Interview A British startup has proposed combining the "maybe one day" technology of fusion power with the "slowly, slowly" tech of ion propulsion to create an engine capable of sending humanity to the stars.
The Register sat down with Richard Dinan, CEO of Oxford-based Applied Fusion Systems (AFS), to learn a little more about the technology.
Dinan is very much an enthusiast of fusion power and AFS has been banging the drum for the technology for the last few years, rattling a tin in 2017 in order to build two small, tokamak reactors.
A tokamak is a torus-shaped magnetic confinement device designed to confine plasma during thermonuclear fusion power generation. Large versions form the basis of hugely expensive fusion power projects, such as the International Thermonuclear Experimental Reactor (ITER). AFS plan their own, car-sized version called the Small Toroidal Atomic Reactor (STAR).
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AFS is now pitching the tech as a way of giving the ion thrusters popular with spacecraft and satellite builders a bit of a boost.
Ion thrusters are great for lengthy space missions as the engines are able to generate thrust over long periods while sipping fuel. The problem lies in the amount of thrust imparted, which is minuscule when compared to the reaction generated by traditional chemical rocketry. AFS reckons that by moving to a fusion-based future, sufficient power will be available to allow ion engine technology to surpass the old-fashioned fireworks of hydrogen, oxygen and their ilk, while also providing enough electrical power to dispense with diminishing returns of solar arrays.
Both the Russian and American space agencies have tinkered with nuclear propulsion for spacecraft. The Americans memorably kicked things off with Project Orion, which worked by detonating a sequence of atomic bombs behind the spacecraft to generate thrust. While Orion, which could have lofted immense amounts of mass at the cost of, er, quite a bit of nuclear fallout, was axed in the 1960s, NASA persevered with nuclear thermal propulsion and its cutely named Pulsed Fission Fusion (PuFF) project. PuFF uses a fission reaction to boost the fusion process, and NASA boffins reckon the technology could see the duration of a trip to Mars cut to a matter of weeks rather than the months or years current missions spend en route to the red planet.
For his part, Dinan dislikes using the word "nuclear", sighing that people "think 'bomb' – it's the worst thing in the world". He hopes that projects such as ITER will serve to educate the public that firing up a fusion reactor won't lead to unimaginable disaster, in the same way that the Large Hadron Collider did not send the world screaming into an artificial black hole 10 years ago.
ITER is a colossal undertaking, both in terms of size and overspending. The 23,000-ton machine, being built in France, is expected to be complete in 2025 and start running in earnest by 2035. Originally budgeted at €5bn, costs have since soared to €13bn and are likely to rise further as scientists struggle with the size of the undertaking. The vacuum vessel at the heart of the tokamak has a plasma major radius of 6.2m and will weigh a hefty 8,000 tons.
The goal of ITER is to demonstrate that commercial power could be produced. A follow-up, called DEMO, will actually generate electricity by 2050. ITER, on the other hand, just needs to show a steady state plasma with a Q value greater than 10 (or 500MW of power in pulses of 400 to 500 seconds for 50MW of heating power injected into the thing). "Q" is the break-even point and represents equal input and output. The higher the Q, the better the result.
Dinan's plan is to ride the fusion wave with a production line of far smaller fusion reactors. He reckons that when ITER finally fires up, there's a good chance it will exceed expectations: "This monster is gonna achieve more likely Q equals 15 plus."
At that point, AFS is gambling that the private sector will ride in and introduce efficiencies and agility that government projects sorely lack. And, of course, Dinan will have his hand up: "Hey, we've been working on this for 10 years."
The AFS reactor is a baby compared to the ITER monster. "The reason that we've chosen to develop on a 1.9m scale Tokamak is because without breaking any new physics, theory shows that you could build the reactor at that level and produce a Q positive result," Dinan said.
The reactor itself could also shrink further as scientists come up with new ways of stabilising the plasma (Dinan suggests nitrogen or argon).
And shrink it must, if Dinan is to realise his other vision of using the technology to power spacecraft thrusters. AFS points to high atmospheric ion thrusters, which it has built and tested, as an alternative to traditional chemical rockets (although there's little expectation that we'll be doing away with exploding stuff to actually get off the ground any time soon). Dinan wants to take things further and look at the potential exhaust speeds from a spherical tokamak. The equations stack up, but nobody has actually tried it out.
And there lies the rub. It is difficult enough to build an electricity-generating tokamak that runs at a reasonably efficient level, let alone see what thrust a spherical tokamak might chuck out. Dinan is, of course, optimistic – "we are planning, at worst, to have our first reactor online within four years" – and has enough scientists on his team to be sure of the physics involved. After all, he points out, governments have managed to build the same types of devices in the same period.
At a "worst-case" estimated cost of a million UK pounds per ton, and the machines weighing in at five, the cost isn't prohibitive. Maybe a billionaire such as Elon Musk might fling some cash at the project? "I think he's pretty busy at the moment," Dinan observed wryly.
The Register will check back in with Applied Fusion Systems in four years. ®