Posts Tagged ‘Fusion’

Fusion Energy breakthrough? Not so much.

December 15, 2022

Click on Image for a larger version. The ‘breakthrough’ was the front page of the BBC News Website. Apparently this was the most important story in the world.

Friends, I find myself lost for words. Why? Because I am apoplectic with disappointment at the breathtakingly bad reporting about the recent ‘fusion breakthrough’ in the US.

Every media organisation whose output I have read has simply regurgitated the line they have been fed by the press office of Lawrence Livermore National Laboratory (LLNL). The BBC made this their headline story with the byline:

The technology is a potential source of near-limitless clean power….

In this article I will outline what actually happened in this ‘breakthrough’, and then explain why this technology will never ever, ever, ever, ever, ever, ever, ever, ever be useful as a power source.

At the end of the article is a list of resources I consulted. Links below to the panel discussion are to timed locations within the video.

The Experiment

The experiment comprised firing a bunch of lasers split into 192 beams at a tiny, hollow, diamond sphere suspended inside an open-ended cylindrical metal capsule. Both the sphere and cylinder were manufactured to extraordinary specifications in terms of their dimensions and surface finish. These extreme specifications are necessary to ensure that the energy is reflected from the inner surface of the cylinder onto the sphere uniformly.

Click on Image for a larger version. Left. The cylinder with the diamond sphere at it’s centre. Right. Illustration of the way in which ultraviolet lasers illuminate the inner surface of the cylinder, which then bathes the diamond sphere in X-rays.

At the panel discussion which followed the press conference, Mark Herman, the LLNL Director for Weapons Physics and Design refused to assign a monetary value to the target, but reasonably it must be on the order of a million dollars per target.

This sphere and cylinder were placed with nanometre precision in the centre of a chamber, and cooled to cryogenic temperatures (less than 20 K). At these low temperatures, the inside surface of the sphere was coated with roughly 60 micrograms (~0.03 mm) of a solid mixture of deuterium and tritium.

When the ultraviolet laser blast hit the metal cylinder, it vaporised and irradiated the sphere with X-rays. The pressure of this blast was so great and so uniform that it rapidly compressed the 4 mm diameter diamond sphere to around 0.1 mm ( from a “basketball to a pea“), accompanied by extreme heating to temperatures in excess of 100 million degrees Celsius.

This extreme temperature and pressure were sufficient to transiently cause the nuclei of deuterium and tritium to collide and fuse, with each fusion releasing 17 MeV (million electron volts) of energy. In more familiar units this amounts to 2.8 x 10^-12 joules per fusion event.

The energy in the laser pulse was estimated to be 2.05 MJ (million joules). I’m afraid I don’t know how that was measured. The energy of the resulting explosion was estimated to be 3.15 MJ. This estimate is made in several ways, but one technique involves putting a metal sphere near the fusion centre. When irradiated by neutrons from the fusion reaction, nuclear reactions cause the metal sphere to be come transiently radioactive, and measurements of this induced radioactivity allow an estimate of the number of neutrons to which it was exposed. This neutron flux is directly linked to the number of fusion events.

The difference between 3.15 MJ and 2.05 MJ = 1.1 MJ is inferred to come from deuterium-tritium fusion reactions. Dividing this yield by the energy per fusion reaction suggests that there were roughly 3.9 x 10^17 fusion reactions. At the panel discussion it was stated that this was 4% of the number of possible fusions, and so this allows us to estimate that there around 10^19 molecules of D and T in the sphere with a volume (in the solid state) of around 4 cubic millimetres.

Energy and Power

Is 1.1 MJ a lot or a little? The answer depends on what you compare it with.

A familiar unit of energy for consumers is the kilowatt hour (kWh) – the units in which we are billed for our gas and electricity. One kilowatt hour is 3.6 MJ, so 1.1 MJ is an appreciable amount of energy. Enough to boil around 3 litres of water.

1 MJ is also the typical energy content of a stick of dynamite. A stick of dynamite weighs ~ 190 grams whereas this same energy was released by ~ 60 micrograms of deuterium-tritium mixture. This gives a sense of the extraordinary power density available in nuclear reactions, and why they make such powerful explosives.

Unsurprisingly, these explosions damage the chamber in which they occur and the optics of the laser used to focus the beams onto the target needs to be repaired after each shot.

Breakeven: the problems emerge.

The hype surrounding this event arose because for the first time an experimental fusion reaction  produced more energy than was required to initiate the reaction.

As was made clear at the panel discussion, this 1.1 MJ of excess energy was the result of the laser imparting 2.05 MJ to the experiment, but the laser itself consumed roughly 300 MJ of electrical power, and this itself would have been derived from around 600 MJ of primary energy, mostly from burning methane in gas-fired power stations.

