How vacuum impacts the world's largest & most powerful particle collider
October 19,2020
3 MIN READ
Situated deep beneath the Franco-Swiss border is a massive ring of metal and magnets: the Large Hadron Collider (LHC), the world's largest and most powerful particle collider.
Housed 100 meters underground at CERN (Conseil Européen pour la Recherche Nucléaire), the LHC is made up of a 27-kilometer ring of superconducting magnets. The collider’s accelerator allows two extremely high-energy particle beams to travel in opposite directions at speeds close to that of light before colliding with one another.
Vacuums inside the large hadron collider
A successful and powerful collision requires that ultra-high vacuum levels be maintained while the LHC is being operated. The following is an overview of the primary vacuum systems employed in the collider.
Beam vacuum
A collision involves two particles that are "beamed" at high speeds in opposite directions, with each particle in its own tube. These two tubes must be kept at extremely high vacuum levels to maximize the duration of the beam and maintain low pressure for the experiments. This is achieved by what is known as the beam vacuum.
Two pumping mechanisms are used to achieve this:
- Cryogenic pumping: residual gas molecules are physically adsorbed into the cold bore surface at a temperature of 1.9 K
- Non-evaporable getter (NEG) pumping: residual gas molecules are chemically adsorbed onto the surface of the beam pipes
Insulation vacuum
The LHC's superconducting magnets are cooled with liquid helium to a temperature of 1.9 K (approx. -271 °C). The LHC employs a powerful vacuum to thermally insulate the magnets and consequently maintain the extremely low temperatures needed for a successful collision.
Pumps inside the large hadron collider
The primary pump technologies employed within the collider are:
Ion pumps
An Ion pump is a type of vacuum pump that operates by sputtering a metal getter.
Turbomolecular pumps
Turbomolecular pumps operate on the principle that gas molecules can be made to undergo repeated collisions with a moving solid surface to attain momentum in the desired direction.
Both pump systems must have the ability to tolerate high radiation and magnetic field levels.
Potential maintenance challenges
A major challenge faced while assembling the LHC was leak detection: leak tightness must be ensured to reliably operate large vacuum systems.
A leak can cause base pressure to rise above or fall below the required levels, resulting in the need for significant — and expensive — re-working.
Future upgrades and the high luminosity large hadron collider
The LHC is currently being upgraded and its successor will be known as the High Luminosity Large Hadron Collider (HL-LHC). The upgrades began in June 2018 and are set to be completed in 2027. The changes are expected to increase the discovery range of new particles by around 20-30% over the current LHC and also extend the LHC's lifetime to 2040.
