Where this command is found:
This command is found in the BCS main window under the pulldown menu Video. Selecting it creates a check mark next to the menu item and lights up the Enabled LED symbols in the Feedback system status section of the BLC main window (if the enabling is permitted of course).
For this to be permitted, there needs to be beam in the storage ring, X-rays coming out of the monochromator (check Imono Out) and the fast shutter needs to be closed
What it does:
Selecting this Menu item activates a video based feedback system that helps stabilizing the X-ray beam focus spot, that is normally tuned using M1 tilt and Chi2.
The status of this functionality is indicated by a series of LED symbols (#6) in the BCS main window.
What it means:
This simple beam position monitor works as follows:
The beam creates a visible image on a YAG crystal attached to the blade of the FastShutter. The image is recorded with a fixed camera. The position of the beam image on the camera serves as reference for the tuned position. Any deviation from the optimal tune creates a vertical and/or horizontal movement of the beam and thus the image on the YAG. This is automatically corrected using either the M2 tilt (vertical) or Chi2 (horizontal).
