The need for higher efficiency and lower costs in fusion engineering has led AFS to the spherical tokamak reactor design model. These reactors offer more favourable magnetohydrodynamic behaviour meaning they can be run for longer bursts and are less prone to damaging plasma instabilities called disruptions. In addition, spherical tokamaks are known to operate more efficiently confining plasma at a higher pressure than conventional tokamaks using less intense and therefore cheaper magnetic fields.


The reactor is part of the new breed of high efficiency spherical tokamaks. The STAR planned Alphpa and Beta reactors are intended to produce 100MW of electricity and will do so using the new generation of materials suited to fusion science; for the toroidal coils REBCO superconductors make the design far easier to service because they are simpler to join. The design also features symmetrical diverter systems which can be used to aid heat extraction from the plasma.

 STAR will make use of recent advanced in additive manufacturing otherwise known as 3d printing. Major components can now be laser sintered rather than cast or milled, reducing build costs and times. Complex geometries become possible with additive manufacturing and so AFS can explore novel approaches to existing design challenges.

 STAR is slightly larger than the MAST reactor at CCFE, to ensure it can meet a minimum commercial standard of 100MW electrical output. 


The Physics

If heat is converted to electricity at 40% efficiency, the reactors need a fusion power of 250MW to produce 100MW of electricity. A steel blanket is widely recognised to support a maximum wall loading of 5MW/mˆ2 so at peak wall loading the STAR reactors A and B require a wall area of ˜50Mˆ2 (250/5). These requirements determine the basic geometry of STAR, major radius = 1.1m minor radius = 0.9m.