In the fifty years that research on nuclear fusion has been carried out, enormous scientific and technological progress has been made. Fusion scientists now manipulate plasmas of hundreds of millions of degrees, in fusion devices on an industrial scale.
Figure 1:The progress of fusion research through the years, measured by the triple
product, which is an indication of the performance of a fusion plasma. Please note
the logarithmic scale on the vertical axis. F or comparison, the development of
computer chips is indicated.
The figure above shows the progress of the so-called "triple product", a figure-of-merit which measures the performance of a fusion plasma. The triple product has seen an increase of a factor of 10.000 in the last thirty years, and another factor of 6 is needed to arrive at the level required for a power plant. In the figure, the progress is compared to that of computer chips.
JET, based in Culham, Great Britain, is the central research facility of the European Fusion Programme. The focusing of significant European fusion research funding on JET has made it the pre-eminent fusion facility in the world and allowed Europe to take major strides in fusion research. JET is complemented by a number of specialized smaller devices run by more than twenty individual EU member states. The largest tokamak experiments outside Europe are the Japanese tokamak JT-60 and the American TFTR device in Princeton.
JET was approved in 1974, began operations in 1983, and met its planned operational goals on schedule in 1990. Since then, a new scientific programme has started, and JET now serves as a research facility hosting a large number of international research efforts.
Figure 2:A look inside the plasma vessel of
the Joint European Torus (JET). JET is located
in Culham, GB.
JET has produced significant fusion power in deuterium/tritium plasmas - up to 16 MW - in the short pulses characteristic of existing experimental devices. "Break-even" conditions, where the fusion output power equals the external input power required to heat the plasma, were almost reached. Moreover, JET has demonstrated that fusion devices can be operated safely with tritium fuel and that radioactive structures can be maintenanced and modified using remote handling techniques.
Although it is the largest in the fusion family, the Joint European Torus (JET) is still too small to generate more energy than is put in: to generate 16MW of fusion power in JET, 25 MW is needed as input. There is a simple physical principle behind this: small things cool down quicker than large things - soup in a spoon cools down quicker than soup in a large bowl. That is why it seems logical to construct a larger device, in which it should be easier to keep a plasma hot. The next step in fusion research is ITER, which has twice the linear size as JET. ITER is designed to generate 500 MW fusion power, ten times more than is needed to keep the fusion plasma in the right condition.
ITER is a large scale, international experiment that should demonstrate the scientific and technological feasibility of using fusion as an energy source on earth. ITER will allow the study of plasmas in conditions similar to those expected in a electricity-generating fusion power plant. It will also test a number of key technologies for fusion including the heating, control, diagnostic and remote maintenance that are expected to be needed for a real fusion power station. Extensive information on ITER can be found in the ITER section of this website, and on the homepage of the ITER-project.
Figure 3:The ITER-device. The man in the
bottom indicates the scale.
ITER started in the 80ies as an initiative of the former presidents Reagan and Gorbatsjov; the current partners in the project are the European Union, Japan, the Russian Federation, China, Korea, India, and the USA, which means that more than half of the global population is represented in the project.
ITER will be a machine of the tokamak type in which the torus-shaped fusion plasma is confined by strong magnetic fields (see illustration). Compared with current conceptual designs for future fusion power plants, ITER will include most of the necessary technology, but will be of slightly smaller dimensions and will operate at about one-fifth of the power output level.
In June 2005, the partners in the project decided unanimously to choose the European site at Cadarache, in the South of France, as the location for the construction of ITER. The design of ITER is ready for the start of construction to begin, and the first plasma operation is expected in 2016.
ITER is a unique project, which needs very advanced technology, and will ask the utmost from materials, scientific understanding, and international cooperation. For sure, ITER is one of the most complex, challenging and innovative project in the world today.
No radioactive products are produced by the fusion reaction itself. However, very energetic neutrons are produced by the fusion reactions, which interact with the walls of the plasma chamber and of the internal components, and activate their materials.
The radioactivity generated by this process will depend on the choice of materials used for the construction of the components, which opens the possibility to reduce the level of waste from future fusion power plants by developing the right materials. This is a field of active research, where low-activation materials such as vanadium and chromium alloys are developed. Ceramics and fibre-composite materials are also being examined because of their potential use as low activation materials in the longer term.
Since the mid-1990´s, design work has been carried out on an International Fusion Materials Irradiation Facility (IFMIF) in which materials can be tested and developed in time for ITER´s successor. The results of the material development studies conducted so far, show that the radioactivity produced during the operation of fusion power stations should decay rapidly to levels where recycling would be possible, typically in about a hundred years.
ITER is not an end in itself: it is the bridge toward a first demonstration power plant that will deliver large-scale electrical power to the grid. The long-term aim of fusion research and development in Europe is to create power station prototypes demonstrating operational safety, environmental compatibility, and economic viability.
The strategy to achieve this long-term aim includes a number of different elements: first of all the development of ITER, followed by a demonstration reactor called DEMO, which will demonstrate large-scale electrical power production. DEMO will be designed using the lessons from ITER. The expectation is that after DEMO, the first commercial fusion power stations can be constructed.