Accelerating News, Issue #19 - Letter from the Editor
"The little prince was not able to reach any explanation of the use of a street lamp and a lamplighter, somewhere in the heavens, on a planet which had no people, and not one house. But he said to himself, nevertheless: "It may well be that this man is absurd. But he is not so absurd as the king, the conceited man, the businessman, and the tippler. For at least his work has some meaning. When he lights his street lamp, it is as if he brought one more star to life, or one flower. When he puts out his lamp, he sends the flower, or the star, to sleep. That is a beautiful occupation. And since it is beautiful, it is truly useful..."
On 11 February 2016, David Reitze, executive director of the LIGO Laboratory, announced the first detection of gravitational waves. “It’s the first time the Universe has spoken to us in gravitational waves. This was a scientific moonshot and we did it. We landed on the Moon,” he said. He had every reason to be proud. In September 2015, the LIGO detectors had picked up a signal of two black holes that collided 1.3 billion light years away, sending shock waves across spacetime. Gravitational waves were first predicted by Albert Einstein a century ago as a consequence of his theory of general relativity, which unifies special relativity and Newton's law of universal gravitation to describe gravity.
Gravitational waves produced during the merge of two black holes have been detected by the LICO collaboration (Image credit: The SXS (Simulating eXtreme Spacetimes) Project)
This discovery comes a couple of years after ESA’s Planck satellite offered a detailed map of our Universe based on cosmic microwave background radiation (CMB); a major source of information used to piece together the history of our Universe. They constitute two important steps/advancements in modern cosmology. However, they both seem to confirm well established theories that were formulated in the course of the 20th century. Gravitational waves was the long-awaited observable predicted by the theory of relativity while the results of the Planck mission confirm the standard cosmological picture of our Universe with ever greater accuracy. However these theories seem to leave many open questions not to mention the fact that the theory of relativity is not so far compatible with the theory of quantum-mechanics.
Looking to the field of high-energy physics, the discovery of the Higgs boson in 2012 at CERN came to conclude the long-standing effort to confirm the Standard model of particle physics. The ATLAS and CMS experiments at the Large Hadron Collider announced the discovery of a new particle in the mass region around 126 GeV, consistent with the properties of the Higgs boson that François Englert, Robert Brout and Peter Higgs proposed in 1964. The discovery of the Higgs boson confirms the existence of the Higgs field, a fundamental field that permeates our Universe and is responsible for giving elementary particles their mass.
The discovery of the Higgs boson was undoubtedly the most astounding achievement in the recent history of physics.(Image credit: CERN)
The Higgs particle is often described as the cornerstone of the Standard Model of particle physics; a theory that attempted to describe experimental observations about the constituents of matter and reconcile them with the theoretical description of the forces through which they interact.
Scientific leaps do not happen in the void; they are often closely linked to broader social changes, the reordering of political power, the emergence of new art movements, and fierce philosophical discussions. The history of science is full of comparable examples and offers valuable insights to the scientists of today. Scientific progress is not only influenced by social contexts, but also exerts great social influence. Breakthroughs such as the shift from the geocentric to the heliocentric system or, in more recent times, the discovery of the DNA sequence radically changed our understanding of the world and simultaneously had a deep social and cultural impact. One could also think the interplay between the study of the human genome and the development of gender studies and the birth of the web and how it changed the meaning of social participation, often empowering previously marginalized groups. Here we do not aim to offer an exhaustive discussion on the highly complex relation between scientific development and its socio-cultural implications, but offer a quick reminder that, as science is increasingly portrayed as a totally autonomous field, its interaction with other fields and its role in the formation of our human identity are sadly neglected.
Reflecting on the long history of scientific developments, one can see that certainties are rare and scientists often have to stand up to defend inconvenient truths or counter-intuitive facts. How uncomfortable scientists—not to mention the general public or funding agencies of the time—must have felt with the discussions on the existence of a new form of matter, the so-called antimatter, which was based on the mathematical solutions of the Dirac equation? How easily could physicists accommodate to Schrödinger’s uncertainty principle, which indicates that reality consists of a superposition of states that can exist with different probabilities. This is summarized in Schroedinger’s cat; a famous thought experiment that also introduced the key role of the observer. The early discussions that gave birth to the field of Quantum Mechanics offered certain inspiration but also valuable lessons for the future of fundamental physics. The list is endless and it is astonishing how far the scientific community has gone in adopting a new mindset - or a shift in scientific paradigm - that allowed some of the major breakthroughs but also important applications in our daily lives.
