Use of multipole magnetic fields for making uniform irradiations

A technique using multipole magnetic fields to shape charged particle intensity distributions is discussed. The concept is to use the nonlinear magnetic field of a multipole to preferentially focus the edges of a particle distribution back to the center in such a way that the final distribution is uniform. The integral transformation theory of this technique is presented. Calculations shows that a Gaussian-shaped intensity distribution can be smoothed to better than 5% uniformity for up to 95% of the initial beam intensity. A sample beamline and variable strength multipole are presented. (orig.)