Speaker
Description
In designing high-intensity proton synchrotrons, discussions often focus on the magnitude of the tune shift, that is, the linear effects of space charge. This is because the strength of space charge is generally considered to be characterized by the magnitude of the tune shift. Consequently, space-charge mitigation has traditionally been almost synonymous with tune-shift mitigation. Typical countermeasures have included accepting large-emittance beams by increasing the ring aperture, raising the injection momentum, and bunch lengthening in the longitudinal direction. These are indeed robust and effective approaches. However, when asked how a ring should be designed for high-intensity operation, it has been difficult to give an answer beyond simply increasing the aperture at additional cost.
A discussion of beam loss requires consideration not only of linear effects but also of nonlinear effects, and the nonlinear space-charge effects cannot be characterized solely by the Laslett parameter. Unlike resonances induced by magnetic fields, the correction of nonlinear space-charge effects is particularly challenging because space charge is inherently intensity-dependent and acts around the entire ring. On the other hand, nonlinear space-charge effects are largely determined at the ring-design stage. It is therefore important to pursue a design that suppresses these nonlinear effects as much as possible.
We have therefore devised a lattice design that locally corrects nonlinear space-charge effects, specifically within the arc sections, thereby suppressing their overall impact. Using the J-PARC MR as an example, we verified the effectiveness of this design through theory, simulations, and experiments.