  We report on the stable and continuous operation of a kilohertz laser-plasma
accelerator. Electron bunches with 2.6 pC charge and 2.5 MeV peak energy were
generated via injection and trapping in a downward plasma density ramp. This
density transition was produced in a newly designed asymmetrically shocked gas
nozzle. The reproducibility of the electron source was also assessed over a
period of a week and found to be satisfactory with similar values of the beam
charge and energy. These results show that the reproducibility and stability of
the laser-plasma accelerator are greatly enhanced on the long-term scale when
using a robust scheme for density gradient injection.
