Misplaced Pages

Large Hadron Collider: Difference between revisions

Article snapshot taken from[REDACTED] with creative commons attribution-sharealike license. Give it a read and then ask your questions in the chat. We can research this topic together.
Browse history interactively← Previous editNext edit →Content deleted Content addedVisualWikitext
Revision as of 20:05, 10 January 2008 editDark Formal (talk | contribs)Extended confirmed users586 edits →Strangelets: removed section because of garbled and repeated references, and inappropriate focus on speculative results← Previous edit Revision as of 02:24, 11 January 2008 edit undoHomocion (talk | contribs)148 edits →OtherNext edit →
(One intermediate revision by the same user not shown)
Line 87: Line 87:
CERN<ref></ref> and others<ref> - Physicist Dave Wark of Imperial College, London reporting for '']''</ref> have pointed out that the probability of such events is extremely small. One argument for the safety of colliders such as the LHC states that if the Earth were in danger of any such fate, the Earth and Moon would have met that fate billions of years ago due to their constant bombardment from space by very high energy ] such as protons and other particles, which are millions of times more energetic than anything that could be produced by the LHC. However, simple Newtonian physics requires that opposite momentum collisions for colliders result in "at rest" MBHs{{Fact|date=January 2008}} , if they are created. This contrasts sharply with cosmic ray induced events from bombardment of the upper atmosphere, which would result in near-relativistic MBHs. {{Fact|date=January 2008}} CERN<ref></ref> and others<ref> - Physicist Dave Wark of Imperial College, London reporting for '']''</ref> have pointed out that the probability of such events is extremely small. One argument for the safety of colliders such as the LHC states that if the Earth were in danger of any such fate, the Earth and Moon would have met that fate billions of years ago due to their constant bombardment from space by very high energy ] such as protons and other particles, which are millions of times more energetic than anything that could be produced by the LHC. However, simple Newtonian physics requires that opposite momentum collisions for colliders result in "at rest" MBHs{{Fact|date=January 2008}} , if they are created. This contrasts sharply with cosmic ray induced events from bombardment of the upper atmosphere, which would result in near-relativistic MBHs. {{Fact|date=January 2008}}




===Ice 9 reaction: strangelet fission ===
In Physics sometimes a new phenomena takes a name from literature. Quarks were taken from Joyce, and in the same tradition Ice 9, the reaction that converts matter into lumps of quarks called strangelets was also taken from literature. An ice-9 reaction is thus the name given to a process of Strange Matter Fission. It was first postulated by Nobel Prize Wilzeck in a Letter to SciAm, July 1999: "There is a speculative but quite respectable possibility that subatomic chunks of a new stable form of matter called strangelets might be produced (…) One might be concerned about an 'ice-9' type transition wherein a strangelet grows by incorporating and transforming the ordinary matter in its surroundings" Wilczek.

The process of strangelet fission converts normal matter into strange superfluid as in Vonnegut's book; and it is the best known model to explain how the iron core of stars becomes a strangelet superfluid, as it seems to happen in pulsars and neutron stars. The theme enjoyed a certain popular attention when in the 90s it was speculated that RHIC, an American accelerator would produce an ice-9 reaction, and the BBC informed about this; but calculus showed RHIC would only create unstable strangelet plasma, with lower energies to be stable and start the fission process, as it was the case.

Still the propeties of the proto-strangelet were considered by experimentalists a 'perfect surprise'. And doubts have been casted again on a possible ice-9 reaction taken place in the 10 times more powerful LHC accelerator. Since then, many articles have advanced the question and it is today fairly established that the parameters of an ice-9 reaction could take place at CERN; regarding the ice-9 process is a theme still argued theoretically . In any case, the ice-9 reaction has drawn again Media attention, which is bound to increase till the LHC switches on next spring, as even a small chance of the Earth becoming a strange liquid, is a notorious event for the 2008.




===Other=== ===Other===

Other disaster scenarios include: Other disaster scenarios include:


Revision as of 02:24, 11 January 2008

This article needs attention from an expert in Physics. Please add a reason or a talk parameter to this template to explain the issue with the article. WikiProject Physics may be able to help recruit an expert. (January 2008)
This article needs attention from an expert in Health & Safety. Please add a reason or a talk parameter to this template to explain the issue with the article. WikiProject Health & Safety may be able to help recruit an expert. (January 2008)

Template:Future scientific facility

The Large Hadron Collider (LHC) is a particle accelerator and collider located at CERN, near Geneva, Switzerland (46°14′N 6°03′E / 46.233°N 6.050°E / 46.233; 6.050). Currently under construction, the LHC is scheduled to begin operation in May 2008. The LHC is expected to become the world's largest and highest-energy particle accelerator. The LHC is being funded and built in collaboration with over two thousand physicists from thirty-four countries as well as hundreds of universities and laboratories.

