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Nature Physics, Published online: 05 February 2024; doi:10.1038/s41567-023-02361-4

Hydro-equivalent scaling of recent direct-drive inertial confinement fusion implosions shows that a burning plasma can be achieved with a higher laser energy.

Nature Physics, Published online: 05 February 2024; doi:10.1038/s41567-024-02389-0

When cracks creep forward in our three-dimensional world, they do so because of accompanying cracks racing perpendicular to the main direction of motion with almost sonic speed. Clever experiments have now directly demonstrated this phenomenon.

Nature Physics, Published online: 01 February 2024; doi:10.1038/s41567-024-02387-2

Understanding the mechanism by which magnons—the quanta of spin waves—propagate is important for developing practical devices. Now it is shown that long-range dipole–dipole interactions mediate the propagation in a van der Waals antiferromagnet.

HiLumi News: protecting the components of CERN’s future accelerator

A major upgrade of the collimation system of the Large Hadron Collider (LHC) began during the first long shutdown of CERN’s accelerator complex (LS1, 2013–2015) and continued during LS2 (2019–2021), in preparation for the High-Luminosity LHC (HL-LHC). As its name suggests, the HL-LHC will surpass the LHC in terms of luminosity, i.e. the number of collisions that take place within the LHC experiments. The accelerator’s equipment therefore requires enhanced protection, which is where the collimation system comes in.

What is a collimator?
Collimators are movable blocks made of materials that can absorb particles. Shaped like jaws, they close tightly around the beam to clean up particles that stray from their path. The materials used for these jaws and their various components are capable of withstanding extremes of pressure and temperature, as well as high levels of radiation.

Why do beams need cleaning?
Particles that stray from the beam path could collide with sensitive accelerator components, such as superconducting magnets, and interfere with their operation or, in the worst case, damage them. To prevent this from happening, collimators are placed at strategic locations around the LHC ring, where they either absorb stray particles or deflect them towards beam dumps. Protection is particularly crucial in the vicinity of the experiments, where the beam size is reduced to increase the chances of collision.

The new collimators are double-beam collimators (here you can clearly see the two beam apertures side by side). This optimised configuration enables both beams to pass through the same vacuum chamber, thus freeing up space for the collimators' jaws. (Image: CERN)

The LHC currently has 118 collimators of different kinds. The future HL-LHC will have 126 collimators, including brand new models custom made at CERN. Recently, two new prototypes (TCLPX and TCTPXH) have been successfully developed and tested, under the supervision of François-Xavier Nuiry, engineer in charge of the HL-LHC collimator production. Destined for LHC interaction points 1 (ATLAS detector) and 5 (CMS detector), they are double-beam collimators. This optimised configuration enables two beams (circulating in opposite directions) to pass through the same vacuum chamber, thus freeing up space for the collimators’ jaws, which are thicker and more powerful in this location.

“These two prototypes are innovative in several ways,” explains Dylan Baillard, a mechanical engineer in CERN’s Targets, Collimators and Dumps section. “They are fitted with a remote alignment and levelling system, which helps reducing the radiation dose received by the teams working on them. The collimator flanges can be connected and disconnected more easily thanks to integrated connection tools. Finally, ion pumps are used to ensure an excellent vacuum quality because the collimators, which are close to the beams, always operate in a vacuum and must not disrupt the circulation of the beams.”

The final tests were successfully completed in December, and series production of the two new types of collimator should begin this year. Twelve double-beam collimators will be installed in the machine during Long Shutdown 3 (LS3, 2026–2028).

anschaef Thu, 02/01/2024 - 11:46 Byline Anaïs Schaeffer Publication Date Wed, 01/31/2024 - 11:49

HiLumi News: cool kickers for the HL-LHC Installation of the MKI-Cool during the 2022–23 year-end technical stop. (Image: CERN)

Kicker magnets are an important part of the LHC accelerator complex. Installed at the intersection of the LHC ring and the SPS transfer lines, they give each injected beam a “kick” at the right time to put it into orbit in the LHC.

