A bremsstrahlung gamma-ray source based on stable ionization injection of electrons into a laser wakefield accelerator

Laser wakefield acceleration permits the generation of ultra-short, high-brightness relativistic electron beams on a millimeter scale. While those features are of interest for many applications, the source remains constraint by the poor stability of the electron injection process. Here we present results on injection and acceleration of electrons in pure nitrogen and argon. We observe stable, continuous ionization-induced injection of electrons into the wakefield for laser powers exceeding a threshold of 7 TW. The beam charge scales approximately linear with the laser energy and is limited by beam loading. For 40 TW laser pulses we measure a maximum charge of almost 1 nC per shot, originating mostly from electrons of less than 10 MeV energy. The relatively low energy, the high charge and its stability make this source well-suited for applications such as non-destructive testing. Hence, we demonstrate the production of energetic radiation via bremsstrahlung conversion at 1 Hz repetition rate. In accordance with Geant4 Monte-Carlo simulations, we measure a gamma-ray source size of less than 100 microns for a 0.5 mm tantalum converter placed at 2 mm from the accelerator exit. Furthermore we present radiographs of image quality indicators

Shock assisted ionization injection in laser-plasma accelerators

International audienceIonization injection is a simple and efficient method to trap an electron beam in a laser plasma accelerator. Yet, because of a long injection length, this injection technique leads generally to the production of large energy spread electron beams. Here, we propose to use a shock front transition to localize the injection. Experimental results show that the energy spread can be reduced down to 10 MeV and that the beam energy can be tuned by varying the position of the shock. This simple technique leads to very stable and reliable injection even for modest laser energy. It should therefore become a unique tool for the development of laser-plasma accelerators

Aménagement de l’estuaire de la Rance. Modèle réduit de la station d’essais de Saint-Malo -Saint-Servan

The Rance estuary project the Saint Malo Saint Servan research station model The Rance model was built by the Laboratoire National d’Hydraulique for Electricité de France (Service d’Etudes sur l’Utilisation des Marées et Région d’Equipement Hydraulique n° 8) to study the stages of the construction and operating characteristics of the projected tidal power plant. At the request of Electricité de France the model was built at Saint Maio near the future site of the dam. . II is built to a 1/150 th scale without distorsion and is 1,500 m2 in area. The Laboratoire National d’Hydraulique has developed and adapted certain measuring instruments for this model (tide control mechanism, automatic point gauges, differential gauges and current recorders, etc.). The operation of the model started with careful calibration tests to see that natural conditions were properly reproduced. The tests described in this paper ware carried out in conjunction with these carried out by the S.O.G.R.E.A.H. laboratory on the overall model of the Ranee and on partial models for details.Le modèle de la Rance a été construit par le Laboratoire National d'Hydraulique, pour le compte d'Electricité de France (Service d'Etudes sur l'Utilisation des Marées et Région d'Equipement Hydraulique n° 8), pour l'étude des phases de construction et des conditions locales d'exploitation de l'usine marémotrice en projet. A la demande d'Electricité de France, le modè.e a été construit à Saint-Malo au voisinage du site du futur barrage. Son échelle est égale à 1/150, sans distorsion, sa surface est de 1.500 m2. A l'occasion de ce modèle, le Laboratoire National d'Hydraulique a été amené à améliorer et aménager certains appareils de mesures (appareils à marée, pointes suiveuses et leur montage en pointes différentielles, enregistreur de vitesse, etc.). La mise en service du modèle a commencé par un étalonnage soigné pour contrôler la bonne reproduction des conditions naturelles. Les essais, dont on décrit la technique, ont été conduits en liaison avec ceux que le Laboratoire Dauphinois d'Hydraulique effectuait sur le modèle d'ensemble de la Rance et sur des modèles de détail.Michon X., Goddet J. Aménagement de l’estuaire de la Rance. Modèle réduit de la station d’essais de Saint-Malo -Saint-Servan. In: Les énergies de la mer. Compte rendu des quatrièmes journées de l'hydraulique, Paris, 13, 14 et 15 juin 1956. Tome 1, 1957

Two-Color Soft X-Ray Lasing in a High-Density Nickel-like Krypton Plasma

International audienc

Single-shot temporal profile measurement of a soft X-ray laser pulse

We report an original method allowing to recover the temporal profile of any kind of soft X-ray laser pulse in single-shot operation. We irradiated a soft X-ray multilayer mirror with an intense infrared femtosecond laser pulse in a traveling wave geometry and took advantage of the sudden reflectivity drop of the mirror to reconstruct the temporal profile of the soft X-ray pulse. We inferred a pulse shape with a duration of a few ps in good agreement with numerical calculations and experimental work