UK News from CERN Issue 69

 

Issue 69 contents

The essential element

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Imagine a top of the range supercar, minus its engine; it’s a feat of outstanding design and precision engineering, but going nowhere. The same is true of the LHC experiments without the Worldwide LHC Computing Grid.

Has the magic gone from Calcium-52?

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For the first time scientists have measured the radius of a calcium nucleus with 32 neutrons – indicating that nuclear physics theories don’t describe atomic nuclei as well as previously thought.

Engineering for extremes

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An innovative approach to modelling mechanical engineering is one of the topics to be showcased at the SET for Britain event in the Houses of Parliament on 7 March.

A slice of Cosmic Pi

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The best way to learn how a particle physics detector works is to design and build your own. That’s exactly what a small group of researchers have been doing in their spare time, and prototypes of their Cosmic Pi detector will be runners-up prizes in the CERN Beamline 4 Schools competition.

Recreating the real CERN

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There’s no denying that particle physics is complicated, but that doesn’t mean that it can’t be made accessible. Microcosm, CERN’s permanent exhibition is open again after a major refurb, and it’s better than ever...


 

The essential element

Ian Bird
(Credit: Claudia Marcelloni; Maximilien Brice)

 

Imagine a top of the range supercar, minus its engine; it’s a feat of outstanding design and precision engineering, but going nowhere. The same is true of the LHC experiments without the Worldwide LHC Computing Grid.

WLCG is both the infrastructure that enables the physical capture, archiving and analysis of data from the LHC experiments, and a collaboration that takes a strategic view of developments in large-scale computing and carries out research and development. It’s no small undertaking; the rolling five year cost of funding LHC computing is equivalent to the one-off construction cost of ATLAS or CMS (approximately £350M).

Ian Bird is the project leader – the equivalent to a Spokesperson in one of the LHC experiments. That difference in job title reflects the different way that WLCG is run; it’s a collaboration that is ‘owned’ by CERN to ensure the long-term evolution of the computing required to support the LHC. The collaboration partners are the many computer centres around the world.

WLCG was approved in 2001 and Ian Bird has been involved since 2002. “Initially, my job was to make the grid work,” explains Ian. A physicist by background, Ian had found himself becoming progressively more involved in software development to enable a series of international physics experiments to capture and process data.

“It’s very important to have someone leading the computing who really understands the physicists,” says Ian, “they have an expectation of how things should work. You need to understand their motivation.”

Ian oversees an infrastructure that comprises 170 computer centres located around the world and the Grid software that binds them together. But that reliance on a physical network is changing, “It’s not going to be a traditional ‘grid’ for much longer – we’re continually evolving.”

Storing data on the Cloud is one option but these private ‘islands’ of computing have individual access requirements; CERN’s user community is accustomed to accessing the Grid through a single sign-on. WLCG is therefore exploring the potential of ‘federated’ clouds.

“We’re always looking for the best value solutions,” explains Ian. “By integrating a range of options, our users don’t have to worry about how to access their data.”

The ongoing requirement of WLCG is to provide the computing requested by its customers. And with pressures on funding across CERN’s member states, Ian’s perpetual challenge is to ‘do more for less’.

“Computing used to be invisible, but now it’s recognised as essential, alongside the accelerators and detectors. I am proud to say that CERN’s computing has never stopped the physics being done.”

CERN has always been at the forefront of computing – it’s one of the biggest producers of data and this continues to drive developments in how high volume data is managed. But it’s not just physics that generates big data - Ian sits on advisory boards for the Square Kilometre Array telescope and European Bioinformatics Institute sharing expertise and looking for opportunities to collaborate on shared challenges.

With software playing such a vital role in data analysis, Ian would like to see physicists get similar recognition for building computing systems or developing software as they do for writing physics papers, “Writing reconstruction software needs a good understanding of the physics and, as a community, we need to recognise this skill and offer long-term positions that retain knowledge and ensure continuity for the development of the software. It’s a very specific skill set.”

Perhaps Ian’s concerns will be addressed as the LHC computing demands increase. The next big challenge is the LHC High Luminosity upgrade, scheduled to start taking data in 2026.

“Extrapolating today’s computing models, the data is going to increase by a factor of 5-10,” explains Ian. “We have to produce a technical design report by the end of the decade but we already know that the current Grid technology can’t give us the economies of scale that we need; we’ll have to be clever – this is what forces creative technical development.”

At this stage, Ian doesn’t know what the solution will be, but reflecting on computing developments to date, he says “the great thing about CERN and high energy physics is that you know you’ll get to an end point, but the journey might not be what you expected!”

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Has the magic gone from Calcium-52?

