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The transition from 3rd to 4th generation synchrotron light sources via Diffraction Limited Storage Rings (DLSRs) is largely de=ined by the reduction of horizontal emittances and, in turn, achieving more uniform transverse X-ray beam pro=iles. Previously at Advanced Photon Source (APS), SPECTRA simulations were performed to compare to the vertical emittance measurements made at the IEX undulator and beamline. The alignment in measurement and simulation drove the desire to measure the horizontal emittance at the APS-Upgrade. Simulations in SPECTRA and ongoing work in Synchrotron Radiation Workshop (SRW) guide our experimental strategy. In the present work, results from SRW will be presented. We will then conclude with commissioning measurements of beam size and emittance in the APS-U as well as a discussion on the advantages to the undulator high harmonics method when compared to other methods at the APS-U.

SPring-8-II is a major upgrade project of SPring-8 that was inaugurated in October 1997 as a third-generation synchrotron radiation light source. This upgrade project aims to achieve three goals simultaneously: achievement of excellent light source performance, refurbishment of aged systems, and significant reduction in power consumption for the entire facility. A small emittance of 50 pm rad will be achieved by (1) replacing the existing double-bend lattice structure with a five-bend achromat one, (2) lowering the stored beam energy from 8 to 6 GeV, (3) increasing the horizontal damping partition number from 1 to 1.3, and (4) enhancing horizontal radiation damping by installing damping wigglers in long straight sections. The use of short-period in-vacuum undulators allows ultrabrilliant X-rays to be provided while keeping a high-energy spectral range even at the reduced electron-beam energy of 6 GeV. To reduce power consumption, the dedicated, aged injector system has been shut down and the high-performance linear accelerator of SACLA, a compact X-ray free-electron laser (XFEL) facility, is used as the injector of the ring in a time-shared manner. This allows the simultaneous operation of XFEL experiments at SACLA and full/top-up injection of the electron beam into the ring. This paper overviews the concept of the SPring-8-II project, the system design of the light source and the details of the accelerator component design.

Extraordinary emittance requirements in the nm range (normalized) and pulse lengths down to a level of ∼10 fs for REGAE bunches demand both operation at low bunch charges on the sub-pC scale and a very careful beam handling. The S-band RF deflecting cavity is intended for diagnostics of the longitudinal bunch parameters. For the first time a deflecting structure, specially developed and optimized for bunch rotation has been realized for the REGAE RF deflector. The developed cavity provides a minimized level of aberrations in the distribution of the deflecting field combined with an improved RF efficiency. The main steps in the cavity design, construction and tuning are described.

Synchrotron light sources worldwide are transforming into next-generation facilities with ultra-low transverse emittances at the diffraction limits. With these parameters, intrabeam scattering (IBS) becomes significant and can spoil the light quality by increasing the natural emittance and energy spread. A harmonic cavity can be installed to mitigate this effect by increasing the bunch length. Another way to reduce the impact of IBS is to operate with the full transverse coupling. This contribution considers the IBS effect on SOLEIL II performance with an up-to-date impedance model, a passive harmonic cavity, different insertion device gap configurations (open, closed), and full transverse coupling for two main foreseen operation modes. The combined effect of IBS and microwave instability (MWI) on the energy spread is reported. It is demonstrated that the contribution of IBS to energy spread increase is as significant as that of MWI for SOLEIL II.

In rf linacs the longitudinal focalization is done by si-nusoidal forces and at high accelerating fields the zero-current longitudinal phase advance per longitudinal fo-cusing period σ 0l_l can be high. The nonlinear compo-nents of the sinusoidal rf field (sextupolar, octupolar and higher order components) can then excite parametric resonances, including the 4th-order resonance (σ l_l = 90°) when σ 0l_l is higher than 90°, inducing strong longitudinal emittance growths and acceptance reductions. As pointed out in previous papers, the longitudinal beam dynamics is therefore complex, even when the space-charge forces are ignored. The parametric resonance excitation by the rf field is analyzed before discussing the additional effect of the space-charge forces, in particular to explain why the zero-current longitudinal phase advance per trans-verse focusing period σ 0l_t is not a relevant parameter. Examples are given in the SPIRAL2 linac case.

