I preface this entry by noting there a lot of things I do not know about the implementation of timing at SLAC. I know in principle what is happening, but the implementation is much more complicated.
The SLAC timing system provides 4 triggers to the S20 laser system. One for the regenerative amplifier (120 Hz) and three at 10 Hz for the pulse slicer, pre-amp pump laser (CFR) and main amp pump lasers (2x SAGA). Thus to change the timing of the laser relative to the electron beam four triggers have to be changed. This is unusual for SLAC and was implemented so that we can change SAGA+IR timing and reduce energy remotely without turning down the pump lasers. At the moment the process of making sure all four triggers are sync'd is done through a python script. If this works well enough an SIOC can be created to streamline the process.
This page shows how to enable synchronization of all four triggers and change the timing of the laser relative to the electron beam.
1)
Open a terminal and connect to facet-srv01 (I dunno if it HAS to be 01, but I know that works). User profile doesn't matter. Then type
source use_python3.sh
pydm /home/fphysics/jemay/code/panels/LaserCoordination.py
It is important that this program is only running on one computer at any given time. It does not have to be on the computer you're using to change the timing.
This will pop a screen that looks like this:
2)
"Load Current Offsets", which will calculate the timing difference between the regenerative amplifier and the other three triggers:
(We know the offset box needs to be bigger).
3)
Select "Tracking Enabled"
4) Adjust the "target time". (PV OSC:LA20:10:FS_TGT_TIME) I have no idea what the absolute value of this PV means, but relative changes are true to expectations. If you change the value by 1 ns the laser will arrive earlier/later by 1 ns. You can change this target time by 1 fs, but I can't recall if that will work. We can test this when EOS is going. The units on the display are nanoseconds.
Once tracking is enabled you can also change the target time in the vitara panel or just writing to the PV.
