José M. Martínez-Val

Analysis of directly driven ICF targets

In this article the current capabilities at DENIM for the analysis of directly driven targets are presented. These include theoretical, computational and applied physical studies and developments of detailed simulation models for the most relevant processes in ICF. The simulation of directly driven ICF targets is carried out with the one-dimensional NORCLA code developed at DENIM. This code contains two main segments: NORMA and CLARA, able to work fully coupled and in an iterative manner. NORMA solves the hydrodynamic equations in a lagrangian mesh. It has modular programs coupled to it to treat the laser or particle beam interaction with matter. Equations of state, opacities and conductivities are taken from a DENIM atomic data library, generated externally with other codes that will also be explained in this work. CLARA solves the transport equation for neutrons, (Boltzmann), as well as for charged particles, and suprathermal electrons (Fokker-Planck), using discrete ordinates and finite element methods in the computational procedure. Parametric calculations of multilayered single-shell targets driven by heavy ion beams are also analyzed. Finally, conclusions are focused on the ongoing developments in the areas of interest such as: radiation transport, atomic physics, particle in cell method, charged particle transport, two-dimensional calculations and instabilities.

Fusion burning waves in proton-boron-11 plasmas

Abstract A method is proposed to exploit the aneutronic proton- 11 B fusion reaction by means of igniting a heat detonation wave that expands across the fuel from a small heated region. The ignition process is triggered by a particle beam (or a couple of beams) impinging on an inertially compressed target. We determine conditions for ignition and burn propagation. Although the requirements on the igniting beam current are very high, the method is a clear hint how to produce the cleanest energy from nuclear reactions.

Volume ignition targets for heavy-ion inertial fusion

Inertial confinement fusion (ICF) targets can be imploded by heavy-ion beams (HIBs) in order to obtain a highly compressed fuel microsphere. The hydrodynamic efficiency of the compression can be optimized by tuning the ablation process in order to produce the total evaporation of the pusher material by the end of the implosion. Such pusherless compressions produce very highly compressed targets for relatively short confinement times. However, these times are long enough for a fusion burst to take place, and burnup fractions of 30% and higher can be obtained if the volume ignition requirements are met. Numerical simulations demonstrate that targets of 1-mg DT driven by a few MJ can yield energy gains of over 70. Although direct drive is used in these simulations, the main conclusions about volume ignition are also applicable to indirect drive.

Inertial fusion targets driven by cluster ion beam: the hydrodynamic approach

Cluster-driven inertial confinement fusion (ICF) is analyzed. A cluster is defined as a charged supermolecule with a charge of one (or of the order 1) and with a very high mass number A, so that Z/A « 1. The energy deposition range is shown to be very small (a few micrometers) for projectiles with a few tens of kev/a.m.u. A significant momentum transfer is therefore possible in its slowing down as it passes through matter. In this case, a high hydrodynamic efficiency seems evident. Three relevant models for cluster beam-target interactions are discussed : (1) the rocket model, where the ablation pressure (P a ) is much larger than the cluster beam direct pressure (II) ; (2) the hammer model, where P a << II (in this case, two possibilities are discussed - an impact interaction between the beam and the target, and an impact interaction between one cluster and its absorption volume) ; (3) an intermediate model, where P a ∼ Π (in this regime, the hydrodynamic efficiency is maximum). Preliminary simulations were performed and the general features of the models were confirmed. Most relevant for ICF, it was found that approximately 75% of the beam energy is converted into X rays, so that the indirect drive is promising in this context.

Inertial Fusion Driven by Intense Cluster Ion Beams

The present state of the art concerning the use of intense cluster ion beams for driving an inertial fusion pellet containing a thermonuclear fuel is reviewed. Emphasis is placed on the fragmentation and stopping of correlated ion fragments in dense target material. The direct drive approach is given a hydrodynamic as well as a full one-dimensional simulation treatment. Indirect drive looks highly promising.

