Laser-driven coherent betatron oscillation in a laser-wakefield cavity

The origin of beam disparity in emittance and betatron oscillation orbits, in and out of the polarization plane of the drive laser of laser-plasma accelerators, is explained in terms of betatron oscillations driven by the laser field. As trapped electrons accelerate, they move forward and interact with the laser pulse. For the bubble regime, a simple model is presented to describe this interaction in terms of a harmonic oscillator with a driving force from the laser and a restoring force from the plasma wake field. The resulting beam oscillations in the polarization plane, with period approximately the wavelength of the driving laser, increase emittance in that plane and cause microbunching of the beam. These effects are observed directly in 3D particle-in-cell simulations.

Incubadoras y aceleradores de crecimiento: modelo de apoyo a las start-up tecnológicas

[ES]Las políticas de apoyo al emprendimiento se han demostrado imprescindibles para el desarrollo económico de los países. En este contexto las conocidas incubadoras de empresas juegan un papel importante, pero los innovadores aceleradores de crecimiento que están logrando convertir pequeñas start-up en grandes compañías de base tecnológica se presentan como una apuesta para el futuro. La unión de ambos conceptos constituye un modelo eficaz de apoyo a las start-up tecnológicas. En el trabajo se presentan varios estudios que demuestran que mientras que, en las incubadoras los recursos más valorados son el ahorro de costes y el mentoring, los aceleradores obtienen muy buena calificación en todos sus ámbitos. Aun así la facilidad para obtener financiación y el mentoring también son los aspectos más valorados por los participantes en la aceleración. Además se han utilizado dos casos de éxito con el objeto de proponer un corolario de buenas prácticas que ayude entre otros, a la mejora de la situación de la Comunidad Autónoma del País Vasco (CAPV) en cuanto a emprendimiento se refiere.

Contributions to the efficient use of general purpose coprocessors: kernel density estimation as case study

142 p.

The effect of beam interruptions on the integrity of ADSR fuel pin cladding: A thermo-mechanical analysis

During its lifetime in the core, the cladding of an Accelerator Driven Subcritical Reactor (ADSR) fuel pin is expected to experience variable stresses due to frequent interruptions in the accelerator proton beam. This paper investigates the thermal fatigue damage in the cladding due to repetitive and unplanned beam interruptions under certain operational conditions. Beam trip data was obtained for four operating high power proton accelerators, among which the Spallation Neutron Source (SNS) superconducting accelerator was selected for further analysis. 9Cr-1Mo-Nb-V (T91) steel was selected as the cladding material because of its proven compatibility with proposed ADSR design concepts. The neutronic, thermal and stress analyses were performed using the PTS-ADS, a code that has been specifically developed for studying the dynamic response to beam-induced transients in accelerator driven subcritical systems. The lifetime of the fuel cladding in the core was estimated for three levels of allowed pin power and specific operating conditions. © 2012 Elsevier Ltd. All rights reserved.

Accelerator-induced transients in Accelerator Driven Subcritical Reactors

Achieving higher particles energies and beam powers have long been the main focus of research in accelerator technology. Since Accelerator Driven Subcritical Reactors (ADSRs) have become the subject of increasing interest, accelerator reliability and modes of operation have become important matters that require further research and development in order to accommodate the engineering and economic needs of ADSRs. This paper focuses on neutronic and thermo-mechanical analyses of accelerator-induced transients in an ADSR. Such transients fall into three main categories: beam interruptions (trips), pulsed-beam operation, and beam overpower. The concept of a multiple-target ADSR is shown to increase system reliability and to mitigate the negative effects of beam interruptions, such as thermal cyclic fatigue in the fuel cladding and the huge financial cost of total power loss. This work also demonstrates the effectiveness of the temperature-to-reactivity feedback mechanisms in ADSRs. A comparison of shutdown mechanisms using control rods and beam cut-off highlights the intrinsic safety features of ADSRs. It is evident that the presence of control rods is crucial in an industrial-scale ADSR. This paper also proposes a method to monitor core reactivity online using the repetitive pattern of beam current fluctuations in a pulsed-beam operation mode. Results were produced using PTS-ADS, a computer code developed specifically to study the dynamic neutronic and thermal responses to beam transients in subcritical reactor systems. © 2012 Elsevier B.V.

A preliminary study of target multiplicity for ADSRs

The Accelerator Driven Subcritical Reactor (ADSR) concept is based on the coupling of a particle accelerator to a subcritical reactor core by means of a neutron spallation target interface. This paper investigates the benefits of multiple spallation targets in ADSRs. The motivation behind this is, firstly, to improve the overall reliability of the accelerator-reactor system, and, secondly, to evaluate other potential advantages such as lower beam power requirements. The results show that a system containing two or three spallation targets, coupled to independent accelerators, offers better neutronic performance. This is demonstrated through the increased effective multiplication factor (keff) in the two- and three-target configurations and a more uniform neutron flux distribution. A multiple-target ADSR also proves effective in mitigating the impact of frequent beam interruptions, a pressing issue that needs to be addressed for the ADSR concept to advance. Assuming no simultaneous beam shutdowns, the two- and three-target configurations reduce the risk of fuel cladding failure due to thermal cyclic fatigue. © 2013 Elsevier B.V. All rights reserved.

