Enhanced betatron x-ray emission in a laser wakefield accelerator and wiggler due to collective oscillations of electrons

We report x-ray emission caused by betatron motion of electrons in a laser wakefield accelerator driven high intensity ($\ensuremath{\sim}4\ifmmode\times\else\texttimes\fi{}{10}^{19}\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$) pulse interaction with 4-mm long helium gas-jet and study the role collective oscillation as well plasma density. The oscillations electrons, inferred from observed wavy pattern electron beam spectrum (up to 300 MeV) led enhance peak flux which was found be further enhanced at higher densities. A similar correlation between enhancement also nitrogen gas target. Possible physical pictures for above observations are suggested discussed. For jet target, typically source brightness is $\ensuremath{\ge}1\ifmmode\times\else\texttimes\fi{}{10}^{20}\text{ }\mathrm{photons}/\mathrm{s}\text{ }{\mathrm{mm}}^{2}\text{ }{\mathrm{mrad}}^{2}$ 0.1% BW, critical energy $35\ifmmode\pm\else\textpm\fi{}5\text{ }\mathrm{keV}$. have demonstrated application high-resolution imaging.