Fusion 2012: A Community Holds Its Breath
December 2011 saw the publication of the Department of Energy and Climate Change’s latest roadmap to a decarbonised Britain. The Carbon Plan sets out a raft of future technologies, implemented on a grand scale, aimed at realising aspirations of an 80% UK emissions cut by 2050. Ultimately it is low carbon electricity that will enable the deepest cuts, opening the door to greener industry and transportation. The contribution of nuclear fission, Carbon Capture and Storage (CCS) and renewable technologies to this mix are discussed in detail, but nuclear fusion as a sustainable energy source is notable only by its absence. Is nuclear fusion a realistic prospect for energy generation in the coming decades?
2012 sees the final year of the three-year National Ignition Campaign (NIC) at California’s Lawrence Livermore National Laboratory. This project has brought fusion technology closer than ever before to achieving so-called ‘burn’ – the elusive net production of energy from a sustained fusion reaction. With fusion showing so much promise as a low carbon technology, why does it persistently fail to make it onto the agenda of policy-makers?
For over 50 years, there has been a dream – some would say a fantasy – of achieving fusion on Earth. The rewards are irresistible – a zero emissions source of energy which could sustain humanity for thousands, if not millions, of years. But is this sort of hyperbole justified? Is nuclear fusion really a panacea for all our energy problems?
What makes fusion so attractive is that it releases enormous amounts of energy from every gram of Deuterium fuel – and there are 33 grams of it in every ton of seawater. Only the annihilation of matter and anti-matter releases more energy per kilo than a fusion reaction – it really is the ultimate energy resource.
Furthermore, fusion also avoids many of the major safety issues associated with nuclear fission: reactions terminate instantly on malfunction, as they must be continuously fuelled, and produce only small volumes of low-level radioactive waste.
Researchers, however, have not yet achieved ‘breakeven’ – the net production of energy coming from a sustained fusion reaction needed for commercial exploitation of the technology. As the NIC programme enters its final year, hopes are high that breakeven energy production levels will be exceeded, and fusion technology will finally move towards contributing to green energy consumption.
The Power of Seawater
All fusion reactions involve the combination of two small atoms (usually hydrogen) to make a single daughter atom. This may be contrasted to conventional nuclear fission in which a single parent nucleus splits into two smaller atoms. In both cases the atom or atoms at the end of the reaction are smaller and the difference in mass (and hence the energy, E=mc2) can be turned into electricity.
The fusion process scientists are currently trying to replicate in the lab involves isotopes of hydrogen – deuterium (D) and tritium (T). If these are raised to high enough temperatures to overcome their electrostatic repulsion and fuse, a fast moving Helium nucleus is released along with a high-energy neutron. The He nucleus passes on some of its energy to the rest of the fuel, triggering further fusion reactions – the fuel begins to ‘burn’. The highly energetic particles released heat a coolant and electricity can be generated from steam in the conventional way.
The Quest for Burn
The challenge of fusion is initiating this burn wave. Only at densities of around 100 times that of lead and temperatures six times hotter than in the core of the sun will fusion fuel ignite. Here matter is in its fourth state – plasma – an electrically charged, light emitting fluid. Containing this super heated material is the unenviable task of fusion scientists. No known material will hold it – instead the fluid must be suspended in a vacuum by high magnetic fields (1,000s of times more powerful than the Earth’s), a process likened to confining a jelly with elastic bands.
If successfully contained, stimulating fusion reactions in the plasma is surprisingly straightforward – it is generating more energy from the fusing plasma than is required to heat and hold it that’s the difficult part. If the burning plasma is sustained over long enough timescales the device can produce an energy surplus.
The rewards are
irresistible – a zero
emissions source of
energy which could
for thousands, if not
millions, of years
There are two related strategies to ensure that the energy of the fusion products is deposited in the fuel before it escapes. The traditional approach is to heavily insulate the burning plasma. This is achieved by wrapping the fusing plasma in cylindrical sheets of strongly magnetised plasma, a process that hinders the flow of particles (and hence heat) through the fluid. To minimize heat loss as far as possible, the ends of this tube of plasma are joined and held in a doughnut shaped device known as a tokamak. Until the last few years Magneto Confinement Fusion (MCF) was the most mature fusion technology, and in 1997 the Joint European Torus (JET) in Oxfordshire enjoyed fusion runs of a full 10s. They achieved a record-breaking 16MW of fusion power but this fell well short of burn – 25MW of heating was required to maintain the reaction.
The ITER (International Thermonuclear Experimental Reactor), the world’s largest and most advanced experimental tokamak, is currently being built at Cadarache in the south of France, with the first plasma expected in 2019. It is hoped that the fusion reactor will produce ten times the amount of energy put in.
NIC @ NIF
Insulation is not the only method by which sufficient plasma for breakeven can be brought to fusion temperatures. Over the last two years a small satellite town of San Francisco has nurtured mankind’s most aggressive campaign for burn to date. Livermore’s National Ignition Facility (NIF) is home to 192 laser beams, the most powerful ever constructed. During each firing sequence (NIF scientists refer to each as ‘shots’) this field of laser beams bears down on a 2mm capsule of fusion fuel. The strategy here is compression – as the fuel is crushed to ever higher densities its temperature reaches fusion conditions in a central hotspot. Confined under its own inertia, should fusion occur here its energy is deposited in the surrounding plasma, sending a burn wave outwards through the fuel. The result is a miniature H-bomb, contained within a heavy-duty steel vacuum chamber.
