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The purpose of this paper is to evaluate the possibility of constructing a large-scale storage-ring-type ion-trap system capable of storing, cooling, and controlling a large number of ions as a platform for scalable quantum computing (QC) and quantum simulations. In such a trap, the ions form a crystalline beam moving along a circular path with a constant velocity determined by the frequency and intensity of the cooling lasers. In this paper, we consider a large leap forward in terms of the number of ions that serve as qubits in QC, from fewer than 100 available in state of the art linear ion-trap devices today to an order of $1{0}^{5}$ crystallized ions in the storage-ring setup. This new trap design unifies two different concepts: the storage rings of charged particles and the linear ion traps used for QC and mass spectrometry. In this paper, we use the language of particle accelerators to discuss the ion state and dynamics. We outline the differences between the above concepts, analyze challenges of the large ring with a revolving chain of ions, and propose goals for the research and development required to enable future quantum computers with 1000 times more qubits than available today. The challenge of creating such a large-scale quantum system while maintaining the necessary coherence of the qubits and the high fidelity of quantum logic operations is significant. Performing analog quantum simulations may be an achievable initial goal for such a device. Quantum calculations and simulations of complex quantum systems will move forward both the fundamental science and the applied research. Nuclear and particle physics, many-body quantum systems, lattice gauge theories, and nuclear structure calculations are just a few examples in which a large-scale quantum simulation system will become a very powerful tool to move forward our understanding of nature.

To harness the full potential of the ultrafast electron diffraction (UED) and microscopy (UEM), we must know accurately the electron beam properties, such as emittance, energy spread, spatial-pointing jitter, and shot-to-shot energy fluctuation. Owing to the inherent fluctuations in UED/UEM instruments, obtaining such detailed knowledge requires real-time characterization of the beam properties for each electron bunch. While diagnostics of these properties exist, they are often invasive, and many of them cannot operate at a high repetition rate. Here, we present a technique to overcome such limitations. Employing a machine learning (ML) strategy, we can accurately predict electron beam properties for every shot using only parameters that are easily recorded at high repetition rate by the detector while the experiments are ongoing, by training a model on a small set of fully diagnosed bunches. Applying ML as real-time noninvasive diagnostics could enable some new capabilities, e.g., online optimization of the long-term stability and fine single-shot quality of the electron beam, filtering the events and making online corrections of the data for time-resolved UED, otherwise impossible. This opens the possibility of fully realizing the potential of high repetition rate UED and UEM for life science and condensed matter physics applications.

Several proposals have been put forward for converting electron accelerators to inverse Compton scattering (ICS) gamma sources. Typical approaches suggest combining near-IR solid-state lasers operating continuously at a multimegahertz repetition rate with e-beams when setting their interaction point inside a field-enhancement, Fabry-Perot optical cavity. We introduce here an alternative method of pairing particle accelerator beams with trains of long-wave-infrared, ${\ensuremath{\lambda}}_{L}\ensuremath{\approx}9--11\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ pulses from a picosecond ${\mathrm{CO}}_{2}$ laser of a novel architecture operating in a repetitive pulse-burst mode. Because of a considerable increase in the laser energy per pulse, combined with an order-of-magnitude higher number of laser photons per joule of laser energy, our approach allows us to increase the ICS peak flux and brilliance by 4 orders of magnitude compared to previous proposals while maintaining high (${10}^{11}--{10}^{12}\text{ }\text{ }\mathrm{ph}/\mathrm{s}$) average flux. This outcome is supported by the examples of the $\mathrm{DA}\mathrm{\ensuremath{\Phi}}\mathrm{NE}$ and CBETA accelerator facilities, where ${10}^{20}--{10}^{21}\text{ }\text{ }\mathrm{ph}/(\mathrm{s}\ifmmode\cdot\else\textperiodcentered\fi{}{\mathrm{mm}}^{2}\ifmmode\cdot\else\textperiodcentered\fi{}{\mathrm{mrad}}^{2}\ifmmode\cdot\else\textperiodcentered\fi{}0.1%BW)$ peak brilliances at 50--1000 keV photon energy range can be achieved and is comparable or exceeds the capabilities of contemporary synchrotron light sources at hard x rays. Such high-brightness ICS sources will find applications in pump-probe and other ultrafast studies that require building up meaningful datasets on a single x-ray pulse.

