Collimation optimization in high intensity rings

In high intensity proton rings, collimation is needed in order to maintain reasonable levels of residual activation and allow hands-on maintenance. A small acceptance to emittance ratio and restrained longitudinal space become important restrictions when dealing with low energy rings. The constraints and specifications when designing a collimation system for this type of machine will be reviewed. The SNS accumulator ring will serve as an example along which we will illustrate the optimization path. Experimental studies of collimation with 1.3 GeV proton beams are currently under way in the U-70 machine in Protvino. The first results will be presented.

1 INTRODUCTION

In high intensity rings, the size of the beam is enhanced to avoid excessive space-charge forces. The beam thus occupies the highly nonlinear region of the magnetic field near the bore and most of the RF bucket. Large fringe fields are inherent to short and wide magnets and decrease further the beam stability [1]. Rapid acceleration produces non-adiabatic trapping on the longitudinal plane. All these effects pump protons from the core of the beam into the tails in all three dimensions. On the other hand, the relative aperture is dramatically small. While in a high energy collider the aperture of the accelerator is around (where is rms beam size), in a high intensity ring the aperture is typically less than .