| Paper | Title | Page |
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| MOPS064 | Longitudinal Beam Stability and Related Effects at the ALBA Storage Ring | 748 |
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| The risk of longitudinal instabilities excited by narrowband and broadband resonator impedance was studied. A campaign for the search of modes trapped in vacuum chamber elements of the ALBA storage ring via electromagnetic simulation was initiated. Several critical vacuum elements in the ring like the vertical scraper, the injection and feedback kickers were identified. The outlets of the injection kicker had to be protected with RF-fingers whereas the scraper only produces dangerous modes in the withdrawn state, both do not pose a real problem. However, the calculated power distribution generated in the feedback kickers could be an obstacle for reaching the nominal current of 400mA. Furthermore, the budget of Z(n)/n of the storage ring was computed and checked on the risk of microwave instability using the Boussard criterion. | ||
| MOPS065 | Transverse Instability Studies at the ALBA Storage Ring | 751 |
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In the first phase of the ALBA storage ring operation 3 NEG-coated aluminum chambers, 2 in-vacuum undulators and one wiggler chamber will be installed. Under particular consideration of the multilayer character of these chambers and the injection kickers the thresholds of the transverse mode coupled instability(TMCI) were calculated using MOSES*. The thresholds 17.5mA/40.5mA vertical/horizontal leave a rather large operative margin. The detrimental effect of the NEG-coating on the TMCI is relatively limited and on the resistive wall instability is even negligible. As well the thresholds of the head-tail instability were computed as function of chromaticity. Also the incoherent tune shifts generated by the quadrupolar resistive wall wake fields due to the flatness of the vacuum chambers were calculated. The computed results have been compared to first measurements of the storage ring commissioning.
* Y.H.Chin, MOSES 2.0, CERN/LEP-TH/88-05 |
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| MOPS066 | Collective Effects in the MAX IV 3 GeV Ring | 754 |
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| We present calculations of collective instability effects in the 3 GeV electron storage ring of the MAX IV facility currently under construction in Lund, Sweden. The storage ring is designed to deliver ultra-low emittance down to 0.24 nm rad so as to provide high brightness synchrotron radiation from undulators. This is achieved in a comparatively small machine (528 m circumference) through the use of a multi-bend achromat lattice and a compact magnet design featuring multi-purpose narrow gap magnet blocks. This design features small dispersion leading to low momentum compaction, which, together with the small circular (11 mm radius) chambers, poses a challenge to reach the design current (500 mA in 176 bunches) without exciting instabilities and degrading beam parameters due to the interaction with the machine impedance. Particularly important are multi-bunch resistive wall effects in the NEG coated copper chamber as well single-bunch instabilities driven by the broad-band impedance. A low RF frequency (100 MHz) and harmonic cavities are foreseen to lengthen the bunches and increase instability thresholds. | ||