We describe the improvements of a Fresnel zone plate (FZP) beam-profile monitor, which is being developed at the KEK-ATF damping ring to measure ultralow emittance electron-beam profiles. This monitor, which is designed to have a submicrometer spatial resolution, is based on x-ray imaging optics composed of two FZPs. Various improvements were performed to the old setup. First, a new crystal monochromator was introduced to suppress the beam image drift. Second, the two FZP folders were improved in order to realize a precise beam-based alignment during x-ray imaging. Third, a fast mechanical shutter was installed to achieve a shorter time resolution, and an x-ray mask system was also installed to obstruct direct synchrotron radiation through the FZPs. These improvements could make beam-profile measurements more precise and reliable. The beam profiles with less than 50 m horizontal beam size and less than 6 m vertical beam size could be measured within a 1 ms time duration. Furthermore, measurements of the damping time and the coupling dependence of the ATF damping ring were successfully carried out with this upgraded FZP monitor.
Recently, a global feedback of beam position was switched on at SOR-RING of Tokyo University. At a low beam current, the vertical orbit drift was suppressed almost within a few μm and the horizontal orbit drift within several μm. On the other hand, the suppression became worse at a high current because of a longitudinal instability, which deteriorated the accuracy of the beam position monitor system. It was also observed that at 21 Hz, the repetition rate of the electron synchrotron close to SOR-RING, the horizontal orbit tends to vibrate uniformly around the ring, i.e., monopolelike expansion and contraction, while the vertical orbit has a dipolelike vibration; a result expected if a uniform magnetic field is impressed on the ring.
Prototypes of the dipole and the fast steering magnet for the VSX project have been fabricated and measured. The field mapping and the end-shim correction were carried out for the dipole, and the frequency response was tested up to 2 kHz for the fast steering. The design of the magnets and measured results are presented.
A high-brilliance VUV and soft X-ray (SX) synchrotron radiation (SR) source is being planned to construct at the University of Tokyo. Designs of dipole, quadrupole and fast steering magnets for the storage ring are presented in this paper. Results of prototype measurements of the dipole and steering are also described.
The beam-bunch lengths in the accelerating stage of the 1.3-GeV electron synchrotron were measured at the operating energies (E
0) 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 E
0=0.6 GeV, is observed. Neither the tracking calculation nor other known bunch-lengthening mechanisms can explain the data.
In the 1992 summer shutdown, beam position monitors (BPM's)[l] [2] have been installed in SOR-RING as one of the R&D's 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 BPM's. 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.
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