These are testing times for the oldest, boldest and most expensive scientific project in history. Crucial experiments are about to begin on the world’s most advanced nuclear fusion reactor, the Joint European Torus (JET) near Oxford, England. And their outcome could decide the fate of the decades-long quest to bring the power source of the stars down to Earth.
Among scientists, it’s a quest that routinely provokes snorts of derision, and jokes along the lines of “Nuclear fusion is the power source of the future – and always will be”. Among the public, it is one that has long been misunderstood.
There’s a widespread belief that even after decades of effort, scientists have so far failed to trigger nuclear fusion, in which the cores of hydrogen-like atoms are heated to temperatures hotter than the Sun’s core and fuse together, releasing energy via Einstein’s famous equation E = mc².
In reality, scientists first achieved nuclear fusion more than 60 years ago – albeit in an uncontrolled form – during tests of thermonuclear weapons on the Pacific island of Eniwetok. Even then they were drawing up plans to build “fusion reactors” that could harness the same energy safely.
Again, contrary to widespread belief, they have also succeeded in doing this. In 1997, the JET fusion machine produced over 16 megawatts of nuclear fusion power.
The real challenge facing nuclear fusion researchers is not one of principle – that was demonstrated long ago. It is one of practice, specifically that of turning fusion into an economically viable form of power.
This is the prism through which all achievements in the long history of fusion tend to be seen. Take that most celebrated of the field’s achievements thus far, the generation of 16 megawatts (MW) of fusion power.
That seems pretty impressive until one looks behind the headline figure. For a start, it was maintained for just two seconds, and even then required an input of 24 MW to achieve – which cynics have pointed out are hardly ideal performance figures for a power station. But this overlooks the fact that JET was never intended as a power station. It is an experiment – and this month sees the start of the most important experiments carried out since those headlines in 1997.
Scientists at JET are about to start testing new materials for the reactor walls, to see how they handle the demands of fusion.
It is not enough for the materials to withstand repeated blasting at temperatures in excess of 200 million°C plus intense radiation. They must not undermine the fusion reactions taking place around them, by cooling or polluting them. And they must be cheap – or, at least, cheap enough to keep fusion economically viable.
The JET team started work on this huge challenge some years ago, replacing the reactor’s original carbon composite walls with panels made from beryllium and tungsten.
Carbon was originally used because it’s both very heat-resistant and cheap. But it’s not good enough for commercial power reactors, as it interacts with tritium, the radioactive hydrogen-like “fuel” they will use.
The replacement materials are far from ideal, however. Beryllium behaves better than carbon with the fuel, but is far less heat resistant. On the other hand, tungsten can withstand high temperatures but can poison the burning fuel, causing huge energy loss. Neither material is cheap, either.
Still, in the absence of obvious alternatives both are being tested in JET – and the results will fed through to JET’s successor, the International Thermonuclear Experimental Reactor (ITER), due for completion in France by 2020.
If all goes well, a fusion machine might finally start feeding power back into the electricity grid rather than extracting it around 30 years from now.
Yet there is a real possibility that the quest for fusion won’t be allowed to run its course. When it began, there was global concern about energy demand outstripping supply. Then came fears of catastrophic climate change triggered by fossil fuels. Both gave fusion a political tailwind.
But since the financial crisis, fears of global warming have given way to demand for cheap energy, and all eyes are on shale gas, huge supplies of which are turning up around the world.
For cash-strapped governments, the case for quitting the international fusion programme has surely never been stronger. After all, is it really plausible that machines harnessing the power source of the stars could ever produce energy as cheaply as drilling holes in the ground?
This is where fusion scientists must themselves combat the biggest misconception about what they’re doing. The truth is that, even after 60 years, there are still major scientific questions to be answered about controlling fusion.
As such, machines such as JET are really multinational experiments in the tradition of the Large Hadron Collider.
That too is part of a decades-long quest that has cost billions so far – and its insights have essentially no relevance to any global problem. In contrast, the experiments planned for JET could uncover utterly unexpected physics that make fusion power easier to attain than anyone thought. Fusion scientists have already seen glimpses of phenomena no one predicted.
Experiments on a small JET-like machine in Germany in the 1980s suggested that a beam of atoms squirted into the intensely hot fusion fuel persuaded it to become much more stable. Theorists hadn't predicted this so-called H-mode
effect, and it took years of experiment to reveal that it's a key benefit of using any machine like JET.
The experiments starting this month will help show whether the new materials used in the walls keep this advantage – or perhaps make it better still. No one knows for sure. But that’s the thing about science – only experiments can reveal the reality.
Finding out if fusion power can be made a reality has taken decades and cost billions of dollars. Yet that’s less than 1 per cent of the annual global energy market. Can anyone be certain today’s energy sources will meet our needs decades from now?
Seen in those terms, the quest for fusion reveals itself to be a small but canny investment in human curiosity.
Robert Matthews is visiting reader in science at Aston University, Birmingham, England
