The Advanced Photon Source (APS) recently completed a transformative upgrade, replacing its 25-year-old storage ring with a state-of-the-art hybrid seven-bend achromat lattice with six additional reverse bends. The new design features a low natural emittance of 42 pm-rad, enabling productions of X-rays up to 500 times brighter than the original APS. The upgrade introduced a pioneering swap-out injection scheme, replacing entire depleted bunches rather than topping them up. This approach enables on-axis injection to accommodate for the reduced dynamic aperture resulting from strong focusing. The paper describes the commissioning process, operating experience with swap-out injection, and gives performance parameters of new systems such as the bunch-lengthening cavity.

The Advanced Photon Source (APS) team is building a fourth-generation storage ring (4GSR), replacing the present double-bend achromat lattice with a multibend achromat system thereby allowing the production of ultrabright x-ray beams. The new lattice enables a 2-order-of-magnitude reduction in horizontal beam emittance and a factor of two increase in beam current. The result is an electron beam of very high energy and power densities. Initial predictions suggest many common ultrahigh-vacuum-compatible materials struck by the full-intensity electron beam will be damaged. Two experimental beam abort studies have been conducted on collimator test pieces in the present APS SR to inform the design of a fully-functional machine protection system for APS 4GSR operations at 200 mA. A comprehensive suite of diagnostics was utilized during the studies. The diagnostics used in these experiments are not new, but employed in different ways to obtain unique data sets. With these sets now in hand, we are developing new numerical tools to guide collimator design using pelegant [M. Borland, elegant: A flexible SDDS-compliant code for accelerator simulation, Technical Report No. LS-287, Advanced Photon Source, 2000; Y. Wang and M. Borland, Implementation and performance of parallelized elegant, in Proceedings of the 2007 Particle Accelerator Conference, http://cern.ch/AccelConf/p07/PAPERS/THPAN095.PDF, pp. 3444--3446], mars [N. V. Mokhov and S. I. Striganov, Fermilab-conf-07/008-ad, AIP Conf. Proc. 896, 50 (2007)], and flash [B. Fryxell et al., flash: An adaptive mesh hydrodynamics code for modeling astrophysical thermonuclear flashes, Astrophys. J. Suppl. Ser. 131, 273 (2000); P. Tzeferacos et al., Laboratory evidence of dynamo amplification of magnetic fields in a turbulent plasma, Nat. Commun. 9, 591 (2018)].

We summarize the community-based consensus for improvements concerning education, public outreach, and inclusion in Accelerator Science and Engineering that will enhance the workforce in the USA. The improvements identified reflect the product of discussions held within the 2021-2022 Snowmass community planning process by topical group AF1: Beam Physics and Accelerator Education within the Accelerator Frontier. Although the Snowmass process centers on high-energy physics, this document outlines required improvements for the entire U.S. accelerator science and engineering enterprise because education of those entering and in the field, outreach to the public, and inclusion are inextricably linked.

For the APS-Upgrade, swap-out injection will require the booster to support up to 17 nC bunch charge, several times what is used in the present APS. Booster injection efficiency drops sharply at high charge, and is the present bottleneck limiting high charge transport through the injectors. Particle tracking simulations have been used to understand what causes are limiting the injection efficiency, and to guide plans for improving it. In particular, bunch length blowup in the injected beam and beam loading in the RF cavities have been identified as the biggest factors. Simulations and measurements have also been done to characterize beam properties along the booster energy ramp. So far, a bunch charge of 12 nC has been successfully extracted from the booster.

Immediately after the installation of the Helical Superconducting Undulator (HSCU) in the APS storage ring, higher than expected heating was observed in the cryogenic cooling system [1]. Steering the electron beam orbit in the upstream dipole reduced the amount of synchrotron radiation reach-ing into the HSCU and allowed the device to properly cool and operate. The simplest explanation of the excessive heat load was higher than expected heat transfer from the vacuum chamber to the magnet coils. However, modeling of the synchrotron radiation interaction with the HSCU vacuum chamber showed that Compton scattering could also result in synchrotron radiation penetrating the vacuum chamber and depositing energy directly into the HSCU coils [2]. In this paper we present experimental evidence that the excessive heat load of the HSCU coils is not caused by the heat transfer from the vacuum chamber but resulted from the synchrotron radiation penetrating the vacuum chamber.

