation in the temperature distribution on axis in the explored ambient pressure range, while the electron density decreases rapidly in the near-surface region. [ABSTRACT FROM AUTHOR]

Plume splitting in low-pressure ambient air was understood in view of ion distribution dynamics from the laser ablated Al plasma (1064 nm 0.57 J/mm2) by combining fast photography and spatially resolved spectroscopy. In the beginning, the spectral lines were mainly from the Al III ion. Then, the Bragg peak in stopping power of the ambient gas to Al III could be the dominant reason for the enhanced emission from the fast moving part, and the recombination of Al III to Al I-II ions near the target surface was response to the radiations from the slow moving/stationary part. As the ambient gas pressure increased, stopping distances of the Al III decreased, and radiation from the air ions became pronounced. The laser shadowgraph image at 1100 Pa indicated that the shock wave front located between the fast moving and slow moving parts. Electron densities of the fast moving plasma, which peaked at the plasma front, were on the order of 1016 cm-3, and the electron temperatures were 2-3 eV. [ABSTRACT FROM AUTHOR]

Nuclear power overhaul can benefit from a fiber-optic laser-induced breakdown spectroscopy (FO-LIBS) setup for in situ composition measurements. Regarding FO-LIBS, the pulsed energy of the fiber-delivery laser is limited, and the spot profile received by the sample surface is distorted from a Gaussian to a flat-top distribution. Therefore, the induced plasma in FO-LIBS is characterized by weakened emission, shortened lifetime, and insufficient sampling of minor components compared with that of conventional LIBS. This could not meet the quantitative demands of the minor component with a concentration of 0.01 wt% or lower in structural steel. In this study, by modifying the mechanical structure of the front-end sensor, a space constraint condition can be created for plasma emission enhancement. By combining the optical diagnostics of fast photograph and shadowgraph, shockwave propagation and plasma expansion can be visualized synchronously. The reflected shockwave decelerates in the process of propagating towards the plasma, accompanied by morphological changes from the oblate cylinder to the hemisphere. It can be demonstrated that the plasma is constricted by the reflected shockwave associated with a significant increase in the plasma temperature and electron number density. The plate spacing determines the time delay of spectral enhancement and also determines the enhancement factor corresponding to the velocity attenuation of shockwave propagation over a long distance. The enhancement factor is found to be inversely proportional to the quadratic square of the propagation velocity of shockwave just after reflection, and shows an upward trend with increasing upper-level energy of atomic transitions. A maximum enhancement factor of ∼3.52 is realized with a time delay of 4 μs at a plate spacing of 3 mm, and trace components Mo, V, and Cu are newly recognized, which cannot be observed in conventional FO-LIBS. Meanwhile, the calibration of trace Cr and Mn suggests that the quantitative results using the sensor coupled with spatial confinement are comparable, and the limits of detection are reduced to 31 ppm and 475 ppm, respectively. [Display omitted] • Spatial confinement is firstly introduced into FO-LIBS for sensitivity improvement. • A portable FO-LIBS sensor with parallel plates is developed to restrict plasmas. • The change of plasma morphology and shockwave propagation is synchronously visual. • The spectral enhancement is in a negative quadratic correlation with plate spacing. • The method of spatial confinement promotes applicability of FO-LIBS in nuclear power. [ABSTRACT FROM AUTHOR]

• The interaction of C 4 F 7 N with α-Al 2 O 3 (0001) surface belongs to chemisorption. • The dissociation of C 4 F 7 N on α-Al 2 O 3 surface is difficult to occur. • C 4 F 7 N and α-Al 2 O 3 shows good thermal compatibility below 170 ℃. • The α-Al 2 O 3 -based materials can be used as insulators in C 4 F 7 N-filled electrical equipment. In this paper, the compatibility between C 4 F 7 N and α-Al 2 O 3 (0001) surface has been evaluated based on the density functional theory (DFT). The adsorption energy, total charge transfer, states analysis, and electron density difference were obtained to analyze the interaction behavior of C 4 F 7 N on α-Al 2 O 3 (0001) surface. The results demonstrated a chemisorption between C 4 F 7 N and α-Al 2 O 3 (0001) surface. Moreover, the pathway of C 4 F 7 N dissociated on α-Al 2 O 3 (0001) surface after the adsorption was determined. However, the activation energy required for the dissociation is too large to achieve, which means that the dissociation of C 4 F 7 N on α-Al 2 O 3 surface is difficult to occur. Additionally, the thermal compatibility between α-Al 2 O 3 and C 4 F 7 N were verified by experiments, which shows a certain compatibility between C 4 F 7 N and α-Al 2 O 3 (0001) under up to 170 ℃. The results demonstrate that α-Al 2 O 3 -based materials can be used as insulators in C 4 F 7 N-filled electrical equipment. [ABSTRACT FROM AUTHOR]

• Interaction between C4F7N and ZnO surface is stronger that on Zn surface. • The CN group shows a strong activity on the ZnO surface. • Activation energy of C 4 F 7 N dissociation on ZnO surface is higher than on Cu and Al. • Zinc shows potentials to be anti-corrosion material when using C 4 F 7 N. Recently, C 4 F 7 N has been considered as one of the most promising candidates to replace SF 6 due to its excellent insulation performance and environmental-friendly property. Metal zinc is widely used as a coating material in gas-insulated electrical equipment. However, its compatibility with C 4 F 7 N has never been explored before. In this paper, the adsorption properties of C 4 F 7 N on Zn(0 0 0 1) and ZnO(1 0 1 ¯ 0) surfaces were theoretically studied by a first-principles calculation. Adsorption energy, total charge transfer, density of states, and electron density difference were calculated to evaluate the compatibility of C 4 F 7 N with Zn and ZnO. The results demonstrated that the interaction between C 4 F 7 N and ZnO(1 0 1 ¯ 0) is stronger than that of Zn(0 0 0 1). The dissociation pathway of C 4 F 7 N after adsorption on the ZnO(1 0 1 ¯ 0) surface was also determined, which shows that ZnO(1 0 1 ¯ 0) has a catalytic effect on the decomposition process of C 4 F 7 N. Compared with Al(1 1 1) and Cu(1 1 1), the dissociation of C 4 F 7 N on ZnO(1 0 1 ¯ 0) has a higher energy barrier, indicating that the reaction is more difficult to occur. As a result, Zn and ZnO have certain compatibility with C 4 F 7 N, which was also verified by experiments. Therefore, we infer that Zn shows potentials to be used as anti-corrosion coating in C 4 F 7 N gas-insulated electrical equipment. [ABSTRACT FROM AUTHOR]