“From “Symmetry”: “How to do particle physics in a climate emergency”

From “Symmetry”

DOE’s Fermi National Accelerator Laboratory Wilson Hall.

DOE’s SLAC National Accelerator Laboratory campus with world’s first x-ray laser- the Linac Coherent Light Source (LCLS) unveiled in 2009.

2.7.23
Emily Driehaus

Scientists in the particle physics community are bringing environmental and climate issues to the table in discussions about future research.

CERN FCC Future Circular Collider details of proposed 100km-diameter successor to LHC.

CERN CLIC Collider annotated

CERN CLIC annotated.

ILC schematic, being planned for the Kitakami highland, in the Iwate prefecture of northern Japan.

Chinese Circular Electron Positron Collider (CEPC) map. It would be housed in a hundred-kilometer- (62-mile-) round tunnel at one of three potential sites. The documents work under the assumption that the collider will be located near Qinhuangdao City around 200 miles east of Beijing.

Using a particle collider requires a lot of energy.

For one, colliders use superconducting magnets to steer the beams of particles they smash together. The fact that the magnets are superconducting means that once they are powered, they conduct electricity with perfect efficiency—without losing anything to resistance.

FNAL magnets such as this one, which is mounted on a test stand at Fermilab, for the High-Luminosity LHC. Credit: Reidar Hahn.

But to stay superconducting, these magnets must be cooled to temperatures chillier than outer space. That takes energy.

Refrigeration is also required to keep rooms full of servers from overheating as scientists collect and sort enormous amounts of data, and running those servers takes energy as well.

As scientists discuss the future of particle physics they are also considering the future of the planet. A white paper [below] produced as part of the Snowmass US high-energy physics community planning process details the ways that building and operating particle accelerators affect the environment—along with ways to mitigate those effects.

“Since we released our white paper on the topic, we’ve been getting quite a lot of interest in this,” says Véronique Boisvert, a professor at Royal Holloway, University of London, one of the authors. “At the Snowmass community meeting [in July 2022], it got quite a lot of acknowledgement, and I think the US community definitely feels that it’s an important topic.”

The paper lays out four areas in which physicists could make a difference: construction, high-power computing, greenhouse gases and travel.

“This has just become, literally, a much hotter topic in the world,” says Ken Bloom, a professor and chair of the physics department at the University of Nebraska, Lincoln, and another author of the white paper. “So to be able to contextualize this for particle physicists has been an interesting opportunity.”

Construction

Constructing a new physics facility, like the proposed Future Circular Collider, is a carbon-intensive process. According to the white paper Boisvert and Bloom worked on, excavation and pouring cement for the main tunnel for the FCC would release 237 kilotons of carbon dioxide, equivalent to the amount released during the redevelopment of a neighborhood in a major city.

Using greener, more sustainable building materials could mitigate some of these effects. For example, green cement, the manufacturing of which does not emit as much carbon as the manufacturing of traditional cement, is becoming a popular alternative.

Changing established processes and using new materials costs money. But Boisvert says she thinks these considerations will become routine for major construction projects in the future.

“These criteria that we’re used to optimizing in terms of the cost, in a sense, need to take into account the context of climate change,” she says. “If we want to minimize emissions, that means using more expensive processes or material, then that goes into the price tag. I think we’ll be forced to do that. I think in 2040, that will just be the kind of world we live in where we’re going to be constantly asked, ‘What are your carbon emissions and how are you minimizing them?’”

Computing

Powering an accelerator is not the only energy expense associated with high-energy physics. Collecting the huge amount of data particle accelerators produce requires high-performance computing.

Data from CERN is transmitted around the world using the Worldwide LHC Computing Grid, which has over 170 computing sites in 42 different countries. The carbon footprint of this activity varies greatly depending on the energy source for the electrical grid in a particular region.

“When we send our computing jobs, we don’t necessarily know exactly where they go because we use farms of computers all over the world,” Boisvert says. “Even two identical, competing jobs might end up using quite different amounts of carbon depending on which computer farm is being used and where it’s located.”

It’s difficult to completely mitigate carbon emissions if a region’s electrical grid runs on fossil fuels. But coordinated efforts to use the smallest amount of energy possible, like performing computing jobs at times of the day when there is less demand on the grid, could help to at least reduce some of these emissions.

European institutions in particular are looking for solutions to this sooner rather than later, Bloom says.

“There’s a lot of concerns about energy supplies,” he says. “The various large computing centers I interact with there, they’re all sort of preparing for possible cutbacks. They might force us to do our computing in a more power-efficient way.”

Greenhouse gases

The gases used in particle physics experiments can also contribute to the overall climate impact of an experiment.

Certain particle detectors use gases like hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and even sulfur hexafluoride (SF6), which the EPA classifies as the most potent greenhouse gas known. These gases have global warming potentials thousands of times higher than carbon dioxide and trap heat when released into the atmosphere, which contributes to rising global temperatures.

These gases are typically used in particle detectors and cooling systems. They’re good candidates for the job, since they are relatively cheap and their molecules can withstand heat and pressure. However, that tolerance is also what allows them to stick around in the Earth’s atmosphere.

“It’s a challenging problem because the gases really have been optimized for what you want to do, for the quality of the measurements you want to take,” Bloom says. “They’re also optimized for safety, you’ve got to pick nonflammable things that won’t explode.”

In accordance with the Kigali Amendment of the Montreal Protocol, which the US ratified in fall 2022, countries will phase out the use of HFCs by 2047. That will affect future detectors, but it would be difficult to replace the gases currently in use.

“Given where we are on the LHC right now with the experiments we’ve already built, we’re sort of committed to a lot of these gases,” Bloom says. “So you’re down to things like trying to fix leaks in the detectors and trying to do what you can to recuperate and recirculate gas.”

Bloom and Boisvert say now is the time to do R&D to figure out alternatives to these gases for the next generation of detectors.