It is equally important to remember that the latest discoveries or theories that have widened our understanding of the world are not the final step in this journey of exploring the Universe. Whether radically new theories or more modest modifications are needed is something that remains to be seen and we have to be patient. Results from the LHC and cosmological experiments may shatter some of our past expectations. Moreover, future results of the LHC and other experiments -including non-accelerator experiments- may call for a fundamental change of scientific paradigm. We live in a period of turbulence of modern physics but we should not neglect that these have been the most fruitful periods in our field, presenting a number of challenges and new opportunities.
The results from the LHC - whether marked by a major discovery or not - are probably going to question our present understanding and some of the concepts that dominate the development of physics in the last decades. It is true that we enter in an era where we should remember the exploratory value of accelerators that can allow us to discover new phenomena. Science is not about offering certainties or confirming existing theories - no matter how attractive they seem - but about discovering the truth and gaining a deeper understanding on nature. As Professor Savas Dimopoulos notes: “Truth is both discovering new things and proving that some preconceptions, speculations, or theories are wrong. For example, the idea of the aether seemed plausible at a time, as it was logical to assume that electromagnetic waves need a medium, but it was disproved by the Michelson–Morley experiment. In this case, it was the non-discovery of something that created the big earthquake that led to relativity. Knowing what is false can be as important as knowing what is true.”
Outstanding questions in fundamental physics can only be successfully addressed through the variety of approaches that the global physics community has developed over the years. We are possibly at the threshold of a new era in modern physics following the numerous observations from various fronts that seem to open more and more questions. This calls for considerable investment in new technologies and large-scale research infrastructures to offer new insights and allow to continue the scientific progress. As James Peebles, one of the pioneers of modern cosmology comments in the hand-in-hand development between fundamental physics and novel technologies: "Our understanding of nature has advanced in step with technological developments. The role of technology in the natural sciences, or curiosity-driven science is important. Astrophysics and HEP experiments that take place today thanks to the latest exciting advancements wouldn’t be possible few years ago. Of course technology is not the entire answer. Discoveries also need fresh ideas and concepts that can be tested either by developing new technologies or by finding new uses for old technologies”.
The LHC and its High Luminosity upgrade (HL-LHC) guarantee the seamless continuation of the physics programme up to 2035. However, given the long lead-times involved in high-energy physics the community of worldwide physics community must start preparing the next accelerator for the post-LHC era now. It has taken more than thirty years to develop, build, and commission the LHC and this proves that we can’t afford to lose a second. The Future Circular Collider (FCC) study is one of the global efforts for thinking about future accelerators complementing existing technical designs for linear electron positron colliders (ILC and CLIC).
To build these machines calls for a coordinated effort to advance key technologies: high-field magnets, superconductors, novel materials, new vacuum systems and efficient cryogenics are some of the fronts where copious R&D efforts are invested and could find applications outside the field of fundamental research. .
The study for a future collider relies and builds on the valuable lessons of previous advancements in the field as well as from other international studies.The future of science lies in strengthening international collaboration while ambitious projects like FCC can have remarkable and unforeseen results. At the same time it is important to note that new concepts for future accelerators based on novel accelerating schemes are presently tested while it is equally important to think what we can learn from non-accelerator experiemnts that could compliment future large-scale research infrastructures.
We are still confronted with questions related to the formation of matter, the domination of matter over antimater in our Universe (though we know from our experiments that they are equally produced), the dark matter content of our universe to mention but a few of the open puzzles. Searching for answers, calls for a coordinated effort in designing and developing the scientific instruments that will allow continuing the exploration - whether new accelerator or accelerator techniques, new telescopes or non-accelerator experiments. More importantly, it could call for a shift in the scientific paradigm similar to the one that took place in the beginning of the 20th century. New results from high-energy experiments or cosmological data may eventually prove that are just now start understanding the deeper structures that lie behind Quantum Mechanics and General Relativity; the two theories that shaped modern physics.
"That is a beautiful occupation. And since it is beautiful, it is truly useful..." (Image: Cannes Film Festival)
In conclusion, the history of physics teaches us that there is room both for the unseen and the unknown. We often tend to neglect that science is more about ambiguity and opening a space for questioning any certainty rather than about confirmation and reassurance. The scientific community in the next decades would most probably have to follow unchartered waters in order to expand our present horizons of knowledge. “Man cannot discover new oceans unless he has the courage to lose sight of the shore.” as Andre Gide’s famously noted.
