Subject: PMTs decommissioning
Nicola.Zaccheo@lngs.infn.it
Date: Wed Nov 17 1999 - 07:49:55 EST
Ciao a tutti,
this is the manual page for decommissioning PMTs. You can read it as
html document by opening (using NETSCAPE menu)the file
disk$scrausa2:[zaccheo.smant]dec_box1.html
A presto,
Nicola
--------------------------------------------------------------------------------
Decommissioning PMTs at MACRO detector - Manual page
N.Zaccheo - M.Orsini
1. Introduction
In this manual we describe the procedures for decommissioning MACRO's
photomultiplier tubes (PMT). This is in order to guarantee PMTs integrity
and workers safety.
All MACRO PMTs live in the tank ends of scintillator counters.
MACRO has two different kind of scintillator counters: horizontal
and vertical. All boxes are PVC made and they have approximately length
of 12m and rectangular cross-section of 75 cm X 25 cm but the horizontal
ones have two PMTs per side, while the vertical boxes have one PMT only
per side as shown below. Notice that MACRO has 476 scintillator counters
for a total of 1540 PMTs.
[Image] (a)
[Image] (b)
Figure 1. Details of scintillator counter end--chambers (a)
horizontal (b) vertical
About 11m of the counter length is filled with mineral-oil based scintillator
while the tank-end chambers contain pure mineral-oil (without scintillator)
and the PMT's.
There are two kind of hemispherical PMT in MACRO: EMI D642 and Hamamatsu
R108. The Hamamatsu PMTs live on the attico vertical counters and on
North/South faces, while the EMI ones are installed in the rest of the
detector.
-------------------------------------------------------------------------------
BEWARE:
All the following operations must be performed
after having turned off the PMT high voltages.
The mineral oil must be filled out from the end
chamber before opening the plastic covers.
-------------------------------------------------------------------------------
2. Tank-end operations for the horizontal counters
Each horizontal tank-end contains roughly 50 litres of mineral oil wich
must be drained out through the proper cap. Particular care is needed in
the cap choice as there are several of each on the tank ends, each serving a
different purpose. Caps #1 and #2 in the figure below are
the ones necessary to unscrew for accessing the oil in a tank end.
[Image]
There are three cables connected to a tank end: the HV cable
(RED), the LED cable (YELLOW) and the SIGNAL cable
(BLACK).
We suggest reading step by step each items of the following
check list
to make sure that any kind of operation will be properly performed
in order.
- Unplug the high voltage cables (red ones) in both sides of the counter.
- Unscrew both plastic caps from the oil/air tubes to the left (RED ones
in previous figure).
- Connect the pump to the oil tube (#1 in the figure) and suck the oil
out from the chamber.
- Unscrew all nuts around the plastic covers and remove both of them:
we suggest to hold on a small container under the cylinder because a little
part of oil is going to drop down on the floor.
- Unplug the HV base from the PMT and carefully unplug the plastic connector
without wiggling cables.
- Remove the HV resistor chain clip installed on pin 20 of the PMT and
clipped to shield.
- Take out all pieces of mylar from the cylinder.
- Take out the magnetic shield cylinder clipped to clamshell.
- Take out all pieces of styrofoam from the cylinder.
- Carefully, take out the first PMT from the cylinder and put it inside
the case as soon as possible to avoid light exposure.
BEWARE! While handling any PMT please notice the following:
Always use protective glasses.
Avoid hiting the glass (photocathode) of the PMT.
Do not shake the PMT as any glass imperfection may
lead to implosion.
Use enough light to guarantee safety during operation,
but in general try minimize exposure of a PMT to light and
especially direct light.
In case the PMT doesn't come out easily, do not force it
and try again moving the PMT glass cylinder to the left/right
or up/down and carefully take it out holding the cables to
the left.
Do not wiggle cables too much.
Before opening the tank end, make sure you have enough paper
next to you as oil might be dripping at any stage of operation.
Make sure you have ready the storage carton for each PMT.
After removing the PMT from the tank end, please clean the
photocathode (glass) with clean paper. The PMT lived for years
in a bath of mineral oil (and Helium!) and we want to remove as
much of it as possible before putting it in the box.
- Remove the second PMT in the same way.
- Unplug mirror to magnetic shield clips.
- Clean up the gasket and re-install the plastic covers.
- After removing the PMTs, please place the cylinder caps without tightening
the nuts beyond the point necessary to hold it in place.
BEWARE:
Do not tighten nuts too much because it can seriously damage the cylinder
(the lip may crack ot the threads will break).
3. Tank-end operations for the vertical counters
The vertical tank-end contains roughly 25 litres of mineral oil wich
must be drained out through the proper cap. As for the horizontal counters,
particular care is needed in choosing the cap as there are several
of each on the tank ends, each serving a different purpose.
Caps #3 and #4 in the figure below are the ones necessary to unscrew for
accessing the oil in a tank end.
[Image]
There are three cables connected to a tank end: the HV cable (RED), the LED
cable (YELLOW) and the SIGNAL cable (BLACK).
We suggest reading each items of the check list below in order to make sure
that any kind of operation will be performed in order. Although the vertical
tank-end operation could be much more complicated, actually it contains only
one PMT per tank-end and usually it comes out easily from the PVC cylinder
which can be completely removed from the tank body.
- Unplug the high voltage cables (red ones) in both sides of the counter.
- Unscrew both plastic caps from the oil/air tubes to the right (RED ones
in previous figure).
- Connect the pump to the oil tube (#4 in the figure) and suck the oil
out from the chamber.
- Take out completely the four long screws around the cylinder, then
unscrew the safety bar.
BEWARE:
During the last above mentioned operation, you must hold on the cylinder
otherwise it will fall down and the PMT could be damaged.
- Try to move the cylinder and it will come out with the PMT inside.
BEWARE:
Do not reverse the cylinder or the PMT falls down. The cylinder contains
a little part of oil that can drop down: for this reason, keep it
vertically and hold the PMT with a hand, then reverse the cylinder to take
out the oil but don't ever leave the PMT.
- Carefully, reverse the cylinder again and let the PMT comes out just
for a little and catch it along the glass cylinder.
- Unplug the high voltage base and put the PMT inside the case as soon
as possible to avoid light exposure.
BEWARE! While handling any PMT please notice the following:
Always use protective glasses.
Avoid hiting the glass (photocathode) of the PMT.
Do not shake the PMT as any glass imperfection may
lead to implosion.
Use enough light to guarantee safety during operation,
but in general try minimize exposure of a PMT to light and
especially direct light.
In case the PMT doesn't come out easily, do not force it
and try again moving the PMT glass cylinder to the left/right
or up/down and carefully take it out holding the cables to
the left.
Do not wiggle cables too much.
Before opening the tank end, make sure you have enough paper
next to you as oil might be dripping at any stage of operation.
Make sure you have ready the storage carton for each PMT.
After removing the PMT from the tank end, please clean the
photocathode (glass) with clean paper. The PMT lived for years
in a bath of mineral oil (and Helium!) and we want to remove as
much of it as possible before putting it in the box.
BEWARE:
In case you must re-install the cylinder,do not tighten the long screws
too much because it can unglue the plastic triangles where the screws
are tightened
In case you need to re-install PMT's in the tank-end, see the check lists
below:
Check list for the horizontal counters
Check list for the vertical counters
This archive was generated by hypermail 2a24 : Wed Nov 17 1999 - 07:49:59 EST