SLAC, Menlo Park, California, USA
ANL, Argonne, USA
ANL, Argonne, USA
As part of an ongoing upgrade of the Advanced Photon Source (APS), a Short Pulse X-ray (SPX) system is being developed based on two sets of crab cavities separated by 180 degrees vertical phase advance. Emittance growth due to incomplete cancellation between the sets of cavities is a concern. Simulations predict that it can be controlled by special adjustment of the sextupoles between the cavities. In order to test these predictions, we can use orbit bumps that reproduce the trajectories of individual particles through the sectors in question. In this paper, we present the results of simulations of such tests, showing the degree to which the emittance growth and other properties of the machine will differ for optimized and unoptimized sextupoles.
ANL, Argonne, USA
The Advanced Photon Source (APS) is a 7-GeV storage ring light source that has been in operation since 1996. In that time, the emittance has dropped from 8 nm to 3 nm. The increasing feasibility of multi-bend-achromat lattices (e.g., the MAX-IV project) promises the possibility of a much greater reduction in emittance. In this paper, we show the design of a symmetric seven-bend-achromat lattice, including linear optics, nonlinear dynamics optimization, magnet requirements, and performance with errors.
ANL, Argonne, USA
ANL, Argonne, USA
ANL, Argonne, USA
One of the unique features of the Advanced Photon Source is operation with a small number of intense bunches – standard operating mode has twenty four 16-nC bunches, while in a special operating mode one of the bunches has a charge of 60 nC. Such high single bunch currents are achieved by a combination of high operational chromaticity and transverse bunch-by-bunch feedback. In the near future, more narrow-gap insertion device vacuum chambers will be installed, which will increase impedance of the storage ring and make operation with high single-bunch current more problematic. Simulations exist that quantify the effect of increased impedance on the APS single-bunch accumulation limit; however, no experimental verification has been performed yet. In this paper, we will present our first measurement of the single-bunch accumulation limit as a function of effective impedance. Different impedance values were achieved by changing storage ring beta functions.
ANL, Argonne, USA
A multi-bend-achromat (MBA) extreme low-emittance lattice has been proposed for the future APS Upgrade. Due to its small dynamic aperture, the traditional injection scheme must be replaced with bunch train swap-out scheme. Several options were considered for the creation of a high-charge bunch train from the injector, and we selected an option that builds the bunch train in the particle accumulator ring (PAR). This option enables both single-bunch mode, which is necessary to support current APS operation, and bunch-train mode. This report provides a description of the injection process, simulation results, and specifications of injector timing, kicker, and rf subsystems.
ANL, Argonne, USA
The APS storage ring has three fill patterns: 24-singlet, hybrid, and 324 singlet. Bunch purity of better than 10-6 is required for +3 and higher bucket numbers for the first two fill patterns during user operations. A PAR bunch cleaning system is used to clean up the satellite bunches. During top-up user operation, beam charge in satellite bunches grows due to the long lifetime of the low charge satellites. Recent storage ring development, including operating with the bunch-by-bunch feedback system, reduction of chromaticity, and lattice correction, has increased the beam dynamic aperture of the storage ring. We have observed unusual beam charge growth in +1 buckets, which indicates leakage of electrons from the main bunches to the +1 buckets. This report describes the observation and the dependency of leakage on chromaticity settings, and our analysis.
ANL, Argonne, USA
Purdue University, West Lafayette, Indiana, USA
The first prototype superconducting undulator (SCU0) was successfully installed and commissioned at the Advanced Photon Source (APS) and is delivering photons for user science. All the requirements before operating the SCU0 in the storage ring were satisfied during a short but detailed beam commissioning. The cryogenic system performed very well in the presence of the beam. The total beam-induced heat load on the SCU0 agreed well with the predictions, and the SCU0 is protected from excessive heat loads through a combination of orbit control and SCU0 alignment. When powered, the field integral measured with the beam agreed well with the magnet measurements. An induced quench caused very little beam motion, and did not cause loss of the beam. The device was found to quench during unintentional beam dumps, but quench recovery is transparent to storage ring operation. There were no beam chamber vacuum pressure issues and no negative effect observed on the beam. Finally, the SCU0 was operated well beyond its design requirements, and no significant issues were identified. The beam commissioning results are described in this paper.
