Effects of drag force of helium gas on a spinning superconducting rotor

A superconducting rotor with the high-speed rotation is driven by the torque generated from stator coils at low temperature in 4.2 K. It is necessary to fill the rotor housing with cold helium gas to remove the heat from the superconducting rotor to the support structure. However, it will bring the drag force from the gas, which has a negative effect on the rotating speed of the rotor. The drag torque of gas to act on the rotating rotor was calculated, and the experiment of deceleration of the rotating rotor was performed. The results show that the angular velocity is decaying with exponential function when the rotor rotates in the gas. It is necessary to calculate rotor deceleration at different gas pressures with different analysis methods.