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more on nuclear fusion: towards ignition!

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I recently wrote about and tried to get a handle on the nuclear fusion facility, ITER, being built in southern France, but I barely mentioned the importance of magnets, and I didn’t mention another essential feature or factor in nuclear fusion – called ignition. That’s because I’m still a learner after all these years. But some news broke recently regarding a completely different experimental fusion facility in the USA, which uses lasers rather than magnets to control and focus the energy, which, as previously described, needs to be – a lot.

The National Ignition Facility (NIF) at the Lawrence Livermore National Lab in California is designed, it seems, to try and achieve exactly that – ignition. The term is kind of self-explanatory, as when you ignite something you get a burst of energy, seemingly more than you put into the igniting, like when you strike a match. But ignition in nuclear fusion is a really difficult thing to achieve, which is presumably why they had to build a whole national facility around it. They’ve been trying to achieve it for decades.

I did write that to achieve fusion – ignition? –  required temps of around 150,000,000 celsius, and obviously to sustain such temperatures requires a fair amount of energy, ten times that at the sun’s centre. Did I get that figure wrong? Pressure comes into it too (there’s a direct proportionality between temperature and pressure at any given volume).

I’ve found a great video explainer of the ignition breakthrough, presented by Anton Petrov, and a recent New Scientist podcast (no 81) also discusses it. So basically the possibilities of nuclear fusion as an energy technology have been on the cards since the development of the H-bomb in the late forties and early fifties. The energy required to set off an H-bomb, and for subsequent neutron bomb technology, was derived from nuclear fission. So that’s a lot of energy to make more energy. Since then, the aim, the holy grail, has been to find a way to create ignition, an energy output that is greater than, and preferably much greater than, the energy input. This is, of course,, essential for real-use thermonuclear energy. A number of technologies for creating thermonuclear fusion have proved successful, except insofar as the input-output ratio is concerned. Out of all these experiments chasing this elusive ignition, two models seemed most promising. Firstly, the toroidal fusion reactor (eg ITER), which is a magnetic confinement reactor, in which super-heated plasma is spun very quickly around a magnetically confined chamber, to create higher-than-the-centre-of-the-sun energy/temperatures. A number of these reactors, or tokamaks, have been built around the world and have successfully created fusion, but not ignition.

The second model is very different. It’s called inertial confinement fusion, and  it uses tiny hydrogen pellets. The idea came from observation of the H-bomb: a small enough hydrogen pellet would require a minimum energy of 1.6 megajoules (million joules) of energy to initiate an explosion – essentially, an ignition. This energy could be provided by lasers. Now this process is complicated – it’s not  simply a matter of fusioning hydrogen into helium because, as described in my previous post about ITER, there are isotopes involved. These isotopes (deuterium and tritium) are used to overcome the electrostatic repulsion which would normally occur when using proteum, the common form of hydrogen. This repulsive force between protons is known as the Coulomb force. The attractive force between protons and neutrons, called the nuclear force, acts against the electrostatic repulsion force, and this helps in overcoming the Coulomb barrier, and facilitating a fusion energy greater than that inside our sun, where plasma particles may not fuse at all over long periods. We’re basically looking at creating a more efficient kind of fusion, which requires the kinds of temperatures and pressures found inside much larger stars than our sun.

The key to the elusive status or point known as ignition is a concept called the Lawson criterion. Wikipedia describes it thus:

The Lawson criterion ….compares the rate of energy being generated by fusion reactions within the fusion fuel to the rate of energy losses to the environment. When the rate of production is higher than the rate of loss, and enough of that energy is captured by the system, the system is said to be ignited.

We haven’t achieved ignition yet, but it seems another baby step has been taken. One of the researchers at the NIF has described it as a ‘Wright brothers moment’, which has led to a bit of head-scratching. Basically, what was achieved at the NIF was a ‘momentary’ ignition – very momentary, and still only releasing some 70% to 80% of the energy input. Yet this was the most significant achievement in 60 years of work – a proof of concept achievement, which is built on previous experiments yielding increasing levels of energy. The process involved almost 200 super-amplified lasers confining and directing energy at a tiny hydrogen pellet for a period of 3 nanoseconds. That’s 3 billionths of a second. This required excruciating accuracy, coordination and timing, with everything – the lasers, the amplifiers, the pellet, the hohlraum chamber (holding the pellet) and so forth, being executed precisely. The precision level has improved markedly in recent times, leading to this breakthrough moment (after all, the ‘Wright brothers moment’ wasn’t exactly the first commercial passenger flight). The 1.3 megajoules released in this most recent ignition experiment was some 25 times what the facility could muster only three years ago. So there doesn’t seem far to go.

And yet. The energy input required is enormous. The lasers would need to fire more or less constantly – machine-gun-like – to produce the output required for human use (the current record of 1.3 megajoules has been described as ‘just enough to boil a kettle’. So we’re talking orders of magnitude, not just for the laser energy but for the hydrogen pellets, which need to be produced en masse at a teeny fraction of current costs. And so on.

This not to minimise the achievement. The publicity already being generated augurs well for the future of a technology that has for so long failed to live up to expectations. Those at ITER and other labs around the world will receive a great fillip from this, not to mention some small mountains of cash. Looking forward to it.

