Shutter Control

This lets you control the shutter (which allows or blocks the the x-ray beam from reaching the microscope chamber).

Automatic

means that the shutter will be opened during a scan and will be closed at all other times. This is the right choice most of the time.

Open / Closed

will keep the shutter permanently opened or closed. To protect the sample from radiation damage, you shouldn't keep the shutter open all the time unless you have a good reason to do so.