[Clas12_rgb] [EXTERNAL] Re: RC meeting: today @ 2pm!

[Daria Sokhan]

Dear all,

Apologies for losing the audio connection in the meeting today, it was
quite heated and I didn't see that the phone switched off from speak-mode
-- I will summarise the main points below.

During controlled access today, while the accelerator vacuum leak was being
repaired:

* Krister worked on the over-heating connector lead on the power supply for
the Moller magnet. He has disconnected it, cleaned it, applied a special
sort of lubricant (details in his logbook entry, will appear tomorrow
morning) and tested it by switching the magnet on for a few hours. The
temperature crept up slightly, but both leads seemed to be behaving
equally, which is a good sign. Krister will test it more extensively
tomorrow morning.
* Rafo adjusted FC offset (from ~40 to 250 Hz).
* Florian tried to debug discriminator channel in slot 20 channel 2 of
BAND, which was giving a slightly lower rate: unplugging and replugging
didn't change that, so it'll be kept as it is.
* Raffaella replaced a broken cable on the missing FT Hodoscope channel and
saw a signal on fADC -- issue appears fixed:
https://logbooks.jlab.org/entry/3750244
* Yuri is looking into possible relation between radiation levels and the
leakage current on SVT. For the moment inconclusive, but he would like to
install an extra gamma monitor between SVT and the solenoid.
* Raffaella and I unplugged and replugged HV cable and fADC connector for
the CND channel S14L1R, which has been occasionally tripping off. It seems
responsive, but needs to be watched.

Raffaella has checked the RF offset for the recent runs and it looks
stable: https://logbooks.jlab.org/entry/3750178

Nick Z has completed gain-matching of the FT Hodoscope and uploaded the new
constants, which will be implemented from the next run:
https://logbooks.jlab.org/entry/3750212

Yordanka is producing monitoring histograms for the runs as they get
cooked, they are now saved here:
https://clasweb.jlab.org/clas12mon/rg-b/pass0/v17_fall2019/offline/

Nick M. presented a study of HTCC response (please find his slides
attached), where he compared the distributions between a spring run and one
from now. There is a spike at low values in the Sping data, no spike in the
current runs -- it was suggested that the difference is due to the new
trigger parameters (addition of DC roads). He also pointed out that the
distribution for S2 HS2 R1 is skewed to lower values and suggested that
this can be corrected by calibrating to the peak position, rather than the
mean of the distribution. Accuracy of the the gain matching for the HTCC
channels is on the order of 5-10%, so the slights skew in that one channel
was not considered to be a big issue.

Yuri S. gave a verbal update on the status of HTCC. The mirror
manufacturers are still not providing info on the exact composition of the
mirror coating (it's therefore hard to evaluate their aging). Near-future
plans include replacement of quartz-window PMTs and of active dividers with
passive dividers. New power supplies have also been ordered but not yet
received.

Valery showed a 2D plot of the number of photoelectrons in each sector of
the HTCC, from the current production data. Many of the half-sectors,
especially in the outer ring, showed a structure where there were many more
nphe in one half of the sector than in another. The half-sectors have a
single mirror, so the sharp separation of these high- and low-nphe regions
was decidedly odd. There was much heated discussion and argument over what
might be causing this and whether this has been observed before (we lost
audio connection in the scuffle). Valery called for HTCC simulations.

Valery then presented a plot of theta vs momentum for the electrons, which
showed a large number of events at low theta. low momentum -- with a Q^2
below 0.5. He suggested that since they don't pose physics interest we
could significantly reduce our electron trigger rate by cutting them out at
the level of triggering (applying a Q^2 cut on DC roads). We agreed that he
would produce new trigger firmware to do this and we would take a short
(~half hour) run to test this. In the meantime we would continue taking
data with the current trigger and only implement this once it's validated
and if RG-B agrees. Current data rate (700 MB/s) is only sustainable if
we're not taking data for about half the time, to meet the limits set for
us. Should we get good, steady beam, our data rate will become a problem.

About that -- the vacuum loss in the accelerator this morning was traced to
a flange which was not properly closed (unclear why that was so or why it's
only become a problem now -- mice?), they have tightened it and are pumping
the vacuum down. This will take all night and it's not known whether it
will fix the problem. Earliest beam delivery is expected tomorrow at noon.
Swing and owl shifts are cancelled.

The hall remains in Controlled Access and we have ramped down the solenoid
and torus to 100A. If anyone needs access to the hall tonight, please
contact me first -- the counting room will be unmanned. Access tomorrow
morning will be as normal.

Planned work for the hall tomorrow: Krister will check Moller magnet again,
Florian will get neutron counters for BAND removed, Yuri plans to install
the extra gamma monitor he needs for SVT studies.

A spin dance was planned for tomorrow (Halls A + C) -- when this eventually
happens the consensus was that we do not participate but use the time to
make a zero-field alignment measurement and take empty target or low
luminosity data. If they change the Wien angle, we will then do a Moller
measurement.

Have a good evening!
Daria









On Mon, 9 Dec 2019 at 11:40, Daria Sokhan <daria at jlab.org> wrote:

> Dear all,
>
> We'll have the usual RC meeting upstairs in the counting house at 2pm.
>
> Bluejeans:   https://urldefense.proofpoint.com/v2/url?u=https-3A__bluejeans.com_230805731&d=DwIBaQ&c=CJqEzB1piLOyyvZjb8YUQw&r=p0fOsYOqPes7kSrF0-ldLy8UQdwZWwpYV125WHZsrFE&m=bxMdN_MgodYZhFpK2RiAA3YZjwbYDgwEepbV0N-VDY4&s=0BPGwMe_soWKRhzk2lK-crzoQtg7vmiNMUWPakyPG00&e= 
>
> There has been another day of quiet physics running until ~5am this
> morning, when everyone returned to work and the accelerator threw a
> tantrum. MCC are currently down over vacuum problems.
>
> Hall B is in controlled access at the moment -- anyone who needs to do
> anything down there, this is your chance! Current best MCC estimate for
> beam return is 1pm -- pre-scale by the usual factor.
>
> Speak to you soon!
> Daria
>
>
>
>
>
>
>
>>
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