Generation of a large amount of energetic electrons in complex-structure bubble

By means of particle-in-cell (PIC) simulations, we found that when the focus size of a laser pulse is much larger than the plasma wavelength and when the laser power is hundreds of times larger than the critical power required for relativistic self-focusing, a large complex bubble is formed. The transversal size of the bubble depends on the laser spot size. Owing to the large bubble size, a bunch of electrons with the total charge in the range of a few tens of nano-Coulombs is trapped and accelerated in the bubble. When the plasma density is 2x1019 cm-3, the charge of the energetic electron bunch with energy above 5 MeV exceeds 45 nC with a laser spot size of 60 μm. Electrons continuously self-injected into such a complex bubble serve as an effective source of high-charge electron bunches.