Laser Wakefield Acceleration Driven By A Few-Terawatt Laser Pulse In A Sub-Mm Nitrogen Gas Jet

Quasi-monoenergetic electron bunches with energies peaked in 10-20MeV are generated from laser wakefield acceleration (LWFA) by focusing few-TW laser pulses onto a sub-mm gas jet of dense nitrogen. A 152-mu m diameter orifice is used to produce transient (<= 20 ms), free-flow nitrogen jets, while the plasma electrons with a 860-mu m wide Gaussian density profile and a density up to similar to 2.8x10(19)cm(-3) enable self-focusing effect and self-modulation instability to develop on the pump pulse, resulting in a high intensity to drive the LWFA. Meanwhile, this Gaussian nitrogen plasma facilitates ionization-induced injection and density down-ramp injection throughout the acceleration process and consequently improves the energy and charge stabilities of output electrons. When 40-fs, 3.2-TW, 810-nm pump pulses are applied, output electrons with a peak energy similar to 11MeV and a chargesimilar to 20 pC are routinely generated with<= 20% energy and charge stabilities, similar to 20 mrad divergence, and similar to 10 mrad pointing variation. A large electron energy spread is attributed to the dominant mechanisms of ionization and down-ramp injections. This scheme represents a viable approach for implementing a high-repetition-rate LWFA, from which stable tens-of-MeV electrons can be generated with less than 150 mJ of on-target laser energy.