The APS-Upgrade presents several challenging demands to the booster synchrotron. Swap-out injection requires the booster to capture a high charge bunch (up to 17 nC), accelerate it to 6 GeV, and maintain a low emittance at extraction for injection into the storage ring. To accommodate these conflicting demands, the RF frequency will be ramped between injection and extraction. However, the RF cavity tuners will remain static, which means the couplers will need to withstand a high reflected power at extraction. This paper presents a plan for a system that will meet the requirements for injection efficiency, extracted emittance, and equivalent power at the coupler. Results from tracking simulations and beam studies with a frequency ramp will also be shown.

The Advanced Photon Source Upgrade (APS-U) is a high-performance fourth-generation storage ring light source based on multibend achromat (MBA) optics. As such, APS-U will require on-axis injection. The injectors will need to supply full-current bunch replacement in the ring; therefore, the injected bunch charge will be up to five times higher than what is typical for APS. A program was conducted to measure the radiation dose above the injector transport line to the APS storage ring for both normal operation conditions and controlled loss scenarios. Standard survey meters were used to record the dose. A review of the dose data identified opportunities to minimize the potential dose under normal APS-U high charge operation and fault conditions; these include improving the supplemental shielding and adding engineered controls. In addition, the dose data provide a benchmark for evaluating new radiation monitors for APS-U.

Next-generation, high-performance storage ring (SR) light sources based on multibend achromat optics will require on-axis injection because of the extremely small dynamic aperture. Injectors will need to supply full-current bunch replacement in the SR with high single-bunch charge for swap-out. For upgrades of existing light sources, such as the Advanced Photon Source Upgrade (APS-U), it is economical to retain the existing injector infrastructure and make appropriate improvements. The challenges to these improvements include achieving high single-bunch charge in the presence of instabilities, beam loading, charge stability and reliability. In this paper, we discuss the rationale for the injector upgrades chosen for APS-U, as well as backup and potential alternate schemes. To date, we have achieved single-bunch charge from the injectors that doubles the original design value, and have a goal to achieve about three times the original design value.

We present the results of experiments on the effects of beam dumps on candidate collimator materials for the Advanced Photon Source Upgrade (APS-U) storage ring (SR). Due to small transverse electron beam sizes, whole beam loss events are expected to yield dose levels in excess of 10 MGy in beam-facing components, resulting in localized melting. Whole beam aborts have characteristic time scales ranging from 100s of ps to 10s of microseconds which are either much shorter than or roughly equal to thermal diffusion times. Aluminum and titanium alloy test pieces are each exposed to a series of beam aborts of varying fill pattern and charge. Simulations suggest the high energy/power densities are likely to lead to damage in any material initially encountered by the beam. We describe measurements used to characterize the beam aborts as well as results of postexperiment inspection. The goal of this work is to guide the design of APS-U SR collimators. Simulations are discussed in a companion paper at this conference.

A design choice for the Advanced Photon Source Upgrade to inject into the storage ring using bunch swap out rather than off-axis accumulation means that the Advanced Photon Source injectors are required to accelerate much higher electron bunch charge than originally designed. In the present work, we outline upgrades to the current monitor and beam position monitor diagnostics for the Particle Accumulator Ring to accommodate bunch charges of 1-20 nC. Through experiments, we compare and characterize the system responses over the range of bunch charge.

