Download UM PPS Lab Activities HV readout

UM PPS Lab Activities
- HV Readout Long Run
- Single Source Saturation Test
PPS meeting April 30, 2012
Waveforms from 1 Run Last Week
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HV Readout Long Run Setup
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HV board with 11 lines [90,100] at 815V
7 out of 11 lines with the circuitry to read them out
4 consecutive HV lines 94-97 connected to the DRS
Signal attenuation of 32 dB (40 times on amplitude)
Source sitting on top of the 1 mm slit graphite collimator
aligned over a single HV line (#96)
• DRS threshold very low (60 mV) so that no matter what line
had a pulse, the trigger line fired (Fan-in/Fan-out not OK)
 at the analysis lever a much harder threshold (200 mV)
was used to select real hit-lines
• Trick: DRS channel 3 signals is always smaller so 3230 dB
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Number of HV Pulses/Event
125
2
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HV Pulses Multiplicity per Channel
Last week result on the left quite different from this long run: now
almost only the closest line has hits, and they have a comparable rate.
Important to check with a larger number of lines (small improvement
the same test with the source on one of the two extreme lines)
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HV Pulse Amplitude
The trigger line (#3) has larger amplitude pulses (and #4 smaller)
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HV Pulse Rise Time (10%-90%)
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HV Pulse Width
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HV Pulse Pseudo-Charge=|A|*W
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Time Between Events
Why this
structure?
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Saturation Test
• Saturation: rate of incoming ionizing particles larger than the
inverse of the pixel recovery time (RHV*Cpixel) limiting the
number of discharges
• PDP geometry fixes Cpixel measured ~10pF, and with HV quench
resistor 200 MΩ RC~ 2ms  max rate O(kHz)
• Sources measured with a Geiger counter after one layer of
glass: (1R=2.58*10-4 C/kg ~2.1*109 ion couples)
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106Ru~130
mR/h ~7 ·104 ions/sec
90Sr~170 mR/h ~ 105 ions/sec
over the entire source area ~1.3 cm2 (pixel ~1.5 mm2)
• Idea: single HV line x 4 RO lines increasing the HV to maximize
the probability of a plasma discharge in the gas. Above a certain
threshold higher voltage should not produce more hits
• Background events/rates are measured without any source and
the data runs are only with 106Ru
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Test with R(HV)=200 MΩ
Based on the fit results at R(HV)=200 MΩ with C(pixel)=10 pF 
RC= 2 ms  saturation @ 500 Hz reached at 1900.6 V
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Test with R(HV)=1 GΩ
Behavior not very linear. Hint of saturation at HV>930V
(different HV line but same rate as before once RHV=200 MΩ s used)
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Extended Test with R(HV)=1 GΩ
The behavior seems more linear (except the first points) and
the hint of saturation at HV>930V has disappeared
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Full Test with R(HV)=1 GΩ
Second set of points the day after: no hints of saturation!
Jump of background events more and more important at higher HV
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No Saturation. Really?!
The ratio of the data rates with the two RHV values agrees with
the ratio of the maximum rates based on the recovery time 
we were saturated the whole time!
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Conclusions
• The HV readout long test shows that almost always only one
line has a pulse (are the nearby dead?)
• A few features (like ΔT between events) not yet understood
• Increasing the HV maybe/likely
– increases the active pixel area
– increases the active distance in the gas gap to have plasma
discharges
– reduces the recovery voltage to have a new discharge (only for
low values of HV it is needed more than one recovery time to
have back the line to a voltage high enough to produce another
plasma discharge)
• To test the saturation effect we will keep the voltage fixed and
just change the quench resistor. We expect that starting from
low RHV the rate will increase until a certain value after which
it is constant
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