Compact Fusion: Opportunities and Challenges with Spherical Tokamaks
Alan Costley and Alan Sykes
Tokamak Energy Ltd, UK
Wed, Jun. 08th 2016, 11:00-12:30
Salle René GRAVIER 506 rdc, CEA Cadarache

Two recent parallel developments -­‐ in one case modelling/physics based, and in the other technological -­‐ potentially open a faster route to fusion power based on relatively small devices. In this presentation we detail both developments and show how they might combine to open a faster route to fusion power.


Modelling with a system code based on an established tokamak physics model has shown that the fusion triple product, nTτE, and hence the fusion gain, Qfus, depend only weakly on device size. Analytical work has shown that this finding is due mainly to the density and beta limits. This result implies that at least from a physics perspective, high fusion performance can be obtained in relatively small devices [1, 2]. High temperature superconductors (HTS) are now approaching a cost and scale for use in tokamak magnets. Such conductors require less space, can carry high currents in strong magnetic fields, and, since they operate at relatively high temperatures, require less cooling. Innovative designs and materials for effective neutron shielding are being developed [3], and advanced concepts for handling high power loads in the divertor are being investigated.


The positive aspects of these advances combine well in the spherical tokamak (ST).  HTS  magnets with relatively thin shielding open the potential of the ST as an efficient compact fusion device. The Tokamak Energy programme concentrates on the ST. Two small experimental STs, including one where all the magnets are made from HTS have been constructed and are used in experimental work [4]; a copper magnet, high field (2T upgradable to 3T) ST is under construction and will be brought into operation early in 2017, and used to develop innovative concepts for plasma start up and to test confinement in an ST at high magnetic field; R&D on critical aspects, especially of the HTS magnets, is ongoing; modelling and analytical work on the concept of modular fusion based on relatively small fusion power modules, including an investigation of the economics of such an approach, are underway.


[1] A E Costley et al, Nucl. Fusion 56, 066003 (7pp) (2016).

[2] A E Costley et al, Nucl. Fusion 55, 033001 (7pp) (2015).

[3] C G Windsor et al, Nucl. Fusion 55, 023014 (10pp) (2015).

[4] A Sykes et al, Fusion Sci. Technol. 68 237–44 (2015).

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