Fusion energy using tokamaks: can development be accelerated?

09:10-09:40 Alternatives to tokamaks: a faster-better-cheaper route to fusion energy?

Daniel Clery, Science magazine

Abstract

The tokamak may be the most successful type of device in fusion research but it is far from the only one. A few other parallel strands have been pursued for decades in government labs, but recently, in part because of slow progress in tokamak development, a new breed of fusion start-up companies has emerged to seek a faster-cheaper-better route to fusion energy. Stellarators, which look superficially like tokamaks but contain plasma differently, are currently championed by Germany’s Wendelstein 7-X which recently began operation. Inertial confinement fusion uses lasers to intensely compress small capsules of fuel and spark a burst of fusion. The leader in this field, the US National Ignition Facility, is currently struggling to get the spark to light but variants such as direct-drive and fast-ignition are waiting in the wings. Magneto-inertial fusion, which uses magnetic confinement followed by explosive compression, is being pursued by US national labs Los Alamos and Sandia, as well as some fusion start-ups. Others are banking on self-confining balls of plasma known as spheromaks or field-reversed configurations, or on electrostatic confinement in a device known as a Polywell. Dan Clery hopes to show there are more ways than one to skin a fusion cat.

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09:40-09:55 Discussion

09:55-10:25 The European Fusion Roadmap towards fusion electricity

Professor Tony Donné, EUROfusion, Germany

Abstract

The European roadmap to the realisation of fusion electricity breaks the quest into eight missions. For each mission, it reviews the current status of research, identifies open issues, and proposes a research and development programme.

ITER is the key facility of the roadmap as it is expected to achieve most of the important milestones on the path to fusion power. The Fusion Roadmap is tightly connected to the ITER schedule and the vast majority of fusion resources in Horizon 2020 are dedicated to ITER and its accompanying experiments. Parallel to the ITER exploitation in the 2030s, the construction of the demonstration power plant DEMO needs to be prepared. DEMO will for the first time supply fusion electricity to the grid. The design, construction and operation of DEMO require full involvement of industry to ensure that, after a successful DEMO operation, industry can take responsibility for commercial fusion power.

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10:25-10:40 Discussion

11:05-11:35 An economical viable fusion reactor based on the ITER experience

Professor Guenter Janeschitz, ITER Organisation, France

Abstract

This is Professor Janeschitz’s personal vision and outlook towards a fusion reactor based on his extensive experience from being part of the ITER design and now construction as well as leading the largest fusion technology program worldwide (KIT) for seven years. In particular he will to discuss how a fusion reactor can be economically viable without employing too advanced (SCFI) physics and technology. It certainly will be a pulsed machine (~ 20000 sec pulses) with thermal energy storage (turbine is steady state). He will also discuss the optimum machine size and toroidal field for such a machine and why he thinks that high field and smaller plasmas may not necessarily make a fusion reactor more competitive. 

When one extrapolates from today’s knowledge on ITER construction, even considering that ITER can be built much cheaper, it is clear that a fusion power plant will cost more than 10 or more likely more than 15 billion Euro / Dollar (the first of a kind even ~ 30 billion). Therefore in order to have an economically attractive fusion reactor it needs to produce a large amount of power (in the order of 2.5 GW electric). The possible size (R~10 m) and reasonably conservative physics basis of such a machine will be briefly described in the presentation. If we are successful in achieving advanced physics in a burning plasma, eg in ITER, then we can make the machine slightly smaller, but the principle arguments for a large machine will not change significantly. 

Key technologies and their status will be discussed with particular emphasis on a realistic blanket and divertor design and the size and issues of a T-plant for such a machine as well as the challenges which have to be overcome beyond what is needed for ITER.

At the end a simple economic consideration will be discussed to show that a large machine could be economically acceptable even in today’s environment, in particular in competition to renewables. 

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11:35-11:50 Discussion

11:50-12:20 The UKAEA Strategy for delivering fusion power

Professor Ian Chapman, UK Atomic Energy Authority, UK

Abstract

The talk will outline the key challenges which must be addressed to deliver fusion power and overview the facilities which UKAEA have now, and plan for the future, to address these challenges. UKAEA is helping UK industry to win key contracts for delivery of systems and components to ITER, and the talk will also explore how this connection to industry is vital for delivering fusion power.

