Though the LHC is the most massive machine on earth, it is but one component in a system of particle accelerators at the CERN Accelerator Complex.

The Large Hadron Collider is a particle accelerator 27 kilometres in circumference that sits 100 metres underground between Switzerland and France near Geneva. The specific type of particle that the LHC deals with is a hadron, more specifically protons or lead ions. A particle accelerator’s function is to increase the speed and energy of particles for collision and research. The LHC directs and collides particles by using magnetic fields to steer them and electrical fields to accelerate or add energy to them. Though the Large Hadron Collider does perform this function, it is but one final stage in a series of accelerators known as the CERN Accelerator Complex.

Before any acceleration can begin, the protons have to be harvested from condensed hydrogen atoms. These atoms are fed at a precisely controlled rate into the first stage: CERN’s linear accelerator the LINAC2. These atoms, while contained in the LINAC2’s source chamber, are stripped of their electrons to leave hydrogen nuclei. The protons are ready to be accelerated by use of an electrical field.

As an alternative to proton packets, lead ions, generated from vaporised lead, are fed into the source chamber of another linear accelerator, the LINAC3. From there, the lead ions travel to the Low Energy Ion Ring (LEIR). From this ring, the ions follow the same path as their proton packet counterparts to acceleration and eventual injection into the Large Hadron Collider.

Once the packet exits the LINAC2, the protons have an energy of 50 MeV and are traveling at one third the speed of light. The LINAC2 feeds the proton packet directly into a four ring stage called the Booster, 157 metres in circumference. The single packet is broken into four separate packets and sent along four vacuum rings to achieve maximum energy and speed. Accelerating the protons in a circular fashion is far more logical at this point than linear acceleration. During the Booster stage, an electrical field is pulsed at a specific point during their travel around the circle. At the same time, powerful magnets exert force at a right angle to the particles’ trajectory, bending the packet along the inside of the rings. This stage accelerates the particles to 91.6% the speed of light and increases their energy to 1.5 GeV.

After the packets have completed the Booster stage, they move on to the 628 metre-in-circumference Proton Synchrotron. The protons travel for 1.2 seconds in this stage, during which they reach 99.9% the speed of light. A very curious quantum physics occurrence happens in the Proton Synchrotron: the protons reach the point of transition. This accelerator continues to subject the packets to electrical fields. Since their speed is so close to the speed of light, they are incapable of traveling any faster. Instead, the particles become heavier, translating most of the energy into mass. Upon leaving the Proton Synchrotron, the particles have an energy of 25 GeV.

The only stage remaining between the packets and the LHC itself: the 7 kilometre in circumference Super Proton Synchrotron—similar to the Proton Synchrotron, the Super Proton Synchrotron increases the packets to an energy of 450 GeV. The packet is ready to be injected into the LHC’s two vacuum pipes.

In the LHC, the packets move in the two tubes in opposite directions. There are two kickers, highly sophisticated machinery that synchronises incoming packets into the LHC’s tubes. Four detector caverns exist inside of the machine where the tubes cross and the beams of protons can be forced to collide. The packets spend 20 minutes being accelerated from 99.9997828% the speed of light and 450 GeV to 99.9999991% the speed of light and 7000 GeV or 7 TeV.

Sources

• “CERN (European Organization for Nuclear Research): The accelerator complex”. CERN. Retrieved October 9, 2011.
• “CERN (European Organization for Nuclear Research): PS - the Proton Synchrotron”. CERN. Retrieved October 9, 2011.
• “CERN (European Organization for Nuclear Research): SPS - the Super Proton Synchrotron”. CERN. Retrieved October 9, 2011.
• “CERN (European Organization for Nuclear Research): The Large Hadron Collider”. CERN. Retrieved October 9, 2011.