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New Method for a Continuous Determination of the Spin Tune in Storage Rings and Implications for Precision Experiments


A new method to determine the spin tune is described and tested. In an ideal planar magnetic ring, the spin tune – defined as the number of spin precessions per turn – is given by νs = γ G (γ is the Lorentz factor, G the gyromagnetic anomaly). At 970 MeV/c, the deuteron spins coherently precess at a frequency of ≈120 kHz in the Cooler Synchrotron COSY. The spin tune is deduced from the up-down asymmetry of deuteron-carbon scattering. In a time interval of 2.6 s, the spin tune was determined with a precision of the order 10-8 and to 110-10 for a continuous 100 s accelerator cycle. This renders the presented method a new precision tool for accelerator physics; controlling the spin motion of particles to high precision is mandatory, in particular, for the measurement of electric dipole moments of charged particles in a storage ring.

D. Eversmann et al. (JEDI collaboration), Physical Review Letters 115 (2015) 094801


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