The feasibility of a fast beam interlock system for the Advanced Photon Source (APS) Particle Accumulator Ring (PAR) is considered for high-charge operations. This system would be based on detection of Cerenkov light generated from lost electrons passing through high-purity, fusedsilica fiber optic cable. The cable acts as both radiator and light pipe to the photomultiplier tube (PMT). Results from a prototype installation have shown excellent sensitivity, linearity, and reproducibility after 10,000 hours of operation, with little change in transmission. The high sensitivity allows a more accurate measure of low-level loss than do current monitors and faster response than installed gamma or neutron detectors. These features will be important as we modify the PAR to accept higher energy electrons from the linac. Initial calibration measurements of the prototype system against radiation monitors for various loss scenarios are discussed. Comparison of the scenarios with simulations are presented.

After decades of successful operation as a 7-GeV synchrotron radiation source, the Advanced Photon Source is pursing a major upgrade that involves replacement of the storage ring with an ultra-low emittance multi-bend achromat design. Using a seven-bend hybrid multi-bend achromat with reverse bending magnets gives a natural emittance of 42 pm operated at 6 GeV. The x-ray brightness is predicted to increase by more than two orders of magnitude. Challenges are many, but appear manageable based on thorough simulation and in light of the experience gained from world-wide operation of 3rd-generation light sources. The upgraded ring will operate in swap-out mode, which has allowed pushing the performance beyond the limits imposed by conventional operation.

A fast photodetector system is used to monitor the bunch duration in the Advanced Photon Source (APS) Particle Accumulator Ring (PAR). The PAR Bunch Duration Monitor (BDM) is based on the metal-semiconductor-metal (MSM) photodetector Hamamatsu G4176-03 MSM with specified rise and fall times of 30 ps. The BDM has sufficient frequency response to resolve the PAR bunch near extraction where, under low-charge conditions, minimum rms pulse durations of 250-300 ps are observed. Beam from the PAR is injected into the Booster; for efficient capture, injected rms bunch duration from the PAR must be less than 650 ps. BDM data show good agreement with streak camera measurements. The MSM detector exhibits a ringing response to fast input signals. To overcome this, the BDM output is de-convolved with the impulse response function of the detector-amplifier circuit. Turn-by-turnbunch duration data is presented versus charge and time in the PAR cycle. Peak detection mode allows for calculation of bunch length over large fractions of the PAR cycle.

Development of superconducting undulators continues at the Advanced Photon Source (APS). Two years after successful installation and commissioning of the first relatively short superconducting undulator “SCU0” in Sector 6 of the APS storage ring, the second 1.1-m-long superconducting undulator “SCU1” was installed in Sector 1 of the APS. The device has been in user operation since its commissioning in May 2015. This paper describes the magnetic and cryogenic design of the SCU1 together with the results of stand-alone cold tests. The SCU1’s magnetic and cryogenic performance as well as its operating experience in the APS storage ring are also presented.

A beam abort system has been implemented in the Advanced Photon Source storage ring. The abort system works in tandem with the existing machine protection system (MPS), and its purpose is to control the beam loss location and, thereby, minimize beam loss-induced quenches at the two superconducting undulators (SCUs). The abort system consists of a dedicated horizontal kicker designed to kick out all the bunches in a few turns after being triggered by MPS. The abort system concept was developed on the basis of single- and multi-particle tracking simulations using elegant and bench measurements of the kicker pulse. Performance of the abort system–kick amplitudes and loss distributions of all bunches–was analyzed using beam position monitor (BPM) turn histories, and agrees reasonably well with the model. Beam loss locations indicated by the BPMs are consistent with the fast fiber-optic beam loss diagnostics described elsewhere [1]. Operational experience with the abort system, various issues that were encountered, limitations of the system, and quench statistics are described.

The APS-Upgrade will require the injector chain to provide high single bunch charge for swap-out injection. One possible limiting factor to achieving this is an observed reduction of injection efficiency into the booster synchrotron at high charge. We have simulated booster injection using the particle tracking code elegant, including a model for the booster impedance and beam loading in the RF cavities. The simulations point to two possible causes for reduced efficiency: energy oscillations leading to losses at high dispersion locations, and a vertical beam size blowup caused by ions in the particle accumulator ring. We also show that the efficiency is much higher in an alternate booster lattice with smaller vertical beta function and zero dispersion in the straight sections.