Betatron coupling resonance has been considered by many low emittance upgrade light sources as a candidate to produce round beams. Due to the limited literature on the topic, last year an experimental campaign was undertaken on the ALBA storage ring to establish limits and requirements to operate a light source in full coupling. The work highlighted how coupling can indeed produce a round beam with certain easiness but not free from shortcomings: the fractional betatron tunes must be set equal, resulting in a substantial constraint to the optics and requiring a sophisticated control of the optics itself in order to keep the resonance condition despite the movement of insertion devices and drifts. To work around these limitations, this year a different approach, based on the excitation of the coupling resonance with an A.C. skew quadrupole was tested. A first experiment was attempted by converting the existing tune excitation stripline into a skew quadrupole, but the limited available power allowed to produce only a barely perceptible coupling. The stripline was then turned into an electric deflector by removing the resistive terminations and allowing to drive the electrodes to higher voltage. Here the newly obtained results with the A.C excitation are presented.

ALBA is working on the upgrade project that shall transform the actual storage ring, in operation since 2012, into a 4th generation light source, in which the soft X-rays part of the spectrum shall be diffraction limited. The project was launched in 2021 with an R&D budget to build prototypes of the more critical components. The storage ring upgrade is based on a 6BA lattice which has to comply with several constraints imposed by the decision of maintaining the same circumference (269m), the same number of cells (16), the same beam energy (3GeV), and as many of the source points as possible unperturbed. At present, the lattice optimization, iterating with the technical constrains of space and performance, is ongoing. This paper presents the status of the project, with the present proposed lattice, first magnet’s designs, the vacuum chamber initial considerations, the girder concept, the proposed RF system with fundamental and harmonics cavities, and the general context of the upgrade.

Measurements of the small beam sizes in current and future low-emittance light sources represent a serious challenge to the accelerator community due to the diffraction effects, and X-ray inteferometric techniques offer an interesting method to overcome this challenge. Here we report on 2D beam size measurements with a novel interferometric technique named Heterodyne Near Field Speckles (HNFS). It relies on the interference between the weak spherical waves scattered by nanospheres suspended in water and the intense transilluminating X-ray beam. Fourier analysis of the resulting speckles enables full 2D coherence mapping of the incoming radiation, from which the beam sizes along the two orthogonal directions are retrieved. We show experimental results obtained with 12.4 keV X-rays at the NCD-SWEET undulator beamline at ALBA, where the vertical beam size has been changed between 5 and 15 micrometers by varying the beam coupling. The results agree well with the estimated beam sizes from the pinhole calculations, proving that the HNFS method can resolve few-micrometer beam sizes.

The ALBA-II upgrade lattice to a diffraction limited soft X-rays storage ring calls for an emittance smaller than 200 pm*rad in a 269 m circumference at an energy of 3 GeV. In this paper we report on progress of the 6BA lattice with distributed chromatic correction. This lattice relies on transverse gradient dipoles and reverse bends to suppress the emittance. Several modifications to the lattice presented in 2021 have been introduced in order to easy the injection with high horizontal beta function and a longer section for the septum, to make more efficient the chromaticity correction with the sextupoles, and to provide room for the orbit correctors. The last performances of the linear and non-linear beam dynamics are presented in this paper.

The ALBA synchotron operates in a Touschek dominated lifetime regime, which depends mainly on the momentum acceptance and the transverse beam size along the machine. Although in the current ALBA machine the RF dominates the momentum acceptance, this will not be the case for the foreseen upgrade of the machine ALBA-II. For this reason, we have developed an algorithm to optimize the beam lifetime by varying the sextupole magnets. This algorithm is based on the Powell optimization of the Robust Conjugate Direct Search (RCDS) method, and several tests have been performed at the present ALBA machine. In this case the sextupole settings are first modified so that the RF is no longer the only limiting factor in the momentum acceptance. The algorithm optimizes the ALBA beam lifetime by varying the sextupoles to follow a constant chromaticity, while the skew magnets are tweaked to keep the beam sizes constant during the optimization. This paper shows the experimental results using this algorithm, and discusses its application to the ALBA-II case.

While the design of the ALBA-II is in progress, it is required to assess the consequences of realistic imperfections such as alignment tolerances and magnetic errors. Compensation of insertion device induced optics variation has been studied, as well as the small impact on the emittance due the introduction of 3 T superbends. We demonstrate that non-linear optics is rather robust in the presence of realistic imperfections, rendering a ±6 mm dynamic aperture sufficient for off-axis injection and a large momentum acceptance that supplies more than 5 hour lifetime including errors. Moreover, studies in preceding low emittance light sources required simulating the full accelerator tuning, starting from the commissioning phase. To this end, the Simulated Commissioning (SC) toolbox has been used intensively. Specific set of tests have been developed to complement the SC simulations including lifetime and dynamical aperture calculations assuming a possible operation in full coupling.

The Future Circular Collider (FCC) R&D study was started in 2021 as a comprehensive feasibility analysis of CERN’s future accelerator project encompassing technical, administrative and financial aspects. As part of the study, Beam Instrumentation (BI) is a key technical infrastructure that will have to face unprecedented challenges. In the case of electron-positron FCC-ee, these are represented, among others, by the size of the accelerator, the amount of radiation produced along the ring and in machine-detector interaction region, the presence of the top-up booster and collider ring in the same tunnel. In this contribution we will present the current FCC-ee BI study and discuss its status and perspectives.