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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:
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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 all, then the HLA has likely died. Please see When I change the "Target Time" the "Counter Time" doesn't 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 died.
When I change the target time the counter time changes, but by the wrong amount
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You'll now need to recalibrate the script following When I change the target time the counter time changes, but by the wrong amount.
Counter Time is 1.2e11 and Doesn't Change
This happened after a power outage. There is a frequency counter on top of the DM controller (Keysight 53230A) that measures the delay between two triggers, at least one of which is the regen. If this counter reads 120 Hz then it is in frequency counting mode, not time interval mode, and is measuring the regen frequency. The EDM panel then converts this number to ns by multiplying by 1e9, hence the 1.2e11 number.
To setup the controller:
- Unplug the ethernet cable from the back and wait a minute or so. The controller needs to have remote control disabled to change settings locally.
- Turn Ch. 2 on if it isn't already.
- Set the device to Time Interval mode by pushing the Time Interval Button.
- Set both channels to 50Ohm, DC coupling.
- Adjust the trigger settings for each channel to Rising slope at -200mV.
- I don't remember exactly how to adjust each setting, but it works similar to an oscilloscope.
- When finished the display should look like this:
Notice the trigger settings in the top tabs.
I'm trying to move the oscillator cavity motor, but the measured frequency isn't changing
Is the motor initialized and homed? The motor homes in place, so it can be safely initialized and homed.