First Observation of a Snake Depolarizing Resonance

Abstract

Using a 104 MeV stored polarized proton beam and a full Siberian snake, we recently found evidence for a so-called ``snake'' depolarizing resonance. A full Siberian snake forces the spin tune ${\ensuremath{\nu}}_{s}$ to be a half integer. Thus, if the vertical betatron tune ${\ensuremath{\nu}}_{y}$ is set near a quarter integer, then the ${\ensuremath{\nu}}_{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}n\ifmmode\pm\else\textpm\fi{}2{\ensuremath{\nu}}_{y}$ second-order snake resonance can depolarize the beam. Indeed, with a full Siberian snake, we found a deep depolarization dip when ${\ensuremath{\nu}}_{y}$ was equal to 4.756; moreover, when ${\ensuremath{\nu}}_{y}$ was changed to 4.781, the deep dip disappeared and the polarization was preserved.