A perennial question exercises the minds of scientists interested in the future of energy supply – how far away is the possibility of generating electricity from nuclear fusion? Struggling to determine an answer, “50 years” has typically been the ballpark figure – the trouble is, that’s been the ballpark figure for the past five decades. How much closer have we come to this holy grail of cheap, clean, bountiful energy?
Scientists now believe we could be on the verge of a breakthrough that might pave the way for engineering companies to join in developing fusion technology. They are not working on the well-publicised magnetic confinement approach to nuclear fusion which is building a facility called Iter in France but instead are preparing for inertial confinement fusion, or “laser energy” as it is sometimes called.
The scientists are excited about the prospect of laser energy soon triggering “ignition” at the Lawrence Livermore National Laboratory in California. They believe it could happen within 18 months. This event, in which the energy generated by fusion would outstrip the energy pumped in to achieve it, is regarded as a significant milestone – perhaps the significant milestone – in proving the inertial confinement laser energy concept.
It is believed that a prototype laser fusion plant could then start to be funded, led in the UK and Europe by a project known as the High Power Laser Energy Research Facility (Hiper). The US has already built a “proof-of-principle” demonstrator at Lawrence Livermore’s National Ignition Facility (NIF), where experiments are now taking place to achieve that all-important first ignition of fusion.
Research on laser energy should not be viewed as competing with the work going on at Iter, British scientists stress. The experimental Iter reactor in Cadarache, France, is scheduled to produce its first plasma in 2019. The consensus is that the goal of commercially viable nuclear fusion should be pursued by as many means as possible.
Professor John Collier, director of the UK’s Central Laser Facility which leads the Hiper project, makes an analogy with the early phase of nuclear power. He says: “Forty to 50 years ago we were talking about choosing between Magnox reactors, PWRs, AGRs and other designs, and in the end we had all of them.
“Our work is complementary to Iter. Laser fusion and magnetic fusion are two radically different ways of trying to achieve the same thing. But, once you’ve produced the energy-carrying neutrons, there is commonality. You have to convert the neutron energy into electricity and breed new fuel. It’s an example of how the approaches differ, but they also have much in common.”
The inertial confinement or laser energy method of producing fusion was proposed in the early days of the laser but at that time no one understood how difficult it would be to achieve. “When people began talking about the use of lasers they realised they had potential for a multitude of purposes, including fusion,” says Collier. “Papers were published on it in the 1960s, for example. But in the early days no one realised how tricky it was.”
So what does this challenging goal of fusion through laser energy involve? At NIF, fusion reactions are set off by heating and compressing a “target” or fuel pellet the size of a pinhead filled with a mixture of deuterium and tritium down to the density of lead. To compress and heat the fuel, energy is delivered to the outer layer of the target high-energy laser beams. The heated outer layer explodes outwards, producing a reaction force of shock waves which accelerate inwards against the remainder of the target.
A sufficiently powerful set of shock waves can compress and heat the fuel at the centre to the extent that fusion reactions begin. The energy released by these reactions then heats the surrounding fuel, which also triggers fusion, thereby “burning” a significant portion of the fuel capsule and releasing huge amounts of energy. It is the same reaction that produces energy in the centre of the sun.
“The question is whether we could build a miniature sun on earth,” says Dr Ed Moses, director of NIF in the US. The key problem is getting more energy out of the system than you put in. Small fusion reactions are demonstrated all the time at facilities such as NIF, and have been carried out at forerunners of Iter such as JET in the UK, which got close to energy “break even” point several years ago.
Assuming that ignition is achieved in the US, industrial partners will be needed to make the first laser energy plants a reality. Fuel for such reactors would not present a problem, the experts say.
Deuterium and tritium are both isotopes of hydrogen. Deuterium can be readily obtained from seawater – 600kg of water could yield the energy of two million tonnes of coal, according to Moses – and tritium can be obtained from lithium, of which there is an abundance. Ten milligrams of this combined fuel has the potential to produce the energy obtained from burning one barrel of oil.
In comparison with the “single shot” set-up of NIF, prototype plants for power generation would have to deliver repeatable laser shots 10 times a second. Fuel pellets would need to be optimised, refined and mass-manufactured – one million would be needed every day for a single power station. Scientists say the global industry could be worth $1 trillion a year.
More powerful designs of diode-powered lasers would be needed and these have yet to be demonstrated commercially – or even in the laboratory. The tracking equipment to allow these advanced lasers to home in on targets with accuracies of microns at very high speeds is another challenge to be addressed.
This all means work for engineers, potentially. The scientific community believes that, once ignition has been demonstrated, industry will rise to the challenge of producing laser energy plants. With that breakthrough expected relatively soon, scientists leading Hiper are keen to talk to companies that might be able to help.
Memorandums of understanding with some companies are already in place, but they have to be able to take the long view to invest in technology that could be used on the UK demonstrator and beyond, says Collier. Government will also need to get involved if the Hiper project is to achieve its aims. Encouragingly, science minister David Willetts has taken an interest. In early September he opened a laser energy conference at the Royal Society and emphasised the need for “game changing” energy technologies such as fusion.
Collier says: “It will definitely require facilitation in some way from government. Laser energy is not something we’re going to be able to do entirely in the private sector. But private companies will make a massive contribution once they see the value of the investment.
“Lasers are a great example: the sort of lasers that you need to do this don’t exist – yet. The market for lasers is huge, so if you introduce a next generation of laser technology you open up new possibilities. Industry will snap them up. And there are so many spin-off potentials in markets such as medical, pharmaceuticals and security.”
Hiper project director Dr Chris Edwards says: “The aim is to hand over a set of technology solutions at the end of the Hiper project which will enable the construction industry to produce a working prototype reactor. At that stage we’ll be ‘in the early days of powered flight,’ as it were, but not yet offering ‘low-cost transatlantic flights’. The power industry will work on commercial and technical enhancements before large-scale roll-out.”
Formidable barriers, then, remain to the development of electricity generation through fusion. But the possible benefits are massive. Collier spells it out: “For the first time since the industrialised age, we might not have to squabble over oil. We could have a clean, safe power source for virtually everybody – a highly-efficient energy technology, with enough fuel readily available on the planet to last for many thousands of years.
“Fusion ticks all the boxes and that is why so much money has been invested in Iter. Fusion is the golden solution but it is scientifically challenging.
“The one thing that will change the old joke that fusion energy will always be 50 years away is the achievement of energy gain at NIF.”
So, over the next two years all eyes will be on the Lawrence Livermore Laboratory. Moses says: “We used to say it’s 50 years away no matter when you ask – but I think we’re changing that paradigm.”
And Edwards adds: “If NIF ignites as expected, then we could be just 20 years away.”