All of these advantages come with a price. The resulting system will be more complicated than a conventional reactor and therefore probably more expensive. Even if the price were higher, however, it is still likely to be competitive with any alternatives once cheap fossil fuels are taken out of the equation, unless somebody comes up with a 100 per cent efficient way to store energy for free. The big challenge, however, is that no proton accelerator of sufficiently high power and reliability to drive such a device currently exists. Partly that is because there has never been a need for such a machine, but it is certainly true that producing a reliable enough accelerator would require substantial improvements to currently available technology. These improvements would probably be embodied in a new kind of accelerator called an FFAG, which is also being developed for medical and other applications. If ADSRs are ever to contribute to our energy future, we urgently need research on higher-power, more reliable accelerators. 

Is the lack of an accelerator the only reason that ADSRs are not already in use? I don't think so. The idea itself is rather old, having been first proposed by the Nobel Prize-winning physicist Ernest Lawrence in the 1950s, and revived by Charlie Bowman at Los Alamos and especially by another Nobel Laureate, Carlo Rubbia, when he was Director-General of Cern in the 1990s. There is current active work on this idea throughout the world, especially on the continent and in Japan. However, this has not yet led to any working device, and there has been little work within the UK until recently. Partly I think this arises from a Catch-22 — if people think the technology is useful they probably don't think it is necessary. That is because for some years people in the UK have usually fallen into two camps on nuclear power. The larger camp thinks it vile, nasty and dangerous and it doesn't want any part of it, accelerator driven or otherwise. The other camp thinks nuclear power is just fine and doesn't see why you need something as complex as an ADSR when normal reactors work so well. I hope that we are going to come to a more considered view of both the strengths and weaknesses of nuclear power, and a more rational evaluation of any dangers, because otherwise we risk ignoring the one workable low-carbon energy generation technology we may actually get in time to avert catastrophic climate change.