Modern physics has shown that the vacuum, previously thought of as a state of total nothingness, is really a seething background of virtual particles springing in and out of existence until they can seize enough energy to materialize as “real” particles. In high energy collisions at accelerator labs, some of the original beam energy can be consumed by ripping particle-antiparticle pairs out of the vacuum. Sometimes this process is the very reason for doing the experiment, but sometimes it is only a detriment.
For example, in the Large Hadron Collider (LHC), under construction at the CERN lab in Geneva, a major source of beam losses (particles exiting from the usable beam) for heavy-ion collisions is expected to be a class of event in which the counter-moving ions pass each other and don’t interact except to spawn a pair of particles---an electron and positron---one of which (the positron) goes off to oblivion while the other (the electron) latches onto one of the ions.
This ion, bearing an extra electric charge, will now behave slightly differently as it races through the chain of powerful magnets that normally steer the particles around the accelerator. Going a certain distance, the modified ion will leave its fellows and smash into the beam pipe carrying the beams, thus heating up the pipe and surrounding magnet coils.
Fearing these future beam losses, accelerator physicists have sought to observe this effect at an existing machine, the Relativistic Heavy Ion Collider (RHIC) at the Brookhaven Lab on Long Island. And they found what they were looking for, a tiny splash of energy amounting to about .0002 watts, or about what a firefly puts out. The RHIC beam for these tests consisted of copper ions each carrying 6.3 TeV of energy (about 100 GeV per nucleon). According to CERN scientist John Jowett (firstname.lastname@example.org, 41-22-7676-643) this troublesome class of events, referred to as bound-free-pair production (or BFPP, the bound referring to the electron and the free to the positron), will be much more formidable at LHC than at RHIC.
First of all, the pair production scales as the atomic number of the nucleus (or the charge of the nucleus, denoted by the letter Z) raised to the seventh power. The LHC heavy-ion collisions will use beams composed of lead ions. The more highly charged nucleus and the larger energies (574 TeV per lead nucleus) mean the BFPP process should be some 100,000 times more prominent than in the test at RHIC.
This would amount to about 25 watts, the equivalent of a reading lamp. That doesn't sound like much but, when deposited in the ultra-cold (1.9 K) magnets of the LHC, it could bring them to the brink of "quenching" out of their superconducting state, interrupting the
operation of the huge machine. (Bruce et al., Physical Review Letters, 5 October 2007)