Copyright 2000, Bert Pool
Superb Web Site on Farnsworth's life: The Farnsworth Chronicles-
Here is an interesting Borderland Science Ftp file on Farnsworth:
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Below are the results of my search through the patents of Philo T. Farnsworth. While
others have chronicled the life and times of P.T. Farnsworth, my interest lies in his
inventions and patents. More specifically, how the design of those separate devices led up
to the final development of the Fusor - the only fusion reactor ever designed and operated
at better than break-even efficiency! Farnsworth's Fusor produced neutron counts measured
in the billions-per-second. No other fusion device built, even 30 years later can match
this performance. It is unfortunate that Farnsworth died before perfecting the device into
a commercial product, but that does not detract from his accomplishment in the least. That
one man could conceive of and design a working fusion reactor is a phenomenal personal
achievement. It would be nice if someone would build another working device.
Please note that the patents were printed from microfilm, then scanned with some
minimal clean-up of the resulting images. Enjoy - it's been a *lot* of work!
Click on the underlined patent numbers below for full patent information.
Note: Patents are currently being added to the Website from the newest (bottom) to oldest
||Aug. 7, 1934
|Photo Electric Apparatus
||Aug. 14, 1934
|Electron Multiplying Device
||Feb. 23, 1937
||Feb 23, 1937
|Multipactor Phase Control
||Feb. 23, 1937
|Radiation Frequency Converter
||Feb. 8, 1938
|Means and Method of Operating
||Aug. 30, 1938
||Nov. 8, 1938
|Secondary Emission Electrode
||Dec. 13, 1938
|Multiplier Coupling System
||Dec. 13, 1938
|Means and Method of Controlling
||Dec. 20, 1938
|Charge Storage Dissector Tube
||Dec. 27, 1938
||Dec. 27, 1938
|Split Cathode Multiplier Tube
||Dec. 27, 1938
|Means for Electron Multiplication
||Jan. 10, 1939
|Means for Producing Incandescent
||Apr. 25, 1939
|Two Stage Electron Multiplier
||Jun. 6, 1939
|RF Frequency Multipactor Amplifier
||Sep. 5, 1939
|Self-Energized AC Multiplier
||Sep. 26, 1939
||Sep. 26, 1939
|Means for Producing an
||Nov. 7, 1939
||Nov. 4, 1939
|Method of Operating Electron
|Cold Cathode Electron Discharge
||Dec. 26, 1939
|Diode Oscillator Tube Construction
||Feb. 6, 1940
|Shielded Anode Electron Multiplier
||Jun. 4, 1940
||Means and Method for Producing
||Jun. 11, 1940
||Split Cathode Multiplier
||Oct. 15, 1940
||X-ray projection Device
||Nov. 12, 1940
||Nov. 12, 1940
||Oct. 28, 1941
||Apparatus for and Method of
Electron Discharge Control
||Feb. 24, 1942
||Electron Control Device
||Jun. 9, 1942
||Jun. 23, 1942
||Electron Control Device
||Feb 23, 1943
||Ion Transport Vacuum Pump
||Apr. 29, 1965
||Electron Gun in the Form of a
||Aug. 17, 1965
||Ion Transport Pump
||Mar. 15, 1966
||Electric Discharge Device for
Producing Interaction Between Nuclei
||Jun. 28, 1966
||Method and Apparatus for Producing
Nuclear Fusion Reactions
||Jun. 4, 1968
Generating Fusion Reactions
This is a New
Item, added 01/19/2000
|Sep. 22, 1970 -
Robert L. Hirsch, Gene A. Meeks - Farnsworth Associates
||Lithium Ion Source In Apparatus
for Generating Fusion Reactions
||Oct. 13, 1970 - Robert Hirsch -
Reviewing the many patents of Philo T. Farnsworth, it becomes apparent that from his
very earliest work, Farnsworth was fascinated with the photoelectric effect. Of the forty
or so patents which led up to patents 3,258,402 - Electric Discharge Device for
Producing Interactions Between Nuclei, and patent number 3,386,883 - Method and
Apparatus for Producing Nuclear-Fusion Reactions, it can be seen that only two or
three of these Farnsworth patents do not utiliz e secondary electron emission in
some way. Below are my notes from reviewing his many patents. These notes include key
technical information from each patent, as well as my thoughts on how the concepts used in
that particular invention would eventually tie into the Fusor patents.
1,969,399 Electron Multiplier
- Uses opposed surfaces inside a special resistor surface sensitized to emit secondary
- The electrons are accelerated by a graduated electrostatic field.
- Secondary emitting material listed - barium, thorium.
- Barium - 1 secondary electron for each 33 volts of potential applied to plates
- Thorium - 1 secondary electron for each 45 volts of potential applied to plates
- This invention only relates to the Fusor in that it heralds the use of secondary
emission of electrons by bombarded surfaces.
1,970,036 Photo Electric Apparatus
- Nickel is an emitter of secondary electrons when struck by CRT electron bombardment.
- Potassium hydride is a photon sensitive material.
- Light sensitive material is on a silver film, which has been deposited on glass.
- Metallic potassium is distilled from a reservoir in the exhaust line and is allowed to
condense upon the silver film. The anode and glass are heated to prevent potassium
condensation upon them. Hydrogen is introduced into the tube and an electric discharge is
provided between anode and cathode, converting the potassium to potassium hydride.
- Relates to the Fusor in that nickel is a component element in stainless steel, and
nickel is a secondary emitter of electrons.
2,071,515 Electron Multiplying Device
- Alternating current of high frequency (60 MHz) is applied to electrodes, which have a
rather high DC potential on them. The AC causes electrons to bounce back and forth between
the sensitized plates, causing showers of secondary electrons. Distance between plates is
chosen so that the electron travel time matches the frequency of the applied current,
augmenting the effect. The multiplicative effect is limited by the space charge of the
accumulated cloud of electrons and the transverse component of the electrostatic field
within the chamber. A tubular electrode is used. Electrons stop short of electrodes and
are accelerated back towards the other electrode.
- Plates are nickel, preferably coated with caesium or other electron emitter.
- Nickel and molybdenum are easily out-gassed metals.
- Peaks in current flow occur when the average time of flight of the electrons is an odd
number of half-cycles, such as 1, 3, or 5.
- It is good to have a small amount of gas in this tube, as the ionization of the gas
tends to reduce the space charge between the plates.
- This device uses a high frequency RF field to provide alternating currents between
plates, helping to control the oscillation of electrons between two or more plates - a
feature of the future Farnsworth patent number 3,258,402 - Electric Discharge Device
for Producing Interactions Between Nuclei.
2,071,516 Oscillation Generator
- The electrodes are pure silver, which is first oxidized, then coated with caesium.
- Time-of-flight is controlled by both electrode spacing and the voltage potential between
- A plate spacing of 5.5 cm and voltages from 350 to 800 allowed tube to oscillate between
30 and 100 MHz.
- This tube can be set up to operate so that there are two clouds of electrons passing
each other while traveling in opposite directions between the plates in the tube.
- Very much a precursor to the future patent 3,258,402 - Electric Discharge Device for
Producing Interactions Between Nuclei and the Fusor patent as well. Both later devices
set up oscillating fields of electrons and ions, which would collide as they tried to pass
2,071,517 Multipactor Phase Control
- First reference to the word multipactor.
- Uses an apertured cathode.
- The screens are silver, which is oxidized and then has caesium vapor deposited upon
- Nickel releases 1.64 electrons per primary electron, when struck by electrons traveling
at the proper velocity.
- Caesium releases from 4 to 6 electrons per primary electron, when struck by an initial
electron that is traveling at the proper velocity.
- The collecting electrodes may be tantalum, tungsten, molybdenum, or preferably, nickel.
- If the surfaces should not emit secondary electrons, then they may be
"carbonized" to prevent emission.
- It is notable that I never do find out exactly how to "carbonize" electrodes
anywhere in Farnsworth's patents.
- We see here the use of curved dynode surfaces, which eventually evolve into spherical
surfaces in Farnsworth's later work. He is also using apertured cathodes, upon which the
Fusor will be critically dependent.
2,107,782 Radiation Frequency Converter
- Zinc and calcium tungstate will fluoresce under electron impact.
- Caesium silver oxide is especially sensitive to infrared radiation between 7,000 and
8,000 angstroms wavelength.
- Farnsworth was able to use the shaping of the electrodes in this device to such good
advantage that no external magnetic field was required for focusing or proper operation.
Such careful attention to electrode shape helped point Farnsworth to the Fusor.
- Perhaps the only other item in this patent relevant to Fusor design is the fact that a
transparent, conductive, metal film is deposited upon a glass surface. This type of film
may have been used to block electron entry into the optical viewing port of the Fusor
2,128,580 Means and Method of Operating Electron Multipliers
- Alkali metal surfaces will always release metal ions when used to produce secondary
- These metal ions can bombard the cathode and cause damage, unless an auxiliary electrode
is put into the operating space to gather them.
- One can use a special nickel-barium alloy, where the barium ends up on the surface of
- Multipactor can be used to efficiently generate high power harmonics of a fundamental
- This patent talks a bit about how dangerous uncontrolled ions can be in a vacuum, and
how their management may take place using auxiliary electrodes.
- Multipactor design allows flexibility of use
- Utilizes cathode with many tiny apertures through which electrons may be accelerated to
- Theoretical gain of 1,460,000 can be had with this tube
- Aluminum can emit secondary electrons greater than unity.
- Symmetrical electrodes allow the tube to operate with AC instead of DC
- The Fusor would also use apertured cathode/anode structures, through which electrons
would be accelerated and trapped in oscillating fields.
2,139,813 Secondary Emission Electrode
- Caesium silver oxide is only good at lower temperatures - cold cathode tubes, low power
- Nickel, alloyed with barium or strontium works at higher temperatures.
- Barium is added to nickel to form an alloy - barium makes up 1 % of the alloy.
- Must be heavily oxidized either before or after insertion into tube. If oxidized after
insertion, use gaseous discharge, make the barium-nickel alloy the negative DC potential.
Gradually heat cathode to remove gas. Continue to heat until barium is distilled out of
the alloy and appears on the walls of the tube. Next, barium "getter" is then
put on the walls of the tube. Cool the tube. Test secondary emission by running the tube
in an oscillator circuit.
- This design can operate with the cathode at red heat!
- This alloy has the potential to overcome a problem Farnsworth would eventually run into
when operating the Fusor - excess heat in the inner cathode sphere. He might have been
able to make the inner sphere of a nickel barium alloy instead of stainless steel and
could have allowed it (the electrode) to run at a dull red heat, which is the temperature
where this alloy best emits electrons!
2,140,285 Multiplier Coupling System
- Electron beam can be focused on a plate (cylinder) so that the heat generated from the
impact of fast electrons is far enough away so that the heat does not damage the sensitive
caesium silver oxide cathode surface.
- Perhaps Farnsworth could have used this lesson in redirection of heat in the Fusor
design, so that the inner electrode would not get so hot.
2,140,832 Means and Method of Controlling Electron Multipliers
- Sodium, potassium, caesium, barium, strontium, thorium are listed secondary emitters.
- Nickel barium alloy, when heated to bright red in vacuum becomes sensitized for
secondary emission of electrons.
- The cathode is a cylinder. Within it is a grid like anode structure of tungsten or
- Farnsworth likes to operate at a frequency high enough that the electrons don't get to
reach the opposite surface before they get reversed - gives higher output current.
- Ion control is important in multipactors, so as to reduce heating effects.
- Claims that a single multipactor tube as described in this patent can operate as an
entire transmitter. Oscillator power is described as 600 watts, or 1,000 watts as an
amplifier, i.e., this device can be the basis for a serious one-tube transmitter!
2,141,836 Charge Storage Dissector Tube
- An insulating layer may be put upon a nickel screen grid by smoking the grid with the
fumes of burning magnesium to deposit a continuous layer of magnesium oxide.
- Silver electrode screen is oxidized by gaseous discharge in oxygen atmosphere.
- Magnesium oxide is placed on back-side of screen only.
- Caesium is deposited on the silver on the front side. Excess caesium can be prevented by
baking the tube at 60 degrees while on a pump.
- The use of metallic films on the inside of a glass cylinder, forming bands, as a means
to control or focus electrons or ions, will be eventually used again in his ion transport
2,141,837 Multistage Multipactor
- Calcium is listed as a secondary emitter, along with thorium, caesium, and potassium.
- Multistage multipactor has multiple cylindrical sensitized plates, with progressively
higher potentials applied.
- Important to note that the cylinders and disks also are progressively larger.
- This nested electrode structure is readily apparent in the design of patent 3,258,402 - Electric
Discharge Device for Producing Interactions Between Nuclei
2,141,838 Split Cathode Multiplier Tube
- Multiple, separate cathode rings arranged near a cone shaped apertured anode electron
- Design is based upon exquisite control of electron paths by the deliberate relationships
and spacing of secondary emissive surfaces, which do not require any external magnetic or
even electrostatic fields to aid in the guiding of the electrons. The use of truncated
cones is later seen in the design of the early ion guns in patent 3,386,883 - Method
and Apparatus for Producing Nuclear-Fusion Reactions.
2,143,262 Means for Electron Multiplication
- Gains of 100,000 to 1,000,000 are possible with a single multipactor.
- Tube is operated in this patent in an "interrupted" mode, i.e., pulsed
- If a tube is sensitive enough to self-oscillate/self interrupt, then no eternal RF
excitation is necessary.
- This tube design has an internal inductance (a silver coil) mounted near the cathodes as
part of the self-oscillation circuitry, which is designed to operate at 200 MHz.
- Nested, circular dynodes are again used. Farnsworth describes a space charge building up
between electrodes to saturation, then stabilizing at the saturation level - exactly the
conditions the Fusor would achieve at the center of the virtual cathode when attaining
optimum operating conditions.
- In this device, Farnsworth uses "interruptions" of the current to control
electron multiplication - something that could have been incorporated into the power
supply of the Fusor, although no specific mention of this method of control is made in the
2,155,478 Means for Producing Incandescent Images
- Annealed tungsten wire .001 inch diameter is woven into cloth, cleaned, then placed in
an etchant bath of hot sodium nitrite, where the wire is etched down to a diameter of
0.00025 inches, making the mesh practically invisible.
- A transparent film of nickel is placed behind the mesh, electrons pass through mesh,
bounce into nickel film, and then form a shower of secondary electrons.
- A wire mesh cloth of mesh size of 50 to 300 per inch was hand made with a special
- A metallic, conductive film is used in this device - such a film may be employed in the
Fusor's viewing port to stop stray electrons from entering the port. This type of film may
also act as a high-density light filter.
2,161,620 Two Stage Electron Multiplier
- Progressively larger potentials are applied to a multi-element structure. Secondary
emitting surfaces are used. The two-stage amplifier provides gain of 100 to 1.
- This device has no direct bearing upon the future design of the Fusor.
2,172,152 RF Frequency Multipactor Amplifier
- Uses helical grid, permeable plates.
- Higher frequency response of the multipactor tube can be done by shining light upon the
photosensitive cathode or by providing electrons via an electron gun - necessary when
operating at frequencies above 10 MHz.
- Again, the nested electrodes appear in a multipactor device.
- The Fusor patents mention that the electrodes should emit electrons when exposed to UV
light; perhaps its operation is not entirely electron dependent? It could be that like
this device, photo-emission of electrons plays an important part in the operation of the
2,174,487 Self-Energized AC Multiplier
- Caesium silver oxide is used both as a photo detector and as a secondary electron
emitter. The device requires differing amounts of caesium for photo versus
electro-activity, but a suitable balance was struck. The best photo-emitters are also the
best secondary electron emitters, though the converse is not always true.
- Device utilizes self-oscillation, i.e., AC to improve gain. Was the Fusor capable of
self-oscillation, and was an AC current partially responsible for its successful
operation? This possibility is not mentioned in the Fusor patents, but occurs repeatedly
in this and other multipactor patents, so it is certainly a very real possibility. If a
researcher attempted to replicate the Fusor and failed to duplicate a necessary
self-oscillatory operation, the device might not w ork!
- Interrupted multiplier frequency is about 2 MHz, while amplifying signal 50 to 150 MHz.
- The anode voltage is interrupted, causing the gain of the tube to increase greatly - the
interruptions allow the space charge to be controlled, and let more electrons reach the
- When operated in this oscillatory mode, operational adjustment is not critical. So
again, the question arises, if a Fusor, which is a large high power multipactor, is
operated in oscillatory mode, perhaps successful operation might not require critical
adjustment and so could be more easily obtained?
2,179,086 Means for Producing an Incandescent Image
- Incandescent screen uses a refractory cloth, much like Coleman lantern mantles.
- Cloth used is a very fine weave cut rayon velvet, impregnated with 99 percent thorium, 1
percent uranium, and some aluminum and/or beryllium nitrate salt, dried, and "burnt
off". Weave count, after burning and shrinkage, is 500 per inch! Screen is fast
enough for TV work, too bright to look at directly.
- This patent has nothing to do with Fusor technology, but it is a fascinating device!
2,179,996 Electron Multiplier
- Progressively gradient potential down an anode wire inside an emissive cylinder creates
multiplication by an electron drift effect down the length of the emissive cylinder.
- It is interesting to note that this design is a clever way to deal with the problem of a
space charge reaching saturation and limiting multiplication. Rather than use simple
self-oscillation to disrupt the space charge, as in patent number 2,174,487, Farnsworth
instead creates a smooth voltage gradient along a resistive wire which "herds"
the electrons down the length of a cylindrical surface. This allows the oscillating
electrons to repeatedly strike fresh areas of the emis sive surface, knocking ever more
- I do not see that the Fusor patents utilize a gradient voltage field along conductors to
control space charge in any way. However, it is possible that a new Fusor design could
utilize electron drift along a voltage gradated electrode surface to improve the creation
of secondary electrons off of the cathode surfaces.
- 2,180,279Method of Operating Electron Multiplier
- Non sinusoidal excitation waveforms are used to insure that all the electrons have the
same "time of flight" times, and thusly the same degree of multiplication.
- Because the Fusor did not appear to be operated in a self-oscillatory mode, nor did it
appear to be driven by an "interrupted" power source, I do not expect the
methods developed for this particular operation of an amplifying multipactor to apply to a
Fusor. However, if the Fusor was operated in an "interrupted" mode, then
the use of a non-sinusoidal waveform might indeed be of importance!
2,184,910 Cold Cathode Electron Discharge Tube
- A simple patent which locks up the use of facing hemispherical/spherical electrodes in a
pure cold-cathode tube.
- The spherical electrode designs shown in this patent absolutely led the way to the
design of the Fusor, and especially the design of patent 3,258,402 - Electric Discharge
Device for Producing Interactions Between Nuclei with it's multiple, nested spherical
- It is interesting to note that two separate physical cathodes were used, while in the
Fusor only one physical cathode was necessary, where the other cathode replaced with a
virtual cathode in the center of the sphere within the anode space.
2,189,358 Diode Oscillator Tube Construction
- Excellent descriptions of how relative electrode size and position of the anode and
cathodes affects the operation mode of a diode oscillator. More spherical elements.
- Here we have a spherical multipactor shown, specifically being used in self-oscillatory
mode, using only an external inductor to achieve resonance. The Fusor would have only
needed an external inductor to do the same thing. It is possible that the Fusor would marginally
operate as shown in the patent without self-oscillating, but would perform best if
operated in an oscillatory mode! This would be an excellent way for Farnsworth to protect
the secret of operation, while still being able to obtain a patent.
2,203,048 Shielded Anode Electron Multiplier
- An electron drift tube, utilizing a carborundum tube coated with secondary emissive
metals. Has an accelerating electrode, which is used to limit space charge effects near
- I see no applications of the principles used in this multipactor were applied in the
Fusor designs, except possibly the use of a screened electrode.
2,204,479 Means and Method for Producing Electron Multiplication
- Interesting zigzag, multistage multiplier designs.
- Apparently it is immaterial what angle electrons strike an emissive surface - they
always leave perpendicularly.
- This device uses accelerating screens in front of the emissive surfaces to accelerate
the electrons. The screens may be biased at the same or higher voltage than the electrodes
themselves. The Fusor uses biased screens.
2,217,860 Split Cathode Multiplier
- Another cone shaped multiplier. Design talks about using anode voltages as high as
10,000 volts for very high power outputs.
- Fundamentally the same as the tube design in patent 2,204,479, but using dual cathodes,
very high power for a single tube.
- It looks like this is the first multipactor that Farnsworth designed that could supply
hefty power outputs.
2,221,374 X-ray projection Device
- CRT uses cells of ionizable gas, which are ionized by X-rays to fluoresce a screen to
produce an image.
- Only device I'm familiar with that uses a scanning electron beam to generate a scanning
- Probably no application toward the Fusor, but perhaps a possible immediate use for
scanning lithography to be used in the manufacture of microchips?
- Uses apertured cathode assemblies. Amplification of 100,000 to 1 million possible. Uses
200 MHz biasing oscillator, which allows for very small device.
- Within a multiplier, the positive ions have a mobility factor of almost precisely 1/500th
that of electrons
- This patent is specifically for an improved dissector tube design, and Farnsworth
substantially reiterates his earlier patent claims on how multipliers can be operated to
amplify RF, self-oscillate, etc.
- Nothing new in this patent as regards Fusor technology.
2,260,613 Electron Multiplier
- Zigzag multistage amplifier, much like 2,204,479.
- Placing fine wire grids in front of the emissive electrodes, and charged to high
potentials, accelerate the electrons and improve operation.
- One design of this tube utilizes a magnetic field, which causes the path of the
electrons to form a spiral, and he places the secondary emissive surfaces in a
corresponding spiral so they will be impacted.
- No appreciable addition to Fusor technology in this patent over previous patents.
2,274,194 Apparatus for and Method of Electron Discharge Control
- As best as I can tell, this is a traveling wave tube design, probably the first ever. A
moving electron beam is played upon two curved plate targets. I am surprised that emissive
surfaces were not employed in the design of this tube.
- No definite application to Fusor technology is evident.
2,286,076 Electron Control Device
- Input electron flow controls number of secondarily emitted electrons, allowing high
ration of mutual conductance value to dc flow in the device
- No Fusor contribution.
- Rectifier has transformer secondary winding inside of tube structure, with transformer
core and primary outside of tube, providing very high voltage isolation, allowing very
high voltages to be rectified, without HV breakdown. High frequency AC (10 kHz) is used in
the filament transformer.
- It is possible that the high voltage power supply for the Fusor utilized such
2,311,981 Electron Control Device
- Multiple electrode multiplier where electrodes are in series - increases amplification
of AC component without necessarily magnifying DC component.
- Interesting electrode design - it seems the more Farnsworth worked with multipactors,
the more he used electrode shape and placement to control the action of the electrons.
3,181,028 Ion Transport Vacuum Pump
- Ion transport pump capable of vacuum of 10-10 millimeters of mercury. Glass envelope.
Electrostatic fields are shaped to force ions into a restricted area then scavenged by a
roughing pump. The vacuum tube should be operated as a multipactor to insure ionization is
continuously done, via using a tungsten rhenium cold cathode, and an RF current, chosen to
oscillate at the electron transit frequency between the two cathodes (dynodes).
- This ion vacuum pump is more difficult to build than his later pump, and this pump also
has only one stage of pumping, versus his later two-stage pump.
- There is a specific note of the very high ion concentration in the center of the anode
space - exactly what was going to be required in the Fusor.
3,201,640 Electron Gun in the Form of a Multipactor
- Produces high-density electron beam with small cross section using multipactor
technology. Uses 50 MHz oscillator as part of multipactor circuit. Cold cathode, no
filament, used in CRT.
- Note the dished cathode, conical director electrodes, annular focusing rings - all these
elemental designs were to be utilized in Farnsworth's patent 3,258,402 - Electric
Discharge Device for Producing Interactions Between Nuclei.
3,240,421 Ion Transport Pump
- Superior, two stage ion vacuum pump. Glass envelope. Uses multipactor design, simple
construction techniques. Incorporates several reflector electrodes with spherical
- Capable of 10-10 mm vacuum. Has magnetic solenoid coils, though a claim is made that the
pump will work without them. Maximum DC voltage is only a couple thousand volts. Pump is
about 18 inches long, and about 6 inches in diameter.
- His ion pumps really allow Farnsworth to gain critical experience with the controlled
movement and directional flow of ions.
- Farnsworth had a knack for designing a complex machine to do a task, then he comes up
with a simpler way - his two ion pumps are an excellent example of this simplification
3,258,402 Electric Discharge Device for Producing Interactions Between Nuclei
Full patent 3,258,402
- An awesome patent, with incredible detail of construction. Farnsworth's pictorials start
out by showing a pure spherical element design, based upon the 95% open mesh anode
construction, then he describes a bizarre nested cup anode that is supposed to provide
field shaping to create a true spherical electrostatic field. Both these designs appear to
be experimental, and were test beds to provide him experimental data and design clues.
Next, he t hrows in ion injection (personally, I'd modify the electron gun he used on the
CRT patent) then he finally gets into serious practical designs using multiple spherical
anodes used in conjunction with ion injection.
- This multi-concentric sphere design would be an absolute nightmare to design, machine,
and construct, not to mention outrageously expensive!
- His early two reflector design required micrometer screw adjustments to precisely
position the dynodes, so as to achieve focusing, but the final 12-gun design does not
appear to have any way of making similar adjustments! I'd say he had nailed down
the electrostatic manipulation and focusing of the beams to perfection by the time he
built the 12-gun unit. The vacuum-tight electrode design is obviously the result of tried
and true work.
- He modulates the anode with RF, but the anode has 140 KV DC on it, no mean task!
- A vacuum of 10-10 mm is required for operation, so his ion transport vacuum pump was
undoubtedly used to pump this baby down!
- The cathode structures have a hole drilled in the center of the spherical reflector,
which forms a "well", into which errant electrons fall and get lost. This is a
definite sign of tweaking the anode current to perfection. An armchair design would never
have this feature.
- There is an incredible wealth of information and formula in the text on electron lenses
and how to direct and focus the electron beams very precisely.
- The "typical" dimensions are an invaluable aid in trying to replicate this
- Farnsworth has included many formula and operational directions, or "user
instructions" which are immaterial to his receiving a patent, indeed, he was
exceptionally wordy and descriptive. This extra information would be very valuable to
anyone trying to construct a copy of his device. My feelings from reading the patent text
are that Farnsworth may have deliberately included a lot of extra information in this
patent to help others duplicate this device.
- The multipactor with the electron emissive surfaces, the curved cathodes, the nested
spherical electrodes, shaped electrostatic fields, ion vacuum pump, conical beam shapers,
ion guns, electron scavenging, etc., all of his past patents start to come together in
this one device!
3,386,883 Method and Apparatus for Producing Nuclear-Fusion Reactions
- This was the last technical patent I could find by Farnsworth - the culmination of a
lifetime of work!
- Practically every vacuum tube concept this man developed during 40 years of research
came together and was utilized in this invention.
- First, it should be noted that he completely turns his previous fusion device inside
out, making the cathode the center of the sphere, instead of the anode.
- This device not only produces huge amounts of heat from the nuclear reactions, but up to
40% of the energy is converted directly into electrical current which may be extracted
from the anode/cathode connections.
- His original Fusor designs discuss the creation of a virtual anode in the center of the
sphere, but now this device uses both virtual anodes and cathodes.
- He describes the bouncing of ions between his virtual electrodes, and coins the term
"inertial containment" of the ions.
- The boundaries of the virtual anodes and cathodes must be kept well defined and
- The emission of secondary electrons from the inner cathode surface is necessary to
produce virtual anodes and cathodes within the inner cathodic space.
- Always run at lowest practical gas density to keep charge-exchange losses to a minimum.
- To reduce scattering losses, the electron current flowing in the cathodic space needs to
be high. This is accomplished by having electron emitters within the cathode - are we
surprised by the use of emissive surfaces to generate extra electrons?
- Many of the electrons traveling in the cathodic space have orbital paths, which sweep
the inside of the cathodic space. Having more than 10% orbiting electrons is undesirable -
they fuzz up the boundaries of the virtual electrodes. The orbiting electrons, on the
other hand, reduce the probability of electron recombination.
- A series of alternating anodes and cathodes is made to exist within the space enclosed
by the inner sphere and this creates a cathodic "singularity" or mathematical
singularity at the center virtual electrode!
- If the ratio of the radius of the virtual anode and virtual cathode is much greater than
3 to 1, then the inner cathode may not form, and if this ratio is smaller, then the
circulatory currents required to maintain the virtual electrodes becomes too large to
- The electron "mesh current", which is the result of secondary electron
emission and the electrons which flow from the real cathode to the cathode apertures to
the real anode, will initially be large while the virtual electrodes form. This current
should immediately drop to insignificant values once the Poissor (virtual electrode
structure) has formed.
- Once the virtual fields are established, and the space charge has stabilized, and the
ions have been injected, the power consumed by the device is a minimum.
- Stainless steel (which happens to contains nickel) and molybdenum are listed as an
electron emitting material for cathodes. Why did he not use his ubiquitous alloy of nickel
and barium? Maybe the cathode does not become red hot? He talks about the difficulty in
removing excess heat from this cathode - maybe the heat can be ignored by using his nickel
with 1% barium alloy, as was used in his earlier patents on high power multipactors
(patent 2,139,813 -Secondary Emission Electrode?)
- Figure 9 shows a working embodiment of the Fusor, using two concentric cathodic
spheres within a spherical anode. The outer cathode is negatively biased, and also serves
to remove ions from the non-space-charged field at turn-on.
- Losses within the Fusor are typically about 10% of the total power created (not
- Heat absorption by the inner cathode is a very serious matter, and Farnsworth deals with
it by conducting heat away through the power supply line (pathetic heat transfer method,
at best!) I suggest that replacing the electrical supply line with a suitably designed
heat pipe (originally designed for space use by NASA) and external heat-sink (part of the
water cooling system of the anode?) would work a hundred times better.
- Increasing the applied voltage will increase the neutron count. The current will
increase by three halves power. Higher voltages decrease the heat losses within the
- Normal gas pressure during operation is 3.535x10^19 molecules or less, or 3.353x10^13
ions/cc at a normal operating pressure of 10-3 mm Hg.
- Fusor is initially pumped down to 10-9 to 10-10 mm Hg, high voltage is turned on, and
deuterium and tritium gas (50/50 mixture) are introduced into the ion guns at a pressure
of 10-6 to 10-4 mm Hg. The virtual electrodes (Poissor) will form.
- Within the larger virtual anode a small virtual cathode will form, and it is within this
small cathodic space that fusion is most likely to occur.
- Neutrons will carry energy out through the walls of the device and represent a loss of
energy at the core of the device, leaving 64% of the energy available to be converted
directly into electricity.
- Only those ions which are created by the actual fusion process will have sufficient
energy to produce electrical energy
- The system is self-regulating, in that a sudden increase in source gas will not produce
a catastrophic surge in output energy - the virtual sheaths change size, modifying plasma
density, performing a self-regulatory action.
- The ions leaving the core of the Fusor can have energy levels ranging from 0.82 meV to
14.7 meV. If the goal is to directly convert the energy into electrical power, it is most
desirable to limit the production of ions to those with the lowest meV level (less heating
of the outer anode.) If the desire is to produce heat which will then be converted into
electrical (or other) power, then it would be best to produce only the faster (higher meV)
- Modifying the gas density and using a high volume vacuum pump allows some leeway in
controlling what elements get to enter the fusion process, but there are limits on what
the operator can do (the highest meV particles will be created regardless.)
- In examining the text of the patent, I noted that Farnsworth did not expend much detail
on his later, improved version of the Fusor, but instead lavishes descriptive detail on
the earlier, unimproved version. This early design uses the weaker ion guns, and the unit
does not have the electrostatic focusing rings that the final design incorporates. The
early unit does not have (or possibly may not require) the ability to make micrometer
adjustments of the inner anode sphere's position within the anode . The later Fusor
design, which eliminates one of the inner concentric spheres, is also much, much easier to
build. I think Farnsworth's strategy was to provide a competitor with detail plans for the
early inferior device, and to provide just enough detail of his more advanced work
so that he could defend his patent should the need arise.
- Examining Figure 23, you will notice that there are visible several screened
holes arranged around the inside of the cathode sphere. The viewing port is aligned with
one of these screens, allowing the user to look all the way into the core of the Fusor. No
explanation of the particulars of the viewing port are given, but the drawing shows some
detail of the viewing port which is not numbered or described. I believe that one of the
undescribed it ems shown in the drawing of the port is a wire screen, which would be
necessary to extend the anode surface across the viewing area. Immediately behind this
undescribed line (screen) is a second item, which also appears to go across the viewing
area. I conjecture that it could be a high-density filter for blocking the intense UV
light produced by the core. A leaded glass or water filled
port might be necessary to block the neutrons produced by the core so that the operator
would not be injured by neutrons coming up t hrough the viewing port. Also, the design
shown makes no provision for cooling the anode jacket, nor does any neutron shielding
material surround the anode. Protection against high-speed neutrons would be mandatory for
safe operation of this device.
- No description is given for the spacing between the holes for the screened ports and the
smaller holes through which the ion jets pass.
- In Figure 27, It is unclear how the cathode sphere can be positioned by the
micrometer adjustments of the 71a electrode assembly, since the 49a assembly
is described as a "rigid" attachment capable of supporting the cathode sphere.
If the mounting 110 consists of two concentric sliding cylinders, then I can see
how the inner sphere could be moved up and down, but not side to side. The drawing shows
an adjustment design that only al lows the sphere to be tilted a small amount , from
side-to-side, and even then only in one axis. It is, however, possible that a second
adjustment screw, for another axis, which is not visible to the observer in this drawing,
might be hidden behind the high voltage bushing. It would also seem necessary that the
physical mounting of the supporting structures, as shown, would necessitate an open bias
screen port to maintain the symmetry of the spherical electrode and the resulting
spherical virtual electrodes. The large, solid mounting, as shown, ruins the symmetry of
the screened ports.
- In Figure 23, there is a lack of detail in the exact implementation of the high
- Also in Figure 23, there is a ceramic feed-through bushing at the high voltage
mount - this should be unnecessary, though it may have served a purpose in the design
shown in Figure 11.
- Figure 26 has the electrical connection (wire 156) to be make from spring
wire, and it looks like the design was to allow for the adjusting movement of the inner
sphere. The patent describes the spring wire as touching metal plug 145, but the
wire is inside a conducting metal tube 144, so it does not seem absolutely
necessary for the wire to touch the plug.
- In Figure 27, the filament loop drops below the radial centerline 165, to
allow ions to pass through the center of the filament? (In Figure 21 the filament
is shown as a loop aligned with the center of the gun.) And there are unidentified plates
or disks at the rear of the tube - are these plates possible ion emitters, as is shown in
some other ion gun patent descriptions?
- The Fusor was quite small - the anode was a sphere 6 inches in diameter, and the cathode
was slightly over 4 inches in diameter, and the electron guns were less than 3 inches in
- The cathode sphere is 60 mil 304 stainless steel; the anode is 93 mil 304 stainless
- Farnsworth's cathode shell is only approximately spherical in shape - there are 12 flat
areas where the biasing screens mount. It should be possible to form perfect hemispheres,
then weld them together, or to have spheres made from 304 stainless (I know of an Internet
Web-site, which is for a company that specializes in making custom balls.) The bias
screens could have flanges machined to fit the radius of curvature, and the screens
themselves could also be curved to help maintain a more spherical catho dic field.
- Farnsworth apparently is sacrificing two bias screen areas for the mounting flanges for
the inner cathode - this should not be necessary! The mounting points can be relocated
between the bias screen positions.
- Note in Figure 11, at one end of rod 58a, there is an undescribed
cone shaped washer with a lip placed near the opening into tube 50. This is likely
an electron shield, which can keep stray electrons in the anode space from traveling down
tube 50. The cone shaped washer may instead serve as an electrostatic field shaper
placed near the opening. Figure 23 does not show this important item.
- Referring back to patent 3,258,402 - Electric Discharge Device for Producing
Interactions Between Nuclei, I have to note that this early design required a source
of RF power, and the newer design apparently does away with this. Also the early design
used a total of four spherical electrodes, one of which had deep cone-shaped ion
guides, which would have been difficult and expensive to machine. The new design only has two
sphe rical sheet-metal electrodes, which are relatively inexpen sive. What parts do
require machining are relatively simple of design, and no exotic metals are used. Indeed,
it should be possible to stamp the spheres out of stainless steel sheet metal, almost
3,530,497 Apparatus For Generating Fusion Reactions
- This patent is by Robert Hirsch and Gene Meeks, associates of Farnsworth. As you will
see, this patent is a Farnsworth Fusor, but the patent was issued after Farnsworth's
death. I know that Hirsch and Meeks did a lot of the Fusor work in the Farnsworh labs, and
many of the successful Fusor innovations were theirs. I will save a detailed examination
of the patent details for another time, but please study this patent and compare Meek's
and Hirsch's changes to Farnsworth's own last patent.
3,533,910 Lithium Ion Source in Apparatus for Generating Fusion Reactions
- This patent is by Robert Hirsch, an associate of Farnsworth. As you will see, this
patent is a Farnsworth Fusor, but the patent was issued after Farnsworth's death. I know
that Hirsch did a lot of the Fusor work in the Farnsworh labs, and many of the successful
Fusor innovations were his. I will save a detailed examination of the patent details for
another time, but please study this patent and compare Hirsch's changes to Farnsworth's
own last patent.
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