The High Energy Photon Source (HEPS) is the first 4th generation light source and the first high-energy storage ring light source in China, with a beam energy of 6 GeV, a circumference of 1360 m and a natural emittance of a few tens of picometers. As a green-field light source, the HEPS construction started in 2019 and is scheduled to be completed in 2025. Now civil construction, component fabrication and tunnel installation, and beam commissioning of the HEPS has been basically finished. In this report, the accelerator and especially the storage ring commissioning results, and main physics issues faced and corresponding measures during the beam commissioning will be presented.

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.

A new beam position monitor (BPM) pick-up, compatible to operate reliably with the high current electron beams foreseen in the 5 - 18 GeV Electron Storage Ring (ESR) of the Electron-Ion Collider (EIC) project, is presented. We discuss a few design options for this button-style BPM pick-up with a focus on output signal levels, position characteristic, and wakefield effects. Regarding the octagonal cross-section geometry of the ESR vacuum chamber, the BPM pick-up analysis relies on numerical methods, here performed using the CST Studio software.

Premature activation of the insertion device (ID) minimum-gap limit switches was observed during beamline commissioning at the Advanced Photon Source Upgrade (APSU). This issue was traced to vertical deformation of the insertion device vacuum chamber (IDVC) due to temperature differences with its strongback. Direct measurements of temperature and vertical displacement of IDVC in a selected sector of the APS storage ring confirmed this effect, and simulations successfully reproduced the thermal deformation mechanism. To address the issue, we developed a simple mechanical constraint to limit the vertical displacement, rather than actively compensating for the temperature difference through enhanced heat transfer. This paper reports the investigations, proposed mechanical solution, simulation, and measurement validation after its installation. Post-installation tests successfully demonstrated its effectiveness, allowing the IDs to reach the minimum gap without triggering the limit switch.

A harp system is being developed for monitoring proton beam profile direct upstream of the proton beam window at the Second Target Station of the Spallation Neutron Source, Oak Ridge National Laboratory. It consists of two sensor planes which have arrays of thin conducting wires aligned vertically and horizontally, respectively. It monitors beam profiles in two transverse directions to the beam axis by measuring the net-charge depositions in the sensor wires, which are caused by ejection of secondary electrons and delta rays driven by electromagnetic interactions with high-energy protons. The net charge deposition in a sensing wire linearly correlates with the number of incident protons on it. This correlation is perturbed when the wire interacts with secondary electrons and delta rays originating from beam-matter interactions in neighboring wires, PBW and residual gases. In this paper, we analyze the physical phenomena that affects the measurement uncertainties of the harp using particle transport simulations.

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.

A prototype colliding beam accelerator has been fabricated for the study of a fusion-based propulsion concept for interplanetary exploration. The purpose of this prototype is to demonstrate collider luminosities commensurate with the requirements of this application. Direct emission of fusion daughters generates the exhaust velocities required for spacecraft speeds in excess of 1% of the speed of light. Past attempts at nuclear fusion energy production with colliding beams have been limited by Coulomb scattering, a deficiency overcome in this collider architecture. Instead of using fusion fuels such as p/Li7 and He3/He3 capable of generating the required thrust characteristics, this prototype employs deuterons. DD fusion produces neutrons that provide a convenient luminosity detection channel. The commissioning campaign described in this paper operates the collider at a peak beam kinetic energy of 60 keV at the interaction point. Axial confinement and radial focusing are achieved electrostatically. Measured data and subsequent analysis in regard to longitudinal and transverse beam dynamics and beam lifetime are presented.

A new lattice for the NSLS-II upgrade is likely to use high strength (> 100 T/m) permanent magnet quadrupoles (PMQs). An ID beam exiting through these quadrupoles will place highly intense x-rays very close (~ 1mm) to the permanent-magnet material. In these tests the PMQs will be placed in the IFE (Instrumentation Front End) front end to assess any degradation of their field strengths and field quality due to long term exposure to an ID beam. The IFE beamline was recently commissioned at NSLS-II and is dedicated to testing the mechanical properties of accelerator materials and components. The description of the source and experimental setup will be given.

The Fermilab Main Injector accelerating cavities have sparking issues when they are run at voltages higher than those required by the PIP-II project. This is a problem Fermilab is working on as planning begins for the next upgrade to the accelerator complex. One of the methods being used to address the issue is the development of a CST Microwave Studio simulation to accurately model the PIP-II dual power amplifier cavities and identify which part(s) of the cavity is causing sparking to develop. The model will also be used to determine if changes to the cavity geometry may allow the cavity to be used at higher voltages before sparking occurs.

Ultra nanocrystalline diamond (UNCD) is a promising material for field emitters because of its mechanical and chemical stability, high thermal conductivity, and low electrical resistivity. We proposed to demonstrate fabrication of a special shape field emitter array to produce a sheet electron beam for high frequency vacuum tubes. At Los Alamos, we established a Field Emitter Array Test Stand (FEATS) where we can apply voltages up to 40 kV to test field emitter arrays in a vacuum level of 10^-7 Torr or lower. At this test stand, we can take beam images, measure beam current and study beam divergence. We fabricated diamond cathodes in form of arrays of 1 by 81 pyramids and used them to demonstrate production of a sheet electron beam. This talk will present details of the emission tests and analyses of the produced sheet beam.

