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The timing between laser and electron beam is monitored and kept constant by a High Level Application (HLA). This is not the application described above (the one above synchronizes the four triggers from the timing system with each other, but not with the electron beam). The HLA is an application that is common to all laser + electron/x-ray synchronization across SLAC.
How do I know the target time is working?
The "Target Time" and the "Counter Time" should match.
When working correctly "Target Time" is repeatable and reliable, so you can go back to previous settings for "Target Time" and expect repeatable results. Caveat:
certain underlying inputs into the RF locking system can change on the scale of once a year, so do not rely on target times and things you dig out of the archiver from months ago.
If you change the "Target Time" and the "Counter Time" does not follow to within 0.1ns, then you should re-calibrate the femtosecond script. To re-calibrate, please see When I change the target time the counter time changes, but by the wrong amount, which is below.
If the "Counter Time" does not change at allIf they do not match, or you adjust the target time and the counter time does not change or changes by the wrong amount, then the HLA has stalled or diedlikely died. Please see When I change the "Target Time" the "Counter Time" doesn't change at all.
When I change the target time the counter time changes, but by the wrong amount
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