Fusion Burning Waves in Degenerate Plasmas

Abstract The outcome of fusion burning waves in non-degenerate plasmas is limited by the strength of ion–electron Coulomb collisions and subsequent energy loss mechanisms as electron heat conduction and radiation emission. In this Letter, an analysis is presented on the degeneracy effects in the stopping power of suprathermal charged particles and in the energy transmitted from ions to electrons by Coulomb collision. Main results of this analysis is that very powerful fusion burning waves can be launched into previously compressed degenerate plasmas. This can be specially suitable for proton–boron fusion, but it also applicable to any type of fusion reaction, where ignition can be triggered by an incoming ion beam or another external source of energy deposited in a small fraction of the compressed plasma (fast ignition).

Neutronic Effects in Inertial Confinement Fusion Targets

AbstractThe effects induced by fusion-born neutrons within inertial confinement fusion targets are analyzed. Some of these effects, such as neutron energy deposition, are always present and play a significant role in propagating ignition. Other effects, such as the suprathermal fusion induced by knocked-on ions, are of marginal importance. The possibility of inducing internal tritium breeding and other interesting neutronic reactions is also studied, but it is found that they usually produce negligible or even negative consequences in the target performance.

DEUTERIUM-TRITIUM FUSION REACTORS WITHOUT EXTERNAL TRITIUM BREEDING

Abstract An inherent property of deuterium fusion burn-up equations is presented, due to which deuterium-tritium reactions can be exploited without needing tritium breeding in external blankets. A small amount of tritium is added to the deuterium plasma in order to trigger ignition at less than 10 keV, and the same amount of tritium is found in the debris of the burnt-up plasma if the burning temperature is higher than 200 keV. Plasma parameters to exploit this property are very similar to those of inertial fusion confinement. Tritium inventory in a reactor would thus be reduced to a minimum value, because the initial composition of the fuel would be of the type DT x , with x ≈ 0.02, and tritium would immediately be reprocessed to fabricate new fuel.

Inertial fusion features in degenerate plasmas

Very high plasma densities can be obtained at the end of the implosion phase in inertial fusion targets, particularly in the so-called fast-ignition scheme ( Tabak et al. , 1994 ; Mulser & Bauer, 2004 ), where a central hot spark is not needed at all. By properly tailoring the fuel compression stage, degenerate states can be reached ( Azechi et al. , 1991 ; Nakai et al. , 1991 ; McCory, 1998 ). In that case, most of the relevant energy transfer mechanisms involving electrons are affected ( Honrubia & Tikhonchuk, 2004 ; Bibi & Matte, 2004 ; Bibi et al. , 2004 ). For instance, bremsstrahlung emission is highly suppressed ( Eliezer et al. , 2003 ). In fact, a low ignition-temperature regime appears at very high plasma densities, due to radiation leakage reduction ( Leon et al. , 2001 ). Stopping power and ion-electron coulomb collisions are also changed in this case, which are important mechanisms to trigger ignition by the incoming fast jet, and to launch the fusion wave from the igniting region into the colder, degenerate plasma. All these points are reviewed in this paper. Although degenerate states would not be easy to obtain by target implosion, they present a very interesting upper limit that deserves more attention in order to complete the understanding on the different domains for inertial confinement fusion.

Fusion-burning waves ignited by cumulation jets

AbstractA totally new target scheme to exploit fusion reactions is presented. It is based on the propagation of a heat-detonation wave across the fuel that reaches fusion temperatures before expanding. The wave is launched from a small region of the target where fusion ignition temperatures are reached by the crash of cumulation jets. These jets are produced by a couple of hollow-charge conical liners placed close to the target. The collapse of each conical liner creates a dispersive supersonic jet with a specific kinetic energy high enough to ignite the small region of the target where the fusion wave is created. The energy gain can be very high, although it depends on the maximum fusion yield allowable in the reactor chamber.