Inside Science at CERN: HL-LHC Upgrades, CLOUD Aerosol Lab and the Future Circular Collider

The episode takes listeners on a guided tour of CERN to unpack the physics driving the Large Hadron Collider upgrade and the tech that makes collisions more frequent. It also dives into the CLOUD aerosol lab where cosmic rays and beams are used to study cloud formation and climate-relevant aerosol chemistry, then looks ahead to the Future Circular Collider proposal for precise Higgs measurements. Interwoven are Open Skylab soil experiments repurposing tunnel mollasse and a glimpse of the broader research ecosystem at CERN.

• HL-LHC upgrade aims for about 10x more collision events by increasing fuel, tightening the beam and using stronger superconducting magnets with crab cavities.
• The CLOUD lab uses beam-induced ionization to simulate atmospheric conditions and investigate aerosol formation, linking fundamental physics to climate modeling.
• The Future Circular Collider concept would tunnel 91 km for electron-positron collisions to measure the Higgs with unprecedented precision.

Overview and setting the stage

The podcast is an on site exploration of CERN on location, with the crew descending into a cavernous setting to observe the scale and ongoing upgrades at the world’s premier particle physics facility. The hosts describe being 100 meters below a French McDonald’s and moving through the massive cavern complexes that connect to the LHC. The episode emphasizes that the detector is currently off as CERN undertakes its most ambitious upgrade in years. The conversation is not solely about high energy physics but also about the engineering feast that makes modern collider experiments possible. The tone balances curiosity about the science with appreciation for the sheer scale of the infrastructure required to run an experiment that can collide particles at unprecedented energies and luminosities. The opening sequence establishes the central threads of the program: the High Luminosity Large Hadron Collider upgrade, the upcoming heavier collision rate, the cosmic ray beam experiments in the CLOUD facility, and the prospect of future collider projects that would transform our ability to study the Higgs boson and other fundamental particles.

The Large Hadron Collider and the HL LHC upgrade

The core topic of the upgrade is explained by Paul Fessia, deputy project leader of Illuminosity LHC. He describes the plan to increase the number of collisions per unit time by a factor of approximately ten, through multiple engineering improvements. The upgrade consists of installing more protons into the machine, concentrating them into a smaller volume, and employing more powerful superconducting magnets to generate higher magnetic fields. A key mechanism is the crab cavity, which tilts the beams so that when crossing, the protons collide in a way that maximizes overlap and thus collisions. The accelerator physics are articulated through analogies to optical lenses, where stronger magnets focus particle beams to a tighter crossing region, thereby increasing the probability that protons meet during crossing. The team also explains that the crossing angle and beam shape (elliptical to a crisper crossing) will be adjusted to improve collision rates. They discuss the infrastructure needed to operate at the higher collision rate and the logistical realities of moving around a 3.3 km per access corridor within the accelerator complex by bicycle, underscoring the scale and necessity of efficient on site mobility for maintenance and upgrades.

The discussion then shifts to why this upgrade matters for physics, focusing on the Standard Model’s limitations and the search for rarer events that could point to new physics or the next layer of fundamental theory. The conversation touches on a physics philosophy: even though the Standard Model provides a robust framework, gaps remain in areas like mass generation, dark matter, or other beyond Standard Model phenomena. The HL LHC upgrade is framed as a mechanism that could unlock a more complete understanding by providing more collision data to analyze rare processes, potentially revealing new particles or interactions that could guide theorists toward a more comprehensive theory of fundamental forces.

Engineering, electricity, and appetite for discovery

The interviewee Anti Onela (mechanical engineer) discusses the physical layout around the LHC and the injection chain of accelerators. He explains that the machine uses multiple accelerators to feed protons into the LHC, and that the HL LHC will enable tenfold more collisions per unit time by using higher density beams, better focusing, and more intense magnetic fields. A recurring theme is energy, with the team noting that the upgrade will raise electricity usage to roughly that of a large city, maybe a city the size of Geneva. The engineers discuss energy recovery possibilities, including the potential to store and reuse energy from the magnets by using battery-like systems to recapture energy when the magnetic field is reduced. This part highlights the intersection of cutting edge physics and practical energy management in large facilities, illustrating the sustainability and systems engineering considerations that accompany such a major scientific infrastructure project.

The episode underscores the human dimension by highlighting the potential excitement of new discoveries. The team emphasizes that the most exciting outcomes would be those that surprise the researchers and open doors to new physics, or to engineering innovations that could affect energy management in large scientific facilities. The interview also touches on the long timeline for major projects: a 2028 project approval, construction in the 2030s, and operations starting in the mid 2040s. The cost of the HL LHC upgrade is framed as an investment with wide community benefit, but with an awareness of controversy and debate within the physics community about the best way to allocate limited research funding across numerous ambitious projects.