The higher luminosity of the HL-LHC will pose a challenge for these magnets, as increased heat load could result in a miskick of the injected beam. To avoid this, engineers in CERN’s Systems department have developed a new version of the kicker magnet for the HL-LHC, called an “MKI-Cool”. One such magnet was installed in the LHC one year ago, replacing a standard kicker magnet. Measurements during its first year of operation, with high-intensity beam, show that the temperature rise of the MKI-Cool is less than one-fifth of that of the other seven kicker magnets in the LHC. This confirms that no heating issues should occur for the MKI-Cool kicker magnets with HL-LHC beams.

“Based on this excellent result, all the kickers will be sequentially upgraded to MKI-Cools,” says Mike Barnes, senior engineer in CERN’s Systems department. “The full upgrade of the MKIs will be completed during Long Shutdown 3.”*

Unlike other magnets in the accelerator, kicker magnets cannot be fully shielded from the beam. Shielding would interfere with the fast magnetic field pulse that they provide to kick the beam. In addition, the high-voltage pulse required prevents the magnets from being water-cooled, which is a serious hurdle as the ferrite they are made from loses its magnetic properties above the temperature of 125 °C. Under these conditions, the MKIs would miskick the injected beams, causing the downstream magnets to lose their superconductivity.

Following years of research and development, the team came up with a new design. The MKI-Cool design works by moving most of the beam-induced heating from the ferrite yoke to a so-called RF damper, which contains a ferrite cylinder and is mounted just upstream of the magnet. The beam-induced heat is then removed from the RF damper using a water-cooling circuit.

“The concept of moving the heat was demonstrated in computer simulations, but it was very challenging to prove this in lab-based measurements,” Barnes continues. “Hence, to fully prove the concept, a prototype with an RF damper, which was not cooled, was installed in the LHC in 2018 and measurements of temperature, with circulating LHC beam, proved that the RF damper concept worked effectively.”

To measure the difference in the beam-induced heat load between the MKI-Cool and the old kicker magnets, the team used temperature sensors attached to a nearby metal side plate. It was not possible to directly measure the temperature of the ferrite because it is pulsed to a very high voltage during the beam injection.

“During 2023 LHC operation with the MKI, the measured temperature of both the RF damper and the side plate remained relatively low,” Barnes continues. “Based on these temperature measurements and simulations, no heating issues are expected for the MKI-Cool in the HL-LHC era.”

*Mike Barnes retired at the end of 2023: Giorgia Favia is now responsible for the MKI kicker magnets and will oversee the full upgrade to MKI-Cools.

ndinmore Wed, 01/31/2024 - 11:35 Byline SY department Publication Date Wed, 01/31/2024 - 11:32

The CERN Accelerator School celebrates 40 years

The CERN Accelerator School (CAS) celebrated its 40th anniversary in the sunshine last September and with its contributors this January.

Back in the 1980s, a group of CERN scientists and engineers saw the need for an educational training programme in the rapidly evolving field of accelerator physics and technology. Textbooks on accelerator physics were sparse at the time, and courses at universities were practically non-existent. As Herwig Schopper, then CERN Director-General, put it: “An enormous amount of expertise is stored in the brains of quite a number of people […]. However, very little of this knowledge has so far been documented or published in book form.” It was into this landscape that the CERN Accelerator School was born in 1983.

The success of CAS in Europe quickly caught the attention of the global accelerator community, leading to a surge in demand for its courses. To accommodate this growing interest, CAS began organising courses outside Europe, in Asia and the Americas, from 1985, in collaboration with other institutions and organisations working in accelerator physics.

Over its 40-year-long history, more than 6000 participants from across the globe have been trained.

Find out more about the history, impact and future of the CERN Accelerator School in the latest CERN Courier: https://cerncourier.com/a/40-years-of-accelerating-knowledge/

anschaef Wed, 01/31/2024 - 11:32 Byline CERN Accelerator School Publication Date Wed, 01/31/2024 - 11:29

Accessible by design: how CERN Science Gateway exhibitions are tailored to people with visual impairments A visitor from ABA testing the Discover CERN: Accelerate exhibition with her guide. (Image: CERN)

Since opening in October, CERN Science Gateway has welcomed almost 100 000 visitors. Among these was a group of around 50 people from the Association pour le Bien des Aveugles et malvoyants (ABA), the reference association in Geneva for blind and visually impaired people, who toured the exhibitions on 28 November. ABA has worked with the CERN exhibitions team since 2019 and this was the chance for its members, including some visually impaired members, to see the fruit of this collaboration.

