Future Circular Collider

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Hadron colliders
Intersecting Storage RingsCERN, 1971–1984
Proton-Antiproton Collider (SPS)CERN, 1981–1991
ISABELLEBNL, cancelled in 1983
TevatronFermilab, 1987–2011
Superconducting Super ColliderCancelled in 1993
Relativistic Heavy Ion ColliderBNL, 2000–present
Large Hadron ColliderCERN, 2009–present
Future Circular ColliderProposed
The future circular colliders considered under the FCC study compared to previous circular colliders.

The Future Circular Collider (FCC) is a conceptual study that aims to develop designs for a post-LHC particle accelerator with an energy significantly above that of previous circular colliders (SPS, Tevatron, LHC).[1][2] After injection at 3.3 TeV, each beam would have a total energy of 560 MJ. At collision energy of 100 TeV this increases to 16.7 GJ. These total energy values exceed the present LHC by nearly a factor of 30.[3]

The FCC study explores the feasibility of different particle collider scenarios with the aim of significantly increasing the energy and luminosity compared to existing colliders. It aims to complement existing technical designs for linear electron/positron colliders (ILC and CLIC).

The study has an emphasis on proton/proton (hadron) and electron/positron (lepton) colliders while a hadron/lepton scenario is also examined. The study explores the potential of hadron and lepton circular colliders, performing an analysis of infrastructure and operation concepts and considering the technology research and development programmes that are required to build and operate a future circular collider. A conceptual design report was published in early 2019,[4] in time for the next update of the European Strategy for Particle Physics.

The FCC's proposed particle accelerator has been criticized for costs, with the larger variant projected to be over 20 billion US dollars.[5] Its potential to make new discoveries has also been questioned by physicists. Theoretical physicist Sabine Hossenfelder criticized the CERN design report for outlining a wide range of open problems in physics, despite the fact that the accelerator will likely only have the potential to resolve a small part of them. She noted that (as of 2019) there is "no reason that the new physical effects, like particles making up dark matter, must be accessible at the next larger collider".[6]

Background[edit]

The study hosted by CERN has been initiated as a direct response to the high-priority recommendation of the updated European Strategy for Particle Physics, published in 2013:

"CERN should undertake design studies for accelerator projects in a global context, with emphasis on proton-proton and electron-positron high-energy frontier machines. These design studies should be coupled to a vigorous accelerator R&D programme, including high-field magnets and high-gradient accelerating structures, in collaboration with national institutes, laboratories and universities worldwide."

This is in line with the recommendations of the United States’ Particle Physics Project Prioritization Panel (P5) and of the International Committee for Future Accelerators (ICFA).

The discovery of the Higgs boson at the LHC, together with the absence so far of any phenomena beyond the Standard Model in collisions at centre of mass energies up to 8 TeV, has triggered an interest in future colliders to push the energy and precision frontiers. A future “energy frontier” collider at 100 TeV is a “discovery machine”, reaching out to so far unknown territories. "New physics" seen at such a machine could explain observations such as the prevalence of matter over antimatter and non-zero neutrino masses.

Motivation[edit]

The LHC has greatly advanced our understanding of matter and the Standard Model (SM). The discovery of the Higgs boson completed the Standard Model of Particle Physics, the theory that describes the laws governing most of the known Universe. Yet the Standard Model cannot explain several observations, such as:

Colliders with a higher energy and collision rate can help solving these questions.

The Future Circular Collider (FCC) study develops options for potential high-energy frontier circular colliders at CERN for the post-LHC era. Among other things, it plans to look for dark matter particles, which accounts for approximately 25% of the energy in the observable universe[7], make precise measurements of the Higgs boson, and explore beyond the Standard Model theories. It might find supersymmetric particles, if they exist, and it can search for additional fundamental interactions.

Five percent of the Universe is directly observable. The Standard Model of Particle Physics describes it precisely. What about the remaining 95%?

Scope[edit]

The FCC study puts an emphasis on proton/proton (hadron/hadron, hh) high-energy and electron/positron (ee) high-intensity frontier machines. A hadron/lepton interaction scenario (he) is also examined.

