I. Sato

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.

High-precision pepper-pot technique for a low-emittance electron beam

Abstract An emittance measurement system employing a high-precision pepper-pot technique has been developed for an electron beam with low emittance, less than π mm mrad. Since luminous spots on a scintillator are very small, each one was magnified and observed individually with high spatial resolution by scanning an optical system mounted on a precise movable platform. The beam from a high-brightness electron gun was evaluated using this system.

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>>

Focusing system of the KEK positron generator

Abstract A distinctive feature of the KEK positron generator is the use of a compact positron focusing system and a high-current linac as a primary electron beam accelerator. The maximum positron peak currents obtained up to the present are 34 mA at 250 MeV and 17 mA at 2.5 GeV. This report describes the focusing system for the electron beam with a current of up to 10 A and for the positron beam with a large divergence. It reports an improvement of the electron/positron converter unit and its performance. In addition, experimental results are shown for interesting features of the positron focusing system: growth of the positron bunch length and electron mixing in the positron beam.

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>>

Improvement of the alignment system for the KEK 2.5-GeV electron linac

The alignment system for the KEK 2.5-GeV electron linac was improved regarding several points: replacement of the large gas laser (He-Ne) with a compact diode-pumped solid laser (Nd:YAG), the introduction of a single-mode, polarization-maintaining fiber between the laser and the light-injection point into the alignment vacuum duct, and the use of new optics for realizing a diffraction-limited beam along the entire linac length of 460 m. The new system works satisfactorily and serves as a light source of good quality. A preliminary measurement of the system resolution for the KEK 2.5-GeV electron linac is reported as well as the main points concerning the improvements. A new design of the linac alignment system for the KEKB injector linac is also proposed.

A simulation study on beam bunching in the KEK 2.5-GeV linac new pre-injector

We have performed a simulation study on beam bunching in the KEK 2.5-GeV linac new pre-injector comprising double prebunchers and a buncher. The dependence of the bunching performance upon the rf power and the phases of the prebunchers is discussed. We obtained an optimum bunch length of 4 ps with the simulation.<<ETX>>

Modulator upgrade of the KEK 2.5-GeV linac

There is a plan to upgrade the energy of the KEK 2.5-GeV linac to 8.5 GeV relevant to the B-factory project. The increase from the present 2.5 GeV requires reinforcing the existing microwave source. In order to realize this reinforcement with a limited budget, the upgraded modulator was designed so as to utilize those components of the old modulator as much as possible, expect for a necessary change in the main line components. This article describes the upgraded modulator specifications and its performance tests.<<ETX>>

High-power test of a traveling-wave-type RF-pulse compressor

A high-power model of an S-band RF-pulse compressor utilizing a coaxial traveling-wave resonator has been designed, manufactured and tested regarding the energy upgrade of the PF 2.5-GeV linac for the KEKB project. An output peak power of 201 MW was obtained at an input RF power of 45 MW with no serious RF breakdown. The average energy gain was estimated to be 1.75.

Upgrade of an RF source of the linac for the B-Factory project

The B-Factory project is a future plan at KEK requiring an energy upgrade of the KEK linac from 2.5 GeV to 8.0 GeV. This paper describes an upgrade plan and recent progress concerning the RF source. A test to increase the RF power using the existing 30-MW klystron is being carried out and an output power of 51.5 MW has been obtained by increasing the beam voltage up to 310 kV while optimizing the focusing magnetic field. Tests using a 60-MW klystron are also planned. The choice between upgrading of the present klystron and the use of a 60-MW klystron depends an the pulse-compression system to be adopted. The most efficient way regarding costs is being surveyed in order to use the existing components, such as the focusing magnet and the pulse transformer with only slight changes.<<ETX>>