PMT Base for Shashlik

8/11/2019 PMT Base for Shashlik

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PMT base for Shashlik:

Advance Report(why did it take so long)

Alam Toro

Juan Ignacio VegaRen Ros


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Index

Part 1: PMT base design considerations

Part 2: PMT base test

Part 3: Connecting R3998-02 to the base Part 4: Proposal on possible failures

Part 5: Results

Part 6: Conclusions


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PMT base design considerations

Based on Sergey calculations, a current of 0.4[A] isestimated to be the output current from PMT attached tothe Shashlik Calorimeter. To operate in this way, a gain of3x105 is needed.

Under this considerations, a current of at least 100 timesthe PMT output is needed to be provided by the resistivenetwork, in order to dont change dynodes potentials andconsequently the PMT gain. We selected a value of currenta little bit bigger to make easier the resistance selection.

We cannot choose a big current, because a very smallpower dissipation is needed. In this way we dont perturbthe PMT with heat coming from the resistors.


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Selected current:

100[A]

Gain:

3x105

Voltage:

820[V]

Total Resistance:

8.2[M]


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This is normal voltage

distribution ratio,

found in Hamamatsu

R3998-02 datasheet.

Also we can find a

suitable base made byHamamatsu


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But in order to improve output linearity, is better to use a

tapered network.

In R3998-02 datasheet there

wasnt a proposed tapered

network, so Sergey suggested

to use the following one:

K G D1 D2 D3 D4 D5 D6 D7 D8 D9 P

3 1 1 1 1 1 1.5 1 1 1.5 2.5


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Finally the desired network was the following

one:

10 K output impedance was selected (bigger output signal, but damping may

appear if connected to 50 equipment). 1K isolation was used between

HVground and HFground (with optional capacitor too). Also additional HVsupplies are used for last dynodes.


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PMT base test

Before 510K resistance arrived to UTFSM, we

made some prototypes using a 470K

resistance, very close to the desired value.

Voltage measurements were done and we

found that even though we had a little

discrepancy between measured and predicted

voltages, the base was good enough to workproperly.


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PMT base test base 1 200 Vsupply

200

Resistance [MOhm] Theorics Voltages Measured Voltages Relative Error

0,22 5,633802817 8,9 58,0%

1,5 38,41229193 33,6 12,5%

0,47 12,03585147 11,66 3,1%

0,47 12,03585147 11,68 3,0%0,47 12,03585147 11,56 4,0%

0,47 12,03585147 11,62 3,5%

0,47 12,03585147 11,64 3,3%

0,75 19,20614597 18,32 4,6%

0,47 12,03585147 11,66 3,1%

0,47 12,03585147 11,66 3,1%

0,75 19,20614597 18,3 4,7%

1,3 33,29065301 30 9,9%

sums 7,81 200 190,6

* this voltage couldn't be measured directly due to base design


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PMT base test base 2 1000 Vsupply

1000

Resistance [MOhm] Theoric Voltages Measured Voltages Relative Error

Measured

Resistance Resistance Error

0,22 28,16901408 45 59,8% 0,217 1,36%

1,5 192,0614597 167,5 12,8% 1,444 3,73%

0,47 60,17925736 58,2 3,3% 0,468 0,43%0,47 60,17925736 58,2 3,3% 0,467 0,64%

0,47 60,17925736 57,6 4,3% 0,464 1,28%

0,47 60,17925736 57,9 3,8% 0,465 1,06%

0,47 60,17925736 58,1 3,5% 0,467 0,64%

0,75 96,03072983 91,2 5,0% 0,75 0,00%

0,47 60,17925736 58,1 3,5% 0,467 0,64%

0,47 60,17925736 58,1 3,5% 0,466 0,85%

0,75 96,03072983 91,2 5,0% 0,752 0,27%

1,3 166,453265 149,9 9,9% 1,281 1,46%

7,81 1000 951

* this voltage couldn't be measured directly due to base design


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PMT base test

Until that moment all measurements

seemed to be correct, so we thoughtimmediately about connecting the

R3998-02 PMT.


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Connecting R3998-02 to the base

The first thing that we were looking at

while connecting the polarized base to

the tube into the dark box was the onephotoelectron signal.

We couldn't find it.


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So in order to compare signals and to see if we

could get at least a small signal, we used a LEDsetup to work with the PMT.

Besides that, we connected a russian PMT (87)

in the same place to be excited by the LED.


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When we connected the Russian PMT to 1KV, with 50 impedance

input in oscilloscope, we could see a signal coming out from

Russian PMT. (Blue is PMT output, Violet is LED input signal).


