1. Setup for Cosmic Ray Test of VPA panel, using MiniDAQ
D. Levin, Feb 8, 2012
VPA: 600 Torr Ar CO2 (1%), filled on Jan 17, 2012
1” DESY mini-scintillator hodoscope placed under panel at intersection of HV and readout lines.
24 RO lines, 14, HV lines.
Hodoscope HV = 850 V., trigger rate = 3.6 muons/min, located 2.5 inches under panel, and offset
Run: run VPA HV = 830 V. After 5 hr, 15 min, 1019 triggers, only 7 have coincident TDC hits.
This is very low rate- less than 1%. However, the hodoscope is offset from the panel, and removed too far away.
At 5 hr, 38 minutes into run, I bring it closer and directly under active region.
Place Ru-106 source in holder, about 2.0 inches over active region on top of panel.
Trigger rate is now 153/4 ~ 38 CPM. But panel coincidence rate is still low- don’t see any additional hits beyond the 7 obtained with cosmics.

4. PDP pick-off card:
Configuration: x200 attenuation. 50 ohms termination HV
200
pixel 49
Signal out to 50 ohm ribbon coax to Hedgehog Card 1 70
Heavy, 1” Ground braid

5. Scintillator Hodoscope
Panel hookup to Minidaq
CSM
Mezzanine hedgehog
50 X attenuation
Row 24
Row 1
Pickoff card
200x attenuation
PDP VPA 600 Torr Ar CO2 (1%) HV
Col Col
Scintillator Hodoscope
To trigger logic and TTCvi

6. Setup for Cosmic Ray Test of VPA panel, using MiniDAQ
D. Levin, Feb 8, 2012
18:15
Make the following changes:
Place source directly on the panel- so tha tit radiates lines 4-7, and also the hodoscope.
Increase HV to 840
Lower minidaq threshold from 200 to 50 mV
Take data run72410
After 2hr, 26 minutes, trigger rate = 4.5 Hz
Events from Ru-106 – Triggered by hodoscope
Hit distribution- corresponds to source location:
Made with ADC > 50 counts (see next page)
Time of hit relative to trigger.

7. These are the ADC distributions for the first 8 channels
These are the ADC distributions for the first 8 channels. The good hits appear to have levels over 50. The cuts on the previous page are ADC> 50
ADC Counts

8. Setup for Cosmic Ray Test of VPA panel, using MiniDAQ
D. Levin, Feb 8, 2012
18:47
Make the following changes:
Remove source
2) Leave HV =840, threshold =-50
3) Take cosmic ray run: data run72411
…check back tomorrow

9. D. Levin, Feb
The work for the past few days is summarized here: Most of the effort has been focused on getting the MiniDAQ to work – without cross talk, and to record accurately the source on the panel in the location where the source is actually positioned. This has proved to be very difficult.
The problems:
The PPS radiates and produces hits on Mezz card even when the mezz is not hooked up.
Remedies:
ground everything, shield the mezz card, and especially ground the Pikov card.
Tried shielding the panel by placing foli on all surfaces. This resulted in HV discharges thru the glass to the foil.
Made foil covered box and placed over whole apparatus. No effect.
In the end found that the Pikov was not properly grounded. Attach ground strap.
b. Use new Pikov card with proper impedance termination.
The ribbon coax that convey the PPS signals for external trigger formation were universally bad. In every cable bundle there was at least one cable with a poor ground.
Remedy: found other higher quality 8 conductor ribbon cables- with lemo connectors.
Needed to properly attenuate at the pikov card and on the Hedeghog.
For Ar CO2 signals (600 Torr), use 200X Pikov and 50X HH card.
The panel has wildly varying discharge voltages depending on the row and colum location. The HV is at column
For rows from 1-24 the HV needs to be varied by V to achiev3 the same response. At other HV locations the panel easily enters constant discharge mode.
Tried using 200 Meg resistors- but the HV card I used seemed to radiate high noise levels. So still using 66 MegOhm.
Spontaneous hit rate on panel VPA has become very high on some channels.- hundred or so Hz at 820 V.
It is very hard to extract reliable results.
Enormous variation in rates across pixels. Cannot find an operating voltage that allows all channels to operate with even remotely the same efficiency.
This panel has become very difficult to use. I will re-evacuate, bake and refill with the same gas
Re-pumping and baking panel, Will refill this panel tomorrow Feb 14, 29

10. Proper configuration for minidaq and reaodut:
200 X pikov card
50 x attenuation on HH
Set external discriminators to 200 mV.
Form OR of 24 channels
Send output to TTCvi trigger input
With long blue ribbon cables (about 20 m) – set
Bunch Counter offset to 4000
Search window 75
Threshold -150 to -250
Match window 50

11. Monda afternoon, 16:00 Feb 13:
Re-install Panel VP-C with the 600 torr CF4
Instrument with new Pikov4 card and Hv on channels
Ramp up HV until ~ 1700 where I hear crackling, frying sounds from panel.
This continues then stops. Increase voltage. Sounds return, then stop.
A few pulses observed- but mostly just hear this crackling sound.
Abandon further testing.