  The improvement of accelerator parameters requires the transition to
superconducting undulator technologies since SCUs allow higher magnetic fields
compared to classical planar undulators with the same gap. The primary method
for characterizing magnetic structures is to measure the magnetic field
distribution along the undulator axis with a Hall probe. Special test rigs
based on vertical cryostats with liquid helium are used to parameterize
superconducting magnetic structures (undulator coils). However, during the
probe immersion and cooling to cryogenic temperatures, its linear dimensions
change, which needs to be taken into account by applying complex thermodynamic
models since the position encoder of the probe is located on the cryostat
flange at room temperature. To eliminate this effect, it is proposed to equip
the probe with two Hall sensors spaced apart half a period of the measured
structure.
