We use numerical simulations to demonstrate that a source of bright collimated vortex $\gamma$-ray with large orbital angular momentum can be achieved by irradiating a circularly polarized laser with an intensity about $10^{ 22}\rm{ W/{ cm^2}}$ on a cone-fan target. In the studied setup, electron beam of energy of hundreds of MeV and vortex laser pulse are formed. And furthermore a high quality vortex $\gamma$-ray is yielded with small divergence of $5^{ \circ}$ and high peak brilliance $\sim5\times10^{ 22}$ photons ${ \rm\cdot s^{ -1} \cdot mm^{ -2} \cdot mrad^{ -2}}$ $0.1\%\mathrm{ BW}$ at $10\mathrm{ MeV}$. A considerable fraction of angular momentum of laser is converted to electron beam and vortex $\gamma$-ray, which are roughly $27.8\%$ and $3\%$, respectively. And the conversion efficiency of energy from laser to electron beam and vortex $\gamma$-ray are around $41\%$ and $3.8\%$. Moreover, comparative simulations for different right radius of cone reveal that there exists an optimal size that makes the highest angular momentum of $\gamma$-ray photons to be around $2.8\times10^6\hbar$. The comparative simulations for different laser modes exhibit that it is more appropriate to choose the circularly polarized laser to generate vortex $\gamma$-ray than the Laguerre-Gaussian one.
Categories: physics.plasm-ph physics.acc-ph