• Y. Funakoshi, T. Abe, K. Akai, Y. Cai, K. Ebihara, K. Egawa, A. Enomoto, J.W. Flanagan, H. Fukuma, K. Furukawa, T. Furuya, J. Haba, T. Ieiri, N. Iida, H. Ikeda, T. Kageyama, S. Kamada, T. Kamitani, S. Kato, M. Kikuchi, E. Kikutani, H. Koiso, M. Masuzawa, T. Mimashi, T. Miura, A. Morita, T.T. Nakamura, K. Nakanishi, M. Nishiwaki, Y. Ogawa, K. Ohmi, Y. Ohnishi, N. Ohuchi, K. Oide, M. Ono, Y. Seimiya, K. Shibata, M. Suetake, Y. Suetsugu, T. Sugimura, T. Suwada, M. Tawada, M. Tejima, M. Tobiyama, N. Tokuda, S. Uehara, S. Uno, Y. Yamamoto, Y. Yano, K. Yokoyama, M. Yoshida, S.I. Yoshimoto, D.M. Zhou
  KEK, Ibaraki

Crab cavities were installed at KEKB at the beginning of 2007. The beam operation with the crab cavities is in progress. In this paper, machine performance with crab crossing is described focusing on a specific luminosity and a beam lifetime issue related to the dynamic beam-beam effects.

• J.W. Flanagan, H. Fukuma, S. Hiramatsu, H. Ikeda, K. Kanazawa, T.M. Mitsuhashi, J. Urakawa
  KEK, Ibaraki
• J.P. Alexander, W.H. Hopkins, B. Kreis, M.A. Palmer, D.P. Peterson
  CLASSE, Ithaca, New York
• G.S. Varner
  UH, Honolulu, HI

Funding: Work supported in part by the US-Japan Cooperation Program

We are working on the development of a high-speed x-ray beam profile monitor for high-resolution and fast response for beam profile measurements to be used at CesrTA and SuperKEKB*. The optics for the monitor are based on a technique borrowed from x-ray astronomy, coded-aperture imaging, which should permit broad-spectrum, low-distortion measurements to maximize the observable photon flux per bunch. Coupled with a high-speed digitizer system, the goal is to make turn-by-turn, bunch-by-bunch beam profile measurements. Following initial tests with a low-resolution mask at large beam sizes (vertical size ~200 um), a high-resolution mask has been made for use with low-emittance beams (vertical size ~10 um) at CesrTA. The first performance results of the high-resolution mask on the low-emittance CesrTA beam are presented.

*J.W. Flanagan et al., Proc. EPAC08, Genoa, {10}29 (2008).

• Y. Suetsugu, H. Fukuma, K. Shibata
  KEK, Ibaraki
• M.T.F. Pivi, L. Wang
  SLAC, Menlo Park, California

Funding: The Japan/US Cooperation Program

Beam instability caused by the electron cloud is expected to be a limiting factor in the performance of future advanced positron and proton storage rings. In a wiggler section of the positron ring of the KEK B-factory (KEKB), we have installed a vacuum chamber with an insertion that can be replaced and including different techniques to study the mitigation of the electron-cloud effect in a high magnetic field region. We have installed an insertion with strip-line clearing electrode, an insertion with triangular grooves and an insertion with a smooth surface, and compared them each other under the same conditions. The electrode insertion is composed of a thin tungsten layer formed on a thin alumina ceramic layer. The groove insertion is composed of TiN-coated triangular grooves running longitudinally. In this paper, we report about the tests in the KEKB and about the large reduction in the measured electron cloud density when the clearing electrode and groove sections are installed with respect to the smooth insertion. These experiments are the first ones demonstrating the principle of the clearing electrode and groove insertions in a magnetic field.

• Y. Cai
  SLAC, Menlo Park, California
• J.W. Flanagan, H. Fukuma, Y. Funakoshi, T. Ieiri, K. Ohmi, K. Oide, Y. Suetsugu
  KEK, Ibaraki

Using a streak camera, we measured the longitudinal profiles of a positron bunch in the Low Energy Ring (LER) of KEKB at various currents. The measured charge densities were used to construct a simple Q=1 broadband impedance model. The model with three parameters not only gave an excellent description of longitudinal dynamics for a positive momentum compaction factor but also for the negative ones, including bunch shortening bellow a threshold and bursting modes beyond the threshold. Furthermore, our study indicated that the threshold of microwave instability was about 0.5 mA in bunch current in the LER. At the nominal operating current 1.0 mA, there was a 20% increase of the energy spread. The results of measurement, analysis, and simulations will be presented in this paper.