The CLOUD aerosol lab: atmospheric science at a particle physics facility

Eva Sommer introduces Open Cloud Run, CERNs CLOUD aerosol chamber, a controlled environment that simulates cloud formation and aerosol physics. The chamber is designed with a thick thermal insulation layer and a low temperature to approximately minus 70 degrees Celsius, creating a nearly pristine environment for aerosol experiments. The chamber’s design allows researchers to control trace gas compositions down to parts per trillion, enabling precise experiments on how aerosols form and act as cloud condensation nuclei. The CLOUD team uses particle beams to modulate ionization rates inside the chamber. Cosmic rays naturally ionize atmospheric molecules at altitude, helping scientists simulate how ionization influences aerosol formation in the real atmosphere. The CLOUD experiment thus acts as a bridge between fundamental particle physics and climate science, creating an experimental microcosm of atmospheric processes that influence cloud cover and climate forcing.

The researchers describe how this setup connects to climate models. Clouds exert a cooling effect by reflecting sunlight, so understanding cloud formation and microphysical processes is essential to reduce uncertainties in climate projections. The CLOUD team’s ambition is to isolate the microphysical steps of aerosol nucleation and growth, including the roles of different acids and compounds that participate in aerosol formation in marine and terrestrial environments. They discuss the specific marine aerosols and compounds like DMS and MSA, which are important for particle formation in the real atmosphere. The lab demonstrates how controlled experiments can reveal natural sources and their influence on aerosol formation rates, providing essential input to climate models and helping scientists quantify uncertainties in climate predictions.

The marine and terrestrial aerosol results: new natural sources identified

The CLOUD team explains findings from marine aerosols, including how DMS influences aerosol formation and how MSA acts similarly to sulfuric acid in particle formation. The researchers highlight the identification of a natural source for aerosol particles that contributes to our understanding of atmospheric chemistry. This work is positioned within the broader effort to refine climate projections by reducing uncertainties around cloud properties, aerosol formation rates, and their interaction with radiation. The researchers discuss how the lab environment enables precise measurements that would be difficult in natural atmospheric conditions, emphasizing the value of such a controlled environment for climate science. The CLOUD project is presented as a core example of how CERNs facilities support cross disciplinary science, linking particle physics with environmental science to address global challenges like climate change.

Open Skylab: turning tunnel waste into soils

The Open Skylab segment introduces a different strand of CERNs research: soil engineering using mollasse rock excavated during future collider construction. Christiana Staudinger explains the project and the rationale behind it. The mollasse is crushed to a particle size distribution of 0 to 20 millimeters and mixed with green waste compost and microbial amendments to create soils with targeted ecological functions. The project’s aim is to optimize soil properties such as water holding capacity, filtration, and biomass production. The narrative highlights the tension between underground construction and sustainable land use by re imagining excavation waste as a resource for future planting substrates. The team also describes hedgerow plantings and pollinator friendly species, illustrating how soil ecosystems can be designed to support biodiversity and microbe-plant networks. They discuss the slow colonization process and the early signs of soil function formation, such as nutrient cycling and soil structure development, along with plant survival metrics in the first year. This segment demonstrates CERNs broader mission to repurpose waste streams and contribute to environmental science beyond fundamental physics.

The Future Circular Collider: physics beyond the LHC

The podcast then shifts to the Future Circular Collider (FCC) concept. The FCC envisions a 91 km circumference tunnel that would house electron-positron collisions in its initial phase, followed by potential reuse for a hadron collider later. The goal is to provide an extremely clean environment for Higgs profiling and precision measurements, enabling a deeper characterization of the Higgs boson. The discussion contrasts electrons and positrons with protons, noting that the cleaner environment reduces backgrounds and improves measurement precision. The potential physics payoff is framed as a journey into precision Higgs physics and broad physics reach beyond the Higgs sector. The estimated cost is discussed, with the figure of about 15 billion Swiss francs, and the time horizon described as long and capital intensive, with project approval anticipated in 2028 and construction potentially starting in the early 2030s. The interview acknowledges that while some physicists see the FCC as a necessary long term investment, others question the allocation of resources and call for support of multiple smaller initiatives. The program presents a balanced view, recognizing both the physics potential and the challenges of building the next generation of large scale accelerators.

Conclusion: CERN as a hub of science and collaboration

The piece closes by highlighting CERNs ecosystem as a living laboratory where high energy physics, environmental science, engineering and soil research converge. The collaborators emphasize the excitement and unpredictability of fundamental research; the line about not knowing what will be found underscores the sense that this is a frontier enterprise, combining bold ideas with incremental engineering progress. The episode ends with a reflection on the ongoing construction, the community of physicists and engineers who work there, and the enduring curiosity that drives such a large, shared scientific enterprise.