Design works of the KEK-PS (Proton Synchrotron and Booster Complex) are outlined. Related works on betatron resonances and collective beam instabilities are sketched. The present paper is based on a talk at my retirement and emphasis is on my contributions.

In order to achieve high luminosities in high-energy e⁺e^－ colliding experiments, positron sources must be reinforced, especially towards the next generation of high-energy e⁺e^－ colliders. In a conventional positron source, positrons are produced by high-energy electrons hitting a heavy-metal target, such as a tungsten plate. However, the allowable heat load on the target limits the beam power of the incident electrons. This result gives the limit of the positron intensity. One promising approach to improve the positron-production efficiency and to reduce the heat load on the target is to use a crystal-assisted positron source because it is expected that channelling radiation and coherent bremsstrahlung contribute to the enhancement of the positron intensity. A new tungsten single-crystal target was successfully employed at the positron source of the KEKB injector linac in September 2006. The previously-used conventional tungsten plate was replaced by the tungsten crystal target without any significant modification of the positron source. The tungsten crystal target increased the positron intensity by ～25% compared to that for the conventional tungsten plate. On the contrary, although the positron intensity increased, the heat load on the crystal target decreased by ～20%. We believe that these results could stimulate new interest in the development and application to high-intensity positron sources in the next-generation of high-energy electron/positron linear accelerators.

A close collaboration between accelerator and experimental physicists have been necessary to proceed physics in the laser electron photon facility in SPring-8 (LEPS). After describing how specific features of the LEPS beamline worked and they were necessary for discovering a pentaquark particle, Θ⁺, we show an example of the collaboration in identifying the energy resolution of the γ beam.The demand for a new beamline and its key concepts are shortly mentioned.

Electron linear accelerators have been widely used in medical applications, especially in radiation therapy for cancer treatment. There are more than 7,000 medical electron linear accelerators in the world, treating over 250,000 patients per day. This paper reviews the current status of accelerator applications and technologies in radiation therapy, and presents the anticipated requirements for advanced radiation therapy technology in the foreseeable future.

For achieving the high luminosity required at the International Linear Collider (ILC), it is critical to focus the beams to nanometer size with the ILC Final Focus System, and to maintain the beam collision with a nanometer-scale stability. To establish the technologies associated with this ultra-high precision beam handling, it has been proposed to implement an ILC-like final focus optics in an extension of the existing extraction beamline of ATF at KEK. The two major goals for this facility, called ATF2, are: (A) Achievement of a 37 nm beam size, and (B) control of beam position down to 2 nm level. The 3rd ATF2 Project meeting was held at KEK in December, 2006 to discuss the detailed design and construction schedule.

A meeting of GDE (Global Design Effort) for ILC (International Linear Collider) was held at IHEP in Beijing from February 4 to 7, 2007. A draft of RDR (Reference Design Report) including cost estimation of the machine construction was released. There have been several important changes in the machine cofiguration in this half year. After the conceptual design phase, the activities are going to the next step, the engineering design. Toward completion of the engineering design, GDE is going to be strengthened and re-organized.