Looking at the present physics landscape one can see an ocean of challenges and opportunities for physicists but also for engineers, innovators, early-stage researchers and for the future of our societies. Despite the possible lack clear evidence for the next big discovery we can’t afford to ignore the unanswered questions about our Universe and our understanding of nature. Perhaps we should remind ourselves the following words, coming from the Austrian physicist Erwin Schrödinger, one of the pioneers in the development of quantum mechanics: “The task is...not so much to see what no one has yet seen; but to think what nobody has yet thought, about that which everybody sees.”
I wish you the best for a creative and exciting new year.
Accelerating News, Editor in Chief
Designing an elevator system for FCC
by Panos Charitos (CERN)
Designing an elevator system for a 300 underground tunnel that could host a future circular collider (Image: CERN - FCC Collaboration)
CERN has come a long way since its foundation in 1954 in advancing our knowledge about the basic components of the Universe. This was made possible due to the advancements in technologies and the building of more complex accelerators and detectors that significantly push the limit of our knowledge. This complexity calls for long-term planning of any future development.
Building a larger and more powerful accelerator sets a number of challenges related to physics and accelerator parameters but also to civil engineering and day-to-day operations. A future collider like those explored under the FCC study will not merely be a scaled-up version of the LHC but a totally new machine. Scientists and engineers are working to develop new technologies and concepts for building and running such a large-scale research infrastructure.
Designing a 100 km tunnel, lying in an average depth of 300 meters that could host a future collider and the experimental detectors is not a trivial task.
First of all, one needs to face open issues related to the installation of the different accelerator parts, including the high-field magnets, the commissioning of the detectors and the need to transfer equipment between the tunnel and surface facilities. There are many more questions when designing such a system like: "How many people will move within such a large underground facility? How often they will need to access the tunnel and from which points? How quickly will the tunnel be evacuated to ensure safety for the personnel?
Volker Mertens, who is in charge of the Infrastructure and Operation studies for the FCC study, notes: "answering these questions becomes more challenging as the answers depend on the available state-of-the-art technologies and a possible project on how they could evolve within the next 20 years."
A key aspect of the construction and operation phase linked to the above questions is the elevator system that will be installed. Engineers are working to design a number of elevators that will efficiently connect the tunnel with the surface giving access to the engineers and technicians that will work in this project. Damien Lafarge, section leader at CERN responsible for lift operation explains: "lifts that give access to underground part are one of the most vital parts in designing a post-LHC collider. They must be operational all time, with an availability rate of 99.6% as any failure can be very costly in the operation of such a large-scale infrastructure".
An overview of the cavern and the elevator system (Image: CERN - FCC Collaboration)
At this early stage engineers are looking nominally at 12 deep access shafts, where approximately 24 lifts could be located at significant locations intervals along the collider ring. Volker notes that: "to ensure quick and successful intervention in the tunnel, the number of shafts around the tunnel, the number of lifts in each shaft and their capacity are key elements". Presently at the LHC sixteen elevators are used to connect the surface to the LHC and its experiments. The one-stop ride between the surface and the tunnel last about one minute while the cabins of these lifts can carry loads from 1 to 3 tons up to a speed of 2.5 m/s.
For FCC a slightly higher speed of 4-6 m/s to keep the duration of the ride to two minutes and a similar load of 3 tons are discussed as baseline parameters. However the greater depth of the tunnel means that one needs larger cables and thus the total weight of the cables becomes a critical issue. In fact, it turns out that the cables weigh much more than the actual cabin load as Lafarge explains. To address this issue we discuss with our industrial partners different scenarios; from using different materials to a more clever design for the elevator system.
The LHC lifts have made nearly 9'140'000 races ranging from 45.35 to 143.54m, over the LEP and LHC run 1 operation periods. You can multiply this by a factor of 2 or 3 based on the depth and number of components of a future collider (3 times bigger than the LHC) to get a rough idea of the wear and tear that the elevator system will be exposed to. That's why a key idea is now to get a redundancy with 2 lifts per shaft in order to reduce constraints on each lift, therefore maintenance costs, and increase the reliability of the function "access to the underground" at the same time!
