As light source facilities evolve, upgrading fast orbit feedback systems is essential for improving beam stability. NSLS-II is planning an upgrade to NSLS-IIU, which introduces stricter stability requirements for advanced experiments. To address this, we developed a next-generation fast orbit feedback prototype system to enhance noise suppression and extend control bandwidth beyond 1 kHz. A system-wide evaluation was conducted, covering beam position monitors, cell controllers, power supply controllers, power supplies, and vacuum chamber effects. Latency and bandwidth bottlenecks were identified in the cell and power supply controllers. A new cell controller was designed to increase the sampling rate from 10 kHz to 31.5 kHz and reduce system latency to under 70 µs. The transfer function and gain measurements of a single-input-single-output system show a 10-dB improvement in noise suppression and an extension of bandwidth into the kHz range. We present the development and performance results of the upgraded system, offering a path toward higher beam stability at NSLS-IIU.

At NSLS-II, the vertical emittance of electron beam is typically blown up to ~30 pm with a coupling wave to increase beam lifetime during user operation. As more and more insertion devices are added to the storage ring, injection efficiency to the ring drops noticeably in certain machine states, apparently due to degraded dynamic apertures. To help alleviate this issue, we have recently performed online multi-objective Bayesian optimization to increase injection efficiency while maintaining beam lifetime, by adjusting the strengths of 15 skew quadrupoles in non-dispersive sections. We report the results of this optimization effort.

The impedance of in-vacuum undulators (IVUs) significantly affect the broadband impedance and, consequently, the beam dynamics in storage rings. During the IVU design phase, numerous iterative discussions between physicists and engineers are required, often involving extensive simulations of the complete 3D geometry, a few meters long, using limited computational resources. In this paper, we propose training a Gaussian process model with limited simulation data to emulate the physical model. We compare the predictions of the trained model to the simulation data and explore its application in optimizing the IVU design.

The NSLS-II is a cutting-edge 3 GeV storage ring light source around the world. The electron beam is initially accelerated in a linear accelerator to an energy of 170 MeV and subsequently accelerated in a booster synchrotron to a beam energy of 3 GeV. Therefore, the performance of the Linac and the Linac-to-Booster beam lines is imperative for beam injection to the booster. Online optimization is an effective solution to improve accelerator performance when there is degradation. This paper presents the results of online optimization employing a machine learning method.

To address the intrinsic dynamic aperture (DA) limitations of fourth-generation diffraction-limited synchrotron light source, we investigate a novel injection scheme utilizing multiple nonlinear kickers (NLKs) with optimized hardware design and phase advances in the storage ring (SR). Positioning the NLKs near the injection point reduces beam perturbation, while their on-axis zero field and gradient enable transparent injection—suppressing orbit and beam-shape oscillations during top-off operations. Particle-tracking simulations were performed using Accelerator Toolbox (AT), alongside the development of automated tools for converting magnetic field maps into AT-compatible kick maps, inserting NLKs at arbitrary lattice locations, conducting tracking, and optimizing NLK configurations. A key challenge is to shift the off-axis magnetic field peak closer to the beam orbit. Our novel NLK design achieves a peak within 5 mm of the axis—a significant improvement over the conventional greater than 7 mm range. Simulations accounting for realistic alignment and magnetic field errors indicate that a relaxed 5 mm DA and injection efficiency > 90% could be feasible for the NSLS-II upgrade lattice.

This paper focuses on the R&D performed for the development of permanent magnets-based dipoles-quadrupoles combined function magnets (PMQs) for the future NSLSII upgrade “complex bend” lattice (CB). This new lattice uses PMQs that provide both bending (dipole) and strong focusing (quadrupole) magnetic field on the electron beam. The permanent magnet (PM) technology is suitable for the high magnetic field strengths (0.5 T, 130 T/m) required for such combine function magnets. PM technology leads to a compact magnet design that is essential in realizing the complex bend lattice concept, as well as a passive magnet solution which does not require electrical power supply reducing power consumption by ~ 80% (from 1.7 MW to 0.3 MW for NSLS-II). Two PMQs magnets designs are under consideration: A hybrid design that use both PM and soft iron poles, and Halbach type that is a pure PM design. Both PMQs designs present challenges in achieving the specified magnetic field quality due to their higher sensitivity to errors (mechanical tolerances and PM properties). This paper presents cost-effective designs and prototypes results for hybrid and Halbach PMQs, addressing various technical challenges while meeting the field requirements of the complex bend lattice for the NSLS-II upgrade.

The NSLSII storage ring contains over 180 RF shielded bellows over its 792 m circumference. Three of these bellows are instrumented with RTD temperature sensors on the internal components to monitor and validate expected performance. The temperature data showed an increasing internal temperature trend during successive 500mA beam operation on one of these bellows. This bellows and many other installed bellows throughout the ring, are near to or over the vertical and horizontal offset tolerance. Offsets can create an RF path between the sleeve and fingers, which raised concern there was degradation of performance resulting from the offset condition. The bellows was removed and inspected with some visual signs of discoloration and loose RTD anchor points were also observed. With the prospects of moving from 400mA to more permanent 500mA operation, a test was conducted to confirm internal temperatures were safe. Two fully instrumented bellows were remotely offset under steady beam operation while observing the internal temperatures. The bellows with offset geometry was also studied with GdfdL code. The experimental results will be presented and compared to the wake-potential calculations.

Since the first light in 2014 at 50 mA, NSLS-II has steadily increased beam current, reaching 500 mA in October 2019. Along the way, various challenges were addressed, including RF power consumption, wakefield effects, and unexpected component heating. Key improvements included enhanced temperature monitoring with 600 new sensors, optimized RF spring installation, and the installation of a superconducting wiggler in 2022 to reduce vacuum heating further. As a result, vacuum temperatures now remain below 70°C at 500 mA. Extensive beam studies ensured stability for 29 beamlines, improving signal intensity, signal-to-noise ratio, and sample throughput. NSLS-II successfully operated at 500 mA in August 2023, with increasing high-current operational periods scheduled each year to enhance user experiments.

For the NSLS-II upgrade, a novel Complex Bend (CB) optics solution has been proposed to achieve near-diffraction-limited emittance. A key challenge in this design is the requirement for high-gradient quadrupoles (150 T/m) in a compact space. To demonstrate feasibility, a CB prototype was developed and tested using the NSLS-II linac beamline, scaling the beam energy to 100–200 MeV while maintaining strong focusing. The prototype utilized a 16-wedge symmetric Halbach permanent magnet design, achieving a gradient of 140 T/m within ultra-compact quadrupoles. The CB beamline was installed and commissioned in two phases, first as a strong periodic focusing element and later as a combined bending and focusing system. The beam commissioning results showed good agreement with theoretical models, confirming that the Complex Bend functions effectively as both a strong focusing and bending element by offsetting CB poles. This validates the strong focusing design of the Complex Bend for future synchrotron light source upgrades.

NSLS-II is planning an upgrade to an ultra-low emittance storage ring using a novel lattice concept, the complex bend, composed of combined-function magnets. To evaluate technical challenges and study beam dynamics with complex bend, two bending magnets of existing NSLS-II bare lattice are proposed to be replaced with complex bends, introducing lattice asymmetry. To study the impact of asymmetry on NSLS-II bare lattice, an asymmetric lattice is developed by adjusting quadrupole triplets in the Cell 8 long straight section. This paper presents the modified linear optics, optimization of nonlinear dynamics, and a comparison with the nominal bare lattice. The optimized asymmetric bare lattice is also experimentally measured in the machine, and dynamic aperture measurements are reported.