When activated, it is hoped 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 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 fundamental forces: electromagnetism, the strong force, and the weak force. The Higgs boson may also help to explain why the remaining force, gravitation, is so weak compared to the other three forces.

Technical design

The collider is contained in a circular tunnel with a circumference of 26.659 kilometres (16.5 miles), at a depth ranging from 50 to 175 metres underground. The tunnel was formerly used to house the LEP, an electron-positron collider.

The 3.8 metre diameter, concrete-lined tunnel actually crosses the border between Switzerland and France at four points, although the majority of its length is inside France. The collider itself is located underground, with many surface buildings holding ancillary equipment such as compressors, ventilation equipment, control electronics and refrigeration plants.

The collider tunnel contains two pipes enclosed within superconducting magnets cooled by liquid helium, each pipe containing a proton beam. The two beams travel in opposite directions around the ring. Additional magnets are used to direct the beams to four intersection points where interactions between them will take place.

The protons will each have an energy of 7 TeV, giving a total collision energy of 14 TeV. It will take around ninety microseconds for an individual proton to travel once around the collider. Rather than continuous beams, the protons will be "bunched" together into approximately 2,800 bunches, so that interactions between the two beams will take place at discrete intervals never shorter than twenty-five nanoseconds apart. When the collider is first commissioned, it will be operated with fewer bunches, to give a bunch crossing interval of seventy-five nanoseconds. The number of bunches will later be increased to give a final bunch crossing interval of twenty-five nanoseconds.

LHC Accelerators

Prior to being injected into the main accelerator, the particles are prepared through a series of systems that successively increase the particle energy levels. The first system is the linear accelerator Linac2 generating 50 MeV protons which feeds the Proton Synchrotron Booster (PSB). Protons are then injected at 1.4 GeV into the Proton Synchrotron (PS) at 26 GeV. Finally the Super Proton Synchrotron (SPS) can be used to increase the energy of protons up to 450 GeV.

The LHC can also be used to collide heavy ions such as lead (Pb) with a collision energy of 1,150 TeV. The ions will be first accelerated by the linear accelerator Linac 3, and the Low-Energy Injector Ring (LEIR) will be used as an ion storage and cooler unit. The ions are then further accelerated by the Proton Synchrotron (PS) and Super Proton Synchrotron (SPS).

Six detectors are being constructed at the LHC. They are located underground, in large caverns excavated at the LHC's intersection points. Two of them, ATLAS and CMS are large, "general purpose" particle detectors. ALICE is a large detector designed to search for a quark-gluon plasma in the very messy debris of heavy ion collisions. The other three (LHCb, TOTEM, and LHCf) are smaller and more specialized.

The size of the LHC constitutes an exceptional engineering challenge with unique safety issues. While running, the total energy stored in the magnets is 10 GJ, and in the beam, 725 MJ. Loss of only 10 of the beam is sufficient to quench a superconducting magnet, while the beam dump must absorb an energy equivalent to a typical air-dropped bomb. For comparison, 725 MJ is equivalent to the detonation energy of approximately 157 kg (347 pounds) of TNT, and 10 GJ is about 2.5 tons of TNT.

Research

A Feynman diagram of one way the Higgs boson may be produced at the LHC. Here, two quarks each emit a W or Z boson which combine to make a neutral Higgs.
A simulated event in the CMS detector, featuring the appearance of the Higgs boson.

When in operation, about seven thousand scientists from eighty countries will have access to the LHC, the largest national contingent of seven hundred being from the United States. Physicists hope to use the collider to test various grand unified theories and enhance their ability to answer the following questions:

As an ion collider

The LHC physics program is mainly based on proton-proton collisions. However, shorter running periods, typically one month per year, with heavy-ion collisions are included in the programme. While lighter ions are considered as well, the baseline scheme deals with lead (Pb) ions. This will allow an advancement in the experimental programme currently in progress at the Relativistic Heavy Ion Collider (RHIC).

Proposed upgrade

CMS detector for LHC

After some years of running, any particle physics experiment typically begins to suffer from diminishing returns. The way around the diminishing returns is to upgrade the experiment, either in energy or in luminosity.