Ingo Ruehl, an expert in CERN's Handling Engineering (HE) Group comments: "the earliest stages of any construction project offer the most opportunity for maximising quality and reducing total project costs. With this in mind, we are working in partnership with world leading engineering consultancies to utilise the latest methods and technology to ensure the best possible outcome from the first stages of design."
Thinking and designing the next generation of elevators that will be used for FCC, reliability and availability are realized to be key factors in future large and high-performance colliders as they can guarantee an efficient operation. CERN is working closely with its industrial partners to explore the latest generation of monitoring system for elevators, allowing to anticipate failures, an essential element to ensure the reliability of our facilities.
In the next years, a detailed presentation of the available technical options for the elevator system of the FCC will be prepared. This will be included in the FCC conceptual design report that will cover every aspect of building and operating such a future large-scale infrastructure. FCC offers a unique opportunity for experts in elevator engineering to think of novel solutions in order to address the unprecedented challenges posed by such a large underground facility.
Designing an efficient elevator is important to guarantee the safety for the people installing, maintaining and operating a future more powerful collider and running new experiments that will allow to go deeper in our understanding of our Universe!
During the FCC Week 2016, the FCC Innovation Award was given to three student collaboration researchers for their outstanding work that was presented during the poster sessions during FCC Week 2016. The posters submitted this year highlighted new concepts and technologies with significant impact to the the FCC-study.
Frederick Brodry, CERN’s Director for Accelerators and Technology opened the award ceremony on 13 April. Each award consists of an engraved glass plate award; a free IEEE student membership for one year along with a travel voucher. In addition the registration fees for FCC Week 2017 will be waived for the winners.
Craig Sturzaker from ARUP, UK. Craig designed and implemented a software solution that measures project risk and cost impacts for large-scale civil engineering projects. The case for a 100 km long accelerator tunnel was the perfect motivation to develop this interactive tool. The tool is presently being used in other large-scale construction engineering projects indicating; clear evidence of the impact of this work for industry.
Antonio della Corte and Bruce Strauss from IEEE Council on Superconductivity presented the the awards to the winners. They were joined by John Osborne, Francesco Cerruti and Amalia Ballarino who were (respectively) the supervisors of the winners in the above projects.
All in all, the award committee is was impressed by the quality and amount of the work put into these projects. The achievements of the winners and the clarity of the explanation in their posters were excellent. Dr. Strauss commented that the projects were among the best student presentations in the last few years.
Frederick Brodry warmly congratulated the three researchers on behalf of FCC Week 2016 organizing committee. He also warmly thanked the local organizing committee and all those who helped to the organization of this year’s meeting.
From 11 to 15 April, more than 450 participants from all over the world met in Rome during the 2016 Future Circular Collider (FCC) Week.
The future of high-energy physics on the timescale of the 21st century hinges on designing and building future colliders that could take us at least one order of magnitude beyond the present energy and intensity frontiers. Reaching this goal in an efficient way calls for a large circular collider. The FCC study explores different options for a post-LHC research infrastructure.
The discovery of the Higgs boson, a particle profoundly different from all other elementary particles, calls for further studies of its properties. Moreover, a number “known unknowns” like the observed asymmetry between matter and antimatter, the dark matter content of our Universe and the non-zero neutrino masses are only a few of the indicators that point to physics that possibly lies beyond the Standard Model. There are several questions related to physics at the TeV scale, exacerbated by the lack of evidence (so far) of new physics whose answer is critical for our understanding of the Universe.
The next results from the LHC may shatter some of our previous theories while they could call for a profound change of scientific paradigm signalling an exciting state for modern physics. Whether marked by a major discovery or not they are probably going to question our present understanding of fundamental theories. Gian Guidice, Head of CERN’s TH department in his talk “the FCC and the present physics landscape” concluded: “We live in one of the most fruitful periods in physics facing a number of challenges and new opportunities”.
With the LHC programme underway, the global particle physics community works to prepare a common vision for the future. The full exploitation of the LHC including its high-luminosity phase (HL-LHC) sets a timescale of 20 years. Given the long lead times in the field of high-energy physics, the FCC study is exploring possible options for the post-LHC era. "As one of the high-priority items on CERN's agenda, the FCC design study is exploring a potential post-LHC accelerator project that will ensure the continuation of the world’s particle physics programme” noted Frédérick Bordry, CERN Director for Accelerators and Technology. "The post-LHC accelerator calls for breakthrough technologies to afford the beam energy, intensity and brightness which are required for a future 'discovery machine'." he affirms. This timescale along with the complexity of the FCC project and the desire to profit from other international studies for future accelerators make the FCC study a timely effort.