ANL, Argonne, USA
Purdue University, West Lafayette, Indiana, USA
The first prototype superconducting undulator (SCU0) was successfully installed and commissioned at the Advanced Photon Source (APS) and is delivering photons for user science. The cryosystem was designed to handle a beam-induced heat load of up to 40 W. Prior to operations, detailed predictions of this heat load were made, including that produced by resistive wall heating by the image current, geometric wakefields, synchrotron radiation, electron cloud, and beam losses. The dominant cw source is the resistive wall heat load. The heat load predictions for standard 100 mA user operation were benchmarked using thermal sensors that measure temperatures at various locations in the SCU0 cryostat and along the electron beam chamber. Thermal analysis using the predicted heat loads from the electron beam, using three independent methods, agrees well with the observed measurements.
ANL, Argonne, USA
Purdue University, West Lafayette, Indiana, USA
The first prototype superconducting undulator (SCU0) was successfully installed and commissioned at the Advanced Photon Source (APS) and is delivering photons for user science. The magnet cores are mounted on but thermally isolated from the beam vacuum chamber. Protecting the SCU0 from high beam-induced heat loads was an important requirement before operating the SCU0 in the storage ring. Precise alignment of the beam vacuum chamber with respect to both the electron beam orbit as well as the synchrotron radiation generated in the upstream dipole magnet was therefore extremely important. The beam vacuum chamber was instrumented with nine thermal sensors. Using the sensors, the chamber alignment was determined with a 100-micron precision. This precision is more than 10 times higher than in a standard aperture scan. Other advantages of the thermal sensor-based alignment method include isolating the SCU0 alignment from other components in the orbit bump and providing good longitudinal spatial resolution. The chamber temperatures agreed well the predicted heat load and dependence on steering. This novel beam-based alignment method and results will be presented.
ANL, Argonne, USA
The APS Upgrade project includes adding more insertion devices (IDs) to the APS storage ring. Perturbations from IDs have been reviewed, and the most significant sources are coming from the IDs that generate circular polarized light. To address this issue, we measured non-linear effects from the existing circular polarized undulator (CPU) and intermediate-energy x-ray (IEX). Measurement results have been compared with the simulation work. Correction schemes have been proposed and tested through experiments.
ANL, Argonne, USA
An ultra-low-emittance light source generally manifests very strong non-linear effects due to the significant focusing force applied and the resultant strong sextupoles. As one of the consequences, the dynamic aperture becomes very small, and only on-axis "swap-out" beam injection is workable. Another consequence is that the intra-beam scattering (IBS) effect and beam instability are much more severe, which limits the maximum achievable single-bunch intensity. As a result, multiple bunches with tight bunch spacing are required to reach high average beam current, which requires injection to be finished in a very short period, e.g., during the interval between bunches. Using a multi-bend-achromat (MBA) lattice designed for the Advanced Photon Source (APS) storage ring as an example, this paper presents an on-axis injection scheme based on the fast stripline technique together with discussions on how the scheme works with different parameter settings.
ANL, Argonne, USA
The horizontal scraper in the sector 37 straight section of the Advanced Photon Source storage ring serves as both a diagnostic to probe the edge of the beam as well as the physical aperture when the store is lost. Initially, the scraper was meant only to be a diagnostic; high-density, short-radiation-length material used in the device was intended to stop halo, not the full beam. Damage to this device was recently discovered, and as a result, we began an effort to model and improve the scraper. Modeling with elegant provides loss distributions for several scenarios such as muting one or both rf systems in combination with firing injection kickers. The loss distributions are used as input to a MARS model of the scraper. Beam dumps from 100 mA dissipates a total of 2600 J. Most of this energy is not deposited locally; however, depending on the geometry and physical make-up, sufficient power density exists to damage the device on beam-facing surfaces. Testing is currently planned to examine the suitability of different beam-facing materials. Because of non-local energy deposition, we are evaluating the secondary role for this scraper as a spoiler rather than a beam dump.
Private Address, Westmont, USA
Private Address, Westmont, USA