PETRA IV Workshop on Research with High-Energy X-rays at Ultra-Low Emittance Sources

Recent advances in storage ring technology pioneered by MAX IV (Sweden) allow synchrotron radiation sources to achieve significantly smaller emittances than those currently in operation. This new, multi-bend achromat technology can thus boost spectral brightness, enabling unprecedented experimental possibilities. The high-energy synchrotron radiation facilities ESRF (France), SPring-8 (Japan), and APS (USA) have settled upgrade plans to improve their storage ring emittance by up to two orders of magnitude at 6 GeV electron energy. PETRA III at DESY has the largest circumference with 2.3 km. As the emittance scales favorably with the storage ring size, an upgrade of PETRA III offers the unique potential to reach a diffraction limit up to X-ray energies of 10 keV. Operating at 6 GeV with an emittance of 10 pmrad, this PETRA IV facility would pave the way for new experimental opportunities, especially for those using high photon energies.     

PEPX-type lattice design and optimization for the High Energy Photon Source

A new generation of storage ring-based light sources, called diffraction-limited storage rings(DLSR), with emittance approaching the diffraction limit for multi-ke V photons by using multi-bend achromat lattice, has attracted worldwide and extensive studies of several laboratories, and been seriously considered as a means of upgrading existing facilities in the imminent future. Among various DLSR proposals, the PEPX design demonstrated that it is feasible to achieve sufficient ring acceptance for off-axis injection in a DLSR, by designing the lattice based on the ‘thirdorder achromat' concept and with a special high-beta injection section. For the High Energy Photon Source(HEPS)planned to be built in Beijing, a PEPX-type lattice has been designed and continuously improved. In this paper, we report the evolution of the PEPX-type design for HEPS, and discuss the main issues relevant to the linear optics design and nonlinear optimization.     

第四代同步辐射光源加速器物理与技术

同步辐射光源是20世纪应用最广泛的高性能X射线源,已成为物理、化学、能源环境、生物医学、先进材料等领域前沿研究的重要工具。进入21世纪,基于电子储存环的同步辐射光源的发展前沿是第四代同步辐射光源(4GLS)。其采用紧凑型的多弯铁消色散结构,可以实现接近甚至达到X射线衍射极限的超低束流发射度,将光源亮度在第三代光源基础上进一步提升2—3个数量级。文章将重点介绍第四代同步辐射光源关键的加速器物理与技术,以及国际范围内第四代同步辐射光源装置的发展情况。     

衍射极限储存环物理设计研究进展

总结了国内外在衍射极限储存环（DLSR）物理设计方面的研究进展。为了在合理的周长范围内实现超低束流发射度,DLSR线性束流光学设计普遍采用紧凑型多二极铁消色散结构。在非线性动力学优化中,通常采用相移控制技术、解析和数值优化技术减小由色品六极铁导致的强非线性效应。DLSR束流接受度较小,主要考虑脉冲多极铁偏轴注入和快速冲击磁铁在轴注入两种注入方案。束流集体效应（尤其是束流内部散射和托歇克散射效应）随发射度降低而增强,需要采用束长拉伸、横向反馈等方法提高DLSR中束流的稳定性。     

衍射极限储存环物理设计研究进展

总结了国内外在衍射极限储存环(DLSR)物理设计方面的研究进展。为了在合理的周长范围内实现超低束流发射度,DLSR线性束流光学设计普遍采用紧凑型多二极铁消色散结构。在非线性动力学优化中,通常采用相移控制技术、解析和数值优化技术减小由色品六极铁导致的强非线性效应。DLSR束流接受度较小,主要考虑脉冲多极铁偏轴注入和快速冲击磁铁在轴注入两种注入方案。束流集体效应(尤其是束流内部散射和托歇克散射效应)随发射度降低而增强,需要采用束长拉伸、横向反馈等方法提高DLSR中束流的稳定性。     

高能同步辐射光源

基于多弯铁消色散结构的超低发射度储存环光源是新一代同步辐射光源发展的一个重要方向。作为国内第一台第四代同步辐射光源,高能同步辐射光源已经完成物理及工程设计,并于2019年启动建设。高能同步辐射光源电子能量6 GeV,流强200 mA,水平自然发射度低于60 pm?rad,可提供能量达300 keV的X射线,在典型硬X射线波段的同步辐射亮度达1×1022 phs·s?1·mm?2·mrad?2·（0.1%bw）?1,可为材料科学、化学工程、能源环境、生物医学、航空航天、能源环境等众多基础和工程科学研究领域提供先进的实验平台。本文将介绍高能同步辐射光源项目的整体方案及物理设计。     

