• D. Teytelman
  Dimtel, San Jose
• J.M. Byrd
  LBNL, Berkeley, California
• J. Cao, J. Yue
  IHEP Beijing, Beijing

BEPC-II is a two ring electron-positron collider designed to operate at 1 A beam currents. Longitudinal and transverse coupled-bunch instabilities have been observed in both electron and positron rings. In this paper we present measurements of both transverse and longitudinal instabilities with the identification of active eigenmodes, measurements of growth and damping rates, as well as of the residual beam motion levels. The measurements will then be used to estimate the growth rates at the design beam currents (yet to be achieved). We will also demonstrate how such data is used for specifying power amplifier and kicker parameters.

• W. Wu, M.D. Busch, Y. Kim, J.Y. Li, G. Swift, P. Wang, Y.K. Wu
  FEL/Duke University, Durham, North Carolina
• I.S. Ko, I.S. Park
  PAL, Pohang, Kyungbuk
• D. Teytelman
  Dimtel, San Jose

Funding: work supported by US Air Force Office of Scientific Research medical FEL grant FA9550-04-01-0086

The coupled bunch mode instabilities (CBMIs) caused by vacuum chamber impedance limit and degrade the performance of the storage ring based light sources. A bunch-by-bunch longitudinal feedback (LFB) system has been developed to stabilize beams for the operation of a storage ring based Free Electron Laser (FEL) and the High Intensity Gamma-ray Source (HIGS) at the Duke storage ring. Employing a Giga-sample FPGA based processor (iGP), the LFB is capable of damping out the dipole mode oscillation for all 64 bunches. As a critical subsystem of the LFB system, kicker cavity is developed with a center frequency of 938 MHz, a wide bandwidth (> 90 MHz), and a high shunt impedance (> {10}00 Ω). First commissioned in summer 2008, the LFB has been operated to stabilize high current multi-bunch operation. More recently, the LFB system is demonstrated as a critical instrument to ensure stable operation of the HIGS with a high intensity gamma beam above 20 MeV with a frequent top-off injection to compensate for the substantial and continuous electron beam loss in the Compton scattering process. In the future, we will perform detailed studies of the impedance effects using the LFB system.

• C. Milardi, D. Alesini, M.E. Biagini, C. Biscari, A. Bocci, R. Boni, M. Boscolo, F. Bossi, B. Buonomo, A. Clozza, G.O. Delle Monache, T. Demma, E. Di Pasquale, G. Di Pirro, A. Drago, A. Gallo, A. Ghigo, S. Guiducci, C. Ligi, F. Marcellini, G. Mazzitelli, F. Murtas, L. Pellegrino, M.A. Preger, L. Quintieri, P. Raimondi, R. Ricci, U. Rotundo, C. Sanelli, M. Serio, F. Sgamma, B. Spataro, A. Stecchi, A. Stella, S. Tomassini, C. Vaccarezza, M. Zobov
  INFN/LNF, Frascati (Roma)
• N. Arnaud, D. Breton, L. Burmistrov, A. Stocchi, A. Variola, B.F. Viaud
  LAL, Orsay
• S. Bettoni
  CERN, Geneva
• P. Branchini
  roma3, Rome
• M. Esposito
  Rome University La Sapienza, Roma
• E.B. Levichev, P.A. Piminov, D.N. Shatilov
  BINP SB RAS, Novosibirsk
• K. Ohmi
  KEK, Ibaraki
• V.V. Smaluk
  BINP, Novosibirsk
• D. Teytelman
  SLAC, Menlo Park, California
• P. Valente
  INFN-Roma, Roma

In 2007 DAΦNE was upgraded to operate in a regime of large Piwinski angle, with a novel IR optics, reduced vertical beta at the interaction point, and additional sextupoles providing for crab waist collisions. The specific luminosity was boosted by more than a factor of four, and the peak luminosity was more than doubled with respect to the maximum value obtained with the original collider configuration. The DAΦNE commissioning as well as the first experience with large Piwinski angle and crab waist collisions scheme will be reported.

Slides