A luminosity upgrade of the LHC, called the Super LHC, has been proposed, to be made after ten years of LHC operation. The optimal path for the LHC luminosity upgrade includes an increase in the beam current (i.e., the number of protons in the beams) and the modification of the two high luminosity interaction regions, ATLAS and CMS. To achieve these increases, the energy of the beams at the point that they are injected into the (Super) LHC should also be increased to 1 TeV. This will require an upgrade of the full pre-injector system, the needed changes in the Super Proton Synchrotron being the most expensive.

Cost

The construction of LHC was originally approved in 1995 with a budget of 2.6 billion Swiss francs, with another 210 million francs (€140 m) towards the cost of the experiments. However, cost over-runs, estimated in a major review in 2001 at around 480 million francs (€300 m) in the accelerator, and 50 million francs (€30 m) for the experiments, along with a reduction in CERN's budget pushed the completion date out from 2005 to April 2007. 180 million francs (€120 m) of the cost increase has been the superconducting magnets. There were also engineering difficulties encountered while building the underground cavern for the Compact Muon Solenoid.

LHC@Home

Main article: LHC@home

LHC@Home, a distributed computing project, was started to support the construction and calibration of the LHC. The project uses the BOINC platform to simulate how particles will travel in the tunnel. With this information, the scientists will be able to determine how the magnets should be calibrated to gain the most stable "orbit" of the beams in the ring.

Safety concerns

This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources in this section. Unsourced material may be challenged and removed. (January 2008) (Learn how and when to remove this message)
This section's factual accuracy is disputed. Relevant discussion may be found on the talk page. Please help to ensure that disputed statements are reliably sourced. (Learn how and when to remove this message)

As with previous particle accelerators, people inside the physics community and in the media have voiced concern that the LHC or similar types of experiments might trigger one of several theoretical disasters capable of destroying the Earth. A study was carried out by physicists at CERN and other recognised institutes to examine these issues.

Black holes

Though the standard model predicts that LHC energies are far too low to create black holes, some non-standard theories lower the requirements, and CERN themselves have published articles that the LHC could create micro black holes at the rate of one per second. The primary cause for concern is that Hawking radiation, a postulated means by which any such black holes would dissipate before becoming dangerous, remains entirely theoretical. In academia, the theory of Hawking radiation is considered plausible, but there remains considerable question of whether it is correct.


CERN and others have pointed out that the probability of such events is extremely small. One argument for the safety of colliders such as the LHC states that if the Earth were in danger of any such fate, the Earth and Moon would have met that fate billions of years ago due to their constant bombardment from space by very high energy cosmic rays such as protons and other particles, which are millions of times more energetic than anything that could be produced by the LHC. However, simple Newtonian physics requires that opposite momentum collisions for colliders result in "at rest" MBHs , if they are created. This contrasts sharply with cosmic ray induced events from bombardment of the upper atmosphere, which would result in near-relativistic MBHs.


Ice 9 reaction: strangelet fission

In Physics sometimes a new phenomena takes a name from literature. Quarks were taken from Joyce, and in the same tradition Ice 9, the reaction that converts matter into lumps of quarks called strangelets was also taken from literature. An ice-9 reaction is thus the name given to a process of Strange Matter Fission. It was first postulated by Nobel Prize Wilzeck in a Letter to SciAm, July 1999: "There is a speculative but quite respectable possibility that subatomic chunks of a new stable form of matter called strangelets might be produced (…) One might be concerned about an 'ice-9' type transition wherein a strangelet grows by incorporating and transforming the ordinary matter in its surroundings" Wilczek.

The process of strangelet fission converts normal matter into strange superfluid as in Vonnegut's book; and it is the best known model to explain how the iron core of stars becomes a strangelet superfluid, as it seems to happen in pulsars and neutron stars. The theme enjoyed a certain popular attention when in the 90s it was speculated that RHIC, an American accelerator would produce an ice-9 reaction, and the BBC informed about this; but calculus showed RHIC would only create unstable strangelet plasma, with lower energies to be stable and start the fission process, as it was the case.

Still the propeties of the proto-strangelet were considered by experimentalists a 'perfect surprise'. And doubts have been casted again on a possible ice-9 reaction taken place in the 10 times more powerful LHC accelerator. Since then, many articles have advanced the question and it is today fairly established that the parameters of an ice-9 reaction could take place at CERN; regarding the ice-9 process is a theme still argued theoretically . In any case, the ice-9 reaction has drawn again Media attention, which is bound to increase till the LHC switches on next spring, as even a small chance of the Earth becoming a strange liquid, is a notorious event for the 2008.


Other

Other disaster scenarios include:

Construction accidents and delays

On October 25, 2005, a technician, José Pereira Lages, was killed in the LHC tunnel when a crane load was accidentally dropped.

On March 27, 2007, there was an incident during a pressure test involving one of the LHC's inner triplet magnet assemblies provided by Fermilab and KEK. No people were injured, but a cryogenic magnet support broke. Analysis revealed that its design, made as thin as possible for better insulation, was not strong enough to withstand the forces generated during pressure testing. Details are available in a statement from Fermilab, with which CERN is in agreement.

Repairing the broken magnet and reinforcing the eight identical copies used by LHC, in addition to a number of other small delays, caused a postponement of the planned November 26, 2007 startup date to May 2008.

See also

Notes and references

  1. New start-up schedule for world's most powerful particle accelerator
  2. LHC Machine Outreach
  3. Ellis, John (19 July 2007). "Beyond the standard model with the LHC". Nature. 448: 297–301. doi:10.1038/nature06079. Retrieved 2007-11-24. There are good reasons to hope that the LHC will find new physics beyond the standard model, but no guarantees. The most one can say for now is that the LHC has the potential to revolutionize particle physics, and that in a few years' time we should know what course this revolution will take.
  4. Symmetry magazine, April 2005
  5. "...in the public presentations of the aspiration of particle physics we hear too often that the goal of the LHC or a linear collider is to check off the last missing particle of the standard model, this year’s Holy Grail of particle physics, the Higgs boson. The truth is much less boring than that! What we’re trying to accomplish is much more exciting, and asking what the world would have been like without the Higgs mechanism is a way of getting at that excitement." -Chris Quigg, Nature's Greatest Puzzles
  6. Ions for LHC
  7. PDF presentation of proposed LHC upgrade
  8. Maiani, Luciano (16 October 2001). "LHC Cost Review to Completion". CERN. Retrieved 2001-01-15.
  9. Feder, Toni (2001). "CERN Grapples with LHC Cost Hike". Physics Today. 54 (12): 21. Retrieved 2007-01-15. {{cite journal}}: Unknown parameter |month= ignored (help)
  10. SciAm, July 1999: "There is a speculative but quite respectable possibility that subatomic chunks of a new stable form of matter called strangelets might be produced (…) One might be concerned about an 'ice-9' type transition wherein a strangelet grows by incorporating and transforming the ordinary matter in its surroundings" Wilczek, awarded Nobel Prize in Physics
  11. New Scientist, 28 August 1999: "A Black Hole Ate My Planet"
  12. Horizon: End Days, an episode of the BBC television series Horizon
  13. Blaizot, J.-P. et al. Study of Potentially Dangerous Events During Heavy-Ion Collisions at the LHC. (PDF)
  14. CERN courier - The case for mini black holes. Nov 2004
  15. American Institute of Physics Bulletin of Physics News, Number 558, September 26, 2001, by Phillip F. Schewe, Ben Stein, and James Riordon
  16. Dimopoulos, S. and Landsberg, G. Black Holes at the Large Hadron Collider. Phys. Rev. Lett. 87 (2001).
  17. Adam D. Helfer: General Relativity and Quantum Cosmology
  18. Safety at the LHC
  19. Tiny Black Holes - Physicist Dave Wark of Imperial College, London reporting for NOVA scienceNOW
  20. Hewett, JoAnne (25 October 2005). "Tragedy at CERN" (Blog). Cosmic Variance. Retrieved 2007-01-15. author and date indicate the beginning of the blog thread
  21. "Message from the Director-General" (Press release) (in English and French). CERN. 26 October 2005. Retrieved 2007-01-15.{{cite press release}}: CS1 maint: unrecognized language (link)
  22. LHC Magnet Test Failure
  23. Updates on LHC inner triplet failure
  24. "The God Particle". www.bbc.com. Retrieved 2007-05-22.
  25. "CERN announces new start-up schedule for world's most powerful particle accelerator" (Press release). CERN. 2007-06-22. Retrieved 2007-07-01.

External links


Articles

European Organization for Nuclear Research (CERN)
Large Hadron Collider (LHC)
Large Electron–Positron Collider (LEP)
Super Proton Synchrotron (SPS)
Proton Synchrotron (PS)
Linear accelerators
Other accelerators
ISOLDE facility
Non-accelerator experiments
Future projects
Related articles
Categories:
Large Hadron Collider: Difference between revisions Add topic