[en] Half-integer resonance extraction at 2ν_H=15 has been utilized for the KEK 12-GeV Proton Synchrotron (KEK-PS). Performance of the slow extraction has been progressing recently. A slow beam extraction system was constructed for the newly build North Counter Hall. For the old East Counter Hall, the power rating of the slow extraction instruments was improved in connection with an elongation of the flat-top. The quality of the extracted beam (extraction efficiency, beam emittances and spill structure) has been systematically measured and improved by concentrated efforts. Further, a new variation of the extraction modes (deuteron beam extraction and lower energy beam extraction) has been achieved in order to contribute to the various fields of physical experiments. This report gives up-to-date descriptions of the slow extraction system of the KEK-PS. (author)

[en] We performed an experiment to detect a temperature rise at cryogenic temperature using a dual-core optical fiber. This fiber has two single-mode optical cores in one fiber. We demonstrated that a temperature rise of 4 K was detectable at 4.2 K. The sensitivity of this method can be improved using a longer fiber. This method may be applicable as a quench detector for superconducting magnets. A quench detector using this optical method is immune from electromagnetic noise, free from troubles caused by break-down of electrical insulator, and has many advantages over a conventional quench detector measuring voltages of a magnet

[en] A compact snake and rotator scheme for polarized proton beams, which can provide variable spin-rotation axis with small orbit displacement, is proposed. This aims to maintain polarization and to obtain both longitudinal and transverse polarization at the collision point in the heavy ion collider (PS-Collider), which has been recently proposed as one of the future projects of the KEK PS. (author)

[en] Transverse head-tail instability has been studied for ordinary RF bunches and super-bunches using KEK 12 GeV PS parameters. Tentative results are reported. An air bag model shows similar stability behaviour in both cases, if bunch lengths are similar, i.e. the beam is unstable except the chromaticity ξ - 0. A water bag model as is the more realistic distribution, has momentum spread. Synchrotron tune spared is almost same for the both cases at the KEK-PS parameters, although there is a big difference in the synchrotron tune itself. The synchrotron tune spread stabilizes the beam due to Landau damping which gives sufficiently large threshold intensity for the super-bunch in the KEK-PS. (author)

[en] A horizontal head-tail instability has been observed at the beginning of acceleration in the KEK-PS main ring. The instability occurs due to a large change in chromaticity produced by the sextupole component of the eddy-current induced field in the dipole beam-pipe. The horizontal chromaticity increases up to a positive value around 80 ms after the beginning of acceleration. The longitudinal mode 0, 1 and 2 have been observed. The impedance model, including resistive wall impedance, kicker impedance and broad band impedance, explains the instability for a single bunch operation very well. (author)

[en] The spin tune is modulated by synchrotron oscillation. Its modulation frequency is the synchrotron oscillation frequency and the amplitude of modulation is proportional to Δp/p. When a beam crosses the depolarizing resonances, polarization suffers from this effect especially in the spin-flip region. The observation of this effect in the intrinsic resonances of the KEK PS and its correction by using vertical chromaticity are described. (author)

[en] A polarized proton beam was accelerated at the KEK-PS in the late 1980's. This report will review the activities for the polarized beam acceleration in both the 500 MeV booster and the 12 GeV Main Ring. Some depolarization resonances were passed using the spin-flip techniques. The effects on the polarization caused by a synchrotron side-band at a strong intrinsic resonance were observed

[en] Investigation of the beam loss at the beginning of acceleration clarified the loss mechanism due to the horizontal head-tail instability. The instability occurs due to a large change in the chromaticity produced by the sextupole field induced in the beam-pipe of the dipole magnets. The horizontal chromaticity increases up to a positive value just around 80 ms after the beginning of acceleration. The longitudinal mode 0, 1 and 2 have been observed. The impedance model explains the instability very well. (author)

[en] Investigations of the depolarization problem at the KEK proton synchrotron indicated that the dominant part of the depolarization in the booster is due to the synchrotron oscillation effect. A major effect comes from the resonant frequency modulation through the vertical chromaticity. One method is to adjust the vertical chromaticity. A sextupole magnet system is planned for the booster

[en] Depolarization of the polarized proton beam accelerator in the 500 MeV booster was investigated as the first step of polarized proton acceleration in the KEK proton synchrotron. Beam polarization was measured in the 20 MeV beam transport line from the linac to the booster and in the main ring at the injection energy of 500 MeV. About 40% of the linac beam polarization was kept in the main ring