1. Role of part

Inside of glass in Rotating X-Ray Tube should maintain a high vacuum about 10-8Torr. Each electrode (cathode, anode) is sealed inside a glass tube. Anode should be rotated at high speed in vacuum by rotating magnetic field of Stator-coil attached outside the X-ray Insert Tube. It is same with the principle of induction motors. 
There are two bearings and an anode shaft inside the Rotor.
And there is W-Re plate, unbrella-formed target, attached to the end of Anode. There are coil-formed W and focusing cup in a cathode and  its location is out of the center of tube. A thermal-electron emitted from the filaments focus by the focusing cup.  It formed the focal spot, crashing into the target space accerlated by the high voltage. The X-ray is produced in this region and it is shot through the window glass. 

2. Model

- M125S20X : Tube voltage(125kV), F/Spot (1.0/2.0) , Target ( 16°)