UM PPS Lab Activities- HV Readout Long Run

- Single Source Saturation Test

PPS meeting April 30, 2012

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Waveforms from 1 Run Last Week

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HV Readout Long Run Setup• 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 3230 dB

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Number of HV Pulses/Event

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125

2

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HV Pulses Multiplicity per Channel

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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

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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

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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) – 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

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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

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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

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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

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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?!

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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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