References

movements in nuclear fusion: ITER

Major Breakthrough in Nuclear Fusion After Decades of Research (Anton Petrov video)

https://en.wikipedia.org/wiki/Lawson_criterion

https://podcasts.google.com/feed/aHR0cHM6Ly9mZWVkcy5idXp6c3Byb3V0LmNvbS84MTQwMzUucnNz/episode/QnV6enNwcm91dC05MDU0NjU3?hl=en-AU&ved=2ahUKEwiasaDm3NryAhUGeH0KHVAaDZMQjrkEegQIBRAI&ep=6

Episode #841

 

Written by stewart henderson

August 31, 2021 at 5:19 pm

movements in nuclear fusion: ITER

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the world’s biggest clean energy project? ITER in southern France

Geographical, the magazine of the UK’s Royal Geographical Society, had an article in its April 2021 edition entitled ‘Caging a Star’, all about the International Thermonuclear Experimental Reactor (ITER) project in Provence, France. Thermonuclear fusion has of course been talked up as an ultimate solution to our energy needs for decades, to the extent that it’s become something of a joke, but in the meantime, practical movements are underway. In fact, they’ve been under way for a long time. An international contract was signed in 1986 to implement research on fusion, though it took another twenty years to agree on the site for ITER. The project now involves 35 countries – largely WEIRD ones (Western Educated Industrial Rich Democracies), producing 85% of global GDP. It’s a long-term project, certainly, but it’s being taken seriously, and construction is happening, big-time.

With the IPCC having recently come out with its 2021 report, nations are looking to their targets and feeling concerned – some more than others (wake up Australia). Boštjan Videmšek, the author of the Geographical article, assesses the current situation in stark terms:

70% of all CO2 emissions pumped into the atmosphere are created through energy consumption; 80% of all the energy we consume is derived from fossil fuels. The EU has formally pledged to start producing half of its electric energy from renewable resources by 2030. By 2050, the bloc’s members are planning to hoist themselves into a fully carbon-neutral society. But, given current trends, this seems like wishful thinking. Renewable energy resources simply won’t be enough for the task.

The ITER project came out of the closet, so to speak, in late July 2020, when the heart of the project, the tokamak, began to be assembled onsite – though construction of various elements of the program have been going on for years. A tokamak is a toroidal or doughnut-shaped chamber, controlled by huge, powerful magnets, in which hydrogen plasma is manipulated to produce energy according to Einstein’s mass-energy equation. We all know, I hope, that fusion is constantly happening in the sun, and in all suns throughout the universe, and that its energy is essential to our existence, but ITER’s scientists are hoping to improve on the sun’s processes. Hydrogen collisions inside the sun don’t always result in fusion – the fusion process is quite slow. Recognising this, researchers looked to isotopes of hydrogen to speed up the process. Hydrogen’s most common form, consisting simply of a proton and an electron, is called protium. However, there are two other isotopes, deuterium and tritium, containing an additional one and two neutrons respectively. The best form of fusion reaction for producing energy is DT fusion, using deuterium and tritium. This produces more energy, at a lower temperature. The problem is with the tritium, a highly radioactive and unstable isotope, which is both rare and expensive, at about US$30,000 per gram. The rarity, though, is related to low demand, and there is potential for ITER to produce its own supply of the isotope.

Of course, none of this is expected to be ready in the near future. ITER is essentially a proof-of-concept project for future power plants, and is expected to spend a decade in testing, finalising in around 2035. Those future power plants are already ready and waiting, at least in terms of design. The key to achieving fusion is a sufficiently high temperature (150,000,000 degrees celsius!) and high particle density, for an optimum fusion rate. Containment of the volatile plasma will also, of course, be an issue. ITER’s experiments will also be about capturing and utilising the energy produced. As Videmšek describes it:

The idea is that heat will build up along the sides of the tokamak, where it will be captured by the cooling water circling the reactor. As in a normal power station, the heat will be used to produce steam and – by way of turbines and alternators – electricity. The water will eventually be released with the help of vast cooling towers. These have already been put in place…

The science itself, as researchers told Videmšek, is straightforward enough, but the infrastructure, the international nature of the project, the politics and the funding can all provide obstacles. The siting in Provence has helped, as France has successfully embraced nuclear fission technology for decades, and the project is a boon for the Provençal economy. And of course there’s the global warming issue. The IPCC has just released its 6th Assessment Report and, among other findings, has confirmed what we here in Australia have experienced regarding extreme weather events:

Human-induced climate change is already affecting many weather and climate extremes in every region across the globe. Evidence of observed changes in extremes such as heatwaves, heavy precipitation, droughts, and tropical cyclones, and, in particular, their attribution to human influence, has strengthened since the Fifth Assessment Report (AR5).

The report argues that, ‘unless deep reductions in carbon dioxide (CO2) and other greenhouse gas emissions occur in the coming decades’, this scenario of extreme weather events will continue into the foreseeable future. These deep reductions, it seems, are a matter of political will, not to mention recognition of the crisis, which is clearly not universal. The way that many nations, including some of the most powerful and impactful on climate, have dealt with the clear and present threat of the SARS-CoV-2 virus, doesn’t provide much cause for optimism. If the ITER project, mostly funded by EU nations, goes off without a hitch over the next few decades, it may just put another nail in the coffin of our self-destructive exploitation of fossil fuels. Better late than never I suppose…

References

Boštjan Videmšek, ‘Caging a star’, in Geographical, April 2021

https://www.ipcc.ch/report/ar6/wg1/#SPM

 

Written by stewart henderson

August 15, 2021 at 7:19 pm