The vacuum tube subject to the present invention comprises a filament and two pairs of a grid and an anode. The filament is tensioned linearly and emitting thermoelectrons. Both of the anodes are formed on the same face on a planar substrate. The filament is arranged parallel to the planar substrate at a position facing both of the anodes. Each of the grids is arranged, such that the grid faces the anode in the same pair at a first predetermined distance from the anode and has a second predetermined distance from the filament, between the anode and the filament. The vacuum tube comprises an intermediate filament fixing part fixing the filament at a position corresponding to an intermediate point between the anodes of the two pairs.

The vacuum tube subject to the present invention comprises a filament and two pairs of a grid and an anode. The filament is tensioned linearly and emitting thermoelectrons. Both of the anodes are formed on the same face on a planar substrate. The filament is arranged parallel to the planar substrate at a position facing both of the anodes. Each of the grids is arranged, such that the grid faces the anode in the same pair at a first predetermined distance from the anode and has a second predetermined distance from the filament, between the anode and the filament. The vacuum tube comprises an intermediate filament fixing part fixing the filament at a position corresponding to an intermediate point between the anodes of the two pairs.

The invention discloses an electrochemical polishing solution, a process for electrochemically polishing a graphite gate electrode and a graphite gate electrode, which are used for providing an electrochemical polishing solution and a polishing process to efficiently remove the contaminant on the surface of a gate electrode and improve the quality of the gate electrode. Said electrochemical polishing solution comprises 900-1000 parts by weight of water; 195-205 parts by weight of an alkaline metal hydroxide; 49-51 parts by weight of a weak acid salt; and 294-306 parts by weight of an additive.

The invention discloses an electrochemical polishing solution, a process for electrochemically polishing a graphite gate electrode and a graphite gate electrode, which are used for providing an electrochemical polishing solution and a polishing process to efficiently remove the contaminant on the surface of a gate electrode and improve the quality of the gate electrode. Said electrochemical polishing solution comprises 900-1000 parts by weight of water; 195-205 parts by weight of an alkaline metal hydroxide; 49-51 parts by weight of a weak acid salt; and 294-306 parts by weight of an additive.