Future RD path on accelerator magnets Xingchen Xu

Future R&D path on accelerator magnets Xingchen Xu, TD Accelerator Science and Technology WG March 16, 2018

General Strategies Push of energy frontier: E ≈ 0. 3 R • B, E: in Te. V; R: in km; B: in Tesla Bigger accelerator, or higher magnetic field? Ø Magnets are the major cost determinant Ø Tunnel is cheaper: $20 K/meter Ø Magnets are at least 10 times more expensive. Larger R more magnets Higher cost So we need cheaper magnets with higher fields: focus on T • m. Two directions: Ø Push Nb 3 Sn magnets to 15 -16 T: focus on cost reduction Ø Explore Nb 3 Sn/HTS hybrid magnets (to 20 T) 2 Presenter | Presentation Title 2/10/2022

Reducing cost of Nb 3 Sn magnets Cost of Nb 3 Sn magnets mainly includes several parts: Ø Nb 3 Sn conductors: major component of whole magnet (for 16 T) Ø Coil fabrication: labor, parts Ø Magnet assembly: materials, labor Ø Magnet test: training 3 Presenter | Presentation Title 2/10/2022

Reducing cost of Nb 3 Sn magnets-I: improving Jc Ø B ∝ W • J. Ø Acoil ∝ (W 2 + a • W). Coil width W Current out B B 50% short in Jc ~2 x of Acoil ~2 x conductors 2 x cost 4. 2 K Ic-B curve Current in Load line: B ∝ W*I Beam pipe Coils wound from superconductors Ø Improving Nb 3 Sn Jc is the key to make coils smaller (and thus cheaper). Ø Especially important for 16 T, for which conductor is the biggest cost driver. Ø A clear path to improve Nb 3 Sn Jc: improving pinning. 4 Presenter | Presentation Title 2/10/2022

Reducing Nb 3 Sn magnets cost -II: reducing training Ø Training itself is costly Ø No more than 5 -10 quenches are allowed for real colliders? Ø Iq/SSL is <80%: need a large operational margin: a very big cost driver. How to reduce Nb 3 Sn magnet training? Ø Understand origins of quenches (e. g. , perturbations) and how to solve Ø Increase enthalpy margin of conductors: a new technique to increase specific heat 5 Presenter | Presentation Title 2/10/2022

Reducing cost of Nb 3 Sn magnets-III: labor & materials Labor takes a big fraction in fabricating Nb 3 Sn magnets. § § Automation? Cost-effective design (e. g. , larger cable)? Combination of steps? …… Parts and structural materials: § § Larger amount lower price? Cheaper way of manufacturing (3 D printing instead of EDM)? Cost-effective design? …… Increase reliability and yield: Based on experience with LARP and HFM program The costs of labor and materials will drop a lot from small to large scale production. 6 Presenter | Presentation Title 2/10/2022

Nb 3 Sn/HTS hybrid magnets: towards 20 T Exciting, but challenging: First, cost-effectiveness (in T • m)? Debatable! Ø HTS is at least 10 times more expensive than Nb 3 Sn Ø >3 times increase in conductor cost for 25% gain in field (16 T 20 T) Ø Definitely not suitable for main accelerator magnets Second, technical feasibility not certain: 15 T Nb 3 Sn dipole with 120 mm bore: Ø On HTS side: many technical issues (quench detection/protection, field errors, stress tolerance, etc. ) Ø On Nb 3 Sn outer coil: bigger bore very high stress Third, timeline: long-term R&D (10+ years, maybe 20+) But, it is a good R&D topic. Maybe used in some special cases? 7 Presenter | Presentation Title 2/10/2022

Summary Ø Push energy frontier: E ≈ 0. 3 R • B: increasing size or field? Ø More design studies needed for different senarios – Nb 3 Sn/Nb. Ti hybrid, whole Nb 3 Sn, Nb 3 Sn/HTS hybrid: achievable field, cost, stress, etc. Ø R&D - two directions: Nb 3 Sn (15 -16 T) cost reduction, Nb 3 Sn/HTS (20 T) Ø For cost effectiveness and near-future realization (before 2040), Nb 3 Sn magnets (or Nb 3 Sn/Nb. Ti hybrid) are the practical plan. Ø Cost reduction of Nb 3 Sn magnets should be a key task, which needs: • Improving conductor Jc (within 5 years) • Reducing magnet training (within 5 years) • Exploring ways to reduce labor and materials cost (within 10 years) Ø Push on the Nb 3 Sn/HTS hybrid magnets as a long-term R&D topic 8 Presenter | Presentation Title 2/10/2022