History ~
The fusor was originally conceived by Philo Farnsworth, the man
who is largely responsible for television. In the early 1930s he
investigated a number of vacuum tube designs for use in
television, and found one that led to an interesting effect. In
this design, which he called the multipactor, electrons
moving from one electrode to another were stopped in mid-flight
with the proper application of a high-frequency magnetic field.
The charge would then accumulate in the center of the tube,
leading to high amplication. Unfortunately it also led to huge
amounts of erosion on the electrodes when the electrons
eventually hit them, and today the multipactor effect is
generally considered a problem to be avoided at all costs.
What particularly interested Farnsworth about the device was
its ability to focus electrons at a particular point. In the
early days of controlled fusion experiments in the 1950s one of
the biggest problems was to keep the heated fuel from hitting
the walls of the container, if this were allowed to happen the
fuel would rapidly cool off, leading to a huge loss of power.
Farnsworth reasoned that he could build an electrostatic
confinement system in which the "walls" of the reactor were
electrons or ions being held in place by the multipactor. Fuel
could then be "injected" through the wall, and once inside they
would be unable to escape. He called this concept a virtual
electrode, and the system as a whole the fusor.
His original fusor designs were based on cylindrical
arrangments of electrodes, like the original multipactors. Fuel
was ionized and then fired from small accelerators through holes
in the outer (physical) electrodes. Once through the hole they
were accelerated towards the inner reaction area at high
velocity. Electrostatic pressure from the positively charge
electrodes would keep the fuel as a whole off of the walls of
the chamber, and impacts from new ions would keep the hottest
plasma in the center. He referred to as inertial
electrostatic confinement, a term that continues to be
used to this day.
Various models of the fusor were constructed in the early
1960s. Unlike the original conception, these models used a
spherical reaction area but were otherwise similar. Farnsworth
ran a fairly "open" lab, and several of the lab techs also built
their own fusor designs. Although generally successful the fusor
had a problem being scaled up, since the fuel was delivered via
accelerators, the amount of fuel that could be used in the
reaction was quite low.
Things changed dramatically with the arrival of Robert Hirsch
at the lab. He proposed an entirely new way of building a fusor
without the ion guns or multipactor electrodes. Instead the
system was constructed as two similar spherical electrodes, one
inside the other, all inside a larger container filled with a
dilute fuel gas. In this system the guns were no longer needed,
and corona discharge around the outer electrodes was enough to
provide a source of ions. Once ionized the gas would be drawn
towards the inner (negativily charged) electrode, which they
would pass by and into the central reaction area.
The overall system ended up being similar to Farnsworth's
original fusor design in concept, but used a real electrode in
the center. Ions would collect near this electrode, forming a
shell of positive charge that new ions from outside the shell
would penetrate due to their high speed. Once inside the shell
they would experience an additional force keeping them inside,
with the cooler ones collecting into the shell itself. It is
this later design, properly called the Hirsch-Meeks Fusor,
that continues to be experimented with today.
New fusors based on Hirsch's design were first constructed in
the later 1960s. Even the first test models demonstrated that
the design was a "winner", and soon they were producing
production rates of up to a billion per second, and has been
reported to have observed rates of up to a trillion per second.
All of this work had taken place at the Farnsworth Television
labs, which had been purchased in 1949 by ITT with plans of
becoming the next RCA. In 1961 ITT placed Harold Geneen in
charge as CEO. Geneen decided that ITT was not going to be a
telephone/electronics company any more, and instituted a policy
of rapidly buying up companies of any sort. Soon ITT's main
lines of business were insurance, Sheraton Hotels, Wonderbread
and Avis Rent-a-Car. In one particularly busy month they
purchased 20 different companies, all of them unrelated. It
didn't matter what the companies did, as long as they turned a
profit.
A fusion research project didn't. In 1965 the board of
directors started asking Geneen to sell off the Farnsworth
division, but he had his 1966 budget approved with funding until
the middle of 1967. Further funding was refused, and that ended
ITT's experiments with fusion. The team then turned to the AEC,
then in charge of fusion research funding, and provided them
with a demonstration device mounted on a serving cart that
produced more fusion than any existing "classical" device. The
observers were startled, but even by this point all available
funding had been locked up by large research projects who
resisted any funds being allocated to "new" systems, no matter
how promising.
Farnsworth then moved to Brigham Young University and tried to
hire on most of his original lab from ITT into a new company.
The company started operations in 1968, but after failing to
secure several million dollars in seed capital, by 1970 they had
burned through all of Farnsworth's savings. The IRS seized their
assets in February 1971, and in March Farnsworth suffered a bout
of pneumonia and died. The fusor effectively died along with
him.
In the early 1980s the round of "big machines" had demonstrated
themselves to be no more practical than the earlier generations,
and a number of physicists started looking at alternative
designs. George Miley at the University of Illinois picked up on
the fusor, and re-introduced it into the field. The fusor has
remained a popular device since then, and has even become a
successful commercial neutron source.
Basic fusion ~
Controlled fusion attempts to cause ions to fuse by forcing them
together at high energies. The lowest energy reaction occurs in
a mix of deuterium and tritium, when the ions have to have a
combined energy of about 4 keV (kilo-electron volts).
Temperature is the average kinetic energy per unit volume, so
any energy measure can be converted into a temperature with the
conversion ratio of 1 eV = 11604.45 K. In this case the D-T
fusion threshold temperature is about 45 million degrees
Celsius.
In order to make such a reaction practical, some significant
fraction of the expensive fuel used must undergo fusion and
generate power. This rate varies with temperature, and the total
number of fusion events with the amount of time that the fuel is
held at a particular temperature. This relation is known as the
Lawson Criterion, and contains a Catch-22 – as the
temperature of the fuel is increased it becomes increasingly
difficult to "contain" it for the needed amount of time.
In traditional designs, this is achieved by slowly heating a
plasma fuel that is being contained by magnets. This approach
has proven to be very difficult to achieve in practice, as the
fuel tends to "leak out" of the reaction area too fast to heat
it to the required temperatures. Increasingly complex systems
have been introduced to quickly heat the plasma, but these
detract from the usefulness of the design for a practical
generator.
Fusor fusion ~
The fusor attempts to avoid heating problems by adding the
required energy directly to the ions. Whereas 45 million degrees
sounds impressive (and is), it is important to remember that it
corresponds to about 4 keV, the energy that an electron would
gain by being accelerated between two electrodes charged to 4
kV. In the grand scheme of things 4 keV is a very minor amount
of energy – it is commonly found in such devices as
neon lights and televisions.
In the original fusor design, several small particle
accelerators, essentially TV tubes with the ends cut off,
provided a small amount of this energy. Once the ions entered
the reaction chamber they found themselves being pushed towards
the center by the charge on the electrodes, which was charged to
about 80 kV.
In the Hirsch version the basic mechanism consists of two
concentric spherical grid electrodes in a vacuum chamber
containing a very dilute fuel gas. Depending on the design, the
inner electrode is negative and thus accelerates ions toward the
center of the chamber, or alternately the inner electrode is
positive and accelerates electrons towards the center. Most
research has focused on ion acceleration: the ions, being
heavier, are much easier to focus and give a consistent energy.
In theory the fusor is perhaps the most promising form of
fusion reactor studied. Energy is added to the fuel directly
through acceleration, as opposed to the various indirect means
required in a Tokamak or similar magnetically confined systems.
Better yet, since the fusor is accelerating the ions (or
electrons) directly, the range of velocities (or temperatures)
is quite narrow. This means that most of the ions have enough
energy to undergo fusion, whereas in a magnetically confined
system it is typically only the "hottest" ions that can.
Finally, failed collisions scatter inside the reaction area,
heating other ions around them, thereby returning some of the
energy to the reaction.
Another advantage to the fusor is that any ion can be
accelerated easily, not just the "low temperature" mixes like
D-T. This makes the fusor particularly useful when running on
other potential fusion fuels with much higher threshold
temperatures. One of the most attractive such combinations is
the proton - boron-11 reaction, which uses cheap natural
isotopes, produces only helium, and produces neither neutrons
nor gamma rays. This is a very clean reaction that would
dramatically reduce waste when decommissioning a plant, and
there is considerable interest in such aneutronic fuels.
Nothing in fusion is ever easy however. In the fusor a number
of problems conspire to rob energy from the ions as they move
towards the reaction area. One problem is the presence of
"cooler" unionized particles of gas in the system, which can
collide with the ions and cool them. Another problem is the
presence of the inner electrodes, since ions often hit them and
spray the reaction area with high-mass ions which soak up
considerable energy from the surrounding fuel through collisions
and then radiate the heat away as X-rays. This problem plagues
traditional fusion designs as well, where it is known as sputtering.
A more serious concern was first outlined in 1994. In his
doctoral thesis for MIT, Todd Rider did a theoretical study of
all non-equilibrium fusion systems, of which the fusor
is one of many. He demonstrated that all such systems will leak
energy at a rapid rate due to Bremsstrahlung, radiation produced
when electrons in the plasma hit other electrons or ions at a
cooler temperature and suddenly decelerate. The problem is not
as pronounced in a hot plasma because the range of temperatures,
and thus the magnitude of the deceleration, is much less.
In most of the systems that he studied, the energy radiated
away from the system was greater than the energy of the fusion
itself. Unless a significant amount of energy from this
radiation, namely X-rays, was captured, the system would never
"break even". The problem is dependent on the mass of the fuel
ions, so D-T and D-D fuels still provide net energy, but many of
the more interesting aneutronic fuels appear to be impossible to
use as an energy source.
Fusor as a Neutron Source ~
Regardless of its eventual use as an energy source, the fusor
has already been proven extremely useful as a neutron source.
Fluxes well in excess of most radiological sources can be made
from a machine that easily sits on a benchtop, and can be turned
off at the flick of a switch. Commercial fusors are now produced
by a number of companies, including such industrial giants as
DaimlerChrysler.
Industrial might is not required to build a fusor however, and
small demonstration fusors that achieve fusion (but not
break-even!) can and have been constructed by amateurs,
including high-school students for science projects. Each
electrode is spot-welded from hoops of stainless-steel wire
(often welding rod) at right angles. The fusor's electrode
dimensions are not very critical. The outer electrode can range
from beach-ball to baseball size, and the inner from baseball to
ping-pong ball size. Usually such projects use the high-voltage
transformer from a neon sign, and high voltage rectifier from a
hobby shop. Spark plug wires carry the power, with spark plugs
to pass it into the vacuum chamber. Deuterium is available in
lecturer bottles and is not a controlled nuclear material.
Neutrons can be sensed by measuring induced radioactivity in
aluminium foil after moderating the neutrons with wax or
plastic, or a plastic neutron luminescent material can be used
with a photodetector. The major expense is the vacuum pump. Note
that the voltages are dangerous (though less dangerous than a
TV), and neutron emissions do present some hazard. The X-ray
emissions are less than those of a color TV since the voltages
are less.
References ~
Tom Ligon: Analog (December 1998); "The World's
Simplest Fusion Reactor, and How to Make It Work".
P.T. Farnsworth, Patent #3,258,402, issued 28 June 1966
Robert L. Hirsch, Journal of Applied Physics 38 (7),
October 1967; "Inertial-Electrostatic Confinement of Ionized
Fusion Gases"
G.L. Kulcinski, Progress in Steady State Fusion of Advanced
Fuels in the University of Wisconsin IEC Device, March
2001
R. A. Anderl, J. K. Hartwell, J. H. Nadler, J. M. DeMora, R. A.
Stubbers, and G. H. Miley, Development of an IEC Neutron
Source for NDE, 16th Symposium on Fusion Engineering, eds.
G. H. Miley and C. M. Elliott, IEEE Conf. Proc. 95CH35852, IEEE
Piscataway, NJ, 1482-1485 (1996).
R.P. Ashley, G.L. Kulcinski, J.F. Santarius, S. Krupakar
Murali, G. Piefer; "D-3He Fusion in an Inertial Electrostatic
Confinement Device"; IEEE Publication 99CH37050 , pg. 35-37,
18th Symposium on Fusion Engineering, Albuquerque NM, 25-29
October 1999.
G.L. Kulcinski and J.F. Santarius: Journal of Fusion Energy
17 (1), 1998; "Reducing the Barriers to Fusion Electric
Power".
J.F. Santarius, G.L. Kulcinski, L.A. El-Guebaly, H.Y. Khater Journal
of
Fusion Energy 17 (1): 33 (January 1998); "Could
Advanced Fusion Fuels Be Used with Today's Technology?".
Presented at Fusion Power Associates Annual Meeting, August
27-29, 1997, Aspen CO.
T.A. Thorson, R.D. Durst, R.J. Fonck, A.C. Sontag: Nuclear
Fusion 38 (4): 495 (April 1998); Abstract, "Fusion
Reactivity Characterization of a Spherically Convergent Ion
Focus".
T. A. Thorson, R. D. Durst, R. J. Fonck, and L. P. Wainwright:
Phys. Plasma, 4:1 (January 1997); "Convergence,
Electrostatic Potential, and Density Measurements in a
Spherically Convergent Ion Focus".
R.W. Bussard and L. W. Jameson: Journal of Propulsion
and Power 6 (5), September-October, 1990; "Fusion as
Electric Propulsion".
R.W. Bussard and L. W. Jameson: Journal of Propulsion and
Power 11 (2); Inertial-Electrostatic Propulsion Spectrum:
Airbreathing to Interstellar Flight", The authors describe the
proton - Boron 11 reaction and its application to ionic
electrostatic confinement.
R.W. Bussard and L. W. Jameson, "From SSTO to Saturn's Moons,
Superperformance Fusion Propulsion for Practical Spaceflight",
30th AIAA/ASME/SAE/ASEE Joint Propulsion Conference, 27-29 June,
1994, AIAA-94-3269
R.W. Bussard, "Method and apparatus for controlling charged
particles", US Patent 4,826,646 (2 May 1989) About avoiding the
grid losses by using magnetic fields.
Irving Langmuir, Katherine B. Blodgett: Physics Review,
23, pp49-59, 1924; "Currents limited by space charge between
concentric spheres"
William C. Elmore, James L. Tuck, Kenneth M. Watson: The
Physics of Fluids 2 (3) May-June, 1959; "On the
Inertial-Electrostatic Confinement of a Plasma"
Inertial Electrostatic Confinement
Inertial electrostatic confinement (often abbreviated as IEC)
of a plasma can be achieved with electrostatic fields which
accelerate charged particles (either ions or electrons)
directly, in a confined space. Ions can be confined with IEC in
order to achieve nuclear fusion.
The Farnsworth-Hirsch Fusor is a specific implementation of an
IEC device which is popular, since costs for building a simple
one can run between $500 to $4000 (in 2003 U.S. dollars). Other
IEC devices include ion guns.
Due to the simple and relatively inexpensive nature of these
devices many backyard, science fair, and university researchers
are working on IEC class devices. They are able to observe
reproducible, convincing evidence of fusion reactions, however,
these devices are orders of magnitude from breakeven (the energy
input far exceeds the energy output).
These devices produce harmful radiation (neutrons, gamma rays,
x-rays), and require high voltages and could therefore be
dangerous if proper care is not taken.
Experts argue whether an IEC fusion device is capable of
breakeven. Some researchers in the field hope that the
inefficiencies of the design could be overcome through optimized
or hybird designs and the IEC could be a low-cost path to
fusion.
Advanced Fusor
"...This is the most advanced fusor that Farnsworth [the
inventor of television] and his team ever built. It was probably
constructed in 1965 just before ITT cut the funding (after
getting those letters from Wall Street).
"This device utilized a deuterium-tritium gas mixture. It had
an operationg voltage around 100 kV and [the] voltage was
modulated by a frequency around 100 MHz. This caused an
osciallation to occur inside the inner grid. In one period the
electrons are in the centre creating a virual cathode, in the
other period the electrons 'jump outwards', and the positive
ions 'jump inwards' and meet in the centre, giving a very dense
plasma, the Coulomb barrier is broken and we have fusion. [...]
Some rumors say this device was self-sustaining..." --- Adam
Szendrey, 12/15/02, Fusor.net
Analog Science Fiction & Fact 118 (#12) Dec. 1998
~
"The World's Simplest Fusion Reactor: And
How to Make It Work"
by Tom Ligon
A really distressing trend has been developing for some time
among science fiction fans I've met. A lot of you are growing
quite pessimistic about the prospects for practical fusion power
in general, and fusion powered space travel in particular. The
roots of this disillusionment are not hard to find.
Fusion, for those of you who slept through high-school physics,
is the process of squashing two atomic nuclei together to
produce a new element. Many lightweight nuclei give off copious
energy when this happens. In the Sun, hydrogen nuclei fuse
(through a complex cycle involving carbon, nitrogen, and oxygen)
to form helium. The process occurs deep in the Sun's core, at
mind-boggling temperatures that cause the nuclei to move
rapidly, where similarly mind-boggling pressure keeps the nuclei
in close proximity, and sheer bulk prevents rapid heat escape.
The physics community often calls these "thermonuclear
reactions" because of the high temperatures driving them in the
Sun, or triggering them in "hydrogen" bombs,
When I was studying Health Physics in the mid-seventies, the
nation was well into a program to develop "practical, clean
thermonuclear fusion power." This was universally acknowledged
to be a considerable technical challenge, but we were told to
expect results in, say, twenty-five to thirty years. Well,
twenty-plus years have come and gone, along with twelve billion
fusion research dollars (over the past 45 years), and those
researchers have announced that they have made a great deal of
progress. They say if we will only fork over the money (another
ten to twelve billion) for the next stage of R&D, they think
they might be able to build a net power demonstration reactor in
another twenty years. This should lead to a workable fusion
powerplant in about forty or fifty years, for another $25
billion. Present indications are that the resulting powerplant
would not be able to run competitively with any current
powerplant technology.
The focus of most of the present Department of Energy (DOE)
research is large tokamaks. How large? The next generation of
research machine planned, with the supporting equipment and
structure, will be about the volume and mass of an aircraft
carrier. It is expected to use gigantic toroidal superconducting
magnets, storing magnetic energy equivalent to 1/40 of a
Hiroshima bomb, which would be released suddenly if the liquid
helium cooling system were ever breached and any one of the
magnets warmed above the critical superconducting temperature.
Surrounding the machine is a blanket of molten lithium one to
two meters thick. The core of the machine is a torus (donut)
sixteen meters high and twenty-two meters across with a
cross-section diameter of five meters, filled with a
stupefyingly potent confined plasma, whose structural material
will become radioactive as the machine runs. This beast might
actually hit breakeven occasionally (i.e., produce as much power
as it consumes), with a little luck. Presuming working power
plants would be even larger and heavier, the system does not
look promising for strapping on the back of a rocket!
Additional work continues on laser and particle beam-fired
fusion. The reaction vessels proposed for this program are
considerably smaller, however the lasers or beam guns and power
systems to run them are even larger and more massive than those
of the tokamaks, making them prohibitive for space propulsion
use.
Both systems struggle to overcome the three competing factors
which have so far made thermonuclear fusion such a formidable
challenge. The goal is to slam fuel nuclei together hard enough
to make them stick and form new elements. Nuclei carry a
positive charge, and like charges repel, and they do so more
vigorously the closer they approach. This Coulomb barrier" is
the force which must be overcome to cause fusion. To make a
useful power reactor, you must have particle velocity, density,
and confinement time sufficient to produce enough reactions to
generate more power than is required to drive the reaction.
Tokamaks use magnetic confinement, and inject energy into the
confined plasma (typically by huge current discharges or bursts
of microwave energy) to heat the plasma to temperatures which
raise the velocity of the nuclei to overcome the Coulomb
barrier. The powerful magnets surrounding the reactor force the
plasma ions (ions are atoms missing some or all of their
electrons) to follow tight circular paths within the machine,
isolating the plasma from the walls and giving high confinement
time, thus opportunity to react. However, there are practical
limits to magnetic field strength, and those limits are felt
most severely under the conditions where trapping is most
needed. Fast-moving ions needed to cause fusion make larger
orbits than slower, cooler ions, and thus temperature and
density are in constant conflict. There is also an inherent
stability problem in these machines: when ions collide without
causing fusion (which is most collisions in a thermal system),
they tend to "jump to new field lines." Just a few collisions
will likely make them jump to the wall of the machine. The net
result is that while large tokamaks using superconducting
magnets placed outside the torus and lithium blanket can confine
hot ions for long times at low density, or cold ions for long
times at higher density, you must build very large machines in
order to achieve sufficiently high temperature (high ion
velocity) and high density at the same time.
Laser- and particle beam-fired approaches (called Inertial
Confinement Fusion, or ICF) use small pellets or capsules of
fusion fuel flash-heated by extremely powerful lasers or
particle beam pulses. The fuel is usually liquid or even solid,
so initial density is fairly high, although this system requires
the fuel to be compressed to a far higher density in order to
react. The capsule is not just a fuel container; it serves to
absorb the laser or beam energy, compress the fuel as the
capsule explodes, and provide mass (and inertia) to confine the
heated fuel long enough to react. The challenges in ICF stem
from the fact that high temperature causes rapid expansion of
the capsule and fuel: temperature and confinement time are in
conflict. ICF machines also have their own instability problem:
once you compress the fuel pellet to a small fraction of its
normal size, it will find any little gap in what you are
compressing it with, and try to squirt out. So far these
problems have frustrated attempts to produce useful ICF fusion.
Both of these methods have achieved some limited success; that
is, they have produced fusion, far below breakeven. However,
both use heat as the means of raising the velocity of the ions,
what physicists call "Maxwellian" (randomly oriented and
distributed) velocity. Stephen L. Gillett would use the term
"Promethean", for Prometheus, the bringer of fire. Both
approaches rely on the principle that a heated plasma contains a
wide distribution of particle velocities. "Temperature," in the
sense of gas and plasma physics, is the average kinetic energy
of the particles involved, and kinetic energy is proportional to
particle mass and the square of the velocity.
The trouble is, neither approach brings the average ion kinetic
energy up high enough to cause fusion. Only the fastest few
percent of ions reach the energy needed to overcome the mutual
repulsion of the Coulomb barrier. Furthermore, the heated ions
move randomly in all directions, thus collisions are at random
angles which usually do not produce fusion. What they need is
particles hitting head-on at fusion energies; but what goes on
in thermal systems, at the particle level, is virtually
uncontrolled chaos: fast and slow particles colliding like
bumper cars at all angles.
Finally, while these heat-based methods do produce some fusion,
they do so only with the easiest of fuels: deuterium ("heavy
hydrogen," with a nucleus of one proton and one neutron),
tritium (one proton with two neutrons), and helium-3 (two
protons and one neutron). Thermonuclear fusion has been pushed
on the public as "clean," i.e. not producing nuclear waste. This
turns out not to be quite the case. Reactions between two
deuterium nuclei (DD), or deuterium and tritium (DT) produce
neutrons. Most of the useable energy in the favored DT systems
comes from the neutrons, and the only way to exploit it is to
slow them down in a blanket of absorbing fluid (usually liquid
lithium) which is then used to make steam to run a turbine (more
Promethean technology). In fact, the DT systems depend on
neutrons reacting with the lithium to produce more tritium fuel,
for tritium is a fast-decaying radioactive isotope not found in
nature. The neutron-lithium reaction also breeds helium-3.
From time to time you may hear about this miraculous nuclear
fuel, helium-3, which supposedly can be mined from the lunar
surface (actually, the Jovian atmosphere is probably afar better
source). The claim often heard is that the reaction between
deuterium and helium-3 produces no neutrons. While this is true,
any such reactor will also produce deuterium-deuterium
reactions, which will produce neutrons. While it is a
substantial improvement over tritium, it is far from aneutronic.
If a DT reactor could kill you in one second, a DHe` reactor
would require about thirty seconds to kill you. Besides, as
mentioned above, that lithium blanket has a purpose: it reacts
with the neutrons to produce tritium and helium-3! The
aneutronic reaction can't breed its own fuel, but the
neutron-producers can.
While the neutrons produced by these reactions can be harnessed
to make heat and more fuel, they have very undesirable side
effects. They render many engineering materials radioactive,
transmute their elements, and produce metallurgical damage.
Thus, after a few years of operation, the inside of the reactor
becomes weakened and possibly even deformed. Repairs and
disposal of the damaged material are greatly complicated because
it is radioactive.
Fusion the Easy Way --- Using Vacuum Tube Technology ~
There are a variety of other potential fusion fuels for which
the necessary temperatures for fusion are simply too high to be
achieved by the thermonuclear technologies DOE is currently
pursuing. How do we know about these reactions? We have been
doing them since 1928, using extremely simple devices called
linear accelerators . Charged particles can be made to
accelerate to enormous velocities and energies by means of
simple electric fields. By charging a grid to a few hundred
thousand volts, you can accelerate protons or other light nuclei
fast enough to fuse with almost any element in the periodic
table. True, it takes far more energy to run such a device than
it produces, but the equipment is extremely simple, and the
"temperatures' achieved are easily sufficient to produce most
transmutation reactions between nuclei.
Let's bury this "temperature" nonsense right here and now.
While you may have heard a figure of something like fifty or a
hundred million degrees being required to produce fusion, in
fact few researchers use those numbers except to impress the
public. The units of temperature they use are "electron volts,"
which are easily understood in terms of linear accelerator
operation. For every electron's worth of charge on a particle,
multiply by the volts on the accelerating grid to get
electron-volts of energy. For purposes of impressing your
friends, for each electron volt, multiply by 11,604 to get
degrees Kelvin. You may be amused to know the electrons hitting
the screen of the typical television set are around 200 million
degrees according to this scheme, and 50 million degrees is a
paltry 4300 electron volts.
At about the same time linear accelerators were first being
developed, development of vacuum tubes, or electron valves, was
being refined. Vacuum tubes use the principle that a very hot
metal surface will emit a cloud of electrons, which can be
caused to cross a gap in a vacuum to a positively charged
"anode." In simple diode vacuum tubes, a hot tungsten filament
or heated thin cylindrical surface (the "cathode") is surrounded
by a cylindrical anode (also called the "plate") and electrons
will flow from cathode to the anode, but not from the anode to
the cathode.
One of the best-known researchers in the field was Irving
Langmuir, who had developed theories and confirmed by
experiments the principles of "space charge limitation" between
tube elements composed of concentric cylinders. In 1924,
Langmuir and Katharine Blodgett investigated the case of
concentric spheres as a vacuum tube configuration. While the
device worked well, the normal configuration was concentric
cylinders, which were much easier to manufacture and also worked
well, so there was no widespread use made of this development at
the time. Limited use of the spherical configuration includes
some "multipactor" tubes and certain specialized light sources.
In the mid-1950's, P. T. Farnsworth (one of the inventors of
television) pondered the bright visible convergent focus glow
that forms in the center of spherical multipactor tubes, and
came up with the idea of using a spherical diode with the inner
electrode in the form of a highly transparent wire grid (i.e. a
very open mesh screen) as a fusion machine. Called the 'Fusor,"
the device, later patented, would cause ions of fusion fuel to
speed to the center of the machine. As they converged on the
central focus region, their density would increase rapidly,
making collisions more likely. Ions which did not collide would
decelerate out the other side, stop, and accelerate back to the
center for another try, conserving energy. The class of machines
based on this principle are "spherical convergent focus
electrostatic ion accelerators," with the abbreviation IXL to
remind us that they use the grids to accelerate ions (see figure
1). Because they use simple electrostatic forces to accelerate
and confine ions, and rely on the inertia of the ions to store
energy for collisions, the term Inertial Electrostatic
Confinement (IEC) is used for machines of this type. Be careful
not to confuse it with ICF, or laser/particle beam fusion.
By 1959, Elmore, Tuck, and Watson explored the idea of using
Farnsworth's gizmo backwards to accelerate electrons from the
outer sphere (a cathode) to the inner sphere (an anode). The
inner sphere of such a machine is a grid, which forms a geodesic
"potential surface" which the electrons aim for as if it were
solid. However, when they get there, most pass right through and
coast in a straight line, converging from all sides to the
center, then they pass out the other side. What results is a
region at the center of the inner sphere with a very high
density of negative charge, called a "virtual cathode." This
region will attract positively-charged ions, which will tend to
oscillate back and forth through the central region. Provided
more electrons are force-fed into the system than ions, a
"potential well" is formed in which the ions are trapped by
excess negative charge. Interestingly, an ion oscillating
entirely inside the inner grid will be trapped almost
indefinitely, thus theory predicted this device might be a
surprisingly efficient ion trap. However, the electrons had to
pass through the grid, which meant eventually most of them would
hit the grid. Depending on the grid's "transparency," an
electron might make 10 to 50 passes before being lost, requiring
another electron and the power to fire it into the system.
Because the electrons had to outnumber the ions by a significant
margin, the researchers expected this device could be harnessed
to produce only tiny amounts of fusion, and decided it could
never make a workable power reactor. The Elmore, Tuck, Watson
concept is an electron accelerator, or EXL machine.
In 1967, Robert L. Hirsch published a paper describing a
concentric sphere device which produced "copious neutron
emission". Hirsch (working at the ITT/Farnsworth Lab under
Farnsworth's enthusiastic encouragement) used the IXL
configuration, with the cathode (negative grid) in the center
and the anode (positive) to the outside. His machine was a
spherical version of a linear accelerator: positive ions formed
at the anode accelerated toward the central cathode grid (the
opposite of the behavior of electrons, which are negatively
charged). Again, the accelerated particles usually miss the
inner grid, continuing on to the center of the device. There
they stood a fair chance of collision, and very importantly, all
of the particles were at the same energy, which was sufficiently
high for fusion to occur. If they missed or collided without
producing fusion, they could travel out the other side,
conserving their energy for another pass through the middle.
Although not all collisions were headon, particles which did not
fuse rebounded with most of their original energy. It did not
matter to which direction they rebounded, as all directions were
uphill" against the potential gradient, so they slowed down, and
came rushing back "downhill" for another try. Like the Elmore,
Tuck, Watson design, the losses due to grid collisions prevented
breakeven, but a lot of fusion was possible, nonetheless.
Dr. Hirsch operated his machine at up to -150,000 volts on the
inner grid, at currents up to 60 milliamps. Using DD and DT, the
machine produced abundant fusion, but far below breakeven. The
neutron emissions he achieved (published results on the order of
a billion neutrons per second, and unpublished results of around
a trillion per second!) would be considered dangerous today.
Hirsch also built an ElmoreTuck-Watson EXL machine, and verified
it would produce a deep potential well.
What Hirsch's machine demonstrated was that, contrary to
popular belief, fusion is actually quite easy to produce, once
the thermo mindset is shed. The problem is to come up with a
configuration that does not waste the drive energy.
The Nuclear Reactor High-School Science Project ~
I notice a few of you have gone glassy eyed on me. Trust me,
this is easy. A Farnsworth-Hirsch machine is so simple it could
be built as a high-school science project (though I caution that
a knowledgeable advisor should be sought, and good safety
practices must be followed). You will need to borrow, buy, or
build some vacuum equipment, obtain a small supply of deuterium,
and figure out some instruments so you can tell if it is
working, but the actual reactor components are trivially simple
to build, and will cost only a few cents!
WARNING! The apparatus described in this article uses
high voltages at potentially lethal currents. High vacuum
apparatus and compressed gasses may also be dangerous if
improperly used. This device may produce ultraviolet radiation
and soft x-rays. Do not attempt to build or operate such a
device unless you have been trained in high voltage safety, and
safe use of compressed gas cylinders and vacuum equipment, and
can verify that no unsafe radiation exposure occurs.
Regarding the presumed danger of building a nuclear reactor,
the simple fact is that the proposed machine would run at the
very bottom end of the voltage required for fusion, and it will
take some skill and effort to even detect the neutron output.
The real danger is in the potentially lethal high voltages used,
and some lesser concerns for safe handling of compressed
flammable gas and operation of vacuum equipment. A metal vacuum
vessel will stop virtually all of the weak x-rays which may be
produced (a little tamer than those produced by a television),
and a thick glass window will stop most ultraviolet radiation
produced. The voltages involved are somewhat lower than those
present in an ordinary television set, which also has a large,
fragile, glass vacuum vessel, and I would characterize the
project as about as dangerous as television repair. They still
teach television repair in high school technical education
programs, don't they? But make no mistake, the insides of a
television set can kill you in a heartbeat.
While you will wish to rig a method for detecting and
quantifying neutron production (that being your proof you are
making fusion), the levels produced by the machine described
below should be so low you would have to stand a meter away from
the machine for twelve days of continuous operation before you
got a 100 mrem dose of neutrons (and that is a trivial dose).
Most likely, the device will be run only for a few minutes at a
time at actual fusion conditions. Still, if for no other reasons
than the educational benefits and common sense, I would advise
the experiment be done with due consideration to nuclear safety.
For those wusses who don't wish to "go nuclear," or who cannot
find qualified advisors, you can still demonstrate the visible
glow by using a non-nuclear gas (the residual air in the vacuum
chamber will do) running at below fusion voltages. In fact, even
without producing fusion, you can do a lot of interesting and
useful science with these devices.
The expensive component is the vacuum system, which may have to
be borrowed or scrounged. The pressure required can be achieved
by a simple mechanical rotary-vane roughing pump (a two-stage
"micron" pump used for refrigeration repair will do) if the
system is compact and tight, although it would be preferable to
have a higher-performance system. Such a pump, used, can cost
around $750 (a lucky scrounger I know has stumbled onto several
for $150 or less), so a borrowed pump will be a real advantage
if you are as broke as I chronically was in high school. A
vacuum chamber and some high-voltage and conventional electrical
feedthroughs will be needed. A metal vacuum chamber with a thick
glass viewport is far preferable, and I managed to find
materials for one at a scrapyard for $30. I have built a small
demonstrator device in a $90 plastic desiccator chamber, but it
did not achieve good enough conditions for fusion, finally
failed due to a stray electron beam heating the walls, and
provided little protection against x-rays or ultraviolet light.
Glass vacuum containers such as bell jars are fragile and
consequently dangerous, and must be used with guards, face
protection, and with great care. Spark plugs will do as high
voltage feedthroughs, and spark plug wire for high voltage
cable, for researchers who are "cash-chalk lenged." Homemade
vacuum instruments can be made from light bulbs or old vacuum
tubes.
I have achieved the blue glow of convergent ion focus using a
furnace ignition transformer and a pair of high-voltage diodes.
This will produce close to five thousand volts, and ignition
transformers are usually current-limited to a level that
probably won't stop a healthy teenage heart. Such a transformer
will not produce significant fusion, but makes a pretty glow
which will demonstrate the convergence effect.
Higher voltage and power can be obtained using a 15,000 volt
(7,500 volt RMS centertapped) neon sign transformer with two
high voltage diodes, which can produce over 10,000 peak volts
DC, and considerably more current than the ignition
transformers. I have successfully pushed such a transformer to
13,000 volts. This power source can produce measurable fusion.
Before buying one, check with an electrical contractor who
remodels commercial property, as they frequently dispose of such
transformers from old neon signs. You would prefer the
higher-current 60mA variety if you can get it, and need at least
a 30mA unit. This transformer can kill, particularly if you use
a capacitor on it to filter the AC ripple.
Deuterium gas is not radioactive, and can be purchased without
special license through many gas suppliers, sometimes even
through welding suppliers. A lecture bottle should cost around a
hundred dollars, and you will also need a suitable regulator,
which you may be able to borrow, or at least re-sell after you
are done with it.
The reactor grids themselves will cost a few cents and take
about an hour to build, if you have access to a small
spotwelder. What, no spotwelder?!! Build one yourself with
common parts from an electronics store . Each grid can be formed
from six rings of stainless steel welding wire. I have used
0.025 inch diameter wire, which is cheap and easy to work. Buy
it from any welding supply dealer. Figure 2 shows how to fit the
rings into geodesic spheres. The dimensions can be adjusted to
fit your apparatus. Typically the outer grid is somewhere
between the size of a beach ball down to the size of a
volleyball, and the inner grid is from the size of a softball
down to the size of a ping-pong ball. You may gather from this
that precision in diameter is not an issue. It also is
surprisingly unimportant that the grids be perfectly spherical
or mathematically precise.
While a specially-built neutron counter is the most convenient
way to detect neutrons, there are at least two cheaper methods.
Neutrons react with many elements to produce new elements, which
are frequently radioactive. Plain old aluminum is one such
element, and another is indium foil. Gamma rays from the
products can be measured by a Geiger counter (I have seen plans
for home-made models in reference 7), or can be detected by
sensitive photographic film. Neutrons from fusion must be slowed
down to make these reactions work, a process called
"moderating." Two good moderating compounds are water and
paraffin wax. There are also special plastics available which
produce tiny flashes of light when hit by neutrons, which can be
electronically or photographically detected.
A professional lab could probably manage to sink $50,000 in
equipment for such a project. Purchasing used equipment, you
could probably build a simple unit for well under $2,000. I
suspect a particularly talented scrounge/beggar could get by for
around $500 out of pocket, which I estimate could be raised in
under a month of flipping burgers, or a couple of days of
computer consulting.
At higher pressures (about one onehundred-thousandth of
atmospheric pressure), the system will work in "glow discharge
mode," the way a neon sign works. This is the easy way to go, as
it requires no fancy electron guns or extra power supplies.
Those of you with access to higher performance vacuum systems
may wish to venture to lower pressures, where the recirculation
becomes far more efficient. This requires a source of electrons
to generate ions. There are a number of ways to do this, but
they are too involved for this article. These methods are
described in the referenced papers, and can also be accomplished
with cheap and available odds and ends.
If you jack the inner grid voltage on this simple little
machine up to l0,000 volts or more, and feed deuterium to the
system at a pressure a little under 10 microns, it should
produce fusion, evidenced by net neutrons I have seen a
17-year-old build a grid that produced 300,000 neutrons a second
at 13,000 volts.
So you see, you can build a fusion reactor with parts from an
electronics store, auto parts store, welding shop, refrigeration
supplier, hardware store, and craft store, perhaps with a bit of
dumpster-diving on the side, and creative use of big, sad,
pleading eyes. It really doesn't take tens of billions of
dollars!
These hints should be enough to get you started. I don't want
to describe the apparatus too completely, because hitting the
books and figuring this out is how you earn that science fair
prize dancing before your eyes right now.
Can The Problems Be Overcome?
While machines based on Farnsworth's Fusor are indeed easy to
build, and worked better than any thermonuclear fusion machines
until quite recently, it was immediately apparent to the
researchers that they could never reach breakeven. The reason,
quite simply, was that either configuration required grids, and
grids simply could not be built more than about 98% transparent
and be expected to support their own weight, especially as they
typically run red hot when fusion conditions are achieved. The
machines seemed doomed to operate at no more than 0.01% of
breakeven. A few researchers struggle on, tantalized by the fact
that the machines seem to have modes of operation which are
better than theory predicted. Dr. George Miley of the University
of Illinois has shown that a "star mode" develops in which
recirculation passes primarily through the grid openings,
reducing grid losses. There also appears to be considerable
fusion occurring immediately outside the convergent focus
region, where head-on collisions dominate, which was neglected
in early analysis. Still, these improvements fall far short of
what is needed for a power reactor.
Basically, the grids had to disappear!
A way may be forthcoming. The actual inventor of the scheme
below asked me to drop my original glowing testimonial. He is
entirely too modest, if you ask me, but I understand his
motives. Still, he isn't getting off without his name being
mentioned here, and at least a few of his extensive
accomplishments. You may have heard of him as the inventor of
the interstellar ramjet concept featured in Tau Zero and many
other science fiction stories: Dr. Robert W. Bussard. In the
1950's, he proposed and designed a workable nuclear fission
rocket engine, which led to KIWI-A, the first predecessor of
NERVA. KIWI-A was ready to test before Sputnik was launched.
Dr. Bussard also worked with Dr. Hirsch in the thermonuclear
fusion program at the old Atomic Energy Commission, predecessor
of the DOE. Both of them recognized the finer points of the IEC
machines, and wondered if a way could be found to get around the
grid problem.
When life hands you a lemon, it has been said, you should make
lemonade. Dr. Bussard was struggling with another of his
inventions, a small tokamak called the Riggatron, which looked
marginally workable, but had turned out to be far too expensive
to build with the available money. The enormous energy required
to bring the magnets up to a field strength that would trap the
plasma would require a monster flywheel-generator that was
simply way over budget. The problem with tokamaks, he realized,
was that ions are so damnably hard to trap with magnetic fields,
particularly under fusion conditions. Yes, using
superconductors, or by putting copper coils very close to the
plasma and pushing them to their limits, it was possible to trap
light ions like deuterium and tritium, but as soon as they
collided they would tend to jump field lines, unless the fields
were especially powerful. Achieving that field strength was
turning out to be a killer problem.
It was a pity, Bussard thought, that ions are not as simple to
trap with magnetic fields as are electrons. Because electrons
are thousands of times lighter than fusion fuel ions, they are
deflected easily by much weaker magnetic fields. If the little
tokamak contained only electrons, they could be held at high
energy and density quite efficiently. And then an epiphany
struck.
It might just be possible to build an EXL machine with
magnetically insulated grids. The magnetized grids would
accelerate electrons just as well as wire grids, but it would be
next to impossible for the electrons to actually bit the grid.
Ions formed just inside the grid would be drawn into the
potential well and oscillate until they collided, totally
unimpeded by grids, and trapped by the one thing that holds them
vigorously-an electrostatic potential. From time to time, theory
seemed to pose a fatal obstacle, but each time a closer analysis
of the obstacle revealed a solution that made the theory work
even better.
Funding was found to build a largescale (1-meter radius)
machine, which demonstrated that the system could produce a deep
potential well. Further small-scale work showed successful
magnetic trapping of dense electron clouds. Theory and computer
simulation seem to support the models and experiments, with no
roadblock problems found, yet.
The theory and preliminary lab studies look good. A few million
dollars would fund a working prototype, and if that doesn't
work, indications are that scaling up a factor of ten in volume
almost certainly would. While not cheap for most of us, compared
to the DOE budget for the last 20 years it is practically petty
cash. Will it succeed? At this point, only time will tell.
The Possibilities ~
If successful, the impact of this type of reactor would be
enormous. I need not describe the overall economic consequences
in too great a detail to this audience: science fiction is
chock-full of stories in which we developed cheap, clean fusion
to replace petrochemical fuels and to power our spacecraft.
However, Bussard's magnetic-grid EXL version of the Fusor shows
promise as a power source that sounds like science fiction. One
reason is that it doesn't have to run on nasty neutron-producing
fuels like deuterium and tritium.
As mentioned earlier there are many nuclei which can produce
net fusion energy besides deuterium, tritium, and helium-3. Most
of them are not commonly discussed, because they require far
higher collision energies than DT reactions. Since DT reaction
conditions themselves are a formidable challenge for
thermonuclear approaches, the other fuels are simply out of the
question for tokamaks or ICF systems. These limitations become
almost trivial in spherical convergent focus accelerators,
however. By simply jacking the voltage up to a couple of hundred
kilovolts, the electrons can be made to produce a deeper
potential well, and the ions race to the focus region faster.
This requires scaling up the hardware, but does not appear to
require any great leaps of technology.
Among the fusion fuels is a favorite of Dr. Bussard: the
reaction between ordinary hydrogen nuclei (protons) and
boron-11. Boron can be mined as borax or other minerals, and is
readily extracted from seawater. About 80% of natural boron is
the boron-11 isotope. The fuel is plentiful.
The p-B11 reaction is ideal: When the two nuclei fuse. they
form excited carbon-12, which is unstable and almost immediately
begins to fly apart. In two rapid stages, it casts off an
energetic alpha particle (a helium nucleus), then the remaining
nucleus splits into a pair of alpha particles. The first
particle, carries 43% of the reaction energy, and comes off at
precisely 3.76 million electron volts, which turns out to be
very handy. The other two alphas come off at an average of 2.46
million electron volts each, over a spread of energies. Finally,
the reaction produces no neutrons or high-energy gamma rays.
There is a little bremsstrahlung ("braking radiation" basically
x-rays) from collisions associated with the reaction, easily
shielded. Alpha particles are dangerous if produced in your
body, but can be stopped by the thinnest of shields, and are
essentially harmless in a reactor vessel. Once they pick up two
electrons, alpha particles become helium, a harmless inert gas.
There is no radioactive waste produced in this reaction!
Lithium can also undergo similar reactions, producing charged
particles, and is an alternative fuel for such a reactor. Most
nuclear power generation systems produce heat by one mechanism
or another, which is in turn used to heat a "working fluid" to
run turbines or otherwise do mechanical work. The process of
converting heat to mechanical energy by such means is inherently
inefficient. Rarely does more than about a third of the energy
end up in usable electrical or mechanical form, and the
theoretical limit is around 40% for most practical fluids,
engine materials, and operating temperatures. This fact has
depressed thermodynamics students for the last century or so,
but there appears to be no getting around it using primitive
"Promethean" technology.
While you could simply, allow the alpha particles from the
p-B11 reaction to slam into the reactor walls producing heat,
there turns out to be a much better way to extract their energy.
Alpha particles, which are helium atoms stripped of their two
electrons, have a charge of +2. Each of the particles produced
by this reaction has a kinetic energy of around 3 million
electron volts. An electron volt is the energy a particle of
charge 1 will pick up when accelerated through a field of 1
volt. The reverse is true, too. To slow down a 3MeV particle
with a charge of +2, simply decelerate it with a
+1.5-million-volt electric field. The particle will just kiss
into the charged surface, and draw two electrons from it,
producing current at high voltage. This method has been used to
extract small amounts of power from alpha-emitting radioactive
substances, and should also work for a large reactor of the
correct configuration. The correct configuration is a spherical
vacuum chamber (which this reactor just happens to be) with
several charged grids to pick off the lower energy alphas, and
the outer walls charged to catch the high energy alpha. It
should be possible to approach 95% conversion of fusion energy
to electricity with such a system (the rest being lost to
bremsstrahlung and a few other minor mechanisms). This is quite
remarkable-a nuclear reaction which allows almost all of the
energy produced to be directly converted to high-grade
electrical power! You might think that if nuclear energy is so
cheap, efficiency would not be a problem. For power plants,
particularly large ones, waste heat release can cause local
environmental changes, either by heating a body of cooling
water, or causing local weather changes when watermist cooling
towers are used. The cooling apparatus is generally massive, and
can easily cost more than the actual power-generating equipment!
Waste heat in spacecraft is even more serious. Any
nuclear-electric powerplant using gas turbines or similar
equipment must get rid of the excess heat in order to operate.
Since there is no air or water in space to conduct away the
heat, it must be radiated. For a thermal-cycle reactor of
sufficient power to operate even a modest manned spacecraft, the
radiators will be on the order of the size of football fields.
They end up being a huge portion of the dry mass of the
spacecraft, and simply ruin the performance. Thus, a reactor
that can produce electrical power directly, at 95% efficiency,
has a tremendous performance advantage over its
thermal/mechanical/electric counterpart.
(By the way, you have seen heat radiators on spacecraft in
Analog artwork many times. Vincent Di Fate tells me that's what
those "fins" are on the back of his sleek designs.)
Dr. Bussard has done some preliminary design studies on
spacecraft that could realistically be built around p-B11
reactors. Most use a large and very powerful reactor of close to
10 billion watts capacity. While fairly bulky, with a diameter
of around 5 meters, the reactor is mostly empty vacuum, with
only the magnetic-grid and a few electron and ion guns in it. It
is thus exceptionally light for the power produced. Supporting
cryogenic and power conversion equipment should also be
practical space hardware, and not especially massive.
Because the reactor produces no radioactive waste and only a
trace of radiation, it will be safe to operate in the
atmosphere. Using high-voltage electron beams to superheat gas,
one could build either an air-breathing jet or a rocket (relying
on on-board reaction mass). In space, the rocket configuration
will be used. Because the reactor can work only if there are far
more electrons in it than fuel ions, it is also "intrinsically
safe": if you feed it too much fuel, it just chokes off.
There are many ways of exploiting the EXL reactor output to
produce rocket thrust, but the fact that the lrB I powerplant
produces high-voltage electricity makes it particularly suited
for arc-jet propulsion's meaner big brother. In a
million-volt-plus electron beam the electrons are pushing
lightspeed, so the term relativistic electron beam (REB) is
used. With some heavy-duty R&D, it is expected that
REB-heating can be made quite efficient, and should be able to
impart high velocity to the reaction mass. Water would be a
perfectly suitable reaction mass, as would almost any other
handy and abundant material. REBs are not picky about what they
blast to plasma. Dr Bussard calls the REB-heated systems "QED"
(Quiet Electric Discharge) engines.
For longer-range missions, where quick acceleration is less
important, a more efficient rocket which uses the fusion exhaust
directly could be built. This would be the system of choice for
trips to the outer planets, or even out to the Oort cloud. Dr.
Bussard calls these more efficient systems "DFP (Direct Fusion
Product) engines.
It would be possible to build a "singlestage-to-anywhere"
(SSTA) rocket, useable in the atmosphere or in space, with this
technology, but, for bulk transport, this would probably be less
practical than having separate atmospheric shuttles (with
wings), space transports (equipped for long voyages but stripped
of wings and landing gear), and landers engineered for the
various destinations. From a science fiction standpoint, though,
the SSTA possibilities are really attractive.
What kind of performance could realistically be achieved? Try
these figures from some of Dr. Bussard's papers9,10,11!
Low Earth Orbit (LEO) to Mars; 33 days, more or less, for high
performance designs, or 6 weeks for economical freight-hauling
variations. The craft are single-stage, with a 15-20% payload
fraction.
LEO to Saturn's Moons:as low as two months, with a short
coasting period. Again, the craft is single-stage, and has a 14%
payload fraction
How would such a rocket affect the economics of space
exploitation? Most estimates you have heard in the past were for
multistaged chemically-propelled rockets, which can barely
achieve Earth orbit, the upper stage of which must limp to the
planets along painfully slow Hohmann ellipse orbits. Chemical
rockets are almost all fuel and barely any payload. While rocket
fuel is fairly cheap, rockets are not, and each flight has a
high operating cost in labor and hardware. Dividing the cost of
a large rocket by a payload mass somewhere just above zero gives
a really depressing cost per kilogram. Efficient EXL fusion
rockets, reusable for many flights, fast enough to make many
flights before becoming obsolete, and with a high payload for
each mission, can improve economics by several powers of ten.
Consider the following colonization figures extracted from a
more recent paper by Dr. Bussard,12 and I recommend you read
these sitting down:
Cost to LEO: $27/kg (a price that compares favorably to the
cost of riding the Concorde across the Atlantic).
4000 people on Earth's moon, each person with 25 metric tons of
equipment, and each person receiving an annual visit back to
Earth: $12 billion over ID years.
1200 people on Mars, each with 50 tons of equipment, and an
annual visit back to Earth: $16 billion over 10 years.
400 people on Titan, each with 60 tons of equipment, and an
annual visit back to Earth. $16 billion over 10 years.
I leave you to ponder these figures, particularly in light of
the projected costs of sending a few people to explore Mars with
chemical rockets, typically estimated on the order of a hundred
billion dollars per trip. In particular, consider what these
numbers would mean to your personal chances of living and
working in space.
References ~
1. Stephen L. Gillett, Ph.D. "Beyond Prometheus," Analog, Dec
1993.
2. "Nucleus", Encyclopedia Britannica, 1955, v. 16, p. 589, re.
the "cascade transformer* of Lauritsen, Crane, et al., and later
work by Cockcroft and Van de Graff.
3. Irving Langmuir and Katharine B. Blodgett, "Currents Limited
by Space Charge Between Concentric Spheres," Physics Review, 23,
pp. 49-59, 1924.
4. P. T. Farnsworth, U.S. Patent No. 3,258,402, issued 28 June
1966.
5. On the Inertial-Electrostatic Confinement of a Plasma,"
William C. Elmore, James L. Tuck, Kenneth M. Watson, The Physics
of Fluids, v. 2, no. 3, May-June 1959.
6. "Inertial-Electrostatic Confinement of Ionized Fusion
Gases", Robert L. Hirsch, Journal of Applied Physics, v. 38, no.
11, October 1967.
7. John Strong, Procedures in Experimental Physics, c. 1938,
Prentis-Hall; reprint c.1986, Lindsay Publications Inc, Bradley
lL. ISBN 0-917914-56-2.
8. R. W. Bussard, "Method and Apparatus for Controlling Charged
Particles," U.S. Patent 4,826,626 (2 May 1989).
9. R. W. Bussard, "Fusion as Electric Propulsion,"Journal of
Propulsion and Power, v 6, no 5, September-October 1990, pp.
567-574.
10. R. W. Bussard and L. W. Jameson, "From SSTO to Saturn's
Moons: Superper for mance Fusion Propulsion for Practical
Spaceflight," 30th AIAA/ASME/SAE/ASEE Joint Propulsion
Conference, 27-29 June, 1994, ALAA 94-3269.
11. Inertia-Electrostatic-Fusion Propulsion Spectrum:
Air-Breathing to Interstellar Flight, R W. Bussard and L. W.
Jameson, Journal of Propulsion and Power, v. 11, no. 2, pp.
365-372.
12. R. W. Bussard, "System Technical and Economic Features of
QED-Engine-Driven Space Transportation," 33rd AIAA/ASME/SAE/ASEE
Joint Propulsion Conference and Exhibit, 69 July, 1997, AIAA
97-3071.
Tom Ligon is a consultant and science fiction writer,
presently working with R. W Bussard at Energy-Matter Conversion
Corporation. Tom would be glad to hear from any science fair
projecteers seriously attempting the project in this article,
either by e-mail (tomligon@compuserve.com), or by mail at
8825 Centreville Rd, #190, Manassas, VA 20110.
Books from Borderland Sciences Research Fdn.
http://www.borderlands.com/catalog/advanced.htm
Distant Vision: Romance and Discovery on
an Invisible Frontier
by Elma G. Farnsworth
The biography of Philo Taylor Farnsworth II, the Utah farmboy
who conceived the basic operating principles of electronic
television at the age of 13 years. Despite his humble
beginnings, this daring young dreamer persevered until his dream
became reality, and his work touched the lives of every man,
woman, and child alive today. Beginning with the first moment of
inspiration -- while plowing a potato field in Rigby, Idaho --
this book traces the unlikely chain of events that enabled
Farnsworth to produce the first all electronic television
picture in San Francisco on September 7, 1927. As television
began to capture the world’s imagination in the 1950’s,
Farnsworth went on to pursue even more daring work. In the
1960’s he designed and built a device capable of producing
nuclear fusion electronically -- a process that would have
changed our world far more than television ever could! With this
lovingly crafted volume, the late inventor’s wife provides an
intimate, first-hand account of their lives together on the
leading edge of discovery.
#B0174, 333pp, hardbound, ... $24.95
Lost Science
by Gerry Vassilatos
Rediscover the legendary names of a suppressed scientific
revolution -- remarkable lives, astounding discoveries, and
incredible inventions which would have produced a world of
wonder. How did the aura research of Baron Karl von Reichenbach
prove the vitalistic theory and frighten the greatest minds of
Germany? How did the physiophone and wireless of Antonio Meucci
predate both Bell and Marconi by decades? How does the earth
battery technology of Nathan Stubblefield portend an unsuspected
energy revolution? How did the geoætheric engines of Nikola
Tesla threaten the establishment of a fuel-dependent America?
The microscopes and virus-destroying ray machines of Dr. Royal
Rife provided the solution for every world-threatening disease.
Why did the FDA and AMA together condemn this great man to
Federal Prison? The static crashes heard on telephone lines
enabled Dr. Moray to discover the reality of radiant space
energy. Was the mysterious "Swedish stone", the powerful mineral
which T. Henry Moray discovered, the very first historical
instance in which stellar power was recognized and secured on
earth? Why did the Air Force initially fund the gravitational
warp research and warp-cloaking devices of T. T. Brown, and then
reject it? When the controlled fusion devices of Philo
Farnsworth achieved the "break-even" point in 1967, the FUSOR
project was abruptly cancelled by ITT. What were the
twisted intrigues which surrounded these deliberate convolutions
of history? Each chapter is a biographic treasure. Ours is a
world living hundreds of years behind its intended stage of
development. Only a complete knowledge of this loss is the key
to recapturing this wonder technology.
Lost Science, #B0387, 304pp, paperback, ... $16.95
Links
http://www.farnovision.com/chronicles/fusion/vassilatos.html
~ Article by J. Vassilatos
http://users.ticnet.com/bertpool/philo/philo.htm
~ List of Farnsworth's US Patents
http://www.farnovision.com/chronicles/fusion_future.html
~ ~ Fusion-Powered Future: excerpts from Farnsworth lectures
http://fusor.net
~ Fusor Forum
http://en.wikipedia.org/wiki/Farnsworth-Hirsch_Fusor
~ Wikipedia page
http://www.earthtech.org/experiments/fusor/bigsys3.html
~ Earthtech.org: developing the Fusor
http://www.kronjaeger.com/hv-old/fusor/construction/
~ J. Kronjaeger's Fusor page
http://www.glubco.com/weaponry/fusor/fusor.htm
~ A working Fusor at WPI
http://www.richmond.infi.net/~rhull/highenergy022.htm
~ Joe Zambelli's Fusor
http://torsatron.tripod.com/fusor/
~ Inertial ES Confinement
http://torsatron.tripod.com/fusor/tips.html
~ IEC Advice
http://www.lib.utah.edu/spc/photo/p437/P0437.txt
~ Farnsworth photo collection at the Univ. of Utah
http://www.orbit6.com/fusor/BussardPatent2.htm
~ Bussard Fusion USP # 5,160,695
http://mr-fusion.hellblazer.com/pdfs/apparatus-creating-controlling-nuclear-fusion-reactions.pdf
~ Bussard Patent
http://www.utahstatesman.com/news/2003/09/24/CampusNews/Student.Builds.Nuclear.Fusion.Reactor-474220.shtml
~ C. Wallace's Science Fair IEC Project
http://www.rtftechnologies.org/physics/fusion.htm
~ RTF Technologies IEC Fusion Reactor
http://www.zalp.com/photolog.htm
~ Adam Parker's Fusor
Farnsworth FUSOR Video ~ A two hour FUSOR videotape has
been produced by Richard Hull. There are three segments in this
first-of-a-series on the FUSOR. * 1. The history of the FUSOR. *
2. Theory/Hardware. * 3. Fifty minutes of FUSORS-in-action. The
price, including priority shipping, is $25 payable to: Richard
Hull, 7103 Hermitage Rd., Richmond, VA 23228
Joe Zambelli's Fusor
Photo Source:
http://www.richmond.infi.net/~rhull/highenergy022.htm
US Patent # 3,258,402
"Electrical Discharge Device for Producing Interactions
Between Nuclei"
Philo Farnsworth
US Patent # 3,386,883
"Method & Apparatus for Producing Nuclear Fusion
Reactions
Philo Farnsworth
US Patent # 5,160,695
Method & Apparatus for Creating & Controlling Nuclear
Fusion Reactions
Dr Robert Bussard
