Introduction
The T7/PS
area has been finally rebuilt during PS/SPS shutdown period 1999/2000
and the new
place for irradiation of the Atlas Pixel Group has been created (IRRAD3).
The x-y stage intended mainly for pixel irradiation is now placed between
SCT x-y stage and the shuttle system. There are two facilities at T7/PS
which can be used by Pixel Group (see please Irradiation
facilities for more details) - IRRAD1
(the shuttle system) and IRRAD3
(remotely controlled x-y stage carrying a cooling box). IRRAD3 is appropriate
for irradiation of larger objects (for instant electronic boards with on-line
read-out) and the use of this system requires an access in the beam area
to install the samples inside.
Cooling box
The irradiation should be done at the temperature similar as operational
temperature at the Atlas experiment environment and therefore irradiated
samples are cooled down during irradiation. The space inside the cooling
box allows to install up to 8 boards (max dimension of PCB 10x10cm).
The boards have to be plugged to the connectors (40
pins female) soldered on the top of the "support board". The pitch
of connectors on the support board is 30mm and they are used just to hold
the boards with samples (chips) in perpendicular position with the respect
to the beam. There are to openings in the box to lead the cables out (flat
cables or coaxial LEMO cables). The movement of the cooling box versus
the beam is remotely controlled from the counting room (x-y direction)
and doesn't require any access into the beam area.
Material restriction for samples
The amount of the material going in the beam should be limited as much
as possible. For instant it is not possible to use robust connectors (as
BNC and so) mounted on the boards and thick sockets + packages for chips.
Such components after irradiation are very highly activated and people
handling samples are unnecessarily exposed. The second reason is that the
beam passing thick material is after significantly scattered and users
working downstream have many problems (calibration uncertainty, secondary
emitted particles). The best solution (recommended solution) is the use
of PCB just as the support frame and in the center where the beam is passing
to use only stretched flex hybrid with the glued chip on the top instead
of robust PCB with the chip package. Non-respecting of this rule could
cause complaints from the side of other users resulting in the requirement
of beam time sharing what could extend significantly the total time needed
for irradiation.
Cables
There are already some cables available at T7/PS leading by the shortest way (@ 15m) from the control room to the irradiation area:
The cooling system
The cooling system has been developed by Jocelyn Thadome and is based
on the phase change liquid-gas of CO2. Compressed CO2 (liquid condition)
is stored in a pressure bottle outside the radiation area and leads via
stainless capillary tube to the cooling box where CO2 is injected from
the cooling platform into the box with ambient atmosphere. The whole system
seems to be very powerful and the temperature bellow 0-degree can be reached
easily and quickly. The temperature in the box is remotely controlled and
the CO2 feeder is automatically closed or open by an electronic valve.
The consumption of CO2 is roughly estimated to be around 1 bottle per 30hours.
To see some pictures from Jocelyn's lab please click here Fig.1,
Fig.2,
Fig.3.
Access rules
Firstly, all of the
installation in the PS/T7 beam zone should be done in time of PS shutdown
or in time of longer MD
(preferably when MD takes more than 1 day). When MD
takes only 1 day the radiation level inside the beam zone is still very
high and does not allow longer stay inside the beam zone (usually up to
10 min only - allowing the simple installation only). The access into the
beam area has to be requested in advance at the meeting of PS/SPS coordinator
with representatives of all beam users (every Friday in the morning).
The reason is that all beam lines in the East Hall have to be inhibited
when an access is required. The beam area is primary beam PS area and therefore
the special authorization is required to enter the beam zone. The authorization
can be granted by PS responsible people on the base of written demand after
passing out the training safety course at CERN, which is organized weekly
- each Tuesday. People from TIS (safety division) will probably
endeavour to have limited number of people having such access!
7th November 2000
Petr Sicho (irradiation coordinator)