Compact IR synchrotron beamline design

Third‐generation storage rings are massively evolving due to the very compact nature of the multi‐bend achromat (MBA) lattice which allows amazing decreases of the horizontal electron beam emittance, but leaves very little place for infrared (IR) extraction mirrors to be placed, thus prohibiting traditional IR beamlines. In order to circumvent this apparent restriction, an optimized optical layout directly integrated inside a SOLEIL synchrotron dipole chamber that delivers intense and almost aberration‐free beams in the near‐ to mid‐IR domain (1–30 µm) is proposed and analyzed, and which can be integrated into space‐restricted MBA rings. Since the optics and chamber are interdependent, the feasibility of this approach depends on a large part on the technical ability to assemble mechanically the optics inside the dipole chamber and control their resulting stability and thermo‐mechanical deformation. Acquiring this expertise should allow dipole chambers to provide almost aberration‐free IR synchrotron sources on current and `ultimate' MBA storage rings.     

A hybrid doubled achromat based on a photon sieve

Photon sieves are diffractive optical elements with large chromatic aberration. To correct the dispersion of a photon sieve, a novel hybrid doubled achromat combined a photon sieve and a refractive lens is proposed. The design of this achromat applies the opposite dispersive characteristics of diffractive and refractive elements. Two design examples for different bandwidths of 300 nm and 80 nm in visible spectrum are given. For analyzing their focusing properties, the intensity distributions both along the axis and at the focal plane are studied. The results illustrate that the achromatic design is achieved and the secondary spectrum can be corrected for a narrow bandwidth. And compared to traditional hybrid achromat, it can focus to a sharper spot.     

Reduction of the beam emittance in the charged-particle storage rings with the help of periodic magnetic wigglers

Periodic magnetic structures (wigglers) have been successfully used for a long time for controlling beam parameters in charged-particle storage rings for various purposes (including the reduction of emittance). In this work, we optimize the optical functions of the storage ring gap into which a wiggler is installed for a more effective reduction of the emittance. Optimal solutions are obtained for the first time for FODOtype and theoretical minimum emittance (TME) structures. An original method is proposed for suppressing the contribution of the wiggler fields to the radiation excitation of the phase volume of the beam by modulating the field period along the wiggler axis.     

Conceptual design of Hefei advanced light source

The conceptual of Hefei Advanced Light Source, which is an advanced VUV and Soft X-ray source, was developed at NSRL of USTC. According to the synchrotron radiation user requirements and the trends of SR source development, some accelerator-based schemes were considered and compared; furthermore storage ring with ultra low emittance was adopted as the baseline scheme of HALS. To achieve ultra low emittance, some focusing structures were studied and optimized in the lattice design. Compromising of emittance, on-momentum and off-momentum dynamic aperture and ring scale, five bend acromat (FBA) was employed. In the preliminary design of HALS, the emittance was reduced to sub nm·rad, thus the radiation up to water window has full lateral coherence. The brilliance of undulator radiation covering several eVs to keVs range is higher than that of HLS by several orders. The HALS should be one of the most advanced synchrotron radiation light sources in the world.     

Minimizing radial emittance of a beam from a synchrotron radiation source

The feasibility of minimizing the radial emittance of a beam from a synchrotron radiation source (storage ring) is studied. It is shown that the emittance can be diminished by producing nonuniform fields in the magnetic storage ring.     

Scaling Law for Lattice Design of a Storage Ring

This paper describes and demonstrates the scaling law in the lattice design of a storage ring.When the size of the storage ring are enlarged or reduced according to a scale,the operating point ν and the beam emittance ε will be invarible.But while the energy of the storage ring is changed,the emittance will vary with the energy square.     

Special-purpose radiation sources based on the Siberia-2 storage ring

Synchrotron radiation (SR) generated by homogeneous magnetic fields of bending magnets is now employed at the Siberia-2 electron storage ring. It is planned that, in the near future, most of the storage ring’s free straight sections will be equipped with insertion devices (undulators and wigglers). Two projects of specialized radiation sources based on the Siberia-2 stor age ring are discussed. The first source is a vacuum milliundulator intended for generation of extremely bright X-ray beams. An X-ray source with vertically limited diffraction is shown to be feasible when the vertical emittance of an electron beam is equal to the diffraction emittance of photons with an energy of 2 keV. The second source uses edge radiation (ER) generated at the ends of bending magnets of the storage ring. Calculations show that, in the infrared and ultraviolet spectral regions, the ER intensity must exceed the intensity of standard SR formed by the homogeneous field of a bending magnet.     

