CERN Accelerating science

Seamless accelerating cavities

Superconducting radiofrequency accelerating cavities are the heart of modern particle accelerators. One of the key challenges for FCC is the development of more efficient superconducting RF cavities. Any progress on substrate manufacturing and preparation will have an immediate impact on the final RF performance, as it was demonstrated by the seamless cavities produced for the HIE-ISOLDE project. The welded ISOLDE Quarter Wave Resonators show the typical Q-slope of thin films cavities (decrease of the Cavity Quality Factor at high accelerating fields). The issue was substantially reduced substituting the welding cavities with seamless ones. Seamless construction helps to reduce the performance limitations arising from defects and irregularities of the welding seams and the area in their vicinity, as well to reduce possible contamination originating from them. FCC studies push in this direction, exploring the seamless cavity production by spinning and electro-hydraulic forming. The cavities will be made both in bulk niobium and in copper coated with a thin film of superconductive niobium.

Spinning is a well-known forming technique since the Middle Ages, however, the SRF community needed to wait for Enzo Palmieri who produced the first seamless elliptical cavity spun and presented it during the SRF conference of 1993 at CEBAF.

In particular, he showed the possibility to spin a copper and niobium monocell, complete with cut-off tubes, starting from planar blanks. The technique is now mature, and it has demonstrated the feasibility to produce a 1.5 GHz nine cell elliptical resonant cavity. For its cheapness, today the spinning technique is largely used by the SRF community for the production of R&D cavities, both in niobium and copper. However, in the production of cavities for accelerators, the standard technique is still preferred. Elliptical cavities traditional fabrication methods consist in the spinning, or deep drawing, of the half-cells and a further electron beam welding on the equator. This protocol guarantees the required dimensional tolerance in a large-scale production, which is a mandatory parameter in the RF design of the accelerator. Due to the non-symmetrical nature of the seamless spinning fabrication method, to guarantee the dimensional tolerance in a large-scale production of thousands cells required from FCC is one of the challenges of this research.

Moreover, since in FCC the 400 MHz cavities are demanded, the cell diameter increases almost 4 times compared to the standard 1.3 and 1.5 GHz produced up to now by seamless spinning methods. The seamless spinning process increases the surface, from the sheet to a final cavity shape, more or less of a factor of 1.5, independently on the cavity frequency and dimension. This means that the increment in surface during the spinning, in absolute values is 15 times higher in a 400 MHz cavity than the same increment in a 1.3 GHz cavity!

When the seamless spinning technique was proposed for the FCC cavities studies, no one knew if the large amount of cold work generated during the spinning of such a huge cavity, could allow to close the cavity without producing any cracks.

In 2017 the aluminum prototype was realized. Aluminum cavity is the first step in seamless spinning production, since aluminum is very machinable compared to copper and niobium and the prototype is used to test the mandrel and the metrology of the cavity. For us, this piece of metal has got a special meaning: it was the last seamless cavity realized by Enzo Palmieri.

During the last year the INFN-LNL SRF group has been carrying out the R&D of the seamless 400 MHz cavities, following the road traced by Enzo, but without benefiting of his genius and his 30 year’s experience.

The first 400 MHz copper cavity spun showed deep cracks near the cell iris, but was fundamental to understand how to improve the process. For a 1.3 GHz a single intermediate annealing between the spinning of the first half cell and the second one allows a complete closure of the cavity. For the 400 MHz cavity, at least three intermediate annealings in ultra high vacuum furnace, at three different stages of spinning process, are necessary for the complete closure.

In November 2018, the first seamless 400 MHz copper cavity in the world was produced. The cavity required three months of work to be finalized, but the more difficult part starts now: to optimize the process and transform a hand-made technology into an industrialized one capable to produce the thousands of cells required by FCC.


 

REFERENCE: V. Palmieri, R. Preciso, and S. Y. Stark, “Seamless 1.5 GHz cavities obtained by spinning a circular blank of copper or niobium,” in Proceedings of 6th International Conference on RF Superconductivity (SRF1993), CEBAF, Newport News, Virginia, USA, 1993.

REFERENCE: V. Palmieri, “Seamless cavities: the most creative topic in RF Superconductivity,” in Proceedings of 8th International Workshop on RF Superconductivity (SRF1997), Abano Terme (Padova), Italy, 1997, vol. 3.

