Application of a laser-heater for advanced guiding of PetaWatt laser pulses in capillary plasmas*

Laser-plasma accelerators (LPAs) form an attractive scheme for developing compact accelerators, due to their high acceleration gradients. In the push to higher electron beam energies, one of the main challenges is to increase the dephasing length $L_d$ over which energy can be transferred to the electrons, while keeping the laser confined to provide the required accelerating fields. Currently, the highest energy electron beams from an LPA have been achieved by using pre-formed density channels from capillary discharge plasmas.\textsuperscript{[1]} Confinement of laser pulses with higher order mode content required higher density than optimum for reaching higher energies. Improved laser confinement at lower density, extending $L_d$, has been proposed through use of a ns-scale heater pulse before the ultrashort, high-powered pulse arrives.\textsuperscript{[2]} Here, we present experimental results of applying this technique to channels of up to 20~cm in length to enhance guiding of PetaWatt pulses from the BELLA laser, including electron and laser properties from the accelerator.\newline [1] W.P.~Leemans \textit{et al.}, Physical Review Letters \textbf{113}, 245002 (2014).\newline [1] N.A.~Bobrova \textit{et al.}, Physics of Plasmas \textbf{20}, 020703 (2013)