Plasmas: Next New Thing?
August / September 2007
Volume 5 Number 4
In the famous 1960s movie, The Graduate, a pompous businessman uses a single word to advise the young hero on a profitable path to the future. "Plastics," he whispers.
Nowadays, perhaps, he'd murmur: "Plasmas."
Not in the sense of the bodily liquid but in the physics fictionally represented by the light-saber swords of the Star Wars movies: energies contained by a magnetic field, designed to have an effect.
In the real world, some exploratory plasma battlefields are the province of astronomers studying the stormy conditions around black holes and neutron stars.
Some are in the national labs, in the effort to create nuclear fusion for peacetime energy or nuclear weapons simulations. And many are in the commercial world, where plasmas etch out the circuits of computer chips from silicon, sterilize instruments, form the screens of televisions, act as scalpels used by surgeons, give light from fluorescent bulbs, toughen metals and medical parts, and much, much more.
In the measured words of the recent National Academy of Sciences report on plasma science, "The expanding scope of plasma research is creating an abundance of new scientific opportunities and challenges. These opportunities promise to further expand the role of plasma science in enhancing economic security and prosperity, energy and environmental security, national security and scientific knowledge."
But if plasmas are really the Rosetta stone, as well as (as some claim) the fourth state of matter after solids, liquids and gases, why isn't plasma more widely acclaimed as the upcoming "in" thing? Why aren't there plasma departments at many colleges? Why doesn't plasma research have a central funding program in the federal government to encourage basic advances across a broad front?
Instead, according to the NAS report, plasma studies often exist as tentative stepchildren of larger programs. This produces a flickering funding not conducive to establishing committed faculty, attracting students, and producing graduates and then entrepreneurs in the field, at least not in the United States.
Still, enough funding is going on across the varied fields of plasma research to make the question worth answering: plasma, what exactly is it?
A plasma is an energetic gas technically called "excited." It's a cloud or beam composed of atoms some of whose electrons have been separated from their nuclei, torn asunder by an external force. Like lonely human singles, the reduced nuclei (called ions, which have a positive electrical charge) and their former traveling companions, electrons, which have negative charges, search energetically for new partners. Their coupling can be intense, with a consequent release of energy.
Ion clouds are different from, say, the gas cloud provided by a cooking stove. The atoms of gas used in a stove are whole and electrically neutral—€”not ionized. Their electrons are ready to link closely and suddenly with oxygen, given a spark or flame, to raise the temperature of the two gases. But by itself, gas emerges from a pipe as serenely as water or any other stable fluid. Magnets have no effect on it. The gas will not transmit electricity.
Plasmas, because of the electrically unbalanced state of their constituents, are readily influenced by magnetic fields and are electrically conductive. In fact, because plasmas have many free electrons, they are much better conductors of electricity than any metal, whose electrons are less available.
Furthermore, plasmas come in many forms. There are hot, cold and ultra-cold plasmas, as well as weakly and strongly ionized ones, and they may contain light or heavy ions. They are thought to be the most frequently occurring form of matter in the universe.
Light ions may be used to harden the surface of materials because their energies can reorganize surface atoms. Heavy ions may impregnate those surfaces with a coating. A hot plasma, where electrons and protons are both energized equally, because of its low mass and high energy may be used to drive a rocket. A cool plasma, where electrons are energized far more quickly than ions, may be used to etch circuits in silicon. And ultra-cold plasmas are cooled to nearly absolute zero and then heated just enough to dissociate electrons from protons. These investigate occurrences at the borders of physics.
There are a lot of choices, so there are a lot of possible products. And there's lots of room for improvement and many entrepreneurial possibilities.
For example, fluorescent light bulbs are four times more efficient than the tungsten light bulb, which converts only about five percent of its energy into visible light.
Therefore there's a market for fluorescent bulbs. But they have a problem beyond their not-quite-right quality of light and their breakability: they contain a plasma of mercury, an environmentally harmful material.
