July-August 1999
Science Observer
Fusion from Television
Just over ten years ago, Stanley Pons and Martin Fleischmann
announced that they had devised a way to carry out nuclear fusion on a
tabletop--and captured the attention of the world. Two humble
chemists, it seemed, had uncovered a simple solution to the thorny
problem of making hydrogen isotopes combine and release energy in a
controlled fashion. The breakthrough promised to provide humanity with
an essentially unlimited power source. Their ingenious method had
apparently eluded physicists, who for decades had spent billions of
dollars on fusion power research without practical result. Several
weeks after the initial news conference, more sober assessments of the
work of Pons and Fleischmann showed little evidence that fusion
reactions had actually taken place, and most scientists lost interest
in the lingering debates about cold fusion.
Simple demonstration device, built by
Worcester Polytechnic Institute sophomore Joshua Resnick as an
extracurricular project, sets up a high voltage between two sets of
spherical electrodes made from joined metal rings. A transparent bell
jar allows the assembly to be placed under low pressure without
obscuring the view of the glowing plasma when the device is energized.
The notoriety of this episode in the history of science obscures
another effort to produce tabletop fusion reactions that is more
interesting and, in fact, successful. Although not quite as unassuming
as the electrochemical cell that Pons and Fleischmann used, a rather
elementary device can generate nuclear fusion using a technique called
inertial electrostatic confinement. Indeed, the equipment is so
straightforward to build that production models will soon go on sale,
albeit not as power generators but as convenient sources of neutrons.
Homebrew versions of this same fusion apparatus have even been built
by amateurs.
The roots of this technology reach into the 1950s, when the first
patent application for a novel fusion device was filed by the very
person who earlier ushered in another technical marvel: the boob tube.
Now recognized as the father of electronic television, Philo
Farnsworth, a self-taught inventor, spent the later portion of his
life investigating whether a machine that is not so different from a
television picture tube could be harnessed to produce fusion
reactions.
Whereas a picture tube shoots electrons into a phosphor-coated
screen, Farnsworth?s patent called for an ?evacuated spherical
electron tube? that accelerates the particles into a central zone.
The cloud of negative charge in turn attracts positively charged
deuterium or tritium ions toward the center, where they collide at
high velocity. Although only a few nuclei hit with enough energy to
allow fusion, the ions that fail to combine the first time will
continue to crisscross the central region under the influence of the
inward-pointing electric field. This focusing effect gives the
accelerated ions multiple opportunities to fuse without losing
significant energy during the failed collisions.
Homebuilt fusion apparatus of amateur
scientist Richard Hull employs ionized deuterium to produce neutrons
using inertial electrostatic confinement. This rendition of the
Farnsworth ?fusor,? like the designs recently built by several
professional research groups, uses a metal vacuum chamber to contain
the plasma. These machines all employ spherical inner electrodes
similar in arrangement to Resnick?s demonstration device.
Robert Hirsch, a physicist Farnsworth hired in 1964, simplified the
early design to accelerate the ions directly, making the device more
efficient, although it was still far short of being a net producer of
power. Asked to address the agency then charged with establishing
nuclear research priorities, the Atomic Energy Commission, Hirsch
hoped to demonstrate the value of funding further work on inertial
electrostatic confinement fusion. So he mounted his prototype on a
stainless-steel dessert cart and wheeled the contraption into the
conference room. ?Just plugging it into the wall, I think I produced
105 neutrons per second,? Hirsch recalls. (His more
carefully controlled trials in 1967 yielded more than 1010
neutrons per second, a benchmark that has yet to be beaten by the
modern versions of this device.) Yet the AEC proved unreceptive. ?I
underestimated the resistance,? Hirsch notes, explaining how it was
difficult even then for the nuclear research establishment to consider
seriously techniques other than the two now-entrenched approaches to
fusion power: magnetic and inertial laser confinement.
Despite the lack of attention--and funding--some physicists have
spent much of the last decade trying to revive interest in
Farnsworth?s second invention. George Miley of the University
of Illinois, for example, has worked on inertial electrostatic
confinement for several years. He and his corporate partners at
DaimlerChrysler Aerospace have used this method to build a compact
neutron generator, one they plan to start selling within months.
?End users are wary of isotopic sources,? says John Sved, the
project manager at DaimlerChrysler, referring to the means some others
employ (a radioactive isotope such as californium-252) to generate
neutrons. Others in need of these particles, say, for conducting
neutron-activation analysis, must place their samples in a nuclear
reactor. So having a portable neutron source that can be flipped on
and off with the push of a button would be a great advantage. Although
switchable neutron generators (small particle accelerators) are
available commercially, Sved anticipates that his product, lacking the
usual solid target for the speeding ions, will have a longer service
life.
Richard Nebel and his colleagues at Los Alamos National Laboratory
are also constructing an inertial electrostatic fusion device. They
anticipate that their equipment will prove useful in the short run as
a high-intensity neutron source for characterizing radioactive
materials. Over the longer term, these physicists hope they can refine
the basic concept to the point where inertial electrostatic fusion
could produce useful amounts of power.
Robert W. Bussard, a physicist who founded the Energy/Matter
Conversion Corporation of San Diego (which goes by the clever acronym
EMC2) is also experimenting with inertial electrostatic
confinement fusion. The U.S. Navy has supported him with about $4
million since 1995, in hopes that this technique will someday provide
a compact fusion power source. Although practical realization may be
far off, Alan Roberts, the official in charge of this Navy research
program notes, ?You can?t put a tokamak on a ship.?
Could Farnsworth?s dream of generating fusion energy using a
technique spawned from the development of the television set ever
become a reality? The people now pursuing this approach are
understandably enthusiastic. But Hirsch, who left lab work for a
career in management three decades ago, has perhaps a more compelling
perspective. He asks why the government has largely neglected various
methods (like inertial electrostatic confinement systems) that are
small in scale and could be studied for much less money than is now
being spent on the colossal facilities needed to advance magnetic and
laser fusion. And given his extensive experience--as director of
federal fusion research for four years and as a vice president for the
Electric Power Research Institute, among other high-level posts--his
question seems too important to ignore--David Schneider