| 摘要 |
An electron beam attenuator decreases the intensity of an electron beam incident on a parallel electron detector by alternately deflecting the electron beam onto and away from the detector. A power supply controlling the attenuator is synchronized with the operation of the detector such that the electron beam only strikes the detector when the detector is not being read-out. The ratio of the time that the electron beam is incident on the detector to the time that the beam is off the detector is varied to give an adjustable attenuation of the detected electron signal. The intensity of the electron beam incident on the detector is monitored by a sensor separate from the parallel detector. When the beam intensity exceeds a pre-determined threshold, the attenuator is automatically activated, in order to prevent damage to the detector.
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