A high voltage feedthrough assembly 100 for providing an electric potential in a vacuum environment comprises a flange connector 10 being adapted for a connection with a vacuum vessel 201, wherein the flange connector 10 has an inner side facing to the vacuum vessel 201 and an outer side facing to an environment of the vacuum vessel 201, a vacuum-tight insulator tube 20 having a longitudinal extension with a first end facing to the flange connector 10 and a second end being adapted for projecting into the vacuum vessel 201, and an electrode device coupled to the second end of the insulator tube 20, wherein the electrode device has a front electrode 31 facing to the vacuum vessel 201 and a cable adapter 32 for receiving a high-voltage cable 214, wherein a flexible tube connector 40 is provided for a vacuum-tight coupling of the insulator tube 20 with the flange connector 10, and a manipulator device 50 is connected with the insulator tube 20 for adjusting a geometrical arrangement of the insulator tube 20 relative to the flange connector 10. Furthermore, an electron diffraction apparatus 200 including the high voltage feedthrough assembly 100 and a method of manipulating an electrode device in a vacuum environment are described.