The physics potential for each of the FCC-study scenarios (proton-proton, electron-positron or electron-proton) was reviewed during the meeting. Each of the scenarios has its specific virtues though there is also a strong complementarity while they set certain challenges for the design of the machine and the experiments. Detector-design concepts for all three scenarios were also presented while areas where further theoretical or experimental input is needed were identified. The FCC physics programme shows that this research infrastructure is not a mere follow up of past machines but could open new horizons in our quest to understand nature.
Among the main R&D programs launched as part of the FCC study are those investigating new superconducting magnets and cryogenic systems, new superconducting RF cavities, innovative vacuum systems as well as innovation in detector technologies to meet the physics challenges. The latest results in these fronts were discussed during the FCC Week 16 and the next steps in R&D activities defined.
Substantial progress has been made on infrastructure and operation studies. Civil engineering studies for a 90-100 km tunnel in the Geneva area were presented. In addition, operational aspects become crucial for FCC; controls and machine protection, as well as energy-consumption, reliability and safety were some of the topics covered during the meeting.
Finally, the FCC week also featured the work of younger researchers. More than 100 of them presented their latest research in the poster sessions. Three of them received the FCC Innovation award that distinguishes early stage researchers or engineers for outstanding work carried out in the scope of the study.
The efforts presented during the 2016 FCC week will culminate into a Conceptual Design Report by 2019. This will serve as a decision aid for a future particle research infrastructure. Michael Benedikt, FCC study leader, concluded: “We have a high responsibility to keep the present momentum and attract more collaborators in our efforts to design future circular machines that will serve the global scientific community”. Following the hard efforts of the last two years: “we must now focus on the established parameters and use them as basis for further optimization that can be done for the machines, detectors, and technologies required to realize such a large-scale research infrastructure.”
The next FCC Week will take place in Berlin from 27 May to 02 June, 2017. This meeting will mark a major review of the study and will be an important step in the launch of the preparation of the FCC Conceptual Design Report.
First hardware for FCC: Designing a novel beam screen system
by Panos Charitos and Cedric Garion (CERN)
For most people vacuum refers to “nothing”, but for an experimental particle physicist it is what enables a particle beam to travel through an accelerator without being scattered away, therefore it has an utmost importance in the performance of a particle collider.
The vacuum pipes of the FCC-hh not only have to maintain an ultrahigh vacuum over 100 km of underground tunnel but must also be able to shield the cold masses from unprecedented levels of synchrotron radiation in proton accelerators.
This radiation may extract electrons and gas molecules from the pipe wall, and so, deteriorate the vacuum, increasing the scattered particles which could lead to heat up or damage the ultra-cold superconducting magnets that keep the high-energy particle beams on track.
Francis Perez, head of accelerators division at ALBA synchrotron, and Paolo Chiggiato, head of the CERN Vacuum, Surfaces and Coatings group, are leading the cryogenic vacuum work package in the EuroCirCol project that gathers different institutes (ALBA, ANKA, CERN, CIEMAT, INFN and STFC).
Similarly to the LHC, the FCC-hh will have a beam screen inserted in the vacuum pipes to intercept the synchrotron light at cryogenic temperatures, with a flow of helium gas circulating in cooling channels to evacuate the heat load. However, the higher power density of the synchrotron radiation expected in the FCC-hh calls for a radically different design.
The team have proposed a novel vacuum system with improved heat transfer, lower impedance, improved pumping, and feasible manufacturing. The design also integrates a new method to mitigate the formation of electron clouds in the proton beam. This method, developed by the STFC and University of Dundee in the UK, consists on modifying the morphology of the beam screen surface by laser treatment to minimize the multipacting of electrons on the screen wall. The team has modelled the new design with dynamic vacuum, thermal and mechanical simulations, it is currently producing a prototype and investigating the process to manufacture the beam screens in the large scale.
The next steps include experimental tests of the new beam screens in the ANKA synchrotron in Karlsruhe. Providing a good approximation of the expected FCC-hh photon spectra, the measurements at ANKA , carried out at room temperature in a first step, will help to determine the heat load distribution, the desorption yield as a function of photon dose, and the photoelectron yield.
