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In the future diffraction-limited light source rings, fully coupled linear optics to generate round beams is preferable. While machine tune approaching to linear difference resonances, small random errors, such as quadrupole rolls, can result in fully coupled optics. Consequently, some uncertainty exists in such optics due to random errors distributions. Given beam position monitors turn-by-turn readings, the harmonic analysis method was used to characterize the coupled Ripken Twiss parameters., Proceedings of the 5th North American Particle Accelerator Conference, NAPAC2022, Albuquerque, NM, USA

We discuss impedance calculations and related heating issues of the titanium-coated NSLS-II kicker ceramic chambers, with the titanium coating thickness estimated from in situ measurements of the end-to-end resistance of each chamber. Power densities are calculated on the titanium coating to allow for thermal analysis with the code ANSYS and comparison with heating measurements. The impedance analysis is performed using a realistic model of the ceramic complex permittivity, and special consideration is given to the impedance calculation in the limit of zero titanium coating thickness., Proceedings of the 5th North American Particle Accelerator Conference, NAPAC2022, Albuquerque, NM, USA

The goal of the NSLS-II online optimization project is to improve the beam quality for the user experiments. To increase the beam lifetime and injection efficiency, we have developed a model-independent online optimization of nonlinear beam dynamics using advanced algorithms, such as Robust Conjugate-Gradient Algorithm (RCDS). The optimization objective is the injection efficiency and optimization variables are the sextupole magnet strengths. Using the online optimization technique, we increased the NSLS-II dynamic aperture and reduced the amplitude-dependent tune shift. Recently, the sextupole optimization was successfully applied to double the injection efficiency up to above 90% for the high-chromaticity lattice being developed to improve the beam stability and to in-crease the single-bunch beam intensity. Minimizing the beam perturbation during injection is the second objective in this project, realized by online optimization of the injection kickers. To optimize the full set of kicker parameters, including the trigger timing, amplitude, and pulse width, we upgraded all kicker power supplies with the capability of tunable waveform width. As a result, we have reduced the injection transient by a factor of 29, down to the limit of 60 um., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

NSLS-II is a 3-GeV third-generation synchrotron light source at Brookhaven National Lab. The storage ring has been in routine operations for over six years and hosts 28 operating beamlines. The storage ring performance has continuously improved, including 500-mA with limited insertion devices closed, and routine 400-mA top off operation with 90% uniform filling pattern. Recently, we are exploring different operation modes, uniform multi single-bunch mode, and camshaft mode with a high single-bunch charge, to support timing-resolved user experiments. In this paper, we explore the potential for scientific experiments using the pulsed nature of the NSLS, summarize the user requirements on the beam parameters and the progress of accelerator studies., Proceedings of the 5th North American Particle Accelerator Conference, NAPAC2022, Albuquerque, NM, USA

The design of the electron-ion collider EIC to be constructed at Brookhaven National Laboratory has been continuously evolving towards a realistic and robust design that meets all the requirements set forth by the nuclear physics community in the White Paper. Over the past year activities have been focused on maturing the design, and on developing alternatives to mitigate risk. These include improvements of the interaction region design as well as modifications of the hadron ring vacuum system to accommodate the high average and peak beam currents. Beam dynamics studies have been performed to determine and optimize the dynamic aperture in the two collider rings and the beam-beam performance. We will present the EIC design with a focus on recent developments., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

We explore the possibility of visualizing the lattice dynamic behavior by acquiring a single time-resolved MeV UED image. Conventionally, multiple UED shots with varying time delays are needed to map out the entire dynamic process. The measurement precision is limited by the timing jitter between the pulses of laser pump and UED probe. We show that, by converting the longitudinal time of an electron bunch to the transverse position of a Bragg peak on the detector, one can obtain the full lattice dynamic process in a single electron pulse. We propose a novel design of a time-resolved UED with the capability of capturing a wide range of dynamic features in a single diffraction image. The work presented here is not only an extension of the ultrashort-pulse pump/long-pulse probe scheme being used in transient spectroscopy studies for decades but also advances the capabilities of MeV UED for future applications with tunable electron probe profile and detecting time range with femtosecond resolution. Furthermore, we present numerical simulations illustrating the capability of acquiring a single time-resolved diffraction image based on the case-by-case studies of lattice dynamic behavior., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