A preliminary design of a mega-electron-volt (MeV) monochromator with 10−5 energy spread for ultrafast electron diffraction (UED) and ultrafast electron microscopy (UEM) is presented. Such a narrow energy spread is advantageous in both the single shot mode, where the momentum resolution in diffraction is improved, and the accumulation mode, where shot-to-shot energy jitter is reduced. In the single-shot mode, we numerically optimized the monochromator efficiency up to 13% achieving 1.3 million electrons per pulse. In the accumulation mode, to mitigate the efficiency degradation caused by the shot-to-shot energy jitter, an optimized gun phase yields only a mild reduction of the single-shot efficiency, therefore the number of accumulated electrons nearly proportional to the repetition rate. Inspired by the recent work of Qi et al. (Phys Rev Lett 124:134803, 2020), a novel concept of applying reverse bending magnets to adjust the energy-dependent path length difference has been successfully realized in designing a MeV monochromator to achieve the minimum energy-dependent path length difference between cathode and sample. Thanks to the achromat design, the pulse length of the electron bunches and the energy-dependent timing jitter can be greatly reduced to the 10 fs level. The introduction of such a monochromator provides a major step forward, towards constructing a UEM with sub-nm resolution and a UED with ten-femtosecond temporal resolution. The one-to-one mapping between the electron beam parameter and the diffraction peak broadening enables a real-time nondestructive diagnosis of the beam energy spread and divergence. The tunable electric–magnetic monochromator allows the scanning of the electron beam energy with a 10−5 precision, enabling online energy matching for the UEM, on-momentum flux maximizing for the UED and real-time energy measuring for energy-loss spectroscopy. A combination of the monochromator and a downstream chicane enables “two-color” double pulses with femtosecond duration and the tunable delay in the range of 10 to 160 fs, which can potentially provide an unprecedented femtosecond time resolution for time resolved UED.

NSLS-II is now one of the brightest synchrotron light sources worldwide, in user operations since 2014. Currently, 20 light-generating insertion devices (IDs) are installed: 3 damping wigglers and 17 undulators of various types. These devices introduce significant distortions into the magnet lattice of the storage ring. For each ID, the distortions have been locally corrected using quadrupole magnets located nearby the ID. The insertion devices have also a significant impact on the electron beam emittance. Precise measurements of the emittance were carried out at the Coherent Hard X-ray beamline for three different lattices: without IDs, with 3 pairs of damping wigglers only, and with all IDs. A minimum horizontal emittance of 0.76 nm was achieved. The radiation energy loss and relative energy spread were also measured using a streak-camera. The measured data show good agreement with analytical formulas and numerical simulations.

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 2·10−4 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. Furthermore, real-time energy measurement enables the filtering process to remove off-energy shots, improving the resolution of time-resolved UED. As a result, this method can be applied to the entire UED user community, beyond the traditional electron beam diagnostics of accelerators used by accelerator physicists.

In our previous publications, we introduced a concept of complex bend, which is a bending element consisting of dipole poles, interleaved with strong focusing and defocusing quadrupole poles. An electron ring built from such elements features low emittance while preserving substantial room for insertion devices and associated lattice elements. In this paper, we present two new optics solutions for the complex bend which offer to substantially reduce the device length by removing the dipole poles. In the first of the solutions, the bending is realized by shifting the quadrupole poles along the curved horizontal axis. For the second solution, we use permanent magnet quadrupole poles installed into a wide gap of the conventional electromagnet. In this case, the resulting bending field in the magnet gap is a superposition of the quadrupole field from the poles and the dipole field from the conventional magnet. We present an analysis of the particle motion and synchrotron radiation emitted in such fields, as well as an assessment of the ring linear lattice that is composed of complex bend elements.

