COMMISSIONING SIMULATION STUDY FOR THE ACCUMULATOR RING OF THE ADVANCED LIGHT SOURCE UPGRADE ∗ Thorsten Hellert † , Philipp Amstutz, Michael Ehrlichman, Simon Christian Leemann, Christoph Steier, Changchun Sun and Marco Venturini, LBNL, Berkeley, California, USA Abstract The Advanced Light Source Upgrade (ALS-U) to a diffraction-limited soft x-rays light source requires the con- struction of an Accumulator Ring (AR) to enable swap-out, on-axis injection. The AR lattice is a Triple-Bend-Achromat lattice similar to that of the current ALS but to minimize the magnet sizes the vacuum chamber will be significantly nar- rower hence requiring a careful evaluation of the magnets’ field quality. This work presents the results of a detailed error tolerance study including a complete simulation of the commissioning process. INTRODUCTION The proposed lattice for the Advanced Light Source up- grade (ALS-U) [1] into a diffraction-limited soft x-rays light source is a 9-Bend Achromat reproducing the 12-fold sym- metric footprint of the existing ALS [2]. The required small emittance is achieved by much stronger focusing than in the present ALS. Stronger focusing leads to larger natural chromaticities and smaller dispersion. Thus a large increase in sextupole strength is needed, resulting in small dynamic aperture on the order of 1 mm 2 even for the ideal lattice. Due to the small dynamic aperture, traditional accumula- tion injection is not feasible. Therefore, the ALS-U Storage Ring requires on-axis swap-out injection, which exchanges a stored bunch train with a replenished bunch train simultane- ously. For this purpose a 2 GeV Accumulator Ring (AR) [3] will be housed in the storage ring tunnel. It will act as a damping ring for the bunches generated by the booster and to store the beam for top-off in between swap-outs. Figure 1 shows a schematic drawing of the ALS-U facility. Figure 1: Schematic drawing of the Advanced Light Source upgrade. Up to four bunches are accelerated every 1.4 s in the existing linac and booster and then injected into the new AR. Every 30 s the bunch train in the AR replaces one bunch train in the SR utilizing a swap-out, on-axis injection. ∗ This work was supported by the U.S. Department of Energy (DOE) under Contract No. DE-AC02-05CH11231. † thellert@lbl.gov In order to minimize dark time of the accelerator, the installation of the ALS-U AR is scheduled during regular ALS maintenance and two annual shutdown periods lasting several months. Beam based commissioning of the AR will take place during regular user operation of the ALS which limits the available number of beam injections into the AR significantly [4]. To address the challenges posed by rapid commissioning and in general to understand how realistic errors will affect the machine operation and to better de- fine an error tolerance budget we have carried out complete simulation of machine commissioning. The studies are per- formed using the Accelerator Toolbox (AT) [5] based Toolkit for Simulated Commissioning (SC) [6]. SIMULATION SETUP AND ERRORS The ALS-U AR lattice is similar to the current ALS lattice, but adjusted to account for the slightly smaller circumference of about 182 m and further optimized considering the smaller physical aperture. The lattice, providing an emittance of 2 nm rad consists of 12 identical arcs, each equipped with 6 BPMs. Horizon- tal and vertical corrector magnets (CM) suitable for slow trajectory correction are installed in six sextupole magnets and a set of skew-quadrupole corrector coils is added to one sextupole magnet per sector. A schematic drawing of the lattice properties including the position of the CMs and BPMs is shown in Figure 2. A variety of errors are considered such as static and shot- to-shot injection errors, calibration errors, offsets and rolls of all magnets and their corresponding girders, diagnostic errors such as BPM offsets and noise, rf frequency, voltage and phase errors and a circumference error. The baseline values can be found in Tables 1 and 2. Furthermore, detailed systematic and random multipole-error tables are included for all magnets and corrector coils. The limits for the CMs and skew quadrupoles are 200 μrad and an integrated K value of 0.1, respectively. COMMISSIONING SIMULATION We have studied different correction strategies and ana- lyzed them statistically with respect to the corrected machine properties and success rate of the algorithm. The follow- ing sequence for the simulated commissioning procedure was found to be the best performing one for a variety of different error assumptions and was therefore used to de- fine an error budget and set diagnostic requirements. The implemented correction chain can be reviewed in the SC applications folder [7]. 10th Int. Particle Accelerator Conf. IPAC2019, Melbourne, Australia JACoW Publishing ISBN: 978-3-95450-208-0 doi:10.18429/JACoW-IPAC2019-TUPGW022 MC2: Photon Sources and Electron Accelerators A05 Synchrotron Radiation Facilities TUPGW022 1445 Content from this work may be used under the terms of the CC BY 3.0 licence (© 2019). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI