Low emittance lattice design from first principles: reverse bending and longitudinal gradient bends

TL;DR

This paper explores innovative lattice designs for storage rings that combine longitudinal gradient bends and reverse bends to achieve significantly lower emittance than traditional methods, with practical examples including upgrades for Swiss Light Source.

Contribution

It introduces a general framework for emittance optimization using LGB and RB in lattice cells, surpassing traditional TME cell limitations.

Findings

Lower emittance achieved with LGB/RB combinations

Optimal phase advance depends on cell class

Practical lattice example for Swiss Light Source upgrade

Abstract

The well-known relaxed theoretical minimum emittance (TME) cell is commonly used in the design of multi-bend achromat (MBA) lattices for the new generation of diffraction limited storage rings. But significantly lower emittance at moderate focusing properties can be achieved by combining longitudinal gradient bends (LGB) and reverse bends (RB) in a periodic lattice unit cell. LGBs alone, however, are of rather limited gain. We investigate the emittance achievable for different unit cell classes as a function of the cell phase advance in a most general framework, i.e. with a minimum of assumptions on the particular cell optics. Each case is illustrated with a practical example of a realistic lattice cell, eventually leading to the LGB/RB unit cell of the baseline lattice for the upgrade of the Swiss Light Source.