Measurement of thermo-mechanical properties of NbTi windings for accelerator magnets

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.