| 摘要 |
PURPOSE:To improve filament heat efficiency by equipping an electronic shield electrode so that it is disposed on the outer peripheral side of a filament and composed of a first shield and a second shield which is disposed on the peripheral side of the first shield. CONSTITUTION:An electronic shield 41 is equipped so that it is disposed on the outer peripheral side of a filament 1 and composed of a first shield 41a and a second shield 41b which is disposed on the outer peripheral side of the first shield 41a. The filament 1 is heated by a first power source 2 to emit thermions, and ion beams 10 are neutralized by their passing through these thermions. Thereupon, the electronic shield electrode 41 composed of the first shield 41a and the second shield 41b functions as a heat shield which is effective for the filament 1, so that heat radiation through the electronic shield electrode 41 can be reduced. The filament 1 can thus be heated effectively.
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