To provide a bearing having multi-helical-grooves for an X-ray tube, which is capable of obtaining more power at the focused point by making its shaft speed faster while reducing of the generated heat with torque and power not changing linearly following the speed.

In this bearing with multi-helical-grooves for an X-ray tube, an assembly consists of an intermediate race 32 having helical grooves on its inside surface 34 and outside surface 36, which are disposed between the outside housing 28 and the inside bearing shaft 30, and gallium layers 42, 22 are disposed between the helically grooved inside surface 34 and the inside shaft 30, and between the helically grooved outside surface 36 and the outside housing 28, respectively. Here, both surfaces of the intermediate race 32 are lubricated with the gallium layers 42, 44, and hence the intermediate race 32 reducer relative velocity between movable components, so that the heat in the bearing assembly is reduced at a given anode rotation speed.