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Electron clouds cause a fast head-tail instability above a threshold density. Experiments at KEKB revealed the presence of a synchro-betatron sideband above the beam blow-up threshold, which indicates the presence of the head-tail instability. The sideband appears near nuy + knus, where 1 < k < 2, which differs from ordinary instability seen near nuy - nus. We study the origin of the sideband using a computer simulation.

In KEKB, synchrotron radiation interferometers (SRMs) are used for measuring the transverse beam sizes. There is also a tool for enlarging the vertical beam size intentionally by making an asymmetric bump, called an ``iSize'' bump, at one of the strongest non-interleaved sextupole magnets in each KEKB ring. The calibrations of the SRMs were checked by comparing the measured vertical beam sizes with those calculated using the computer code ``SAD''. The obtained correction factors are 1.000$\pm$0.045 for HER and 0.971$\pm$0.060 for LER, which are consistent with the calibration factors of SRMs\cite{SRMcalib} within errors. Using the obtained calibration factor, x-y coupling of each ring was calculated ., Comment: 3 pages, 4 figures, Particle Accelerator Conference 07, Albuquerque

Crab cavities have been installed in the KEKB rings in order to increase the luminosity. This paper describes the measurement of a crabbing angle by streak cameras.

Damping ring at the Accelerator Test Facility (ATF) is a storage ring with 714 MHz RF frequency and harmonic number of 330. The ring is used in both single and multi- bunch regimes. In both cases, significant longitudinal dipole motion has been observed in the ring. A prototype longitudinal feedback channel using a Gproto baseband processing channel and a set of horizontal striplines has been constructed for the machine. The prototype allowed both suppression of the longitudinal motion and studies of the motion sources. In this paper, we present the results of these studies including measurements of steady-state oscillation amplitudes, eigenmodal patterns, and growth and damping rates. Using measured growth rates we estimate the driving impedances. We also present the effect of the longitudinal stabilization on the energy spread of the extracted beam as documented by a screen monitor.

Recently, we have observed vertical betatron sidebands in the transverse beam spectra of positron bunches at the KEKB LER which are associated with the presence of electron clouds.[1] When the LER is operating in single-beam mode (no colliding bunches in the HER), these sidebands are sharply peaked. When the bunches are in collision for physics running, the sidebands are still present but are found to be smeared out. The bunch-by-bunch specific luminosity is lower for bunches with sidebands than for those without sidebands. In this paper, the behavior of the sidebands in collision and the effects on luminosity are discussed.

Synchro-beta side band signal caused by electron cloud instability has been observed at KEK-B factory. The side-band appears above the threshold of beam size blow-up and disappears by exciting solenoid magnets which covers whole ring. The side-band is an evidence of strong head-tail instability caused by electron cloud. The side-band appears in tune spectrum with positive shift ν β + aν s (1 β − aν s (a > 0). We study the synchro-beta spectrum using a code, PEHTS, which simulates single bunch electron cloud instability.

We summarize the machine operation of KEKB during past one year focusing on progress for this period.

Coupled bunch instability caused by electron cloud has been observed in the KEKB-LER. Time evolution of the instabilities just after the turning-off the transverse bunch feedback have been recorded with several solenoid-field conditions to suppress the blowup due to electron cloud. The mode spectra of the coupled-bunch instabilities have been compaired with the simulations of electrons moving in drift space, weak solenoid field and strong bending field.

Transverse beam-size enlargement due to dynamic beta and emittance effects has been observed in the KEKB Low Energy Ring (LER) and High Energy Ring (HER). In order to observe these effects, a retrofocus optics system has been developed and installed in the horizontal SR interferometers at the HER and LER. This system allows us to vary the apparent beam size to match the dynamic range of the interferometer. We report on the retrofocus optics system and measurement results, and compare the measured effects with those expected from dynamic beta simulations.

Beam behaviour of KEKB was studied by measurement of the beam size using a streak camera. The effects of electron-clouds and beam-beam interactions on the vertical beam size were examined in beam collision. We injected a test bunch of positrons 2 RF buckets after a bunch to enhance the electron cloud effect and changed electron beam conditions to see the beam-beam effect. The beam size was also measured in a single positron beam condition and compared with that during collision. The result of the measurement is reported in this paper.

We have recently replaced the synchrotron light extraction chamber for the KEKB Low Energy Ring (LER) SR monitor. The beam pipe was changed to copper to minimize resistive-wall heating, and the optical apertures were made as small as permitted by light extraction requirements in order to reduce HOM power leakage. The new chamber shows almost none of the heating problems of the old chamber, and previous problems with the orientation of the extraction mirror changing due to heat expansion of the beam pipe have been essentially eliminated. The design and performance of the new chamber are presented.

We have designed and constructed two optical beamlines for the KEK B-factory synchrotron radiation monitors, one for each ring. Each beamline transports the SR beam 30-40 meters to an external optics hutch along two parallel paths. One path is used for direct imaging with adaptive optics, the other is used for transverse beam size measurements via SR interferometer and longitudinal profile measurements via streak camera. We designed and installed relay lens systems for the adaptive optics paths. We also provide remote alignment control for components which are inaccessible during beam operation (14 mirrors and 2 pairs of lenses total), with monitoring provided by a set of remote-controlled optical screen monitors. We describe the design of the relay lens and alignment systems along with performance results.

Transverse bunch-by-bunch feedback systems for damping coupled-bunch instabilities in the KEKB rings have been working since the early stages of the commissioning of the rings. Stabilization of the beams with the system has been successful, permitting tests of higher beam currents and various filling patterns. The performance of these systems has been demonstrated under the normal physics run pattern of an 8 ns bunch spacing over long-term operation, and also under special filling patterns with a minimum bunch spacing of 2 ns.