An advanced charge selector is currently under development at the Facility for Rare Isotope Beams (FRIB) to intercept unwanted charge states of stripped heavy ion beams. Rotating graphite wheels are employed to absorb beams with a power up to 5 kW and a size as small as an rms width of 0.7 mm × 1.25 mm. The implantation of beam ions and accumulated radiation damage affect the material properties, potentially leading to its structural failure. Determining the foreign ion accumulation behavior is one critical aspect for predicting the operational lifetime of the graphite wheels. In this study, ion implantation distribution was first characterized using SRIM simulations, then coupled with Monte Carlo analysis to account for wheel geometry and rotational dynamics. The evolution of the ion concentration profiles was subsequently determined considering the diffusion effects. The analysis reveals that strategic beam positioning optimization, combined with diffusion effects, substantially reduces peak ion concentrations and implantation rates, providing essential data for graphite wheel lifetime assessment.

We report on the quantum efficiency (QE) and mean transverse energy (MTE) of photoemitted electrons from cadmium arsenide (Cd₃As₂), a three-dimensional Dirac semimetal (3D DSM) of interest for photocathode applications due to its unique electronic band structure, characterized by a 3D linear dispersion relation at the Fermi energy. Samples were synthesized at the National Renewable Energy Laboratory (NREL) and transferred under ultra-high vacuum to Arizona State University (ASU) for measurement using a photoemission electron microscope (PEEM). The maximum QE was measured to be 3.37 × 10⁻⁴ at 230 nm, and the minimum MTE was 55.8 meV at 250 nm. These findings represent the first reported QE and MTE measurements of Cd₃As₂ and are an important step in evaluating the viability of 3D DSMs as low-MTE photocathodes. Such photocathodes, constrained to lower MTEs by the electronic band structure, may prove effective in advancing beam brightness in next-generation instruments and techniques.

The IOTA ring is vital to the advancement of accelerator sciences, and a large part of its attractiveness to accelerator physicists is its modularity and the versatility that this function provides. Up until this point, the FAST accelerator has provided electron beam for the studies in IOTA. With the soon to be commissioned IOTA Proton Injector in lieu, the requirement for better vacuum to support future proton studies in the ring have arrived. Our solution is the IOTA Bake System which has the goal of facilitating this requirement.

Medium temperature baking (300- 350 °C) enhances the quality factor of niobium superconducting radio frequency cavities. However, surface contamination introduced during vacuum furnace baking limits the quench field and may also degrade the quality factor of the cavity. To investigate this effect, a 1.3 GHz single-cell Nb cavity underwent mid-T baking, followed by a chemical treatment to remove the surface contaminants. Post-treatment measurements revealed a significant improvement in both the quality factor and the quench field.

LANSCE uses 44 805MHz klystrons to power the Coupled Cavity Linac (CCL). Modulated anode tubes such as the 1.25 MW LANSCE klystrons need high volt-age testing and processing prior to full operation. This not only verifies the klystron can hold-of HV but also allows the klystron to process out some internal imperfections prior to being pulsed by the modulator for the accelerator. The LANSCE accelerator is a relatively long pulse machine, and improper processing can lead to premature degradation in the performance of the tube. This paper describes recent improvements to the 1.25 MW 805MHz klystron HV check and conditioning process through the development of a new high-potting test stand. High-potting setup and techniques that were historically used are contrasted with the new implementation. Our goal is to improve LANSCE operations by accelerating the high-potting process and reducing expert time and dependence. The new test stand will optimize legacy processes by improving diagnostics, automating control and reducing inconsistencies and process invariability due to human factors. Analysis and automation efforts for this critical process are discussed along with current benefits and future work.

Throughout its operation, the RHIC triplet magnets have been subject to a mechanical vibration around 10 Hz. These mechanical vibrations were found to produce a beam orbit jitter that was detrimental to the collider luminosity. During RHIC operation, this has been effectively mitigated by the implementation of a fast feedback orbit control system. For the Electron Ion Collider (EIC) Hadron Storage Ring (HSR), the RHIC triplet package will be modified, magnets will be removed, and the cryogenic lines will be rearranged inside the cryostat. A comprehensive analysis of the RHIC triplet vibration has been undertaken to ensure that the planned triplet piping modifications would not increase the current triplet magnet vibrations and overwhelm the existing fast feedback control system. This paper aims to describe the current understanding of the root cause and kinematic of the RHIC triplet vibrations and offer mitigation options for EIC.