The aluminum seamless 400 MHz cavity prototype realized under the supervision of Enzo Palmieri 

The teamwork with the first copper seamless 400 MHz cavity

Panagiotis Charitos (CERN)
Quadrupole magnets for FCC-ee
8 Oct 2018

Quadrupole magnets for FCC-ee

First tests of a twin quadrupole magnet for FCC-ee took place last summer in CERN's new magnetic measurement laboratory.

Romain Muller (CERN)
And the winners of the ARIES Proof-of-Concept fund are…
3 Jul 2018

And the winners of the ARIES Proof-of-Concept fund are…

Take a closer look at the potential of the selected projects

Maurizio Vretenar (CERN)
Accelerator-Industry Co-Innovation Workshop
15 Mar 2018

Accelerator-Industry Co-Innovation Workshop

Tools and strategies to enhance industry-academia cooperation in the particle accelerator community

A big step towards the superconducting magnets of the future

Last April, the FRESCA2 dipole magnet reached a field of 14.6T. This field value sets a new world record for dipole magnets with a free aperture, and breaks the old record established in 2008 of 13.8T by LBNL with the HD2 dipole magnet.

The development of magnets with fields beyond 10T started in Europe in 2004 with the FP6-CARE-NED project where the basic technologies were developed and specifically the Nb3Sn conductor which is the workhorse for the HL-LHC 11 T magnet, the LHC luminosity upgrade programme and baseline option for the more powerful 16T magnets for the Future Circular Collider study.

“FRESCA2 has already played an important role in the development of the new magnets for the High Luminosity LHC and will soon help develop the next generation of magnets." says Gijs de Rijk, head of the FRESCA2 programme.

The FRESCA2 dipole magnet design and construction was started in the framework of the FP7-EuCARD-HFM project in 2009 and has been co-financed by HL-LHC. The FRESCA2 magnet is much larger than a LHC magnet, measuring 1.5 m in length and 1 m in diameter. This allows the magnet to have a large aperture, measuring 10 centimetres, so that it can house the cables being tested, as well the sensors to monitor their behaviour. 

The FRESCA2 magnet before the start of the tests. (Image: Maximilien Brice/CERN). 

The magnet is the outcome of a successful collaborative effort between CERN and CEA-Saclay. The technology developments for FRESCA2 were essential for the new Nb3Sn magnets of HL-LHC. Formed by the superconducting niobium-tin compound and cooled to 1.9 kelvin (-271°C), it had already reached a field of 13.3 teslas in August 2017. Then, with a modification of the mechanical pre-stressing, it started a new series of tests in April before reaching its record intensity.

FRESCA2 will also be used to test coils formed from high-temperature superconductors. The goal is to test not only the maximum electrical current but also study in depth the effects of so high magnetic fields and the behaviour of the coil. Results from these measurements feed current efforts to design high-field magnets for future energy-frontier colliders. 

The magnet was tested to the nominal operating field, and achieved 13.3T in August 2017 after a very rapid training of 5 quenches. As a second step, the mechanical preload was increased and the magnet was retested in April 2018 to explore the ultimate operating limit. In this configuration FRESCA2 reached a maximum bore field of 14.6T at a temperature of 1.9K with additional 6 training quenches. The tests are currently being performed in the new purposely built test cryostat of the SM18 cryogenic test station at CERN.

This result is a major milestone in the progression towards high field accelerator magnets beyond HL-LHC. The future of FRESCA2 is to provide background fields for tests of cables and small coils, a new facility that will provide unique test capabilities.

Panos Charitos (CERN)
A big step towards the superconducting magnets of the future
28 Jun 2018

A big step towards the superconducting magnets of the future

FRESCA2 reaches an important milestone, a magnetic field of 14.6 T a record for a magnet with a “free” aperture

Ubaldo Iriso (ALBA-CELLS)
Different techniques of emittance measurements for SLS and FELs
2 Mar 2018

Different techniques of emittance measurements for SLS and FELs

The status of different techniques and some new approaches of emittance measurements for SLS and FELs were analyzed in a topical workshop at ALBA.

Panagiotis Charitos (CERN)
Advancing superconductivity for future magnets
8 Oct 2018

Advancing superconductivity for future magnets

Collaboration between researchers and industry is key for unlocking the potential of this technology.

