The Frontier of Nuclear Fusion Research
Ultimate Energy for Creating the Future
All of the stars in the universe are bright because of nuclear fusion energy. It is a great dream for humanity to realize the controlled nuclear fusion reaction on Earth and utilize the energy for life.
The nuclear fusion reactor can produce a great amount of energy, and ensures safety, good environmental acceptability, and a rich resource. The nuclear fusion reactor has the following advantages and problems for its realization.
- The fuel is inexhaustible because it exists in the sea.
- The emitted CO2 and/or air pollution material is small.
- The produced energy density is high.
- The nuclear fusion reaction is intrinsically safe. When accidents occur, the reaction automatically stops.
- High-level radioactive waste is not generated.
- The fuel plasma must be steadily confined at an extremely high temperature and in a high density condition. These have not yet been attained simultaneously.
- The in-vessel structure of the reactor, which has the property of high heat resistance as well as low radioactivation, is under development.
- A reliable system that converts the nuclear fusion energy to heat energy is being developed.
- This costs a great amount of money because of the large facility that is necessary for research and development.
The nuclear fusion reactor is currently expected to be realized in 30 years.
Nuclear Fusion Research in the World
There are two principal systems for plasma confinement. One is the “magnetic confinement system” as represented by the helical type and the tokamak type. The other is the “inertial confinement system.” In the magnetic confinement system, high temperature plasmas are confined using a strong magnetic field. At the National Institute for Fusion Science, plasma physics, technology, and simulation research are being conducted concentrating on the Large Helical Device (LHD), which is the world’s largest helical system. The concept of the helical system originated in Japan. The helical system has the excellent property of steady-state plasma operation because the confinement magnetic field can be produced using only the external magnetic coils. The best performance of the steady-state plasma has been achieved at the LHD. Plasma research using a helical device has been conducted in Japan, Germany, Spain, Australia,and other countries. A tokamak-type device achieved the world record of the fusion criterion, which is determined as the product of the ion temperature, the ion density, and the energy confinement time. The tokamak system requires a plasma current to produce the confinement magnetic field. The accurate control method of the plasma current is one of the most important issues of the tokamak system in order to realize the steady-state operation. Tokamak plasma physics have been investigated in Japan, the United States, the United Kingdom, Germany, China, Korea, and other countries. For the inertial confinement system, the nuclear fusion reaction occurs by implosion of the fuel by an instantaneous strong force using high energy lasers or ion beams. The inertial confinement system has been investigated mainly in the United States and Japan.
TOPICInternational Thermonuclear Experimental Reactor (ITER)
he energy confinement property of fusion plasma improves as the plasma volume grows. Thus, the upsizing of the fusion experimental device and the increasing costs are inevitable for realizing the reactor. Also, there still remain technological problems relating to the reactor structure. In response to this present situation, the project of constructing the unprecedentedly large fusion experimental device to obtain comprehensive understanding of the fusion plasma has started under international collaboration.
The device is a tokamak type and is called “International Thermonuclear Experimental Reactor (ITER).” The ITER project started in 1985, and Japan, the European Union, Russia, the United States, China, Korea, and India are participating in the project. ITER is now under construction at Cadarache in France with a total cost of 14.5 billion Euro. ITER is expected to operate for 20 years from 2020.
In Japan, the “ITER Broader Approach (BA)” activity has been conducted. The objective of the ITER-BA is (1) to complement and support the ITER project and (2) the establishment of the technological basis required for the prototype reactor, in particular, the material testing of the reactor components, computer simulation of the fusion plasma, and the simulation experiment using a satellite tokamak device. The ITER project is typically called “big science”, and is now off and running.