Laser wakefield electron acceleration (LWFA) with high-intensity laser system is a powerful method to provide a high-energy electron beam in a quasi-table top configuration. The high-energy and high-charge density electron beams are employed across several experimental proposals that different research activity groups are promoting at Extreme Light Infrastructure (ELI-NP). The campaign experiment of LWFA in 2019 was performed at the National Institute for Quantum and Radiological Science and Technology (QST), Kansai Photon Science Institute (KPSI) in Japan.
LWFA with several type of mixed gases was studied. Selecting doping gas species and doping rate played an important role in controlling ionization potential and providing seed electron bunches resulting in high-charge density and collimated electron beam. We tested pure gases of H2 and He, and the combination of gases of H2 + N2 (0.2%), H2 + Ne (0.2%), He + N2 (0.2%), H2 + N2 (2%) He + N2 (2%), H2 + Ne (2%). As a consequence, H2 + N2 (2%) proved to be a good candidate to obtain high-energy and high-charge electrons with good reproducibility.
Another attempt in the campaign experiment was improving emittance of electron beam by shock wave production in a plasma channel. Plasma density transition is employed for trapping electrons. Two configurations with a combination of a gas jet and a blade, and double gas jets are tested. In any case, the first gas jet on the focal spot contributed to laser-driven electron generation and acceleration. A blade or another gas jet with higher density was used to make turbulence when the gas jet from the first nozzle strikes them. Subsequent production of plasma density transition was adjusted by changing the position of the gas nozzles and a blade. From initial experiment, we can conclude a gas jet and a blade has an advantage to get high-charge electrons, in contrast to the experiment with double gas-jets which favours the collimated electron beam