New plasma sources for long laser wakefield plasma accelerators

Electron accelerators based on laser-plasma interaction have been demonstrated to achieve energy gains of 1 GeV over a distance of 33 mm [1]. Plasma channels provide a means to extend the interaction length of a laser with a plasma many times beyond the Rayleigh length. Numerical simulations suggest that plasma channels with typical lengths of one meter are suitable for producing good-quality electron bunches with energies of the order of tens of GeVs. The implementation of such long plasma channels is however a great challenge. In our setup, plasma channels are formed by a low rise-time and high-power high-voltage electric discharge between two electrodes in a structured gas cell [2] that are separated by 20 mm. The rapid free expansion of the plasma leads to electron densities with an approximate parabolic radial profile. These plasma channels are structures that are suitable for guiding highpower laser pulses. The low rise-time of the high-voltage pulse suppresses the temporal jitter associated with the formation of the plasma channels, while the apertures in the blades inside the structured gas cell define the path of the discharge. A current-limited continuous pre-discharge can optionally be used to improve the reproducibility. Moreover, the structured gas cell allows for interferometric diagnostics along the transverse direction. We report on recent results and describe current improvements to our experimental setup.