Pipe-like plasma targets for the production of gamma-beams using high-power lasers

We report numerical results from three-dimensional Particle-in-Cell simulations on the emission of collimated gamma-beams from structured targets irradiated by a high-power laser (1 PW, with a peak intensity of 5x10(22) W/cm(2)). The target has been given a cylindrical shape, with a prefilled cylindrical channel. We have analyzed how the photon yield changes with the channel radius and we have obtained an increasing trend up to a point of saturation which corresponds to a value close to the laser beam waist radius.