Increased bandwidth and fluctuations are hurdles on the path towards generating intense fully coherent X-ray free-electron laser output. A recent experiment at FERMI Trieste demonstrated that these difficulties can be overcome by an approach called echo-enabled harmonic generation.

We discuss recent work on the construction of a numerical simulation of the fast orbit feedback system at NSLS-II. The simulation operates in the time domain and also includes the spatial domain, i.e. all beam position monitors (BPMs) and correctors. It can accept inputs of the real beam orbit and the measured orbit response matrix. It can also add errors to every stage of the calculation. We present methods to verify the simulation results by comparing the simulation results with experimental data collected at NSLS-II. The results are in very good agreement. The effects of errors from BPMs and correctors, as well as the amplitude of excitation, on the feedback performance, are also explored. This simulation can be used to predict the behavior and performance of the system for a future upgrade.

An interleaved sextupole scheme using cross-cell betatron phase cancellation technique is adopted as a candidate for the future NSLS-II upgrade lattice. The lattice uses as many NSLS-II installed magnets as possible, including 30 dipoles, to compose a triple bend achromat lattice. A 300 pm.rad horizontal beam emittance is achieved. The emittance can be further reduced to around 200 pm rad with damping wigglers. Various design concepts used in modern 4th-generation light sources, such as adopting longitudinal gradient dipoles and anti-bend scheme, are incorporated into the design as well. The betatron phase-advance between sextupoles is designed to have a cross-cell interleaving cancellation pattern in the transverse planes. The dynamic aperture is big enough for the conventional off-axis top-off injection. At the same time, a large energy acceptance looks promising to ensure a sufficiently long beam lifetime., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

We explore the possibility of visualizing the lattice dynamics behavior by acquiring a single time-resolved mega-electron-volt ultrafast electron diffraction (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 the pump laser and the electron probe, the intensity fluctuation of probe pulses, and the premature sample damage. Inspired by the early transient spectroscopy studies via an ultrashort-pulse pump/long-pulse probe scheme, we show that, by converting the longitudinal time of an electron pulse to the transverse position of a Bragg peak on the detector, one can obtain the full lattice dynamic process in a single electron pulse. This time-to-position mapping can be achieved by the combination of longitudinally shaping the electron beam and introducing a time-dependent transverse kick after electrons are diffracted from the sample. We propose a novel design of time-resolved UED facility with the capability of capturing a wide range of dynamic features in a single diffraction image. To achieve the best possible temporal resolution, we implement a real-time tuning scheme for optimizing the match between the electron bunch length and the lattice dynamic timescale, varying in the sub-picosecond to tens of picosecond (ps) range depending on the specific process. This timescale match is in favor of the ultrafast phenomenon, which requires a 10 fs temporal resolution for resolving the sub-ps oscillation. A state-of-the-art photocathode gun being developed by Euclid could extend the timescale to hundreds of ps. To study the radiation damage and to mitigate such effect, longitudinally shaping the photocathode drive laser pulse (demonstrated in a previous study) can control and manipulate the electron beam current profile with a tunable periodical structure. Furthermore, we present numerical evidence illustrating the capability of acquiring a single time-resolved diffraction image based on the case-by-case studies of different lattice dynamics behaviors.

The National Synchrotron Light Source II is a third generation light source, which was constructed at Brookhaven National Laboratory. This project includes a highly-optimized 3 GeV electron storage ring, linac preinjector, and full-energy synchrotron injector. Budker Institute of Nuclear Physics built and delivered the booster for NSLS-II. The commissioning of the booster was successfully completed. This paper reviews fulfilled work by participants.

This paper discusses improvements made to the fast orbit feedback (FOFB) system at NSLS-II in 2019. We first characterized the system by measuring the transfer function and the closed-loop gain of the system. We also constructed a model to predict the performance, which was based on physical behaviors. After finding and fixing the sources of the latency, we improved the closed-loop gain’s bandwidth from 250 Hz to 400 Hz in the horizontal plane and 250 Hz to 300 Hz in the vertical plane. The orbit beam instability improved by 30% and 10% in the horizontal and vertical planes, respectively.

