| 摘要 |
PURPOSE:To ensure stable exposure constantly through control of the electron beam according to the results of the measurement thereof with the second slit when it passing through the first slit. CONSTITUTION:Electron beam emitted from the electron gun 1 is received by the second rectangular slit 5 after passing through the first rectangular slit 3 and a deflector 4. Current developed here is sent to a central processing unit 11 through a preamplifier 9 and an A-D converter 10, where it is compared with the preset value of the electron beam. The results are fedback to a heater transformer 7 through a D- A converter 81 to control the heater current. An alignment coil 2 corrects the electron beam if any abnormalty is found in the current density distribution, thereby dissolving the horizontal drift associated with the aging of the cathode section. |
