| Paper |
Title |
Page |
| THPC026 |
Measurement of Complex Coupling Driving Term of Linear Difference Resonance Using Turn-by-turn Beam Position Monitors
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3035 |
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- M. Masaki, K. Soutome, S. Takano, M. Takao
JASRI/SPring-8, Hyogo-ken
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X-Y emittance coupling is one of the important measures of beam quality in an electron storage ring for high brilliant light source. We have developed a method of measuring complex coupling driving term C of linear difference resonance using turn-by-turn beam position monitors (BPMs), assuming the perturbation theory with the single resonance approximation. Since both amplitude and phase of the driving term are derived, we can uniquely determine the strength of two-degree-of-freedom skew quadrupole magnets for correction of the linear resonance coupling. Before the correction, the driving term was measured by the developed method at the SPring-8 storage ring where small skew quadrupole components are distributed as error magnetic fields. On the other hand, the linear resonance coupling was corrected using the counter skew quadrupole magnets, the strength of which was adjusted to minimize vertical beam size near the linear difference resonance. The measured driving term C was broadly consistent with the counter term calculated from the adjusted strength of skew quadrupole magnets for the coupling correction.
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| THPC072 |
Impact of Betatron Motion on Path Lengthening and Momentum Aperture in a Storage Ring
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3152 |
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- M. Takao
JASRI/SPring-8, Hyogo-ken
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The amplitude of the betatron motion in an electron storage ring becomes large in some cases, e.g. Touschek scattered electrons or injected beam. Then we cannot ignore the effect of a finite amplitude of betatron motion on the beam dynamics. The path lengthening of the central trajectory of betatron motion is one of the most serious manifestations of such an influence. Due to the synchrotron motion, the variation of the path length is converted into the energy deviation, so that the betatron motion gives the impact on the momentum aperture in the storage ring. In this paper the path lengthening by a finite amplitude betatron motion is calculated by means of the canonical perturbation method. The derived formula for the path lengthening is simply represented by the product of the chromaticity and the invariant amplitude. Using the formula, we discuss the impact of the betatron motion on momentum aperture in a Touschek effect.
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| THPC070 |
Symmetry Restoration of the SPring-8 Storage Ring by Counter-sextupole Magnets
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3149 |
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- K. Soutome, S. Daté, T. Fujita, K. Fukami, C. Mitsuda, A. Mochihashi, H. Ohkuma, M. Oishi, S. Sasaki, J. Schimizu, Y. Shimosaki, M. Shoji, M. Takao, K. Tsumaki, H. Yonehara, C. Zhang
JASRI/SPring-8, Hyogo-ken
- S. Matsui, H. Takebe, H. Tanaka
RIKEN/SPring-8, Hyogo
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In the SPring-8 storage ring there are four magnet-free long straight sections of about 30m. These were realized in 2000 by locally rearranging quadrupole and sextupole magnets. In modifying the optics we took care of the periodicity of cell structure, especially of sextupole field distribution along the ring. To keep the periodicity high and hence the dynamic aperture large, we adopted a scheme in which "betatron phase matching" and "local chromaticity correction" are combined. In this scheme the dynamic aperture for on-momentum electrons is kept by the phase matching and that for off-momentum electrons is enlarged by the local chromaticity correction with weak sextupoles (SL). After modifying the lattice, we tried to recover the symmetry of the ring further and found that a harmful effect of nonlinear kick due to SL can be minimized by additional "counter-sextupole magnets" placed 180 degrees apart in horizontal betatron phase from SL. We installed such counter-sextupoles in every long straight sections and confirmed that the aperture was improved. In the paper we discuss these topics showing experimental data of injection efficiency, momentum acceptance, etc.
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| THPC127 |
Filling of High Current Singlet and Train of Low Bunch Current in SPring-8 Storage Ring
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3284 |
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- T. Nakamura, T. Fujita, K. Fukami, K. Kobayashi, C. Mitsuda, M. Oishi, S. Sasaki, M. Shoji, K. Soutome, M. Takao, Y. Taniuchi
JASRI/SPring-8, Hyogo-ken
- T. Ohshima
RIKEN/SPring-8, Hyogo
- Z. R. Zhou
USTC/NSRL, Hefei, Anhui
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We performed the storage of high current singlet of 10mA/bunch and a train of bunches of 0.3mA/bunch under the bunch by bunch feedback systems with newly developed bunch current sensitive automatic attenuators with FPGA. The automatic attenuator reduces the signal level of the high current bunch by factor three to five to avoid the saturation of the feedback systems. With this system, the feedback systems suppress horizontal and vertical mode-coupling instabilities and raise the bunch current limit from 3.5mA/bunch to 12mA/bunch, and simultaneously the systems suppress the multi-bunch instabilities by resistive-wall and cavity higher order mode impedances. The improvement of the automatic attenuation system to fit to the final target of the bunch current in the train, 0.06mA/bunch, are being performed. The other problems which limit the filling patterns, such as saturation of the readout electronics of the beam position monitor system and the heating of vacuum components by high current bunches, will be briefly presented.
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