H. Kobayakawa

Highly polarized electrons from GaAs-GaAsP and InGaAs-AlGaAs strained-layer superlattice photocathodes

GaAs–GaAsP and InGaAs–AlGaAs strained-layer superlattice photocathodes are presented as emission sources for highly polarized electron beams. The GaAs–GaAsP cathode achieved a maximum polarization of 92(±6)% with a quantum efficiency of 0.5%, while the InGaAs–AlGaAs cathode provides a higher quantum efficiency (0.7%) but a lower polarization [77(±5)%]. Criteria for achieving high polarization using superlattice photocathodes are discussed based on experimental spin-resolved quantum efficiency spectra.

Suppression of beam instabilities induced by accelerating cavities

A requirement for electron storage rings for the synchrotron radiation experiments is that circulating beam is very stable. In particular, for small emittance machines, obtaining a high‐quality beam is the most important subject. Though the rf‐accelerating cavities are essential for the storage rings, sometimes they cause serious beam instabilities, and lead to a current limit and an emittance growth. The Photon Factory storage ring (KEK) is a dedicated synchrotron radiation source. There are four single‐cell cavities in the ring. Beam instabilities arising from the cavities have been investigated. The resonant frequencies of these cavities were trimmed by choosing the proper length of blank‐flanges attached to the cavity ports, to avoid the conditions unstable for all existing coupled‐bunch instabilities. Reduction of the instabilities was remarkable.

Measurement of the asymmetry for π+ photoproduction from polarized protons between 300 and 900 MeV

Abstract The asymmetry of the cross section for π+ photoproduction from a polarized butanol target has been measured at a c.m. angle 90° and photon energies between 300 and 900 MeV by a single-arm spectrometer detecting positive pions. Our results indicate that the asymmetry has clear positive peaks at photon energies 400 and 700 MeV with a deep valley at about 600 MeV. The general feature of the results is well reproduced by the phenomenological analyses made by Walker and ourselves; however, the best fit to the polarized target asymmetry data seems to give a somewhat different set of parameters from that given by Walker.

Measurement of polarized target asymmetry on γp → π0p below 1 GeV

Abstract The polarized target asymmetry in the reaction γ p → π 0 p has been measured at c.m. angles of 30°, 80°, 105° and 120° for incident photon energies below 1 GeV. Two decay photons from π 0 were detected in coincidence at 30°, and at the other angles recoil protons and single photons from π 0 were detected. The results are compared with recent phenomenological analyses.

Observation of the ion trapping phenomenon with bremsstrahlung

Abstract The ion trapping phenomenon was studied at the Photon Factory storage ring. The accumulating process of ions in the electron beam orbit was directly observed by detecting bremsstrahlung from electron-ion collisions.

Differences in the ion trapping between uniform and partial bunch fillings

Abstract Ion trapping was studied at the Photon Factory storage ring at KEK with bremsstrahlung from electron-ion collisions. Differences in the bremsstrahlung yields were found in the operations between the partial and uniform filling modes. Observed count rates for the uniform bunch filling were always higher than those for the partial filling, indicating that a small number of ions were captured in the latter case. The results clearly show the reason why ion-trapping problems can be alleviated in the partial filling.

POLARIZATION OF RECOIL PROTONS FROM NEUTRAL PION PHOTOPRODUCTION.

The polarization of the recoil proton in the process γ+ P → p +π° was measured for a pion angle of 120° in the center of mass system at photon energies 450, 500, 550 and 600 Mev. Magnetically-analyzed protons were detected by a counter telescope consisting of three scintillation counters, which triggered the spark chamber system designed as a polarization analyzer. About 150 thousand spark chamber photographs were taken, and the tracks of protons quasi-elastically scattered by the carbon plates of the spark chamber and by a carbon block in its front were selected by manual scanning. Data from about 5000 photographs thus selected were processed by an electronic computer. Results obtained are: -0.07±0.18 for 450 MeV, -0.25±0.14 for 500 MeV, -0.38±0.12 for 550 Mev and -0.43±0.18 for 600 meV.

Critical Test of Coupled-Bunch Instability Theory

Longitudinal and transverse coupled-bunch instabilities were observed in the Photon Factory storage ring. They were all caused by the high shunt impedances of the RF accelerating cavities and their properties were studied in detail. The frequency dependences of threshold currents of these instabilities were measured, and well described in terms of the frequency dependent structures of the cavity impedances. Absolute values of the thresholds are discussed in a comparison with perturbation theory.

Upgrade of the Photon Factory storage ring for a high brilliance configuration

A high brilliance configuration of the 2.5‐GeV Photon Factory storage ring has been designed and proposed. In the new configuration, the beam emittance will be reduced to 27 nm rad, which is one‐fifth of the present value (130 nm rad). The brilliance will be typically increased by a factor of 10. The beam lifetime and beam stability are discussed from a standpoint of the total effective brilliance. All of the improvements for this upgrade are being carefully designed and planned so as to be achieved (1) with minimum influence for the existing beamlines, (2) within the shortest shutdown time, and (3) at low cost.

Elastic and inelastic p - α collisions at 55 MeV

Differential cross sections were obtained for elastic p- alpha scattering and for /sup 4/He(p,d)/sup 3/He reaction for 55-Mev protons. Reaction mechanisms are discussed. (R.E.U.)