The maximum of permeability of such ferromagnetic materials as lamination for magnets appears at a middle excitation level between a positive coercive force and saturation magnetization. In addition, an equation of rotB=0 is possibly valid at not only the boundary between iron core and magnet gap but also the boundary between the iron core surrounded by coils and its outer area in a unique point of magnetization curve around a middle excitation level despite the fact that magnets are energized by coil current although a proof will be given somewhere else; so that a field distribution of magnets at the unique point is expressed by a gradient of scalar potential. It is proposed for synchrotron magnets with wide range from low to high excitation levels that three-dimensional shape of magnets is based on equi-potential surface of the scalar potential at the unique point.

Outlines of bunch-by-bunch feedback systems for suppressing multibunch instabilities in electron/positron storage rings are presented. The design principles and functions of the feedback components are reviewed. Recent topics of applying very fast and dense FPGA as feedback signal processor are also shown.

In large-scale accelerator projects such as TRISTAN and J—PARC, approximately half of the total project costs are spent on the civil and utility engineering work for the accelerator. In addition, the quality of civil and utility engineering has a large effect on the quality of the beam. With increasing scale of projects, there is growing specialization of the people in charge of the accelerator on the one hand, and the people in charge of civil and utility engineering on the other. Mutual understanding between the people in charge is therefore important in such cases. From the experience I have accumulated working on the facilities of many large projects, I have become keenly aware of the necessity for both accelerator-literate civil engineering specialists and civil engineering-literate accelerator researchers. A straightforward method for satisfying this requirement is to systematize accelerator science as a science with civil and utility engineering for accelerators recognized as its sub-field. When new projects launched, the methodology of the natural sciences should be incorporated whereby past experience is fully utilized and then new technologies and knowledge are accumulated.

Factories are high-luminosity colliders that provide high rate production of particular particles such as B, Taucharm, and φ-mesons. Two B-factories, KEKB and PEP—II, and a φ-factory DAΦNE have been operating successfully. We discuss present luminosity performance and limitations of these factories as well as upgrade plans and new ideas in view of the next generation of meson factories with ～100-times more luminosity.