A Faster Way to Fusion Our Mission

“To deliver to mankind a cheap, safe, secure and practically limitless source of clean energy – fusion power”

“a sustainable oil well” The Challenge

• Traditional view for fusion power & tokamaks is that bigger is better (ITER) • Huge investment and timescales to progress • Spherical Tokamaks are much more efficient than traditional ‘doughnut’ shape tokamaks. • This allows for smaller more compact designs • But: there are space constraints at the centre of spherical tokamaks • conventional (copper / low temperature superconducting) magnets cannot create conditions required to produce fusion energy The Tokamak Energy Solution

Spherical Tokamaks High Temperature Squashed shape Superconductors Highly efficient High current at high field

Fusion Power smaller, cheaper, faster Our approach

• Rapid development of:

• Working prototype devices • Know-how & Patents • A path to energy break even supported by experimental data • Supportive sources of capital • A plan to rapidly deliver a sustainable source of energy to replace fossil fuels

CONFIDENTIAL Endorsements

• Selected by the International Energy Agency “as one of three most promising innovative fusion concepts” 2017 • Recognised as a Technology Pioneer 2015 by the Davos World Economic Forum • Our peer-reviewed article “On the power and size of tokamak fusion pilot plants and reactors” is the most downloaded paper ever from the Nuclear Fusion journal • Collaborations with MIT whose ARC Reactor combines HTS magnets and tokamak reactors MIT’s “ARC” Fusion • Jointly authored paper with Princeton Plasma Physics Laboratory: Power Plant concept “Fusion nuclear science facilities and pilot plants based on the spherical tokamak” • Director of Princeton Plasma Physics Laboratory gave evidence to Congress in April 2016 and selected spherical tokamaks with HTS magnets as the most promising route to fusion power PPPL / Tokamak Energy ST concept The Tokamak

• Magnetic Confinement Fusion uses strong magnetic fields to hold an extremely hot fuel mixture known as a plasma • The Tokamak is by far the most established device for controlled fusion • Over 200 devices have been operated • More than £30Billion invested to develop a robust scientific understanding • Tokamaks have already produced 16MW of fusion power and have been close to a major breakthrough – energy breakeven • where more power is produced in fusion reactions than is required to sustain the plasma • Only spherical tokamaks can be self-sustaining for plasma current and plasma heating • The compressed plasma geometry of the spherical tokamak allows high performance in a compact device Our People

• A world class team of over 40 full time scientists and engineers with expertise in the field of fusion and high temperature superconducting magnets

• Dr David Kingham, Chief Executive Officer • PhD Theoretical Physics • Ex-MD Oxford Innovation • VG Instruments

• Dr Mikhail Gryaznevich, Chief Scientist • PhD Fusion Physics • World-leading expert in small tokamaks • Ex - Culham Centre for Fusion Energy

• Paul Noonan, R&D Director • Ex Technical Architect – Agilent Technologies • Ex Chief Engineer – Oxford Instruments • 30 years’ experience in superconducting and cryogenic technology Scientific Advisory Board

• Lord Hunt of Chesterton, FRS • Leader in Applied Mathematics of turbulence; House of Lords Science and Technology committee

• Professor George Smith, FRS • Leader in Materials Science of Nuclear Reactors

• Professor Jack Connor, FRS • Leader in theoretical plasma physics

• Professor Colin Windsor, FRS • Leader in neutronics

• Professor Bill Lee, FREng • Director of Centre for Nuclear Engineering, Imperial College Leading Consultants & Collaborators

Consultants Collaborators • Dr Melanie Windridge

• Dr Paul Thomas

• Dr David Hawksworth

• Professor Valery Chuyanov

• Dr Alan Costley

• Professor Jan Hugill

• Dr Guy Morgan

• Dr Martin Wilson

• Dr Elwyn Baynham Competitive Landscape

In the last decade privately low physics funded companies have risk emerged
Prompted by a lack of progress in mainstream publicly funded fusion and the recognition that fusion needs to happen sooner $500M – 1Bn of investment Slow, big fast, small,
Capital intensive Low capital
Competition pursuing high risk, low technology readiness, designs that require scientific validation
The Tokamak Energy approach is alone in having established theoretical and high physics experimental foundation risk

CONFIDENTIAL ‘Compact Fusion’ concepts

Lockheed Martin ‘skunkworks’ General Fusion

Helion

All deviate significantly from the well characterized tokamak route

Tri-alpha All have very low nT τ at present HIT SI3 (Jarboe, UW) Fusion

2H 4He + 3.5MeV

3H n + 14.1MeV Lawson criterion

Balance cooling against reaction rate for self sustaining equilibrium e.g. 5x10 21 m-3 s keV at 150x10 6 K Magnetic confinement

Larmor radius

= ⏊

• mm for ions • 10s of µm for electrons

Ideal magnetic pressure (i.e. no instabilities)

2 = 20

5T ⇒ ~100 bar at 100% efficiency (β) Early days

The 1946 Fusion Reactor patent of Thompson & ZETA 1957/8 Blackman [1] (Imperial College 1946) was indeed Compact Fusion

- But all sorts of instabilities appeared..