Phase space is a mathematical construct that encompasses particle positions and their corresponding momenta. In general, discrete phase space structures are experimentally measured due to the limited spatial and angular resolutions of individual devices. From the perspective of beam focusing characteristics, beams are discussed in terms of core components and halo components. While the beam core is typically the primary component with low divergence, it may occasionally consist of multiple components with different velocity distributions. Mathematical modeling of the beam core in phase space is essential for accurately quantifying beam divergence and emittance. This paper presents a model that can be applied to beam cores with inner structures and reconstructs the phase space structure using kernel density interpolation. The reconstructed phase space structure is then utilized to determine beam divergence and emittance with greater precision. Additionally, these insights contribute to an enhanced understanding of beam physics.

A wiggler is a high‐power insertion device that was used in the past to produce a smooth wide‐band X‐ray spectrum. It is widely believed that on low‐emittance synchrotrons this X‐ray source loses its spatial and spectral homogeneity and therefore becomes less ideal than a scanning undulator. In this paper, we report on experimental and computational studies of an in‐vacuum wiggler installed on the first fourth‐generation synchrotron MAX IV. We investigate how several physical parameters affect the wiggler spectrum and propose a combination of a few of them that results in significant spectral smoothing. We also examine EXAFS spectra for possible distortions originating from the source imperfection. For this purpose, we scrutinize samples of various homogeneity. We conclude that wigglers are still an appropriate class of insertion devices, also on low‐emittance synchrotrons. Experimental and computational studies of wigglers on low‐emittance storage rings are reported. EXAFS spectra for possible distortions originating from the source imperfection are also examined. It is concluded that wigglers are still an appropriate class of insertion devices, also on low‐emittance synchrotrons.

Passive radiative cooling (RC) enables the cooling of objects below ambient temperature during daytime without consuming energy, promising to be a game changer in terms of energy savings and CO2 reduction. However, so far most RC surfaces are obtained by energy‐intensive nanofabrication processes or make use of unsustainable materials. These limitations are overcome by developing cellulose films with unprecedentedly low absorption of solar irradiance and strong mid‐infrared (mid‐IR) emittance. In particular, a cellulose‐derivative (cellulose acetate) is exploited to produce porous scattering films of two different thicknesses, L ≈ 30 µm (thin) and L ≈ 300 µm (thick), making them adaptable to above and below‐ambient cooling applications. The thin and thick films absorb only ≈5% ${\\approx}5\\%$of the solar irradiance, which represents a net cooling power gain of at least 17 W m−2, compared to state‐of‐the‐art cellulose‐based radiative‐cooling materials. Field tests show that the films can reach up to ≈5 °C below ambient temperature, when solar absorption and conductive/convective losses are minimized. Under dryer conditions (water column = 1 mm), it is estimated that the films can reach average minimum temperatures of ≈7–8 °C below the ambient. The work presents an alternative cellulose‐based material for efficient radiative cooling that is simple to fabricate, cost‐efficient and avoids the use of polluting materials. Thin cellulose‐based films are prepared via phase separation with unprecedented scattering efficiency in the UV–visible range (down to 300 nm), that radiate heat in the mid‐infrared, and exhibit radiative cooling. Field tests show that the films can reach up to 5 °C below ambient temperature, when solar absorption and conductive/convective losses are minimized. They are cost‐effective and environmentally friendly.

The J-PARC 3 GeV Rapid-Cycling Synchrotron (RCS) delivers a high intensity proton beam to the 30 GeV Main Ring (MR). The improvement of longitudinal beam matching between RCS and MR is desired to suppress the beam loss in the MR. A scenario to improve the longitudinal beam matching between RCS and MR is designed. For the RCS, the bunch lengthening scheme using the unstable fixed point generated by the second harmonic is considered. For the MR, the RF voltage pattern is adjusted to match the longitudinal beam emittance of the RCS. The details of the scenario for improving the longitudinal beam matching between RCS and MR and the results of beam simulation studies are reported.

The PF Hybrid Light Source (PF-HLS) has been proposed in the High Energy Accelerator Research Organization (KEK), capable of utilizing both high-quality beams from a superconducting linac and beams from a low-emittance storage ring. The coupling impedance will cause beam instability, which must be carefully handled. It is essential to benchmark impedance models using analytical methods and different simulation codes. This paper focuses on the impedance benchmarking of resistive wall and tapered transitions in PF-HLS.