A 100 TeV hadron collider in a 100 km long tunnel defines the overall infrastructure for the FCC study. The development of baseline designs for an energy-frontier hadron collider and a luminosity-frontier electron/positron collider forms the core of the study.

The FCC study identifies the technological advancements required for reaching the planned energy and intensity and performs technology feasibility assessments for critical elements. The study provides an analysis of the infrastructure and operation cost while cost optimization, greater efficiency and reliable operation are key parameters in the study.

The FCC study explores the physics cases for all collider scenarios for discovery and precision physics. Scientists and engineers are working on the detector concepts needed to address the physics questions in each of the scenarios (hh, ee, he). The work programme includes experiment and detector concept studies to allow new physics to be explored. Detector technologies will be based on experiment concepts, the projected collider performances and the physics cases. New technologies have to be developed in diverse fields such as cryogenics, superconductivity, material science, and computer science, including new data processing and data management concepts.

Accelerators[edit]

The FCC study developed and evaluated three accelerator concepts for its conceptual design report.

FCC-hh (proton/proton and ion/ion)[edit]

A future energy-frontier hadron collider will be able to discover force carriers of new interactions up to masses of around 30 TeV if they exist. The higher collision energy extends the search range for dark matter particles well beyond the TeV region, while supersymmetric partners of quarks and gluons can be searched for at masses up to 15-20 TeV and the search for a possible substructure inside quarks can be extended down to distance scales of 10−21 m. Due to the higher energy and collision rate billions of Higgs bosons and trillions of top quarks will be produced, creating new opportunities for the study of rare decays and flavour physics.

A hadron collider will also extend the study of Higgs and gauge boson interactions to energies well above the TeV scale, providing a way to analyse in detail the mechanism underlying the breaking of the electroweak symmetry.

In heavy-ion collisions the FCC-hh collider allows the exploration of the collective structure of matter at more extreme density and temperature conditions than before.[8][9]

FCC-ee [formerly TLEP] (electron/positron)[edit]

A lepton collider with centre-of-mass collision energies between 90 and 350 GeV is considered a potential intermediate step towards the realisation of the hadron facility. Clean experimental conditions have given e+e storage rings a strong record both for measuring known particles with the highest precision and for exploring the unknown.

More specifically, high luminosity and improved handling of lepton beams would create the opportunity to measure the properties of the Z, W, Higgs, and top particles, as well as the strong interaction, with increased accuracy.[10][11]

The measurements of invisible or exotic decays of the Higgs and Z bosons would offer discovery potential for dark matter or heavy neutrinos. In effect, the FCC-ee could enable profound investigations of electroweak symmetry breaking and open a broad indirect search for new physics over several orders of magnitude in energy or couplings.

FCC-he (electron/proton)[edit]

With the huge energy provided by the 50 TeV proton beam and the potential availability of an electron beam with energy of the order of 60 GeV, new horizons open up for the physics of deep inelastic scattering. The FCC-he collider would be both a high-precision Higgs factory and a powerful microscope that could discover new particles, study quark/gluon interactions, and examine possible further substructure of matter in the world.

Technologies[edit]

As the development of a next generation particle accelerator requires new technology the FCC Study has studied the equipment and machines that are needed for the realization of the project, taking into account the experience from past and present accelerator projects.[12]

The FCC study drives the research in the field of superconducting materials.

The foundations for these advancements are being laid in a focused R&D programmes:

  • a 16 Tesla high-field accelerator magnet and related super-conductor research,
  • a 100 MW radiofrequency acceleration system that can efficiently transfer power from the electricity grid to the beams,
  • a highly efficient large-scale cryogenics infrastructure to cool down superconducting accelerator components and the accompanying refrigeration systems.
The CERN magnet group produced a 16.2-Tesla peak field magnet – nearly twice that produced by the current LHC dipoles - paving the way for future more powerful accelerators.
New superconducting Radiofrequency (RF) Cavities are developed to accelerate particles to higher energies.

