The CERN accelerator complex at the CERN SPS

The 33 TeV Lead beam at the CERN SPS

The highest energy density ever produced in the terrestial laboratory, in highly excited and compressed "fireballs" of nuclear matter, has become accessible for research at the 33 TeV total energy SPS beam of highly relativistic nuclear projectiles: the isotope ²⁰⁸Pb, one of the heaviest nuclear species, made up from 82 protons and 126 neutrons in a tight spherical packing that we call "nuclear matter", is accelerated to about 99.9 % of light velocity.

The CERN chain of successively higher velocity or energy accelerators (injector Linac, Booster synchrotron, PS synchrotron, SPS synchrotron) was initially built to provide high energy beams of electrons, positrons, protons and antiprotons for particle physics studies of the elementary constituents of matter: leptons and quarks. This accelerator complex was ingeniously adapted to the acceleration of heavy nuclei which, from their initially neutral atomic state, are getting successively stripped of their electrons in the course of passage through the accelerator chain, being shifted to higher ionization states (hence the term heavy ions) until they are fully stripped down to bare 208Pb nuclei of charge +82 upon injection to the last element of the accelerator chain: the SPS (Super Proton Synchrotron) is versatile enough to accelerate charge 82+, mass 208 nuclei - instead of charge 1+, mass 1 protons - to its maximal energy which, for this charge to mass ratio, is about 160 GeV per projectile nucleon. The term "nucleon" refers to the constituents of nuclei, e.g. protons and neutrons.

The heavy nuclear species Pb is built up of 208 nucleons, hence the final total SPS beam energy is 160 x 208 GeV approx 33 TeV, the highest accelerator energy reached world wide.

Extraction of the circulating beam, at top SPS energy, feeds beam splitter systems that distribute the Pb projectiles into several external beam transport lines ending on target in up to seven concurrently operating experiments.

Such targets are thin foils of metallic Lead: the Lead beam projectiles hit stationary Lead nuclei in the foils creating violent Pb+Pb nuclear collisions if they hit head-on. The 33 TeV beam energy gets consumed in a process of heating and compressing the extended, initially cold volumes of nuclear matter, thus creating "fireball" matter through the strong interaction, occurring initially in violent nucleon collisions at the microscopic level that stop down the relative motion and sap the beam kinetic energy into a collective excitation of an emerging volume of fireball matter. All the initial content of the nucleons from target and projectile, in terms of internal quarks and gluons, might melt away under such heating and compression, to give rise to a continuous extended state of strongly interacting matter made up by quarks and gluons propagating freely in this fireball of extreme energy density.

Such a primitive "Urzustand" of matter under the influence of the elementary strong force/interaction was predicted by Quantum Chromodynamics theory (QCD) to occur in extended volumes of extreme temperature and energy density - that is why we collide extended nuclear matter volumes here, instead of investigating the small volume elementary collisions of protons or electrons that probe into the properties of elementary particles. The Lead beam experiments thus analyze extended quark-gluon matter properties, not the properties of individual elementary particles. Thus the term Quark Matter research.

For more details see:
The Pb Injector at CERN
The CERN Hadron Ion Sources, The CERN Hadron Linacs

See also photographs of:
Heavy Ion Linac (Linac 3), PS Booster, Inside the PS tunel, Inside the SPS tunel,

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