Impact of Stark Shifts on the Radiation Cooling of Cu-Dominated Plasmas

We study the impact of Stark line shifts reported recently for Cu I transitions on the radiative cooling of Cu-dominated plasmas. The observed detuning in absorption between the hot core and cold shell of the arc leads to a reduction in radiation reabsorption compared to the case where Stark line shifts are neglected. Using a modeling based on a phenomenological treatment of the Stark line shift, we show that this reduction is below 2%

Investigation of Vacuum Arc Anode Temperatures of Cu-Cr and Pure Cu Contacts

The present contribution reports on investigations of electrode temperatures for pure Cu electrodes and Cu–Cr electrodes of different diameters exposed to vacuum arcs with sinusoidal currents of 5-15 kA and an axial magnetic field up to 180 mT. It is found that surface temperatures of pure Cu electrodes are significantly lower than for Cu–Cr electrodes of the same diameter. This must be explained by different thermal properties of both materials. Reducing the diameter of Cu–Cr electrodes it is found that surface temperatures increase, but moreover it is shown that the enthalpy stored in the electrode bulk material may effect electrode temperatures on timescales much longer than the current pulse width, particularly if there is no effective heat dissipation after current zero

Cladoc\ue8res de la r\ue9gion du lac Victoria Nyanza

Volume: 25Start Page: 77End Page: 9

Nitriding of tetragonal zirconia in a high current d.c. plasma source

Surface nitriding of tetragonal zirconia (t-ZrO2) has been performed with the aim of combining the optical properties of zirconium nitride (ZrN) with the hardness and toughening properties of tetragonal zirconia. A high current d.c. arc plasma source has been used to create a reactive environment of atomic hydrogen and NH radicals. Plasma analysis showed that a highly reductive atmosphere is necessary to transform the tetragonal zirconia. X-ray diffraction and transmission electron microscopy analysis show an efficient transformation of the t-ZrO2 at the surface which exhibits the typical yellow-gold color of ZrN and high wear resistance. For a 2 h treatment at 750 degreesC the nitriding is accompanied by the formation of a 250 nm thick gradient layer of ZrN structure and a partial transformation of t-ZrO2 into cubic zirconia deeper in the bulk. (C) 2002 Elsevier Science B.V. All rights reserved

Rapid deposition of hydrogenated microcrystalline silicon by a high current DC discharge

Microcrystalline hydrogenated silicon films (muc-Si:H) have been deposited by a high current DC plasma in argon-silane-hydrogen mixtures at growth rates up to 10 nm/s and at substrate temperatures below 500 degreesC. Scanning electron microscopy, X-ray diffraction and FTIR analyses show that these films are highly crystallized. The surface morphology depends strongly on the experimental conditions and varies from a cauliflower structure to a prismatic one. The crystalline orientation of the films also changes with the experimental conditions whereas other properties such as crystallite size, columnar growth, and crystallinity of the films remain unchanged. (C) 2001 Elsevier Science B.V. All rights reserved

A Lagrangian Approach to the Simulation of a Constricted Vacuum Arc in a Magnetic Field

The use of numerical simulations of vacuum arcs can be very useful in order to improve the performance of vacuum interrupters. Standard computational fluid dynamics methods based on the Eulerian approach have difficulties to deal with this kind of problem, so a new technique is proposed, based on a Lagrangian approach. In order to focus on the performance of the new approach and not on specific details of a full model, a simplified arc model is used to investigate the capabilities of a Lagrangian approach in the context of vacuum arc simulations. The focus of this initial study is on implementing the necessary ingredients, that is, the development of a compressible flow solver, the introduction of the relevant boundary conditions and the coupling with the current conservation equation for the electric current. In addition, the stability of such a numerical scheme is evaluated. Furthermore, comparisons with results obtained using commercial software are also provided to demonstrate the validity of the results obtained with the new methodology