Développement d'un prototype d'injecteur laser-plasma à 150 MeV

par Pierre Drobniak

Projet de thèse en Physique des accélérateurs

Sous la direction de Kevin Cassou.

Thèses en préparation à université Paris-Saclay , dans le cadre de École doctorale Particules, Hadrons, Énergie et Noyau : Instrumentation, Imagerie, Cosmos et Simulat , en partenariat avec Laboratoire de Physique des deux Infinis Irène Joliot-Curie (laboratoire) et de Faculté des sciences d'Orsay (référent) depuis le 01-10-2020 .

  • Résumé

    Voir la description en anglais ci dessous.

  • Titre traduit

    Development of 150 MeV laser-plasma injector prototype

  • Résumé

    Laser-plasma acceleration is one of the promising paths for designing future particle accelerators. Numerous spectacular demonstrations in terms of high accelerating gradients and compactness have been made over the last twenty years. However, the transition to an accelerator designed as a daily operating machine requires the removal of several technological bottlenecks. In accelerator, the injector can be a crucial subsystem; it usually delivers an electron beam at the MeV level, and its characteristics— such as emittance, bunch duration and energy spread—strongly impact the parameters of the final beam. In similar way, in laser-plasma accelerator the injection and acceleration at few millimeters scale can be decoupled. However, injecting electrons into the laser-driven plasma wakefield accelerating structure is not an easy task: the wavelength of the accelerating structure is on the order of $lambda_p. sim 10-30,mu$m for density $10^{18} -10^{19},$cm$^{-3}$. Several methods have been proposed and demonstrated for injecting plasma electrons into an existing plasma wakefield. One is to create electrons at the right phase in the wakefield by ionization triggered injection. Another is to slow down the plasma wakefield to ease the electron trapping. The phase velocity of the wakefield locally can be decreased by tailoring the plasma density and leads to controlled injection dubbed injection in downward density ramps. A laser-plasma injector (LPI) prototype is being built in the LAL laboratory using the 40 TW laser driver to provide an electron beam at 150-200 MeV, with a 30 pC charge, 1 mm.mrad emittance, an energy spread < 5%, and a bunch length in the femtosecond range with stability and reliability comparable to conventional RF electron accelerator. This project aimed to be test facility elaborated with three strategic design guidelines: (a) Laser quality control identified as the main factor to determine the electron beam quality with enhanced laser beam diagnostics - (b) High repetition rate machine operation with an ad hoc high rep-rate data acquisition and command control - (c) Targetry, engineering of the target with a multi-zone density tuning for a controlled injection and acceleration with a precise tailoring of plasma-density profiles. This has been identified as one of the critical points in achieving stable and reproducible conditions in LWFA accelerators. A compact cost-efficient dual zone plasma cell target integrated as a beam line module will be developed using new opportunities of additive manufacturing process. The target development will be the central part of the pHD work. The pHD student or the M2 trainee will realized the design of a first prototype of dual zone target from simulation to realization and test on a dedicated test bench. Then, the candidate will participate to the commissioning of the LPI. A complete study of the LPI will be performed in during at least one year of the thesis to achieve a complete optimization for a stable and reliable operation. These achievements are not possible without simulations support by a PIC code to understand and optimize the laser wakefield acceleration process. The candidate will use a state-of-the-art open source SMILEI code for LPI target optimization in combination with CFD software.