Table of Contents

Regen Laser Issues

If the regen pulse train isn't visible on the scope above the regen, then the regen isn't running. Most likely this is because an interlock was tripped and needs to be reset.

Resetting the Regen Interlock

  1. Check and fix any laser room interlocks that are tripped, view the interlocks by looking at the LSS control panel → Interlock Status Screen, see Figure 1.
  2. Reset the regen signal delay box by clicking the Reset button (Figure 2, at the end of the table near the oscillator)

Pre-amp Laser Issues

If the pre-amp output isn't visible on the MPANear/MPAFar cameras, then there is likely a problem with the pre-amp pump laser (CFR laser). The most common issue is the Q-switch of the pump laser getting set to an internal trigger. See bellow for how to change the trigger settings.

If the pump laser refuses to turn on, check the controller for errors. A low water error for the CFR chiller is the most common. See below for how to refill the chiller.

Internal Trigger

Sometimes the laser ends up with the Q-switch set to an internal trigger rather than external. To fix: 

  1. Click the down arrow to get to Q-Switch.
    1. If Q-Switch doesn't appear you are probably in a sub menu, navigate to the top to find the option to go up a menu.
  2. Hit enter.
  3. Click down to QS sync.
  4. Click +/- to change to EXT.

Low Water Error

If the chiller water for the pre-amp pump laser is low, the laser will not turn on. To refill the chiller, follow the instructions in the chiller manual: Link to chiller manual

Shutters Won't Open

The LSS has two categories of shutter: the laser room shutters and the transport shutters. All of them are in the laser room, but the transport shutters are all located right before the transport to control sending laser into the tunnel.

In addition, there is an EPICS controlled shutter behind the transport shutters that can also block the laser.

Laser Room Shutters Won't Open

  1. Check and fix any laser room interlocks that are tripped, view the interlocks by looking at the LSS control panel → Interlock Status Screen, see Figure 1.

Transport Shutters Won't Open

  1. Check and fix any tunnel interlocks that are tripped, view the interlocks by looking at the LSS control panel → Details for the FEA LSS-2, see Figure 1.

EPICS/EPS Shutter Won't Open

This can occur because of interlocks within the Experimental Protection System (EPS), things like the oven being inserted. If this occurs, call the FACET contact responsible for the laser system.

Auto-aligner Issues

Auto-aligner Sum Counts or Ref RMS Errors

The auto-aligner compares each image against a reference to make sure it doesn't try to align the beam when it isn't supposed to. For example, if a shutter has been inserted upstream and blocked the laser from reaching the alignment camera. If the auto-aligner detects a difference between the reference image and the current image, it will throw an error explaining what differed between the two image. Often these errors will appear while the laser is warming up as the profiles change. Taking new references will typically fix the issue.

  • "Sum counts has changed" means that the total pixel sum does not match the reference image within the tolerance.
  • "RMS spotsize has changed" means the width of the fit to the spot does not match the reference image within tolerance.
  • "Camera exposure time changed" means the exposure readback value doesn't match the value recorded for the reference image.
  • To fix, do the following:
    1. Check the image on the multi profile monitor and verify the beam looks normal, isn't clipping, etc. 
    2. If the beam looks okay, stop the auto aligner by pressing Stop Alignment.
    3. Grab new reference images by pressing Grab References.
    4. If the error pops back up, wait a couple minutes, then repeat the process.
  • "Image timestamp more than 10s old" means the image is not current. Sometimes this occurs due to latency/network issues and will fix itself. If the problem persists: 
    1. Check if the camera is acquiring images.
      1. Open the pydm all cameras panel (FACETHOME→Profile Monitor→LI20→PYDM All Cameras).
      2. Find the problem camera, probably in either the Laser Room 1 or Laser Room 2 tabs.
      3. Check that the camera is acquiring: The camera should have a green box around the FPS field (the box might blink yellow/green if the exposure is long). 
        1. If it is acquiring, then the issue is likely somewhere else, proceed to step 2.
        2. If it is not acquiring, see Camera Servers.
    2. Check if the timing system is working. When the timing system is down the images don't get timestamps.
      1. If the timing system is down, disable the timestamp check from the auto-aligner expert panel.

Figure 1: LSS interlock screens.


Figure 2: Regen signal display box front panel.

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