On the Critical Behaviour of Heat Conducting Sphere out of Hydrostatic Equilibrium

We comment further on the behaviour of a heat conducting fluid when a characteristic parameter of the system approaches a critical value.Comment: 4 pages, emTex (LaTex 2.09), submitted to Classical and Quantum Gravity (Comments and Addenda

Breakdown of the linear approximation in the perturbative analysis of heat conduction in relativistic systems

We analyze the effects of thermal conduction in a relativistic fluid just after its departure from spherical symmetry, on a time scale of the order of relaxation time. Using first order perturbation theory, it is shown that, as in spherical systems, at a critical point the effective inertial mass density of a fluid element vanishes and becomes negative beyond that point. The impact of this effect on the reliability of causality conditions is discussed.Comment: 11 pages (Latex2.09) To appear in Physics Letters

Baseline Design of a Solid Neutron Converter Driven by 160 MeV Protons

The European Isotope Separation On-Line Radioactive Ion Beam Facility Design Study (EURISOL DS) aims at the design of several spallation and fission targets for the production of radioactive isotopes. Namely, direct targets, where high-energy protons interact directly with the fission targets, as well as the design of a Multi-MW proton-to-neutron converter coupled with a fission target. For the later, several options have been proposed, including the use of a relatively low energy (in the hundreds of MeV) high intensity proton beam. In this scope, the neutronic characteristics of a tantalum n-converter/fission-target system have been established (although not yet optimised) for a reference proton energy of 160 MeV. A set of simulations has been carried out for different design requirements and different characteristics of the proton beam. An extensive comparison of the main physical parameters has also been carried out, in order to allow the optimal engineering design of the whole target station

EURISOL-DS Multi-MW Target Neutronic Calculations for the Baseline Configuration of the Multi-MW Target

This document summarises the study performed within the Task #2 of the European Isotope Separation On-Line Radioactive Ion Beam Facility Design Study (EURISOL DS) [1] to design the Multi-MW proton-to-neutron converter. A preliminary study [2] was carried out in order to understand the nature of the interactions taking place in the proton-to-neutron converter and their impact on the design of the facility. Namely, the target dimensions and material composition, type of incident particle, its energy and the beam profile were analysed in the aforementioned technical note, and their optimum values were suggested in the conclusions. The present work is based on the results of the previous study and uses the same methodology, namely Monte Carlo simulations with FLUKA [3]. This note describes the performance of a Hg target design and addresses more detailed issues, such as the composition of the fission target and use of a neutron reflector. It also attempts to integrate those components together and estimate the whole performance in terms of number of fissions, isotopic yields and power densities. The results of these calculations show the feasibility of this Multi-MW target design and the possibility of achieving the aimed fission rates with a reduced fission target. The assembly has been characterised in terms of neutronics and power densities, both key factors in the technical design, due to the high isotopic yields aimed and the large power densities foreseen

EURISOL-DS Multi-MW Target Comparative Neutronic Performance of the Baseline Configuration vs. the Hg-Jet Option

This technical report summarises the comparative study between several design options for the Multi-MW target station performed within Task #2 of the European Isotope Separation On-Line Radioactive Ion Beam Facility Design Study (EURISOL DS) [1]. Previous analyses were carried out, using the Monte Carlo code FLUKA [2], to determine optimal values for relevant parameters in the target design [3] and to analyse a preliminary Multi-MW target assembly configuration [4]. The second report showed that the aimed fission rates, i.e. ~1015 fissions/s, could be achieved with such a configuration. Nevertheless, a preliminary study of the target assembly integration [5] suggested reducing some of the dimensions. Moreover, the yields of specific isotopes have yet to be assessed and compared to other target configurations. This note presents a detailed comparison of the baseline configuration and the Hg-jet option, in terms of primary and neutron distribution, power densities and fission product yields. A scaled-down version of the baseline configuration (i.e. reduced radius and length), is proposed and compared with the other designs. The results confirm the feasibility of the reduced target configuration, while obtaining fission product yields comparable to those of the Hg-jet layout, without the technical problems of the latter. Significant fission rates may be obtained with 4 MW of beam power and few one-litre UnatC3 targets. Moreover, the energy deposited in the liquid metal may be evacuated with reasonable flow rates

Dissipative fluids out of hydrostatic equilibrium

In the context of the M\"{u}ller-Israel-Stewart second order phenomenological theory for dissipative fluids, we analyze the effects of thermal conduction and viscosity in a relativistic fluid, just after its departure from hydrostatic equilibrium, on a time scale of the order of relaxation times. Stability and causality conditions are contrasted with conditions for which the ''effective inertial mass'' vanishes.Comment: 21 pages, 1 postscript figure (LaTex 2.09 and epsfig.sty required) Submitted to Classical and Quantum Gravit

Thermal Conduction in Systems out of Hydrostatic Equilibrium

We analyse the effects of thermal conduction in a relativistic fluid, just after its departure from hydrostatic equilibrium, on a time scale of the order of thermal relaxation time. It is obtained that the resulting evolution will critically depend on a parameter defined in terms of thermodynamic variables, which is constrained by causality requirements.Comment: 16 pages, emTex (LaTex 2.09). To appear in Classical and Quantum Gravit