Masaaki Izawa

Characteristics of a SiC microwave absorber for a damped cavity

Development of a SiC microwave absorber for a damped cavity is presented. The SiC studied has a resistivity of 101–102 Ω cm, which is the expected value to damp higher‐order modes (HOMs) in the cavity and also has high thermal conductivity. The absorber is attached to the cavity as a part of the beam duct. Since the SiC duct receives a large amount of energy from the electron (or positron) stored beam, it is very important to estimate the dissipation power in the SiC duct and to design a cooling mechanism. The heat load problem of the SiC duct is discussed and the results of high power testing of the SiC duct are presented. The damping mechanism for HOMs is based on the power dissipation due to the resistivity of SiC. The fine control of the resistivity of SiC in fabrication is very important. The preliminary results on this problem are also presented.

Reconstruction for the brilliance-upgrading project of the Photon Factory storage ring

Reconstruction of the Photon Factory storage ring (PF ring; 2.5 GeV) is now in progress to provide very brilliant synchrotron radiation to users, i.e. the emittance is being reduced by a factor of five. Components, such as the quadrupole and sextupole magnets, vacuum chambers, beamlines and beam-position monitors, are being replaced by new ones in 16 normal-cell sections of the PF ring. The accelerating cavities, injection systems and control systems are also being replaced. Operation will commence when the improvements are completed on 1 October 1997.

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.

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.

Design and Cold Model Test of 500 MHz Damped Cavity for ASP Storage Ring RF System

TOSHIBA is manufacturing the storage ring RF system for the Australian Synchrotron Project(ASP). Two pairs of the 500MHz Higher Order Mode(HOM) damped cavities will be applied for this system. The cavity is a modified KEK-PF type with silicon-carbide(SiC) microwave absorber and has three rod-shaped HOM couplers for damping the longitudinal HOM impedance less than 20kΩ/GHz to comply with ASP Performance Specification. The shunt impedance has been improved more than 5% in comparison with the original design by reducing the beam bore diameter without degrading HOM damping capability. The design of the cavity and the test results of an aluminum (Al) cold model are described.

Commissioning of the PF Ring after the Reconstruction for the Straight‐sections Upgrade

At the 2.5‐GeV ring of the Photon Factory, a large reconstruction of the lattice around the straight sections has been accomplished in 2005. Thus reconstruction is the main part of the straight‐sections upgrade project to rebuild existing undulators and to increase the number of undulator beamlines. As a result of the reconstruction, four short straight sections have been newly created and the lengths of the existing straight sections have been much extended. To exploit the new straight sections, short‐period narrow‐gap undulators which have a sufficiently high brilliance in hard x‐ray range have been developed. The reconstruction work of the ring was completed in a seven‐month shutdown from March to September, 2005. In the area over two thirds of the storage ring, all the quadrupole magnets and all the beam ducts have been renewed and rearranged to construct the new lattice. Recommissioning of the storage ring was finished at the end of October, 2005. Though we made no in‐situ baking for the beam ducts, ...

Development of an asymmetric power divider for a high-power RF distribution system

We have developed a radio-frequency (RF) power divider that is used for an RF distribution system in high-energy electron storage rings. This power divider has four waveguide ports, and it can split a high RF power by a ratio of 1:2 at an operating frequency of about 508.6 MHz. Since other properties are very similar to those of a magic-T it is very suitable for accelerator applications. By combining this device with a conventional magic-T, one can design an RF distribution system in which three cavities are driven by a single klystron. The design procedure of the power divider, a low-power measurement, and a high-power test result are presented.

Installation of new damped cavities at the Photon Factory storage ring

New damped cavities have been installed in the Photon Factory (PF) storage ring and successfully operated in the last scheduled user run of 1996. The new damped cavity is a simple single-cell cavity with somewhat large beam-duct holes. The part of the beam duct that is attached to the cavity is made of SiC, which works as a microwave absorber and damps the higher-order modes excited in the cavity. Because of its simple structure, the operation of the cavity is very stable and also a high power input of more than 150 kW is possible. No coupled-bunch instabilities due to the new cavity were observed during operation.

Impedance measurements at the Photon Factory storage ring

The loss parameters of the ducts in the Photon Factory (PF) storage ring were evaluated using the wire method and the code tbci. Both the measurement and the calculation were done for different bunch length σ ranging from 25 to 80 ps. The ring impedance was estimated to be ‖Z/n‖=3.19 Ω using the broadband impedance model. The measurements in frequency domain were also carried out to investigate the resonances of some duct components such as the gate valves without rf shield and the flange gaps. The results are presented.