  CO2 laser-driven electron acceleration is demonstrated with particle-in-cell
simulation in low-density plasma. An intense CO2 laser pulse with long
wavelength excites wakefield. The bubble behind it has a broad space to sustain
a large amount of electrons before reaching its charge saturation limit. A
transversely propagating inject pulse is used to induce and control the ambient
electron injection. The accelerated electron bunch with total charge up to 10
nC and the average charge per energy interval of more than 0.6 nC/MeV are
obtained. Plasma-based electron acceleration driven by intense CO2 laser
provides a new potential way to generate high-charge electron bunch with low
energy spread, which has broad applications, especially for X-ray generation by
table-top FEL and bremsstrahlung.