“We’re used to thinking of a new facility in terms of the physics performance that it needs to achieve, and also in reducing the cost of it to make it easier for funding agencies to approve this project,” Boisvert says. “But I want to add to that list of criteria to take into account the sustainability of it.”

Travel

The white paper also addressed considerations related to travel.

“In some ways, we are in the lead on this, in that we already have these international collaborations that are highly distributed in terms of where the people are,” Bloom says. “We’re good at doing work without having to actually meet up.”

However, scientists still regularly fly to other cities and countries to attend scientific conferences, to spend time required by their collaborations taking shifts collecting data or working on their experiment’s detector, and to meet with other researchers on their experiments.

The rise of virtual events during the pandemic has made it even more possible to attend conferences on the other side of the world without taking a long-haul flight. The white paper suggests continuing to organize virtual and hybrid events. For in-person events, the paper recommends optimizing the location to minimize the distance participants must travel.

The authors propose creating regional hubs for international collaborations, following models such as the LHC Physics Center at Fermilab, a gathering place for US-based scientists working on the CMS experiment at the Large Hadron Collider.

However, implementing changes like these needs to happen in a way that does not isolate scientists from smaller countries or place undue burden on groups historically excluded from science, says Xavier Bertou, a physicist who worked on the regional strategy for high-energy physics, astrophysics and cosmology research in Latin America. A solution that may be convenient for researchers in North America or Europe may not be as convenient for researchers in South America or Africa.

“I am personally a bit worried that these discussions are actually very first-world centered,” Bertou said in an email. “I remember a survey where the first question was, ‘Would you agree to travel by train instead of plane?’ Which just makes no sense for us. There are no trains here, the only options are a 24-hour bus, or a 2-hour plane.”

Boisvert says she wants to find a solution to ensure all can participate fully, no matter where they are in the world. “I think we can’t just go back, we need to sort of keep moving forward,” Boisvert says. “We’ve been at the forefront, so we have to think, ‘Okay, what are the novel, creative ideas to make this happen?’”

All in this together

Climate and environmental impacts are coming up in discussions and planning processes for particle physics around the world.

Along with fellow London-based physicists Chamkaur Ghag, Francesco Spano and David Waters, Boisvert co-authored a white paper on climate impacts for the European Strategy Update. It was signed by almost 300 physicists working in Europe. In September 2022, CERN hosted a workshop about how to make particle physics more sustainable, from using different materials when building new facilities to making changes to the kind of food provided at catered events.

More recently, members of the Energy Working Group for the ongoing African Strategy for Fundamental and Applied Physics have been discussing the environmental impacts of different energy sources.

Discussions about sustainability have also been part of planning the proposed International Linear Collider in Japan. Known as the “Green ILC,” a group of researchers are working on ways to make the facility more environmentally friendly, such as using renewable energy to power the collider and recovering and reusing energy for local communities.

Bloom and Boisvert continue to spread the word about climate change in the context of particle physics. Both have given talks at universities and events, and they created a webpage where members of the particle physics community could register their support for sustainability initiatives in the field.

“Now is the time to start thinking about those criteria to make sure we don’t have to start from scratch,” Boisvert says. “We can put our minds to it. It sends a powerful message to other scientists, it sends a powerful message to government and society that we think, ‘Yes, this is what it means to live in a climate emergency. Whatever you do, you need to take into account the climate change context and what you are doing to minimize it.’”

white paper

See the full article here .

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Symmetry is a joint Fermilab/SLAC publication.

From The European Organization for Nuclear Research [La Organización Europea para la Investigación Nuclear][ Organization européenne pour la recherche nucléaire] [Europäische Organization für Kernforschung](CH)[CERN]: “Higgs10:: inventing the future of Higgs research”

The European Organization for Nuclear Research [La Organización Europea para la Investigación Nuclear][Organisation européenne pour la recherche nucléaire] [Europäische Organization für Kernforschung](CH) [CERN].

From The European Organization for Nuclear Research [La Organización Europea para la Investigación Nuclear][ Organization européenne pour la recherche nucléaire] [Europäische Organization für Kernforschung](CH)[CERN]

8.10.22
Matthew McCullough

3D cut of the LHC dipole CERN LHC underground tunnel and tube

In 1975, three CERN theorists, John Ellis, Mary K. Gaillard and Dimitri Nanopoulos, undertook the first comprehensive study of the collider phenomenology of the Higgs boson. Almost 40 years later, it was discovered at the LHC.

Higgs

European Organization for Nuclear Research [La Organización Europea para la Investigación Nuclear][Organisation européenne pour la recherche nucléaire] [Europäische Organisation für Kernforschung](CH) ATLAS Higgs Event June 18, 2012.

European Organization for Nuclear Research [La Organización Europea para la Investigación Nuclear][Organisation européenne pour la recherche nucléaire] [Europäische Organisation für Kernforschung](CH)CMS Higgs Event May 27, 2012.

Peter Higgs – University of Edinburgh [Oilthigh Dhùn Èideann] (SCT).

_______________________________________________

Now, ten years on, might we have such long-term foresight in anticipating the varied paths that future Higgs research may follow?

On 4 July 2022, enjoying the many beautiful presentations at the Higgs@10 symposium, a phrase kept ringing in my ears: “Compatible with Standard Model (SM) predictions”.

Standard Model of Particle Physics via Particle Fever movie.

Alarm bells were ringing. Really? Are we sure? Whether or not the Higgs is SM-like is a question that will shape the experimental future of Higgs research.

We may quantify an answer through the language of effective field theory, which is a mathematical manifestation of the notion that the most effective way to describe an object depends on the length scale you’re viewing it from. To astronauts, Earth is very effectively described as a smooth sphere. For summer students hiking to Le Reculet, it is not. So, too, of the quantum world. Far from a neutral atom, it effectively appears as a point-like particle with some leftover multipolar interactions with photons. At shorter distances, getting in amongst the electrons, this description fails entirely.