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12:20-12:35 Discussion

13:30-14:00 Technical challenges to fusion power

Professor Howard Wilson, University of York, UK

Abstract

The technical challenges to fusion power are wide and varied, from advanced engineering and manufacturing methods, through novel materials in extreme environments to the swirling, writhing plasma we are seeking to contain. This talk will focus on just one area, that is rich in physics and sits at the heart of any fusion reactor – the plasma. In a tokamak, the plasma is confined in a toroidal geometry by magnetic field. Professor Wilson will explore how turbulence degrades the confinement, and is the main driver for pushing up the size of fusion reactors. However, there are circumstances when the turbulence is suppressed, resulting in regions of steep pressure gradient in the plasma. While good for confinement, the associated free energy drives filamentary plasma eruptions, like miniature solar flares, which on a device like ITER would cause excessive damage. This has led to methods to control these eruptions, which we shall review. The heat and particles that leak from the magnetic confinement system are handled in a region that is remote from the plasma core, called the divertor. Design of the divertor is one of the biggest challenges facing fusion, driving innovative solutions such as the 'Super-X' divertor on the UK’s MAST-U tokamak which will begin operation during 2018.

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14:00-14:15 Discussion

14:15-14:45 JT-60SA and Japanese tokamak programmes

Dr Yutaka Kamada, National Institutes for Quantum and Radiological Science and Technology, Japan

Abstract

The construction of JT-60SA by Japan and Europe is progressing on schedule towards its first plasma in September 2020. As of February 2018, more than 90% of the component manufacture has been completed and closure of the vacuum vessel is close to be accomplished. The objectives of the JT-60SA project are i) contribution to the success of ITER, ii) complementation of ITER for DEMO in all major areas of plasma development, and iii) fostering the next generation who are leading ITER and DEMO. JT-60SA is a highly-shaped large superconducting tokamak (maximum plasma current 5.5 MA, major radius ~3 m, aspect ratio ~2.6, elongation ~1.8, triangularity ~ 0.4) with a variety of plasma control actuators including high power heating (41 MWx100 s). This device is capable of confining break-even-equivalent class deuterium plasmas lasting for a duration (typically 100 s) longer than the time scales characterizing the key plasma processes in the ITER and DEMO-relevant plasma regimes. JT-60SA also pursues fully non-inductive steady-state operations with high plasma pressure (beta-value) exceeding the no-wall ideal MHD stability limit. The JT-60SA Research Plan ver.3.3 has been documented by ~ 400 scientists in Japan and the EU. Nationally coordinated research is being carried out in Japanese universities using various specialized 8 Spherical Tokamak (ST) devices towards realization of a component test facility and a power reactor. Research topics pursued on these devices include plasma current start-up using RF waves and coaxial helicity injection etc, advanced fuelling using compact toroid injection, ultra-high-beta plasma formation using magnetic reconnection heating by plasma merging. Including JT-60SA, tokamak research in Japan systematically studies highly-shaped high-beta plasmas with non-inductive current drive.

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14:45-15:00 Discussion

15:30-16:00 On the size of tokamak fusion power plants

Professor Hartmut Zohm, Max-Planck-Institute of Plasma Physics, Germany

Abstract

Studies for conventional tokamak power plants usually end up with a major radius R0 of the order 8-9 m, ie significantly beyond the largest existing tokamak, JET (R0 = 3m), and also in excess of the size of ITER (R0 = 6.2 m). This can be understood from a simple 0-D scaling [1] by the need to operate in a state of large power amplification Q=Pfus/PAUX > 30, where Pfus is the fusion power and PAUX the auxiliary heating power to compensate for residual plasma energy loss. However, these considerations assume a technical limit of the confining magnetic field B in line with the limits of the ITER design. Recent advances in High Temperature Superconducting Coil technology have led to proposals based on higher B, leading to more compact devices, i.e. smaller R0 [2], [3].

