| 摘要 |
PURPOSE:To prevent the deterioration of a discharge gas and the fall of insulating property, by forming a discharge path, with which plasma comes directly in contact, of boron nitride. CONSTITUTION:The central aperture 10 of a circular plate type member 7 of ceramic is provided with a laser fine tube serving as a discharge path with which plasma comes directly in contact. A boron nitride member 9 in the form of a cylinder is fitted to the aperture, and nitrogen gas due to the sputter of plasma does not generate which generates when aluminum nitride is used. As the member 7 is made of ceramic, graphite powders due to sputter do not generate, which generate when graphite material is used. As the result, the deterioration of a discharge gas and the fall of insulating property between electrodes can be prevented even in the case of a long-term service. |