The comparison of amplitude tune dependence measured for NSLSII lattices with models indicated the large change of amplitude tune dependence over time apparently can not be solely explained by magnets variation or beta function changes, but it seems can be explained by energy changes. On the other hand, the energy change required by fitting with the amplitude tune dependence change is too large to be explained by the RF frequency change and the change of the sum of correctors in the period of the measurements. To explain this apparent contradiction, our analysis shows the long term storage ring circumference change can explain the apparent energy change. Our data indeed shows a seasonal change of the amplitude tune dependence over long term observation. This clearly also indicated a relation to long term closed orbit drift. Hence the current work indicates a new strategy to study how to use amplitude tune dependence as a guideline to analyze long term lattice parameter shifts and closed orbit drift, and improve the orbit and machine performance stability., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

As the new generation of light sources are pushing toward diffraction limited storage rings with ultra-low emittance beams, nonlinear beam dynamics become increasingly difficult to control. It is a common practice for modern designs to use a sextupole scheme that allows simultaneous correction of natural chromaticity and energy independent, or geometrical, sextupolar resonances. However, the remaining higher order terms arising from the cross talks of the sextupole families set a strong limitation on the achievable dynamic aperture. This paper presents a simulation-based recipe to use octupoles together with this sextupole scheme to provide simultaneous self-compensation of linear amplitude dependent tune shift together with phase-dependent octupolar and higher order geometrical resonant driving terms. The correction method was built based on observations made on a simple FODO model, then applied to a realistic low emittance lattice, designed in the framework of the upgrade of the National Synchrotron Light Source II (NSLS-II)., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

The head-tail instability caused by the beam interaction with short-range wakefields is a major limitation for the single-bunch beam intensity in circular accelerators. The combined effect of the transverse feedback systems and chromaticity suppressing the instability is discussed. Theoretical and experimental studies of the head-tail instability and methods of its mitigation are reviewed. Results of experimental studies of the transverse mode coupling carried out at NSLS-II are compared with the theoretical model and numerical simulations., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

The horizontal/vertical emittances, the bunch length, and the energy spread increase have been studied in the NSLS-II as a function of a single bunch current. The monotonic growth of the horizontal emittance dependence and the energy spread dependence on the single bunch current below the microwave instability threshold can be explained by the Intrabeam Scattering Effect (IBS). The IBS effect results in an increase in the bunch length and the microwave instability thresholds. It was observed experimentally by varying the vertical emittance. To compare with experimental data, particle tracking simulations have been performed with the ELEGANT code including both IBS and the total longitudinal wakefield calculated from the 3D electromagnetic code GdfidL. The same particle tracking simulations have also been applied for the APS-U project, where IBS is predicted to produce only a marginal effect., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

A real-time, nondestructive, Bragg-diffracted electron beam energy, energy-spread and spatial-pointing jitter monitor is experimentally verified by encoding the electron beam energy and spatial-pointing jitter information into the mega-electron-volt ultrafast electron diffraction pattern. The shot-to-shot fluctuation of the diffraction pattern is then decomposed to two basic modes, i.e., the distance between the Bragg peaks as well as its variation (radial mode) and the overall lateral shift of the whole pattern (drift mode). Since these two modes are completely decoupled, the Bragg-diffraction method can simultaneously measure the shot-to-shot energy fluctuation from the radial mode with 2,10������ precision and spatial-pointing jitter from the drift mode having wide measurement span covering energy jitter range from 10-4 to 10-1. The key advantage of this method is that it allows us to extract the electron beam energy spread concurrently with the ongoing experiment and enables online optimization of the electron beam especially for future high charge single-shot ultrafast electron diffraction (UED) and ultrafast electron microscopy (UEM) experiments., Proceedings of the 11th International Particle Accelerator Conference, IPAC2020, Caen, France

