In the framework of the development of superconducting accelerator magnets,
one has to determine the apparent elastic modulus and thermal contraction
of the NbTi windings. This knowledge is required to calculate the prestress
needed to compensate thermal shrinkage differentials during cool-down and
stress redistribution due to Lorentz forces during excitation. A compressio
n mold was developed to measure the apparent elastic modulus of ten alterna
tely stacked insulated superconducting cables, both at room temperature and
in a cryostat at liquid helium temperature. The thermal contraction is mea
sured in another stainless steel mold, designed to simulate the prestress a
pplication. A force sensor based on a strain gage measurement technique is
inserted between the conductor stack and the cover of the mold to monitor t
he applied prestress during cool-down. The force sensor is calibrated at ro
om and liquid helium temperature. Reference samples made with known materia
ls such as stainless steel, copper, aluminum and titanium have been also me
asured to calibrate the test apparatus.