In this contribution, Professor Zohm argues that the definition of tokamak ‘size’ should include the magnetic field to remove the ambiguity in the discussion of ‘size dependence’ of the performance of fusion power plants [3], [4]. He also analyses the possibilities that higher B would offer, using an extension of the 0-D model used in [1]. Different routes of taking advantage of higher field are discussed. It is shown that, one also has to consider consistently the assumptions about plasma performance, such as confinement quality, operational limits or exhaust schemes. Finally, Professor Zohm discusses some of the significant implications for future R&D needed to make higher magnetic field in reactor-grade devices a reality.  

[1] H. Zohm, Fusion Sci. Technology 58 (2010) 613.
[2] B. Sorbom et al., Fus. Eng. Design 100 (2015) 378.
[3] A. Costley et al., Nucl. Fusion 56 (2016) 066003.
[4] W. Biel et al., Nucl. Fusion 57 (2017) 038001.

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16:00-16:15 Discussion

16:15-16:30 Smaller and quicker with STs and HTS

Dr Melanie Windridge, Tokamak Energy UK Ltd, UK

Abstract

Research in the 1970s and 80s by Sykes, Peng, Jassby and others showed the theoretical advantage of the spherical tokamak (ST) shape. Experiments on START and MAST at Culham throughout the 1990s and 2000s, alongside other international STs like NSTX at the Princeton Plasma Physics Laboratory, confirmed their increased efficiency (namely operation at higher beta) and tested the plasma physics in new regimes. However, whilst interesting devices for study, the perceived technological difficulties due to the compact shape initially prevented STs being seriously considered as viable power plants.

Then, in the 2010s, high temperature superconductor (HTS) materials became available as a reliable engineering material, fabricated into long tapes suitable for winding into magnets.  Realising the advantages of this material and its possibilities for fusion, Tokamak Energy proposed a new spherical tokamak path to fusion power and began working on demonstrating the viability of HTS for fusion magnets. The company is now operating a compact tokamak with copper magnets, R₀~0.4m, R/a~1.8, and target I_p=2MA, B_t0=3T, whilst in parallel developing a 5T HTS demonstrator tokamak magnet.  

Here Dr Windridge will discuss why HTS can be a game-changer for tokamak fusion. She will outline Tokamak Energy’s solution for a faster way to fusion and discuss plans and progress, including benefits of smaller devices on the development path and advantages of modularity in power plants. She will indicate some of the key research areas in compact tokamaks and introduce the physics considerations behind the ST approach, to be further developed in the talk by Alan Costley.   

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16:30-16:45 Towards an ST fusion pilot plant

Dr Alan Costley, Tokamak Energy UK Ltd, UK

Abstract

System code and analytical studies have shown that in addition to the conventional large size, high aspect ratio approach to realising fusion power, there could be an approach based on the low aspect ratio spherical tokamak at much smaller size [1]. Small devices would enable accelerated tokamak development because they offer relatively rapid and less expensive development cycles. However, small devices require novel technology and advanced engineering. High temperature superconductors are potentially the enabling technology because they can provide and withstand the necessary high fields used in the toroidal magnets. Other areas are important too, for example plasma start-up and ramp down with a limited, or without, a solenoid, divertor loads, and stresses in the magnet structure. Tokamak Energy is pursuing a development programme that aims to realise this alternative route to fusion power. In this presentation, the physics basis of the approach will be outlined and the key technology and engineering aspects will be highlighted and potential solutions identified. A technology roadmap to deal with the physics and engineering challenges on this path to fusion is under development and will be briefly introduced.

[1] A. E. Costley, J. Hugill and P Buxton, 2015, ‘On the power and size of tokamak fusion pilot plants and reactors’, Nuclear Fusion 55, 033001.  

