WAMHTS-5 Budapest, Hungary Aril 11-12, 2019

A PATHWAY TO FUSION ENERGY BASED ON HIGH-FELD REBCO SUPERCONDUCTING MAGNETS

Joseph V. Minervini Massachusetts Institute of Technology Science and Fusion Center Cambridge, MA USA

WAMHTS-5, Budapest, April 11-12, 2019 1 Fusion energy is the power source of the universe

Fusion is the dominant source of energy Terrestrial fusion combines light in the universe isotopes of hydrogen (tritium and deuterium) into helium, releasing energy in the process.

Achieving fusion energy generation on Earth has been a goal since humanity discovered that is powered the stars. WAMHTS-5, Budapest, April 11-12, 2019 2 The advantages of fusion energy are compelling …

Low carbon Inexhaustible fuel Deployable Highly complementary

Load-following energy Intrinsically safe Zero fissile materials Civilization-scale energy

“Unlimited energy for everyone forever” WAMHTS-5, Budapest, April 11-12, 2019 3 Time is running out to address climate change……

WAMHTS-5, Budapest, April 11-12, 2019 4 Scaling up fusion in time is possible… if it can be demonstrated

• Historically, energy technologies experience exponential early growth (~1% total energy) and then slow linear growth

• Precedents of new energy sources in 20th century provide insight into potential for fusion energy to contribute

• Fusion scale-up required is compatible with solar mitigating worst effects of climate change

and contributing to mid-century CO2 goals…

… but first demonstration must happen by the mid-2030’s at the latest!

WAMHTS-5, Budapest, April 11-12, 2019 5 … but achieving the conditions for fusion energy is challenging

What is needed to “burn” nuclei? The same things needed to burn a campfire.

Fuel density Fuel temperature Energy confinement Get enough of the wood together Get the wood hot enough Keep the energy in to keep reactions to start reactions going without an external heat source

The requirements for fusion are similar: except at 100,000,000 degrees and with 1/10,000,000 of the fuel

WAMHTS-5, Budapest, April 11-12, 2019 6 … but achieving the conditions for fusion energy is challenging

Fuel density Fuel temperature Energy confinement Plasma ~10,000,000x less dense Plasma ~10,000,000x hotter ~millions of times better than a than wood than wood campfire

It has units of a pressure x time This is called the “triple product” Fusion requires >8 atmosphere seconds It is the figure of merit for fusion x x n T τE (Sometimes expressed in units m-3 keV s) The three things required for fusion energy … known since 1955! But a plasma has never been created that makes more power than it takes to keep it hot. The principal challenge has been reaching these conditions in an actual machine.

WAMHTS-5, Budapest, April 11-12, 2019 7 Enormous progress has been made; net fusion energy is within reach

• Fusion made extreme progress for 30 years • Then progress stalled in the late 1990’s • The world decided to go to large devices to continue to increase performance

This was faster than Moore’s law

This is a big JET Now operating step Created 17MW of ITER fusion energy in the Continually delayed… Now late 1990s projected to do DT in 2037

WAMHTS-5, Budapest, April 11-12, 2019 8 But the traditional path to fusion energy is not attractive

Approximately to scale

JET JT-60SA ITER FNSF (US) DEMO (EU)

2015 2020 2025 2030 2035 2040 2045 2050

This graphic embodies the typical tokamak critique: We completely agree and recognize that this is: 1. are too big 1. Caused by decisions on what tokamaks to build 2. Tokamaks are too complex 2. Caused by organizational complexity at this scale 3. Tokamaks are too slow 3. Not a reason to abandon the tokamak

WAMHTS-5, Budapest, April 11-12, 2019 9 How do we radically improve the tokamak’s prospects?

How well a plasma is insulated via the gyro-radius: How stable the plasma is from MHD: Plasma temperature, set by T fusion nuclear cross-section Make many of these r ~ fit inside the device ion B , set by device magnets Plasma pressure

Magnetic pressure ~ B2

How reactive the plasma is: Volumetric fusion rate ∝ (plasma pressure)2 ∝B4 2 2 β H Pfusion β  ENERGY GAIN: nT τ  N R1.3B3 POWER DENSITY:  N RB4 (science feasibility) E q2 (economics) S q2 * wall *

WAMHTS-5, Budapest, April 11-12, 2019 10 Magnetic field strength sets size, cost, and time to build

