Yukihide Kamiya

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.

Experiment on direct irradiation of a beryllium window by undulator radiation

Beryllium windows were tested as the first target in a project for experimental simulations of heat load effects on beamline optical elements under direct irradiation of undulator and wiggler radiation. Maximum temperature at the window center, vertical temperature distribution, and cooling capability by thermal conduction were studied. It turned out that thermomechanical failure occurred when the temperature difference between the window center and its peripheral edges exceeded about 200 °C. This fact was in good agreement with a simple maximum‐shearing‐stress theory of the failure condition.

Damped‐structure cavity for a high‐brilliant vacuum ultraviolet and soft x‐ray storage ring

This paper describes a new 500 MHz cavity which has a simple damped structure for the 2.0 GeV high‐brilliant synchrotron radiation source. The damping of higher‐order modes (HOMs) is achieved by large hole beam ducts, a part of which is made of microwave absorber. We have adopted as the microwave absorber a sintered SiC named CERASIC‐B manufactured by Toshiba Ceramics Co. Ltd. The latest design of the cavity with CERASIC‐B beam ducts is presented in this paper. We have fabricated a prototype model of the cavity. The results of the low power measurement are also reported here. It was confirmed that by using the CERASIC‐B beam ducts the Q values of HOMs were strongly damped.

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.

The effects of the insertion devices at the Super SOR light source

The Super SOR ring is a third generation light source constructed at Kashiwa Campus of the University of Tokyo. In this paper, we present the formalization of the circularly polarizing undulator and beam optics correction.

Development of a damped cavity with SiC beam-duct

The recent status of the R&D on a damped structure cavity being developed at ISSP and Photon Factory is presented. For the cavity, the higher-order modes (HOMs) damping is obtained with the large beam duct, a part of which is made of sintered SiC. A prototype cavity has been built and tested at low power levels. It was confirmed that the HOMs, which can propagate out of the cavity through the beam duct, were strongly damped by the SiC duct. Recently, fabrication of a high power model has been completed. High power conditioning of the model is now prepared.

Error analysis of a new COD correction method uniting global and local orbit feedbacks

A new COD correction method suitable for orbit feedback has been already proposed. This is the eigenvector method with constraints, which can have both functions of global and local COD corrections. In this paper, we will present the effects of errors in beam position monitor (BPM) reading and steering magnet setting on the orbit correction. We will give analytical expressions of these errors. In addition, we will show results of computer simulations for the VSX light source, a VUV and soft X-ray high-brilliance synchrotron radiation source being planned at the University of Tokyo, and compare them with the analytical results.

Beam position monitoring system using PIN diode switches

We have developed a BPM system that uses PIN diodes for switching and attenuating RF-signal, being intended as more high-speed and reliable than using mechanical switches instead. This system has already been working in the SOR-RING of ISSP. Large unevenness of BPM data that would unexpectedly occur in a case of mechanical switches has never been observed. Moreover, relative accuracy of the order of sub-micron has been attained with this system.<<ETX>>

Design and calibration of pickup-electrodes for beam position monitoring at SOR-RING

Described in this paper are the design and calibration of button-type pickup-electrodes, which have been incorporated in the beam position monitoring system (BPM system) at SOR-RING. The BPM system that has been developed as an R&D for a third-generation VUV synchrotron light source is aimed at testing the key components of the system, PIN diode switches. This system is also aimed at measuring the beam position of SOR-RING and correcting it. In addition, briefly described in the paper are ion-clearing electrodes installed in the ring.<<ETX>>

Measurement of the orbit parameters at SOR-RING

In the 1992 summer shutdown, beam position monitors (BPMs) have been installed in SOR-RING as one of the R&Ds for the future plan of a VUV high-brilliant source. They have been also aimed at measuring the closed orbit of the ring and correcting it by beam steerings that have been also installed at the same time as the BPMs. With these systems, we measured the closed orbit distortion (C.O.D.) at the first time since the ring had been constructed. Horizontal and vertical C.O.D.s were then corrected within 1 mm by exciting the steerings and changing the RF frequency. We also measured the other orbit parameters such as betatron and dispersion functions, chromaticity and RF-cavity parameters. Moreover, it was proved in a recent machine study that SOR-RING is capable of accelerating the electrons up to 450 MeV or more from the present energy of 380 MeV.<<ETX>>