The first measurements will probably take place in 2017. However, important challenges remain ahead, like measuring the electron cloud density and the beam impedance. Further tests will assess the mechanical integrity of the beam screens after a magnet quench, the low-temperature gas adsorption on the laser treated surfaces, the generation of dust, etc.
In summary, the new concept for the beam screen of the FCC-hh fulfils the stringent vacuum requirements, easily removes the much higher than LHC synchrotron light power, and integrates e-cloud suppression. The preliminary design has been tested with mechanical, thermal, and gas density simulations, and the first prototype is ready for further tests while a two meter long version will be manufactured by end 2016.
Accelerator Reliability and Availability Training
By Johannes Gutleber (CERN)
Participants of the Accelerator Reliability and Availability (ARA) training programme trial in March 2016 (Image: CERN)
Reliability and sustainability is a key issue for present and future accelerators. The Future Circular Collider (FCC) study launched a training programme on Accelerator Reliability and Availability (ARA) engineering at CERN. The goal is to build a common foundation in the field of reliability engineering for particle accelerators and to create an active network of accelerator engineers who can assess and address reliability topics. Within the next three years a community of about 150 accelerator experts will be trained in reliability engineering.
A trial session was organized end Februaruary 2016 at CERN, which was attended by more than 20 engineers currently involved in the operation of the LHC, the HL-LHC construction, as well as in the conceptual design study of a post-LHC circular collider.
The training establishes a common terminology and set of methods used by experts from different technical domains, ranging from mechanical engineering, electronics, and software to cryogenics, superconductivity, vacuum, radiofrequency, and power engineering. The course conveys the mathematical foundations of reliability analysis and creates a sensibility to the importance of gathering field data and controlling the data quality as the pre-requisite for any reliability engineering activity. Over the coming six months, the course organisers will further develop the practical examples from the particle accelerator domain ranging from modelling vacuum systems, cryogenics supply, machine protection to beam production. This will allow the participants to profit from the methods and tools taught in their everyday operation and design work. The organizers also put special focus on equal opportunities which was already reflected in the attendance of the trial session with an outstanding 25% of female participation. The training is provided by University of Stuttgart, Tampere University of Technology and spin-off company Ramentor.
The “Foundations in Accelerator Reliability and Availability Engineering” course will start in autumn 2016 and it will run twice a year until 2018. The course will be free of charge for personnel involved in the conceptualisation and design of future circular colliders at CERN.
Read more about the training programme here.
A first concept for the FCC-ee main dipoles, with an X iron yoke (blue) and two aluminium busbars (red). The dimensions are about 40 cm wide per 12 cm high (Image: CERN).
The FCC-ee (Future Circular Collider lepton-lepton scenario) machine requires about 65 km of such magnets, to steer the counter-rotating electron and positron beams, before they collide at the energy of 350 GeV. As the preparation for the upcoming FCC week (11-15th April) is in full swing, researchers from CERN have presented a first concept for the main bending magnets for FCC-ee.
The proposed design for the FCC-ee main bending magnets features a twin aperture geometry, with a common iron yoke and two busbars, operated at room temperature. The dimensions are about 40 cm wide per 12 cm high. The design shows how compact these dipoles could be – at the moment their cross section fits on an A3 sheet. This concept will be further refined, to match the evolving requirements coming from the other FCC-ee work packages, including those on beam dynamics and vacuum.
The idea presented recently is based on a novel layout, where two classical C shapes are arranged back to back to create an unconventional X geometry. The great advantage of the novel design is that the magnetic field in one of the apertures comes at no extra cost, since it is generated by the return conductor of the other aperture. Compared to a system with separate magnets for the two rings, this solution reduces electrical consumption by 50% and of course the number of units to be manufactured, transported, installed and (eventually) removed, for the installation of FCC-hh.
“The FCC-ee main dipoles require a different type of R&D,” says Attilio Milanese, the CERN engineer who proposed the concept. He explains “at the moment, the focus is to work on the design while optimising the costs and the environmental impact.”
The yoke can be assembled from sheets of electrical steel, of a similar kind used in electric machines like transformers or generators. The excitation current is provided by two busbars in aluminium, which is lighter and cheaper than copper for the same power consumption. Full recycling the raw materials after dismantling the collider is also an option explored, with the team running simulations to understand how these materials will be activated from the high synchrotron radiation emitted by the beams.