Ditto the Higgs. Whatever is going on in there, at energies near enough to mh, it is effectively described as a point particle with a handful of additional “operators”, which are essentially new particle interactions that aren’t contained in the SM (don’t feature on that mug or T-shirt) but do involve SM particles. By eye, the astronaut may be able to make out some features on Earth and surmise that there may be mountains, but they couldn’t actually estimate the students’ elevation gain. Similarly, the non-SM Higgs operators can capture the long-distance leftover effects of the microscopic innards of the Higgs, but not reveal their full glory in detail. If all of these extra operators vanish, the Higgs is SM-like. Let’s consider two hand-picked examples and investigate just how SM-like the Higgs is…

How “fuzzy” is it? Is it point-like down to the smallest distance scales or is it, like the pion, made up of other as-yet-unidentified new particles? In the latter case, much as for the pions and their constituent quarks and gluons, directly observing the new stuff would require going to higher energies. Alternatively, it could be point-like but probing it closely may reveal the telltale clues of a cloud of new particles that it interacts with. For your interest, the operator that can capture these properties is written (∂μ|H|2)2. If it vanishes, the Higgs is entirely point-like. If not, it’s fuzzier than expected. How fuzzy is it? Present LHC Higgs coupling measurements suggest it is effectively point-like down to a length scale merely a factor three below the electroweak scale. It could still be very fuzzy indeed! As fuzzy as a pion. If so, hardly an SM-like Higgs! We must do better and, through much more precise coupling measurements at the 0.2% level, a future Higgs factory like the FCC-ee could determine if the Higgs is point-like as far down as the 6% level.

Does the Higgs find itself attractive? Yes, according to the SM. New particles means new forces and so it follows that if the Higgs boson interacts with new heavy particles they will generate a new force between the Higgs and itself. The operator effectively capturing this is |H|6 and it literally shapes the way in which the Higgs field gave mass to particles during the very nascence of our universe! So, how SM-like is the Higgs self-attraction? With present experimental constraints, we know the Higgs self-attraction could be 530% stronger than the SM value (not merely self-attraction, more like outright vanity) or even −140% less (self-repulsive, more like). Hardly SM-like in either case! To have any idea of whether the self-attraction is SM-like, we must do a lot better. A future facility, such as the FCC-hh, CLIC or a muon collider, could probe the self-attraction at the much more precise 5% level.

CERN CLIC Collider annotated

CERN CLIC collider

Possible futures for Higgs

ILC schematic, being planned for the Kitakami highland, in the Iwate prefecture of northern Japan.

CERN FCC Future Circular Collider details of proposed 100km-diameter successor to LHC.

Chinese Circular Electron Positron Collider (CEPC) map. It would be housed in a hundred-kilometer- (62-mile-) round tunnel at one of three potential sites. The documents work under the assumption that the collider will be located near Qinhuangdao City around 200 miles east of Beijing.

Patience is a virtue; complacency is not. It is far too early to call time at the bar for the Higgs boson. Who knows, we may even be served with something completely unexpected, like a new window into the dark sector of the universe. Truly exploring all facets of the nature of the Higgs boson, understanding whether or not it is SM-like, will take time (measured in decades) and a lot of hard work. But it can and should be done. This is the experimental future of Higgs research that we look forward to.

All that said, it’s no secret that many theorists expected the Higgs to be much less SM-like than it appears to be already. Heads duly scratched, a theoretical coup d’état is now silently under way. There were good reasons to expect something different: chiefly the hierarchy problem. This problem is not simply aesthetic. The SM breaks down at high energies, ultimately making pathological predictions, thus it can only be a long-distance effective field theory description of something else more fundamental. If, as was the case for pions, the Higgs mass is determined by the more fundamental parameters, then for the Higgs there is no mechanism to keep it lighter than the mass scale of the new particles in that theory. Yet colliders tell us there is a gap between the mass of the Higgs and that of those new particles. In the past, this motivated the discovery and development of new mechanisms to explain a light Higgs, such as the venerated low-scale supersymmetry, thus far a no-show at the LHC physics party, with its attendant non-SM-like Higgs.

Rudely awoken by the deluge of exclusion plots, coffee reluctantly smelled, theorists have, in recent years, put forward what could well transpire to be revolutionary theoretical developments. The hierarchy problem hasn’t gone away and neither has the data, so the other foundational assumptions covertly injected into the old theories, often linked to symmetry or aesthetic principles such as simplicity or minimality, have been interrogated and found wanting. In response, intrepid new classes of theories have been developed that can address the hierarchy problem whilst being consistent with all those bothersome exclusion plots. They range from relatively modest conceptual tweaks of existing structures, to the abandonment of aesthetic principles, and then all the way out the other side to attempts to link the Higgs mass to the origins of the universe, cosmology, the nature of the Big Bang and, at an extreme, speculations about possible links between the Higgs mass and the existence of life itself. You name it, we’re boldly going.

It’s no fait accompli. None of these ideas are as intoxicating as supersymmetry or as stupefying as extra dimensions, each leaving those who study them with more of a “watch this space” feeling than the “eureka” that Archimedes enjoyed. Variously, they’re not radical enough, too radical or simply not to taste. No Goldilocks moment just yet. However, in my view these issues are cause for hope. In similar moments in the past, we have been essentially on the right track, having to wait a little longer than expected for the confirming experimental data (top quark). At other times, the right ideas have been too radical for most to stomach in one sitting (quantum mechanics). Yet for others the correct approaches languished in relative obscurity far too long, simply for not being à la mode (quantum field theory). Look up the citation records of the original Brout-Englert, Higgs, Guralnik-Hagen-Kibble papers or Weinberg’s “A Model of Leptons”, all foundational to the physics of the Higgs boson, and you’ll see they are important cases in point that we would do well to remember. Nature made no promises that understanding the origins of the Higgs should have been easy, nor should it be in the future, but history teaches that those who explore relentlessly and fearlessly are often the ones rewarded with the greatest prize of all: the truth.

