[en] The new 4π multidetector INDRA, designed for the study of hot nuclear systems decaying by multifragmentation, is available for experiments since the beginning of 1993. First results emphasize its very high detection capabilities. Preliminary results on multiplicity distributions and elemental charge distributions in the most violent collisions for the ³⁶Ar + ⁵⁸Ni and ¹²⁹Xe +^natSn systems are presented. (author) 5 figs., 22 refs

[en] The INDRA 4π multidetector for light charged particles and heavy fragments is mainly dedicated to the study of the deexcitation of hot nuclear systems formed in nucleus-nucleus collisions in the intermediate energy domain under peculiar conditions of temperature or compression, and especially to the study of the multifragmentation. After a brief description of the detector and its capabilities to identify particles and fragments, the scientific program for the next three years is presented. (author) 15 refs.; 9 figs.; 1 tab

[en] Angular distribution and correlations of fission fragment induced by light projectiles (p,d,α) on ²³²Th and ¹⁹⁷Au targets from 70 to 1000 MeV have been measured. The distributions of the forward component of the linear momentum imparted to the target nucleus are deduced. They give information about the dominating process leading to fission on a wide range in energy. We propose a classification into three different regimes. Analysis is made with two high energy models: - intra-nuclear cascade model, in which the collison is described with incoherent successive nucleon-nucleon collisions; - a model, called absorption, which is an extension of the fireball model, completely developped by ourself. One of the main results of this analysis is that at twice the Fermi energy the collective effects must be take into account for light projectiles

[en] A brief review of exclusive measurements performed at GANIL in order to study hot nuclei will be given. Heavy-ion induced reactions on heavy targets have been investigated over a wide range of incident energy, using various techniques: - fission fragment angular correlations. - 4 π neutron multiplicity measurements. - light charged particle correlations. In each case, a selection of the most violent collisions can be achieved. For central collisions induced by ⁴⁰Ar, a same excitation energy of about 650 MeV is deduced from the totally different and independent sets of data, corresponding to an average temperature of 5 MeV. At 60 MeV/u, this value is quite low as compare to the total available energy for central collisions A tentative explanation based on Landau-Vlasov simulations will be proposed: the excitation energy dissipated in the system could be stored in a highly excited compression mode as well as under a thermal form. Some recent results on the Kr+Au system at 32 MeV/u will be presented indicating that heavier projectiles than ⁴⁰Ar can lead to a temperature of the hot system approaching 7 MeV

[en] The full text follows. Equilibrium reconstruction is the essential tool for determining the field structure and current density in a tokamak discharge. For performance reasons, tokamaks are designed to provide a field structure which is close to being axisymmetric around the torus axis. Due to the limited number of toroidal field coils, there are however small deviations from the axisymmetry, the magnetic field ripple. We present a generally applicable algorithm for the calculation of the three-dimensional perturbed field due to the ripple. The response of the plasma to a non-axisymmetric external field is difficult to obtain due to the nonlinearity of the equilibrium calculation. We consider tokamak discharges where the magnetic field is always dominated by the external toroidal field. This allows for applying an expansion with a small parameter related to the ratio of poloidal vs toroidal field component and the magnitude of the perturbation. The algorithm gives the Grad-Shafranov equation in lowest significant order, and the perturbed plasma current as response to the toroidal magnetic field variation in the next higher order. This correction term is shown to be sufficient for those tokamaks where the deviation from axisymmetry is mainly caused by the field ripple. We present the implementation of the ripple correction for the equilibrium reconstruction code EFIT. The code is applied to discharges of the Tore Supra tokamak with 18 toroidal coils, resulting in a field ripple up to 7%, which has to be taken into account for precise equilibrium calculations. It is shown that the generalised algorithm preserves the convergence behaviour of the code and increases the computational cost only marginally. The results are compared with the real-time boundary code used for Tore Supra that uses an inverse mapping for the ripple correction. Both methods that use completely different algorithms agree on the position of the plasma boundary within a few milli-metres. The code therefore serves as routine equilibrium analysis code for Tore Supra discharges. The algorithm is straightforward to implement for different tokamaks. We present a reconstruction for the ripple experiment on the JET device, where the ripple was generated on purpose by using half of the 32 toroidal field coils. We also propose the algorithm for ITER discharges, where the field ripple is not negligible in the present design. (authors)

[en] The multifragmentation process has been deeply studied with the Nautilus apparatus. Model independant results on the emission time scale of the fragments have been obtained. We have investigated dynamical effects in multifragmentation through the kinetic energy spectra of emitted fragments in central collision. To go further in this field, the INDRA 4π multidetector has been built by four laboratories (DAPNIA-Saclay, GANIL-Caen, IPN-Orsay, LPC-Caen) with the technical collaboration of the LAL-Orsay. First results indicate that the expected high qualities of the detector are fulfilled. Preliminary results on multiplicity distributions and angular correlations of light particles and fragments are presented. (orig.)

[en] The present study was mainly achieved on a ²³²Th target nucleus because of its high fission cross section which might be closed to the reaction cross sections. We present briefly the experimental procedure. The momentum distribution imparted to nuclei is deduced from angular correlation measurements and differential and integrated cross sections are presented

[en] Correlations between light particles in ⁴⁰Ar induced reactions on ¹⁹⁷Au at E/A = 60 MeV have been measured in coincidence with a multidetector system. The correlations decrease monotonously with increasing charged particle multiplicity. With the help of a participant-spectator model, this multiplicity is tentatively connected to the impact parameter. The correlation function is analyzed in the framework of the final state interaction model in order to extract the space-time extent of the emitting source

[en] Plasma equilibrium codes solve numerically Grad-Shafranov and Maxwell equations on a two-dimensional finite element meshing of a tokamak, assuming a global axial symmetry to compute the poloidal magnetic field everywhere in a meridian plane of the machine. To provide relevant results, this modelling must take into account accurately the plasma facing components, and the iron circuit, with a consistent magnetic permeability, for machines with iron core. For a better prediction of optimized pre-magnetization configurations and long discharge analysis with the PROTEUS code, the modelling of the Tore Supra tokamak iron circuit and new plasma facing components has been refined: a new meshing has been built, respecting the limiter positions and the inner surfaces of the iron return arms. The magnetic permeability has been adjusted to minimize errors between the code results and magnetic measurements during special calibration shots, at different levels of iron saturation. With this new modelling, magnetic configurations with field lower than 1 mT over the whole vacuum vessel have been predicted, and plasma slow derive during long pulses in preparation to the giga-joule discharges has been confirmed by the PROTEUS code. (authors)

[en] The Tore Supra data acquisition system has been upgraded during the Tore Supra 2000/2001 shutdown to fulfill the request to run long duration discharges. The Tore Supra Tokamak is a large and complex device and needs to share information from different systems and to record data not only during plasma discharges but also between discharges (calorimetry, vacuum, magnetic field...). The data acquisition system for infrared cameras, new plasma control and continuous data acquisition are major upgrades. The experimental campaign from September 2001 to November 2002 provides the first results for these upgrades. (authors)