Critical field of several HTS. Continuous lines indicate the maximum value as a function of temperature, where dashed lines indicate the maximum value at which these materials can be used as practical current carriers, such as in accelerator magnets. Image Credit: CNR-SPIN.
A recently formed collaboration aims at developing beam screens for the FCC study based on the little-known HTS thallium cuprate in order to drastically reduce the beam impedance.
The research on HTS (High-Temperature Superconductors) has mainly been focused on two different families of materials, YBCO and BSCCO, which differ in terms of composition and crystal structure. BSCCO is used for example for the current leads of the LHC superconducting magnets, while YBCO-coated ribbons are a potential candidate for winding magnets of accelerator-grade quality reaching 20 T, as needed for the future circular collider designs examined under the FCC study.
In addition, the FCC study demonstrated on theoretical grounds that HTS could also be used to minimize the electromagnetic interaction of the beam with the surrounding vacuum pipe.
The proton beams circulating in the accelerator will produce several tens of watts per meter of synchrotron radiation due to their 50 TeV energy. To prevent this power from impinging on the dipoles, which are cooled to 1.9 K, they have to be protected, like in the LHC, by a beam screen.
Other considerations related to vacuum stability dictate that the beam screen has to be kept at a temperature between 40 and 60 K. At these temperatures, common electrical conductors such as copper may have not low enough beam impedance. HTS materials offer the only viable solution to overcome this obstacle. However, a study of the required performance has shown that BSCCO would be inadequate for the FCC requirements. YBCO could cope with the requirements, but is currentlyavailable only in the form of thin coated ribbons. Scaling the YBCO fabrication procedure to the beam screen shape remains a tough challenge, and would require a thorough rethinking of the coating technology.
Example of a beam screen for the LHC. Image Credit: CERN
To address this problem, a new collaboration between CNR-SPIN (Superconductors, oxides and other innovative materials and devices), TU Wien (formerly Vienna University of Technology) and CERN has recently been formed, with the goal of developing HTS coatings based on the little-known superconductor thallium cuprate (Tl-1223 / Tl-1212).
Tl-cuprates bear the potential for an exceptional performance. Their Tc (critical temperature) and Hc2 (upper critical magnetic field) are among the highest found so far, and their thin film deposition properties should be scalable to large dimensions and complex geometries. This seemingly superior HTS is not widely used because the required texture could not be established in previous studies leading to an unsatisfactory in-field performance – and the toxicity of thallium did certainly not contribute to its popularity.
CNR-SPIN in Genova possesses comprehensive knowledge and in-house expertise regarding the preparation of this compound, and will explore new production routes aimed at the fabrication of Tl-based HTS with a significantly improved microstructure in order to overcome the previously found limitations. The feedback required for optimizing the production process will be supplied by TU Wien, where both the microstructure of the samples and the superconducting properties will be analysed. It is the possibility of using advanced characterization techniques to correlate the local superconducting properties (flux pinning, grain coupling, current percolation) with microstructural features, which fuels the hope of developing a Tl-based HTS coating with satisfactory performance.
Collaboration agreements have been signed mid-November, and a Kick-off meeting at CERN has successfully attracted all collaborators, helping finalize the work plan. Other institutes from Spain have also expressed their interest in collaborating with CERN on HTS coatings.
This R&D project and its direct application are at the crossroads of several fields: accelerator science and technology, RF and beam dynamics, vacuum and cryogenics, materials and surface science, and of course superconductor science and technology. Both CNR-SPIN and TU Wien are leaders in the superconductor R&D field and the ideal partners to carry out this work together with CERN, who will guarantee the final validation of the material for the accelerator environment. As a welcome side effect, this research project might open up the possibility of introducing Tl-based HTS into the mainstream domain of conductor cables for the fabrication of high power devices, such as magnets or motors.
Read more about this project
This September, experts from the CERN Magnet Group in the Technology Department celebrated the achievement of a 16.2T peak field in the Racetrack Model Coil (RMC). This is twice the nominal field of the LHC dipole and the highest field ever reached with this configuration. The result, which pushes forward existing boundaries for high-energy accelerators, is the product of a successful cooperation between several R&D programmes within the physics community.