A conducting vessel helped, but … Early announcement of success proved wrong τ ~ 1ms → T~ 0.17keV

A small ‘pinch’ device:

R / a = 1.30m / 0.3m, Ip = 0.5MA classical confinement was assumed : but all sorts of instabilities appeared → τ = 65s →T = 500keV Hence DD----DD fusion would be achievable 20 msec Add a strong toroidal field

The tokamak is born The tokamak

In 1969 the T-3 tokamak was claimed to be much hotter than the pinches studied in the Western world. A team of Culham scientists spent a year at the Kurchatov, proving this was indeed the case, using a Thomson Scattering diagnostic.

The rest of the World began building tokamaks! Developments and improvements of the Tokamak have controlled all the major plasma instabilities. But energy confinement still poor; scaling approximately as 2 1.5 τ ~ R x B T To obtain a Gigawatt size power plant, leads to the ITER project 3 R = 6.2m, Vol ~ 850m , B T (at R) = 5.3T Tokamak progress Tokamak progress

Triple product, n x T x τ, vs time

Progress has been impressive, but at the expense of building ever larger machines Why a toroidal current?

6

4

⏊ Gradient + = => drift 2 Toroidal flux density Toroidal rrt id tit 0 Why spherical? Flux density

At high field ions are more tightly bound to field lines => 8 1 α = β [1] 6

4 ST40 at R = 0.4m is modest compared to JET maj JET with Rmaj = 2.96m

2 … but has a region of higher flux density close S to the centre column ST40

How is this of use? densityFlux [T] 0 Normalised major radius

1 On the fusion triple product and fusion power gain of tokamak pilot plants and reactors. Nucl. Fusion 56 (2016). Costley et al Efficiency

Ideal magnetic pressure (i.e. no instabilities)

= RECORD βββ ON START (achieved through NB Heating) but not in practice (i.e. there are 50 1996 instabilities), so we define: 6 1997 = β N 1998 β = 40

And this is high in spherical 30 .5 tokamaks DIII-D, #80108 3 β , % = it) T β N lim

on 20 oy conventional Tr • High magnetic flux density and ( tokamak sheer gradients supress the propagation if instabilities 10 • ‘Good curvature’ dominates = β the ions' trajectory 0 o High ‘safety factor’ 0 2 4 6 8 10

o High natural elongation normalised plasma current, I p/aB T Current drive

Magnetic mirror Current drive

High field gradient ⇒ high bootstrap current ⇒ steady state with minimum external drive ST summary

• High field in compact device = β • High β

• Good scaling compensates for low volume

⇒ Power production in smaller machine

• High bootstrap current

⇒ Reduced capital cost and recycled power for current drive

Development cycle time and cost/cycle reduced

⇒ Faster route to market So what’s the catch?

So far we have:

22.4MA • high β • enhanced stability

∗ but B has been low (~0.5T) due to the slender copper centre column = T 2

3.2T at 1.4m

= β Low temperature superconductors?

Space is required for a neutron radiation shield … shield plasma centre column

18T For the previous example field on a 0.5m diameter centre column is ~18T

BT α 1/R

so there is only enough room for shielding to reduce the neutron heat load to several 10’s kW

Challenging at LTS temperatures of 2 ~ 5K = − … and it gets worse

1000000 Can get ~2T improvement by further cooling, but the practical 100000 limit is ~20T

BT α 1/R 10000 NbTi With shielding low B T in plasma ] ] 4.2K at 2 Internal tin [A/mm 1000 c J

Nb 3Sn 100

Bronze route 10 0 5 10 15 20 25 30 35 40 45 Tesla

LTS performance in field HTS

Even with shielding we can have

high B T in plasma Business case

Spherical tokamak + HTS

⇒ the possibility of small modular fusion reactors of ~100MWe

Rapid, affordable, development

Then the size of the deployed reactor becomes a choice …. HTS key technologies

REBCO conductors Quench protection ~100 kA cable design • I surface • Current sharing C • AC losses • Boundary resistance • Detection • % copper content • Tape construction • Dump • Cooling • Quality / variability

Joints Mechanical design • Size, shape, position • PF / TF coil locations • Heatload - many or • Forces few ? • Demountable coils ?

I degradation Cryogenics C Power supplies • Neutron damage • Neutron heating Current leads • Thermal cycling • • Joint heating Dump circuits • Mechanical • • Suspension Cold rectification ? • Fatigue • • Vacuum vessel TRLs

Targets as of 2017 2018 2019 Fusion D-T Feb-17 target target target demo reactor Cable design 3 5 6 6 8 9 Joint design 2 4 5 6 8 9 REBCO tape characterization 3 5 6 6 8 9 Core model 2 4 5 6 8 9 TF EM model 3 5 6 7 8 9 PF EM model 1 5 6 7 8 9 Integrated magnet EM model 3 5 5 6 8 9 Magnet mechanical design 1 3 4 6 8 9 Quench Detection system 2 5 6 7 8 9 Quench Protection system 2 5 6 7 8 9 PSU 2 4 5 6 8 9 Current leads 2 3 5 6 8 9 Cryostat 2 3 5 6 8 9 Cryoplant 2 3 5 6 8 9 IIICCC (BBB,TTT,θ) between manufacturers