Where will all this go in coming years? Will we be tenacious enough to build the accelerator, the detectors and the village it will take to measure the Higgs self-attraction or discover the fuzziness of the Higgs? Will some plucky theorists unlock the door to the fundamental theory beyond the SM? Will future phenomenologists lay the first foundational stones on the path to discovering it?

As Dennis Gabor, the inventor of holography, put it: “The future cannot be predicted, but futures can be invented.” We’re working on it.

See the full article here.

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Meet CERN in a variety of places:

Quantum Diaries

Cern Courier

THE FOUR MAJOR PROJECT COLLABORATIONS

ATLAS
The European Organization for Nuclear Research [La Organización Europea para la Investigación Nuclear][ Organization européenne pour la recherche nucléaire] [Europäische Organization für Kernforschung](CH)[CERN] ATLAS.

ALICE
The European Organization for Nuclear Research [La Organización Europea para la Investigación Nuclear][ Organization européenne pour la recherche nucléaire] [Europäische Organization für Kernforschung](CH)[CERN] ALICE.

CMS
The European Organization for Nuclear Research [La Organización Europea para la Investigación Nuclear][ Organization européenne pour la recherche nucléaire] [Europäische Organization für Kernforschung](CH)[CERN] CMS.

LHCb
The European Organization for Nuclear Research [La Organización Europea para la Investigación Nuclear][ Organization européenne pour la recherche nucléaire] [Europäische Organization für Kernforschung](CH)[CERN] LHCb.

LHC

The European Organization for Nuclear Research [La Organización Europea para la Investigación Nuclear][ Organization européenne pour la recherche nucléaire] [Europäische Organization für Kernforschung](CH)[CERN] map.

3D cut of the LHC dipole CERN LHC underground tunnel and tube.

The LHC magnets surround the beampipe along its 27 km circumference- Image CERN

CERN SixTrack LHC particles.

The European Organization for Nuclear Research (Organization européenne pour la recherche nucléaire)(EU), known as CERN, is a European research organization that operates the largest particle physics laboratory in the world. Established in 1954, the organization is based in a northwest suburb of Geneva on the Franco–Swiss border and has 23 member states. Israel is the only non-European country granted full membership. CERN is an official United Nations Observer.

The acronym CERN is also used to refer to the laboratory, which in 2019 had 2,660 scientific, technical, and administrative staff members, and hosted about 12,400 users from institutions in more than 70 countries. In 2016 CERN generated 49 petabytes of data.

CERN’s main function is to provide the particle accelerators and other infrastructure needed for high-energy physics research – as a result, numerous experiments have been constructed at CERN through international collaborations. The main site at Meyrin hosts a large computing facility, which is primarily used to store and analyse data from experiments, as well as simulate events. Researchers need remote access to these facilities, so the lab has historically been a major wide area network hub. CERN is also the birthplace of the World Wide Web.

The convention establishing CERN was ratified on 29 September 1954 by 12 countries in Western Europe. The acronym CERN originally represented the French words for Conseil Européen pour la Recherche Nucléaire (European Council for Nuclear Research), which was a provisional council for building the laboratory, established by 12 European governments in 1952. The acronym was retained for the new laboratory after the provisional council was dissolved, even though the name changed to the current Organization Européenne pour la Recherche Nucléaire (European Organization for Nuclear Research)(EU) in 1954. According to Lew Kowarski, a former director of CERN, when the name was changed, the abbreviation could have become the awkward OERN, and Werner Heisenberg said that this could “still be CERN even if the name is [not]”.

CERN’s first president was Sir Benjamin Lockspeiser. Edoardo Amaldi was the general secretary of CERN at its early stages when operations were still provisional, while the first Director-General (1954) was Felix Bloch.

The laboratory was originally devoted to the study of atomic nuclei, but was soon applied to higher-energy physics, concerned mainly with the study of interactions between subatomic particles. Therefore, the laboratory operated by CERN is commonly referred to as the European laboratory for particle physics (Laboratoire européen pour la physique des particules), which better describes the research being performed there.

Founding members

At the sixth session of the CERN Council, which took place in Paris from 29 June – 1 July 1953, the convention establishing the organization was signed, subject to ratification, by 12 states. The convention was gradually ratified by the 12 founding Member States: Belgium, Denmark, France, the Federal Republic of Germany, Greece, Italy, the Netherlands, Norway, Sweden, Switzerland, the United Kingdom, and “Yugoslavia”.

Scientific achievements

Several important achievements in particle physics have been made through experiments at CERN. They include:

1973: The discovery of neutral currents in the Gargamelle bubble chamber.
1983: The discovery of W and Z bosons in the UA1 and UA2 experiments.
1989: The determination of the number of light neutrino families at the Large Electron–Positron Collider (LEP) operating on the Z boson peak.
1995: The first creation of antihydrogen atoms in the PS210 experiment.
1999: The discovery of direct CP violation in the NA48 experiment.
2010: The isolation of 38 atoms of antihydrogen.
2011: Maintaining antihydrogen for over 15 minutes.
2012: A boson with mass around 125 GeV/c2 consistent with the long-sought Higgs boson.

In September 2011, CERN attracted media attention when the OPERA Collaboration reported the detection of possibly faster-than-light neutrinos. Further tests showed that the results were flawed due to an incorrectly connected GPS synchronization cable.

The 1984 Nobel Prize for Physics was awarded to Carlo Rubbia and Simon van der Meer for the developments that resulted in the discoveries of the W and Z bosons. The 1992 Nobel Prize for Physics was awarded to CERN staff researcher Georges Charpak “for his invention and development of particle detectors, in particular the multiwire proportional chamber”. The 2013 Nobel Prize for Physics was awarded to François Englert and Peter Higgs for the theoretical description of the Higgs mechanism in the year after the Higgs boson was found by CERN experiments.

Computer science

The World Wide Web began as a CERN project named ENQUIRE, initiated by Tim Berners-Lee in 1989 and Robert Cailliau in 1990. Berners-Lee and Cailliau were jointly honoured by the Association for Computing Machinery in 1995 for their contributions to the development of the World Wide Web.

