To precisely measure ultra-high vacuum pressure with a simple structure by constituting an energy filter of a cylindrical electrode, an end plate electrode, and a baffle plate electrode, and providing a ring electrode within a cylinder to prevent a light, excited neutron particle, or soft X-ray from being incident on an ion detecting part.
An energy filter 2 has a cylindrical electrode 6 and end plate electrodes 7. Each end plate electrode 7 has a hole 7a for passing ions. The cylindrical electrode 6 has a disc-like baffle plate electrode 8 having a diameter about the same as or larger than the hole 7a in the inside center part, and the same potential as the cylindrical electrode 6 is imparted thereto. An annular ring electrode 15 is formed in the inner part of the cylindrical electrode 6 to form an annular ion passage 16. The optical visual field capable of seeing the ion incident part 3a of an ion detecting part 3 through an ion generating part 1 is narrowed from the circumferential side of the baffle plate electrode 8 by the ring electrode 15, and a light, excited neutron, or soft X-ray directed to the circumference of the baffle plate electrode 8 can be collided to the ring electrode 15 and removed.
TAKEUCHI KIYOUKO
TSUJI YASUSHI
KUROKAWA YUJIRO
HAYASHI TOSHIO
