Bringing the sun to earth

As energy resources become increasingly constrained, now is an opportune time to look at the latest advances in nuclear fusion.

Although oil prices have recently retreated, the highs seen back in July are still uppermost in peoples’ minds in terms of our long-term energy needs. Indeed, there are a number of factors that make a pressing case for the development of new and cleaner ways to produce energy. These include forecasts that suggest the world’s population will exceed a staggering 9bn by 2050, the rapid urbanisation underway in developing economies and the growing threat posed by global climate change. One well-known means of eventually solving the world’s energy problems is the harnessing of nuclear fusion to generate energy in a manner which maybe more familiar to the man or woman on the street, given that it is the very same process which fuels our Sun and every star in the night sky.

The most popular form of nuclear fusion research is in the form of Torus or Tokamak machines, which are usually doughnut-shaped and use magnetic fields produced by superconducting coils to trap plasma (gas heated to the point where it loses its electrons), in such a way as to prevent it from hitting the sides of the machine. Generally, the vessel must be heated up to over 100m^oC before fusion reactions can occur. This is typically done by passing an electric current through the plasma, although other methods such as using the magnetic fields to compress the plasma are also used.

One recent step towards the goal of a sustainable fusion reaction is the news that the Korean Superconducting Tokamak Advanced Reactor (KSTAR) succeeded in generating plasma for 0.3 seconds at a temperature of 10m^oC. Korea’s National Fusion Research Institute, which operates KSTAR has set itself the target of bettering this result by a factor of 100 by 2016.

The world’s largest Tokamak is the Joint European Torus (JET), located in the UK. It features plasma heating systems, which have the capacity to deliver up to 30MW and other refinements. One of JET’S most impressive successes has been reaching the so called ‘break-even point’, when the fusion reaction is producing the same amount of energy as that being fed into the reactor.

Although JET has helped to expand our knowledge and expertise in working with plasma, many scientists are increasingly looking to what will be the next major research project in the field: the International Thermonuclear Experimental Reactor (ITER). Its purpose is to demonstrate that electrical power can be produced from fusion and to obtain the data needed to produce a commercial plant. The project is being funded by the EU, USA, Russia, China, India, Korea and Japan. The EU is expected to provide half of the funding, with the other partners contributing equal shares. However, the USA has suspended its funding for budgetary reasons, which affected the entire US physics establishment, causing many redundancies in the process. Yet, according to ITER’s Neil Calder, the proposed budget for 2009 is more favourable, although it is still subject to review. He also explained in an interview, that ITER’s international nature gives it a certain amount of resilience, but this is not limitless and therefore the extent of future US funding is a serious matter.

ITER once built, will be the largest Tokamak in the world.
It is expected to be complete by 2016.

The project had been delayed for over 18 months due to fierce competition between France and Japan for the right to host the project. Eventually a compromise deal was reached in which Japan received 20 per cent of the research posts and won the right to host a materials research facility, to be half funded by the EU, while ITER itself is to be built in Cadarache in the south of France.The project has been set more ambitious goals than KSTAR, with scientists looking to maintain the plasma for 500-1000 seconds at a time, generating 500MW of power. Nevertheless, the energy produced is not expected to be a net gain and will not be connected to a grid.

ITER, like the projects before it, will benefit significantly from the openness and the good communications that characterise the field of nuclear fusion research. However, it is expected to result in novel technologies with highly-valuable applications and therefore will be subject to intellectual property rights. These will no doubt be convoluted, given the number of countries providing funding.

ITER’s Torus is to be made from nine sectors, each one 13m high and weighing a heavy 250t. The organisation called for EU companies to place tenders for seven of the sections in a July 17 note in the EU Official Journal. The first full experiment is to take place in 2018.

Although ITER will steal a great deal of JET’s limelight, JET will be able to support the efforts of its successor, particularly as it is better suited to the study of fast alpha particles, which need to be contained during a fusion reaction. Its unique tritium handling capacity also means that JET can investigate burning plasmas, which have a high rate of deuterium-tritium reactions. JET was significantly updated in 2004-5 and a further programme of development is in progress, with an “ITER-like wall”, “Neutral beam enhancement” and a “high frequency pellet injector” due for installation over the course of this year.

