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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Professor Hartmut Zohm, Max-Planck-Institute of Plasma Physics, Germany
Professor Hartmut Zohm, Max-Planck-Institute of Plasma Physics, Germany
Professor Hartmut Zohm received his PhD in Physics from Heidelberg University in 1990. In 1991, he got the Otto-Hahn-Medal by the Max-Planck Society for his PhD work. In 1996, he received his Habilitation at Augsburg University and became a professor in Plasma Research at Stuttgart University. Since 2000, he is a director at Max-Planck-Institute for Plasma Physics.
Professor Zohm’s main fields of interest are the magnetohydrodynamic stability of fusion plasmas and their heating by Electron Cyclotron Resonance Heating. By combining these two fields, he pioneered active stabilisation of neoclassical magnetic islands, which set a major performance limit to the tokamak. For this work, he received the John Dawson Award by the APS in 2014 and the Hannes Alfvén Prize in 2016. His present field is the study of tokamak physics on the ASDEX Upgrade tokamak which is operated by his department. More recently, he became involved in the European studies for a demonstration fusion power plant (DEMO).
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 Ip=2MA, Bt0=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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Dr Melanie Windridge, Tokamak Energy UK Ltd, UK
Dr Melanie Windridge, Tokamak Energy UK Ltd, UK
Melanie is Communications Consultant for Tokamak Energy. She has a PhD in Plasma Physics from Imperial College London during which time she worked on vertical stability in the MAST tokamak at Culham Centre for Fusion Energy. Subsequently she worked with Swiss inventions company Iprova and is named inventor on various patents.
Melanie’s communication work is wide-ranging and she regularly engages with the media, education institutions and the general public to talk about science and the role it can play in shaping the future. She is an ambassador for the government-led Your Life campaign encouraging more students into science and maths careers.
Melanie is the author of an introductory book on fusion energy, entitled Star Chambers: the race for fusion power, and of the narrative popular science book Aurora: In Search of the Northern Lights, for which she was awarded the Institute of Physics Rutherford Plasma Physics Communication Prize 2017.
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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Dr Alan Costley, Tokamak Energy UK Ltd, UK
Dr Alan Costley, Tokamak Energy UK Ltd, UK
Alan Costley studied physics at Brunel University and Imperial College graduating with a PhD in 1976. Early professional years were spent at the National Physical Laboratory where he developed techniques in sub-millimeter wave spectroscopy. In 1983 he joined the JET project at the Culham Laboratory as leader of one of the diagnostic groups. From 1994 – 2009 he was Head of the Diagnostics in ITER. He now works as a consultant and in recent years has consulted for the ITER Organisation, the Princeton Plasma Physics Laboratory, and Tokamak Energy Ltd. He was awarded the Charles Vernon Boys Prize of the Institute of Physics for distinguished research in experimental plasma physics by a young researcher. In 2008 he was elected a Fellow of the American Physical Society. He has published about 300 papers including about 40 invited papers at international conferences mainly in the areas of plasma physics and plasma diagnostics.