At the event, Emma Sanders, head of the CERN exhibitions team, and Bernard Jost, ABA’s accessibility project manager, explained how they had developed the exhibitions with accessibility and inclusivity at the forefront.

“We learnt very early on that making content more accessible usually benefits more than one kind of audience group,” Emma explained. “Tactile content is great for people who are blind or who have visual impairments, but it is also appreciated by many children. Wheel-chair accessible furniture is also good for parents pushing kids in buggies.”

“The idea came from CERN,” says Jost. “While the law requires cultural sites in Geneva to be as accessible as possible, what’s praiseworthy about CERN Science Gateway is that they made a point of taking accessibility into account from the beginning. We haven't created a parallel accessible exhibition: it's the same exhibition with some additional accessible features.”

The exhibition Our Universe: Back to the Big Bang features a tactile timeline of the Universe. (Image: CERN)

The permanent Science Gateway exhibitions comprise three parts: Discover CERN, Our Universe and Quantum World. Many installations incorporate an audio description and many also include tactile features, where visitors can touch and explore to interpret the content for themselves.

“One of the exhibitions that impressed me the most was Discover CERN, where I was able to go around the tunnel that the particles pass through and, thanks to the guide's description, experience the entire journey they take. It was impressive,” says Anne Gaugaz, one of the ABA visitors with visual impairments. “I also liked, in Back to the Big Bang, being able to touch the planets of the solar system that were in relief. That helped me to understand how big they were.”

A visitor from ABA touring the ​​​​Discover CERN: Collide exhibition with his guide and guide dog. (Image: CERN)

“Thanks to the guided tour, I enjoyed my visit to the Science Gateway exhibitions, in particular the accelerator exhibition and the part that takes us back in time to the Big Bang. It was very interesting and informative,” says Bertram Paul, a blind member of the ABA group who also worked with the exhibitions team to advise on the audio descriptions.

While the visit in November was a success, there is still work to be done. “Of course, it’s an evolving process,” Jost continues. “Some more alterations need to be made, so we will keep in touch.”

Content designed for people with visual impairments is just one aspect of Science Gateway’s effort to be accessible to all. And to complement the exhibitions, there is now a new CERN guides course focusing on accessibility, which is run by another local group, Culture Accessible. Visit this link to find out how you can become a Science Gateway guide.

For colleagues across CERN who are interested in making their work more accessible, the exhibitions team can share more about the process. As Emma recommends, “It’s always easier to ensure accessibility when you build it in from the start of your project. Working together with the community is essential: it brings creative and sometimes unexpected solutions that often work better for everyone.”

ndinmore Wed, 01/31/2024 - 09:43 Byline Naomi Dinmore Publication Date Wed, 01/31/2024 - 09:33

Nature Physics, Published online: 31 January 2024; doi:10.1038/s41567-024-02397-0

Multiple mechanisms can create electrons with reduced kinetic energy in solids. Combining these mechanisms now appears as a promising route to enhancing quantum effects in flat band materials.

Nature Physics, Published online: 31 January 2024; doi:10.1038/s41567-024-02386-3

Magnons—quanta of spin waves—have potential applications in signal processing technology. But it is challenging to obtain coupling between different magnons. Now a study achieves this by demonstrating nonlinear magnon mixing in an antiferromagnet.

Nature Physics, Published online: 31 January 2024; doi:10.1038/s41567-023-02374-z

The electronic transport properties of charge-ordered kagome metals are controversial. Now careful measurements on unperturbed samples show that previously measured anisotropy in the transport occurs only when external perturbations are present.

