Find the Klystron (SLAC) power supply EPICS screen
Choose "RF Operations" -> "RF/Klystron Control"
Choose "Klystron HV Ready Chain"
Look at the state on this screen
In the upper-right corner, look for "Delay Warmup"
If this says "30 minutes", then proceed to "Warmup On" below
If this says "0 minutes", then proceed to "Standby Reset" below
If the power supply has been completely shut off, then you have to start the "Warmup On" countdown, which will take 30 minutes to finish. After the timer, the power supply will be ready to have the HV turned up.
Click "Warmup On" at the bottom of the Klystron HV Ready Chain screen
On the popup window, click "On"
Close the popup screen if it doesn't automatically go away.
You will notice on the original screen that the "Delay Warmup" begins counting down from 30.0 minutes
If the power supply has been used recently, it is better to keep it in standby, because it is faster to turn back on, and also to not over-excercise the filament.
Click "Standby Reset" at the bottom of the Klystron HV Ready Chain screen.
Click "Reset" on the popup window
You will notice the "Filament PS I" timer for each klystron counting down from 5.0 minutes
After the timer, the power supply will be ready to have its high voltage turned on