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.
>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 Alarcon617-253-9508 (ph) 617-253-9599 (fax) --
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