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16:45-17:00 Discussion

09:00-09:30 Fusion Nuclear Science Facility and Pilot Plant studies at PPPL

Dr Jonathan Menard, Princeton Plasma Physics Laboratory, USA

Abstract

A Fusion Nuclear Science Facility (FNSF) could play an important role in the development of fusion energy by providing the nuclear environment needed to develop fusion materials and components. The spherical torus/tokamak (ST) is a leading candidate for an FNSF due to its potentially high neutron wall loading and modular configuration. A key consideration for the choice of FNSF configuration is the range of achievable missions as a function of device size. Possible missions include: providing high neutron wall loading and fluence, demonstrating tritium self-sufficiency, and demonstrating electrical self-sufficiency. Progress in ST-FNSF missions vs configuration studies including dependence on plasma major radius R for a range 1m to 2.2m are described for devices with copper toroidal field coils. Further, an A=2, R = 3m device incorporating high-temperature superconductor toroidal field coil magnets capable of high neutron fluence and both tritium and electrical self-sufficiency is also presented following systematic aspect ratio studies. Lastly, previous pilot plant studies have shown that electricity gain is proportional to the product of the fusion gain, blanket thermal conversion efficiency, and auxiliary heating wall-plug efficiency. The interplay between a range of physics and technology innovations for enabling compact tokamak/ST pilot plants will also be described.

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09:30-09:45 Discussion

09:45-10:15 Small, modular and economically attractive fusion enabled by HTS superconductors

Professor Dennis Whyte, Massachusetts Institute of Technology, USA

Abstract

The origin, development and new opportunities of an accelerated strategy for fusion energy based on the high-field approach are developed. In this approach confinement devices are designed at the maximum possible value of vacuum magnetic field strength, B. The integrated electrical, mechanical and cooling engineering challenges of high-field on coil (B_coil), large-bore electromagnets are described. These engineering challenges are confronted because of the profound science advantages provided by high-B: high fusion power density, ~B⁴, in compact devices, thermonuclear plasmas with significant stability margin, and, in tokamaks, access to higher plasma density. Two distinct high-field strategies were previously considered. The first was compact, cryogenically-cooled copper devices (BPX, IGNITOR, FIRE) with B_coil>20 T, while the second was a large-volume, Nb3Sn superconductor device with B_coil < 12 T; with the second path exclusively chosen ca 2000 with the ITER construction decision. The reasoning, advantages and challenges of that decision are discussed. Yet since that decision, a new opportunity has arisen: compact, Rare Earth Barium Copper Oxide (REBCO) superconductor-based devices with B_coil > 20 T; a strategy that essentially combines the best components of the two previous strategies. Recent activities examining the technology and science implications of this new strategy are examined. On the technology side, REBCO superconductors have now been used to produce B_coil>40 T in small-bore electromagnets, enabled by rapid progress in manufactured REBCO conductor quality, coil modularity and flexible operating temperature range. Specific tokamak designs on this path will be described.

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10:15-10:30 Discussion

11:00-11:30 Engineering challenges for Accelerated Demonstrators

Dr Elizabeth Surrey, Culham Centre for Fusion Energy, UK

Abstract

There are numerous engineering challenges in realising fusion as an economic source of power; some have been discussed for decades, such as the degradation of materials under irradiation by the neutron spectrum created by the burning plasma and some have become more visible since the advent of international studies on demonstration reactors, such as the need for efficient remote maintenance schemes. These have been explored in various detail and with different approaches that may depend upon the size of the fusion device under consideration. For example, it is well known that the stress and critical current density in the central column magnet is a limiting factor in reducing the size of tokamaks. Similarly, the power loading (neutron, plasma and radiative) on the first wall limits the feasible fusion power for a given size of tokamak. Then there are a number of challenges that the various DEMO concept designs have revealed and yet another set that remain relatively unexplored and these could prove to be obstacles to the timely development of fusion regardless of the size of the tokamak considered. The use of uncommon materials for structural and functional purposes, for example, raises issues not just of component manufacture and standards but also of availability in the required quantities and quality. Interpreting ‘accelerating fusion’ in a wider sense, issues relating to the design and construction of small tokamaks, large tokamaks and areas in common will be analysed, particularly in respect of developmental timescales.

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11:30-11:45 Discussion

11:45-12:15 Materials for fusion, with special reference to the spherical tokamak design

Professor George Smith FRS, Trinity College Oxford, UK

Abstract

Fusion energy systems present unique materials challenges. Extreme temperatures, intense levels of radiation damage, rapid sputtering of plasma-facing surfaces, tritium retention and transmutation of elements within key engineering structures are just a few of the difficulties that need to be managed. Approaches include the use of highly refractory materials, materials that have the potential to self heal, and the use of liquid layers to absorb damage.