This paper is dedicated to the analysis of our recent experience from ramp-up of operating current at NSLS-II from 25 mA at the end of commissioning in 2014 to 475 mA achieved in studies today. To approach the design level of the ring intensity we had to solve major problems in overheating of the chamber components. Since the beginning of the NSLS-II commissioning, the temperature of the vacuum components has been monitored by the Resistance Temperature Detectors located predominantly outside of the vacuum chamber and attached to the chamber body. A couple of vacuum components were designed with the possibility for internal temperature measurements under the vacuum as diagnostic assemblies. Temperature map helps us to control overheating of the vacuum components around the ring especially during the current ramp-up. The average current of 475mA has been achieved with two main 500MHz RF cavities and w/o any harmonic cavities. In this paper we discuss the heating results for a 15ps bunch length (at low current) of the following vacuum components: Large Aperture BPM, Small Aperture BPM, Bellows, Flanges, Ceramics Chambers and Stripline Kickers., Proceedings of the North American Particle Accelerator Conference, NAPAC2019, Lansing, MI, USA

All modern projects of low-emittance synchrotrons follow Multi-Bend Achromat approach*. The low emittance is realized by arranging small horizontal beta-function and dispersion in the bending magnets, the number of which varies from 4 to 9 magnets per cell. We propose an alternative way to reach low emittance by use of a lattice element that we call "Complex Bend"**, instead of regular dipole magnets. The Complex Bend is a new concept of bending magnet consisting of a number of dipole poles interleaved with strong alternate focusing so as to maintain the beta-function and dispersion oscillating at very low values. The details of Complex Bend, considerations regarding the choice of optimal parameters, thoughts for its practical realization and use in low-emittance lattices, are discussed., Proceedings of the North American Particle Accelerator Conference, NAPAC2019, Lansing, MI, USA

We report the bunch length measurement of low-energy 3 MeV electron beams in picosecond regime with the charge from 1.0 to 14 pC. It is the first time that we demonstrate single-cycle nano-joule coherent terahertz (THz) radiation from 3MeV electron beam can be meas-ured via a far-infrared Michelson interferometer using a QOD. At this low energy range, when charge is about 1 pC, the signal from the conventional helium-cooled sili-con composite bolometer is too low. Compared to the bunch length measurement via the ultrafast-laser-pump and electron-beam-probe in the timescale 10⁻¹⁴ to 10-12 s which is determined by the phase-transition dynamics in solids, the advantages are: there are no needs of pump laser and probe sample, greatly simplifying the experi-ment; the timing jitter between laser and electron beams contributes no error to the bunch length measurement; furthermore, the method can be extended to sub-picosecond regime enabling bunch length measurement in a much broader timescale 10-14 to 10-11 s for low-energy electron beams. In the current experiment the bunch length is limited to 1 ps only because the setup of driving laser to cathode with a large 70° incident angle, effective-ly lengthening the laser pulse to ≥1 ps., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The Electron-Ion Collider (EIC) is being envisioned as the next facility to be constructed by the DOE Nuclear Physics program. Brookhaven National Laboratory is proposing eRHIC, a facility based on the existing RHIC complex as a cost effective realization of the EIC project with a peak luminosity of 10³⁴ cm⁻² sec⁻¹. An electron storage ring with an energy range from 5 to 18 GeV will be added in the existing RHIC tunnel. A spin-transparent rapid-cycling synchrotron (RCS) will serve as a full-energy polarized electron injector. Recent design improvements include reduction of the IR magnet strengths to avoid the necessity for Nb₃Sn magnets, and a novel hadron injection scheme to maximize the integrated luminosity. We will provide an overview of this proposed project and present the current design status., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

With the completion of the National Academies of Sciences Assessment of a US Electron-Ion Collider, the prospects for construction of such a facility have taken a step forward. This paper provides an overview of the two site-specific EIC designs: JLEIC (Jefferson Lab) and eRHIC (BNL) as well as brief overview of ongoing EIC R, Proceedings of the North American Particle Accelerator Conference, NAPAC2019, Lansing, MI, USA

