Electrostatic Fusion

Keywords: P. T. Farnsworth, Robert Hirsch, fusor, Analog Science Fiction and Fact, proton-boron 11 or p-B11, direct conversion

"The World's Simplest Fusion Reactor," by Tom Ligon

     Rather than give sample paragraphs for the article I wrote for Analog Science Fiction and Fact, which appeared in the Dec 1999 issue, I'll tell you a little about the project, and where it is heading.
     The world's simplest fusion reactor is the Hirsch/Farnsworth machine, sometimes called the "Farnsworth Fusor". This device is almost trivially simple, a spherical wire grid suspended in a vacuum chamber, connected to a high negative voltage. There's usually a grounded outer grid or spherical chamber walls, but they are not absolutely necessary. A trace of fusion fuel, typically deuterium gas, perhaps a deuterium-tritium mix, is introduced to the chamber. In the simplest form, ions are produced by the glow-discharge process, the positively-charged ions rush to the inner grid due to simple electrostatic attraction, and converge on a point in the center of the device. At a sufficiently high voltage, at the right pressure conditions, a significant number of these ions undergo nuclear fusion. The reactor is literally simple enough to build as a high-school science project, and there are, in fact, several kids working on it right now, due mostly to the Analog article!
     I'm shopping for a good digital camera, and don't have a photo of my machine in operation. Here is a photo of Richard Hull's Fusor 2 in full "star mode", the mode that is most successful in making fusion. Richard is now up to Fusor 4.
     This is not cold fusion! This is good, old-fashioned, hot fusion! The kinetic energy of the ions (which have a charge of +1 electron), as they pass a grid at a typical operating voltage of 18,000 volts (in DP-2, my own machine), is 18,000 electron-volts. Multiply that figure by 11,604 to get degrees K: thats about 209 million degrees! And most folks toying with these devices run even higher voltages. Yet the big government programs, using tokamaks and lasers, or other brute-force measures designed to heat the gas in the conventional sense, struggle to reach these conditions.
     Part of the conceptual problem in achieving fusion is this notion that the reaction is thermonuclear. Actually, the formula that defines fusion rate is

n1 n2 sigma V

where

n1 and n2 are the densities of the two colliding ion species
sigma is the reaction crossection (effective target size)
V is the particle velocity

     The formula above occurs often in rate reactions -- it would predict the rate of hits on aircraft at density n1 and size sigma when being fired on by anti-aircraft shells of density n2 and velocity V. You will notice that nowhere in that formula does temperature appear! High temperature is just one way to achieve particle velocity. It is velocity which is the key to achieving fusion. The simple, direct way of achieving high velocity is electrostatic acceleration. Always has been -- we discovered the nuclear fusion reactions using electrostatic linear accelerators, starting around 1928.
     The Hirsch/Farnsworth machine has its roots in a spherical vacuum tube design by Langmuir and Blodgette, dating to about 1924. It was picked up by P. T. Farnsworth, one of the inventors of television, and head of ITT-Farnsworth Labs, in the 1950's, as a possible means of producing fusion. Work continued thru most of the 1960's, with significant contributions by Robert Hirsch, until ITT was unable to secure government funding and dropped it. The politics behind that are a long, sad story, but the fact is that Hirsch/Farnsworth machines, built on remarkably small budgets, out-performed all other fusion machines until quite recently, and probably still do if you judge them by fusion reactions per dollar.
     More important, since electrostatic fusion machines can reach stupendous particle velocities by the simple expedient of jacking up the voltage, they have the potential to burn fuels that no thermonuclear machine ever will. Our favorite is the proton-boron 11 reaction. Boron 11 is 80% of natural boron, and is abundant, found in borax. It is a micronutrient, but somewhat toxic in large amounts. The fusion reaction between boron 11 and a hydrogen nucleus produces three alpha particles, which are helium stripped of the electrons. Thus, the reaction takes a poison and turns it into a harmless inert gas, a refreshing change in nuclear technology. There are no neutrons produced, and no radioactive byproducts. Almost all of the reaction energy comes off as fast-moving alpha particles, over a fairly narrow spread of energies, and this makes it possible to do a neat trick, direct conversion of fusion energy to high voltage electrical power, by electostatic de-celeration! How 'bout that, no moving parts, no steam, no turbines, no generators, and somewhere between 80 and 95% efficient!
     I managed to land a great job in this field for a few years, starting as a consultant. I finally had to leave - the project relocated to California, and I moved there for two years, but finally had to come back to my wife and home in Virginia. However, I continue my fascination with this approach to fusion, and sincerely believe that it is the key to harnessing this great energy source, literally our chance to save the world and open up space travel in a major way. Please, don't bother asking me any questions about the company I worked for or their method for exploiting electrostatic fusion: I signed a confidentiality agreement and I'll stick with it. All you get is what's in the Analog article.
     Shortly after starting my fusion research career, I was allowed to write "The World's Simplest Fusion Reactor." I built my own demonstration unit, DP-1 (Dog and Pony 1), which I took down to Richmond, VA, for one of Richard Hull's "Teslathon's", along with a draft of the article. Richard and the other Tesla-coilers fell in love with the machine at first sight, and, as a result, there's a strong amateur movement to build and study these devices.
     If you'd like to learn more about this topic, click the "Fusor website" link below, to hook up with Richard Hull and his pack of amateur fusion researchers. Before you do, though, please bookmark my home page - you may get lost in the fascinating wealth of information Richard has assembled!
     If you run a science fiction convention reasonably close to me, or would like me to demonstrate it at a school in the Northern Virginia area, e-mail me. DP-2 was designed to demonstrate the principle to the public. I've been invited to bring it to the Philadelphia WorldCon around Labor Day, 2001. It was presented at PhilCon in 1999, and LepreCon (32 kB JPG) in 2000, where it made big impressions.
     "The World's Simplest Fusion Reactor" won the 1999 Analab award for best science fact article. To all the Analog readers who voted for it, I say a hearty "Thank you!" The article easily generated more fan mail and e-mail than anything else I have written, thousands of pieces, and I keep getting more! My apologies to the people I never answered -- I initially answered everyone, but it finally got to be overwhelming, particularly as so many of my replies turned into ongoing dialogs.

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