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Russian PMT 87 resistor network

Its the same type of divider.


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Russian

PMT

datasheet


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Signal in PMT due to LED is very

large, because the LED generates

a very big amount of light. This

of course is not good for PMTgain, because dynodes voltages

vary a lot, so after a short big

peak, signal goes down fast.


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When we connected the Hamamatsu PMT polarized

to 1.2kV to the oscilloscope at 50 input impedance,we couldnt see any signal again.


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Connecting R3998-02 to the baseNormally PMT works perfectly well connected to a 50 impedance

input. If we remember that cable impedance is 50 too, we get

smaller signal damping in this case, and almost no damping if PMT

has also 50 output impedance.

But we have to remember that PMT output is a current pulse. Thismeans that it will go through the way that shows smaller resistance.

Signals that we can see in the oscilloscope are voltage signals, so in

the case of using 50 input impedance, a big amount of current will

go directly to the oscilloscope, and voltage signal in the output PMTresistor will be small. If we use 1M input in the oscilloscope, almost

all the current will go through the PMT output resistor, and we will

have a bigger signal, but more damping as I explained before.


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Because we were curious about this, we changed scope impedance

to 1M, and we could see a very small signal (russian in blue,hamamatsu in yellow)



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We couldnt explain this at the moment, but we

thought it might be explained by a small PMTgain.

So we tried to make the russian PMT to behave

in the same way that Hamamatsu.

In order to do this, we had to change russian

PMT supply to 525[V].


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In this way both Hamamatsu and Russian PMT behave almost

exactly in the same way. Hamamatsu in yellow, russian in green.


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1 Photoelectron signal at 1.2

kV

Very small1Photoelectron

signal at 1 kV

NO 1 Photoelectron signal can

be seen at 963 V. Its only

noise.

So russian pmt behaves as

Hamamatsu for small voltages.

Its a gain problem!


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Proposal on possible failures

First guess about possible errorwas about resistance distributionratio. Hamamatsu PMT has a grid,and NO information about asuitable tapered network wasgiven by Hamamatsu. So I thought

that gain might be small because itwasnt a good idea to make atapered network for this PMT.

Normally, as seen for R7525 PMTgraphic at the right (the first optionto be use for Shashlik), taperednetworks have smaller gain.

I made the change, check the newbase, made measurements, but NOSIGNIFICANT CHANGE IN SIGNALAPPEARED.


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In that moment I was withno ideas in my mind until Iremember I had noticedsomething important in the

current given by the HighVoltage Supply.

At 1.2kV applied toHamamatsu base (with PMT

connected) we should have153A, but sourcemeasured 218A. Why?


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So in that moment I tookthe PMT and noticedsomething reallyimportant:

All PMT pins were actuallyconnected to some placein the PMT (none wasunconnected but the

short pin).Even those which werentconnected to a specificdynode.


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Base pins were in this waynamed in datasheet. WhatIC actually means isInternal Connection.

We used those pins

connections in PCB tobypass some voltages. Andthere was a problem withthis, because we actually

welded all female pins inthe socket to the PCB base.


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Proposal on possible failuresSo actually THIS was

the problem, because

this made a SHORT

CIRCUIT between

some of the dynodes

(D3 and D5, bypassing

D4). Current wentthrough this wire and

not through some of

the resistors. This

made those dynodes(D3 to D5) to be at the

same potential, with a

big lack of gain.

To repair this,

we removed

those pins from

socket, so PMT

is not

connected

anymore to thecircuit through

Pin 4 and Pin 11

(which are

internallyconnected the

one with the

other inside the

PMT).

PIN 4PIN 11

Connection between pins


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Results

Now we get a very big signal at 1M input impedance with the LED.

(Hamamatsu in yellow, russian in blue)


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Results

To answer Will question, I measured russian PMT signal at 1.2 kV

(same than before), and 1 [V/div] in 1M scope input (same scale than

Hamamatsu in previous slide). A lot of damping is appreciated.


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Results This is normal because it is due to BIG level of light. Also if we turn off the

LED we still get signal, from a small amount of photons.

1.2 kV supply. Dark box without

LED blinking.


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Results

1 photoelectron signal

at 1.2 kV


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Results

1 photoelectron signal at 1 kV


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Results

Several photoelectron signal at 1 kV


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Conclusions

PMT base design is ready and working.

We have bases, so we can start manufacturing

them today (we already started).

Documents

PMT Base for Shashlik