The first 802 MHz prototype cavities for CERN’s future circular collider

A general memorandum of understanding between JLab and CERN has been established to cooperate in the development of superconducting radio frequency (SRF) accelerator technologies for the future circular collider (FCC). Both partner laboratories agreed to build a small series of 802 MHz prototype cavities. A key element is the design of a high current, five-cell Energy Recovery Linac (ERL) SRF cavity to support R&D efforts for the Large Hadron electron Collider (LHeC) and the FCC electron-hadron collider (FCC-he). For both machines it is proposed to use five-cell 802 MHz SRF cavities in a 60 GeV three-pass racetrack ERL for a linac-ring hadron-electron collider configuration. At the same time, the development addresses the need for five-cell 802 MHz SRF cavities required for the ttbar configuration of the FCC lepton-lepton collider (FCC-ee).

JLab’s SRF institute houses a complete set of infrastructures covering cavity design, mechanical fabrication, chemical surface post-processing of the delicate cavity interior, clean-room assembly, as well as high-field characterization of SRF cavities. The latter is facilitated in JLab’s test area housing dedicated liquid helium dewars for so-called ‘vertical’ tests. This capability provides a rather quick turnaround time from a ‘paper’ design towards the realization and high power testing of an SRF cavity prototype. The main goal of the 802 MHz development was to validate the basic RF cavity design in a vertical test setup at 2 K temperature for both a single-cell and a five-cell cavity made from fine-grain, high purity niobium sheets. 

First, the conceptual ERL cavity design was finalized with extensive use of numerical analyses resulting in a five-cell cavity that balances key performance parameters with regard to RF, mechanical and beam-dynamical aspects. A single-cell cavity is simply made up of end half-cells attached to beam tubes.  Manufacturing of production tools commenced based on the conceptual design, starting with deep-drawing of metal discs into cavity half-cells as well as rolling of metal plates into beam tubes. Cavity sub-assemblies were joined by the standard, yet critical, electron beam welding process to complete the mechanical fabrication.

Though the focus of the project was on the bulk niobium cavity development, JLab also produced two single-cell cavities from OFHC copper to support ongoing Nb thin-film coating R&D at CERN. In addition, an OFHC copper cavity was built for low power bench measurements, in which multiple half-cells can be mechanically clamped together. Presently, a mock-up can be created with up to two full cells. This can be used for example for higher-order-mode (HOM) coupler development.

The first metal sheets were pressed in April 2017, and the fabrication of the cavities was completed in March 2018 (see figure below), including successful vertical tests of the single-cell and five-cell niobium cavities.

Standard interior surface post-processing methods were applied to the niobium cavities, including bulk buffered chemical polishing, high temperature vacuum annealing, light electropolishing, ultrapure high-pressure water rinsing, and low temperature bake-out.

The test results were extremely encouraging, since both cavities reached accelerating fields, Eacc, slightly above 30 MV/m ultimately limited by thermal breakdown (quench). Moreover, the RF losses were rather small due to the relatively low RF frequency, which provides a small BCS surface resistance. This resulted in unloaded quality factors, Q0, as high as ~5e10 at 2 K at low fields, while Q0-values of 3e10 could be maintained for the five-cell cavity up to ~27 MV/m (see plot below).

These performance values already exceed present specifications for the LHeC, FCC-he and FCC-ee machines that are set at Eacc ≤ 20 MV/m and Q0 ≤ 2e10, respectively. This provides generous headroom for a potential reduction in performance when the cavities are equipped with all the ancillary components and installed in cryomodules. More R&D is envisioned with the single-cell niobium cavity to explore the recently developed N-infusion technique that can further lower the BCS resistance as well as chemical vapor deposition of Nb3Sn onto the niobium surface.

Meanwhile, the five-cell cavity design has been adopted for the Powerful ERL for Experiments (PERLE) facility at Orsay/France, which is proposed as a test bed to demonstrate LHeC and FCC-he principles. With the successful completion of the prototyping effort, future work must concentrate on the development towards a fully-equipped cavity production unit for installation in a cryomodule, i.e. a five-cell cavity dressed with a helium tank and featured with all ancillary components such as an input power coupler, HOM couplers, and a pickup probe.

