The UK is to cooperate with a US project to develop nuclear fusion - the energy that makes the stars shine. If fusion works it will change everything giving us plentiful energy from a limitless fuel, and a world free from the geopolitics of oil and carbon pollution. But don't get carried away just yet.
Nuclear fusion power is a long-held dream. It was first suggested during World War 2 when atomic weapons were being developed. The first atom bombs were based on nuclear fission - the explosive power of radioactive atoms. But soon afterwards far more powerful atomic weapons were made based on fusion - the coming together of hydrogen atoms. It was realised that nuclear fission could be used for power plants, and some hoped fusion would work too.
Nuclear fission power, involving heavy atoms such as Uranium and Plutonium is relatively simple when compared to fusion. You just need to get enough of the naturally occurring radioactive material and mould it into a suitable shape. Radiation from the nuclear fuel can be used to create steam and drive turbines. It's a successful technology. There are today 440 nuclear power stations in operation with a further 65 under construction. But there are problems. Radioactive waste and the potential to use the technology to make bombs, nuclear or dirty.
In the 1950's it was thought plentiful fusion power had been achieved. UK scientists announced to the world they had achieved a breakthrough using their ZETA project that stood for Zero Energy Thermonuclear Assembly. Soon afterwards it was realised they had been mistaken, and the incident has dogged the fusion effort ever since.
Fusion is a much more complicated route to energy than nuclear fission. High temperatures are required to force hydrogen together to liberate the energy. There are broadly two major approaches. The first is to heat a gas to temperatures of about fifty million degrees - hotter than the centre of the sun. The gas becomes what is termed a plasma as the heat breaks apart atoms into their constituent nuclei and electrons. Hopefully, the nuclei of hydrogen atoms will be pushed together by the heat. The problem has been that far from being a simple thing a plasma is among the most complex and cantankerous substances known to man. They are incredibly difficult to confine - requiring a "magnetic bottle" - and control being prone is all sorts of instabilities and unpredictable effects.
Nonetheless some progress has been made using the JET experiment reactor near Oxford. The next stage is ITER, a multinational project being constructed in the south of France. It is designed to define the broad parameters of a commercial fusion reactor. It is anticipated that it will create its first plasma around 2020, and carry on researching for a further 15 - 20 years.
The other way, the subject of the UK-US agreement, is to achieve the high temperatures required for fusion by firing powerful lasers from all directions at a hydrogen isotope pellet. The pellet gets crushed and hopefully heated to a degree where fusion can occur. Technically it's a nightmare involving marshalling high-power lasers, amplifiers and optics using tuners and delay devices to allow the laser pulse to arrive at the pellet from 192 different directions at precisely the same instant. Progress in solving these problems has been good and the project's director Ed Moses sees a significant milestone ahead - ignition. This is when more power comes out than is put in, "our goal is to have ignition within the next couple of years," he says.
The Sun in a Box
But the lesson of fusion is that it's always harder, takes longer and is more expensive that one predicts. Trying to put the power of the sun in a box is an audacious goal, especially when we don't know how to design the box.
We've walked on the moon, sequenced the human genome, invented the internet, so why has commercial fusion eluded us? There are very few science projects that have been going on for over sixty years that have still not come anywhere near a conclusion. Perhaps in a world awash with oil it hasn't had the urgency it could have had, or perhaps it's not been managed as aggressively as it could have been, or funded as much as it needed. Perhaps it will never be possible to do it commercially. In heralding the new agreement the UK's science minister David Willetts was more than a tad too optimistic when he proclaimed that fusion could "no longer be dismissed as something on the far distant horizon."
The fact is it is on the far distant horizon. It always has been. Only the very youngest of the scientists working on fusion power will still be working when and if we get a commercial reactor. But we have no choice and we don't have more decades to wait. With the international imperative to phase out carbon-based energy sources we have to face the fact that renewables, wind, wave and solar cannot provide the energy density required to support the needs of a high population industrial society. Fusion power, with its minimal carbon footprint, is just what we need. It is powerful, concentrated and uses water as fuel.
I wonder if in a hundred years' time clusters of fusion reactors positioned alongside the coast or major inland waters will be providing us all with reliable, almost pollution free energy? Is nuclear fusion power as far away in the future as the first Beatles' hit is in the past, or will it be a scientific gamble that will fade in the face of technical complications?