Simulation of spiral beam scanning for uniform irradiation on a large target

A new circular beam scanning method for uniform irradiation over a large area has been developed. A beam follows a spiral trajectory on a target, which guarantees continuous circular irradiation. A scanning speed and a trajectory spacing in a radial direction are invariable to make a particle distribution uniform. A radial position of a beam spot and an angular frequency of the spiral scanning are expressed by an irrational function of time. Relative variation in a two-dimensional particle distribution has been investigated by using a simulation program. In case a radial pitch of the spiral trajectory is much smaller than a beam width, uniformity of the particle distribution depends completely on the ratio of the minimum radius of the trajectory to the beam width. Less than ±10% uniformity of the particle distribution can be obtained for the minimum radius to beam-width ratio of less than 0.3.