| 摘要 |
PURPOSE:To prevent the lowering of brightness of an ion source and the temperature rising of an emitter by setting the distance S between the tip of the emitter and a drawing electrode smaller than the mean free path of ionized gas, and setting the bore diameter of the drawing electrode under the distance S. CONSTITUTION:In an electric field ionization type ion source, the distance S between the tip of an emitter 11 and a drawing electrode 12 is set smaller than the mean free path of ionized gas. Whereby, there is no possibility that gas molecules (or atoms) which are ionized at the tip of the emitter 11 lose charges by impinging on another molecules (or atoms), and the gas molecules are freely discharged from an aperture 13 into a vacuum chamber. Further, it is necessary that the diameter of the aperture 13 is approximately equivalent to the distance S or is under the distance S. The smaller the diameter of the aperture 13, the smaller the flow rate of ionized gas, the thus there is an advantage that the temperature rising of the emitter 11 is prevented.
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