 

Ruben Garcia Alia (CERN)
RADECS 2017: radiation resistance for electronics
7 Dec 2017

RADECS 2017: radiation resistance for electronics

Addressing radiation effects with RADECS and RADSAGA

Panagiotis Charitos (CERN)
Advancing superconductivity for future magnets
8 Oct 2018

Advancing superconductivity for future magnets

Collaboration between researchers and industry is key for unlocking the potential of this technology.

Panagiotis Charitos (CERN)
Quadrupole magnets for FCC-ee
8 Oct 2018

Quadrupole magnets for FCC-ee

First tests of a twin quadrupole magnet for FCC-ee took place last summer in CERN's new magnetic measurement laboratory.

Education for innovation in Hilumi and FCC

HiLumi and FCC organised their first innovation course in collaboration with IdeaSquare and CERN Knowledge Transfer (KT) on 31 January and 1 February, 2018. Twenty students and young professionals from HiLumi and FCC interested in innovation and entrepreneurship participated in the two-day course and will continue working on their ideas for a few weeks. The purpose of the induction session was twofold: to let the participants explore potential ways to apply their knowledge and skills outside the CERN context, and to familiarize them with established innovation practices. The aim was to inspire students/young professionals to think “outside the box” and teach them basic skills on how to think like an innovator and an entrepreneur thus offering them new skills and competences, which they may find useful later on in their careers. “It has been a real pleasure to host the course at IdeaSquare”, says Markus Nordberg who is a recognised expert in open innovation and manages other innovation courses such as the Challenge Based Innovation CBI.

During the two days, the participants gained insight into how to deliver innovation, assess knowledge transfer opportunities and identify different applications of CERN technologies from presentations given by the IdeaSquare team and distinguished visiting presenters. Harri Toivonen from Aalto University introduced the participants to the design thinking philosophy, opening minds on how to approach challenges with no clear solution. Giovanni Anelli from KT demonstrated how CERN technologies have turned into applications that benefit society in sectors such as medicine, safety and environment. He also put a focus on the innovation opportunities offered by KT. Philipp Topic from Vienna University of Economics and Business introduced Technological Competence Leveraging, a systematic, proactive and crowdsourcing-based method to identify new application fields for technologies. Marcello Losasso presented the QUACO project as a case study of a Pre-Commercial Procurement initiative, a mechanism that boosts innovation and attracts potential industrial partners. Creating a network of like-minded people is also a key to success in innovation and this is why Laure Esteveny presented the CERN Alumni activities and IdeaSquare and KT student programs were presented to open up ideas on how to reach to peers.

The participants were encouraged to bring their own innovation topics to the course, and if so had the chance to display them in an elevator pitch on both days. Using the knowledge and tools introduced during the course, the participants then worked in four groups, developing and refining their ideas. During the group sessions, some ideas were dropped, and the groups  developed detailed presentations for 10 ideas they most believed in, to defend their views. At the end of the second day, three ideas were subsequently voted as most promising and three groups were put in place to further refine and work on them. At the time of publication of this article each group is developing their ideas with expert support.

The results will be presented in an award ceremony to an invited audience on 21 March. “It has been extremely impressive how the participants have used the information received during the course”, says Isabel Bejar Alonso, organizer of the course. “From the first presentation to the last there has been a complete revolution moving from vague ideas to credible proposals.” This innovation course has demonstrated how important it is for young researchers to see that entrepreneurship can be an option for their careers. Even more so as they realised that there is no real frontier between industrial innovation and the work they do every day.

 

Header image: The participants refined their ideas during group workshops in the HiLumi FCC Innovation course at IdeaSquare (photo by Isabel Bejar Alonso, CERN)  

Daniela Antonio (CERN)
A reverse hackathon with CERN
8 Oct 2018

A reverse hackathon with CERN

What if we selected a few CERN Technologies and put them in the hands of professionals that help create highly successful start-ups?

P. Ferracin, E. Todesco (CERN)
Power tests of HL-LHC quadrupole
8 Oct 2018

Power tests of HL-LHC quadrupole

Successful results from the power test of the fourth short model of a Nb3Sn quadrupole for the High Luminosity upgrade.