Interview with Ronald Fernando Garcia Ruiz, lead scientist COLLAPS experiment, ISOLDE
(Credit: CERN)

 

For the first time scientists have measured the radius of a calcium nucleus with 32 neutrons – indicating that nuclear physics theories don’t describe atomic nuclei as well as previously thought.

The study, conducted by CERN scientists at the ISOLDE facility and published in the latest issue of the journal Nature Physics, aimed to understand whether calcium has more than two magic numbers.

Magic numbers appear in nuclei when they have the right number of protons and neutrons to make them particularly strongly bound. This in turn has an influence on their nuclear charge radii.

Previous indications suggested that 52Ca, an isotope with 20 protons and 32 neutrons, is doubly-magic, having magic numbers of both protons and neutrons. To test this, the team of researchers set out to measure how the radii of calcium isotopes change as neutrons are added. Calcium with the magic proton number 20 already has two doubly-magic isotopes when it also has 20 or 28 neutrons. Scientists found evidence that other doubly-magic isotopes might exist for 32 and 34 neutrons.

“The previously known doubly-magic isotopes, 40Ca and 48Ca, have similar and smaller charge radii than their neighbours because they are particularly strongly bound. When we measured charge radii for larger neutron numbers they kept growing. Based on observations from other doubly-magic nuclei, we would have expected a relative drop in the charge radius if 52Ca were doubly-magic, too. However, it increases as other non-magic nuclei in this region of the nuclear chart,” explains Ronald Fernando Garcia Ruiz (Manchester), one of the researchers on the project.

Several nuclear models had already computed what would happen, but none predicted the radius growing as much as the experiment found. First-principles computations using state-of-the-art nuclear interactions and the supercomputer Titan at Oak Ridge National Laboratory in the US reproduced the similarity of the charge radii for 40,48Ca, and showed an increase of radii beyond 48Ca. However, to understand the unexpectedly large difference between the charge radii of 52Ca and 48Ca still poses a theoretical challenge.

“Theory before this was happy, because it described other aspects of neutron-rich calcium isotopes. But all of the theoretical models employed underestimated this growth in charge radii. We’ve shown there are missing components in our knowledge,” says Garcia Ruiz.

The ISOLDE researchers used lasers to measure how the electrons surrounding the nucleus shifted in energy depending on the neutron number of the calcium isotope. The amount of shift, combined with their understanding of electromagnetic forces, enabled them to determine the charge radius of the nucleus.

Since the shift from one isotope to the next is so tiny the study was only able to show the change in nucleus radius by using high-resolution techniques.

The study, at the COLLAPS installation at ISOLDE, was able to measure this to very high precision and sensitivity: one of the highest ever reached with optical detection techniques.

The team are now developing a higher sensitivity technique that will allow them to extend their research to study the radii of calcium nuclei beyond 52Ca, to 53,54Ca.

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Engineering for extremes

Marco Morrone with the first prototype beam screen
(Credit: STFC)

 

An innovative approach to modelling mechanical engineering is one of the topics to be showcased at the SET for Britain event in the Houses of Parliament on 7 March.

Imperial College London PhD student Marco Morrone is one of the finalists in this prestigious competition which celebrates the work of outstanding young researchers.

Marco, who is based at CERN, has developed an innovative 3d modelling technique which is proving to be an essential tool for designing new beam screens – a vital component for the 2024 upgrade of the Large Hadron Collider that will see the machine generate higher luminosities than ever before.

The new beam screens shield the cryogenics system in the focussing magnets from the heat induced by the beams of protons travelling at almost the speed of light. The screens must be able to withstand temperatures close to absolute zero, high magnetic fields, very low pressures, high energies stored in the magnets, and radiation. In these extreme conditions, the properties of materials change, and Marco has carried out more than 1200 computer simulations to see how the designs respond to different parameters. The key objective of the project is to design a beam screen that can maintain its mechanical integrity if the magnet quenches.

At LHC beam energies, the electric currents in the magnets required to control the particle beams are extremely high, up to 12,000 Amperes, and superconducting cables have to be used. Superconductivity is a low-temperature phenomenon, so the magnet coils have to be kept very cold, just 1.9 degrees above absolute zero to be precise, or about -271°C. Even a tiny amount of energy released into the magnet for any reason can warm up the coils, stopping them from superconducting. When this happens, the current has to be safely extracted in a very short time. This is called a quench, and just one millijoule – the energy deposited by a 1p coin falling 5 cm – is enough to provoke one. Magnet protection in case of quenches is a crucial part of the design of the LHC’s magnetic system.

