The use of the ESS Bilbao installations for laser fusion studies

In this work the use of ESS-Bilbao fast neutron lines for irradiation of materials for nuclear fusion is studied. For the comparison of ESS-Bilbao with an inertial fusion facility a simplified model of HiPER chamber has been used. Several positions for irradiation at ESS-Bilbao have been also compared. The material chosen for the damage analysis is silica due to its importance on IFC optics. In this work a detailed comparison between the two facilities for silica irradiation is given. The comparison covers the neutron fluxes, doses, defect production and PKA spectra. This study is also intended as a methodological approach or guideline for future works on other materials

Tunable Fano resonance in symmetric multilayered gold nanoshells

Fano resonances (FRs) are produced when a discrete state is coupled with a continuum. In addition to fundamental scientific interests, FRs in plasmonic systems give rise to the so-called plasmon-induced transparency. In this work we have studied the evolution of dipole-dipole all-plasmonic FRs in symmetric multilayered nanoshells as the function of their geometrical parameters. We demonstrate that symmetry breaking is not mandatory for controlling the Fano resonance in such multilayered nanoshells. Generation of FRs in these symmetric nanostructures presents clear advantages over their asymmetric counterparts, as they are easier to fabricate and can be used in a wider range of technological applications

MMonCa: A flexible and powerful new Kinetic Monte Carlo simulator

Kinetic Monte Carlo (KMC) is a widely used technique to simulate the evolution of radiation damage inside solids. Despite de fact that this technique was developed several decades ago, there is not an established and easy to access simulating tool for researchers interested in this field, unlike in the case of molecular dynamics or density functional theory calculations. In fact, scientists must develop their own tools or use unmaintained ones in order to perform these types of simulations. To fulfil this need, we have developed MMonCa, the Modular Monte Carlo simulator. MMonCa has been developed using professional C++ programming techniques and has been built on top of an interpreted language to allow having a powerful yet flexible, robust but customizable and easy to access modern simulator. Both non lattice and Lattice KMC modules have been developed. We will present in this conference, for the first time, the MMonCa simulator. Along with other (more detailed) contributions in this meeting, the versatility of MMonCa to study a number of problems in different materials (particularly, Fe and W) subject to a wide range of conditions will be shown. Regarding KMC simulations, we have studied neutron-generated cascade evolution in Fe (as a model material). Starting with a Frenkel pair distribution we have followed the defect evolution up to 450 K. Comparison with previous simulations and experiments shows excellent agreement. Furthermore, we have studied a more complex system (He-irradiated W:C) using a previous parametrization [1]. He-irradiation at 4 K followed by isochronal annealing steps up to 500 K has been simulated with MMonCa. The He energy was 400 eV or 3 keV. In the first case, no damage is associated to the He implantation, whereas in the second one, a significant Frenkel pair concentration (evolving into complex clusters) is associated to the He ions. We have been able to explain He desorption both in the absence and in the presence of Frenkel pairs and we have also applied MMonCa to high He doses and fluxes at elevated temperatures. He migration and trapping dominate the kinetics of He desorption. These processes will be discussed and compared to experimental results. [1] C.S. Becquart et al. J. Nucl. Mater. 403 (2010) 7

Silica final lenses under HiPER laser fusion reactor operation conditions

We have studied the thermo-mechanical response and atomistic degradation of final lenses in HiPER project. Final silica lenses are squares of 75 × 75 cm2 with a thickness of 5 cm. There are two scenarios where lenses are located at 8 m from the centre: •HiPER 4a, bunches of 100 shots (maximum 5 DT shots <48 MJ at ≈0.1 Hz). No blanket in chamber geometry. •HiPER 4b, continuous mode with shots ≈50 MJ at 10 Hz to generate 0.5 GW. Liquid metal blanket in chamber design

An overview on armor research for the laser fusion project HiPER

During the current preparatory phase of the European laser fusion project HiPER, an intensive effort has being placed to identify an armour material able to protect the internal walls of the chamber against the high thermal loads and high fluxes of x-rays and ions produced during the fusion explosions. This poster addresses the different threats and limitations of a poly-crystalline Tungsten armour. The analysis is carried out under the conditions of an experimental chamber hypothetically constructed to demonstrate laser fusion in a repetitive mode, subjected to a few thousand 48MJ shock ignition shots during its entire lifetime. If compared to the literature, an extrapolation of the thermomechanical and atomistic effects obtained from the simulations of the experimental chamber to the conditions of a Demo reactor (working 24/7 at hundreds of MW) or a future power plant (producing GW) suggests that “standard” tungsten will not be a suitable armour. Thus, new materials based on nano-structured W and C are being investigated as possible candidates. The research programme launched by the HiPER material team is introduced

