• X. Sun, G. Decker
  ANL, Argonne

There are two parallel feedback systems to correct the transverse orbit at the Advanced Photon Source (APS) storage ring: a real-time feedback system that runs at 1.5 kHz using 38 fast correctors and up to 160 beam position monitors (BPMs), and a DC feedback system that runs at 10 Hz using up to 317 correctors and over 500 BPMs. An algorithm that uses the open- and closed-loop beam motion data to spatially locate strong noise sources in the storage ring is described. A simulation code has been developed to predict the ideal closed-loop beam motion data from measured open-loop beam motion data assuming no steering corrector noise. With the difference between predicted and measured closed-loop beam motion data and the full inverse response matrix, we compute the source candidate locations and infer their relative strengths for narrowband sources. The simulation process and experimental results with beam will be presented.

• W.X. Cheng, W.J. Corbett, A.S. Fisher
  SLAC, Menlo Park, California

A dual-axis, synchroscan streak camera was used to measure temporal bunch profiles in three storage rings at SLAC: the PEP-II low-energy and high-energy rings, and SPEAR3. At high currents, both PEP rings exhibit a transient shift in synchronous phase along the bunch train due to RF-cavity loading. Bunch length and profile asymmetry were measured along the train for a range of beam currents. To avoid the noise of a dual-axis sweep, we accumulated a single-axis synchroscan image over multiple turns while applying a 50-ns gate to the microchannel plate. To improve the extinction ratio, we synchronized this 2-kHz gate with an upstream mirror pivoting at 1 kHz to deflect light from other bunches off the axis. At SPEAR3 we compared the bunch length as a function of current for several lattices: achromatic, low-emittance and low momentum compaction. In the first two cases, resistive and reactive impedance components were extracted from the longitudinal bunch profiles. In the low-alpha configurations, we observed natural bunch lengths approaching the camera resolution, requiring special care to remove instrumental effects, and saw evidence of instability and periodic bursting.

• A.H. Lumpkin
  Fermilab, Batavia
• M. Cestelli Guidi, E. Chiadroni
  INFN/LNF, Frascati (Roma)
• A. Cianchi
  Università di Roma II Tor Vergata, Roma
• C. Yao
  ANL, Argonne

We have previously experimentally observed and modeled the near-field optical diffraction radiation (ODR) generated by a 3-nC micropulse of a 7-GeV electron beam at the Advanced Photon Source (APS). Due to the high gamma of ~14,000, the scaling factor of γλ/2π was about 1.4 mm for 0.628 um radiation. Thus, a standard CCD camera was sufficient for imaging at an impact parameter of 1.25 mm. The extension of this technique to γ 10⁰⁰ is challenged by the ·10¹⁴ reduction in visible light photon production compared to the APS case. We discuss the feasibility of monitoring at a new Fermilab facility a high average current linac beam of 3000 times more charge in a video frame time and with a more sensitive 12- to 16-bit camera. Numerical integrations of our base model show beam size sensitivity for ±20% level changes at 200- and 400-um base beam sizes. We also evaluated impact parameters of 5 σy and 12 σy for both 800-nm and 10-um observation wavelengths. The latter examples are also related to a proposal to apply the technique to an ~ 0.94 TeV proton beam, but there are trades on photon intensity and beam size sensitivity to be considered at such gammas.