Current complex

CERN operates a network of six accelerators and a decelerator. Each machine in the chain increases the energy of particle beams before delivering them to experiments or to the next more powerful accelerator. Currently (as of 2019) active machines are:

The LINAC 3 linear accelerator generating low energy particles. It provides heavy ions at 4.2 MeV/u for injection into the Low Energy Ion Ring (LEIR).
The Proton Synchrotron Booster increases the energy of particles generated by the proton linear accelerator before they are transferred to the other accelerators.
The Low Energy Ion Ring (LEIR) accelerates the ions from the ion linear accelerator LINAC 3, before transferring them to the Proton Synchrotron (PS). This accelerator was commissioned in 2005, after having been reconfigured from the previous Low Energy Antiproton Ring (LEAR).
The 28 GeV Proton Synchrotron (PS), built during 1954—1959 and still operating as a feeder to the more powerful SPS.
The Super Proton Synchrotron (SPS), a circular accelerator with a diameter of 2 kilometres built in a tunnel, which started operation in 1976. It was designed to deliver an energy of 300 GeV and was gradually upgraded to 450 GeV. As well as having its own beamlines for fixed-target experiments (currently COMPASS and NA62), it has been operated as a proton–antiproton collider (the SppS collider), and for accelerating high energy electrons and positrons which were injected into the Large Electron–Positron Collider (LEP). Since 2008, it has been used to inject protons and heavy ions into the Large Hadron Collider (LHC).
The On-Line Isotope Mass Separator (ISOLDE), which is used to study unstable nuclei. The radioactive ions are produced by the impact of protons at an energy of 1.0–1.4 GeV from the Proton Synchrotron Booster. It was first commissioned in 1967 and was rebuilt with major upgrades in 1974 and 1992.
The Antiproton Decelerator (AD), which reduces the velocity of antiprotons to about 10% of the speed of light for research of antimatter.[50] The AD machine was reconfigured from the previous Antiproton Collector (AC) machine.
The AWAKE experiment, which is a proof-of-principle plasma wakefield accelerator.
The CERN Linear Electron Accelerator for Research (CLEAR) accelerator research and development facility.

Large Hadron Collider

Many activities at CERN currently involve operating the Large Hadron Collider (LHC) and the experiments for it. The LHC represents a large-scale, worldwide scientific cooperation project.

The LHC tunnel is located 100 metres underground, in the region between the Geneva International Airport and the nearby Jura mountains. The majority of its length is on the French side of the border. It uses the 27 km circumference circular tunnel previously occupied by the Large Electron–Positron Collider (LEP), which was shut down in November 2000. CERN’s existing PS/SPS accelerator complexes are used to pre-accelerate protons and lead ions which are then injected into the LHC.

Eight experiments (CMS, ATLAS, LHCb, MoEDAL, TOTEM, LHCf, FASER and ALICE) are located along the collider; each of them studies particle collisions from a different aspect, and with different technologies. Construction for these experiments required an extraordinary engineering effort. For example, a special crane was rented from Belgium to lower pieces of the CMS detector into its cavern, since each piece weighed nearly 2,000 tons. The first of the approximately 5,000 magnets necessary for construction was lowered down a special shaft at 13:00 GMT on 7 March 2005.

The LHC has begun to generate vast quantities of data, which CERN streams to laboratories around the world for distributed processing (making use of a specialized grid infrastructure, the LHC Computing Grid). During April 2005, a trial successfully streamed 600 MB/s to seven different sites across the world.

The initial particle beams were injected into the LHC August 2008. The first beam was circulated through the entire LHC on 10 September 2008, but the system failed 10 days later because of a faulty magnet connection, and it was stopped for repairs on 19 September 2008.

The LHC resumed operation on 20 November 2009 by successfully circulating two beams, each with an energy of 3.5 teraelectronvolts (TeV). The challenge for the engineers was then to try to line up the two beams so that they smashed into each other. This is like “firing two needles across the Atlantic and getting them to hit each other” according to Steve Myers, director for accelerators and technology.

On 30 March 2010, the LHC successfully collided two proton beams with 3.5 TeV of energy per proton, resulting in a 7 TeV collision energy. However, this was just the start of what was needed for the expected discovery of the Higgs boson. When the 7 TeV experimental period ended, the LHC revved to 8 TeV (4 TeV per proton) starting March 2012, and soon began particle collisions at that energy. In July 2012, CERN scientists announced the discovery of a new sub-atomic particle that was later confirmed to be the Higgs boson.

European Organization for Nuclear Research [La Organización Europea para la Investigación Nuclear][Organisation européenne pour la recherche nucléaire] [Europäische Organisation für Kernforschung](CH) ATLAS Higgs Event June 18, 2012.

European Organization for Nuclear Research [La Organización Europea para la Investigación Nuclear][Organisation européenne pour la recherche nucléaire] [Europäische Organisation für Kernforschung](CH)CMS Higgs Event May 27, 2012.

Peter Higgs – University of Edinburgh [Oilthigh Dhùn Èideann] (SCT).

In March 2013, CERN announced that the measurements performed on the newly found particle allowed it to conclude that this is a Higgs boson. In early 2013, the LHC was deactivated for a two-year maintenance period, to strengthen the electrical connections between magnets inside the accelerator and for other upgrades.

On 5 April 2015, after two years of maintenance and consolidation, the LHC restarted for a second run. The first ramp to the record-breaking energy of 6.5 TeV was performed on 10 April 2015. In 2016, the design collision rate was exceeded for the first time. A second two-year period of shutdown begun at the end of 2018.

Accelerators under construction

As of October 2019, the construction is on-going to upgrade the LHC’s luminosity in a project called High Luminosity LHC (HL-LHC).

This project should see the LHC accelerator upgraded by 2026 to an order of magnitude higher luminosity.

