Field errors decay and ''snap-back'' in LHC model dipoles

The magnetic field in accelerator magnets decays when the current is kept constant during the particles injection phase, and returns quickly (snaps back) to the original values as soon as ramping is restarted. Here we show results of measurements of the decay of the field errors in 10 m long LHC model dipole magnets, In accordance with previous findings, precycles and stops at intermediate current levels influence the decay, We discuss a possible mechanism causing the decay and snap-back, based on the internal field change in the cable.