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Focusing the Large Hadron Collider Creating Black Holes Swallowing All Up
:: 13 July, 2008
With a circumference of 27km the large hadron collider (LHC) at Cern in Switzerland is about to become the world’s highest-energy particle accelerator. The plan is to collide opposing beams of 7 TeV protons to produce never-before-seen particles that can teach us more about the nature of the universe. Paul Collier, whose intricate task it is to thread the beams through the machine over the next two months, describes what it’s like to be part of Cern at this exciting time.
There seems to be some concern in the media about our work on the large hadron collider (LHC) creating black holes swallowing us all up, but here at Cern we are all utterly convinced that this is not a problem. None of us would be doing this if we thought we might destroy the world. We are not total megalomaniacs.
My career at Cern began in the 1980s. I was lecturing at Sheffield Hallam University in England, and met Nobel prize winners Carlo Rubbia and Simon van der Meer when they came over to lecture on their discovery of the Z and W bosons.
They suggested I come over to Cern to work, so I went over to Switzerland and began working on the big machine they were in the process of building – the LEP (large electron-positron collider). It was in the same tunnel that the LHC (large hadron collider) is in now.
I worked on the LEP until it was dismantled in 2000. First I was with the radio frequency group and later I became one of the control room physicists who work on the big machines. I started to work on the LHC about 13 years ago, recently preparing the injector complex that delivers the beam to the machine. [The LHC experiments will centre around the collision of two 7 TeV proton beams travelling in opposite directions.]
It’s always exciting to bring a new machine on, but the LHC is very special. It’s exactly the same size as the LEP, but it’s a huge, complicated and very challenging machine for us to run. Our only frustration is that we would like to be running it now but the beam is not quite ready.
My operations team has put a huge amount of work into preparing the procedures and making sure we know what we’re doing when we start. We are very interested in the end result and we’re always fascinated to find out what is being discovered, but our principle job is the machine and to deliver the beams in a good condition. We’re very conscious that we’re piloting the world’s largest experiment and there is professional pride involved in doing that as well as possible.
Getting the beam to the door of the LHC is quite a big challenge; by the time the beam arrives at the machine it has already travelled roughly 6m kilometres. It starts life in a hydrogen bottle, goes through a linear accelerator, and then a booster synchroton and other synchrotons, and is finally injected into the LHC. It has taken us several years to polish this process.
The next challenge is to make it go the last 27km, which is from the entrance of the collider, all the way around and back to the start again. That will determine whether there are any fundamental problems. Once we’ve gone around once it will be a lot easier to go twice, three times and then millions of times.
It’s a bit like threading a very long needle with a very small eye. Once the beam is through we have to correct its position all around the machine to make sure it goes back to the beginning. We do something called "closing the trajectory" to make the beam stay in the centre of the vacuum chamber. Once we’ve done that we start to slowly bring more equipment to bear on the machine.
The whole process will be fairly long. Initially we work with a very small beam and take things carefully to make sure we understand what’s happening – because anything we miss will come back and bite us later on. We start with the least intensity we can get away with for our instrumentation, and only when we’re ready will we increase its strength. So it’s going to be another couple of months before the machine can start taking collision data.
As far as the outside world is concerned, I know that the exciting bit is the end result – the recreation of the big bang. I know not many people are interested in the mechanics of making the accelerator. But here at Cern the control centre and the operations team are very much the centre of activities. And it’s thrilling to be at the centre of something so immense. The level of anticipation in the physics world and outside it is extremely high, and I’m sure we’ll be popping champagne corks before long. But in the control room itself we’ll be celebrating the smaller things – things that don’t perhaps mean much to other people but to us are important milestones.
About Large Hadron Collider
The Large Hadron Collider (LHC) is a particle accelerator complex intended to collide opposing beams of 7 TeV protons. Its main purpose is to explore the validity and limitations of the standard model, the current theoretical picture for particle physics. This model is known to break down at a certain high energy level.
