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Persistent URL http://purl.org/net/epubs/work/48853
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Record Id 48853
Title Spin Motion Near Snake Resonances
Abstract At SPIN2002 [1] we presented new results on features of the invariant spin field (ISF) at the so?called snake resonances in ring accelerators. This is the name given to the loss of polarisation in rings with Siberian Snakes, occurring during acceleration at certain vertical orbital tunes, namely tunes with fractional part [Q2]=1/6, 5/6, 1/10, 3/10, 7/10, 9/10, 1/14, 3/14, 5/14, 9/14, 11/14, 13/14, ยทยทยท. In particular, we found that within our simple model, the ISF is unusual in that it is irreducibly discontinuous at snake?resonance tunes. Furthermore, its segments are close to horizontal at energies far from those of the parent resonance. In the meantime we have extended this work with the aim of understanding why polarisation should be lost during acceleration at such tunes. We concentrated on the representative tune [Q2] = 1/6. The key outcome is that exactly at snake resonances the non?standard evolution, during acceleration, of initially vertical polarisation can be understood by invoking the concept of adiabatic invariance of the spin action and by considering the special geometry of the ISF together with the evolution of the eigentune of the appropriate multiturn spin map. The results of that study together with references to background material, an explanation of important concepts and our notation are available in [2]. In order to appreciate the contents of this paper, the reader should read [1, 2]. Thus we do not explain the concepts and notation again here. Here, we give a brief account of further, and on?going, studies aimed at understanding spin motion near to, but not at, snake?resonance tunes. As in [1, 2] we work with a model ring containing two point?like Siberian Snakes at diametrically opposite sides of the ring with their snake axes at 0◦ and 90◦ to the longitudinal direction. Then the spin tune on the design orbit, ν0, is 1/2 at all energies. The effect on the spin of vertical betatron motion is described by the so?called single resonance model. We illustrate our work by focussing on a [Q2] near 1/6.
Organisation CCLRC , CI
Keywords Physics
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Language English (EN)
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Preprint CI Preprints Cockroft 06-88 2006. Submitted to: 10th European Particle Accelerator Conference (EPAC06), Edinburgh, UK, 26-30th June 2006 Cockcroft-06-88.pdf 2006