Simulation study of a bright attosecond $\gamma$-ray source generation by irradiating an intense laser on a cone target

The interaction between an ultrastrong laser and a cone-like target is an efficient approach to generate high power radiations like attosecond pulses and terahertz waves. The object is to study the $\gamma$-ray generation under this configuration with the help of 2D particle-in-cell simulations. It is deciphered that electrons experience three stages including injection, acceleration and scattering to emit high energy photons via nonlinear compton scattering (NCS). These spatial-separated attosecond $\gamma$-ray pulses own high peak brilliance ($>{10}^{22}$ photons/($\mathrm{s}\cdot \mathrm{m}{\mathrm{m}}^2\cdot \mathrm{m}\mathrm{r}\mathrm{a}{\mathrm{d}}^2\cdot 0.1\mathrm{\%}\mathrm{B}\mathrm{W}$)) and high energy (6MeV) under the case of normalized laser intensity $a_0=30$ ($\mathrm{I}=2\times {10}^{21}\mathrm{W}\mathrm{/}\mathrm{c}{\mathrm{m}}^2$). Besides, the cone target turns out to be an order of magnitude more efficient in energy transfer compared with a planar one.