Tested in the CERN SM18 vertical test station at a temperature of 1.9 K, the RMC, which consists of two racetrack coils, trained up to a maximum current of 18.5 kA, within less than 5% of the projected critical current of the cable. Based on the calculation of the field, this current corresponds to peak fields of 16 T on the 33-turns Powder-In-Tube (PIT) coil and 16.2 T on the 35-turns Rod Restack Process (RRP) coil. Three major ingredients made this achievement possible. First, such high fields are only possible thanks to the use of Nb3Sn, a intermetallic and brittle compound which withstands a much higher magnetic field intensity compared to the previously-used Nb-Ti alloy. Secondly, RMC uses new technologies that allow the coil to resist increasingly high electromagnetic forces. An example of this is the “bladder-and-keys” structure developed at LBNL (USA). The third and perhaps most important ingredient was the close relationship with European and overseas R&D programmes, which joined efforts and synergies to push through existing technology barriers.
The RMC result feeds in a larger objective shared by most high-energy accelerator projects: reaching high magnetic fields to permit higher beam energies – in the case of dipoles - or to squeeze the beam in the experiments, which is the case for high-gradient quadrupoles. RMC-type tests are now a part of the technology programme that supports the EU-funded EuroCirCol design study, which, in turn, is part of the Future Circular Collider study. This aims to be a conceptual design study for a post-LHC research infrastructure focuses on an energy frontier 100 TeV circular hadron collider. The test setup and measurement provide evidence for the feasibility of a 16 T dipoles based on low-temperature Nb3Sn superconductors. For this reason, the personnel in charge of setting up the testbed, working with industry and performing the test, are also working for the FCC 16 T magnet R&D programme.
RMC tests are a major step for many other R&D projects. In fact, they serve as technology support for the new High Luminosity LHC Interaction Region quadrupole QXF and for the 11 T dispersion suppressor dipoles. Finally, RMC is using wires and cables of the same class as those being used to build FRESCA2, a 13 T dipole magnet with a 100 mm aperture that will be used to upgrade the CERN cable test facility (FRESCA). FRESCA2 coils are currently under construction and will be ready for testing by summer 2016.
Figure 1: Schematic layout of the FCC-hh collider ring.
The core of the Future Circular Collider (FCC) project is a hadron collider called "FCC-hh" which aims at colliding proton beams with a centre of mass energy of 100 TeV - more than seven times the energy that can be reached in the LHC.
A team of experts from a large number of collaborating institutes and led by Daniel Schulte from CERN is designing FCC-hh and has reached the first important milestone at the end of September: a baseline for the machine layout and the main parameters of this collider. This will now form the basis for a more detailed design and in particular for a conceptual design report that is foreseen in 2018.
The dimensions of this collider are impressive; it would be hosted in a 100 km-long tunnel and consists of eight straight sections connected by arcs, as illustrated in Figure 1. It is currently planned that two of these sections accommodate high-luminosity experiments, two others could house additional, lower-luminosity experiments, whilst the other insertions would be used to inject fresh beams, clean the beams during operation, and extract the used beams.
The collider parameters have been chosen to fulfil the requests from the theoretical and experimental physics community. The collider layout permits using the LHC as an injector, and is compatible with CERN’s existing accelerator chain, though other options will also be explored.
The collider layout sets demanding goals for the designers of each subsystem. To meet these goals the R&D in the coming years will push a variety of technology frontiers to come to a feasible technical design. This includes for example very high field magnets, a powerful cryogenic vacuum system and a beyond state-of-the-art beam collimation system.
To achieve the envisioned high beam energies the magnets in the storage ring arcs need to reach twice the field strength of the magnets used in the LHC. This requires the use of novel superconducting materials and magnet designs. The synchrotron radiation emitted by the beams when forced on their circular orbit will be 100 to 1,000 times larger than in the LHC. This will require a new approach to the design of the beam pipes and associated cooling systems. Finally, the energy stored in the two beams will be about 16 GJ. The collimation system will need to clean these beams and protect the machine from an accidental beam loss.
In addition, in the FCC-hh scenario, the rate of proton-proton collisions is very high to provide a large number of interesting events to the detectors. The debris of these collisions has a power of 500 kW. An efficient shielding is being designed to protect the detector and machine components. Two sets of machine parameters that have now been determined are summarized in Table 1.
Table 1: Key beam parameters, comparing FCC-hh to LHC and the planned LHC luminosity upgrade
The column “Baseline” describes the initial performance whilst the column “Ultimate” represents the performance that could be expected after several years of operation.
The collaboration will now design and optimise the different systems of the collider to present a conceptual design in 2018 that reaches the target performances.