The aim of this paper is to provide data on the influence of the geometry of the fins on the acceleration performance of a ram accelerator projectile in the subdetonative mode. The data that are presented in this paper are derived from a non reacting computation performed at the French Research Institute (ISL) with the commercial numerical code TascFlowTM from AEA Technology. This code calculates the pressure and temperature profiles in a non-reactive flow around the ram accelerator projectile. Three types of projectiles were studied with respectively three, four and five fins. Furthermore, different fin geometries were studied. The wall temperature behavior was investigated, in order to explain the high erosion of the projectile that is observed as the projectile comes out of the tube. Moreover, the high temperatures that were derived from the calculation explain the initiation process of the reactive at some point of the projectile, which, in turn, explains the unstart process. These calculations were conducted during ram accelerator operations at ISL and were used to explain some effects observed on the experimental data obtained in both the 30-mm and 90-mm caliber facilities.

In this paper, we report the results on the influence of a top oxide layer on the He-cavity formation in silicon samples. Si samples with top oxide layers of different thickness together with the pure silicon (used as reference) were implanted at room temperature with 1 MeV 3He at a dose of 5 × 1016 He/cm2. After implantation, the oxide layer was removed by using HF solution. Cross-sectional transmission electron microscopy (XTEM) was used to study the induced cavities followed by annealing. The results show that He implantation induces a well-defined-damaged layer with a thickness of about 180 nm in the reference Si. The defects are mainly made up of big cavities in the middle of the projected range and a large population of smaller ones both towards the surface and into the bulk. Very few stacking faults and dislocations loops can be seen around this band. The creation of cavities in Si with a 2.3 μm oxide layer, however, is a little different. Regions containing a chain of the biggest cavities surrounded by few smaller ones have also been found. Unexpected results are obtained in Si with a 1.2 μm oxide layer. In this case, only a monolayer of big cavities is observed at the depth corresponding to the projected range. The results are discussed in combination with SIMS measurements and SRIM simulations.

Nanostructured ferrites have been prepared by milling starting from commercial ferrite powders. Subsequent compaction and sintering were applied to obtain cylindrical pieces. The magnetization as a function of the grain size follows the non magnetic grain boundary (NMGB) model. The boundary thickness is estimated as about 1.5 nm, which is consistent with that calculated from the Mössbauer absorption areas. Due to the high lattice distortion, the small exchange length impedes the averaging of the anisotropy.

This paper describes how to forecast copper losses in a bus bar, composed of thin copper layers and several access points. The main difficulties are, first to determine current path and associated electrical characteristics, and second to propose electrical equivalent circuits of the bus bar, allowing copper losses representation. For bus bar electrical modeling, the choice of an integral method, PEEC method, is justified. Then, several equivalent circuits are proposed and their validity for copper losses computation discussed.

In the frame of the thermal step method (TSM) used to characterize the space charge in dielectric materials, we present an original numerical technique for determining the electric field distribution in the bulk of a dielectric plate or cable. The first stage of our technique is the application of the finite element method (FEM) in order to find instantaneous distributions of temperature profiles. The calculation of the electric field distribution is based on these obtained profiles. During the stage of the determination, our mathematical treatment is based on the TSM charge q(t) in order to avoid numerical instabilities on the temperature derivatives. Therefore, we have transformed the integral equation for the TSM current I(t) used in previous works to an integral equation for the TSM charge q(t). The control of the instantaneous propagation of the thermal wave front, produced by submitting one face of the dielectric to a thermal step, and the application of Simpson's method to the integral equation of the TSM charge q(t), allow to determine the electric field distribution. The results of the electric field distribution are validated with those obtained in previous works. A good agreement and an improvement near the dielectric thickness boundaries are observed on these results. The numerical space charge density within the material is obtained by numerical derivation of the field according to Poisson's equation.