Longitudinal momentum mining of beam particles in a storage ring

I describe a scheme for selectively isolating high density low longitudinal emittance beam particles in a storage ring from the rest of the beam without emittance dilution. I discuss the general principle of the method, called longitudinal momentum mining, beam dynamics simulations and results of beam experiments. Multi-particle beam dynamics simulations applied to the Fermilab 8 GeV Recycler (a storage ring) convincingly validate the concepts and feasibility of the method, which I have demonstrated with beam experiments in the Recycler. The method presented here is the first of its kind.     

Coupling measurement and correction at the SSRF storage ring

Brightness is an important parameter for 3^rd generation light source. Correcting the emittance coupling is a realistic way to increase brightness without any additional equipment in a machine under operation. The main sources of emittance coupling are betatron coupling and vertical dispersion. At the SSRF storage ring, tune split and LOCO are used to measure the respective betatron and emittance coupling. Both of these sources can be corrected by skew quadrupoles. By measuring the skew quadrupole-coupling response matrix, betatron coupling can be changed from 0.014% to 2%. But the vertical dispersion changes at the same time. LOCO can find the suitable setting to correct simultaneously the betatron coupling and vertical dispersion. The emittance coupling can be reduced to 0.17% by this method. More simulations show the potential for smaller emittance coupling if more skew quadrupoles are employed.     

束内散射效应下HALF储存环物理参数的优化设计

合肥先进光源（HALF）是我国规划建设的软X射线与VUV衍射极限储存环光源（DLSR）。如何有效地实现衍射极限束流发射度,是DLSR物理设计中的核心问题之一。基于束流发射度演化方程,针对HALF预研项目的储存环物理设计方案,计算了束内散射（IBS）效应带来的发射度增长,研究了DLSR中关键参数选择对IBS造成的发射度增长的影响。研究表明,在中低能DLSR物理设计中需要综合考虑储存环的周长、同步辐射阻尼时间等关键参数,以更好地抑制束流发射度的增长。在此研究基础上,通过综合考虑用户需求与储存环物理要求,提出了HALF当前工程项目的储存环物理设计方案。进一步综合应用束团拉伸、全耦合等措施后,更高效地抑制了HALF储存环内IBS造成的束流发射度增长。     

Beam dynamics of the superconducting wiggler on the SSRF storage ring

In the SSRF Phase-II beamline project, a superconducting wiggler(SW) will be installed in the electron storage ring. It may greatly impact on the beam dynamics due to the very high magnetic field. The emittance growth becomes a major problem, even after correction of the beam optics. A local achromatic lattice is studied, in order to combat the emittance growth and keep the performance of the SSRF storage ring as high as possible. Other effects of the SW are also simulated and optimized, including the beta beating, the tune shift, the dynamic aperture, and the field error effects.     

Bunch length manipulation in a diffraction-limited storage ring

In an electron storage ring,the bunch length can be increased or decreased by using harmonic cavities.Taking the High Energy Photon Source as an example,we test the bunch length manipulation with harmonic cavities in a diffraction-limited storage ring(DLSR).The most important collective effects in a DLSR,intra-beam scattering and Touschek effects,are evaluated for different bunch-length patterns.Our study shows that it is feasible to produce long and short bunches simultaneously in a DLSR,without causing severe emittance growth and reduction in lifetime.     

Conceptual design of Hefei advanced light source

The conceptual of Hefei Advanced Light Source, which is an advanced VUV and Soft X-ray source, was developed at NSRL of USTC. According to the synchrotron radiation user requirements and the trends of SR source development, some accelerator-based schemes were considered and compared; furthermore storage ring with ultra low emittance was adopted as the baseline scheme of HALS. To achieve ultra low emittance, some focusing structures were studied and optimized in the lattice design. Compromising of emittance, onmomentum and off-momentum dynamic aperture and ring scale, five bend acromat (FBA) was employed. In the preliminary design of HALS, the emittance was reduced to sub nm·rad, thus the radiation up to water window has full lateral coherence. The brilliance of undulator radiation covering several eVs to keVs range is higher than that of HLS by several orders. The HALS should be one of the most advanced synchrotron radiation light sources in the world.     

Low emittance lattice for the storage ring of the Turkish Light Source Facility TURKAY

The TAC(Turkish Accelerator Center) project aims to build an accelerator center in Turkey. The first stage of the project is to construct an Infra-Red Free Electron Laser(IR-FEL) facility. The second stage is to build a synchrotron radiation facility named TURKAY, which is a third generation synchrotron radiation light source that aims to achieve a high brilliance photon beam from a low emittance electron beam at 3 Ge V. The electron beam parameters are highly dependent on the magnetic lattice of the storage ring. In this paper a low emittance storage ring for TURKAY is proposed and the beam dynamic properties of the magnetic lattice are investigated.