The heat transfer analysis has been performed for the stripline kicker, design of which is used at many accelerator facilities as a part of the transverse bunch-by-bunch feed-back system, including NSLS-II. The experimental data of the electrode temperature have been collected from a special diagnostic stripline designed with six infrared view ports. The temperature analysis is based on the power loss calculations and the loss factor computed by the 3-D electromagnetic simulation code GdfidL. To estimate the power loss, we analyze the real part of the longitudinal impedance and the loss factor for two different regimes. We use the ANSYS finite element code to correlate the temperature with the power loss. Lambertson and Shafer formalisms of the longitudinal and transverse beam impedances are discussed for the simplified stripline geometries. The required characteristic impedances and the geometric factors are determined analytically for the simplified geometries and compared with the results for the designed stripline geometry using the 2-D POISSON code by solving the Laplace’s equation in two dimensions. Lambertson’s equations are compared with numerical results. We introduce the frequency range, within which we can apply the analytical approach.

Modern synchrotron light sources are competing intensively to increase x-ray brightness and, eventually, approach the diffraction limit, which sets the final goal of lattice emittance. All recent synchrotron facility upgrades follow the multibend achromat approach by arranging small horizontal beta function and dispersion inside discrete bending dipoles. In this paper we propose a concept of a lattice element that we call ``complex bend,'' which has the potential of becoming a main building block for low emittance lattices. The complex bend is a sequence of dipole poles interleaved with strong alternate focusing so as to maintain the beta function and dispersion oscillating at low values. Comprising the ring lattice with complex bends, instead of regular dipoles, will minimize the $H$-function and reduce horizontal emittance while localizing bending to a small fraction of the storage ring circumference, which should provide more space for insertion devices. In this paper we present the details of the complex bend, considerations regarding the choice of optimal parameters, and thoughts for its practical realization. We focus here on complex bend physics and engineering design, rather than integration of this complex bend into a specific ring lattice.

In this article, we report our proof-of-principle design and experimental commissioning of a broadly tunable and low-cost transverse focusing lens system for MeV-energy electron beams. The lens system based on electromagnetic (EM) quadrupoles has been built as a part of the existing instrument for ultra-fast electron diffraction (UED) experiments at the Accelerator Test Facility II (ATF-II) at Brookhaven National Laboratory (BNL). We experimentally demonstrated the independent control of the size and divergence of the beam with the charge ranging from 1 to 13 pC. The charge density and divergence of the beam at the sample are the most important factors determining the quality of the Bragg-diffraction image (BDI). By applying the Robust Conjugate Directional Search (RCDS) algorithm for online optimization of the quadrupoles, the transverse beam size can be kept constant down to 75 µm from 1 to 13 pC. The charge density is nearly two orders of magnitude higher than the previously achieved value using a conventional solenoid. Using the BDI method we were able to extract the divergence of the beam in real-time and apply it to the emittance measurement for the first time. Our results agree well with simulations and with the traditional quadrupole scan method. The real-time divergence measurement opens the possibility of online optimization of the beam divergence (

Commissioning of the first X-ray beamlines of NSLS-II included detailed measurements of spectral and spatial distributions of the radiation at different locations of the beamlines, from front-ends to sample positions. Comparison of some of these measurement results with high-accuracy calculations of synchrotron (undulator) emission and wavefront propagation through X-ray transport optics, performed using SRW code, is presented.

The National Synchrotron Light Source II at Brookhaven National Lab is a third-generation synchrotron radiation facility that has been commissioned in 2014. The facility is based on a 3 GeV electron storage ring, which will circulate 500 mA of beam current at 1 nm rad horizontal emittance. The storage ring is 792 meters in circumference and will accommodate more than 60 beamlines in the final built-out. The beamline sources range from insertion-devices located in straight sections, bending magnets or three-pole-wigglers configured in multiple branches. The NSLS-II storage ring commissioning was successfully completed in July 2014 and the facility delivered the first user light on October 23, 2014. Currently the storage ring reached 300 mA beam current and achieved 1 nm rad of horizontal emittance with 3 sets of Damping Wigglers. At this point six NSLS-II project beamlines are routinely taking photons with beam current at 150 mA. This paper reviews the NSLS-II accelerator design and commissioning experience.

