[PEPPo] Daily RC Report 5/31

[voutier at lpsc.in2p3.fr]

https://positron.jlab.org/wiki/index.php/Thu%2C_May_31%2C_2012_%28Voutier%29

Daily RC Report


In brief : the spectrometer set in positive polarity at 4 MeV/c, a  
clear coincidence signal of 511 keV produced by e+ annihilation is  
observed in the annihilation detectors, also a clear coincidence  
signal between TS1 and the PMT5 is obtained, and the central crystal  
measures a bremsstrahlung like spectra which end-point is about 4 MeV/c.

WE ARE PRODUCING, TRANSPORTING, AND MEASURING POSITRONS !!


Configuration change

http://opsweb.acc.jlab.org/CSUEApps/elog/entry/1788695

The shielding configuration on the beam right side at the polarimeter  
was changed and later tested with beam. The fiber array detector was  
removed in order to allow for this change. This leads to a factor 4  
reduction of the rates in the external crystals.

http://opsweb.acc.jlab.org/CSUEApps/elog/entry/1788708

The shielding around the annihilation detectors was also improved, but  
modestly because of the lack of free space.

Beam

Optimizing the beam for positron collection it was found that the beam  
left collimator is acting very strongly on the accidental rate. It is  
not clear whether this originates from a direct view of the target or  
from the interaction of the beam with the collimator, but the fact is  
that in retracted position the signal-to-noise ratio is once again  
improved.

http://opsweb.acc.jlab.org/CSUEApps/elog/entry/1788717

Early on day shift a new attempt to improve shielding around the left  
collimator occured. This was again reducing the noise but the  
collimator feature remains.

http://opsweb.acc.jlab.org/CSUEApps/elog/entry/1788901

Optimization of S1 and S2 currents for the collection of positrons  
with collimators wide open was performed. The optimum current is less  
pronounced than in the previous configuration but still exists.

Detectors

The annihilation detector was successfully tested. A wonderfull  
signature of the 511 keV gammas has been observed : there are indeed  
positrons at the exit of the spectrometer !!

http://opsweb.acc.jlab.org/CSUEApps/elog/entry/1788743

The Compton polarimeter check-out continued : the trigger is now made  
via a CFD which allows for a clear coincidence spectra. The effort is  
now put on measuring reproducible experimental asymmetries in rough  
agreement with expected values.

http://opsweb.acc.jlab.org/CSUEApps/elog/entry/1788794

DAQ

Some modifications of the DAQ scheme have been implemented to  
establish the coincidence between TS1 and PMT5. The buffering read-out  
mode was also implemented in order to reduce the dead-time. This  
modification will be validated over the next shifts.


Next 24 hours:

Thursday, 5/30 - SWING SL=Arne

   Change beam energy for 6.8 MeV/c
   Annihilation detector measurements
   e+ collection optimization at 3 and 4 MeV/c
   Compton polarimeter check-out

Friday, 5/31 - OWL SL=Jean-Sebastien

   Testing of the buffering mode
   Compton polarimeter measurements
   Establish parity Quality Beam

Friday, 5/30 - DAY, SL=Joe

   Set-up for 5.5 MeV/c
   Mott measurement of the beam polarization


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