If we wanted to “improve” this facility so that the same laser produced enough thermal energy to run a power plant that could generate the electrical energy (at 33% efficiency) to run itself, then we would need to increase the yield by a factor 3 x 300 MJ/1.1 ~800. Where might this gain come from?

  • Only 4% of the deuterium-tritium in the experiment reacted so we could gain a factor 25 by arranging for the all the deuterium-tritium charge to burn. Now we just need a factor 33.
  • We might increase the efficiency of the laser from 1% to (optimistically) 20% and then we would just need a factor 1.6 from ‘somewhere’ to break even.

For the sake of argument, let’s assume we got that factor 1.6 somehow – perhaps by increasing the charge of deuterium-tritium. We would then have a system that could in raw energy terms sustain itself. But we would not yet be generating any extra energy at all!

At this point we would have an experiment that once every few weeks could produce an explosion yielding 900 MJ i.e. the equivalent of 900 sticks of dynamite or about 200 kg TNT.

No feasible path to a reactor.

Let’s suppose we want a fusion reactor which can produce 100 MW of electrical power to an external load. This is a small generating plant on a national scale – the UK peak requirement is around 40,000 MW (40 GW) and the planned Hinkley C reactor (if it ever operates) should produce 3,200 MW (3.2 GW).

To achieve 100 MW of electrical output we would need to generate around 300 MW of thermal power to operate a turbine and generator set with an output of 100 MW of electricity. This means that having gone to considerable trouble to generate energy via fusion we would then throw away two thirds of it as heat!

300 MW of thermal power corresponds to 300 MJ/second so assuming that we can (somehow) produce 900 MJ explosions, we need one explosion every 3 seconds to generate enough electricity to ‘breakeven’ i.e. just to operate the plant! So an additional 300 MW of heat would be required to make electricity for other uses: this would require an explosion every 1.5 seconds.

So to summarise, to produce a power plant outputting 100 MW of electricity the designers would need to:

  • Find a way to manufacture tritium.
  • Find a way to capture the energy of the explosions and turn it into heat.
  • Improve laser efficiency by a factor 20 and improve repetition rate by a factor 80,000 from around 1 laser pulse per day to around 1 laser pulse per second.
  • Build a chamber which could withstand a small nuclear explosion (0.2 tonnes of TNT equivalent) every second for (say) 30 years. Remember that the reaction chamber itself would become intensely radioactive and no human could enter it once its service life began.
  • Within this chamber a cryogenically-cooled target must be put in place with nanometre precision once a second.
  • No debris from the previous explosion can remain because this would affect the path of the lasers.
  • To achieve electricity output at a cost of $1 per kWh – around 10 times current use US prices – the cost of the target could not exceed $40. More realistically – considering the other costs involved, the target would need to cost ~$4 and around 58,000 would be required every day.

In short, there is no feasible path to turn this physics experiment into a reactor. And even if all the achievements above were somehow solved, the electricity would still be extraordinary expensive.

Why the hype?

Friends, we are being ‘gaslighted‘.

As Wikipedia puts it:

This term may also be used to describe a person (a “gaslighter”) who presents a false narrative to another group or person, thereby leading them to doubt their perceptions and become misled, disoriented or distressed. Often this is for the gaslighter’s own benefit.

Lawrence Livermore National Laboratory is a nuclear weapons research institute, and one can see how being able to create ‘mini’ nuclear explosions might be useful for them. And that is what this facility is for. As Mark Herman, the LLNL Director for Weapons Physics and Design said in the panel discussion .

“... the ignition work we’re doing is for stockpile stewardship. Our thermonuclear weapons have Fusion ignition … and so studying Fusion ignition is something we do to support the stockpile stewardship program.

In other words it is a technology which allows the US to design and test nuclear weapons without contravening the Comprehensive Nuclear Test Ban Treaty.

Any attempt to frame this technology as having any application whatsoever to energy generation is a deception.

The answers to our energy needs are already available to us.

And finally…

My comments in this article refer to Inertial Confinement Fusion (ICF). In contrast, Magnetic Confinement Fusion (MCF) does have an unlikely, but conceivable path to making a power plant.

In July 2020 I wrote about MCF in this article: Are fusion scientists crazy? The article includes a précis of (and a link to) an excellent talk from Zach Hartwig which I think is the best summary of all approaches to fusion that I have seen.

My other articles about fusion – dating back to 2013! – can be found here:

If you liked this article, you will likely be disappointed with the following articles that I looked at while preparing this:

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