27 July 2012
A reader asked, “Is there a specific temperature that plasma could not exceed, or would increasing heat create stronger plasma?”
So, let’s talk about plasma. What is it? Plasma is different from solids, liquids and gases; some say that it is the fourth state of matter. Actually, plasma consists of free moving electrons and atomic nuclei. Like gas, plasma has no definite shape or volume but this is where the comparison ends. It can be highly charged and accelerated, moved, by electromagnetic fields. There must be energy applied to strip electrons from their nucleons to make plasma. The energy can come from various sources such as light, electrical and thermal. If the continuous flow of energy ceases then the plasma state will recombine to form natural gas, the cool, electrically neutral state.
Dubbed the most abundant phase of matter, since it makes up over 99% of the visible universe, plasma has many uses here on earth, as well. Neon signs, fusion energy, plasma TV’s, lightning, fluorescent lamps, electric arc, etching, and tesla coils are a few things we can use and see.
Plasma temperature, typically measured in Kelvin, ranges widely. In its crystalline state, plasma can approach absolute zero Kelvin. In contrast, some plasmas, the center of a star for example, can range to 107 Kelvin and more.
In order for plasma to exist, ionization is necessary – this occurs when atoms lose or gain electrons, and become charged. Temperature is largely responsible for this phenomenon. One primary area of research in the understanding of plasma physics, and thus over 99% of the visible universe, is fusion energy.
Plasma and Fusion Energy
Fusion powers stars – this includes our own sun. Science understands the process of fusion: fusing two hydrogen atoms to form helium, and the release of energy that follows, all accomplished under the right conditions. This source of energy would naturally lend itself to experimentation on Earth, but the exploration of fusion energy is a scientific challenge more arduous than any other we face today. We have yet to even achieve the point where the amount of energy put into the reaction equals the energy extracted. Then, why continue? The payoff, once the process has been mastered, is huge, as fusion will result in an inexhaustible form of energy with no pollution. Who wouldn’t want virtually unlimited, cheap, and clean electricity? So, despite the difficulties, fusion experiments abound across the world.
How Does a Fusion Reactor Work?
In a fusion reactor, two light atomic nuclei pull together to produce a heavier nucleus, and release a large amount of energy. This is done by heating the atoms to high temperatures and forming a plasma; the joining of the two nuclei and the release of energy. The leading designs for a fusion reactor follow two different paths: magnetic confinement and inertial confinement.
- Magnetic confinement is just that: it uses magnets to control a charged plasma, which will follow the magnetic field lines. Built in a shape like a donut, the magnetic field is curved in a closed loop to prevent the particles from coming into contact with the reactor, and losing energy. The most promising design is the tokamak. The largest experiment has been the Joint European Torus (JET) in the UK. Others have been TFTR at Princeton in the USA and its successor, ITER, a seven country consortium, currently under construction in France.
- Inertial confinement uses laser or ion beams focused on the surface of the target to control the plasma. The extreme heat produces the right conditions for plasma formation and combining of the nuclei. Experiments are being conducted at the United States National Ignition Facility (NIF) and the European Union High Power Laser Energy Research facility (HiPER).
Alternative Energy: Fusion Fuel
The most promising fuels for fusion power, at present, are Deuterium and Tritium (D-T), both isotopes of hydrogen. Deuterium (hydrogen-2) is naturally occurring in our oceans and readily available. Tritium (hydrogen-3) is found in negligible amounts in nature due to its half-life of only 12.32 years. The reaction products are helium and neutrons (kinetic energy). Tritium can be produced as a by-product from the lithium used in the reactor.
Why Haven’t We Seen More Fusion Reactors?
Many problems keep this technology at bay. Due to the extreme conditions needed to create the plasma that culminates in the energy-producing reaction, finding suitable interior materials is difficult next to impossible. JET has had its interior 4,500 carbon tiles replaced with hopefully more neutron resistant tiles of beryllium and tungsten. Also, creating the necessary gravitational forces for the reaction, magnetic confinement, requires a large amount of energy. The main problem is producing more energy than is used in the energy-production process. Shooting a beam (inertial confinement) is expensive, and the technology is also a problem; there is no model. And the biggest question: who will stand to benefit financially? With the rush to patent and protect, discoveries might not be shared, as in the past, when one scientific community creates a solution such as an interior of neutron resistant material.
Fusion Reactions and Plasma: Reader’s Question Answered
So, to answer our reader’s question: From galaxies to controlled fusion, our lack of understanding has fostered its own research in a difficult area of physics, today. Yes, sustained energy is needed to maintain the plasma. Is there a limit? Only continued research will tell.
Fifty years ago, fusion technology was 50 years away. It is still estimated to be at least that or more, but acquiring the golden egg of viable fusion energy production has always been the dream, and this technology is definitely going to be a part of our future.