Ignition at the NIF is tantalizingly close. The last two years have witnessed meticulous alignment of the 192 beams onto a dummy capsule. Both laser and hohlraum – the small metal cylinder which catches the laser energy and re-directs it uniformly onto the fuel pellet - have been fine-tuned and now deliver a full 1.6MJ to the target – over twice as much energy as in early tests. Latest results indicate symmetrical implosions can be achieved to the required precision to achieve burn.
It is also possible to simultaneously exploit both magnetic and inertial confinement in a device known as a Z-pinch. Here a column of fusion plasma is magnetised around its vertical (‘z’) axis and then rapidly compressed along the same axis by a pulse of high electric current through the cylindrical liner holding the fuel. Known as MagLIF (Magnetic Liner Inertial Fusion) the concept has yet to be tested in its full form but remains the most theoretically efficient method of raising fuel to fusion conditions.
In September 2011, NIF announced record neutron yields from a DT capsule. They had achieved densities of more than a kilo per cubic centimeter – less than a factor of three short of the 1.5-3kg/cm3 they predict will sustain a burn wave. With another year of fine tuning ahead, and a further 0.2MJ of laser energy in hand, fusion scientists are on the edge of their seats – will 2012 see the birth of a fusion future? Will we see ignition at NIF?
On paper, there is no doubt burn should, and it will, be possible. Yet some serious technical questions must be answered before energy derived from fusion becomes a reality. Current designs plan to harvest the fusion energy by encasing the reaction chamber interior in a flowing wall of metallic Lithium. This process neatly addresses the twin problems of extracting heat energy from the vessel and generating fresh Tritium fuel – each fusion neutron deposits its energy in the Lithium blanket and transmutes a Lithium atom into one of precious Tritium. But can this process be realized safely? Will it deliver sufficient Tritium and can we extract it? Above all, will it transfer sufficient heat to the steam turbines to generate profitable amounts of electricity/electric power?
Lab to Grid
In the low carbon future painted by The Carbon Plan1, over 30% of UK electricity will be drawn from renewable sources by 2030, 20% from CCS coal fired plants and a further 20% from an armada of proposed fission reactors. The plan, however, states “It is impossible to predict what the power generation sector will look like in 2030” – clearly there is still room for fusion to be a powerful ally in the quest for 80% lower emissions.
The premise behind fusion-generated power is that, with ignition in hand, we have a process that can take socket electricity and release around ten times more fusion energy. But can we capture it? And can we sell it? These are difficult questions given the uncertainty surrounding future energy prices and capital costs – the only answer for now is: we will certainly try.
The economics favour larger fusion power plants as fusion is capital-intensive with low operating costs. Pricing projections are very difficult at this stage given that demonstration plants are not likely to be fully operational for up to 20 years, but models suggest that fusion could play a major role in the second half of the century2. This will depend on the cost of fusion power relative to the cost of alternatives and environmental and market constraints such as carbon pricing.
If NIF succeeds, the reaction of the international community will be swift as it is well prepared. NIF scientists have already drafted plans for an ICF power plant – taking the ignition process and getting its energy onto the grid. The LIFE project plans for a NIF scale facility to be generating 400MW by the mid 2020s. Similar timelines apply to DEMO, a follow-on commercial demonstration plant proposed by ITER. If successful, GW scale stations could be on the market as early as the mid 2030s.
Fusion is an expensive experimental-facility dependent science. With a single NIF fuel pellet costing £25,000, and the entire project at £2.5bn3, it is no surprise that global economic conditions affect these world-leading facilities. Indeed, such is the level of investment and international cooperation required per reactor that it was Thatcher, Reagan and Gorbachev who commissioned the ITER tokamak in 1985, construction of which ultimately began in 2007. Today, it finds itself in an economic environment unable to shell out for its spiralling construction costs.
At a 34% stake, it is the EU who bears the financial brunt of this crunch – last year’s £1.2bn shortfall in construction payments, ultimately resolved by a heroic re-jig of some future EU budgets, is the tip of the iceberg when it comes to financing the facilities required to steer towards DEMO.
The US hedges their bets with a 13% stake in ITER – ensuring their plasma scientists will be at the cutting edge in the tokamak community should the NIF fail. With a 10% share in ITER, China is involved in cutting-edge fusion for the first time, and they claim4 to be training 2,000 new plasma specialists to ensure a return on their investment.
A Future for Fusion?
All eyes are on Livermore. Will laser-driven fusion finally unlock the power of the hydrogen atom? If NIF achieves ignition this year it will be a long overdue morale boost for the scientists and politicians who have supported these long-running fusion initiatives. It will also ensure future funding for LIFE, DEMO and other demonstration fusion power-plant projects, and support for further research on tokamak and Z-pinch approaches: it is too early to rule out any alternative, potentially more efficient, fusion strategies.
Investment in renewables is at an all time high, with global spending at over £130bn5 in 2011. The British nuclear industry alone anticipates a £300bn6 bill for the next generation of fission plants. The global environment is at stake and the future of the energy sector is to play for – whatever happens at NIF next year there is surely room to drive their findings ahead with renewed intensity to realise the incredible potential of fusion.
Philip de Grouchy & Arthur Turrell are PhD students in the Plasma Physics group at Imperial College London.
 Smith C. L. & Ward D. (2008) Fusion. Energy Policy. 36(2008): 4331–4334.
 National Ignition Facility
 Ministry of Science and Technology of the People’s Republic of China (2011) [press release] 22 March. Available at: < http://www.most.gov.cn/kjbgz/201103/t20110321_85526.htm >
 UNEP & Bloomberg New Energy Finance (2011) Global Trends in Renewable Energy Investment 2011.
 Nuclear Industry Association (2010) UK Nuclear: Powering the Future.