Resonant Spin Depolarisation Measurements at the Spear3 Electron Storage Ring

Accurate electron beam energy measurements are valuable for precision lattice modelling of high-brightness light sources. At SPEAR3 the beam energy was measured using the resonant spin depolarisation method with striplines to resonantly excite the spin tune and a sensitive NaI scintillator beam loss monitor to detect resulting changes in Touschek lifetime. Using the combined apparatus an electron beam energy of 2.997251 (7) GeV was measured, a relative uncertainty of 3× 10. The measured momentum compaction factor was found to be in close agreement with the numerical model value using rectangular defocussing gradient dipoles with measured magnetic field map profiles. In this paper we outline the chosen experimental technique, with emphasis on its applicability to electron storage rings in general.