11 October 2013

US fusion lab almost breaks even, takes a big step towards clean, limitless power

The National Ignition Facility in California has become the first fusion power facility to create a fusion reaction that generates more power than it requires to get the reaction started. This is perhaps the most important step ever towards the always-just-out-of-reach realization of clean, self-sustaining, limitless fusion power.

The NIF, operated by the Lawrence Livermore National Laboratory (LLNL), creates a fusion reaction by focusing the world’s most powerful laser (some 500 terawatts), split into 192 separate beams, onto a small capsule (called a hohlraum) containing a mix of deuterium and tritium (isotopes of hydrogen), situated in a fusion chamber (pictured above). The lasers strike the hohlraum (pictured bottom) with precision timing, causing a perfectly uniform explosion, which creates a massive reaction force that causes the deuterium/tritium fuel to perfectly and uniformly implode — hopefully starting a fusion reaction. This process is called inertial confinement fusion, as opposed to magnetic confinement fusion, which before today was generally considered to be a more mature technology.

Laser pre-amplifiers at the National Ignition Facility

For the past half-century, fusion power has always remained tantalizingly out of reach. Whenever we think we’re getting close, another roadblock pushes us back a few years. This has led to the coining of the phrase, “fusion is always 20 years away.” The irritating thing is, we have an almost complete understanding of how fusion should work, but transporting those theoretical ideas into the physical universe has proven to be surprisingly difficult, usually due to various system or material inefficiencies that weren’t evident until they were put under enormous strain.

A hohlraum, which carries a few grams of deuterium/tritium fuel

With this latest breakthrough, it seems that the NIF overcame an inefficiency in how energy from the laser beams is transferred to D/T (deuterium/tritium) fuel. Previously, the ablator — a plastic shell that surrounds the D/T fuel — had been breaking up improperly and interfering with the implosion. By changing the shape of the laser pulse, the scientists reduced the asymmetricity of the explosion/implosion, reducing the and thus increasing overall efficiency. The end result is that the fusion of the D/T fuel produced more energy than the energy delivered to the hohlraum — but the overall energy consumption, measured at the (large) wall outlet, was still higher than the energy produced. This is due to other inefficiencies in the system.

The next step, of course, is actually achieving the NIF’s eponymous goal: ignition. To do this, the facility will have to develop a system that is efficient enough that the fusion reaction actually creates enough energy to sustain itself. Realistically, we still have some way to go — and even if NIF does reach ignition, it’s not set up to act as a fusion power plant; it’s a research facility, nothing more. As far as actual, usable fusion power goes, the European ITER fusion reactor in France is probably our best bet, with a tentative timeline of 2027 for the first D/T fusion.

How the laser beams are focused on the NIF’s hohlraum. The white ball is a pellet of deuterium/tritium fuel.

For a lot more information about the fusion power, 500MW from half a gram of hydrogen: The hunt for fusion power heats up has a few more that you might like.

Read now: Cold fusion reactor independently verified, has 10,000 times the energy density of gas. 


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