Re: temperature test

[beni zihlmann <bzihlman@indiana.edu>]

Hi All,

Attached is a file showing a scope shot from a FEU-84-3 pmt with
Cockcroft-Walton base. the Voltage is set to 1950V.
There are signals as the PMT is not completely shielded from the
ambient light.
Now some comments:
1) if I assume a signal height of 1V and as signal shape  a triangle
    with base 50ns. I get a peak current of 20mA and the signal results
    in 5*10^-12C.
    assuming a very high rate of 50kHz this will lead to 0.25*10^-6C.
    this charge corresponds to a effective DC current 0.25uA.
    Taking the 1V*0.25uA=0.25uWatt. That is what the PMT will consume
    as power.
    please correct me if this is all wrong.

2) as you pointed out the base consumes more power than the PMT but
    since it is a Cockcroft-Walton type base it will consume about 0.1Watt
    according to Paul Smith.

3) the holes in the plastic are very tight for the bases so I can not fit
    a temperature probe next to the base in the plastic block, but rather
    feed the temperature probe from the PMT side into the hole so that
    it is located next to the pmt.
    From the above estimate in 1) I will not see a temperature change as
    the power dissipation must be small also since the actual signals are
    much smaller than 1V. But rather I have to make the holes bigger such
    that a temperature probe fits next to the base.

4) Maybe we make an elefant out of a mosquito:
    assuming 0.1 Watt per pmt we talk about 300 Watt in total. While this
    number is not negligible we have to see that this power is distributed
    over a rather larger area of more than 2 x 2 meters. And also the volume
    is not small as the base is about 15cm long and 1/3 will stick out 
of the plastic
    wall. The whole thing sits in a light tight hut that can be equipped 
with fans
    and exhausts to provide substantial air cooling. Note 300Watt  is 
1PC power
    supply.

5) I am currently repeating the test and making sure that at the 
location where
    I measure the temperature I have no air exchange. however the PMT is 
cooled
    where it sticks out of the plastic block by the surrounding air.  
and as indicated  
    in the attached picture the signals are only 50 to 100mV.

As usual I am looking forward to  your comments and suggestions.

cheers,
Beni