Time dependence of persistent-current field distortions in the superconducting HERA magnets

The time dependence of the persistent-current sextupole and dipole components has been measured in more than 250 HERA dipoles. The drift of these two multipole components is correlated and almost logarithmic in time. The initial current cycle of the magnet has surprisingly strong influence on the decay rates. By introducing a break in this cycle the time drift at the HERA injection energy can be greatly reduced, thereby relieving the requirements on time-dependent sextupole corrections considerably. Reference dipoles with diagnostic equipment will be used to determine and correct the time and field dependent dipole and sextupole errors in the HERA proton ring. (author) 4 refs.; 7 figs.; 2 tabs