26 April 2014

The UK will be the first to break even with fusion power, leading us towards a future of clean, infinite energy

JET tokamak reactor
The world’s best fusion reactor, situated in the heart of the merry, Hobbit-inspiring motherland of Oxfordshire in England, will soon attempt to become the first fusion power experiment to surpass the mythical “break-even” point. This experiment, known as the Joint European Torus (JET), has held the world record for fusion reactor efficiency since 1997 despite the USA’s recent laser-based fusion experiments at the National Ignition Facility. If JET can reach break-even point, there’s a very good chance that the massive ITER reactor currently being built in France will be able to obtain the holy grail of everlasting green power generation: self-sustaining fusion.

Way back in 1970, the European Community (a precursor to the European Union) decided that fusion power should be taken seriously. In 1977, after lots of planning, construction of the JET began at a former Royal Navy airfield near Culham in Oxfordshire. Rather uniquely for an advanced science experiment, JET was actually finished on schedule in 1983, and was officially opened in 1984 by fair old Blighty’s Supreme Leader Queen Elizabeth II. In 1997, 16 megawatts of fusion power was produced from an input power of 24 megawatts, for a fusion energy gain factor (usually expressed by the symbol Q) of around 0.7. No other fusion reactor, including the National Ignition Facility in California, has come close. (The NIF is hampered by the fact that its its ignition method 500 terrawatts of laser power is incredibly inefficient.)

The target chamber at the National Igniftion Facility, where 192 lasers combine to create fusion
The fusion chamber at the National Ignition Facility in California. Fusion reactors look pretty awesome, eh?

While JET itself is a fairly low-power experiment (38 megawatts), it’s still very exciting because it’s essentially a small-scale prototype of the massive (500 megawatts) ITER fusion reactor being built in France that will (hopefully) fuse deuterium-tritium (D-T) fuel by 2027. Over the last few years, JET has been upgraded with the ITER-Like Wall (yes, that’s its scientific name) basically a wall of solid beryllium that can withstand being bombarded by ultra-high-energy neutrons and temperatures in excess of 200 million degrees.

NSTX internal
Another fusion chamber, this time the NSTX at Princeton. Click to zoom in.

With this new wall in place, the scientists at JET think they’re ready to throw some D-T fuel into the tokamak, pump up the magnetic field, and pray that more energy is released from the fuel than was put in to start the reaction. The key to sustained fusion is keeping the plasma hot and focused — and a big part of that is using a wall that bounces the hot neutrons back into the reaction, rather than letting them escape and thus losing energy and heat to the environment.

After years of working with just deuterium, JET is now ready to use a deuterium-tritium fuel mix that will burn a lot hotter and have a better chance of reaching break-even. When ITER comes online in the 2020s, it will use a D-T fuel mix. Speaking to the BBC, JET director Steve Cowley said, “We hope in the next runs of Jet that we’ll approach a [fusion energy gain] of one.” (Q = 1). For self-sustaining fusion that can be harnessed for energy production, though, we need to reach a Q of 20 or more we need a confinement method (magnets, walls) that is so good that very little external energy is required to keep the fusion reaction going. ITER is aiming for a Q of 5 or 10 and if it proves to be successful, say in 2030 or so, then maybe we’ll finally be ready to produce a real fusion power plant.

Courtesy extremetech


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