Time variations of fields in superconducting magnets and their effects on accelerators

The time dependence of magnetic fields in the superconducting magnets of the Fermilab Tevatron is discussed. A field variation of order 1 G at the aperture radius is observed. Studies on both full-sized Tevatron dipoles and prototype magnets have been used to elucidate these effects. Explanations based on eddy currents in the coil matrix or on flux creep in the superconducting filaments are explored with these tests. Measurement results and techniques for controlling the effect based on novel laboratory tests and the latest accelerator operation are presented. It is shown that small but important changes in the fields occur with (ln t) time dependencies. For accelerator operation, in both laboratory and accelerator measurements, some events which might be associated with nonsmooth behavior (sudden changes on the relevant time scale) and with deviations at long times from observed (ln t) behavior have been seen.< >