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• W1574117611 abstract "DIAGNOSTIC SYSTEMS PLAN FOR THE ADVANCED LIGHT SOURCE TOP-OFF UPGRADE* Walter Barry, Mike Chin, David Robin, Fernando Sannibale, Tom Scarvie, Christoph Steier, LBNL, Berkeley, CA 94720, U.S.A. Abstract The Advanced Light Source (ALS) will soon be upgraded to enable top-off operations [1], in which electrons are quasi-continuously injected to produce constant stored beam current. The upgrade is structured in two phases. First, we will upgrade our injector from 1.5 GeV to 1.9 GeV to allow full energy injection and will start top-off operations. In the second phase, we will upgrade the Booster Ring (BR) with a bunch cleaning system to allow high bunch purity top-off injection. A diagnostics upgrade will be crucial for success in both phases of the top-off project, and our plan for it is described in this paper. New booster ring diagnostics will include updated beam position monitor (BPM) electronics, a tune monitoring system, and a new scraper. Two new synchrotron light monitors and a beam stop will be added to the booster-to- storage ring transfer line (BTS), and all the existing beam current monitors along the accelerator chain will be integrated into a single injection efficiency monitoring application. A dedicated bunch purity monitor will be installed in the storage ring (SR). Together, these diagnostic upgrades will enable smooth commissioning of the full energy injector and a quick transition to high quality top-off operation at the ALS. BOOSTER RING Orbit Monitoring The BR has 32 BPMs distributed along its circumference, equipped with original ALS electronics that allow for both single and multi turn measurements. Since the larger of the BR betatron tunes is less than seven, 13-14 BPMs will be sufficient for sampling the orbit in the booster. The existing 13 year old single turn electronics will be refurbished and, in the second phase of the project, modern multi turn electronics will be purchased to complete the upgrade of the BPM system. The BPMs will have two functions for top-off operations. During commissioning, single turn or few turn measurements will be helpful for establishing circulating beam and critical for dynamics studies. Once routine top- off operations are established, an orbit measurement and feedback system will improve injection and bunch cleaning efficiency. A high level application, similar to the one existing for the ALS SR, will be developed to monitor and control the orbit in the BR. Bunch Cleaning Four weeks per year are dedicated to “two-bunch” operations at the ALS, in which two diametrically opposed buckets are filled with relatively high currents of about 30 mA/bunch. The 328 ns delay between these bunches is large enough to enable experiments with long relaxation times. The “two-bunch” user community is continuously growing and the scientific quality of their work is very high, so ensuring bunch purity during top-off operation is a high priority. Our requirement on bunch purity is that the number of undesired electrons in the nominally empty buckets is kept to a level below ~ 0.01% of the number of electrons in the main two bunches. Several mechanisms during the injection process can contribute to contamination, and even when injection is well tuned, contamination can still reach levels of 0.1%, necessitating a bunch cleaning procedure. Presently, bunch cleaning is performed in the SR after every injection and energy ramp to 1.9 GeV. The beam impedance of the ALS vacuum chamber induces betatron tune shift with current amplitude, so the small-current parasitic bunches have a tune significantly different from that of the high-current main bunches. Exciting the beam at the betatron frequency of the parasites generates large transverse oscillations of these undesired bunches with minor effects on the main bunches. A scraper is inserted far enough to clean out the oscillating particles. Unfortunately, the whole procedure requires about four INTRODUCTION The diagnostics in the BR and BTS transfer line will play a major role during the commissioning and operation of top-off mode at the ALS. Injection efficiency and short and long term stability of the BR operational conditions are the fundamental requirements for proper operation in this new mode. The BR is currently operated with sextupole magnets off and without any orbit monitoring or control. The operators compensate for long-term drifts by making empirical readjustments. In top-off operation, tolerances on injection parameter fluctuations will be much tighter and will require more efficient diagnostics systems. For example: synchro-betatron resonance control is required during energy ramping, closed orbit and current monitoring are necessary for preserving injection efficiency, and bunch cleaning requires accurate control of tunes, chromaticities and orbit. The BTS will be upgraded with two new synchrotron light monitors and a beam stop for tuning, a beam transmission monitor for the entire injector chain will be created, and a dedicated bunch purity monitoring system will be installed in the SR. *Work supported by the Director, Office of Science, of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098." @default.
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• W1574117611 date "2005-05-10" @default.
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• W1574117611 title "Diagnostic Systems Plan for the Advanced Light Source Top-Off Upgrade" @default.
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