K. Kakihara

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.

Experimental study of positron production from a W single crystal by the KEK 8-GeV electron linac beam

Abstract We have measured the positron production efficiency from tungsten single-crystal targets using an 8 GeV electron beam. A single-bunch beam with a bunch width of 10 ps, a repetition rate of 2 Hz, and an intensity of 0.2 nC/bunch was incident on a target mounted on a precision goniometer. Positrons produced in the forward direction were detected by a magnetic spectrometer in the 10–20 MeV/c momentum range. Systematic data on the target-thickness dependence and the momentum distribution of the produced positrons were obtained for crystal targets. The results show that, when the crystal axis 〈1 1 1〉 is aligned to the electron beam direction, the positron yield increases compared to the amorphous case by factors of 6.5, 3.4 and 2.3 at 10 MeV/c for 2.2, 5.3 and 9.0 mm thick crystals, respectively. We observed that the positron yield from the 9.0 mm thick crystal is larger than the maximum yield attainable with 18–20 mm thick amorphous targets at 8 GeV.

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>>

Status of C-band accelerator module in the KEKB injector linac

For future energy upgrade of the KEKB injector linac, we have been developing a C-band accelerator module which can yield twice higher acceleration field gradient (42 MV/m) than the present S-band modules. This paper reports on a development of the sixth prototype accelerating section and recent performance of the C-band module which recorded an average field gradient of 45 MV/m.

Progress of 7-GeV SuperKEKB Injector Linac Upgrade and Commissioning

KEK injector linac is being upgraded for the SuperKEKB project, which aims at a 40-fold increase in luminosity over the previous project KEKB. SuperKEKB asymmetric electron and positron collider with its extremely high luminosity requires a high current, low emittance and low energy spread injection beam from the injector. Electron beams will be generated by a new type of RF gun, that will inject a much higher beam current to correspond to a large stored beam current and a short lifetime in the storage ring. The positron source is another major challenge that enhances the positron bunch intensity from 1 to 4 nC by increasing the positron capture efficiency, and the positron beam emittance is reduced by introducing a damping ring, followed by the bunch compressor and energy compressor. The recent status of the upgrade and beam commissioning is reported.

Absolute energy calibration of FD by an electron linear accelerator for Telescope Array

The primary energy of the ultra‐high energy cosmic rays(UHECR) are measured with the number of fluorescence photons which are detected with fluorescence detectors(FD) in the Telescope Array experiment(TA). Howevery since there is large uncertinty as 19% in the measurement of the energy scale, the most important theme is improvement of the energy calibration. The electron light source(ELS) is a small electron linear accelerator for new energy calibration. The ELS is located 100 m far from the FD station, and injects electron beam which is accelerated to 40 MeV energy into the sky. We can calibrate the FD energy scale by detection the air shower directly which is generated by the electron beam. The ELS was developed in KEK Japan, and moved to the TA site in March 2009. We started the beam operation in September 2010, in consequence we detected the air shower which was generated by electron beam in the air. The output kinetic energy of the electron beam was 41.1 MeV, we adjusted the output charge from 40 to ...