Spherical tokamak designs which incorporate superconducting magnets present unique issues. The sections of the toroidal field coils that lie within the central column are more exposed to heat and radiation than in a ring-shaped torus design. The superconducting magnets require careful shielding from radiation damage, and this shielding must be compact, yet highly efficient. Recent progress with the development of cerment-based shielding materials will be described.

A further issue with fusion engineering is the lack of a well-developed regulatory environment. It not yet clear what standards will be required to be met in order to obtain an operating licence for such a plant. This is an issue which needs to be addressed as soon as possible, otherwise progress in the field may be inhibited.

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12:15-12:30 Discussion

13:30-14:00 What is the value proposition of fusion energy?

Professor Niek Lopes Cardozo, Eindhoven University of Technology, The Netherlands

Abstract

Fusion faster? If we had a working DEMO fusion plant today, how would it fare in the dynamic of the energy transition? What would it offer to the world that cannot be obtained cheaper and/or more reliably from the combination of existing carbon-free technologies: generation, conversion and storage? Why would governments invest in First Generation (Gen1) fusion plants? These questions can be analysed, even if we don’t yet know if the outstanding technical issues of fusion energy will be solved. 

Because of the large overnight investment cost, the intrinsic complexity of the reactor and the long construction time, Gen1 fusion power plants will have a high financial and technical risk profile. Moreover, the first fusion power plants are likely to have a low availability, even apart from the shut down periods for divertor and blanket replacement. So, it is far from obvious that a DEMO today would present a compelling business case. 

However, we don’t have a working DEMO plant today. The ITER – DEMO roadmap leads to a first generation of fusion plants towards 2070. To put this into perspective: 10 Gen1 fusion power plants represent an effective electric power output comparable to wind power around 2000. 

Before we address the question how we can develop fusion power faster, we need to articulate why we develop fusion power in the first place: the value proposition. Or else be satisfied with the academic challenge: can we make it work? and worry about the economics when we get there.

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14:00-14:15 Discussion

14:15-14:45 The economics of size

Dr Paul Thomas, Tokamak Energy Ltd, UK

Abstract

The cost of energy produced by fusion, like fission or, indeed, other non-carbon sources, will be dominated by servicing the capital charge. Therefore, a fusion power plant must maximise the output for the capital spent, the plant availability and its lifetime in order that the cost of energy is minimised. Experience with fission power plants has demonstrated that the scale of investment should be a fraction of the annual turnover of the operating companies so that the commercial risk is reduced and the decision-taking process expedited. This, together with the ‘Learning Curve’ cost reductions arising from Many Of A Kind construction, is the primary driver for the interest in Small Modular Reactors.  Fusion has advantages in respect of safety, long term environmental impact and plentiful, well distributed fuel.

The implications for the fusion load assembly requirements are: that it should have ‘high capital efficiency’, or a high value of the ratio of average plasma pressure to magnetic field pressure(β); that it should have the lowest possible, ‘recirculating’ power required to keep it operating by maximising the plasma current driven by the plasma pressure (‘bootstrap current’); that the plasma current during burn not depend on transformer action; and that it should be of a physical size that factory production of all the major components be possible, so that the ‘Learning Curve’ economies be realised. This would also reduce maintenance duration and the cost of the associating tooling. 

The talk will describe a concept for Modular Fusion[1] power plants that, in principle, satisfies all these requirements using Spherical Tokamaks, with High Temperature Superconducting magnets. Clearly, these requirements are best met if the fusion load assemblies are as physically small as possible. However, the most significant ‘size’ of the paper’s title is that of the capital investment. Preliminary cost estimates of Modular Fusion plants, based on Tokamak Energy’s approach, indicate that the requirement on economic ‘size’ can be met.

[1] MP Chuyanov and MP Gryaznevich, Fusion Engineering and Design 122(2017)p238 

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14:45-15:00 Discussion

15:30-16:30 Open discussion: a road map to accelerated fusion

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16:30-17:00 Summary and closing remarks

Professor Colin Windsor FRS, Tokamak Energy UK Ltd, UK
Matt Ridley, House of Lords, UK

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