Hello. I'm now taking accelerator physics class and the lectures said in the thermionic electron gun, anode metal mesh should be grounded in order to prevent electrons which traveled beyond the mesh from coming back due to the electric field lines. Without grounding of the anode, I believe that the field lines look like the following picture. - charged plate is heated cathode to emit thermal electrons and + charged plate is the anode metal mesh in the thermionic electron gun. According to this field lines, electrons eventually comes back to the anode when they go beyond the anode. So...with grounding of the anode, I guess that there is no electric field beyond the anode and this only explains what the lecturer said in the class, but why? Could you give me a simple picture of how the field lines look like for two plates when the anode is grounded? When the anode is grounded, I think the anode becomes neutral but I hardly imagine what is next to draw field lines.