Tokamak Energy High-Temperature Superconducting Magnet Technology for Fusion Energy Dr. Alexander Davies Maxwell Centre, Cambridge 10th Nov. 2023 Nuclear Fusion in Cambridge Photograph: Cavendish Laboratory, 1933 (featuring early fusion researchers including Mark Oliphant and Ernest Rutherford) Solar fusion image © 2023 Tokamak Energy Nuclear Fusion Graphs and Diagrams: - Average binding energy per nucleon (MeV) vs mass number showing fusion of light elements (e.g. 2H, 3H to 4He) and fission of heavy elements. - Fusion reaction schematic: 2H + 3H -> 4He (3.5 MeV) + n (14.1 MeV) - Cross section (m^2) vs Center-of-Mass Energy (keV) for fusion reactions: D-T, D-3He, Total D-D, p-11B, 3He-3He. © 2023 Tokamak Energy Engineering Fusion Devices Lawson Triple Product Comparison: - n_i0 * T_i0 * tau_E (m^-3 keV s) vs T_i0, (T_i)_n (keV) - n_i0 * T_i0 * tau_E (m^-3 keV s) vs Year (1960 - 2040) Devices plotted include Tokamak, Laser ICF, Stellarator, MagLIF, Spherical Tokamak, Z Pinch, FRC, Spheromak, Mirror, RFP, Pinch (Alcator C, PLT, TFTR, JET, JT-60U, DIII-D, MAST, NSTX, ST40, SPARC, ITER, NIF). Sources: S. Wurzel, S. Hsu, Phys. Plasmas, 29, 062103 (2022) © 2023 Tokamak Energy Global Energy Challenges – the need for nuclear By 2050, we need to deliver safe, reliable power to an extra 3.4 billion new energy customers from emerging economies, while reducing our total CO2 emissions to zero. Nuclear Fusion: - Zero CO2 generation - High energy density fuel - Abundant fuel source - No long-lived nuclear waste - Safe, controlled reaction - Energy security - Deployable and scalable Graph: Global energy consumption (1900-2022) in TWh by source (Traditional biomass, Coal, Oil, Natural gas, Nuclear, Hydropower, Wind, Solar, Modern biofuels, Other renewables). Sources: Energy Institute Statistical Review of World Energy (2023); Vaclav Smil (2017) © 2023 Tokamak Energy Fusion in the Private Sector - Total funding to date: $6,210,890,875 ($6.2bn) [Private: $5,939,271,000 ($5.9bn), Public: $271,620,000] - Companies that have raised > $200M in funding: Commonwealth Fusion Systems ($2bn+), TAE Technologies, ENN, General Fusion, Helion Energy, Tokamak Energy, Zap Energy, SHINE Technologies. - Fusion companies categorized by approach: Tokamak, Stellarator, Laser fusion, FRC, Other MCF, Other ICF, Other. - Primary HQ distribution map: USA (25), UK (3), Germany (3), Japan (3), Canada (1), France (1), Italy (1), Sweden (1), Israel (1), China (2), Australia (1), New Zealand (1). Sources: Fusion Industry Association, Annual Report (2023) © 2023 Tokamak Energy Tokamak Energy Spherical Tokamak + HTS Magnets = Efficient Fusion - Founded in 2009 - Based in Oxfordshire, UK - 300+ employees (70 PhDs, 75 MScs) - Raised > $250M - Pioneering HTS magnet technology for fusion and other applications - Over 75 families of patents - Only private company with operating spherical tokamak Partners and collaborators: University of Oxford, Sumitomo Corporation, University of York, Sandia National Laboratories, Paul Scherrer Institut, University of Tokyo, University of Illinois Urbana-Champaign, National High Magnetic Field Laboratory, PPPL, UNSW Sydney, CERN, Victoria University of Wellington Te Herenga Waka, Oak Ridge National Laboratory, Imperial College London, University of Cambridge, Little Beast Engineering, UK Atomic Energy Authority. © 2023 Tokamak Energy The Leading Global Fusion Company Key Milestones: - 2015: First HTS tokamak sustained pulse for >24 hours (ST25 HTS). - 2017: Designed, built and operate the world’s highest-magnetic field spherical tokamak (ST40). - 2020: World-record 24 Tesla field at 20 K with patented HTS magnet technology. - 2022: First private fusion company to achieve 100M °C plasma ion temperature in a tokamak. - 2022: Highest plasma ‘triple product’ of any private fusion company (6±2x10^18 m^-3 keV s). Sources: S. A. M. McNamara et al, Nucl. Fusion, 63, 054002 (2023) © 2023 Tokamak Energy Our Operating Spherical Tokamak - ST40 (R = 0.4 m, B = 2.1 T) - Uses 250 kA pulse in copper magnets - Enable rapid validation of plasma physics and control, with simple, cheap magnets - World-record holding 100 M °C temperatures - Very compact, low aspect tokamak - Total cost ~ $50 M - Build time (2016-2017) - Scaling law: P_fus ~ B_T^4 Diagrams: Aspect ratio comparison (Standard tokamak vs Spherical tokamak); Electron confinement with and without magnetic field. Sources: A. E. Costley et al, Nucl. Fusion, 55, 033001 (2015) © 2023 Tokamak Energy High-Temperature Superconducting ReBCO Tape - Structure: Substrate (Hastelloy), Buffer