Revision as of 18:41, 19 November 2015

A collection of TOF tools for experts only!

Command line scaler display

While EPICS provides a GUI display of TOF scalers, there may be situations when a simple text view of scalers is desired. For example, such simple viewer can be run in a terminal app on your smartphone or tablet while working in the Hall away from a monitor (checking cables, searching for light-leak holes in the wrapping, etc.). To do that:

1. Open a shell (terminal) window

2. Login to ROCTOF3 under hdtofops account:

   ssh -X hdtofops@roctof3

3. Execute

   scaler/ao/jledScaler -n

4. Current rates in Hz will be shown for all TOF channels. Pay attention to the top line where MIN and MAX rate is printed. Under normal running conditions, minimal rate of 0 indicates that one or more channels have problems (tripped HV, bad cable connection, broken discriminator, etc). Max rate with beam off shouldn't exceed 600-700 Hz. Higher rates need to be investigated for a possible light leak.

Notes:

• -n option above means "do not initialize the scalers and use their current settings". This is almost always desirable during the run in order to not disturb DAQ or EPICS scaler daemon. In a rare circumstances when ROCTOF3 power was reset and DAQ hasn't been run yet, this option should be replaced with "-i" to initialize the discriminator thresholds to default 30mV values.
• -t option can be used to change the default 5 seconds timing interval for rate averaging.
• if you are troubleshooting one particular TOF channel then -c option can be used to display this channel only (for example, "-c N5" or "-c B43").
• this program can be run concurrently with DAQ or EPICS scalers without disturbing them.

Testing for potential light leaks

Significant light leaks will be obvious in the scaler rates going into kHz or even MHz range with beam off. However, small "micro-holes" in the wrapping will increase rates by hundreds of Hz and may not be noticed. To conduct a periodic check or to investigated a suspected light leak:

1. Physical access to the Hall is required to turn the ceiling lights on/off.

2. Before proceeding, verify with everybody working in the Hall that they'll be OK with dimmed lights in the Hall for a few minutes.

3. Login to ROCTOF3 under hdtofops account:

   ssh -X hdtofops@roctof3

4. Insure that ceiling lights in the Hall are on and TOF is well illuminated.

5. Execute

   scaler/ao/jledScaler -n -L

The program will run for 30 seconds measuring the rates and then pause.

6. At this point, use the light switches near the entrance door to turn off all ceiling lights.

7. Unpause the program (hit "Enter"). Rates with lights off will be collected for another 30 seconds.

8. Turn on the ceiling lights.

9. The program will show change in the counting rates between lights on and off, with the worst offenders printed at the bottom. If the variation in rates exceed 20%-30% then notify the FSU crew about the need to examine TOF wrapping for potential small holes.

Searching for small holes in the TOF light-tight wrapping

IMPORTANT! While the bottom half of the TOF can be reached from the floor or from the step-ladder, the higher part of TOF should be serviced from the man-lift in the Hall. Only people with man-lift training and certification can operate and work on the man-lift! Do not attempt to repair higher areas of TOF if you do not have such certification!

If, after following the previous section, a light leak was detected and the hole needs to be found and repaired:

1, One, obviously, needs Hall access with beam off. A small and well-focused flashlight and a piece of black felt (from TOF cabinet in the Hall) is required. You also need to run terminal app on your smartphone or, alternatively, position one of the monitors so that the screen is visible from your work area, and zoom the font in the shell window to the max so that it is visible from many feet away.

2. As before, login as hdtofops into roctof3 and excute

  scaler/ao/jledScaler -n -t 1 -s -c NAME

where NAME is the name of PMT which exhibits alight leak (for example, N5 or S14 or T22 or B42).

3. While monitoring the displayed counting rate, start illuminating the small areas of a suspected TOF module with a flashlight until a sudden increase in the rate is observed.

4. Carefully examine tedlar warpping in the found area for any signs of micro-holes, wrinkles, non-uniformities, etc. Cover each suspected spot with the black felt until a decrease in counting rate is observed. You have found it!

5. Apply a small patch of black tedlar (available in the TOF cabinet) to the damaged area. Verify with the flashlight that this spot is no longer sensitive to the external light.