Transport and analysis of electron beams from a laser wakefield accelerator in the 100 MeV energy range with a dedicated magnetic line

Electron bunches generated by laser driven wakefield acceleration are transported and analyzed using a magnetic line composed of a triplet of quadrupoles and a dipole. Short pulse bunches with a total charge of ≈130pC, and broad band energy spectra in the range 45 to 150MeV are generated by ionization assisted injection in a gas cell. The electron source is imaged about one meter away from the exit of the gas cell by the magnetic line, delivering electron bunches at a stable position in the image plane where a charge density of ≈2.9pC∕mm² at an energy of 69.4±0.6MeV is achieved. This magnetic line improves dramatically the accuracy of energy determination of this electron source, leading to an energy error as low as 8.6‰ in the 70MeV range for 5mrad divergence electron bunch and considering the resolution of the entire detection system. The transport of bunches with improved stability and energy selection paves the way to various applications including multi-stage laser plasma acceleration.