As part of the HL-LHC upgrade project, also other CERN accelerators and their subsystems are receiving upgrades. Among other work, the LINAC 2 linear accelerator injector was decommissioned, to be replaced by a new injector accelerator, the LINAC4 in 2020.

Possible future accelerators

CERN, in collaboration with groups worldwide, is investigating two main concepts for future accelerators: A linear electron-positron collider with a new acceleration concept to increase the energy (CLIC) and a larger version of the LHC, a project currently named Future Circular Collider.

CERN CLIC collider

CERN FCC Future Circular Collider details of proposed 100km-diameter successor to LHC.

Not discussed or described, but worthy of consideration is the ILC, International Linear Collider in the planning stages for construction in Japan.

ILC schematic, being planned for the Kitakami highland, in the Iwate prefecture of northern Japan.

Participation

Since its foundation by 12 members in 1954, CERN regularly accepted new members. All new members have remained in the organization continuously since their accession, except Spain and Yugoslavia. Spain first joined CERN in 1961, withdrew in 1969, and rejoined in 1983. Yugoslavia was a founding member of CERN but quit in 1961. Of the 23 members, Israel joined CERN as a full member on 6 January 2014, becoming the first (and currently only) non-European full member.

Enlargement

Associate Members, Candidates:

Turkey signed an association agreement on 12 May 2014 and became an associate member on 6 May 2015.
Pakistan signed an association agreement on 19 December 2014 and became an associate member on 31 July 2015.
Cyprus signed an association agreement on 5 October 2012 and became an associate Member in the pre-stage to membership on 1 April 2016.
Ukraine signed an association agreement on 3 October 2013. The agreement was ratified on 5 October 2016.
India signed an association agreement on 21 November 2016. The agreement was ratified on 16 January 2017.
Slovenia was approved for admission as an Associate Member state in the pre-stage to membership on 16 December 2016. The agreement was ratified on 4 July 2017.
Lithuania was approved for admission as an Associate Member state on 16 June 2017. The association agreement was signed on 27 June 2017 and ratified on 8 January 2018.
Croatia was approved for admission as an Associate Member state on 28 February 2019. The agreement was ratified on 10 October 2019.
Estonia was approved for admission as an Associate Member in the pre-stage to membership state on 19 June 2020. The agreement was ratified on 1 February 2021.

From Scientific American (US) : “Plasma Particle Accelerators Could Find New Physics”

From Scientific American (US)

July 2021
Chandrashekhar Joshi

Credit: Peter and Maria Hoey.

At the start of the 20th century scientists had little knowledge of the building blocks that form our physical world. By the end of the century they had discovered not just all the elements that are the basis of all observed matter but a slew of even more fundamental particles that make up our cosmos, our planet and ourselves. The tool responsible for this revolution was the particle accelerator.

Standard Model of Particle Physics, Quantum Diaries

FNAL/Tevatron CDF detector

CERN LHC underground tunnel and tube.

The pinnacle achievement of particle accelerators came in 2012, when the Large Hadron Collider (LHC) uncovered the long-sought Higgs boson particle.

European Organization for Nuclear Research [Organisation européenne pour la recherche nucléaire] [Europäische Organisation für Kernforschung](CH)ATLAS Higgs Event

European Organization for Nuclear Research [Organisation européenne pour la recherche nucléaire] [Europäische Organisation für Kernforschung](CH) CMS Higgs Event May 27, 2012.

The LHC is a 27-kilometer accelerating ring that collides two beams of protons with seven trillion electron volts (TeV) of energy each at CERN near Geneva.

European Organization for Nuclear Research [Organisation européenne pour la recherche nucléaire] [Europäische Organisation für Kernforschung](CH) [CERN]

European Organization for Nuclear Research [Organisation européenne pour la recherche nucléaire(CH) map .

It is the biggest, most complex and arguably the most expensive scientific device ever built. The Higgs boson was the latest piece in the reigning theory of particle physics called the Standard Model. Yet in the almost 10 years since that discovery, no additional particles have emerged from this machine or any other accelerator.

Have we found all the particles there are to find? Doubtful. The Standard Model of particle physics does not account for dark matter—particles that are plentiful yet invisible in the universe. A popular extension of the Standard Model called supersymmetry predicts many more particles out there than the ones we know about.

Standard Model of Supersymmetry

And physicists have other profound unanswered questions such as: Are there extra dimensions of space? And why is there a great matter-antimatter imbalance in the observable universe? To solve these riddles, we will likely need a particle collider more powerful than those we have today.

Many scientists support a plan to build the International Linear Collider (ILC), a straight-line-shaped accelerator that will produce collision energies of 250 billion (giga) electron volts (GeV).

ILC schematic, being planned for the Kitakami highland, in the Iwate prefecture of northern Japan.

Though not as powerful as the LHC, the ILC would collide electrons with their antimatter counterparts, positrons—both fundamental particles that are expected to produce much cleaner data than the proton-proton collisions in the LHC. Unfortunately, the design of the ILC calls for a facility about 20 kilometers long and is expected to cost more than $10 billion—a price so high that no country has so far committed to host it.

In the meantime, there are plans to upgrade the energy of the LHC to 27 TeV in the existing tunnel by increasing the strength of the superconducting magnets used to bend the protons. Beyond that, CERN is proposing a 100-kilometer-circumference electron-positron and proton-proton collider called the Future Circular Collider.

CERN FCC Future Circular Collider details of proposed 100km-diameter successor to LHC.

Such a machine could reach the unprecedented energy of 100 TeV in proton-proton collisions. Yet the cost of this project will likely match or surpass the ILC. Even if it is built, work on it cannot begin until the LHC stops operation after 2035.

But these gargantuan and costly machines are not the only options. Since the 1980s physicists have been developing alternative concepts for colliders. Among them is one known as a plasma-based accelerator, which shows great promise for delivering a TeV-scale collider that may be more compact and much cheaper than machines based on the present technology.

