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The properties of fragments and light charged particles emitted in multifragmentation of single sources formed in central 36 A.MeV Gd+U collisions are reviewed. Most of the products are isotropically distributed in the reaction c.m. Fragment kinetic energies reveal the onset of radial collective energy. A bulk effect is experimentally evidenced from the similarity of the charge distribution with that from the lighter 32 A.MeV Xe+Sn system. Spinodal decomposition of finite nuclear matter exhibits the same property in simulated central collisions for the two systems, and appears therefore as a possible mechanism at the origin of multifragmentation in this incident energy domain.

Disruptions are a major threat for future tokamaks, including ITER. Disruption-generated heat loads, electromagnetic forces and runaway electrons will not be tolerable for next-generation devices. Massive noble gas injection is foreseen as a standard mitigation system for these tokamaks. Disruption mitigation experiments have been carried out on Tore Supra to study various injection scenarios and to investigate gas jet penetration and mixing. Comparisons of different gases (He, Ne, Ar, He/Ar mixture) and amounts (from 5 to 500 Pa m3) were made, showing that light gases are more efficient regarding runaway electron suppression than heavier gases. Eddy currents in the limiter are moderately reduced by all the gases, and may be more dependent on the time constants of the structures than on the gas species. The density rise induced by the massive injection before the thermal quench is higher and faster with light gases. Gas jet penetration in the cooling phase is observed to be shallow and independent of the gas nature and amount. The gas cold front is stopped along the q = 2 surface where it triggers MHD instabilities, expelling thermal energy from the plasma core.

Multifragmentation of a "fused system" was observed for central collisions between 32 MeV/nucleon 129Xe and (nat)Sn. Most of the resulting charged products were well identified due to the high performances of the INDRA 4pi array. Experimental higher-order charge correlations for fragments show a weak but nonambiguous enhancement of events with nearly equal-sized fragments. Supported by dynamical calculations in which spinodal decomposition is simulated, this observed enhancement is interpreted as a "fossil" signal of spinodal instabilities in finite nuclear systems.

International audienceThe 4π array INDRA was used to detect nearly all charged products emitted in Ar + Ni collisions between 52 and 95 MeV/u. The charge, mass and excitation energy E∗ of the quasi-projectiles have been reconstructed event by event. Excitation energies up to 25 MeV per nucleon are reached