Global scale

National lab scale Q Fusion Gain

University/company scale

WAMHTS-5, Budapest, April 11-12, 2019 11 Magnetic field strength sets size, cost, and time to build

Space accessible for net energy fusion

Global scale Not accessible using existing magnet technology

National lab scale

Fusion Gain University/company scale

WAMHTS-5, Budapest, April 11-12, 2019 12 The combination of plasma and ITER’s choice of magnet technology fundamentally constrains it’s size … therefore, cost, timeline, complexity…

Reactors

Global scale ITER

Inaccessible magnetic fields with traditional superconductors National lab scale Q Fusion Gain

University/company scale

WAMHTS-5, Budapest, April 11-12, 2019 13 The successful construction of HTS magnets would opens the path to achieving net fusion energy gain devices at significantly smaller size

Global scale ITER

Net fusion National lab scale energy devices Q Fusion Gain

University/company scale

WAMHTS-5, Budapest, April 11-12, 2019 14 Higher field HTS magnets would enable ARC (a conceptual design) to produce the same as ITER in a device roughly ~10 X smaller in volume

ITER ARC R [m] 6.2 3.2 Magnet LTS HTS ITER B [T] 5.3 9.2 ITER

Pfusion [MW] 500 500

Pelectric [MW] 0 200 ARC

ITER ARC Q Fusion Gain

WAMHTS-5, Budapest, April 11-12, 2019 15 Higher field HTS magnets will enable a tokamak to achieve net energy fusion gain (Q > 2) in a university-scale tokamak.

SPARC (Smallest Possible ARC) will make the logical next step and be ITER about twice the size of Alcator C-Mod

ARC

SPARC Fusion Gain

C-Mod

Alcator C-Mod (MIT PSFC)

WAMHTS-5, Budapest, April 11-12, 2019 16 MIT and Commonwealth Fusion Systems (CFS) announced a new approach to fusion energy based on REBCO superconducting magnets

• CFS is a private company spun out of MIT; it has announced $50M in private financing and raising more • MIT and CFS will collaborate closely to demonstrate large-bore, high-field REBCO magnets in ~3 years • If successful, we will then build SPARC, a ~100MW net energy device, in following ~4 years

WAMHTS-5, Budapest, April 11-12, 2019 17 SPARC is a net-energy tokamak using REBCO magnets

SPARC technical mission: • Demonstrate break-even fusion energy production • Demonstrate fusion-relevant REBCO magnets at scale • Demonstrate high-field fusion plasma scenarios for ARC

SPARC strategic mission: • Rapidly bootstrap to fusion energy as fast as possible • Reinvigorate fusion energy efforts and provide urgency • Enable parallel efforts in complementary fusion R&D

• Compact: R0 < 2m • High-field: B ~12T, B ~21T SPARC is small enough to be built: 0 max • By the MIT, CFS, and partnering teams in <5 years • Fusion power: 100 MW • Within precedent of several other tokamaks • Net-energy: Q>2 • With existing or near-term technology • Pulsed: 10+ seconds • Leveraging existing MIT infrastructure for speed

WAMHTS-5, Budapest, April 11-12, 2019 18 The new, fastest track to fusion energy

DEMO Old Way (World) ITER First (World) power JET (UK) Net- plant Largest energy operating experimen ~ to scale tokamak t

2015 2020 2025 2030 2035 2040 2045 2050 2055 2060

SPAR C-MOD C ARC (MIT) (MIT/ (CFS) Plasma CFS) First physics Net- power New Way fusion- plant WAMHTS-5, Budapest, April 11-12, 2019 energy 19 Proposed Development Path

Retiring the key technical risks early and and at low cost WAMHTS-5, Budapest, April 11-12, 2019 20 The TF magnet in SPARC is the same scale as DIII-D and ASDEX-U We know how to build TF magnets at this scale

WAMHTS-5, Budapest, April 11-12, 2019 21 Purchasing schedule based on 3-year magnet R&D plan followed by construction of SPARC TF system

• Goals for 3-year R&D plan (Phase I) • Fully qualified HTS cable • Fully built and tested TF coil • Continuous engagement with HTS manufacturers to scale up production for Phase II

Quantity of Tape Delivery Date Use of tape 250 kA*m 2018 Build small pieces (~5m) of cable for qualification 13,000 kA*m 2019 Build and test full-length cable 50,000 kA*m 2020 Build full TF Model Ccoil

• Goals for SPARC TF construction (Phase II) **Note that kA*m specs are for • Construction of 18 TF coils based on design from Phase I 700 A/mm2 @ 20T, 20K tape specified previously**

