Optimizing a CO₂ Cooling Manifold for CERN

Introduction

The Compact Muon Solenoid (CMS) experiment at CERN is one of the world’s most advanced particle physics detectors. To support the upgrade to the Inner Tracker (IT), CERN required lightweight, highly efficient cooling manifolds to manage the thermal load of its sensitive electronics. Carbon dioxide (CO₂) was selected as the cooling medium due to its low environmental impact and high cooling performance. However, CO₂ cooling presents unique engineering challenges: it operates at high pressure and low temperature, and must be delivered through complex internal geometries with extreme precision.

The challenge was to design a compact, low-mass manifold that could deliver uniform flow across multiple outlets while remaining manufacturable via additive manufacturing under tight spatial constraints.

CERN partnered with Nadya Collantes from the University of Bath to solve this challenge using ToffeeX’s physics-driven generative design, enabling faster and more efficient development than conventional tools could provide.

The result: an optimized CO₂ supply manifold designed in just 5 hours of engineering time instead of weeks.

Background

CERN’s Large Hadron Collider (LHC) is the world’s most powerful particle accelerator. One of its core detectors, the Compact Muon Solenoid (CMS), is designed to study the fundamental building blocks of matter by analyzing the particles produced in high-energy proton collisions. At the heart of CMS is the Inner Tracker, a precision subsystem that reconstructs particle trajectories just nanoseconds after each collision.

To maintain the tracker’s accuracy and performance, thermal control is essential. As collision rates and data volumes increase, traditional cooling solutions like C₃F₈ (octafluoropropane) have become inadequate due to environmental concerns and thermal performance issues. 

CO₂ offers a more sustainable alternative with superior thermodynamic properties—but it comes with engineering challenges. Operating at high pressures and low temperatures, CO₂ systems demand components with tight tolerances and complex internal flow paths—requirements that conventional CAD tools and standard manufacturing methods struggle to meet.

Three interconnected challenges hindered conventional design approaches:

1. Traditional cooling methods posed environmental concerns.
    → CERN selected CO₂ for its low environmental impact and superior cooling performance at the target temperature of 35 ^oC.
   
2. However, CO₂ systems operate at high pressures and low temperatures, requiring precise control of flow and structural integrity. This has led to complex internal geometries that are challenging to manufacture using traditional methods.
    → Additive manufacturing (AM) was selected to produce the part.
   
3. Designing for AM added a third layer of difficulty.
   Traditional CAD tools were unable to easily generate the intricate internal flow paths required to maximize the potential of AM, resulting in a slow, manual, and difficult-to-optimize process.
    → ToffeeX’s generative design software automated the process, generating physics-validated, manufacturable geometries in hours.

Project goals 

Design objectives for the new supply manifold:

• Reduce overall part mass below the previous manifold’s 119 grams
• Ensure uniform velocity distribution across all 8 outlets
• Minimize pressure drop throughout the manifold
• Guarantee manufacturability with 3D printed 316L Stainless Steel
• The design pressure is 186 bar, and the operating pressure is 30 bar.

Implementation using ToffeeX

The design process began with a clean design domain and the direct input of boundary conditions and objectives into the ToffeeX platform. The process was fully automated, requiring minimal manual input.

Design methodology

1. Design domain – Boundary body set to define spatial and structural constraints
   
2. Define inputs – Objectives and requirements configured within ToffeeX
   
3. Optimization – Solid and fluid geometry generated through multi-physics optimization
   
4. Analysis – Performance evaluated against pressure, velocity, and mass criteria
   
5. Refinement – Final geometry post-processed in Meshmixer for manufacturing

Steps 2–4 were repeated iteratively, allowing rapid convergence on a manufacturable, high-performance solution.

Results

Conclusion

The University of Bath achieved a solution that would have been prohibitively time-consuming to achieve using traditional design methods. In high-stakes environments like particle physics, where precision, reliability, and sustainability are non-negotiable, generative design tools fundamentally better outcomes—especially for complex applications like optimizing a CO₂ cooling manifold for the CMS Inner Tracker upgrade.

About CERN

The European Organization for Nuclear Research (CERN) is one of the world’s leading centers for particle physics research. Home to the Large Hadron Collider (LHC), the world’s most powerful particle accelerator, CERN enables scientists to explore the fundamental structure of the universe. Its experiments—such as the Compact Muon Solenoid (CMS)—drive advancements in detector technology, high-performance computing, and engineering innovation on a global scale.

CERN team: Axel Filenius – Engineer, CMS 

About the University of Bath

The University of Bath is a leading UK institution recognized for excellence in engineering, technology, and applied research. Its Department of Mechanical Engineering is internationally renowned for work in fluid dynamics, materials, and sustainable design. Through close industry collaboration and advanced simulation capabilities, Bath supports cutting-edge innovation across aerospace, automotive, and energy sectors.

The University of Bath team: Nadya Collantes & Alexander Lunt (supervisor)