Re: [BLAST_SHIFTS] Fri 05/23/03 0-8am

From: Karen Dow (kdow@mit.edu)
Date: Fri May 23 2003 - 09:56:51 EDT


        The problem with the event rate is due to a "feature" of the Trigger
Supervisor that we discovered last summer. If the TS is in Common
Strobe mode (which it is, for physrun), AND a trigger input is enabled
(we enable the first 4), AND an enabled trigger input is disconnected --
THE CS WILL FIRE THE EVENT TRIGGER. Evidently one of the chips inside
the TS does not operate as advertised; with no input connected, floats
true.

        This morning, I found that one of the 2-pin ribbon headers (PHYS0) was
almost disconnected at the level adapter before the TS. So the CS (the
OR of TOF meantimes) was triggering events; rate limited by a lot of
junk in the wire chambers. That's why Runcontrol trigger rate was
independent of selected trigger, or even beam (OR of all TOFs runs at
600+Hz on cosmics).

        You can see this on a scope, by looking at PHYS0 (or 1,2,3) and CS
before the TS, and L1A from the TS. L1A should only be present if
PHYS0 is. L1A<=PHYS0<=CS.

        Doug suspects the wire chamber junk is because the low-voltage supply
for the thresholds is off; will check with hall access soon.

                                        Karen
Michael Kohl wrote:
>
> Dear colleagues.
>
> this night's shift was a debugging shift, unfortunateley again with no
> useful data.
>
> CCR provides improved beam with BQM TBLR=180,50,120,90, with slits at
> LRTB=-8,8,2,-8. Max. injection 100mA, lifetime 15-20 min.
>
> /scratch/dblast07 appeared to be full, runs pro2003-01...99.dat removed
> after checking that they are all identically present on spuds (see
> md5sum-* on ~blast/ ).
>
> Again like last night, a lot of noise showed up in the wire chamber when
> displaying events with nsed.
>
> Noticed that the Coda event rate was constantly about 170 Hz, independent
> of ring current (!). Also, the coda event rate differed very much from the
> PHYS* and BPHYS* rates shown in visual_scal. Further analysis showed that
> 170 Hz event rate was also stable against change of trigger settings
> (varied between elastic_only, elastic_coinc, elastic_een and physics, and
> with a highly biased craptrigger.settings.
>
> At 3am, CCR optimized beam quality a little more, resulting in
> BQM TBLR=140,40,100,70, with slits at LRTB=-6,8,1,-8. Max. injection
> 100mA, lifetime 15-20 min.
>
> Still, nsed shows Xmas trees. Noticed that in most triggered events less
> than two Tofs have fired (either one or none).
> Doubting if a poor beam quality is really the reason for the noise events.
> Requesting to switch off the beam, we find that still we have 170 Hz event
> rate and Xmas trees (run #481). This is also the case after switching off
> the Wch HV's (run #483).
>
> Assuming we have a problem with the Trigger Supervisor (TS), we
> power-cycle the VME crate in rack 4 (didn't help)
>
> Noticing that there are Camac problems (cnaf 1 23 0 0 etc.), we reset and
> power-cycle also the camac crates and the VME crate in rack 3.
>
> Still, Coda takes data without beam and Wch off at 170 Hz, nsed showing
> Xmas trees. We have no further idea and wait for Karen and Doug to come
> in.
>
> Hall not yet open, not until technicians are ready to work on ion
> polarimeter.
>
>
> Regards,
>
> Michael and Aaron
>
> --
>
> +-------------------------------------+--------------------------+
> | Office: | Home: |
> |-------------------------------------|--------------------------|
> | Dr. Michael Kohl | Michael Kohl |
> | Laboratory for Nuclear Science | 5 Ibbetson Street |
> | MIT-Bates Linear Accelerator Center | Somerville, MA 02143 |
> | Middleton, MA 01949 | U.S.A. |
> | U.S.A. | |
> | - - - - - - - - - - - - | - - - - - - - - -|
> | Email: kohlm@mit.edu | K.Michael.Kohl@gmx.de |
> | Work: +1-617-253-9207 | Home: +1-617-629-3147 |
> | Fax: +1-617-253-9599 | Mobile: +1-978-580-4190 |
> | http://blast.lns.mit.edu | |
> +-------------------------------------+--------------------------+
>
>



This archive was generated by hypermail 2.1.2 : Mon Feb 24 2014 - 14:07:29 EST