| Research Abstract |
In this project tribological properties of magnet structual materials were investigated at cryogenic temperatures in vacuum, because frictional heating in a magnet caused the quench of it, and frictional resistance determined the deflection of the structural components in vacuum.
1. Frictional properties
In the friction test at cryogenic temperatures in vacuum, the temperature dependence of friction was examined from 4 K to 150 K for seven combinations of JN1-JN1, JN2-JN2, SUS316L-SUS316L, JN1-Cu, JN2-Cu, Cu-Cu and JN2-CuNi. There were three types of the frictional properties : (1) independent on temperature, where the friction was high at about 4.0 for Cu-Cu, JN2-CuNi, and SUSU316L-SUS316L, (2) gradual increase with temperature for JN1-JN1 and JN2-JN2, and (3) higher friction from 40 to 90 K for JN1-Cu and JN2-Cu. The composition of residual gases in a vacuum chamber was examined. H_2 gas at 20 K, N_2 gas at 50 K and CO_2 at 100 K appeared. The change in hardness of metals would determine the frictional properties.
2. Temperature rise in vacuum
Temperature rise due to frictional heating was tried to measure. However, the temperature of the moving specimen was not cooled enough, which resulted in the unsuccess of the measurement. The cooling was only the thermal conduction through the contact area between specimens. The new method to cool the moving specimen should be developed hereafter.
3. Assessment of coated film in Nb_3Sn superconduction wire
Usually Cr was plated on Nb_3Sn superconductiong wire to reduce AC loss. However, the coated film was separated by the small sliding, and Cu substrate appeared. The friction test and contacting resistance measurement were carried out in liquid helium for wires with different coating metals. Cr coated film was broken in the first 200 cycles, which was detected by the increase in coefficient of friction and the decrease in contacting resistance. Tungusten amorphous film with certain heat treatment showed the good performance.
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