Numerous other technologies from various fields (accelerator physics, high-field magnets, cryogenics, vacuum, civil engineering, material science, superconductors, ...) are needed for reliable, sustainable and efficient operation.

Magnet Technologies[edit]

High-field superconducting magnets are a key enabling technology for a frontier hadron collider. To steer a 50 TeV beam over a 100 km tunnel, 16-Tesla dipoles will be necessary, twice the strength of the magnetic field of the LHC.

Evolution of superconducting Nb-Ti magnets for particle accelerator use.

The magnet R&D aims to extend the range of operation of accelerator magnets based on Low Temperature Superconductors (LTS) up to 16 T and explore the technological challenges inherent to the use of High Temperature Superconductors (HTS) for accelerator magnets in the 20 T range.

Superconducting Radiofrequency Cavities[edit]

The beams that move in a circular accelerator lose a percentage of their energy due to synchrotron radiation: up to 5% every turn for electrons and positrons, much less for protons and heavy ions. To maintain their energy, a system of radiofrequency cavities constantly provides up to 50 MW to each beam.

Cryogenics[edit]

Liquefaction of gas is a power-intensive operation of cryogenic technology. The future lepton and the hadron colliders would make intensive use of low-temperature superconducting devices, operated at 4.5 K and 1.8 K, requiring very large-scale distribution, recovery, and storage of cryogenic fluids.

Improving refrigeration cycle efficiency from 33% to 45% leads to 20% reduced cost and reduced power.

As a result, the cryogenic systems that have to be developed correspond to two to four times the presently deployed systems and require increased availability and maximum energy efficiency. Any further improvements in cryogenics are expected to find wide applications in medical imaging techniques.

The cryogenic beam vacuum system for an energy-frontier hadron collider must absorb an energy of 50 W per meter at cryogenic temperatures. To protect the magnet cold bore from the head load, the vacuum system needs to be resistant against electron cloud effects, highly robust, and stable under superconducting quench conditions.

It should also allow fast feedback in presence of impedance effects. New composite materials have to be developed to achieve these unique thermo-mechanics and electric properties for collimation systems. Such materials could also be complemented with the ongoing exploration of thin-film NEG coating that is used in the internal surface of the copper vacuum chambers.

Collimation[edit]

A 100 TeV hadron collider requires efficient and robust collimators, as 100 kW of hadronic background is expected at the interaction points. Moreover, fast self-adapting control systems with sub-millimeter collimation gaps are necessary to prevent irreversible damage of the machine and manage the 8.3 GJ stored in each beam.

To address these challenges, the FCC Study searches for designs that can withstand the large energy loads with acceptable transient deformation and no permanent damage. Novel composites with improved thermo-mechanical and electric properties will be investigated in cooperation with the FP7 HiLumi LHC DS and EuCARD2 programmes.

Timescale[edit]

The Large Hadron Collider at CERN with its High Luminosity upgrade is the world’s primary instrument for exploring the energy frontier until 2035. This defines the time window for preparing a post-LHC high-energy physics research infrastructure.

LEP and LHC have shown that a time-frame of 30 years is appropriate for the design and construction of a large accelerator complex and particle detectors. The significant lead time calls for a coordinated global effort. The goal is to ensure the seamless continuation of the world’s particle physics programme after the LHC era.

The experience from the operation of LEP and LHC and the opportunity to test novel technologies in the High Luminosity LHC provide a basis for assessing the feasibility of a post-LHC particle accelerator. The study delivered a Conceptual Design Report (CDR) by the end of 2018, in time for the next European Strategy for Particle Physics.[3]

The significant lead time of approximately twenty years for the design and construction of a large-scale accelerator calls for a coordinated effort.

Organisation[edit]

The FCC study, hosted by CERN, is an international collaboration of more than 150 institutes from all over the world. This ensures that the entire worldwide scientific community is involved from the very start of the project.

The FCC study was created as response to the recommendation made in the update of the European Strategy for Particle Physics 2013, adopted by the organisation's council. The study is governed by three bodies: the International Collaboration Board (ICB), the International Steering Committee (ISC), and the International Advisory Committee (IAC).

