Beam transport for uniform irradiation: nonlinear space charge and the effect of boundary conditions

Abstract

Proposed high-intensity ion accelerators required for Accelerator Driven Transmutation Technologies (ADTT) and the International Fusion Materials Irradiation Facility (IFMIF) demand careful control of beam shape and distribution on target; for example, uniform irradiation of a rectangular area. Nonlinear magnetic elements can yield the desired beam on target; however, nonlinear space charge forces also play a significant role. We consider the importance of boundary conditions used when modeling space charge effects in such a transport line. Simple analytical criteria are derived for determining when nonlinear space charge forces will be significant and for when proper treatment of boundary conditions is required. Two computer codes employing different boundary conditions for their respective space charge models, the PIC code BEAMPATH and the high-order optics code TOPKARK, are used to simulate an example transport line in order to demonstrate our results.