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User name V. Sulkosky/M. Cummings
Log entry time 18:59:14 on March 15, 2012
Entry number 366584
Followups:
keyword=RHRS Deadtime and DAQ ChangesOver the weekend and earlier this week, we saw instances where the RHRS
deadtime was much worse than the LHRS at comparable rates. Melissa and I
checked and found that after runs 22163/3077 that the beam current was
reduced from 100 nA to 50 nA. The real currents were probably closer to
80 nA and 15 nA from what I was told earlier this week. With the reduced
current the RHRS deadtime was much better and could even take about
6.4 kHz with about 18% deadtime (from run 22193). This current dependence
could have been related to a trigger that was double-pulsing.
I had Melissa look at the T1 trigger connected to a multi-hit TDC in the
RHRS. Below is a summary of what we found. We see for the higher
raw rate runs that about 25-30% of the events have more than one hit
in the TDC for T1 and T3 (as measured in the LHRS). Hence both HRS
see about the same rate and number of additional hits for their
respective triggers. However, for some reason, the RHRS sees a much
higher deadtime. A summary of a few runs is presented in the table below:
Run Raw T1 Rate [kHz} Prescaled Rate [kHz] Multi-hits [%] Deadtime ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 22163 235.1 2.8 27.1 19.85 % 22164 45.0 1.1 6.0 3.24 % Run Raw T3 Rate [kHz} Prescaled Rate [kHz] Multi-hits [%] Deadtime ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 3077 236.5 3.9 25.4 4.57 % 3078 45.8 1.5 5.8 1.45 % 3107 25.9 6.5 3.4 15.38 %During the controlled access, I tried to search for a double-pulsing T1
in the right arm. I was not able to see any additional pulses with cosmic
rates. I changed T1 to be the or of S1 and S2m, which gave me a rate of
about 1.6 kHz with ps1 the deadtime was about 9 %. I also reduced
the S1 discriminator threshold from 15 mV to 40 mV to get more rate.
I still saw very little multi-hits in the TDCs (1%). Before leaving, I set the
S1 threshold back to 40 mV and T1 to be the "AND" of S1 and S2m.
All this was done before we looked at the multiple hits for run 3077 and
realized this might not be the issue.
I did make some changes. I removed the signals that would go to T5 and
T6 in the TS2 module. T5 was the S2mor and T6 was the Gas Cherenkov
sum. I moved the GC sum to channel 9 in the level translator, which
will show up as channel 8 in the normalization scaler display. I also
removed the twisted-pair cables going to the TS2 except for T1, T2 and
T8. Some of these cables had signals that were not properly terminated
and hence at high rates could have caused reflections.
We will continue to monitor the deadtime and trouble-shoot the problem if
it still exists.
A copy of this log entry has been emailed to: brads,melissac,rbziel,camsonne,rom
RHRS Run # 22163
RHRS Run # 22164
LHRS Run # 3077
LHRS Run # 3078
