| Paper |
Title |
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| WEOBC01 |
Beam Instability Observations and Analysis at SOLEIL
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2019 |
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- R. Nagaoka
- L. Cassinari, M.-E. Couprie, M. Labat, M.-P. Level, C. Mariette, R. Sreedharan
SOLEIL, Gif-sur-Yvette
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Due to reduced vertical chamber aperture around the machine, the impedance was systematically evaluated and optimized 3D-wise at SOLEIL during the design stage, whose budget was then utilized to predict instability thresholds for multi and single bunches. These theoretical calculations are compared with observed instabilities. Transverse multibunch current thresholds are followed as a function of chromaticity, identifying the transition of different head-tail regimes that reflects the broadband impedance spectrum. Although low thresholds due to resistive-wall are basically confirmed, its combined effect with ion-induced instability is found to be significant, exhibiting a strong beam filling pattern dependence. To analyse the involved dynamics, a multibunch tracking code is developed in a structure that allows parallel computations with a cluster of processors. The obtained results are compared with empirical data. Analysis of single bunch instabilities is also made with an aim to identify the enhanced reactive impedance due to NEG coating.
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Slides
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| WEOBC02 |
Vertical Instability at IPNS RCS
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2022 |
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- S. Wang
- F. R. Brumwell, J. C. Dooling, K. C. Harkay, R. Kustom, G. E. McMichael, M. E. Middendorf, A. Nassiri
ANL, Argonne, Illinois
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Funding: This work is supported by the U. S. Department of Energy under contract no. W-31-109-ENG-38.
The Intense Pulsed Neutron Source (IPNS) Rapid Cycling Synchrotron (RCS) accelerates 3.2x 1012 protons from 50 MeV to 450 MeV at 30 Hz. During the 14.2 ms acceleration period, the RF frequency varies from 2.21 MHz to 5.14 MHz. The beam current is limited by a vertical instability. By analyzing turn-by-turn Beam Position Monitor (BPM) data, large amplitude mode 0 and mode 1 vertical beam centroid oscillations were observed in the later part of the acceleration cycle. The oscillations develop in the tail of the bunch, build up and remain localized in the later part of the bunch. This vertical instability was compared with a head-tail instability that was intentionally induced in the RCS by adjusting the trim-sextupoles to make the horizontal chromaticity positive (below transition). It appears that our vertical instability is not typical head-tail instability. More data analysis and experiments were performed to characterize the instability.
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Slides
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