Kenji Shinoe

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>>

Drift Velocity and Pulse Response of Trapped Ions in a Circulating Electron Beam

Response of trapped ions in a circulating electron beam to a sharp pulsed voltage applied to a clearing electrode was successfully observed with a NaI scintillator, detecting γ-rays caused by the trapped ions. It was found that velocity distribution of trapped ions is 3.3 times wider than the Maxwell-Boltzmann distribution of CO+ ions. The pulse response was also analyzed considering transmission, elimination and production of trapped ions.

Quadrupole HOM damping with eccentric-fluted beam pipes

An eccentric-fluted beam pipe was proposed to damp quadrupole modes. The eccentric-flute acts as a mode converter from quadrupole to dipole. Optimized parameters permit to damp both degenerate modes of the quadrupole with the eccentric-flute. External Q-values measured with a low power model agreed well with those calculated with MAFIA.

Development of Copper Coated Chamber for Third Generation Light Sources

We describe the development of the copper coated chamber, which is suitable for the 3rd generation light sources. This chamber aims to reduce the resistive-wall impedance[1]. However, this coating might affect the ultra-high vacuum condition worse. In order to check the validity of this chamber for the ultra-high vacuum condition, we have produced the copper coated chamber and built the test bench. The measured outgassing from the inner surface of the newly developed copper coated chamber is sufficiently small to utilize in ultra-high vacuum condition.

Electron-beam size measurement with a beam profile monitor using Fresnel zone plates

We have designed and constructed a non-destructive and real-time beam profile monitor in the KEK-ATF damping ring to measure the extremely small electron-beam size. The monitor has a microscopic structure where two Fresnel zone plates (FZPs) constitute an x-ray imaging optics. In the monitor system, synchrotron radiation from an electron beam is monochromatized by a silicon crystal and the transverse electron-beam image is twenty-times magnified by the two FZP and detected on the x-ray CCD camera With this monitor, we have succeeded in obtaining a clear electron-beam image and measuring the electron-beam size less than 10 /spl mu/m. The measured magnification of the imaging optics was in good agreement with the design value.

Observation of Beam-Bunch Lengthening in the 1.3-GeV Electron Synchrotron

The beam-bunch lengths in the accelerating stage of the 1.3-GeV electron synchrotron were measured at the operating energies (E0) of 0.6-0.9 GeV. Both of the obtained behaviors: the bunch-length reduction from 1.0 ns (rms width) to 0.35 ns and the position variation on the rf phase, are described well by a tracking-simulation calculation. An intensity-dependent bunch lengthening: 0.19 ns at 0.5 mA and 0.30 ns at 100 mA for a voltage pattern of the rf accelerating field at E0=0.6 GeV, is observed. Neither the tracking calculation nor other known bunch-lengthening mechanisms can explain the data.