Effect of defect accumulation on ion-beam damage morphology by electronic excitation in lithium niobate: A MonteCarlo approach

We present a MonteCarlo approach to the non-radiative exciton-decay model recently proposed to describe ion-beam damage in LiNbO3 produced in the electronic excitation regime. It takes into account the statistical (random) spatial distribution of ion impacts on the crystal surface. The MonteCarlo approach is necessary to simulate the evolution of the damage morphology with irradiation fluence from the single track regime to the overlapping track regime. A detailed comparison between the morphologies found for sub-threshold and above threshold irradiations is presented. Moreover, a good representation of the Avrami’s type kinetics for amorphization has been achieved and it is in fair accordance with experiment. For moderate fluences where homogeneous amorphous layers are generated, the new approach predicts that the amorphous and crystalline layers are separated by a diffuse (thick) boundary that includes a mixed amorphous-crystalline composition

Ion Beam irradiation of copper nitride: electronic vs elastic-collision mechanism

Copper nitride is a metastable material which results very attractive because of their potential to be used in functional device. Cu3 N easily decomposes into Cu and N2 by annealing [1] or irradiation (electron, ions, laser) [2, 3]. Previous studies carried out in N-rich Cu3 N films irradiated with Cu at 42MeV evidence a very efficient sputtering of N whose yield (5×10 3 atom/ion), for a film with a thickness of just 100 nm, suggest that the origin of the sputtering has an electronic nature. This N depletion was observed to be responsible for new phase formation ( Cu2 O) and pure Cu [4

Ionoluminescence on α-quartz: mechanisms and modeling

Ionoluminescence of α - quartz exhibits two dominant emission bands peaking at 1.9 eV. (NBOHCs) and 2.7 eV (STEs. The evolution of the red emission yield does not show a correlation with the concentrations of neither the NBOHC nor with that of other color centers. The blue emission yield closely follows the amorphization kinetics independently measured by RBS/C spectrometry. A simple theoretical model has been proposed; it assumes that the formation and recombination of STEs are the primary event and both, the light emissions and the lattice structural damage are a consequence this phenomenon. The model leads to several simple mathematical equations that can be used to simulate the IL yields and provide a reasonable fit to experimental kinetic data

Refractive index changes in amorphous SiO2 (silica) by swift ion irradiation

The refractive index changes induced by swift ion-beam irradiation in silica have been measured either by spectroscopic ellipsometry or through the effective indices of the optical modes propagating through the irradiated structure. The optical response has been analyzed by considering an effective homogeneous medium to simulate the nanostructured irradiated system consisting of cylindrical tracks, associated to the ion impacts, embedded into a virgin material. The role of both, irradiation fluence and stopping power, has been investigated. Above a certain electronic stopping power threshold (∼2.5 keV/nm), every ion impact creates an axial region around the trajectory with a fixed refractive index (around n = 1.475) corresponding to a certain structural phase that is independent of stopping power. The results have been compared with previous data measured by means of infrared spectroscopy and small-angle X-ray scattering; possible mechanisms and theoretical models are discussed

Direct formation of InAs quantum dots grown on InP (001) by solid-source molecular beam epitaxy

We have developed a growth process that leads to the direct formation of self-assembled InAs quantum dots on InP(001) by solid-source molecular beam epitaxy avoiding the previous formation of quantum wires usually obtained by this technique. The process consists of a periodically alternated deposition of In and As correlated with InAs(4×2)(2×4) surface reconstruction changes. Based on the results obtained by in situ characterization techniques, we propose that the quantum dots formation is possible due to the nucleation of In droplets over the InAs(4×2) surface during the In deposition step and their subsequent crystallization under the As step.The authors acknowledge the financial support of the Spanish MICINN (TEC2008-06756-C03-01), Consolider-QOIT (CSD2006-0019), and CAM (S-505/ESP/000200). P.A.G. and A.R. thank the I3P program. B.A. thanks the Ramón y Cajal program.Peer reviewe