The Particle Zoo

The story of particle accelerators began in 1897 at the Cavendish physics laboratory at the University of Cambridge (UK).

There J. J. Thomson created the earliest version of a particle accelerator using a tabletop cathode-ray tube like the ones used in most television sets before flat screens. He discovered a negatively charged particle—the electron.

Soon physicists identified the other two atomic ingredients—protons and neutrons—using radioactive particles as projectiles to bombard atoms. And in the 1930s came the first circular particle accelerator—a palm-size device invented by Ernest Lawrence called the cyclotron, which could accelerate protons to about 80 kilovolts.

Ernest Lawrence’s First Cyclotron, 1930 Stock Photo – Alamy.

Thereafter accelerator technology evolved rapidly, and scientists were able to increase the energy of accelerated charged particles to probe the atomic nucleus. These advances led to the discovery of a zoo of hundreds of subnuclear particles, launching the era of accelerator-based high-energy physics. As the energy of accelerator beams rapidly increased in the final quarter of the past century, the zoo particles were shown to be built from just 17 fundamental particles predicted by the Standard Model [above]. All of these, except the Higgs boson, had been discovered in accelerator experiments by the late 1990s. The Higgs’s eventual appearance [above] at the LHC made the Standard Model the crowning achievement of modern particle physics.

Aside from being some of the most successful instruments of scientific discovery in history, accelerators have found a multitude of applications in medicine and in our daily lives. They are used in CT scanners, for x-rays of bones and for radiotherapy of malignant tumors. They are vital in food sterilization and for generating radioactive isotopes for myriad medical tests and treatments. They are the basis of x-ray free-electron lasers, which are being used by thousands of scientists and engineers to do cutting-edge research in physical, life and biological sciences.

Scientist tests a prototype plasma accelerator at the Facility for Advanced Accelerator Experimental Tests (FACET) at the DOE’s SLAC National Accelerator Laboratory (US) in California. Credit: Brad Plummer and SLAC National Accelerator Laboratory.

Accelerator Basics

Accelerators come in two shapes: circular (synchrotron) or linear (linac). All are powered by radio waves or microwaves that can accelerate particles to near light speed. At the LHC, for instance, two proton beams running in opposite directions repeatedly pass through sections of so-called radio-frequency cavities spaced along the ring.

SixTRack CERN LHC particles

Radio waves inside these cavities create electric fields that oscillate between positive and negative to ensure that the positively charged protons always feel a pull forward. This pull speeds up the protons and transfers energy to them. Once the particles have gained enough energy, magnetic lenses focus the proton beams to several very precise collision points along the ring. When they crash, they produce extremely high energy densities, leading to the birth of new, higher-mass particles.

When charged particles are bent in a circle, however, they emit “synchrotron radiation.” For any given radius of the ring, this energy loss is far less for heavier particles such as protons, which is why the LHC is a proton collider. But for electrons the loss is too great, particularly as their energy increases, so future accelerators that aim to collide electrons and positrons must either be linear colliders or have very large radii that minimize the curvature and thus the radiation the electrons emit.

54 mile Superconducting Super Collider map, a particle accelerator complex under construction in the vicinity of Waxahachie, Texas, cancelled in 1993 by the U.S. Congress for having no immediate economic benefits, and the loss of support by California and other nearby states, because California desired the project. A loss all around as the project never went forward and the U.S. ceded the lead in HEP to Europe.

The size of an accelerator complex for a given beam energy ultimately depends on how much radio-frequency power can be pumped into the accelerating structure before the structure suffers electrical breakdown. Traditional accelerators have used copper to build this accelerating structure, and the breakdown threshold has meant that the maximum energy that can be added per meter is between 20 million and 50 million electron volts (MeV). Accelerator scientists have experimented with new types of accelerating structures that work at higher frequencies, thereby increasing the electrical breakdown threshold. They have also been working on improving the strength of the accelerating fields within superconducting cavities that are now routinely used in both synchrotrons and linacs. These advances are important and will almost certainly be implemented before any paradigm-changing concepts disrupt the highly successful conventional accelerator technologies.

Eventually other strategies may be necessary. In 1982 the U.S. Department of Energy’s program on high-energy physics started a modest initiative to investigate entirely new ways to accelerate charged particles. This program generated many ideas; three among them look particularly promising.

The first is called two-beam acceleration. This scheme uses a relatively cheap but very high-charge electron pulse to create high-frequency radiation in a cavity and then transfers this radiation to a second cavity to accelerate a secondary electron pulse. This concept is being tested at CERN on a machine called the Compact Linear Collider (CLIC).

CERN CLIC collider

CERN CLIC Collider annotated

Another idea is to collide muons, which are much heavier cousins to electrons. Their larger mass means they can be accelerated in a circle without losing as much energy to synchrotron radiation as electrons do. The downside is that muons are unstable particles, with a lifetime of two millionths of a second. They are produced during the decay of particles called pions, which themselves must be produced by colliding an intense proton beam with a special target. No one has ever built a muon accelerator, but there are die-hard proponents of the idea among accelerator scientists.

Finally, there is plasma-based acceleration. The notion originated in the 1970s with John M. Dawson of the University of California-Los Angeles (US), who proposed using a plasma wake produced by an intense laser pulse or a bunch of electrons to accelerate a second bunch of particles 1,000 or even 10,000 times faster than conventional accelerators can. This concept came to be known as the plasma wakefield accelerator.

It generated a lot of excitement by raising the prospect of miniaturizing these gigantic machines, much like the integrated circuit miniaturized electronics starting in the 1960s.

The Fourth State of Matter

Most people are familiar with three states of matter: solid, liquid and gas. Plasma is often called the fourth state of matter. Though relatively uncommon in our everyday experience, it is the most common state of matter in our universe. By some estimates more than 99 percent of all visible matter in the cosmos is in the plasma state—stars, for instance, are made of plasma. A plasma is basically an ionized gas with equal densities of electrons and ions. Scientists can easily form plasma in laboratories by passing electricity through a gas as in a common fluorescent tube.

