On page 36 of Dangerous Voyage to Alpha Centauri a scientist developed his findings on the applications of fusion energy saying:
“By magnetic forces these ions are focused to the fusion reactor and produce energy in abundance. Some of the energy will be used for the ion-thrusters to propel the spaceship. Some of it is needed to recycle all products of Dr. Turner’s ecosystem.”
What are the facts of energy production on fusion today?
As described in Solar Power Satellites our Sun and all other stars produce energy mainly by fusing hydrogen to helium.
In the core of our Sun at temperatures of ten to fifteen million Kelvin, the electron of each hydrogen atom is stripped off. Left in the core of the Sun are hydrogen nuclei. All matter composed solely of nuclei at high temperatures we call plasma. The charged particles in the plasma are protons. They repel each other as they are equally charged.
In the Sun’s core next to high temperatures there is a huge pressure due to the gravitational forces of our massive Sun. High pressure in the Sun’s center means that the protons get close to each other.
At temperatures of about fifteen million Kelvin the protons possess a very high speed. It allows a proton to surmount the repelling electrical forces of another proton. When they crash into each other another force comes into action which makes the protons stick together. We do not know this force in every day life. It exists only at extremely small distances as between protons and neutrons. This force is called Strong Force. Indeed, it is mightier than the repelling electrical force and allows two positive charged protons to stay together.
This nucleus with two protons (and two neutrons which carry no charge) is a helium nucleus. In the process of fusing a little bit of mass of protons and neutrons is changed into energy according to Einstein’s famous equation: E = m times c2, called fusion energy.
On Earth we hope to solve our energy problem imitating the Sun to produce energy by fusing. It is no problem at all for us to give protons the speed they have in the center of the Sun. Any x-ray tube can achieve that.
A real problem to master fusion is to establish pressures as high as within the Sun. We just cannot gain these pressures here on Earth. But there is a way to overcome this disadvantage: We just care for higher temperatures, say, several hundred millions Kelvin instead of poor 15 million Kelvin. We could accelerate hydrogen ions by electrical forces as in x-ray tubes until they have speeds representing temperatures of some hundred million Kelvin.
You can imagine that it has no sense to fuse particles on a mile-long line. Rather you will agree to let a certain number of fusion processes occur continuously in a small area.
We succeed in harnessing superfast ions in a rather small area by magnetic forces. Thereafter fusion energy can be converted into electrical energy as any other energy gained by combustion in a power station.
As I said, it is a minor problem to speed up nuclei to gain high temperatures. Some hundred million Kelvin we are able to obtain by using high electrical currents, additional neutral particles, and high-energetic microwaves. This will help to gain plasma which can be compared to that one in the Sun’s core.
Another idea will help to bring the fire of the Sun to Earth. Instead of protons we will use hydrogen-isotopes so-called heavy hydrogen. One kind of this heavy hydrogen is deuterium, of which each nucleus consists of one proton and one neutron. Using these ions means that temperatures around 200 million Kelvin are sufficient to cause fusion instead of extreme 500 million Kelvin.
Much more complicated than heating up the nuclei for fusing is to keep the plasma in a small and fixed area. In the 1950s the Russians Igor Tamm and famous dissident Andrei Sakharov proposed to confine plasma in a magnetic cage. The name of this cage, toriodal chamber in magnetic coils, abbreviated Tokamak, is still in use today.
All tokamaks in the world are still working on a research level. Scientists are still trying to bring the Sun to Earth. Some of the most promising tokamaks are:
JET in Culham, England, where fusion is studied since 1978;
Tokamak Fusion Test Reactor at Princeton, from 1982 to 1997, which gained plasma temperatures of 510 million Kelvin;
JT 60 at Naka, Japan since 1985, where 520 million K were received;
DIII-D tokamak at San Diego;
Tokamak ITER at Cadarache, France, is being built since 2006. This tokamak is supposed to operate after 10 years of construction. ITER is by far the most challenging project in fusion with a tokamak worldwide. It is designed by scientists at Naka, Japan and Garching, Germany. Participants in this expensive and challenging project are the European Union, Japan, Russia, Korea and Canada. After the US-Congress voted to leave the planning-stage, the US returned again as a participant of ITER in 2003.
One important characteristic of all tokamaks is the use of a transformer to speed up the particles of the plasma. The electrons in the plasma are used as the transformer’s second coil. But this current reaches its optimum only in the short time when the current in the first coil of the transformer is rising. Thus fusion in a tokamak could only be observed periodically. To gain energy not continuously but in pulses seems to be quite uneconomical. Additional means to avoid disruptions of the fusion were searched for, and won!
Already in the 1950s the US scientist Lyman Spitzer proposed the confinement of plasma without a transformer and thus without a pulsing fusion. Spitzer used a magnetic cage for the plasma which should be perceived solely by an elaborated system of magnetic coils. He called this fusion facility stellarator. To realize his ideas the Project Matterhorn was founded. Years later this project was re-named to Princeton Plasma Physics Laboratory (PPPL).
To research fusion in a stellarator the Large Helical Device (LHD) is operating in Japan. Another stellarator, Wendelstein 7-X, is under construction in Germany. This one is supposed to be operating in 2010.
In the US the construction of a compact stellarator is planned at Princeton in partnership with Oak Ridge National Laboratory. This National Compact Stellarator Experiment (NCSX) is the centerpiece of the U.S. effort to develop plasma physics and to determine the attractiveness of the stellarator as the basis for a fusion power reactor. First plasma is scheduled for July 2009.
More about this you can read in my thrilling novel, you can order here: ORDER
Final Report of Coordinated Research Project 2000-2004,Elements of Power Plant Design for Inertial Fusion Energy, International Atomic Energy Agency, Sept. 2005 ISBN 9–2020–7005-5