Ag layer ReBCO Cu shell θ

Hastelloy substrate

Angle θ

Image courtesy of Jeroen van Nugteren, CERN thesis Nov 2016 Magnet conductor requirements

• For any stored energy, E = LI 2/2 we can choose
low I & high L or high I & low L • Peak voltage considerations during quench drive us to I ~ 20-100 kA (depending on choice of quench protection strategy)

• Critical current capability of HTS tapes: IC(B,T,θ) • Single tapes can carry ~500-3000 A/cm-width, depending on local B,T,θ • We need ~30 to 200 1 cm wide tapes in each turn needed to carry 100 kA

Image courtesy of Jeroen van Nugteren, CERN thesis Nov 2016 Quench – risk #1 !

Stored energy: ST25 ~4000 J < ST60 ~300 MJ < ST140 ~ 1800 MJ…

RCC = 20 cm, t detect = 3 s, 54% copper

RCC = 20 cm, t detect = 1 s , 54% copper

RCC = 17 cm , t detect = 1 s, 54% copper

A hot spot thermal runaway could destroy the magnet …… Quench modelling at CERN

Image courtesy of Jeroen van Nugteren, CERN thesis Nov 2016

System of Equations Energy management

We have the option of using our return limbs as the energy dump

E3SPreSSO, A Quench Protection System for High Field Superconducting Magnets J. van Nugteren, J. Murtomäki, G. Kirby, P. Hagen, G. De Rijk, H. ten Kate and L. Rossi ST TF coil magnetic fields

3-8 T radial ~16-22 T toroidal Neutrons and HTS

Studies by Eisterer et al, HTS4 Fusion conductor workshop, PSI, Jan 2014 show that at low temperatures <60K, neutron bombardment improves tape performance at least up to 2.3 x 10 22 n/m 2

Caution

• Recent good performance has been obtained with extensive artificial pinning – how do effects interact? • Performance is very sensitive to operating conditions (B and T) • Is the neutron spectrum relevant? • Is the effect dependent on temperature (samples irradiated at ~room temperature Testing?

1.E+22

) 1.E+21 Neutrons: WC -1 At surface of centre column

MeV 1.E+20

-2 Gamma:WC m -1 1.E+19 -2.3

(s Fast E

/dE 1.E+18 Φ d Epithermal E -0.5 1.E+17 ` `

1.E+16

1.E+15 Differential flux Differential

1.E+14 "Fast" energies

1.E+13 1.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 Energy (MeV) 1.0E+21 1.0E+20 1.0E+19 Maxwellian 25 meV 1.0E+18 Triga flux

) 1.0E+17

-1 1/E epithermal flux 1.0E+16 Mev

-1 1.0E+15 s

-2 1.0E+14 1.0E+13

/dE (cm /dE 1.0E+12 φ d 1.0E+11

1.0E+10 11 φ(E)=10 /E" 1.0E+09 1.0E+08 1.0E+07 TRIGA fission source 1.0E-10 1.0E-08 1.0E-06 1.0E-04 1.0E-02 1.0E+00 1.0E+02

Neutron energy (MeV) Mitigation

Very difficult to quantify experimentally or theoretically Plasma

There is no fusion neutron source Joints • Replaceable components • Replaceable fusion core • Include more shielding => a slightly larger reactor

Driven by economics Neutron shield

Different cable / ReBCO in HTS capability high field region Cables, joints, quench detection

• Test small pancake coil stacks using 2-pair soldered cable • Compare wire manufacturers: • Initially in LN2 then conduction cooled at staged temps down to ~20K • Milestone of 3T (on coil) • Test cable joints • Measure current sharing • Integrate RIOF fibre optic detector • Test other QD ideas High current coil & joint test

Use a pair of stacks as primary to induce a large current in a single turn secondary shorted via a scarf joint: • Turns ratio 48:1 • Assuming 50% coupling, 6000 A in primary = 144000 in secondary ! • Measure joint resistance via decay time constant

With addition of some means of rectification his could form the basis for a transformer drive for the magnet. AC losses

Our aim is to make a DC machine but highly elongated plasmas are vertically unstable

• Active feedback is required

• Physics to be determined on ST40

• Initial calculations suggest this shouldn’t be a problem, but we need to be vigilant Physics program and ST40

Stress limited copper

• 3T at R=40cm (7T at centre tube limiter)

• Phase 1 air/water cooling

• Phase 2 LN cooling Merge compression coils

Required for start up – our solenoid is fairly small Inner vacuum case

Inner vacuum case and centre column TF coils PSU manufacture

Other than merge compression power supplies are based on ‘transport’ super- capacitors.

Phase one TF PSU has been installed ST40 system layout

Power supplies

Load assembly Summary

1. Demonstrate scientific viability of STs 2. Develop HTS technology towards commercial viability 3. Combine STs and HTS in a series of engineering prototypes

ST25 Cu ST40 Cu

ST25 HTS Test coils ST40 magnet ST150~200

HTS engineering

Other engineering (Divertor, shielding, power conversion, breeding …. )