The Magnetic Compensation Scheme of the FCC-ee Detectors

TL;DR

This paper discusses a magnetic compensation scheme for FCC-ee detectors that minimizes beam disruption, ensuring high luminosity performance even at demanding energies with a simple coil arrangement.

Contribution

It introduces a simple yet effective magnetic compensation scheme using two additional coils per interaction point to reduce emittance blow-up.

Findings

Vertical emittance blow-up is minimized at the IP.

The scheme maintains high performance at Z energies (~45 GeV).

Performance is unaffected even with four experiments in the ring.

Abstract

A crucial part of the design of an FCC-ee detector is the minimisation of the disruption of the beam due to the presence of a large and powerful detector magnet. Indeed, the emittance blow-up of the few meters around the interaction point (IP) at lower energies is comparable to the emittance introduced by the rest of the 100 km ring. Vertical emittance is the single most important factor in achieving high performance (luminosity, in this case) in a modern e^+ e^- storage ring such as the FCC-ee. The design adopted is the simplest possible arrangement that can nevertheless deliver high performance: two additional coils per IP side. The performance achieved is such that vertical emittance blow-up will not be a limiting performance factor even in the case of a ring with four experiments, and even in the most demanding energy regime, that of the Z running (about 45 GeV beam energy).