There are many dangerous processes in cryogenic experiment. Cryogenic operators must understand cryogen characteristics and the structure and functions of basic cryogenic equipments, such as storage dewars, transfer tubes and compressed gas cylinders and some other useful instruments, such as level meters, manometers, flow meters, which are installed in the cryostat for safety and effective handling of cryogen. Precooling using liquid nitrogen is effective for liquid helium saving. But, according to circumstances, cool-down by making good use of gaseous helium would be a better selection from the view point of safety and experimental efficiency.
Superconducting wires in a cable-in-coduit conductor are plated with chromium for reducing AC loss. However, the wire will suffer from fretting motion with a very small slip amplitude by the repeated pulse operation of the coil, which would damage the plated layer. In this paper, tribological properties, i.e., frictional and wear properties, of Cr-plated (NbTi)3SN wire were examined under a crossed-cylinder contact at mainly 4.2K in liquid helium. Coefficient of friction of Cr-plated wire ranged between 0.2 and 0.5, which was lower than that of copper. Wear volume was small at 4.2K, compared with those at 293 and 77K. The significant damage was the plastic deformation of the plated layer in the wear scar at 4.2K. However, the plated layer was broken and separated at the boundary of the wear scar. The cracks propagated from the circumferential cracks existing before the test. The particles formed were rectangular with a length of about 20μm. When the plated layer was broken, the coefficient of friction increased to that higher than unity.