Ultra-thin 242mAm fuel elements in nuclear reactors

There is a growing interest in using 242mAm as a nuclear fuel. The advantages of 242mAm as a nuclear fuel derive from the fact that 242mAm has the highest thermal fission cross section. The thermal capture cross section is relatively low and the number of neutrons per thermal fission is high. These nuclear properties make it possible to obtain nuclear criticality with ultra-thin fuel elements. The possibility of having ultra-thin fuel elements enables the use of these fission products directly, without the necessity of converting their energy to heat, as is done in conventional reactors. There are three options of using such highly energetic and highly ionized fission products. 1. Using the fission products themselves for ionic propulsion. 2. Using the fission products in an MHD generator, in order to obtain electricity directly. 3. Using the fission products to heat a gas up to a high temperature for propulsion purposes. In this work, we are not dealing with a specific reactor design, but only calculating the minimal fuel elements' thickness and the energy of the fission products emerging from these fuel elements. It was found that it is possible to design a nuclear reactor with a fuel element of less than 1 μm of 242mAm. In such a fuel element, 90% of the fission products' energy can escape.

Electron beam and laser testing on the novel stripixel detectors

The novel Si stripixel detector, developed at BNL (Brookhaven National Laboratory), has been applied in the development of a prototype Si strip detector system for the PHENIX Upgrade at RHIC. The Si stripixel detector can generate X-Y two-dimensional (2D) position sensitivity with single-sided processing and readout. Test stripixel detectors with pitches of 85 and 560 mu m have been subjected to the electron beam test in a SEM set-up, and to the laser beam test in a lab test fixture with an X-Y-Z table for laser scanning. Test results have shown that the X and Y strips are well isolated from each other, and 2D position sensitivity has been well demonstrated in the novel stripixel detectors. (c) 2005 Elsevier B.V. All rights reserved.

First charge collection and position-precision data on the medium-resistivity silicon strip detectors before and after neutron irradiation up to 2x10(14) n/cm(2)

Test strip detectors of 125 mu m, 500 mu m, and 1 mm pitches with about 1 cm(2) areas have been made on medium-resistivity silicon wafers (1.3 and 2.7 k Ohm cm). Detectors of 500 mu m pitch have been tested for charge collection and position precision before and after neutron irradiation (up to 2 x 10(14) n/cm(2)) using 820 and 1030 nm laser lights with different beam-spot sizes. It has been found that for a bias of 250 V a strip detector made of 1.3 k Ohm cm (300 mu m thick) can be fully depleted before and after an irradiation of 2 x 10(14) n/cm(2). For a 500 mu m pitch strip detector made of 2.7 k Ohm cm tested with an 1030 nm laser light with 200 mu m spot size, the position reconstruction error is about 14 mu m before irradiation, and 17 mu m after about 1.7 x 10(13) n/cm(2) irradiation. We demonstrated in this work that medium resistivity silicon strip detectors can work just as well as the traditional high-resistivity ones, but with higher radiation tolerance. We also tested charge sharing and position reconstruction using a 1030 nm wavelength (300 mu m absorption length in Si at RT) laser, which provides a simulation of MIP particles in high-physics experiments in terms of charge collection and position reconstruction, (C) 1999 Elsevier Science B.V. All rights reserved.

CHARACTERIZATION OF HIGH FLUENCE NEUTRON-INDUCED DEFECT LEVELS IN HIGH-RESISTIVITY SILICON DETECTORS USING A LASER DEEP-LEVEL TRANSIENT SPECTROSCOPY (L-DLTS)

Neutron irradiated high resistivity (4-6 kOMEGA-cm) silicon detectors in the neutron fluence (PHI(n)) range of 5 X 10(11) n/cm2 to 1 X 10(14) n/cm2 have been studied using a laser deep level transient spectroscopy (L-DLTS). It has been found that the A-center (oxygen-vacancy, E(c) = 0.17 eV) concentration increases with neutron fluence, reaching a maximum at PHI(n) almost-equal-to 5 X 10(12) n/cm2 before decreasing with PHI(n). A broad peak has been found between 200 K and 300 K, which is the result of the overlap of three single levels: the V-V- (E(c) = 0.38 eV), the E-center (P-V, E(c) = 0.44 eV), and a level at E(c) = 0.56 eV that is probably V-V0. At low neutron fluences (PHI(n) < 5 X 10(12) n/cm2), this broad peak is dominated by V-V- and the E-centers. However, as the fluence increases (PHI(n) greater-than-or-equal-to 5 X 10(12) n/cm2), the peak becomes dominated by the level of E(c) = 0.56 eV.