Ricardo Torres (University of Liverpool)
EuPRAXIA marks two years of research into plasma accelerators
11 Dec 2017

EuPRAXIA marks two years of research into plasma accelerators

EuPRAXIA is designing the world’s first multi-GeV user-ready plasma accelerator

Science transcends boundaries

For a third year, the European Union (EU) Delegation to Japan, together with EU Member State embassies, European and Japanese research laboratories organized a number of events during the Science Agora 2017, Japan’s largest science fair. Every year, Science Agora offers a unique opportunity for scientists to interact with policymakers and the general public to discuss how science and technology transform our daily lives and occupy a central place in economic growth and societal change.

The key theme of the 2017 Science Agora was “Beyond the Boundaries”. In this regard, international collaboration and geographical diversity are just as important as diversity of disciplines. The FCC study, supported through EC’s H2020 EuroCirCol programme, was presented as an example of how international scientific collaboration transcends different boundaries and could help us address a number of inter-connected global challenges. In total five projects were selected to showcase how collaboration between European and Japanese institutes boosts frontiers in particle physics, sustainable energy sources, the internet of things, nuclear fusion, smart cities and climate change.

EU's "participation in Science Agora is thus driven by our twofold desire to show in a tangible manner some of the best science and innovation which are being developed in Europe, and to demonstrate the diverse ways in which European and Japanese researchers and scientists are cooperating", said EU Ambassador Viorel Isticioaia-Budura.

The opening ceremony of EU's participation to Science Agora 2017 in Tokyo. EU Ambassador to Japan Viorel Isticioaia-Budura (right) and Leonidas Karapiperis, Head of S&T Section, Delegation of the EU to Japan (left) (Image Credits: EU delegation to Japan).

Frank Zimmermann (Deputy FCC-study leader) discussed how the FCC study strengthens the role of global collaboration in science, technology and innovation, leveraging the competencies of experts from different fields and countries. “We are facing a changing reality that not only opens up the opportunity for collaboration, but which actually necessitates the latter, as it becomes increasingly difficult for individual scientists or even individual countries to conduct groundbreaking research on their own. We have witnessed how scientific research has evolved over the past decades, requiring R&D efforts beyond institutes and even countries to develop novel enabling technologies.” International cutting-edge research helps us cross the boundary between the present and the future, and allows us to envisage a much more powerful post-LHC collider.

Moreover, Zimmermann presented the joint efforts with KEK and University of Tokyo in developing a new generation of superconductors that will meet the requirements of the high-field magnets needed for a 100 TeV energy frontier collider. It is key to the success of any high-tech project to involve the entire scientific and engineering community from the very early days onwards.

Frank Zimmermann (CERN) presenting the scope of the study for a Future Circular Collider and highlighting aspects of the collaboration with Japanese research institutes and universities.

The European Union’s participation in the Science Agora also included lively demonstrations of superconductors, a video illustration of the FCC collider, poster presentations, and small tokens for the young visitors! This event offered the opportunity for European and Japanese researchers to present their joint projects and, conversely, to listen to the voices of the general public, including Japanese high-school, middle-school and primary-school students fascinated by science. This next generation will eventually provide the researchers to work on the proposed future accelerator complex. At the Agora, the participating scientists also shared their original motivation and the questions they are trying to address through their research, thereby inspiring many young students who were curious about a researcher’s life.

The stand of the EU delegation in the Science Agora 2017 giving information about a number of EC supported projects.

The FCC study along with the other collaborative projects that were presented at the Science Agora 2017 are helping to expand the area of world-leading scientific and technological collaboration between Japan and Europe – an area that will create growth and that will offer to young people, from around the world, the space to dream, to aspire and to develop.

Panagiotis Charitos (CERN)
Discussing the next step for circular colliders
12 Dec 2017

Discussing the next step for circular colliders

The 2018 Future Circular Collider collaboration meeting will take place in Amsterdam, the Netherlands (9-13 April 2018).

Panagiotis Charitos (CERN)
Science transcends boundaries
8 Dec 2017

Science transcends boundaries

European and Japanese collaboration in the framework of the FCC study was highlighted during Science Agora 2017

Marco Zanetti (INFN & Univ. Padua), Frank Zimmermann (CERN)
Workshop shines Light on Photon-Beam Interactions
7 Dec 2017

Workshop shines Light on Photon-Beam Interactions

The ARIES Photon Beams 2017 Workshop was held in Padua, Italy in late November 2017.