Nuclear Fusion is the process that powers the Sun and all the stars. It is the power that drives the Universe. Fusion power, also called fusion energy, is the use of nuclear fusion reactions to provide controlled energy production.
Fusion energy can:
Such is the hope attached to this technology that many people say-“it is too good to be true.” But just as airplane pioneers like the Wright Brothers knew flight was possible from the flight of birds, we know fusion works in the sun and the stars. The challenge is to control this natural process. And researchers have begun to do this.
A fusion reaction occurs when two nuclei of atoms collide with such force that they, at least briefly, stick together or fuse. Sometimes they immediately break apart forming other nuclei. But the key points are that these reactions happen between the electrically-charged nuclei and that they release large amounts of energy.
Fusion is a different physical process than nuclear fission, the process that drives what is today called “nuclear energy”. In nuclear fission, a neutral particle—a neutron—reacts with a nucleus, breaking it apart and producing more neutrons and a lot of energy. In fission, the resulting nuclei are generally radioactive—they emit radiation as they decay. The neutrons can react with a reactor’s structure to produce more radioactive elements. Together these huge amounts of radioactive elements constitute radioactive waste.
So fusion differs from fission in what “ingredients” go into the reaction:
Fusion ingredients: two charged nuclei
Fission ingredients: one nucleus and one neutron
A key part of the science of fusion is plasma physics. Plasma is the fourth state of matter, in addition to solid, liquid and gas. Plasma is a state of matter which occurs when electrons have been knocked off their atoms, generally due to high temperatures, and are free to move and respond to electromagnetic fields. Well over 99% of the matter in the universe is in the plasma state—stars and the matter between the stars are all plasmas. On earth, we see plasmas in fire and lightning. Plasma technology stretches beyond fusion energy research and is applied industrially in TVs, lighting and manufacturing.
There are two different types of fusion reactions, depending on what products are generated by the reaction. In neutronic fusion, one of the products is a neutron, while the others are charged nuclei. In aneutronic fusion, all the products are charged nuclei—no neutrons are produced.
Most fusion energy research involves neutronic fusion, with the fuel being two isotopes of hydrogen—deuterium and tritium. This fuel was chosen because it reacts—burns—at the lowest temperatures of any fusion fuel, so was thought to be the easiest one to use. But neutronic fusion has two strong disadvantages. Neutrons can produce some radioactive waste, although much less than from fission. They also can destroy the reactor structures over time. Second, the only way we know of getting energy out of neutrons is by using them to generate heat. So if you use energy to heat something up we are stuck with the way we have produced electricity since Thomas Edison invented the light bulb. We use heat to boil water, to produce steam, to turn a turbine, to turn a generator. All of which is very expensive and wasteful of energy at every step. More on neutronic fusion
Aneutronic fusion, producing only charged nuclei as products eliminates these disadvantages. Without neutrons, there is no radioactive waste. Since the energy output is now in the form of the motion of charged particles, and moving charged particles are electricity, energy can be obtained by direct conversion—much cheaper than turbines and generators. Aneutronic fusion is the only energy source we know that is potentially both much cleaner than other energy sources and much cheaper.
The best fuel for aneutronic fusion is a mixture of hydrogen with boron. This fuel is also known as pB11, from the scientific symbols for the ingredients. When the hydrogen nucleus—a single proton(p) —and the boron-11 (B11) nucleus come together at high temperature, they react to form three helium nuclei—and a lot of energy.
This fuel is essentially inexhaustible. Hydrogen of course comes from water and the amount of boron mined right now is 10 times as much as would be needed to replace ALL existing energy sources with aneutronic fusion. Boron is also the 12th most abundant element in seawater. The boron in the oceans would provide enough fuel for billions of years of energy consumption at triple the present level.
Main types: tokamaks, laser inertial confinement, stellerator, liner implosion
Main types: dense plasma focus, inertial electrostatic confinement, laser side-on ignition, field-reversed configuration
The DPF device has been in existence since 1964, and many experimental groups around the world have worked with it. The dense plasma focus device’s core consists of two cylindrical metal electrodes nested inside each other. The outer electrode is generally no more than 15 cm in diameter and 30 cm long. The electrodes are enclosed in a vacuum chamber with a low pressure gas filling the space between them.
A pulse of electricity from a capacitor bank (an energy storage device) is discharged across the electrodes. For a few millionths of a second, an intense current flows from the outer to the inner electrode through the gas. This current starts to heat the gas and creates an intense magnetic field. Guided by its own magnetic field, the current forms itself into a thin sheath of tiny filaments; little whirlwinds of hot, electrically-conducting gas called plasma.
This sheath travels to the end of the inner electrode where the magnetic fields produced by the currents pinch and twist the plasma into a tiny, dense ball only a few tenths of a mm across called a plasmoid. All of this happens without being guided by external magnets.
The magnetic fields in the plasmoid change very quickly, and these changing magnetic fields induce an electric field which causes a beam of electrons to flow in one direction and a beam of ions—atoms that have lost electrons—in the other. The electron beam and the friction (viscosity) of the plasma heat the plasmoid to extremely high temperatures, the equivalent of billions of degrees C (particles energies of 100 keV or more).
Collisions of the ions with each other cause fusion reactions, which add more energy to the plasmoid. This happens even though the plasmoid only lasts 10 ns (billionths of a second) or so, because the very high density in the plasmoid, which is close to solid density, makes collisions very likely and they occur extremely rapidly.
The ion beam of charged particles is directed into a decelerator which acts like a high-tech transformer. The energy in the ion beam is transferred to an electric current in a circuit. This in turn feeds into a second capacitor bank. Some of this electricity is recycled to power the next fusion pulse while the excess (net) energy is the electricity produced by the Focus Fusion generator. Some of the X-ray energy produced by the plasmoid can also be directly converted to electricity through the photoelectric effect (as in solar panels).
Unlike other devices that attempt to control plasma, the DPF works to harness the instabilities inherent in the plasma. By using the instabilities, the DPF works with the plasma’s natural tendencies rather than trying to make it stable.
When the DPF is used with pB11 fuel, the combination is called “Focus Fusion”. Due to the extremely compact size of the generators, Focus Fusion can be extremely cheap. Researchers estimate the cost of Focus Fusion electricity at around 0.3 cent per kWh, more than ten time cheaper than any existing energy source. The capital cost of about $100 per kW of capacity is also ten times less than any existing power source.
Each Focus Fusion generator would generate about 5 MW of power, enough for a small town or neighborhood of 5,000 people. Given the complete safety of such generators, they can be located in a decentralized manner, increasing the reliability of the grid.
However, Focus Fusion is not yet available. It is still in the research phase. Right now, only one company, LPPFusion, Inc. in Middlesex, NJ has an experimental program to research and then develop Focus Fusion. So far, this effort has demonstrated the second-highest fusion yields per unit energy input of any effort in the world, although they have only spent $5 million. LPPFusion, currently funded by private investments, estimates that they require another $2 million to complete the research phase, perhaps by as soon as 2018. The engineering phase, developing a working generator, will take more resources, perhaps $50-$100 million and three to four more years.