On a packed (and very hot day) we were privileged to visit six locations in the establishment, in a manner not available to the general public, and not to be repeated for 10 years or so, as once the LHC resumes operation, nobody is allowed access to the tunnel or detector caverns due to the risk of radiation contamination. I will take a brief look at these in turn.
The first visit was to the ISOLDE ('Isotope On-line Separator Device') facility. This is the radioactive ion beam facility dedicated to the production of a large variety of radioactive ion beams for many different experiments in the fields of nuclear, astro, medical and atomic physics, solid-state physics, materials science and life sciences. This is done by impinging a high energy beam of protons - up to 1.4 GeV and with 3.3 x 1013 protons per pulse. Its purpose is to create, and explore the properties of new isotopes of familiar elements (same number of protons but different numbers of neutrons). They can even make gold!!
Our second visit was to the 'Antimatter Factory' which prompted jokes about what kind of lorry does one employ to deliver antimatter (general opinion was that it would float above ground level!) This is the only facility in the world that can create antihydrogen. Using the CERN anti proton decelerator (AD), protons are slowed and mixed with electrons to create antimatter of various forms. One of the studies is to understand the current make up of the universe with respect to amounts of matter and antimatter.
Personally I found the key experiment quite esoteric, which was to allow 'neutralised' antiprotons (i.e. with an added antielectron - a positron) and therefore unaffected by any E/M forces, to free-fall, and to measure the speed, to confirm that the normal laws of gravity apply to antimatter also! This visit concluded with a descent to the Antiproton Decelerator. Started in 2000, The AD is a ring composed of bending and focussing magnets that keep the antiprotons on the same track, while strong electric fields slow them down - this was our first glimpse of a particle beam construction, and it was fulfilling a dream to be able to descend to, and walk around the underground tunnel.
On average, the antimatter factory sees only one atom of antimatter for every 1 million atoms of matter created.
Next was the awe-inspiring data centre! With the Large Hadron Collider alone producing some 1 GByte of data every second, the challenge to sift, sort and store all the information CERN is generating on a daily basis for later study and analysis is mind boggling. Clever algorithms are used to
detect patterns of data (after preliminary assessment by teams of scientists) that may be relevant to an experiment, and to separate those for storage and later scrutiny. The on-site CERN facility is linked to 100 data centres around the world to provide back-up and allow for off-site analysis. The CERN centre, itself, comprises 230,000 processor cores and 15,000 servers run 24/7!
Following the data centre we visited one of the public exhibition centres to see a video projected onto the Synchrocyclotron, (the world's first accelerator) and followed that up with a visit to the ATLAS ('A Toroidal LHC Apparatus') experiment control room, and then down to the ATLAS detector itself. ATLAS is one of the seven particle detector experiments constructed at the Large Hadron Collider (LHC). The experiment is designed to take advantage of the unprecedented energy available at the LHC and observe phenomena that involve highly massive particles which were not observable using earlier lower-energy accelerators. ATLAS is one of the two LHC experiments involved in the discovery of the Higgs boson in July 2012, the other being CMS ('Compact Muon Solenoid').
Finally, and the 'pièce de résistance' we were bussed to ALICE, ('A Large Ion Collider Experiment') - yet another one of the detectors on the Large Hadron Collider, in the village of Sergy, one of the largest experiments in the world devoted to research in the physics of matter at an infinitely small scale. ALICE actually outdates the LHC, originally being built for LEP ('the Large Electron Positron collider') and is optimized to study heavy-ion (Pb-Pb nuclei) collisions at a centre of mass energy of 2.76 TeV per nucleon pair. The resulting temperature of collisions inside the LHC (100,000 times hotter than the centre of our sun) and energy density are expected to be high enough to produce quark–gluon plasma, a state of matter wherein quarks and gluons are freed. Similar conditions are believed to have existed a fraction of a second after the Big Bang before quarks and gluons bound together to form hadrons and heavier particles. Over a billion particles will collide each second in the centre of ALICE but of these, only around 20-30 collisions are of note.
After picking up our individual keys from the ALICE control centre, authorising us to enter the facility one at a time, we descended the 60 meters or so to the viewing platform to stand in front of this awe inspiring piece of mechanical and electronic complexity that defied belief! Layers of detector materials of different types surround the tiny core, through which the particle streams are driven. It was even possible to see the LHC beam pipe protruding through the centre of the detector. All told the structure stands only 16m high and 16m in width but weighs more than the Eiffel Tower!
This was a truly breath-taking finale to an inspiring day, on an impressive technological site that felt like a large university campus.
Once again, a very deep appreciation to Bridget Donaldson and her ability to organise such a concentrated glimpse into this world leading centre of nuclear and atomic excellence.