LA³NET results in NIMA – selection of abstracts I
Special section on Laser Applications at Accelerators: selection of research highlights from the European network LA3NET has recently been published in Nuclear Instruments and Methods in Physics Research Section A. In the next weeks we will present selection of abstracts from this special edition. Below are papers by LA3NET Fellows, Andreas Döpp and Thomas Hofmann.
‘A bremsstrahlung gamma-ray source based on stable ionization injection of electrons into a laser wakefield accelerator’,A. Döpp, E. Guillaume, C. Thaury, A. Lifschitz, F. Sylla, J-P. Goddet, A. Tafzi, G. Iaquanello, T. Lefrou, P. Rousseau, E. Conejero, C. Ruiz, K. Ta Phuoc, V. Malka, Nucl. Instr. Meth. A (2016), doi:10.1016/j.nima.2016.01.086
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 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 γ-ray source size of less than 100 μm for a 0.5 mm tantalum converter placed at 2 mm from the accelerator exit. Furthermore we present radiographs of image quality indicators.
‘Experimental results of the laserwire emittance scanner for LINAC4 at CERN’, Thomas Hofmann, Gary E. Boorman, Alessio Bosco, Enrico Bravin, Stephen M. Gibson, Konstantin O. Kruchinin, Uli Raich, Federico Roncarolo, Francesca Zocca, Nucl. Instr. Meth. A (2016), doi:10.1016/j.nima.2016.02.018
Within the framework of the LHC Injector Upgrade (LIU), the new LINAC4 is currently being commissioned to replace the existing LINAC2 proton source at CERN. After the expected completion at the end of 2016, the LINAC4 will accelerate H− ions to 160 MeV. To measure the transverse emittance of the H− beam, a method based on photo-detachment is proposed. This system will operate using a pulsed laser with light delivered via an optical fibre and subsequently focused onto the H− beam. The laser photons have sufficient energy to detach the outer electron and create H0/e− pairs. In a downstream dipole, the created H0 particles are separated from the unstripped H− ions and their distribution is measured with a dedicated detector. By scanning the focused laser beam across the H− beam, the transverse emittance of the H− beam can be reconstructed. This paper will first discuss the concept, design and simulations of the laser emittance scanner and then present results from a prototype system used during the 12 MeV commissioning of the LINAC4.