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
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
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.