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User name Jin Huang
Log entry time 20:33:14 on November23,2009
Entry number 302171
This entry is a followup to: 302096
keyword=RHRS Optics Problem
As a search for proof that RHRS Q3 polarity is inversed, we ran a quick optics check on single carbon foil.
How does the check works.
As shown on page 8 of hall A NIM paper, HRS magnets have a focus effect on y direction. Say for central carbon foil, no matter the phi direction of out coming particle, it will be focused to a specific focal plane y position. When Q3 is inversed, this focus will be broken. The approach of this study is by checking this focus property before and after HRS polarity changes.
We selected a positive and a negative polarity runs for each spectrometer. For each run, 2 plots are generated: Focal Plane Y hit distribution (Left) and React Z Distribution (Right)
first plot :
Top : LHRS Positive Polarity
Bottom : LHRS Negative Polarity
Top : RHRS Positive polarity
Bottom : RHRS Negative Polarity
As you can see, LHRS Y-Phi optics properties remain similar before and after polarity change. However, VZ reconstruction on RHRS positive run is messed up. Also the Y focusing is gone.
Therefore, RHRS optics has problem at positive polarity. Compiling previous information, it's most likely that Q3 is inversed.
Besides optics study, we also recorded trigger rate before/after turning off Q3 on RHRS.
Conf. Current/uA LHRS T1/Hz RHRS T1/Hz
Q3 ON 10 810 700
Q3 OFF 10 800 850
Which means we are getting better acceptance after turn off Q3. Therefore we move to low current production with RHRS Q3 off