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prepare various particles for a wide range
of experiments. These include muons for
researching the structure of the proton,
heavy ions for creating states of matter
and radioactive ion beams for observing
exotic nuclei.
The LHC is the world’s largest and most
powerful particle accelerator. It is located
around 100 metres underground in
a circular tunnel with a circumference of
27 kilometres. The LHC uses strong elec-
tric fields in order to transmit energy to
particle beams and guides the beams
through the system using magnetic
fields. The particles acquire more and
more acceleration energy until they travel
around the LHC at close to the speed of
light – 11,245 times per second. When
they collide, four huge detectors – CMS,
ATLAS, ALICE and LHCb – record what
happens.
Safety always takes priority
The CMS detector is a technologically
advanced detection device measuring 21
metres in length, 15 metres in diameter
and weighing 12,500 tonnes. Composed
of 100 million individual measuring elem-
ents, it takes up to 40 million measure-
ments per second and is one of the most
complex and precise scientific instru-
ments ever built. To prevent measurement
errors, all influencing factors must remain
within defined tolerances.
These influencing factors also include the
composition of the ambient and venting
air in the underground caverns. To ensure
consistently correct operation, air is
continuously extracted and analysed at
more than 100 measuring points inside
and outside of the detector. This is all the
more important given that the word
‘Compact’ in the name also means that
it is not possible to intervene quickly any-
where at any time. In a critical situation,
such as a gas leak or a fire in the detector,
it would take up to two weeks to reach
the emergency openings to access the
inner areas.
Intelligently automated
In the past, each individual air pick-off
point had a separate analytical device,
which led to high costs. Furthermore,
the maintenance costs and probable failure
rate were too high for CERN standards.
Since the beginning of 2016, valve termin-
als type VTSA have been ensuring that
the air flows are guided to the analytical
devices by the fastest route possible.
The new solution reduces the number of
analytical devices required by a factor
of 10. The air flows are now combined
centrally and assigned to downstream
analytical devices. The main valves of the
VTSA are piloted with compressed air and
have the advantage of being insensitive
to the magnetism of the CMS detector.
The valve terminal was configured to the
specific requirements of CERN. The most
important technical adaptation was
reversible operation.
In normal operation, the air from a meas-
uring line is routed through the valve ter-
minal to the downstream analysis station.
At the same time, all the other measuring
lines are permanently primed in low
pressure operation. The ambient air is
therefore available at the valve when
changing over to the next measuring line.
This flexible application shows that the
“The tailored solution from Festo has improved
safety and efficiency in the CMS experiment.”
Gerd Fetchenhauer, CMS Gas Safety Officer, CERN