The first of these developments reflects the fact that many of the challenges involved in nuclear fusion revolve around finding and developing materials capable of surviving the enormous temperatures associated with superheated plasma, while at the same time, without interfering with the experiments. Currently, JET uses carbon composite tiles for the first wall between the reactor and the plasma. However, this is not suitable for experiments involving tritium. Therefore, JET is to be refitted with a wall which uses carbon, tungsten and beryllium in the areas most suited to each material. Such an approach is also to be employed with ITER. Tungsten is highly temperature resistant but does ionise, which can cause energy losses, while beryllium melts at just 1284°C, but due to its low atomic number, does not ionise to the same extent as tungsten.

Interestingly, materials scientists have gained insight into how steel is affected by high temperatures due to the meticulous research into the collapse of the World Trade Centre on September 11, 2001. The current theory is that steel loses a great deal of its strength at high temperatures, as tiny flaws in its structure disrupt its internal magnetic fields, making it softer. This explains why the steel supports of the towers collapsed despite temperatures well below the metal’s melting point. Scientists at the UK’s Atomic Energy Authority (UKAEA) are now looking to alter the composition of the steel to be used in ITER to eliminate this phenomenon.

ITER certainly won’t be the last word in large-scale magnetic containment research projects. Its successor, DEMO (Demonstration power plant) is already being discussed. It is expected to one day produce 2GW of power continually (25 times that required for break-even). To achieve this, it would have to be 15 per cent larger than ITER and boast a plasma density 30 per cent higher than its predecessor. DEMO is still a long way off, with initial estimates suggesting that it will go into operation in 2033.

Other magnetic containment fusion projects on the drawing board include the KTM in Kazakhstan, the Next Step Spherical Torus (NSST) in Princeton, USA, Proto-Sphrea in Italy and QUEST, which is expected to be commissioned soon in Kasuga City, Japan.

There seems to be a healthy trade in secondhand Tokamak reactors. The Czech Republic received delivery of the Compass Tokamak in October 2007, which was originally used by British scientists and became surplus to requirements thanks to a larger reactor called Mast. Compass will replace a small Tokamak called Castor, developed by Russia in the 1970s. The field of nuclear fusion owes much to Russia. Even the word ‘tokamak’ is of Russian origin and although the first patent associated with nuclear fusion was registered in the UK, much of the early development occurred in Russia in the 1950s.

Chris Llewellyn Smith, the former Director-General of CERN, has made it clear that the timescales involved are long, with perhaps a decade needed to fully understand the results from ITER and “considerably more than 30 years before fusion can be rolled out on a large scale,” (CERN Courier). However, he pointed out that given the finite nature of fossil fuel resources, “we have to go with fusion as fast as we can.”

Neil Calder is of a similar opinion. In an interview with IFandP, he explained that the main limitations in terms of nuclear fusion research are funding and labour. He pointed to the Manhattan project and the Apollo programme as examples of incredibly technically demanding goals that were realised quickly thanks to huge financial backing and massive amounts of manpower.

While speculating as to what could trigger such an attitude towards nuclear fusion research, Mr Calder suggested that dramatic impacts from global warming could be more significant than increasing energy prices, although he cited the latter as a key reason behind the level of backing already provided to ITER. In his opinion, a major obstacle to further support for nuclear fusion is its association with conventional nuclear power within the public mindset, along with related concerns regarding radiation, nuclear waste and safety.

While environmentalists attack nuclear fusion on the grounds that its benefits will take a long time to materialise in comparison to the same investment in renewables, Mr Calder believes that fusion is a long-term solution to the problem of global warming and fossil fuel depletion, especially as while climate change may be a pressing issue, “the world doesn’t end 50 years from now.”

Fusion through laser technology

There is another method by which a successful nuclear fusion reaction could be achieved. Known as inertial fusion energy (IFE), this makes use of incredibly highly- powered lasers. To a certain extent, the basic processes are an exaggerated version of those seen in the internal combustion engine: compression, followed by ignition. A small spherical capsule containing a mixture of deuterium and tritium is cooled, so the gas freezes as a film on the inner surface of the capsule. A laser pulse, which can be a mere few billionths of a second, would then heat the interior of the capsule to several hundred times the temperature of the sun. The resulting plasma is under immense pressure, equivalent to hundreds of millions of atmospheres. The intense conditions are theoretically enough to trigger a propagating nuclear fusion reaction within the residual gas at the centre of the chamber. With refinement, it is expected that this technique can generate 70 times the energy required for ignition.