Interaction of a particle beam with the vacuum chamber impedance is one of the main effects limiting the beam intensity in accelerators. Minimization of the impedance is an essential part of the vacuum chamber design for any new accelerator project. The impedance can be estimated experimentally by measuring beam dynamics effects caused by the beam-impedance interaction. Experience obtained at many accelerator facilities shows the beam-based measurements are often different from the pre-computed impedance budgets, the discrepancy of a factor of two or even more is not unusual. The measurements of broadband longitudinal impedance carried out at NSLS-II are discussed in comparison with the numerically simulated impedance budget., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The future electron-ion collider (EIC) aims at an electron-proton luminosity of 10³³ to 10³⁴ cm⁻² sec⁻¹ and a center-of-mass energy range from 20 to 140 GeV. The eRHIC design has been continuously evolving over a couple of years and has reached a considerable level of maturity. The concept is generally conservative with very few risk items which are mitigated in various ways., Proceedings of the North American Particle Accelerator Conference, NAPAC2019, Lansing, MI, USA

A new lattice design has been proposed recently based on a Complex-Bend concept [1,2] for low emittance syn-chrotrons. The dipoles of a standard DBA lattice are replaced in the Complex Bend by high-gradient (~ 450 T/m) quadrupoles interleaved between discrete dipoles. In another version of the Complex Bend [3] the high gradient quadrupoles are displaced transversely along the beam trajectory to generate the required dipole field. In the latter version the quadrupole strength is reduced to ~ 250 T/m for a lattice that will conform to the layout of the existing NSLS-II 3-GeV storage ring. In this paper we present conceptual designs of a Halbach permanent-magnet (PM) quadrupole, a hybrid PM quadrupole, and a superconducting quadrupole, that can produce the de-sired quadrupole strengths for the Complex Bend appli-cation. REFERENCES [1] T. Shaftan, V. Smaluk and G. Wang, ’The Concept of Com-plex Bend’, NSLS-II Tech note No. 276, Jan 2018. [2] G. Wang et al., ’Complex Bend: Strong-focusing magnet for low emittance synchrotrons’, Physical Review Accelerators and Beams, 21, 100703 (2018). [3] G. Wang et al., ’Complex Bend II’, paper submitted to Physi-cal Review Accelerators and Beams., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

In the eRHIC, to compensate the geometric luminosity loss, local crab cavities on both sides of the interaction points are to adopted. The previous strong-strong beam-beam simulations showed that the luminosity degradation depends on the crab cavity frequency, proton synchrotron tune, proton bunch length and so on. In this article, we apply a combined strong-strong and weak-strong beam-beam simulation to investigate the incoherent and coherent beam motions with crabbed collison, and to calculate more realistic beam emittance growth rates and luminosity degradation rate., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

We report our proof-of-principle design and experi-mental commissioning of broadly tunable and low-cost transverse focusing lens system for MeV-energy electron beams at the ultra-fast electron diffraction (UED) beam-line of the Accelerator Test Facility II of BNL. We exper-imentally demonstrate the independent control over the size and divergence of the electron beam at the sample via tunable quadrupoles. By applying online optimiza-tion, we achieve minimum beam sizes 75 µm from 1 to 13 pC, two orders of magnitude higher charge density than previously achieved using conventional solenoid tech-nique. Finally, we experimentally demonstrate Bragg-diffraction image (BDI) with significant improvement up to 3 times brighter and 2 times sharper BDI peaks via the optimized quadrupoles, improvement larger with higher charge. The result could be crucial for the future single-shot ultra-fast electron microscope development., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The NSLS-II storage ring uses the standard four bump injection scheme to inject beam off axis. BESSY and MAX IV are now using a pulsed multipole magnet as an injection kicker. The injected beam sees a field off axis for injection while the stored beam experiences no field on the magnet axis. The principle advantage of using a pulsed multipole for injection is that the stored beam motion is greatly reduced since the field on axis is negligible. The number of pulsed magnets is reduced from five in the nominal scheme (septum and four bumps) to two or three thereby reducing the possible failure modes. This also eliminates the need to precisely match the pulse shapes of four dipole magnets to achieve minimal stored beam motion outside of the bump. In this paper we discuss two schemes of injecting into the NSLS-II using a pulsed multipole magnet. The first scheme uses a single pulsed multipole located in one cell downstream of the injection septum as the injection kicker. The second scheme uses two pulsed multipoles in the injection straight to perform the injection. We discuss both methods of injection and compare each method., Proceedings of the North American Particle Accelerator Conference, NAPAC2019, Lansing, MI, USA

