Main Ring Decapole Content

Stan Pruss

December 18, 1989


The first attempt to understand how the field errors in main ring magnets effect the beam may have been TM-543 REMNANT FIELDS IN THE MAIN RING BENDING MAGNETS by B. A. Prichard, Jr. This paper showed measurements of the gradient of the field. These measurements showed a remnant sextupole field of ~0.46 gauss/in2 and a remnant decapole field of ~ -5% of the sextupole for the B1 dipoles. This led to the one inch non-magnetic back-leg spacer in the correction sextupoles. Recent measurements (TM-1412 MAGNETIC MEASUREMENTS OF THE CORRECTION AND ADJUSTMENT MAGNETS OF THE MAIN RING by D. Trbojevic) give a decapole field in the sextupoles with a 1" back-leg spacer of -4.83%. This is certainly consistent with TM-543. However, ecent measurements (private communication from Rod Gerig) of the B1 field errors give a sextupole content of -.00073 of the 400 gauss injection field at one since, (i.e. 0.29 gauss/ in2). These measurements also give a decapole content of -32% of the4 sextupole content. The smaller sextupole content of the dipole results in the correction sextupoles being run at lower currents. This, in turn, means that only 10% of the decapole in the dipoles is caused by the pole tip shape, not just remnant fields. In fact, the decapole content of the B1 field increases as the current increases from 97 amps to 210 amps. The sextupole content decreases for the same conditions. This indicates that if decapole magnets were ever built, they would need to be ramped with the main field at least up through transition.