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

??

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

-1.8

-1.6

-1.4

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

0 2 4 6 8 10 12

HV (kV)

Cu

rre

nt

(nA

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

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

-1.4

-1.35

-1.3

-1.25

-1.2

-1.15

-1.1

-1.05

-1

0.0 0.2 0.3 0.4 0.6 0.8 1.0 1.2 1.4

B (Tesla)

Cu

rre

nt

in n

A

0

10

20

30

40

50

60

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 (CERN B157)

-1

-0.5

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)

HPD 291 no Angle

0

10

20

30

40

50

60

70

80

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

HPD 503 at 0.7 Tesla

05

101520253035404550

0 20 40 60 80 100 120 140

Angle (deg)

Bia

s C

urr

ent

(nA

)

bias curr

Big Pulses

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

Lifting the HPD windowWe cut the HV cableWe milled of this the plastic and rubber on the top on a lay After that you should heat the Indium Tin seal to 80CWe had to poke with a needle to break vacuum before we could lift theWindow.

What also could be tried is don't pop the window but just heat it ones until the solder is melted and liquid (at that piont the vacuum is not broken ) and then let cooldown and re-measure noise. It could be that there are some variation from HPD to HPD in the seal  ?????