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The betatron tune and the synchronous phase of individual bunches were measured at KEKB, an asymmetric electron/positron circular collider. The measurement was performed under three conditions: a single bunch, and multibunches with and without collision. The coupling impedance of the rings can be estimated from the current dependence of the parameters of a single bunch. The betatron tune along a positron-bunch train indicates variations of the electron cloud density that cause electron cloud instability. Comparing the betatron tune between colliding and noncolliding bunches, the beam-beam tune shift was investigated in regular operation. The coherent beam-beam parameter was evaluated in the two-ring collider with unequal tunes. Transient beam-loading effects were experimentally demonstrated by a phase shift along a bunch train in both rings. A rapid advance in the beam phase was observed, which is considered to be due to the effects of longitudinal wakes.

For the stable high-luminosity operation and luminosity-increase, the electron and positron storage rings of the KEK B-Factory (KEKB) is equipped with various beam instrumentations, which have being working well since the start of the commissioning in December, 1998. Details and performance of the beam-position monitor system based on the spectrum analysis using DSPs, the turn by turn BPM with four dimensional function available for measurements of the individual bunch position, phase and intensity, the parametric beam-DCCTs designed so as to avoid the magnetic-core-selection problems for the parametric flux-modulation, the bunch by bunch feedback system indispensable to suppress the strong multibunch instabilities in KEKB, the various optical beam diagnostic systems, such as synchrotron radiation interferometers for precise beam size measurement, the tune meters, the bunch length monitors and the beam-loss monitors are described. Delicate machine tuning of KEKB is strongly supported by these instrumentaions.

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