The organization of the FCC Study

The ICB reviews the resource needs of the study and finds matches within the collaboration. It so channels the contributions from the participants of the collaboration aiming at a geographically well-balanced and topically complementary network of contributions. The ISC is the supervisory and main governing body for the execution of the study and acts on behalf of the collaboration.

The ISC is responsible for the proper execution and implementation of the decisions of the ICB, deriving and formulating the strategic scope, individual goals and the work programme of the study. Its work is facilitated by the Coordination Group, the main executive body of the project, which coordinates the individual work packages and performs the day-to-day management of the study.

Finally, the IAC reviews the scientific and technical progress of the study and shall submit scientific and technical recommendations to the International Steering Committee to assist and facilitate major technical decisions.

Similar studies[edit]

The Compact Linear Collider (CLIC) examines the feasibility of a high-energy (up to 3 TeV), high-luminosity lepton (electron/positron) collider, while the International Linear Collider is a similar project, planned to have a collision energy of 500 GeV. In 2013, the two studies formed an organisational partnership, the Linear Collider Collaboration (LCC) to coordinate and advance the global development work for a linear collider. Concerning the LHC, a high-luminosity upgrade is planned to extend its operation lifetime into the mid-2030s. The upgrade will facilitate the detection of rare processes and improve statistically marginal measurements.

See also[edit]

References[edit]

  1. ^ Benedikt, M.; Zimmermann, F. (28 March 2014). "The Future Circular Collider Study". CERN Courier. Retrieved 4 July 2018.
  2. ^ Benedikt, M.; Zimmermann, F. (Spring 2015). "Future Circular Collider (FCC) Study". FIP Newsletter. Retrieved 4 July 2018.
  3. ^ a b https://cds.cern.ch/record/2651300/files/CERN-ACC-2018-0058.pdf pg. 248, Beam Parameters gives GJ of total energy based on number of protons per bunch and number of bunches [10,400] in FCC-hh: https://www.wolframalpha.com/input/?i=10400*1.0*(10%5E11)*100*(10%5E12)*1.602*(10%5E-19)
  4. ^ "Future Circular Collider: Conceptual Design Report". FCC Study Office. CERN. 2018. Retrieved 15 January 2019.
  5. ^ https://www.nature.com/articles/d41586-019-00173-2
  6. ^ https://www.vox.com/future-perfect/2019/1/22/18192281/cern-large-hadron-collider-future-circular-collider-physics
  7. ^ https://physicstoday.scitation.org/do/10.1063/PT.6.2.20190205a/full/
  8. ^ Zimmerman, F.; Benedikt, M.; Schulte, D.; Wenninger, J. (2014). "Challenges for Highest Energy Circular Colliders" (PDF). Proceedings of IPAC2014, Dresden, Germany. p. 1–6. ISBN 978-3-95450-132-8. MOXAA01.
  9. ^ Hinchliffe, I.; Kotwal, A.; Mangano, M. L.; Quigg, C.; Wang, L.-T. (2015). "Luminosity goals for a 100-TeV pp". International Journal of Modern Physics A. 30 (23): 1544002. arXiv:1504.06108. Bibcode:2015IJMPA..3044002H. doi:10.1142/S0217751X15440029.
  10. ^ Ellis, J.; You, T. (2016). "Sensitivities of Prospective Future e+e Colliders to Decoupled New Physics". Journal of High Energy Physics. 2016 (3): 89. arXiv:1510.04561. Bibcode:2016JHEP...03..089E. doi:10.1007/JHEP03(2016)089.
  11. ^ d'Enterria, D. (2016). "Physics case of FCC-ee". arXiv:1601.06640 [hep-ex].
  12. ^ Barletta, W.; Battaglia, M.; Klute, M.; Mangano, M.; Prestemon, S.; Rossi, L.; Skands, P. (2014). "Future Hadron Colliders: from physics perspectives to technology R&D". Nuclear Instruments and Methods in Physics Research Section A. 764: 352–368. Bibcode:2014NIMPA.764..352B. doi:10.1016/j.nima.2014.07.010.

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