A step towards this goal has already been taken. Earlier this year, the Vulcan laser, located at the Central Laser Facility, concentrated power equal to 100 times the entire world’s electricity generation, into a target a few millionths of a metre across. The pulse lasted for one trillionth of a second and the target reached 10m^o, one-tenth that required for fusion.

According to Richard Petrasso, a senior research scientist at MIT’s Plasma Science and Fusion centre, a successful reaction requires a perfect spherical shape to be maintained for the duration of the implosion. Having invented methods by which the magnetic fields around the pellet can be monitored during implosion, the centre is working to fine tune the process.

As with magnetic confinement fusion reactors, the resulting heat would be captured and used to generate steam. According to Professor Peterson of the University of California, Berkely, large-scale commercial IFE plants will one day be made up of three separate facilities: a target chamber with an attached heat recovery plant, a target fabrication plant and a driver.

The American National Ignition Facility (NIF) in California is looking to use 192 lasers, each of which is more powerful than any currently in operation, to induce inertial fusion. The facility is expected to be up and running by 2010.

2014 is anticipated to see the completion of HiPR, the High Power Laser Energy Research Facility. Currently, the UK is favourite to host the project, which will represent a collaboration between 11 European countries and has already entered a three year preparatory phase, with detailed design to follow in 2011. As the facility’s official site indicates, inertial fusion is expected to be achieved by 2010, HiPR’s role is likely to be concerned with refining the technology to the point where it can actually be used in a power plant.

Implementing nuclear fusion

Once nuclear fusion has developed to the point at which it can deployed, it won’t immediately result in limitless energy for everyone. As Mr Calder points out, once it is suitable for commercial use, the costs and construction times of fusion plants will be comparable to those of current nuclear plants. Although fusion reactors will be safer and produce far less radioactive waste, he expects planning permission and other regulatory processes to still take around the same amount of time.

However, it will mean that countries that are deemed too unstable and are today considered nuclear proliferation risks will be able to build their own fusion reactors.

Importantly, both nuclear fusion technologies once they mature to the point where they can be used by power utilities, will not represent a total reinvention. They will use many of the technologies already used by today’s nuclear reactors and coal-fired plants, primarily in terms of electricity generation from steam and heat recovery. However, it is anticipated that nuclear fusion reactors will be used solely to provide baseload power, due to economic reasons as such high levels of availability and reliability will be an essential requirement.

One idea that has recently been proposed, has gained much of its inspiration from the rapidly growing LNG industry. The concept – that of “fusion islands”, proposed by William Nuttall and Bartek Glowacki – involves using nuclear fusion to produce hydrogen by electrophoresis or the more thermodynamically favourable high temperature sulphur-iodine cycle, which can then be cryogenically cooled and transported in a manner similar to today’s LNG carriers, before being used in hydrogen-powered fuel cells or internal combustion engines, to power vehicles.

Too much of a good thing?

One of the hopes associated with nuclear fusion is that it will eventually lead to limitless and clean energy to be harnessed for the good of civilisation. What could be the effect of such an abundance? Well, for one thing, a great deal of waste. Given that essentially free energy would remove the incentive for consumers to be efficient in their usage, it is easy to envisage a scenario where energy consumption rockets upwards and with it, heat. Although nuclear fusion doesn’t produce greenhouse gases, which trap heat in the earth’s atmosphere, a great deal of heat is produced by the electrical devices we use. Taken to an extreme, we could find ourselves warming up the earth, even after decarbonising our energy system.

That said, if fusion reactors, as and when they become a reality, cost as much as the current nuclear fleet, then that combined with the practical constraints in building huge numbers of reactors, should prevent such a scenario. Additionally, at the point where the cost of energy reaches close to zero, it is to be hoped that we will have matured to the point where we can use energy in a ecologically responsible way.

In any case, perhaps as Mr Calder points out, “it is a much safer and better situation to have too much energy, as opposed to everyone fighting over it.”

For more information, consider visiting the following websites:
www.hiper-laser.org/
www.iter.org
www.jet.efda.org/