Microcavity Multipixel Performance Report 4

• HV Card and Dead Time• Pixel Uniformity• Run with 3 Rows of Pixels• Hardware challenges• Comments

April 22, 2014 University of Michigan PPS 1

C. Ferretti, D. Levin

Quick Recap of Single Pixel Results• Microcavity (MC1) filled with AAT0001 at 737 Torr• Quench: 100 MΩ HV card + 1GΩ pixel• Waveform similar for all the pixels:

|A|~1V, FWHM~2ns, Rise Time~2ns• Three main results:

April 22, 2014 University of Michigan PPS 2

64h single pixel <rate>10’

Rate stable over daysSix single pixel rate vs HVPlateau similar for all pixelscollimated 106Ru ~4-6 Hz

Single pixel (R5-3) arrival time σ≈5 ns (at 1150V)

Pixel Quench 1GΩ 100 MΩ

April 22, 2014 University of Michigan PPS 3

X-axis 500 μs/div Y-axis 200 mV/div

~1.3 ms dead timewith 1GΩ

X-axis 500 μs/div Y-axis 500 mV/div

• RC=200 M x 0.25 pF dead time=3 *RC= 3*50 μs = 150 μs𝝮• With 100MΩ at 1050V the single pixel 106Ru rate is doubled respect to 1GΩ

dead time not long enough back to the 1G , but this time on the HV card𝝮• Dead time is expected to be again ~1.3 ms. Instead it was still below 200 μs• Added an extra 1G in line with the HV, but this too had no effect on dead time!𝝮• The HV card itself is a capacitor (~2.6 nF, two ground planes) replenishing the

little pixel capacitance (fraction of a pF), while recharging with a characteristic time much longer new HV card and back to 1GΩ at the pixel

~150 μs dead timewith 100MΩ

Line 10 Recovery

April 22, 2014 University of Michigan PPS 4

The RO cable for line 10 (and the ground line nearby) was disconnected re-attached just soldering and worked and then got detached again

Line 1 Recovery

April 22, 2014 University of Michigan PPS 5

RO line 1 disconnected because of a damaged pad due to sparks between it and the nearby ground line re-attached with conductive epoxy (John)

Pixel by Pixel Test

“Current” result:51/63 OK (81 %) 2/63 Dead (3 %) 3/63 Noisy (5 %) 7/63 Sparking (11%)

April 22, 2014 University of Michigan PPS 6

Each pixel tested at 1050V as the only one in HV-RO crossing

Single Pixel Background Rate

April 22, 2014 University of Michigan PPS 7

Included one not-too-noisy pixel

Single Pixel Collimated 106Ru–bkg Rate

April 22, 2014 University of Michigan PPS 8

No systematic error includedfor the source positioning

Multi-Pixel Tests

April 22, 2014 University of Michigan PPS 9

Instrumented the first 3 lines (HV #3, 5, 7 and partially 10) without any dead or sparking pixel (and RO line #10). Total 23/29 pixels.

Multi-Pixel Background

April 22, 2014 University of Michigan PPS 10

2 3 2 3 2 2 3 3 3 0

Number of active pixel/line

106Ru 15 cm Above the PanelThe illumination was more or less uniform. The rate (at 1050 V) on each line is proportional to the number of active pixels on that line!Pixel rate(~ 0.3 Hz) more thanone order ofmagnitudeabove background(~0.015 Hz)

April 22, 2014 University of Michigan PPS 11

2 pixels line

3 pixels line

Going for The Full Test

April 22, 2014 University of Michigan PPS 12

1 GΩ on All Good Pixels• 1st time: one pixel sparked at ~970 V. The solder flowed across the

bottom of the resistor and shorted it out fixed• 2nd time: another pixel sparked at ~1000 V. While not shorted out,

the resistor had solder flows creating a current path fixed• 3rd time: around 1030 V, visible glowing of a dozen of the new

resistors discharges at a very high rate, suggesting that nearly all the newly installed resistors were providing an effectively very small resistance dismounted all of them and adding only a few new resistors at the time following the HV lines

• 4th time: readout line (#5) completely dead. Cable disconnected from the pad as for line 10? It turned out that both 50Ω on the RO card were fried (~26MΩ and 4.6MΩ) by one sparking pixel. Once replaced the line was OK

April 22, 2014 University of Michigan PPS 13

Lesson Learned• The accepted technique of microdrop of Kester solder-in-flux

deposited on the resistor pads is inappropriate as the tiny Pb-Ag balls can float around and underneath the component creating an archipelago of solder balls that can bridge the 1 GΩ (differently from PCB missing raised separator between the pads).

• The preferred method, so far, is to pre-tin the resistors and the pads, clean off the residue then solder the resistors into place

• One pixel showing high noise was recovered by dismounting, cleaning and re-soldering the pixel quench resistor. Likely it is possible to recover at least a few more sparking

• We will try to use the digital soldering iron (at 850°F) and the special solder 96.5% Sn / 3.0% Ag / 0.5% Cu used for the cables

April 22, 2014 University of Michigan PPS 14

More Pixel, Igor!Added a fourth row of pixels (HV #13) and things start to change - Background rate remains OK - Rate collimated source on pixel ~ OK - Noise on other lines is higher and higher as we get far away from RO

April 22, 2014 University of Michigan PPS 15

One More HV RowBackground and pixel close to RO still OK

April 22, 2014 University of Michigan PPS 16

But not the position of the collimated source is barely recognizable

Correlated Pulses on Scope

April 22, 2014 University of Michigan PPS 17

X=50 ns Y=500 mV RO Line2, Line 3, Line 4

The problem increases far from RO: with HV#18 on. It is not evenpossible to reach 1050V, background rates ~100Hz at 1020V!Possible explanations

18

Why? Possible ways that cells communicate1) Photon propagation

1) However, the cavities are metalized and embedded. 2) There is no obvious path for photons to move from one cavity to

another.3) The observed delay time of 100 ns is much too long for photons.

2) Ion-propagation. While the gas channels do not directly connect one pixel to another, there could be a significant gas gap between the top layer and bottom substrate:

Exaggerated view if top plate is not flush with bottom substrate

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Positive ions or charged CF4 can migrate through the gap to a nearby pixel

April 22, 2014 University of Michigan PPS 20

Conclusions• Collimated source over the nearest neighbor or 5 pixels away in both cases gives

~ 2 x background collimator works well• Current HV board prevents splitting quench resistors between pixel and HV line

(only pixel count) new one without ground planes near HV already designed• Hardware very sensitive: adding new pixels is very tricky and takes quite a bit of

practice and time, RO line can loose connection and the repair is difficult, … (Resistive paste in the via seems risky)

• The initial single spark often seen on newly connected pixel suggests the possible presence of dust next prototype better if assembled in a clean room

• Important to image the cavities before the assembly in order to match eventual imperfections with faulty/noisy/uncharacteristic pixels

• Suspect of not perfect parallel assembly of the two substrates (possibly due to uneven epoxy, not parallel planes, distortions, …)

• Results of pixels test results both in single and in combinations – pixel background rate much lower than the one whit (collimated) source– the rate of a line can be predicted by the number of pixels instrumented

they are really working as isolated entities