CERN Headquarters
2013-04-22 07:16 UTC |
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Our group met outside the
CERN
headquarters building, waiting to board a CERN shuttle
bus to see the first of the
Large Hadron
Collider (LHC) detector experiments we were to visit.
“CERN” is an acronym of
“Conseil
Européen pour la Recherche Nucléaire
(European Council for Nuclear Research), which organised
the laboratory between 1952 and 1954. The official
name of the organisation, as it appears on the building,
is
“Organisation
européenne pour la recherche nucléaire
(European Organization for Nuclear Research). The acronym
“CERN” was retained, both for historical
reasons and the fact that acronyms of the official name
are awkward in both French and English.
Between two of the CERN headquarters buildings is a park in which
some of the hardware from CERN's past is exhibited.
The Gargamelle
bubble chamber was used in conjunction with the original CERN
Proton Synchrotron
to study neutrino interactions. Unlike most bubble chambers which
use liquid hydrogen as the medium, Gargamelle was filled with
liquid halon
(bromotrifluoromethane)
which, being denser, increased the probability of neutrinos interacting
with it. It was Gargamelle which confirmed the existence
of weak neutral currents
in 1974.
The
Big
European Bubble Chamber (BEBC) was the largest bubble chamber in the world
when it entered service in 1973, and incorporated what was then the
largest superconducting magnet. The chamber contained
35 cubic metres of liquid medium (hydrogen, deuterium, or a neon-hydrogen
mixture depending on the experiment) and recorded interactions from the
beam of the
Proton Synchrotron
and later the
Super Proton Synchrotron.
When retired in 1984, it had produced 6.3 million photographs of
particle interactions in the chamber.
Here we are looking up into the BEBC from below. The cylindrical
portion at the bottom is where the piston operated. By retracting
the piston, the pressure in the chamber was reduced to the point
where the fluid was momentarily above its boiling point. Charged
particles would serve as a nucleation source for bubbles, which
would track the motion of the particles. The superconducting magnet
caused particle tracks to curve, allowing the mass and charge
of the particles to be deduced from photographs of these tracks.
This piston was activated for each photograph taken in the BEBC,
a total of 13 million strokes over its 11 years in service. Each
stroke exerted a force of 350 tonnes. When you are doing something
that violent so many times, there's always the possibility of
things ending badly, so the building which housed the BEBC was
designed with a roof which would be blown off in case of a
hydrogen explosion. Fortunately, that never happened.
The actual acceleration of electrons and positrons in the
Large
Electron-Positron Collider was performed in radio frequency cavities
like these. A total of 128 such cavities were distributed around the
accelerator ring. The copper sphere at the top stored the acceleration
energy between particle bunches, saving energy and reducing heat
dissipation in the cavity.
This
Cockcroft-Walton voltage
doubler, initially installed in 1964,
provided the 600 kilovolt high voltage supply which provided the
first acceleration of protons to the linear accelerator which fed
the Proton Synchroton.
This wooden building, said to be the largest in the world,
was originally built for
Expo.02
in Neuchâtel,
as the
Palais
de l'Equilibre, a celebration of
anti-human
“sustainable
development”. After the end of the exposition, it was dismantled
and re-assembled at CERN to be a
visitor
and outreach centre. We did not have an opportunity to visit it.
This document is in the public domain.