My last couple of posts have been about projects for developing nuclear fusion. Today I am going to discuss the work of Robert Bussard on nuclear fusion. Bussard developed his own innovative fusion reactor design that he called the Polywell. He formed a company called Energy/Matter Conversion Corporation in 1985 to work on the Polywell. He was able to build and test fifteen experimental devices between 1994 and 2006 with funding from the U.S. Navy. He sought more funding from the Navy to build a full scale nuclear fusion power reactor for about half a billion dollars. The Navy was not willing to fund this stage of the project so Bussard started looking for funding from other sources. He died in 2007.
The Polywell fusion reactor is based on a cube of stainless steel donut-shaped magnets that is called a magrid. The magrid is fed a positive charge of fifty thousand volts. The coils inside the steel donuts produce a magnetic field of two Tesla. For comparison, the magnetic field of the Earth is less than one thousandth of a Tesla. Beams of hydrogen and boron atoms are shot through four of the holes in the stainless steel donuts. Beams of high energy electrons are shot through the holes in the remaining two donuts. All the beam meet in the center of the cube. The cloud of electrons from the two electron beams creates a strong negative potential at the center of the cube. This spherical electric field forces the positively charged hydrogen and boron nuclei into the center of the cube. The hydrogen and boron ions collide and this results in a nuclear reaction that produces high energy alpha particles (helium nuclei) which carry energy away from the center of the cube. There is a spherical metal shell around the Polywell which uses electrical repulsion to slow down the alpha particles. This results in electrons being pushed down power cables forming an electrical current that can be fed to the power grid. One of the benefits of the Polywell reactor is that it does not produce any dangerous radiation such as high energy neutrons that some other nuclear reactions generate.
The optimum size for the Polywell reactor is about ten feet in diameter. If the Polywell is much smaller, it will not be able to put out enough power to even heat the plasma and generate more power than it consumes. If the Polywell reactor is much bigger than ten feet in diameter, it will explode because there is no known material that could withstand the stress of operation. One Polywell power reactor should be able to produce about one hundred megawatts. This would be enough power for a community of about twenty thousand people. The production cost for a commercial Polywell should be about three hundred and fifty million dollars.
The U.S. Navy allocated one million eight hundred thousand dollars to the research in 2007 and eight million dollars in 2009 to continue research on the Polywell. The research has continued up to the present day and the company is working on obtaining sufficient funding from other sources to build a full scale Polywell power reactor.
Artist's rendering of the Polywell:
