Why does LHC have 8 interaction points?

In summary: Eight points are around 528 meters long each and have lifts, surface installations, and underground infrastructure.
  • #1
kelly0303
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Hello! I attached a picture of the LHC main rings. I see 8 interactions points labeled, even if there are only 4 experiments (and the other 4 points don't even intersect). What are these 4 other points? Thank you!
 

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  • #2
From here-
The Large Hadron Collider (LHC) at CERN


The LHC has 8 arcs and 8 straight sections between the arcs. The straight sections are around 528 m long. Each straight section has associated with it surface and underground installations, lifts, and a wide variety of technical infrastructure. These locations are referred to as the LHC points.

  • The four main experiments are situated at point 1 (ATLAS), point 2 (ALICE), point 5 (CMS) and point 8 (LHCB).
  • Injection of clockwise beam (beam 1) takes place at point 2. Injection of anti-clockwise beam (beam 2) takes place at point 8.
  • The main collimator installations are at points 3 and 7.
  • The radio frequency (RF) system is situated at point 4.
  • The beam dump system is situated at point 6.
Functionally the LHC is divided into 8 sectors (namely sectors 12, 23, 34, 45, 56, 67, 78, 81). A sector spans the underground installation between 2 LHC points - thus sector 12 lies between point 1 to point 2 etc. Importantly a sector can be cooled and powered independently.
 
  • #3
LHC was built in the same tunnel as LEP, an electron-positron collider. At LEP the particles lost a significant amount of energy to synchrotron radiation in each turn, so LEP needed long straight sections for RF cavities to accelerate the particles again. That lead to a design with eight 45 degree turns with straight sections in between. Four of them were occupied by experiments (ALEPH, DELPHI, OPAL, L3).
For LHC the energy is limited by the curvature radius and it doesn't need so many straight sections - a more circular tunnel with shorter straight sections would be better. Changing the tunnel layout would have been very expensive so it was decided to use the existing tunnel.

One experiment (ATLAS) is directly at the main CERN site, two more are reasonably close, only CMS is quite far away. There are shuttle buses but it is still annoying if you have to move between experiments and CERN site every day (e.g. for shifts).
 
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Why does LHC have 8 interaction points?

The Large Hadron Collider (LHC) has 8 interaction points in order to increase the chances of particle collisions and to allow multiple experiments to be conducted simultaneously.

How do the interaction points in LHC work?

The interaction points in LHC are where the beams of particles cross and collide with each other, creating high-energy collisions that can produce new particles. These points are carefully designed and monitored to maximize the chances of collisions occurring.

Why are there 8 interaction points specifically?

The number of interaction points in LHC was determined based on a balance between the number of experiments that could be conducted simultaneously and the complexity and cost of the collider. The current number of 8 interaction points was deemed to be the most efficient and effective for scientific research.

What types of experiments are conducted at the interaction points in LHC?

The interaction points in LHC allow for a wide range of experiments to be conducted, such as studies of the Higgs boson, searches for dark matter, and investigations into the nature of the universe at the smallest scales.

Are all 8 interaction points used at the same time?

No, not all 8 interaction points are used simultaneously. The LHC is capable of running multiple experiments at the same time, but typically only a few of the interaction points are used for experiments while the others are used for maintenance or upgrades.

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