S. Ohsawa

The KEKB injector linac

Abstract An 8-GeV electron/3.5-GeV positron injector for KEKB was completed in 1998 by upgrading the existing 2.5-GeV electron/positron linac. The main goals were to upgrade its accelerating energy from 2.5 to 8 GeV and to increase the positron intensity by about 20 times. This article describes not only the composition and features of the upgraded linac, but also how these goals were achieved, by focusing on an optics design and commissioning issues concerning especially high-intensity single-bunch acceleration to produce positron beams.

Performance of an electron gun for a high-brightness X-ray generator

The development of an electron gun for a high-brightness X-ray generator whose target brilliance is 60 kW mm−2 is reported.

Beam monitor utilizing transition radiation

Beam monitors utilizing electromagnetic waves, especially visible light radiated by charged particles, have several excellent features for beam diagnostics in accelerators: they are essentially free from environmental electromagnetic noise and are characterized by a high-speed time response. A beam monitor based on transition radiation is one of the most promising monitors concerning positions, sizes, emittance, energy and time structures of bunches for high-intensity, short-pulse beams. We started to develop beam monitors utilizing transition radiation for the beam diagnostics of high-intensity electron beams. Bunch-length measurements were performed at the KEK 2.5-GeV linac with this monitor and a streak-camera system.<<ETX>>

Highly bright X-ray generator using heat of fusion with a specially designed rotating anticathode.

A very compact X-ray generator, 4.3 times more brilliant than can be attained by a conventional rotating-anticathode X-ray generator, has been developed using a U-shaped rotating anticathode and a high-flux electron gun with focusing bending magnet.

Present status and beam-stability issues of the KEKB injector linac

The KEKB injector linac was completely upgraded for the KEK B-Factory (KEKB) project in March, 1998. Many difficulties have been overcome during the elaborate commissioning of the upgraded linac since the end of 1997. The 3.5-GeV positron and 8-GeV electron beams have been injected to the KEKB rings with good performance. Much effort has also been continuing to stabilize the intensity and quality of the beams. Some experimental results on the beam stability issues am shown together with the recent operation status in this report. A beam test on a new scheme of a two-bunch injection was started in order to increase the positron intensity since March, 2001.

Absolute Beam-Charge Measurement for Single-Bunch Electron Beams

The absolute beam charge of a single-bunch electron beam with a pulse width of 10 ps and that of a short-pulsed electron beam with a pulse width of 1 ns were measured with a Faraday cup in a beam test for the KEK B-Factory (KEKB) injector linac. It is strongly desired to obtain a precise beam-injection rate to the KEKB rings, and to estimate the amount of beam loss. A wall-current monitor was also recalibrated within an error of ±2%. This report describes the new results for an absolute beam-charge measurement for single-bunch and short-pulsed electron beams, and recalibration of the wall-current monitors in detail.

Construction and development of an UV free electron laser under the cooperation of Nihon U., KEK, PNC, ETL and Tohoku U.

Abstract The construction and the development of an UV free electron laser at Narashino Campus, Nihon U. have been started under the cooperation of Nihon U., KEK 1 , PNC 2 , ETL 3 and Tohoku U. The project requires a 125 MeV S-band electron linear accelerator to expand the oscillation of FEL to the UV region using fundamental mode. The injection system consists of a thermionic RF-gun with a LaB 6 cathode and a magnet for magnetic bunching. We are studying to reduce the back-bombarding electrons to realize the macropulse length of 20 μs. Electron beams, up to the energy of 125 MeV, are injected into the optical cavity. Changing the accelerating energy and/or undulator parameters, this system will cover the range from infrared to ultraviolet for the applications in the various fields.

New pre-injector of the KEK 2.5-GeV linac and its performance

The injection system (pre-injector) of the KEK 2.5-GeV linac has been upgraded so that we can investigate intense beam acceleration for the KEK B-factory project. It requires intense beams to achieve a short injection time in practice. An outline of the new pre-injector and its performance is given.<<ETX>>

U-shape rotating anti-cathode compact X-ray generator: 20 times stronger than the commercially available X-ray source

A new type of U-shape anti-cathode X-ray generator in which the inner surface of a cylindrical target is irradiated by an electron beam has been made by modifying a conventional rotating anti-cathode X-ray generator whose brightness in the catalog is 12 kW mm−2. A brightness of 129 kW mm−2 was thereby obtained with this new U-shape-type X-ray generator. This new X-ray generator is expected to be of keen interest for applications in academia, industry and in hospitals.

Status of R&D efforts toward the ERL-based future light source in Japan

The energy recovery linac is a very promising synchrotron light source in future. We are contemplating to realize a ERL_based next generation light source in Japan, under a collaboration between KEK, JAEA, ISSP, and other SR institutes. To this end, we started R&D efforts on its key technologies, including a low-emittance photocathode gun and superconducting cavities. We also plan to assemble these technologies into a small test ERL, and to demonstrate their operations. We report our R&D status.