Optically Controlled Laser-Plasma Electron Acceleration for Compact γ-Ray Sources

Thomson scattering (TS) from electron beams produced in laser-plasma accelerators may generate femtosecond pulses of quasi-monochromatic, multi-MeV photons. Scaling laws suggest that reaching the necessary GeV electron energy, with a percent-scale energy spread and five-dimensional brightness over 1016 A/m2, requires acceleration in centimeter-length, tenuous plasmas ( n 0 ∼ 10 17 cm−3), with petawatt-class lasers. Ultrahigh per-pulse power mandates single-shot operation, frustrating applications dependent on dosage. To generate high-quality near-GeV beams at a manageable average power (thus affording kHz repetition rate), we propose acceleration in a cavity of electron density, driven with an incoherent stack of sub-Joule laser pulses through a millimeter-length, dense plasma ( n 0 ∼ 10 19 cm−3). Blue-shifting one stack component by a considerable fraction of the carrier frequency compensates for the frequency red shift imparted by the wake. This avoids catastrophic self-compression of the optical driver and suppresses expansion of the accelerating cavity, avoiding accumulation of a massive low-energy background. In addition, the energy gain doubles compared to the predictions of scaling laws. Head-on collision of the resulting ultrabright beams with another optical pulse produces, via TS, gigawatt γ-ray pulses having a sub-20% bandwidth, over 106 photons in a microsteradian observation cone, and the observation cone, and the mean energy tunable up to 16 MeV

The LUNEX5 project

http://accelconf.web.cern.ch/AccelConf/FEL2012/papers/froa03.pdfInternational audienceLUNEX5 (free electron Laser Using a New accelerator for the Exploitation of X-ray radiation of 5th generation) aims at investigating the production of short, intense, and coherent pulses in the soft X-ray region. The project consists of a Free Electron Laser (FEL) line enabling the most advanced seeding configurations: High order Harmonic in Gas (HHG) seeding and Echo Enable Harmonic Generation (EEHG) with in-vacuum (potentially cryogenic) undulators of 15 and 30 mm period. Two accelerator types feed this FEL line : a 400 MeV Conventional Linear Accelerator (CLA) using superconducting cavities compatible with a future upgrade towards high repetition rate, for the investigations of the advanced FEL schemes; and a 0.4 - 1 GeV Laser Wake Field Accelerator (LWFA), to be qualified in view of FEL application, in the single spike or seeded regime. Two pilot user experiments for timeresolved studies of isolated species and solid state matter dynamics will take benefit of LUNEX5 FEL radiation and provide feedback of the performance of the different schemes under real user conditions

The challenge of dual career expatriate management in a specific host national environment: An exploratory study of expatriate and spouse adjustment in Switzerland based MNCs

The number of expatriates from global firms has been continuously increasing over the past decades as multinational companies still view expatriation as an important tool for sharing and transferring knowledge, controlling subsidiaries and developing workforce competencies. Expatriate management is still a costly and complex task for multinational companies. Adjustment, which has been defined as an individual's degree of comfort, familiarity and ease with several aspects of a new cultural environment, is considered to play a central role in expatriation success. In a context characterized by the rise of dual career couples, the increasing number of female expatriates and the growing awareness concerning work life balance, private life issues are increasingly important for multinational companies. On the basis of 126 expatriate couples' questionnaires, this paper compares adjustment of male and female expatriates working in multinational companies in a specific host country environment: the Geneva Lake region in Switzerland where many MNCs have settled their European headquarters. Furthermore, our paper investigates the impact of two variables - gender and employment status - on adjustment of expatriate spouses

ALL-OPTICAL CONTROL OF ELECTRON TRAPPING IN TAPERED PLASMAS AND CHANNELS

The radiation pressure of a multi-terawatt, sub-100 fs laser pulse propagating in an under-dense plasma causes complete electron cavitation. The resulting electron density “bubble” guides the pulse over many Rayleigh lengths, leaving the background ions unperturbed while maintaining GV/cm-scale accelerating and focusing gradients. The shape of the bubble, and, hence, the wakefield potentials, evolve slowly, in lockstep with the optical driver. This dynamic structure readily traps background electrons. The electron injection process can thus be controlled by purely optical means

Facteurs culturels de l’intégration du personnel soignant étranger ::une étude exploratoire dans le secteur suisse de la santé

Dans notre étude, nous nous intéressons à l’intégration du personnel soignant francophone dans le secteur de la santé en Suisse romande. Sur la base de deux séries d’entretiens, notre étude vise à identifier les dynamiques culturelles de l’intégration de travailleurs étrangers, au-delà de la seule question de la langue et de la culture nationale. L’originalité de notre approche est de mettre l’accent sur la culture professionnelle, en analysant la formation du personnel soignant dans les contextes institutionnels nationaux et leur relation avec d’autres sphères culturelles. Cette analyse nous permet d’identifier une variété de pratiques et recommandations utiles aux managers d’hôpitaux publics pour une meilleure intégration des personnels soignants étrangers

Improved modellisation of laser–particle interaction in particle-in-cell simulations

International audienceA new method named B-TIS (Bourgeois & Davoine, J. Comput. Phys. , vol. 413, 2020, 109426) has recently been proposed for suppressing the influence of numerical Cherenkov radiation that appears in particle-in-cell (PIC) simulation of laser wakefield acceleration (LWFA). However, while this method provides good results when applied to the already accelerated electrons, we show here that it cannot model correctly most of the plasma electron bulk interacting with the laser field. We thus investigate in this paper the origins of this limitation and propose an improved method for which this limitation is removed. This new method, named B-TIS3, can now be applied to a much broader variety of problems and improve the performance in comparison with the standard PIC algorithm. We show that, for an electron interacting directly with a laser pulse, this new technique offers greater accuracy in terms of momentum and motion than the conventional scheme used in many PIC codes. These improvements translate into more faithful energy spectrum and electric charge for the accelerated beam in simulations of vacuum laser acceleration (VLA) or LWFA involving direct laser acceleration (DLA) at low plasma density. This new method, easy to implement and not computationally demanding, should then prove useful to study in depth and help develop novel VLA, DLA and LWFA techniques