ANL, Lemont, Illinois, USA
The fast orbit feedback (FOFB) bandwidth for Advanced photon source upgrade (APS-U) will be DC-1 kHz and the synchrotron frequency will be between 100-560 Hz. This frequency overlap places coupled bunch mode 0 (CBM0) induced horizontal orbit motion inside the orbit feedback bandwidth, potentially affecting our ability to achieve beam stability goals. Longitudinal feedback kicker is not strong enough to damp CBM0 oscillations. We developed new beam-based feedback method to suppress CBM0 oscillations with low level RF phase as actuator. It uses existent FOFB framework with no changes to the feedback algorithm. Effectiveness of this method is verified using present APS operations lattice where synchrotron frequency is outside orbit feedback bandwidth*. In the present work, low alpha lattice is created to emulate APS-U setting where synchrotron frequency is inside the orbit feedback bandwidth. Experiments with this lattice successfully demonstrated CBM0 correction within FOFB bandwidth. Combined operation of orbit feedback and CBM0 correction is stable, and CBM0 oscillations are damped. We achieved better orbit motion suppression and corrector drive efforts are reduced as well.
* P. Kallakuri et al., ’Coupled bunch mode zero correction using orbit measurements and RF system phase feedback’, doi:10.1103/PhysRevAccelBeams.25.082801
ANL, Lemont, Illinois, USA
RadiaSoft LLC, Boulder, Colorado, USA
UCSC, Santa Cruz, California, USA
We present results from a recent collimator irradiation experiment conducted in the Advanced Photon Source (APS) storage ring. This experiment is the third in a series of studies to examine the effects of high-intensity electron beams on potential collimator material for the APS-Upgrade (APS-U). The intent here is to determine if a fan-out kicker can sufficiently reduce e-beam power density to protect horizontal collimators planned for the APS-U storage-ring. The fan-out kicker (FOK) spreads the bunched-beam vertically allowing it to grow in transverse dimensions prior to striking the collimator. In the present experiment, one of the two collimator test pieces is fabricated from oxygen-free copper; the other from 6061-T6 aluminum. As in past studies, diagnostics include turn-by-turn BPMs, a diagnostic image system, fast beam loss monitors, a pin-hole camera, and a current monitor. Post-irradiation analyses employ microscopy and metallurgy. To avoid confusion from multiple strikes, only three beam aborts are carried out on each of the collimator pieces; two with the FOK on and the other with it off. Observed hydrodynamic behavior will be compared with coupled codes.
