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 20 MeV are generated from laser wakefield acceleration (LWFA) by focusing few TW laser pulses onto a sub mm gas jet of dense nitrogen. A 152 mm diameter orifice is used to produce transient 20 ms) free flow nitrogen jets, while the plasma electrons with a 860 mm wide Gaussian density profile and a density up to ~2.8 x 1019 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 ~11 MeV and a charge 20 pC are routinely generated with =20% energy and charge stabilities, ~20 mrad divergence, and ~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.