Quantity of Tape Delivery Date Use of tape 850,000 kA*m Phased delivery from Build SPARC TF system 2021 to 2024

WAMHTS-5, Budapest, April 11-12, 2019 22 TSTC Conductor : Scale-up industrial fabrication

H-Channel TSTC CICC mockup of Multiple-stage conductor Conductor TSTC conductor

One channel cable

3x3 cable Hexa-cable By Supercon CICC

40 tape dual-stack cable 40 YBCO tapes

3 channel cable

12 sub-cable conductor

3 x 6 CICC 20 YBCO tapes in each helical groove

WAMHTS-5, Budapest, April 11-12, 2019 23 TSTC is scalable to ~100 kA

WAMHTS-5, Budapest, April 11-12, 2019 24 Several countries are developing HTS conductors for Fusion

Germany USA Italy USA

CORC (ACT) Roebel (KIT) TSTC (MIT) SCHCC (ENEA)

CERN (CICC) Switzerland RSCCCT (CRPP) Japan STARS (NIFS)

WAMHTS-5, Budapest, April 11-12, 2019 25 National Institute for Fusion Science (NIFS)

NIFS New Superconductor Test Facility Max. Field: 13 T Nb SnNbTi Bore: 700 mm Diameter 3 Sample Current: 50 kA Temperature: 4-50 K

Spacer Winding Insulato r Support

> φ685 > φ700 < φ1350

Bmax13 T S. Imagawa

WAMHTS-5, Budapest, April 11-12, 2019 N. Yanagi, et al., 3rd HTS4Fusion, ENEA/Tratos, September, 2015. 26 Single-Turn TSTC Conductor Coil to be Tested at NIFS TSTC Sample Hendecagon shape 650 mm diameter single turn coil fabricated by Stacked-Tape Twist-Wind method with 6 mm width 680 mm Dia. Half twist REBCO Tapes Objectives • 13 T, 16 kA, 200 kN/m load conductor test • Critical current test at 4.2 K – 50 K at up to 13 T 180 mm and 50 kA • Cyclic test of critical current Coolant Piping • Current charge ramp-rate test Conductor cross-section

16 mm WAMHTS-5, Budapest, April 11-12, 2019 27 Copper Sheathing in G10 Sample Holder

Copper U-shape sheath

Cable in U-shape sheath

WAMHTS-5, Budapest, April 11-12, 2019 28 MIT Sample on NIFS Probe

Termination

NIFS Current lead extension

Termination sideview WAMHTS-5, Budapest, April 11-12, 2019 29 Probe in Dewar

WAMHTS-5, Budapest, April 11-12, 2019 30 Cryogen Property Assessment

• Evaluating several cryogenic fluids for cooling magnets with supercritical fluid conditions

!" = 0.20 MPa Helium (3.5 MPa) Hydrogen (1.5 MPa) Neon (3.0 MPa) Optimum Operating Temperatures [K] 5-15 15-35 27-46 Peak Heat Transfer Coefficient [W/(m2-K)] 7,370 32,330 17,450 Mean Heat Transfer Coefficient Over Optimum Temperature 6,510 12,410 8,110 Range [W/(m2-K)] Normalized Cost (to He) 1.0 0.2 58.0 Gas Classification Inert Flammable Inert

WAMHTS-5, Budapest, April 11-12, 2019 31 Development of a High Pressure, Forced Flow Cryogenic Cooling Loop

• Developing a high pressure cryogenic fluid flow loop to do fluid flow experiments.

• Measure transient and steady state heat transfer coefficients under typical tokamak operating conditions for P, T, "̇ .

• System being designed now for supercritical helium.

• Potential future experiments with neon and hydrogen.

WAMHTS-5, Budapest, April 11-12, 2019 32 Summary

• Commercial production of HTS REBCO tape is sufficiently advanced to start using it for building small, high field coils now. Ø Using even today’s performance, advanced fusion reactors can be designed now using this material. • REBCO changes the whole reactor design paradigm. Ø MIT and CFS are taking advantage of the high field and high temperature performance and applying it to an advanced, high field, compact tokamak to demonstrate a burning plasma with net fusion power on a short time scale. • R&D and magnet and tokamak design for SPARC has begun.

WAMHTS-5, Budapest, April 11-12, 2019 33 SPARC

WAMHTS-5, Budapest, April 11-12, 2019 34