Marco is part of a multidisciplinary team that includes cryogenic and magnet experts, “I really love the project – I like the fact that I’m working on something that will be realised to find new physics. Every member of the team brings something to the collaboration - I’ve been doing the mechanical simulations. This type of 3d modelling has not been done before and it’s allowing us to investigate what happens to the beam screen in the z direction as well as the x and y.”

Modelling the beam screen during a magnet quench
(Credit: CERN/M Morrone)

“The new beam screen design is much more complex than the screens currently in use in the LHC; the thermal link is very delicate so the only way to investigate what happens in a quench is to model it in 3d,” explains Marco.

His results showed that stress concentrations in the components could have threatened the mechanical integrity of the beam screen, and as a result aspects of the design have been modified. It’s a process that saves time, and money.

Based on the design changes, the team now has a physical prototype which they plan to test in a quench later this year. “I’m excited to see real results,” says Marco, “it’s great to have something in your hands and be able to say ‘this works’!”

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A slice of Cosmic Pi

Cosmic Rays Concept
(Credit: Rik57 Dreamstime)

 

The best way to learn how a particle physics detector works is to design and build your own. That’s exactly what a small group of researchers have been doing in their spare time, and prototypes of their Cosmic Pi detector will be runners-up prizes in the CERN Beamline 4 Schools competition.

Motivated by a shared interest in citizen science and a passion for technology that goes well beyond their day jobs, James Devine, Justin Salmon and Hugo Day (all CERN) first started working on a low cost cosmic ray detector at the annual CERN Webfest in 2013.

Cosmic ray detectors are nothing new, but with a price tag of up to £14K and the size of a large filing cabinet, few schools and colleges were likely to buy one, even with the promise of being part of an international collaboration. James (an electrical engineer), Justin (a computer scientist) and Hugo (an applied physicist) want to produce a £200-300 kit for students aged 14-18 to build their own open source cosmic ray detector and become part of global cosmic ray telescope.

The first design was based on smartphone technology but it wasn’t ideal and the advent of the versatile (and cheap) Raspberry Pi computer and Arduino electronics platform got the team thinking, and growing.

Through hackathons and other events, the team has gained members Cosimo Cantini (ETH Zurich), Etam Noah, Leila Haegel, and Ruslan Asfandiyarov (all University of Geneva) and Julian Lewis (retired CERN engineer) with expertise in detector design, microcontrollers, readout electronics and particle physics.

With most of the development work taking place at the weekends, what’s the motivation for the project? “We all want to learn how to build an entire detector,” says James, “from the power supply and detector design to the electronics and data analysis. We’ve all learnt from each other.”

The kit that runner-up teams in the Beamline 4 Schools competition will receive is still a prototype, and that means that their feedback will be extremely valuable as Cosmic Pi develops. The goal is to produce an open source design and make it available through crowdfunding.

“None of us are cosmic ray scientists, but we’re building a community science project,” explains Hugo, “You don’t have to sit back and wait for scientists to do science!”

Want to know more about the project? Checkout the CosmicPi website or watch James speaking at TEDxGeneva.

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Recreating the real CERN

Microcosm
(Credit: CERN)

 

There’s no denying that particle physics is complicated, but that doesn’t mean that it can’t be made accessible. Microcosm, CERN’s permanent exhibition is open again after a major refurb, and it’s better than ever, showing how the LHC works from following the path of a proton to high energy collisions, data management and what else you can do with the innovative technology.

“Tap the hydrogen bottle! Go on, tap it!” says Emma Sanders (CERN), who masterminded the transformation of the exhibition space. As the hydrogen ions are liberated, the exhibition comes alive and the protons start accelerating through a section of a real linear accelerator.

To get this far, we’ve already travelled back in time to the Big Bang, and entered the subterranean world of CERN. The combination of genuine components, realistic models, clever technology, real time LHC status screens and creative imagery is narrated by people who work in each of the areas. It feels right.

And that’s down to Emma and her team of passionate science communicators, designers, animators, videographers and crane operators.

“We wanted to create real spaces where visitors can meet real CERN people and hear about the laboratory in their own words”, says Emma. “The spaces need to feel authentic – CERN people should feel at home in the exhibition.”

Extensive evaluation of the old exhibition helped with the new. It has shaped the language used to describe the science and technology – the lab is full of jargon and what has a clear meaning to a CERN person can mean something very different to a member of the public, or a school student. And with such a rich resource of stories to tell, the biggest challenge has been to keep it clear and simple.

And if you think it’s all going to be rather serious, think again! The exhibits intrigue and engage, and the passion and excitement of the people that you meet flows as energetically as the protons!

Microcosm is completely free and you don’t need to book a visit. It’s open Monday to Friday: 8:30 to 17:30 and Saturday: 9:00 to 17:00.

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