Decoupling of beams previously coupled by effective stand-alone solenoid fringe fields

TL;DR

This paper explains how beams affected by solenoid fringe fields can be effectively decoupled using a beam line that provides decoupling, maintaining stable Twiss parameters despite variations in fringe field strength.

Contribution

It demonstrates that any decoupling beam line can reliably remove coupling introduced by solenoid fringe fields, extending previous understanding to a more general context.

Findings

Decoupling is effective across varying fringe field strengths.

Twiss parameters remain stable after decoupling.

Previous results are generalized to broader beam line configurations.

Abstract

Beams passing through a solenoid fringe field experience x-y coupling and change of their eigen-emittances. As reported previously (C.~Xiao et al., Phys. Rev. ST Accel. Beams 044201, {\bf 16} 2013) constant settings of a subsequent decoupling section can be found such that variation of the fringe field strength will not change the Twiss parameters $\beta$ and $\alpha$ in both transverse planes at the exit of the decoupling section. For time being this feature was understood for a generic beam line but not to the generality to which it is observed. This report is on explanation of the convenient decoupling of fringe-coupled beams by any beam line that provides decoupling. For better coherence this report includes recapitulation of previous works.