Computer Security: 300 computer security articles and counting

We begin the year by celebrating the 300th Bulletin article focusing on various computer-security-related topics. Three hundred hopefully informative articles about the cybersecurity situation at CERN. About best practices, guidelines and useful tools. About risks, threat scenarios and attack vectors. About new or established means of mitigation. About the workings of the Computer Security team, the services and tools it’s providing and the complexity of its detection infrastructure. About policies and dos and don’ts. Three hundred articles trying to raise your awareness and help you improve your approach to computer security – the security of your laptops, smartphones and tablets, of your accounts and passwords, of your email inbox and web browser, of software programming and system development – both at CERN and at home.

While some articles were published a long time ago – the first ones were released in 2008 – they’ve never lost their relevance. Sometimes it’s useful to delve into the past and dig out information from them; often these articles also provide guidelines for us when advising users. So for this 300th anniversary, we have updated our compilation of all the articles published so far. This compilation covers a plethora of topics, sorted into the notorious themes of “computer security”, i.e. the literal cybersecurity of computers, “mobile and cloud security”, “network and data centre security”, “account and password security”, “control systems and IoT (Internet of Things)”, “secure software development”, “data protection and privacy”, “copyrights”, “rules and policies” and more. Giving a deeper insight into the computer security landscape, these articles complement our Monthly Reports, which usually depict the operational side of what’s currently happening at CERN.

You can download this compilation here. It’s public – published under CC-BY-NC-SA. So please feel free to share it with your colleagues, family and friends in order to spread the word, raise awareness and help them improve the security and protection of their own digital assets and resources!

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Do you want to learn more about computer security incidents and issues at CERN? Follow our Monthly Report. For further information, questions or help, check our website or contact us at Computer.Security@cern.ch.

anschaef Tue, 01/30/2024 - 11:03 Byline Computer Security team Publication Date Tue, 01/30/2024 - 11:00

Nature Physics, Published online: 30 January 2024; doi:10.1038/s41567-023-02288-w

Phonons do not carry spin or charge, but they can couple to an external magnetic field and cause a sizable transverse thermal gradient. Experiments suggest that phonon handedness is a widespread effect in magnetic insulators with impurities.

Nature Physics, Published online: 30 January 2024; doi:10.1038/s41567-024-02384-5

The thermal Hall effect of phonons does not yet have a definitive explanation. Now a careful study of doped Sr2IrO4 suggests that the mechanism involves the scattering of phonons by impurities embedded in an antiferromagnetic environment.

Nature Physics, Published online: 30 January 2024; doi:10.1038/s41567-024-02385-4

Heterostructures of transition metal dichalcogenides are known to simulate the triangular-lattice Hubbard model. Now, by combining a monolayer and bilayer of different materials, this idea is extended to multi-orbital Hubbard models.

Nature Physics, Published online: 29 January 2024; doi:10.1038/s41567-023-02365-0

Understanding the three-dimensional nature of fracture formation and dynamics is challenging. Experiments now show that a fracture front, after originating at a particular locus in a material, propagates jump-wise and expands transversely at high speed.

Nature Physics, Published online: 26 January 2024; doi:10.1038/s41567-023-02382-z

Electronic transport measurements of the anomalous Hall effect can probe properties of a frustrated kagome spin ice that are hidden from conventional thermodynamic and magnetic probes.

Nature Physics, Published online: 26 January 2024; doi:10.1038/s41567-023-02366-z

Physical ageing in glassy materials can be described in a linear way through the concept of material time. Multispeckle dynamic light scattering is now shown to provide experimental access to the material time, in terms of which fluctuations become statistically reversible.

Nature Physics, Published online: 26 January 2024; doi:10.1038/s41567-023-02378-9

Most quantum simulations of spin models with trapped ions have been restricted to one dimension. Now, tunable simulations of Ising models with single-site detection have been demonstrated in two-dimensional ion crystals.

Nature Physics, Published online: 26 January 2024; doi:10.1038/s41567-023-02362-3

Observations of strong electron correlation effects have been mostly confined to compounds containing f orbital electrons. Now, the study of the 3d pyrochlore metal CuV2S4 reveals that similar effects can be induced by flat-band engineering.

Nature Physics, Published online: 25 January 2024; doi:10.1038/s41567-023-02375-y

Experiments with unprecedented energy and momentum resolution reveal the nature of the pairing symmetry in KFe2As2 and pave the way for a unified theoretical description of unconventional superconductivity in iron-based materials.