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User name silwal
Log entry time 15:02:57 on November 20, 2009
Entry number 301377
keyword=FFB woes and ditheringRecently we have had problems with FFB being paused for much longer than
dithering requires, which has resulted in beam instabilities.
The most recent long pause that I could trace (going through the
archives) was on Wednesday, Nov18th @ 10:55 pm or so. This was right
after the compton epics was rebooted:
http://www.jlab.org/~adaq/halog/html/0911_archive/091118224856.html
The red trace on the first attachment is the compton orbit lock pause,
which is 1 during a dithering cycle and 0 otherwise. The blue trace is
the hall A FFB pause, which is also 1 during dithering cycle and 0
otherwise. Before the epics reboot, dithering cycle is normal. After the
reboot, the connection to the compton server is lost, and the connection
seems to have been restored (according to the archive) only at about
12:46 am or so, after about 2 hrs, after which dithering is back to its
normal cycle. So the compton epics hungup seems to have interrupted the
dithering cycle is this case (something I will try to adapt the dithering
script to so that this does not happen again).
The second attachment shows a slightly longer than usual compton/FFB
pause. This is due to CODA hungup:
http://www.jlab.org/~adaq/halog/html/0911_archive/091116043318.html
Looks like the counting house crate (this is where the dithering script
is run) hungup in the middle of the dithering cycle, before the script
got to compton/FFB unpause commands.
Besides these I can't see anything unusual in the dithering cycle. There
are periods where it has been turned off/on manually, but only spotty
records of it in halog. It would be nice to have shift crews log every
time they turn the dithering on/off.
For now, as long as we make sure that the compton epics channels are up,
dithering should be fine. For compton tuning or compton epics reboot, we
should turn the dithering off.
A copy of this log entry has been emailed to: paschke@jlab.org, xiaochao@jlab.org, rom@jlab.org, riordan@jlab.org
Figure 1
Figure 2