layer stack, ReBCO layer (1-2 µm), Ag cap layer, Cu stabilisation (optional); dimensions ~12 mm width, 0.1 mm thickness. - Crystal structure: YBaCuO (ReBCO). - Critical current I_c vs Field angle θ and Magnetic Field (T) across various temperatures (4.2 K to 77.5 K). - Cable designs: CORC® cable (Advanced Conductor Technologies LLC), VIPER cable (Commonwealth Fusion Systems), Roebel cable (KIT and General Cable, NZ). Sources: J. van Nugteren, High-Temperature Superconducting Accelerator Magnets, PhD Thesis (2015) © 2023 Tokamak Energy Non-Insulated HTS Magnets Key Demonstrations: • Solder Consolidated HTS Coils ✓ Proven robust and defect tolerant. ✓ Enable low loss current sharing. ✓ Reliable re-mountable joints. ✓ Thermally stable, conduction cooled. • HTS Conductor Performance ✓ Commercial tape evaluated in real coils up to B > 20 T @ 20 K. • HTS Magnet Quench Testing ✓ No spontaneous quenching. ✓ Bespoke modelling tools validated. Configurations & Achievements: - World-record 24 Tesla field at 20 K - Solder Consolidated NI Coil - Mixed supplier coil stack (>16.5 T re-mounted QA coils) - Compact, robust, modules with “ETI” Plates - Intentionally Damaged Coils: Operate stably despite gross damage © 2023 Tokamak Energy Partially-Insulated HTS Magnets Key Demonstrations: • PI Coil Design and Fabrication ✓ Designed by modelling to be quench-safe. ✓ Tuneable PI implemented. ✓ Modular, conduction-cooled design maintained. • Proven benefits of HTS + PI ✓ No spontaneous quenching. ✓ Stable against >40 J heat pulses. ✓ No degradation from forced 200 kJ quenches. ✓ Peak quench voltage limited to <0.1 V. ✓ Quench models proven. Features: - Multi-Tape Winding incorporating partial insulation - Partially Insulated Coils testing - Forced Quench Simulation Movie (Temperature, Current Density, % Ic - Real behaviour reproduced) - Forced Quench Measurement Data Subset (Quench propagation captured: Voltages and Magnetic Fields vs Time) © 2023 Tokamak Energy HTS Magnets Robust to Compression Cryogenic coil compression system (CCCS): - Allow us to apply up to 500 MPa compressive force onto cold, energised HTS magnets - Instrumented with voltage taps, temperature and Hall sensors, and FBGs to monitor strain - Monitor response and degradation of HTS tape under compressive and tensile stress in real time and representative operational conditions ✓ System designed, built, and operated in-house Diagram showing G10 compression column, plunger, coil outer support disk, coil, and G10 support. © 2023 Tokamak Energy HTS Magnets Robust to Irradiation Gamma: - Irradiate HTS magnets using 60Co γ sources at fusion operating conditions (20 K while energised near I_c) up to 10 MGy doses - Monitor any degradation in I_c in real-time via voltage taps, and instrumented with Hall and temperature sensors - Outcomes guide understanding of shielding requirements for future tokamak designs (field strength on plasma vs lifetime in service) ✓ System designed and built in-house ✓ Experiments ongoing in USA Basic Shielding Schematic: Plasma -> Shield -> Magnet (residual neutrons and secondary gammas irradiate the HTS magnet) © 2023 Tokamak Energy HTS Magnets for Fusion Demo4: World-first complete set of HTS magnets in a fusion configuration. 44 HTS magnets operating at 18 Tesla at 20 K (1.5 m diameter) Key Objectives: - Demonstrate operation of balanced toroidal field (28 TF coils in 14 limbs) - Demonstrate representative compressive stress at centre column - Demonstrate partial insulation for TF coils and quench protection at 16.5 MJ energisation - Explore PF field shine effects on TF coils - Explore transient control and AC losses - Simulate plasma heating and stresses at centre column © 2023 Tokamak Energy Demo4 – HTS Magnets Poloidal Field (PF) Coils: - 2 PF magnets each containing a stack of 8 PF coils - Fully-insulated HTS magnets operating at 4 kA at 20 K - Required fast ramp rate to modulate plasma shape in real tokamak - Incorporates additional Cu for AC loss dissipation absorption and quench protection. Toroidal Field (TF) Coils: - 14 TF limbs each containing 2 TF coils (28 TF coils in total) - Partially-insulated HTS magnets operated at 8 kA at 20 K - Required high-field steady state to confine plasma © 2023 Tokamak Energy Demo4 – Cooling Power and Instrumentation - System is conduction cooled by 10 closed-cycle cryocoolers driven by cryofans - Pressurised 4He gas circulates in parallel through magnets via heat exchangers - 500+ instrumentation sensors (temperature, magnetic field, voltage taps, FBG strain gauges, and heaters) Images: Plant Room, OVC Top Plate, Cutaway schematic of cryostat and magnet assembly. © 2023 Tokamak Energy Demo4 Progress – Poloidal Field Coils ✓ Preliminary testing at 77 K indicate HTS tape is not degraded by manufacture ✓ All 16 PF coils manufactured and tested Images & Data: PF magnet concept design, Manufactured PF magnet, Test results at 77 K (Backing voltage, Magnetic Field, Current vs Date/time). © 2023 Tokamak Energy Demo4 TF Coils – All the coils are wound and impregnated - 28 TF coils (1 pair of coils per limb, 14 limbs) - TF coils include wound-in partial insulation - An additional 4 TF coils (not shown) for spare limbs - 16 PF coil pancakes - Assembled into 2 PF coil stacks. Images: Coil winding / impregnation workstation, Team photo surrounded by 14 pairs of TF coils and 2 PF coil stacks. © 2023 Tokamak Energy Demo4 TF Limb Assembly Exploded view components: 1. SS clam shell 2. Resin infill 3. Cooling loop 4. ETI plate 5. Insulation 6. HTS coil 7. Insulation © 2023 Tokamak Energy Demo4 TF Limb Instrumentation Images: CAD model of limb structure, engineers assembling instrumentation on TF limb, disassembled view showing internal cooling and sensor routing. © 2023 Tokamak Energy Demo4 TF coils – Limb #1 assembled and tested at 77 K! Testing in liquid nitrogen bath Coils instrumented with voltage taps and Hall probes. Like Demo2, the Demo4 TF coils have voltage taps trough the windings. Tests include: 1. Slow ramp to I_c to determine the integrity of the coils (2 coils per limb including coil-to-coil joint). 2. Step and hold ramp to determine radial resistance and I_c (Determine by S-E voltage). 3. Multiple thermal and energisation cycles in progress to check for any performance degradation. Graph: demo4TFLimb1 VTAP-COILB-SE-FILTER 77 K Icn fit (V vs I, R_linear = 0.13 µΩ, I_c = 876.90 A, n = 13.22). © 2023 Tokamak Energy Demo4 - Looking Ahead Summary: - All 16 PF coils manufactured and tested - All 28 TF coils manufactured and tested, and now being assembled and tested as 14 TF limbs - Interlimb jointing and magnet assembly - Instrumentation integration and control systems - Final integration of cold mass, top plate, radiation shielding, and OVC with power and cooling - Commissioning and test campaigns (Q2 2024) Diagram: Full cutaway of Demo4 assembly. © 2023 Tokamak Energy Tokamak Energy Development Timeline - 2014: ST25 (ST Concept, Plasma heating and current drive development) [Completed] - 2015: ST25-HTS (First HTS TF coils, H plasma held for 29 hours) [Completed] - 2016 – on-going: ST40 (Highest field ST worldwide at 2.1 T on-axis, 100M °C D-H plasma temperature, On-going development programme) [Completed] - 2018: QA NI coils (Tape QA, Defect tolerant coils, Robust jointing & ETI plates, Modular magnet build) [Completed] - 2019: Demo3 (First, conduction-cooled all REBCO magnet to exceed 22T field on tape at 20K) [Completed] - 2020: Demo2 (PI development, Validation of bespoke transient modelling tools Racoon, Quench resistant, Magnet dynamics very closely correlated to model predictions) [Completed] - 2020 - 2022: AMR WP4 (Demonstrated cryogenic PSU technology, Developed EFC coil design code, Coil scale-up study, Coil Cryogenic Compression System designed and built, Quench modelling code developed and validated) [Completed] - 2019 - 2023: Demo4 (Demonstrate PI for TF coils, Operation of balanced set of TF coils, Explore transient control and losses in PF coils, Explore PF field shine on TF coils, Quench protection and energy dumping trials) - 2021-2023: Gamma (Irradiate small test coils wound from selected REBCO tapes, Co60 irradiation up to 10MGy dose, Coils are cooled to 20K and energised to Ic, Ic degradation measured in real time) [Completed] - 2022 - 2026: BB01 (Developing prototype coils for ST-X(80), Developing coil manufacturing processes and tooling, Developing magnet assembly processes and tooling) - 2026: ST-X(80) [Build completion] (Demonstrate long pulse operation, Control and protection of mid-scale HTS magnets) - Early 2030s: ST-E1 (Up to 200MW of net electrical power, Prototype energy generating ST, Full scale HTS magnets, Demonstrate plasma control and fault condition recovery at scale) © 2023 Tokamak Energy Magnetic Confinement Size Comparison Size comparison illustration: - Demo4 - ST-X(80) - ST-E1 (ST380) - ITER © 2023 Tokamak Energy We are hiring! CONTACT US: Alex Davies [email protected] [email protected] [email protected] www.tokamakenergy.com Tokamak Energy Ltd 173 Brook Drive Milton Park Oxfordshire OX14 4SD United Kingdom Thank you © 2023 Tokamak Energy