Realization of locally-round beam in an ultimate storage ring using solenoids

TL;DR

This paper proposes a novel method using solenoids and an anti-solenoid to achieve a locally-round beam in ultimate storage rings, enhancing photon brightness and coherence for advanced X-ray sources.

Contribution

The paper introduces a new technique employing solenoids and anti-solenoids to generate a locally-round beam in USRs, demonstrated through theoretical analysis and application to a specific storage ring design.

Findings

Successful theoretical demonstration of the method

Application to Beijing Advanced Photon Source design

Potential for improved beam quality in USRs

Abstract

Ultimate storage rings (USRs), with electron emittance smaller than 100 pm.rad and on the scale of the diffraction limit for hard X-rays in both transverse planes, have the potential to deliver photons with much higher brightness and higher transverse coherence than that projected for the rings currently operational or under construction. Worldwide efforts have been made to design and to build light sources based on USRs. How to obtain a round beam, i.e. beam with equivalent transverse emittances, is an important topic in USR studies. In this paper, we show that a locally-round beam can be achieved by using a pair of solenoid and anti-solenoid with a circularly polarized undulator located in between. Theoretical analysis and application of this novel method, particularly to one of the Beijing Advanced Photon Source storage ring design having natural emittance of 75 pm.rad, are presented.