The National Synchrotron Light Source II (NSLS-II) is a state of the art 3 GeV third generation light source at Brookhaven National Laboratory. During spring/ summer of 2014, the storage ring was commissioned up to 50 mA without insertion devices. In the fall of 2014, we began commissioning of the project beamlines, which included seven insertion devices on six ID ports. Beamlines IXS, HXN, CSX-1, CSX-2, CHX, SRX, and XPD-1 consist of elliptically polarized undulator (EPU), damping wigglers (DW) and in-vacuum undulators (IVU) covering from VUV to hard x-ray range. In this paper, experience with commissioning and operation is discussed. We focus on reaching storage ring performance with IDs, including injection, design emittance, compensation of orbit distortions caused by ID residual field, source point stability, beam alignment and tools for control, monitoring and protection of the ring chambers from ID radiation.

The first eight insertion devices (IDs) at the NSLS-II were commissioned during the fall run of 2014. In this paper we discuss commissioning of the synchrotron radiation protection (SRP) system and beamline frontends (FE) for the respective IDs. We describe the diagnostics utilized if FE commissioning and a procedure that was used for the alignment of the photon beam from insertion devices in the beamline frontends. Then we discuss the current status of the SRP system and operation of the commissioned frontends.

Recently strong modulation of the electron bunch longitudinal phase space was obtained in the DUVFEL accelerator at NSLS. The chirped beam energy spectra exhibit a spiky structure with a subpicosecond spike separation. A model based on the longitudinal space-charge effect has been suggested as an explanation of the observed effect. For characterization of the structure and comparison with the model we performed several experiments. In this paper we present experimental data and discuss them in relation to the model.

We report the first experimental results on a high-gain harmonic-generation (HGHG) free-electron laser (FEL) operating in the ultraviolet. An 800 nm seed from a Ti-Sapphire laser has been used to produce saturated amplified output at the 266 nm third-harmonic. The results confirm the advantages of the HGHG FEL: stable central wavelength, narrow bandwidth and small pulse energy fluctuation. The harmonic output at 88 nm, which accompanies the 266 nm radiation, has been used in an ion pair imaging experiment in chemistry.

The DUV-FEL facility has been in operation in the High Gain Harmonic Generation (HGHG) mode producing a 266-nm output from 177-MeV electrons for 1 year. In this paper, we present preliminary results of the Chirped Pulse Amplification (CPA) of the HGHG radiation. In the normal HGHG process, a 1-ps electron beam is seeded by a chirped 9 ps long, 800-nm Ti:Sapphire laser. The electron beam sees only a narrow fraction of the seed laser bandwidth. However, in the CPA case, the seed laser pulse length is reduced to 1 ps, and the electron beam sees the full bandwidth. We introduce an energy chirp on the electron beam to match the chirp of the seed pulse, enabling the resonant condition for the whole beam. We present measurements of the spectrum bandwidth for various chirp conditions.

Temporal profile of a simple bunch distribution may be obtained by measuring the horizontal density profile of an energy-chirped electron beam at a dispersive region using the rf zero-phasing technique. For an energy-modulated beam, the horizontal profile obtained by this technique is also modulated with an enhanced amplitude. We study the microbunching experiment at the NSLS source development laboratory and show that the horizontal modulation observed by the rf zero-phasing technique can be explained by the space–charge-induced energy modulation in the accelerator.

The Deep Ultra Violet FEL (DUV-FEL) experiment is being commissioned in the Source Development Laboratory at NSLS in Brookhaven National Laboratory. The goal of the project is to produce coherent radiation below 100 nm wavelength using High-Gain Harmonic Generation utilizing a seed laser. As a first step of this experiment, self-amplified spontaneous emission (SASE) has been achieved at 400 and 266 nm with electron beam energies at 140 and 171.7 MeV. As an intermediate stage of the experiment, direct seeding with the 266 nm laser also has been accomplished. We report the measurements of the SASE and direct seeding. We measure the FEL properties for various electron beam conditions and discuss the performance of the FEL.