20 December 2011
ITER Organization’s Krista Dulon gives an overview of how the organisation is paving the way for fusion as a viable and virtually limitless energy source
In a global context of rising oil and gas prices, decreased accessibility to low-cost fossil fuel sources, and an estimated three-fold increase in world energy demand by the end of this century, the ‘energy question’ finds itself propelled to the front of the stage. How will we supply this new energy, and how can we do so without adding dangerously to atmospheric greenhouse gases?
Fusion scientists believe that they can make an important contribution to the sustainable energy mix of the future. Fusion, the nuclear reaction that powers the sun and the stars, would provide a safe, non-carbon emitting and virtually limitless source of energy. Consequently, during next 30 years, the world will be watching the ITER project in southern France, where a consortium of nations is building the world’s largest fusion device.
A global collaboration
ITER is a large-scale scientific experiment intended to prove the viability of fusion as an energy source, and to collect the data necessary for the design and subsequent operation of the first electricity producing fusion power plant. Six nations plus Europe have agreed to pool their financial and scientific resources to realise this unique research project; and although it will never produce electricity, it will take fusion to the point where industrial applications can be designed.
The project was the fruit of a 1985 summit in Geneva between Soviet Secretary General Mikhail Gorbachev and US President Ronald Reagan, during which the leaders agreed to cooperate to develop fusion as a ‘source of energy…for the benefit of all mankind’. The design for a large, international fusion facility was collaboratively developed by the Soviet Union, the US, the EU and Japan from 1988 to 2001, and this has provided the basis for the project that is taking shape today.
The members of the project are: China, the EU, India, Japan, Korea, Russia and the US, each of whom contribute components to the machine and share in the management aspects of the project, including scientific collaboration, finance, staffing and auditing. ITER is staffed by approximately 500 people from the member communities, and as nearly as many contractors. Domestic agencies located in each ITER member country organise procurement activities and conclude contracts with industry.
Construction of the ITER scientific buildings began in 2010. Over the next eight years, the facilities will be erected; components shipped from all around the world will be assembled into the ITER device; and a commissioning and testing phase will ensue. The operational campaign will begin with First Plasma in 2019, followed by 20 years of physics experiments. The project is truly an international endeavour. The seven members together represent over half of the world’s population and 80% of the world’s GDP. The ITER tokamak will be the flagship device of the world fusion programme.
Fusion: at work in the stars
Fusion is one of nature’s most spectacular achievements. Billions and billions of fusion furnaces, the sun among them, are flaring in the universe, creating light and energy. Some 70 years ago, scientists discovered the physics behind this wonder: the sun and stars transmute matter, tirelessly transforming hydrogen nuclei into helium atoms and releasing huge amounts of energy in the process.
In the sun, fusion reactions take place in a context of enormous gravitational pressure and very high temperature (15 million degrees Celsius) – conditions that enable the natural electrostatic repulsion that exists between the positive charges of two nuclei to be overcome. The fusion of two light hydrogen atoms (H-H) produces a heavier element, helium. The mass of the resulting helium atom is not the exact sum of the two initial atoms, however, as some mass has been lost and great amounts of energy have been gained. This is what Einstein’s formula E=mc² describes: the tiny amount of lost mass (m), multiplied by the square of the speed of light (c²), results in a very large figure (E), which is the amount of energy created by a fusion reaction.
Capturing fusion on Earth
With the understanding of the process of celestial fusion came the ambition to reproduce, here on Earth, what was happening in the stars. The first fusion experiments in the 1930s were followed by the establishment of fusion physics laboratories in nearly every industrialised nation. By the mid-1950s ‘fusion machines’ of one kind or another were operating in the Soviet Union, the UK, the US, France, Germany and Japan. A breakthrough occurred in 1968 in the Soviet Union where, by using a doughnut-shaped magnetic confinement device called a tokamak, researchers were able to achieve temperature levels and plasma confinement times – two of the main criteria for achieving fusion – that had never before been attained. The tokamak became the dominant concept in fusion research, and such devices multiplied across the globe.
Experimentation allows physicists to identify the most promising combination of elements to reproduce fusion in the laboratory: the reaction between the two hydrogen (H) isotopes deuterium (D) and tritium (T). The D-T fusion reaction produces the highest energy gain at the ‘lowest’ temperatures, nevertheless still requiring temperatures of 150,000,000°C – 10 times higher than the H-H reaction occurring at the sun’s core. At these extreme temperatures, electrons are separated from nuclei and a gas becomes plasma – a hot, electrically charged gas. In a fusion device – as in a star – plasmas provide the environment in which light elements can fuse and yield energy. The D-T fusion produces one helium nuclei, one neutron and energy.
To achieve net fusion power in a D-T reactor such as a tokamak, the three conditions of the fusion triple product must be fulfilled:
•A very high temperature (greater than 100 million degrees Celsius);
•Plasma particle density of at least 10²² particles per cubic metre; and
•An energy confinement time – the time in which the plasma is maintained at a temperature above the critical ignition temperature – for the reactor on the order of one second.
From the 1950s onwards, it has been clear that mastering fusion would require the marshalling of the creative forces, technological skills, and financial resources of the international community. A first step in this direction was the Joint European Torus (JET) in Culham, UK, which has been in operation since 1983. In 1991, the JET Tokamak achieved the world’s first controlled release of fusion power, and steady progress has since been made in such devices around the world. The Tore Supra Tokamak (France) holds the record for the longest plasma duration time of any tokamak: six minutes and 30 seconds. The Japanese JT-60, meanwhile, achieved the highest value of fusion triple product of any device to date, and US fusion installations have reached temperatures of several hundred million degrees Celsius.
To yield more energy from fusion than has been invested to heat the plasma, it must be held at this temperature for some minimum length of time. Scaling laws predict that the larger the plasma volume, the better the results. The ITER tokamak chamber will be twice as large as any previous tokamak, with a plasma volume of 830m3. It is designed to produce 10 times the energy that is required to make the plasma: 500MW of fusion power for 50MW of input power (Q≥10). Although ITER will not convert this power to electricity, it will be an important demonstration of the potential of fusion.
One of the tasks awaiting ITER is to explore fully the properties of super-hot plasmas and their behaviour during the long pulses of fusion power the machine will enable. The challenge will be very great. ITER’s plasma pulses will be of a much longer duration than those achieved in other devices, creating intense material stress. It will be used to test and validate advanced materials and key technologies for the industrial fusion power plants of the future.