> A comment about the high rates w/o start counter:
>
> If we are swamped at forward angles a possibility to handle the rates is to include the forward Cerenkov boxes (R and L) into the trigger. At NIKHEF this was always done in Bigbite.
the cerenkovs were in the trigger for the forward angle paddles. Also, I
realized I should have been more precise: the *total* rate w/o start counter
is too high, but it should be possible to measure with just 1L paddle and
1R paddle (w or w/o Cer.) in coincidence (maybe only at moderate currents).
So, without start counter, the global coinc rate is about 1 KHz at 50 mA
and is not coming from the cell. This is too much for coda (note also we are
running w/o ADC sparsification until we settle tof voltages). Note
also that the coda max fastbus rate is close to that value (see coda manual)
regards,
tancredi
> >From the Cerenkov plots I have seen it looks to me that the forward Cerenkov are working well. With respect to efficiencies, I think is too early to use that term yet.
>
> ---------- Original Message ----------------------------------
> From: Tancredi Botto <tancredi@mitlns.mit.edu>
> Date: Sun, 21 Jul 2002 17:56:10 -0400 (EDT)
>
> >
> >some good data, more checks, considerations about background/trigger,
> >vacuum trip and software update.
> >
> >
> >Good elastic runs: 790 and 792 (the latter w/ modified trigger, requiring
> >================= or excluding cerenkov where appropriate). Run 790 (1 sccm)
> > is very long (ca 70k events).
> >
> >Background and rates: When I take start coutner out of the trigger (still
> >===================== requiring a L/R coinc) the trigger rate goes up by
> > a factor 20/30 - ca. 20 Hz/mA which we can't handle.
> >Conclusion: we are actually *swmaped* by background but have never
> >looked at it yet. This coincident stuff is clearly coming from upstream of
> >the target as the start counter integrates everything coming out of the IT
> >point. Later in the day I play with the slits. The values at which slits
> >start affecting the beam are slightly different that what compton people
> >found. After injection, I am able to reduce the normalized rate by a
> >factor of 10, without many changes to the lifetime (anyways short today,
> >5.5 mins at 1 sccm). I can inject 60 mA with slits at some intermediate
> >position, reducing the normalized rate a factor of 3. Note slits movement
> >is slow (can be changed) so I decide not to ask for a dynamic setting yet
> >(inject, close, measure, open, re-inejct..). CLearly beam position should
> >be as stable as possible, but experience tells you may end up doing the
> >slits game over and over again. Sure it'll be more fun with a collimator
> >and field on.
> >
> >KEEP start counter in trigger or coda will immediately crash.
> >
> >Trigger studies: given the above, can not take out start counter
> >=============== to study the missing e-p coinc with protons on left.
> > Still missing. I play with cerenkovs (see logbooks) and
> >enofrce them in the trigger for selected paddles, can improve S/N ratio
> >of elastics a factor about 3 (!!) in L11-L12. This should also come out
> >of analysis (see later).
> >
> >Vacuum problem: after overnight compton we are about to start. Set target
> >============== flow to 1 sccm. We then realizing injection valve was
> > closed and open it right away. Results in a vacuum
> >trip of the IT are. The transient flow (according to the epics screen)
> >went as high as 13 sccm (we know that don't trip at 10 sccm) at there
> >was beam on target. LIGIT switches off and turbos protected. Bad bad bad!
> >We understand that this could have happened at the flow controller, since
> >the gas pressure is not buffered. Found no comments about this
> >possible scenario in manual. It resulted in losing about 3 hrs before a
> >tech came in, brought roughin pump downstairs (no bypass either).
> >
> >
> >Workaround: it is very important to prevent operator dumbness.
> >========== I suggest that the control screens must inhibit setting
> > a flow if injection valve is not open.
> >
> >During down time for vacuum crash we confirm that we are definitely over
> >any mis-cabling issue regarding tof's and cerenkov. Everything is in the
> >right place in the data and the analysis now. Finally!
> >
> >Software: Little to add to jason's email. A number of people are taking
> >========= over this task and soon will have public utility routine. The
> > first goal is reproduce the 16x16 matrix plot, including
> > now making use of pid with the C data. Have fun!
> >
> >
> >
> >Plan: as discussed with John. Tavi will progress in our studies of the
> > retiming issues (seem solved) and trigger electronics. In general,
> > cerenkov are still very hot, and some suspiciously low efficient put
> > go to back burner tonight.
> >
> >Regards,
> >-- tancredi
> >
> >________________________________________________________________________________
> >Tancredi Botto, phone: +1-617-253-9204 fax: +1-617-253-9599
> >research scientist MIT/Bates, 21 Manning Av Middleton MA, 01949
> >^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> >
> >
>
> --
> Ricardo Alarcon
>
> 617-253-9508 (ph)
> 617-253-9599 (fax)
> --
>
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