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Beam Status, Shutter, accelerator and moderator information
Wiki > Accelerator Information
Information about the beam current and instrument shutter status is stored in the main accelerator control computer system, though a shutter is local to an instrument it is part of a safety system and we do not have direct access to it ourselves. Also the accelerator computer system can only read main shutter status - opening/closing a main shutter can only be performed using a physical button in the cabin.
This information is fed from an IOC running on a machine on the accelerator network (merckx.isis.rl.ac.uk). This is a Open VMS machine with the EPICS distribution from here. The IOC is set to run on boot time and is auto-restarted if it is not present, it will also auto-restart if it receives too many errors, but some failures can cause it to hang.
You can log onto this machine using details on usual access page (you will need to use ssh via something like PuTTY)
The most likely cause of a problem is that the local database has stopped updating, thus giving an unchanging value. You can can check the server log file with:
cd beamlogdir
type isisbeam.log
And see if there are errors about parameters not updating. Probably easiest thing to do is to kill the service and let it restart, then see if errors continue in the log. First type:
pipe sh sys | sea sys$input isisbeam
you will see a line like
26E12DAA ISISBEAM LEF 6 132040 0 00:00:01.40 284 241
26F991FC ISISBEAM_1 HIB 4 2416385 0 00:08:24.20 9589 3173 MS
[ISISBEAM_1 is a sub-process of ISISBEAM and will die when you kill ISISBEAM] The first number is the process id, in this case type
stop /id=26E12DAA
to kill it, then wait for it to restart (may take up to 30 seconds). Use the above pipe command to see then it has restarted, and then check isisbeam.log again. Look for messages after the Starting iocInit line in the file
The asyn parameters that are served by the IOC are mapped to VISTA parameters (this is the accelerator control system). You can see the mapping with:
type params.txt
a line like
beam_ions float t 0 IDTOR::IRT1:CURRENT
means asyn parameter beam_ions (in the IOC Db files) is mapped to VISTA parameter IDTOR::IRT1:CURRENT. The other columns are related to data type and how the programs tries to check for stale (non updating) values. If the isisbeam.log indicated a huge number of errors for a particular parameter, then this could affect reading other parameters - after a certain number of errors the program restarts, but if it starts restarting too frequently this can cause PVs never to reconnect properly. In that case you may need to temporarily remove a line, but seek advice first.
You can read the VISTA parameter directly on MERECKX if you think the issue is with the IOC e.g.
db_access IDTOR::IRT1:CURRENT
db_access t1shut::n1_overview:sta
you can search for errors about a particular parameter by e.g.
sea isisbeam.log IDTOR::IRT1:CURRENT
If you killed the ISISBEAM process above it has restarted, then the isisbeam.log file will only contain values since that restart. you can look at the previous log file by adding ;-1 to the file name
sea isisbeam.log;-1 IDTOR::IRT1:CURRENT
To see all log file versions type dir isisbeam.log
If something does appear to have gone wrong with this service (e.g. values are not updating) you should get in touch with the accelerator controls group. The easiest way to do this is to call the MCR and find out who is on call.
A "Beam current" block may not be showing the accelerator beam current, it may be showing the effective beam current from the DAE. Blocks read from the accelerator will all be referring to global PV names starting AC: and TG: so if the block refers to an IN: it will be something on the local instrument. The DAE:BEAMCURRENT value is the effective DAE beam current, but if the dae is not counting (SETUP, WAITING, PAUSED) then this value will be zero. If the DAE is vetoing this value will vary between 0 and something else depending on what % of frames are being vetoed. If the chopper is being run at a lower frequency, the value will be lower too as the DAE is seeing less pulses and hence a lower effective beam current.
If the third column in params.txt contains a z (e.g. tz) then this means that the parameter will be monitored for a stale (non updating) state and if this is detected it will send 0 as the value to IBEX/SECI. At time of writing this had only been requested for the decoupled methane, sending 0 when the value is uncertain means they will go into a WAITING state as they run control on methane temperature and it is important that they are not collecting data when a methane charge-change happens. In future the value could be EPICS alarmed, but for SECI instruments we need to send 0
You may be able to confirm a value is not updating by running db_access on it a few times with a reasonable time delay inbetween, but some values are quite stable or fluctuate only a bit so this may be difficult to determine. You can view the typical value and variation in an accelerator parameter by following the links on values at http://beamlog.nd.rl.ac.uk/status.xml
If this is after a shutdown, check the st.cmd and see if epicsEnvSet("SIM_ISISBEAM", "1") has been uncommented to stop out of cycle errors, if so comment it out and then kill the ISISBEAM process so it can restart
if you type
dir [--.db]
you will see all the db files used by the program, you can display one to screen using e.g.
type/page [--.db]isisbeam.db
On MERCKX $(P) is "" so there is no prefix to PVs you see listed. To use caget you first need to set an epics address list as broadcasts do not work (they require privileges). So type
def EPICS_CA_ADDR_LIST merckx
and then you can use caget or camonitor on values e.g.
camonitor TG:TS2:DMOD:METH:TEMP
You can browse the Db file source on the web
The program will restart after too many errors are detected. If you run:
camonitor ICS:IB:ERRCNT ICS:IB:CHANERRCNT
ERRCNT is the total number of channel reads errors since last successful read, CHANERRCNT is the number of channels currently in error. When ERRCNT passes a threshold, the program restarts and you will see these PVs as well as other beam PVs briefly become disconnected. Note that CHANERRCNT may be non-zero while ERRCNT remains 0, this means that there isn't an actual read error on the channel, but it is considered in error for another reason. You would typically need to look at isisbeam.log to tell. This usually means the program thinks the channel is stale. Each channel, even if it does not change value, should have its timestamp updated by the accelerator control system. Also things like beam current are flagged as suspicious if their value (when non-zero) is exactly the same value for a long period of time.
check isisbeam.log but could be a scaled up version of intermittent dropouts leading to extremely frequent restarts and so no time for PVS to get connected. In bad cases you may need to remove lines from the params.txt file described above to stop the erroring reads being attempted.
db_access LOCAL::BEAM:TARGET2
on merckx will show the local database TS2 beam, if this seems unusually stable then the accelerator controls vista system may have frozen.