Multi-GeV electron beam and high brightness betatron x-ray generation in recent Texas Petawatt laser-driven plasma accelerator experiments

Compact laser-plasma accelerators (LPAs) driven by petawatt (PW) lasers have produced highly collimated, quasi-monoenergetic multi-GeV electron bunches with $\sim$ 100 pC charge [1], which are promising sources of ultrafast x-rays. Here we report three recent advances in PW-LPA performance brought about by optimizing the focal volume of the Texas PW laser with a deformable mirror. First, we accelerated electrons up to 3 GeV with hundreds of pC over 1GeV and \textless 0.5mrad divergence. Second, we significantly improved shot-to-shot reproducibility (90{\%} shots \textgreater 1GeV, 10{\%} \textgreater 2GeV). Third, by introducing a double-peaked laser focus, creating a ``double bubble'' that subsequently merged [2], we significantly increased electron charge (0.5 nC) above 1 GeV, while producing brighter (10$^{22}$photon/mm$^{2}$/rad/0.1{\%}), harder (up to 30keV) betatron x-rays, characterized by a multi-metal filter pack and phase-contrast imaging. We observe evidence of dimuon production [3] by irradiating a high-Z target with this high-charge, GeV electron beam. [1] Wang \textit{et a}l., Nature Commun. \textbf{4}, 1988 (2013); Kim \textit{et al}., Phys. Rev. Lett. 11, 165002( 2013). [2] Wen \textit{et al}., Phys. Plasmas \textbf{17}, 103113 (2010). [3] Titov \textit{et al}., Phys. Rev.-ST AB \textbf{12}, 111301 (2009).