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Production #291HV

HV

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3 7 12

Before After

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Production # 503HV

HV

Before After

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Diode scan (no HV) from damaged tube fromCERN HPD #291

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Setup and readout

HV =10 kV

Ortec Preamp

A~0.5 mv/pe

Keithly 80 V BIAS and ampmeter

80.00 V 05.956 nA

B

LED pulser

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Noise seen with ortec QI amplifier in Pixel10

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-1.00E-03 -8.00E-04 -6.00E-04 -4.00E-04 -2.00E-04 0.00E+00

(s)

(V)

We see the same noise at CERN in B-field (Ortec amplifier is a QI, fast rise time and slow decay)

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HPD 291 no Angle

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0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

B (T)

Bia

s cu

rren

t (n

A)

Bias Curr

Big Pulses

We can see the small pulses with keithly bias supplyWithout amplifier we see also large pulses in bursts

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HPD 503 at 0.7 Tesla

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101520253035404550

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Angle (deg)

Bia

s C

urr

ent

(nA

)

bias curr

Big Pulses

When getting on an angle small pulses increase but large ones disappear

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Tube 291

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0.12

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-4.E-06 1.E-06 6.E-06

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pixel 5

pixel 10

Pulse shape of large pulses seen in the two pixels (smaller ones are later in time)At 10 V bias pulse becomes very wide(10 micro seconds) > so it looks like a real photo current

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Tube 291

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2.5

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-4.00E-06 1.00E-06 6.00E-06

(s)

(V)

pixel 19 (x 50)

pixel 1

Two pulses seen in two opposite side pixelsHere PIXEL 1 is the biggest(smaller ones are later in time)

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Tube 291

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-4.00E-06 1.00E-06 6.00E-06

(s)

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pixel 19

pixel 1 (x 10)

Two pulses pulses seen in two opposite side pixelsHere PIXEL 19 is the biggest(smaller ones are always later in time)

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Tube 291 using QI-preamp on pixel 10 while triggered on pixel5

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-2.00E-03 -1.00E-03 0.00E+00 1.00E-03 2.00E-03

(s)

(V)

pixel 5 triggered

pixel10 through Amplifier

Relation between Large and small noise signalsWe triggered on the big pulse in channel 5 and look at the amplified signal from Pixel 10 (small pulses disappear for some time after a big pulse )

AC coupling to scope

Total 4 ms

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Tube 291 using QI-preamp

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-2.00E-02 0.00E+00 2.00E-02

(s)

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pixel5 triggered

pixel10 amplified

Relation between Large and small noise signalsWe triggered on the big pulse in channel 5 and look at the amplified signal from Pixel 10 (small pulses disappear for some time after a big pulse )

Total 40 ms

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We also took data where we KNOW that we triggered on the pixel which was EARLIER in time and had the Amplifier on the one that “reacted” later.

(sorry, but the data on the file was corrupted and Brian is trying to recover it now…)

In this case, the later one did NOT have the small pulses either before or after the big pulse.

Thus, pixels with small pulses are the ones which start the “cascade” and the other pixels which follow have been quiet just before (and after).

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HV

10 M Voltmeter20 Mohm

OR

HPD HV gnd

RBX gnd

PC

diode

1G

VB

Scope on 50 ohm

Setup to look at the HV current on side walls of HPD (diode is isolated from this current path)

Cable capacitance

??

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HV vs current (B=0) HPD =~10Tohm

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HV (kV)

Cu

rre

nt

(nA

)HV current to Ground through ~5Mohm Previous measured at CERN

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DC measured current to ground and noise counts measured in pedestal vs B ( B, E = 20 degree, HV=6 kV)

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B (Tesla)

Cu

rre

nt

in n

A

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No

ise

ev

en

ts a

bo

ve

10

fC

DC current[nA]

noise counts

Correlation between DC measured current through the side-walls of HPD and Noise

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1

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-5.00E-07 5.00E-07(s)

(V)

current to ground (offset 1V and x10)

Pixel 1 (triggered)

Correlation between AC measured current through the side-walls of HPD and Large noise pulses(Pulse in the HV current is first) (negative so it is opposite from photo current)

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-1

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0

0.5

1

1.5

-5.00E-07 5.00E-07(s)

(V)

current to ground (offset 1V and x10)

Pixel 1 (triggered)

Correlation between AC measured current through the side-walls of HPD and Large noise pulses(Pulse in the HV current is first) (negative so it is opposite from photo current)

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-2.00E-06 -1.00E-06 0.00E+00 1.00E-06 2.00E-06 3.00E-06 4.00E-06(s)

(V)

current to ground (offset 1V and x10)

Pixel 1 (triggered)

Correlation between AC measured current through the side-walls of HPD and Large noise pulses(Pulse in the HV current is first) (negative so it is opposite from photo current)

20

NO Angle

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B (Tesla)

Bia

s C

urr

en

t(n

A)

HPD 291

HPD 503

HPD 193

The worst HPD has his noise completelyreduced at 4 Tesla(we did 18 hour test at 4 Tesla with no increase)(We are currently running the best one at 1.3 Tesla for a 1 day)