A plasma wakefield accelerator takes advantage of the kind of wake you can find trailing a motorboat or a jet plane. As a boat moves forward, it displaces water, which moves out behind the boat to form a wake. Similarly, a tightly focused but ultraintense laser pulse moving through a plasma at the speed of light can generate a relativistic wake (that is, a wake also propagating nearly at light speed) by exerting radiation pressure and displacing the plasma electrons out of its way. If, instead of a laser pulse, a high-energy, high-current electron bunch is sent through the plasma, the negative charge of these electrons can expel all the plasma electrons, which feel a repulsive force. The heavier plasma ions, which are positively charged, remain stationary. After the pulse passes by, the expelled electrons are attracted back toward the ions by the force between their negative and positive charges. The electrons move so quickly they overshoot the ions and then again feel a backward pull, setting up an oscillating wake. Because of the separation of the plasma electrons from the plasma ions, there is an electric field inside this wake.

If a second “trailing” electron bunch follows the first “drive” pulse, the electrons in this trailing bunch can gain energy from the wake much in the same way an electron bunch is accelerated by the radio-frequency wave in a conventional accelerator. If there are enough electrons in the trailing bunch, they can absorb sufficient energy from the wake so as to dampen the electric field. Now all the electrons in the trailing bunch see a constant accelerating field and gain energy at the same rate, thereby reducing the energy spread of the beam.

The main advantage of a plasma accelerator over other schemes is that electric fields in a plasma wake can easily be 1,000 times stronger than those in traditional radio-frequency cavities. Plus, a very significant fraction of the energy that the driver beam transfers to the wake can be extracted by the trailing bunch. These effects make a plasma wakefield-based collider potentially both more compact and cheaper than conventional colliders.

The Future of Plasma

Both laser- and electron-driven plasma wakefield accelerators have made tremendous progress in the past two decades. My own team at U.C.L.A. has carried out prototype experiments with SLAC National Accelerator Laboratory physicists at their Facility for Advanced Accelerator Experimental Tests (FACET) in Menlo Park, Calif.

SLAC National Accelerator Laboratory(US) FACET

SLAC National Accelerator Laboratory(US) FACET-II – upgrading its Facility for Advanced Accelerator Experimental Tests (FACET) – a test bed for new technologies that could revolutionize the way we build particle accelerators.

We injected both drive and trailing electron bunches with an initial energy of 20 GeV and found that the trailing electrons gained up to 9 GeV after traveling through a 1.3-meter-long plasma. We also achieved a gain of 4 GeV in a positron bunch using just a one-meter-long plasma in a proof-of-concept experiment. Several other labs around the world have used laser-driven wakes to produce multi-GeV energy gains in electron bunches.

Plasma accelerator scientists’ ultimate goal is to realize a linear accelerator that collides tightly focused electron and positron, or electron and electron, beams with a total energy exceeding 1 TeV. To accomplish this feat, we would likely need to connect around 50 individual plasma accelerator stages in series, with each stage adding an energy of 10 GeV.

Yet aligning and synchronizing the drive and the trailing beams through so many plasma accelerator stages to collide with the desired accuracy presents a huge challenge. The typical radius of the wake is less than one millimeter, and scientists must inject the trailing electron bunch with submicron accuracy. They must synchronize timing between the drive pulse and the trailing beam to less than a hundredth of a trillionth of one second. Any misalignment would lead to a degradation of the beam quality and a loss of energy as well as charge caused by oscillation of the electrons about the plasma wake axis. This loss shows up in the form of hard x-ray emission, known as betatron emission, and places a finite limit on how much energy we can obtain from a plasma accelerator.

Other technical hurdles also stand in the way of immediately turning this idea into a collider. For instance, the primary figure of merit for a particle collider is the luminosity—basically a measure of how many particles you can squeeze through a given space in a given time. The luminosity multiplied by the cross section—or the chances that two particles will collide— tells you how many collisions of a particular kind per second you are likely to observe at a given energy. The desired luminosity for a 1-TeV electron-positron linear collider is 10^34 cm^–2s^–1. Achieving this luminosity would require the colliding beams to have an average power of 20 megawatts each—10^10 particles per bunch at a repetition rate of 10 kilohertz and a beam size at the collision point of tens of a billionth of a meter. To illustrate how difficult this is, let us focus on the average power requirement. Even if you could transfer energy from the drive beam to the accelerating beam with 50 percent efficiency, 20 megawatts of power will be left behind in the two thin plasma columns. Ideally we could partially recover this power, but it is far from a straightforward task.

And although scientists have made substantial progress on the technology needed for the electron arm of a plasma-based linear collider, positron acceleration is still in its infancy. A decade of concerted basic science research will most likely be needed to bring positrons to the same point we have reached with electrons. Alternatively, we could collide electrons with electrons or even with protons, where one or both electron arms are based on a plasma wakefield accelerator. Another concept that scientists are exploring at CERN is modulating a many-centimeters-long proton bunch by sending it through a plasma column and using the accompanying plasma wake to accelerate an electron bunch.

The future for plasma-based accelerators is uncertain but exciting. It seems possible that within a decade we could build 10-GeV plasma accelerators on a large tabletop for various scientific and commercial applications using existing laser and electron beam facilities. But this achievement would still put us a long way from realizing a plasma-based linear collider for new physics discoveries. Even though we have made spectacular experimental progress in plasma accelerator research, the beam parameters achieved to date are not yet what we would need for just the electron arm of a future electron-positron collider that operates at the energy frontier. Yet with the prospects for the International Linear Collider and the Future Circular Collider uncertain, our best bet may be to persist with perfecting an exotic technology that offers size and cost savings. Developing plasma technology is a scientific and engineering grand challenge for this century, and it offers researchers wonderful opportunities for taking risks, being creative, solving fascinating problems—and the tantalizing possibility of discovering new fundamental pieces of nature.

See the full article here .

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