New research on the design of stellarators is opening the way for their further development as a potential source of fusion energy.
Stellarators, like tokamaks, are a device for confining a hot plasma in the shape of a doughnut or torus to enable fusion to take place.
Conceptualised in the early 1950s by the Princeton astrophysicist Lyman Spitzer, they have, however attracted less attention in the fusion race than the Russian conceptualised tokamaks of the same decade, largely because of their lag in performance.
But interest is renewing and new research from the University of Maryland described as a “breakthrough” on magnetic confinement of the plasma in stellarators – one of their major challenges – is expected to add further impetus to their development.
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The chief difference between stellarators and tokamaks is in how the hot plasmas are confined – in the former using external coils to generate a twisting magnetic field while in the latter inducing electric currents inside the plasma.
While stellarators have benefits, such as the need for less injected power to sustain the plasma, with the complexity of the magnetic field coils, the twisting magnetic fields have been less effective at confining plasmas than the symmetrical, doughnut shaped fields in tokamaks, thus lowering the efficiency of the fusion process due to the extreme heat loss.
The new research by Princeton University post-doctoral fellow Elizabeth Paul and University of Maryland research scientist Matt Landreman has used open source optimisation software to more precisely shape the enclosing magnetic fields in the device.
By slowly refining the simulated shape of the boundary of the plasma that marks out the magnetic fields, they were able to produce ‘quasisymmetry’ in stellarators to nearly match the confining ability of a tokamak’s symmetrical fields.
“The key thing was developing a piece of software that allows you to rapidly try out new design methods,” explained Paul.
“We’ve made some simplifying assumptions but the research is a significant step going forward because we’ve shown that you can actually get precise quasisymmetry that for a long time was thought not to be possible.”
One of these assumptions was that the pressure and electric current in the plasma were small.
Also needing further development before the findings can be realised are new stellarator coils and detailed engineering of the stellarator design, aspects of which are under development at the US Department of Energy’s Princeton Plasma Physics Laboratory.
