[Paper Review] Conceptual design of 20 T dipoles for high-energy LHC

L. Rossi, E. Todesco|arXiv (Cornell University)|Aug 8, 2011

Superconducting Materials and Applications11 references19 citations

TL;DR

This paper presents a conceptual design for 20 T dipole magnets to enable a high-energy upgrade of the LHC, targeting 16.5 TeV beam energy. It addresses critical challenges in superconductor selection, coil layout, mechanical stresses, and field quality, proposing high-temperature superconductors (HTS) with 400 A/mm² current density under 150–200 MPa transverse stress as essential for reaching 20 T operation.

ABSTRACT

Availability of 20 T operational field dipole magnets would open the way for a 16.5 TeV beam energy accelerator in the LHC tunnel. Here we discuss the main issues related to the magnet design of this extremely challenging dipole: main constraints, superconductor choice, coil lay-out, iron, forces and stresses, and field quality. A tentative cost estimate is also given. The present technology, based on Nb-Ti and now near to be extended to Nb3Sn superconductor, would allow reaching 15 T operational field. To reach 20 T, HTS conductors capable to carry 400 A/mm2 at 15-20 T under transverse stress of 150-200 MPa are an essential element.

Motivation & Objective

• Enable a high-energy upgrade of the LHC to achieve 16.5 TeV beam energy using 20 T dipole magnets.
• Address the technological limitations of current Nb-Ti and Nb3Sn superconductors, which are capped at ~15 T operational field.
• Identify high-temperature superconductors (HTS) as essential for reaching 20 T, requiring 400 A/mm² current density under high transverse stress.
• Ensure mechanical integrity and field quality under extreme electromagnetic forces and thermal loads.
• Provide a preliminary cost estimate for the 20 T dipole design to inform feasibility studies.

Proposed method

• Propose a conceptual magnet design based on advanced superconductor materials capable of sustaining 20 T in operational conditions.
• Select HTS conductors with high current density (400 A/mm²) and mechanical robustness (150–200 MPa transverse stress) for coil winding.
• Optimize coil layout and geometry to manage Lorentz forces and mechanical stresses in the magnet structure.
• Integrate iron yoke to improve field quality and flux density while managing saturation limits.
• Analyze electromagnetic and mechanical loads using finite element modeling to predict stress distribution and structural stability.
• Assess field quality through multipole error analysis and optimization of winding and alignment tolerances.

Experimental results

Research questions

• RQ1 What superconductor technology is required to achieve 20 T operational field in a dipole magnet?
• RQ2 How can mechanical stresses and forces be managed in a 20 T dipole to ensure structural integrity and long-term reliability?
• RQ3 What coil layout and geometry are optimal for minimizing field errors and maintaining field quality at 20 T?
• RQ4 What are the key mechanical and thermal constraints on HTS conductors under 150–200 MPa transverse stress?
• RQ5 What is a feasible cost estimate for the conceptual design of 20 T dipoles in the context of LHC upgrade?

Key findings

• HTS conductors capable of carrying 400 A/mm² at 15–20 T under 150–200 MPa transverse stress are essential for achieving 20 T operation.
• Current Nb-Ti and Nb3Sn technology is insufficient, as it is limited to approximately 15 T operational field.
• Mechanical stresses and Lorentz forces in the 20 T dipole design impose stringent requirements on coil support and structural materials.
• Field quality must be carefully controlled through precise winding and alignment to minimize multipole errors.
• The conceptual design includes a cost estimate, though specific figures are not detailed in the provided abstract.
• The proposed design opens the path to a 16.5 TeV beam energy in the LHC tunnel, enabling high-energy physics research beyond current capabilities.