The LHC is being built by the European Organization for Nuclear Research (CERN), and lies under the Franco-Swiss border near Geneva, Switzerland. The LHC will become the world's largest and highest-energy particle accelerator. It is funded and built in collaboration with over two thousand physicists from thirty-four countries as well as hundreds of universities and laboratories.
The collider is currently undergoing commissioning while being cooled down to its final operating temperature of approximately 2 K (−271.15 °C). The first particle beams are due for injection in August 2008, with the first collisions planned to take place about two months later.
When activated, it is theorized that the collider will produce the elusive Higgs boson, the observation of which could confirm the predictions and "missing links" in the Standard Model of physics and could explain how other elementary particles acquire properties such as mass. The verification of the existence of the Higgs boson would be a significant step in the search for a Grand Unified Theory, which seeks to unify three of the four known fundamental forces: electromagnetism, the strong nuclear force and the weak nuclear force, leaving out only gravity. The Higgs boson may also help to explain why gravitation is so weak compared to the other three forces. In addition to the Higgs boson, other theorized novel particles that might be produced, and for which searches are planned, include strangelets, micro black holes, magnetic monopoles and supersymmetric particles.
The collider is contained in a circular tunnel with a circumference of 27 kilometres (17 mi) at a depth ranging from 50 to 175 metres underground. The 3.8 metre diameter, concrete-lined tunnel, constructed between 1983 and 1988, was formerly used to house the LEP, an electron-positron collider. It crosses the border between Switzerland and France at four points, although most of it is in France. Surface buildings hold ancillary equipment such as compressors, ventilation equipment, control electronics and refrigeration plants.
The collider tunnel contains two adjacent beam pipes, each containing a proton beam (a proton is one type of hadron). The two beams travel in opposite directions around the ring. Some 1232 bending magnets keep the beams on their circular path, while an additional 392 focusing magnets are used to keep the beams focused, in order to maximize the chances of interaction between the particles in the four intersection points, where the two beams will cross. In total, over 1600 superconducting magnets are installed, with most weighing over 27 tonnes. Approximately 96 tonnes of liquid helium is needed to keep the magnets at the operating temperature, making the LHC the largest cryogenic facility in the world at liquid helium temperature.
About Large Electron-Positron Collider
The Large Electron-Positron Collider (LEP) was one of the largest particle accelerators ever made. It was built at CERN, a multi-national center for research in nuclear and particle physics near Geneva, Switzerland. LEP was a circular collider with a circumference of 27 kilometers built in a tunnel straddling the border of Switzerland and France. It was used from 1989 until 2000. To date, LEP is the most powerful accelerator of leptons ever built.
When the LEP collider started operation in 1989 it accelerated the electrons and positrons to a total energy of 45 GeV each to enable production of the Z Boson, which has a mass of approximately 91 GeV. The accelerator was upgraded later to enable production of a pair of W Bosons, each weighing approximately 80 GeV. LEP collider energy eventually topped at 209 GeV at the end in 2000. At the end of 2000, LEP was shut down and then dismantled in order to make room in the tunnel for the construction of the Large Hadron Collider (LHC).
The Super Proton Synchrotron (an older ring collider) was used to accelerate electrons and positrons to nearly the speed of light. These are then injected into the ring. As in all ring colliders, the LEP's ring consists of many magnets which force the charged particles into a circular trajectory (so that they stay inside the ring), RF accelerators which accelerate the particles with radio frequency (RF) waves and quadrupoles that focus the particle beam (i.e. keep the particles together). Rather than increasing the particles' velocities (which are already very close to the speed of light), the function of the accelerators is really to increase the particles' energies so that heavy particles can be created when the particles collide. When the particles are accelerated to maximum energy (and focused to so-called bunches), an electron and a positron bunch is made to collide with each other at one of the collision points of the detector. When an electron and a positron collide, they annihilate to a virtual particle, either a photon or a Z boson. The virtual particle almost immediately decays into other elementary particles, which are then detected by huge particle detectors.
In figure, A photographer stands in front of the magnet core of the LHC particle accelerator
Tags: large hadron collider (LHC) , particle accelerator , Paul Collier , Sheffield Hallam University in England , large electron-positron collider ,
