A Semi-exclusive study of heavy-residue production in the40Ar + Ag reaction at 35 MeV/u incident energy

Heavy residues created in the reaction Ar + Ag at 35 MeV/u have been detected at various forward angles. Their velocity spectra (quite different from the corresponding spectra measured at 27 MeV/u) show that these events result both from central and peripheral reactions and that the fusion component has dramatically decreased. Coincident light charged particles spectra have been obtained in a large solid angle forward hodoscope. The analysis of these spectra allows to differentiate peripheral and central collisions. The proton spectra are analysed in terms of emitting sources. There is no need for a participant zone in peripheral reactions. Instead protons are emitted either from the target like or from the projectile like fragments. However projectile sequential emission is not sufficient to explain all the high energy protons.     

Systematics of fragment observables

Multifragmentation is observed in many reaction types: light-ion-induced reactions at large incident energies (in the GeV region), central heavy-ion collisions from 30 to 100MeV/u, and peripheral heavy-ion collisions between 30 and 1000MeV/u or above. When nucleus-nucleus collisions are considered, another entrance channel parameter is the corresponding mass asymmetry. The first question which is addressed in this contribution is: do we observe similar reactions in each case? Multifragmentation may be related to a phase transition of nuclear matter. Some others features indicate that dynamical features are dominant. It is a priori possible that the underlying mechanisms are different in proton- and nucleus-induced reactions, in central and in peripheral collisions, at limited and at large bombarding energies. In order to see to what extent they can reflect similar behaviour, it is useful to compare the results of various reactions. The observables can be the fragment multiplicity, the mass distributions or the kinematical properties. In this contribution, we are looking for such general features. We will limit the discussion to the observations themselves, rather than the interpretation, which is the subject of numerous entries in this volume. The experimental results indicate that multifragmentation exhibits at the same time universal and entrance-channel-dependent properties.     

An alternating direction scheme on a nonuniform mesh for reaction-diffusion parabolic problems

In this paper we develop a numerical method for two-dimensionaltime-dependent reaction-diffusion problems. This method, whichcan immediately be generalized to higher dimensions, is shownto be uniformly convergent with respect to the diffusion problems.This method, which can immediately be generalized to higherdimensions, is shown to be uniformly convergent with respectto the diffusion parameter.     

Penalization modeling of a limiter in the Tokamak edge plasma

An original penalization method is applied to model the interaction of magnetically confined plasma with limiter in the frame of a minimal transport model for ionic density and parallel momentum. The limiter is considered as a pure particle sink for the plasma and consequently the density and the momentum are enforced to be zero inside. Comparisons of the numerical results with one-dimensional analytical solutions show a very good agreement. In particular, the penalization scheme followed in this paper tends to ensure an almost sonic plasma condition at the plasma-obstacle interface, Bohm-like criterion, with relatively weak dependence on the target Mach number profile within the obstacle. The new system being solved in a periodic obstacle free domain, an efficient pseudo-spectral algorithm based on a Fast Fourier transform is also proposed, and associated with an exponential filtering of the unphysical oscillations due to Gibbs phenomenon. Finally, the efficiency of the method is illustrated by investigating the flow spreading from the plasma core to the Scrape-Off Layer at the wall in a two-dimensional system with one, then two neighboring limiters.