The fluorescent process works like this: Electricity ionizes mercury atoms within the glass shaft; the process produces ultraviolet light that strikes a coating on the inner wall of the bulb. The coating then emits visible light.
Mercury is very efficient at this, but a big economic prize would await the person or company that could find an environmentally harmless substitute for mercury. General Electric has tried and failed, according to published reports, though it learned a few things along the way. Who's next?
The same principle works in plasma TVs. Tiny cells of noble gases are ionized very rapidly by computer control to produce ultraviolet light. This light causes a pixel display in front of the bead to give off either red, blue or green color. The intensity of the light is controlled by the amount of ultraviolet released, which is controlled by the amount of electricity sent by the computer. Improving these screens so they don't burn out rapidly and move images with rapidity has taken much ingenuity. There's room for more.
NASA has signed an agreement with Houston-based Ad Astra Rocket Co. to commercialize what it calls "a promising advanced plasma rocket system." The plasma, which would power a rocket, is expected to reach temperatures approximating the interior of the sun. Thrust energies of this magnitude (temperature is a measure of energy) would considerably exceed that of present-day chemical rockets because of its very high exhaust speed. How would a rocket contain a plasma that hot? Through use of magnetic fields, which would keep the plasma from contacting the rocket's walls. How to do this? They're working on it, and, in a series of press releases, report progress.
The $12 billion ITER project in the south of France is an international effort to create controlled high-yield nuclear fusion. (The acronym was stripped for public relations reasons of its original title—€”International Thermonuclear Experimental Reactor—€”and now stands alone.) It involves, among many other players, Sandia and Oak Ridge national laboratories. If successful, the effort would eventually satisfy the entire world's electricity needs using only sea water as an energy source. Its method involves creating a very hot plasma consisting of isotopes of hydrogen. These would be contained by a magnetic field, because no material on earth could contain a plasma of such energy. The principle is simple and Einstein-approved: energize these ions to high enough speeds and a certain number of traveling nuclei will collide, overcoming the resistance of their mutually positive electrical charges to become, among other things, the larger nuclei of a helium atom. In the process, they will release enough energy that, captured and used to turn water to steam to drive a turbine, would create from a half-bathtub of seawater as much energy as that produced by 40 train cars full of coal. The timescale? At least a decade.
"There's a fundamental similarity between all types of plasmas," says University of Texas at Austin physics Professor Todd Ditmire. "So maybe we can learn about supernovas by studying plasmas in labs. We can simulate solar winds hitting Earth's magnetosphere to give us fundamental understanding that would let us predict when the solar wind would knock out satellites. Petawatt lasers could be used to accelerate protons for cancer cures without building huge accelerators.
What will move the field forward? According to Steven C. Cowley, a physics professor at UCLA and co-chair of the NAS plasma report, the key is science's increasing ability to predict the behavior of plasmas through computational modeling.
"This means we can explore new processes and products before performing expensive experiments," he says. "This is the key to using science to generate innovative products. It is also essential to fusion research—€”the ultimate plasma product on the horizon."
But the canker in this rosy picture is, again, there is almost no government support in the area of basic plasma research most relevant to industrial processes and products, according to Cowley. "No U.S. entity has taken up the role of steward for this field," says the report.
Too bad, Cowley says, because for industry to develop new products and optimize them without expensive experiments will require understanding of particles and energies, the excitation of energy levels, and the interaction of plasmas with liquid or solid surfaces. "The point of public investment is not directly to create a single product, but the basic research will benefit all," he says. And a relatively small investment by the government in this area would vastly improve our knowledge, as well as the availability to this field of skilled graduates."
More than 200 pages of the NAS report testify that there's certainly enough going on in the plasma field to watch with interest—€”and maybe participate in—€”any upcoming steps to fund, control, contain and deploy it.
Neal Singer is a freelance writer who reports on science and technology.
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