Magnetic Length of LHC Prototype Dipoles in Warm and Cold Conditions

We have used magnetic measurements performed in warm and cold conditions on the 10-m long LHC dipole prototypes tasted during the past four years to establish a correlation between the magnetic length in warm and cold conditions. We show that the magnetic length shrinks during cool-down by approximately 0.33 %. The magnetic length was found to change by 1 10^-4 between low field (injection) and high field (flat-top). Systematic effects between apertures in curved magnets, if present, are below 0.5 10^-4 .