| 摘要 |
PURPOSE:To provide a small size beam stopper apparatus which is capable of measuring beam current with a high accuracy by suppressing an error generated by the secondary electrons. CONSTITUTION:In order to stop the travelling of charged particle beam B in a beam stopper apparatus 21, a beam stopper electrode 24 is lifted in order to close a beam output aperture 30 of the secondary electron absorbing electrode 23 and a negative potentialis given to the secondary electrona suppresing electrode 33 by a switch 38 from a DC power supply 39. Thereby, the charged particle beam B travelling through the cylindrical path of secondary electron suppressing electrode 33 and secondary electron absorbing electrode 23 entering from the beam input aperture 27 of vacuum duct 22 is caused to stop to travel by the beam stopper electrode 24. The secondary electrons emitted from the surface of beam stopper electrode 24 with entrance of charged particle beam B are absorbed by the secondary electron absorbing electrode 23. However, since this secondary electron absorbing electrode 23 is electrically connected to the beam stopper electrode 24 through a contact 25, influence of secondary electrons is mutually cancelled and an ammeter 26 can measure an accurate beam current. |