Over a few months in 2018, we observed occasional episodes of relatively quick accumulation of correction strengths for the fast correctors (used by the fast orbit feedback) near Cell 4 (C04) region at NSLS-II Storage Ring. We immediately started investigating the problem, but the cause remained unclear. However, after coming back from the Fall shutdown, we experienced even faster drifts, at a rate of as much as 10 urad per day in terms of orbit kick angle accumulation. The risk of damage on the ring vacuum chambers by the continuing orbit drift without explanation eventually forced us to take emergency study shifts and temporarily lock out the C04 IVU beamline. After extensive investigation by many subsystem experts in Accelerator Division, ruling out many suspicious sources one by one, we were finally able to conclude the cause to be the localized ground motion induced by large temperature jumps of the utility tunnel right underneath the C04 straight section. We report the details of this incident., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

Modern high performance circular accelerators require sophisticated corrections of nonlinear lattices. The beam betatron tune footprint may cross many resonances, reducing dynamic aperture and causing particle loss. However, if particles cross a resonance reasonably fast, the beam deterioration may be minimized. In this paper, we present the experiments with the beam passing through a half-integer resonance stopband via chromatic tune modulation by exciting synchrotron oscillations. This is the first time that beam dynamics have been kept under precise control while the beam crosses a half-integer resonance. Our results convincingly demonstrate that particles can cross the half-integer resonance without being lost if the passage is reasonably fast and the resonance stopband is sufficiently narrow., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The electron-ion collider eRHIC aims at a luminosity around 10³⁴cm⁻²sec⁻¹, using strong cooling of the hadron beam. Since the required cooling techniques are not yet readily available, an initial version with a peak luminosity of 3*10³³cm⁻²sec⁻¹ is being developed that can later be outfitted with strong hadron cooling. We will report on the current design status and the envisioned path towards 10³⁴cm⁻²sec⁻¹ luminosity., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

In the present design of the future electron-ion collider eRHIC at the Brookhaven National Laboratory, a crossing angle of 22~mrad between the electron and proton orbits at the interaction region is adopted. To compensate the geometric luminosity loss, a local compensation scheme with two sets of crab cavities for each beam is considered. In this article, we first carry out strong-strong beam-beam simulation to study possible coherent beam-beam instability. Under the assumption of no coherent beam-beam motion, we then carry out a weak-strong beam-beam simulation to determine the long-term stability of the proton beam with the equilibrium electron beam sizes extracted from the strong-strong beam-beam simulation., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

The NSLS-II injector consists of a 200 MeV linac and a 3 GeV full-energy booster synchrotron. The linac contains five traveling-wave S-band accelerating structures driven by two high-power klystrons, with a third klystron as spare. In the event that the spare klystron is not available, the failure of one klystron will prohibit the linac from injecting into the booster as the energy is too low. Therefore, we wish to develop a new operational mode that the NSLS-II injector can operate with a single klystron providing 100 MeV beam from the linac. A decremented approach with intermediate energies 170 MeV, 150 MeV, etc., takes advantages of pre-calculated booster ramps and beam based online optimization. By lowering the booster injection energy in a small step and online optimizing at each step, we were able to achieve 100 MeV booster injection. 170 MeV operation mode of the NSLS-II injector has been implemented since May 31, 2017, with a similar overall performance compared to the standard 200 MeV operation but fewer klystron trips. 100 MeV single-klystron operation has been successfully demonstrated with 20-30% overall efficiency, which is limited by booster acceptance., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

The impedance budget for the eRHIC project is discussed at its earlier stage of development. As a first step, with the eRHIC lattice and beam parameters , we use the geometric impedances of the vacuum chamber components simulated for the NSLS-II project. The impedance budged will be updated next with more impedance data simulated for the optimized eRHIC vacuum components. It will allows us to keep track on the collective effects changes with more realistic components added to the ring., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada