An Ultra-Precise Storage Ring for the Muon g — 2 Measurement

An ultra precise 3 GeV/c storage ring with a 14.5 kG super-ferric magnet is under construction at the Brookhaven AGS for the measurement of the muon anomalous magnetic moment to 0.35 PPM accuracy. This requires a magnetic field which is constant to ≈ 1 PPM and is known sufficiently well that the magnetic field integral averaged over the muon orbits can be calculated to 0.1 PPM. First the magnetic field will be statically shimmed by various techniques. Pole face winding will be used for final small static and dynamic corrections. Very elaborate NMR field monitoring techniques are required. A “movable trolley” located inside the vacuum chamber and the electrostatic focusing quadrupoles will measure the field throughout the muon storage volume. The trolley “siding” is 180˚ from the injection point where no electric quadrupoles are located. Injection can be interrupted so the trolley can circle the ring. Also ≈ 200 NMR probes located outside the vacuum chamber monitor the field during physics running and control the pole face windings. The very large (≈ 15 m diameter) superconducting coils (SC) are designed. Test winding will soon commence. Orders for the magnet steel can now be placed. R and D on various pulsed and SC dc injection methods is ongoing.