The properties of the photoemitting electron sources are the most determining factors contributing to the performance of the most advanced electron accelerator applications such as particle colliders, X-ray free electron lasers, ultra-fast electron diffraction and microscopy experiments. Therefore, low mean transverse energy (MTE), high quantum efficiency (QE) along with long operational lifetime and robustness under high electric fields and laser fluences must be demonstrated by the photocathode for these bright beam applications. Recent investigations have revealed that the epitaxial growth of single crystal cesium antimonides can be achieved by photocathode growth on lattice matched substrates. In this letter, the experimental setup for highly promising alkali antimonide photocathode growth by molecular beam epitaxy on lattice matched substrates and in-situ characterization with reflection high-energy electron diffraction (RHEED) has been presented. To adapt the L-band RF gun of Argonne Cathode Test-stand (ACT) for extensive testing of alkali antimonides in real accelerator conditions, compatible cathode plug design and smooth transportation process have been developed and also described in this paper.

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.

A fixed-beam, two room suite with upright chairs for patient positioning, is being installed at the McLaren Proton Therapy Center (MPTC). The MPTC is an operational, multi-room cancer treatment center. The new suite adds a third (A) and fourth (B) room by branching off upstream of the two clinically active half-gantry treatment rooms. This imposed a number of constraints on the beamlines of the new suite. The new beamline uses a Y-shaped selection dipole to switch between the suite’s room A and room B. The design was further constrained by the need to replicate the clinically active rooms’ beam characteristics at the new patient locations. This paper provides an overview of the methodology of the design studies for the new beamlines together with selected results. The work helped to establish the feasibility of installing a two-room treatment suite into a space originally designed for a gantry-based single treatment room.

The Coherent Electron Cooling (CeC) technique is a breakthrough in accelerator science, enhancing ion beam brightness in facilities like the Electron-Ion Collider (EIC). The success of CeC relies on high-performance photocathodes (PCs) for photoinjectors, where ideal PCs exhibit high QE, low emittance, long lifetimes, and minimal dark current. Alkali antimonide PCs meet these requirements. Among these, Na-K-Sb shows enhanced robustness, particularly under high-temperature conditions from high-power laser illumination, which generates high current electron beams. It also demonstrates improved vacuum stability and long-term QE consistency compared to other alkali antimonides like K2CsSb and Cs3Sb. These attributes make Na-K-Sb an effective choice for applications requiring both thermal and vacuum stability. This work presents the growth of Na-K-Sb PCs using the CeC cathode deposition system, alongside detailed QE measurements and spatially resolved QE maps. These findings highlight the potential of Na-K-Sb PCs to advance CeC performance significantly and foster the development of high current, high-brightness electron sources for broader applications

The concept of the AGU has been proposed for some time*. However, utilizing a permanent magnet-based device complicates the design due to the necessity of independent gap control for each segment and, in the case of an in-vacuum undulator, the requirement for a flexible continuity sheet to mitigate image current heating. The adoption of SC magnets eliminates these concerns. The SC-AGU prototype will comprise three sections of magnetic arrays with a total length of 120 cm, with the central section featuring a smaller gap than the end units. To achieve this, a UHV chamber will be designed for eventual fabrication, incorporating a non-uniform aperture that conforms to the beam envelope. Furthermore, to maintain a constant fundamental photon energy and maximize on-axis spontaneous emission, each SC section will be engineered with distinct period lengths, with the central section possessing a shorter period than the end units. This paper presents the methodology for end-field analysis, encompassing detailed simulations to characterize the magnetic field distribution at the extremities of each magnetic array. Particular emphasis is placed on the impact of field quality at junctions and its influence on radiation properties, ensuring the optimization of on-axis spontaneous emission while preserving the electron beam’s ‘stay-clear’ area and mitigating impedance constraints imposed by the undulator magnet structure.

Understanding synchrotron induced gas desorption plays an important role in predicting vacuum behavior of accelerators. Investigations of new materials and coatings require careful study of their desorption yield for potential use in upgrading NSLS-II as well as other accelerator facilities. A beamline at NSLS-II, dedicated to the study of novel and proposed vacuum materials has been constructed and commissioned to advance further research into desorption behavior. The PSD of stainless steel, OFHC copper and NEG coated copper, some of which for use in the future Electron-Ion Collider at BNL, have been measured and will be presented. These newly established desorption rates will be used as inputs to advanced modeling tools such as MolFlow+ and SynRad+ for accurate predictions of vacuum behavior and design optimization. The existing layout and future plans for the beamline will be presented.

Spin-transparent storage rings, where any spin direction repeats after one full turn, can be used in conjunction with ion traps as a new quantum computing platform [1]. Advantages of spin-transparent rings for quantum computing include: large numbers of stored qubits; long quantum coherence times of up to several hours; long storage lifetimes; and room temperature operation. These exceptional qualities mean rings could provide a scalable way to implement algorithms with deep complexity requiring many quantum operations while simultaneously providing a large number of qubits. This new platform where the qubit has long quantum coherence time can also be used as a quantum sensor or a part of a quantum memory.

We present a hybrid permanent magnet-based adjustable phase undulator, featuring a period length of 17.2 mm, a gap of 8.5 mm, and a total length of 2.4 m. This planar polarized undulator adjusts field intensity through longitudinal jaw movement, with mechanically linked magnet arrays ensuring smooth motion. Building on previous work, this report focuses on newly developed tuning techniques for trajectory and phase error correction. Our engineering experience demonstrates the effectiveness of these methods in optimizing undulator performance.