Fusor - AbsoluteAstronomy.com

The Farnsworth–Hirsch fusor, or simply fusor, is an apparatus designed

Invention

An invention is a novel composition, device, or process. An invention may be derived from a pre-existing model or idea, or it could be independently conceived, in which case it may be a radical breakthrough. In addition, there is cultural invention, which is an innovative set of useful social...

by Philo T. Farnsworth to create nuclear fusion

Nuclear fusion

Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...

. It has also been developed in various incarnations by researchers including Elmore, Tuck, and Watson, and more recently by George H. Miley

George H. Miley

George H. Miley is a physicist, inventor, and professor emeritus of the University of Illinois at Urbana–Champaign.In 1955 Miley received his B.S. in Chemical Engineering/Physics from Carnegie Mellon University. He obtained his M.Sc. and his Ph.D...

and Robert W. Bussard

Robert W. Bussard

Robert W. Bussard was an American physicist who worked primarily in nuclear fusion energy research. He was the recipient of the Schreiber-Spence Achievement Award for STAIF-2004. He was also a fellow of the International Academy of Astronautics and held a Ph.D...

. Unlike most controlled fusion systems, which slowly heat a magnetically confined

Magnetic confinement fusion

Magnetic confinement fusion is an approach to generating fusion power that uses magnetic fields to confine the hot fusion fuel in the form of a plasma. Magnetic confinement is one of two major branches of fusion energy research, the other being inertial confinement fusion. The magnetic approach is...

plasma

Plasma (physics)

In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...

, the fusor injects "high temperature" ion

Ion

An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

s directly into a reaction chamber, thereby avoiding a considerable amount of complexity. The approach is known as inertial electrostatic confinement

Inertial electrostatic confinement

Inertial electrostatic confinement is a concept for retaining a plasma using an electrostatic field. The field accelerates charged particles radially inward, usually in a spherical but sometimes in a cylindrical geometry. Ions can be confined with IEC in order to achieve controlled nuclear fusion...

.

Hopes at the time were high that it could be quickly developed into a practical source of fusion power

Fusion power

Fusion power is the power generated by nuclear fusion processes. In fusion reactions two light atomic nuclei fuse together to form a heavier nucleus . In doing so they release a comparatively large amount of energy arising from the binding energy due to the strong nuclear force which is manifested...

. However, as with other fusion experiments, development into a generator has proven to be difficult. Nevertheless, the fusor has since become a practical source of free neutron

Neutron

The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...

s, and it is produced commercially for this purpose. Fusors have been assembled in low-power forms by hobbyists.

History

The fusor was originally conceived by Philo T. Farnsworth, better known for his pioneering work in television

Television

Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...

. In the early 1930s he investigated a number of vacuum tube

Vacuum tube

In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...

designs for use in television, and found one that led to an interesting effect. In this design, which he called the multipactor, electron

Electron

The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...

s moving from one electrode

Electrode

An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...

to another were stopped in mid-flight with the proper application of a high-frequency magnetic field

Magnetic field

A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

. The charge would then accumulate in the center of the tube, leading to high amplification. Unfortunately it also led to high erosion on the electrode

Electrode

An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...

s when the electrons eventually hit them, and today the multipactor effect

Multipactor effect

The multipactor effect is a phenomenon in radio frequency amplifier vacuum tubes and waveguides, where, under certain conditions, secondary electron emission in resonance with an alternating electric field leads to exponential electron multiplication, possibly damaging and even destroying the RF...

is generally considered a problem to be avoided.

What particularly interested Farnsworth about the device was its ability to focus electrons at a particular point. One of the biggest problems in fusion research

Fusion power

is to keep the hot fuel from hitting the walls of the container. If this is allowed to happen, the fuel cannot be kept hot enough for the fusion reaction

Nuclear fusion

to occur. Farnsworth reasoned that he could build an electrostatic plasma confinement system in which the "wall" fields 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 it would be unable to escape. He called this concept a virtual electrode, and the system as a whole the fusor.

Design

Farnsworth's original fusor designs were based on cylindrical arrangements 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 charged electrodes would keep the fuel as a whole off the walls of the chamber, and impacts from new ions would keep the hottest plasma in the center. He referred to this 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: as the fuel was delivered via accelerators, the amount of fuel that could be used in the reaction was quite low.

Robert Hirsch

Things changed dramatically with the arrival of Robert Hirsch

Robert L. Hirsch

Robert L. Hirsch is a former senior energy program adviser for Science Applications International Corporation and is a Senior Energy Advisor at MISI and a consultant in energy, technology, and management. His primary experience is in research, development, and commercial applications...

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

Corona discharge

In electricity, a corona discharge is an electrical discharge brought on by the ionization of a fluid surrounding a conductor that is electrically energized...

around the outer electrodes was enough to provide a source of ions. Once ionized, the gas would be drawn towards the inner (negatively 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.

Work at Farnsworth Television labs

New fusors based on Hirsch's design were first constructed in the late 1960s. The first test models demonstrated that the design was effective. Soon they were showing production rates of up to a billion neutrons per second, and rates of up to a trillion per second have been reported.

All of this work had taken place at the Farnsworth Television labs, which had been purchased in 1949 by ITT Corporation

ITT Corporation

ITT Corporation is a global diversified manufacturing company based in the United States. ITT participates in global markets including water and fluids management, defense and security, and motion and flow control...

, as part of its plan to become the next RCA

RCA

RCA Corporation, founded as the Radio Corporation of America, was an American electronics company in existence from 1919 to 1986. The RCA trademark is currently owned by the French conglomerate Technicolor SA through RCA Trademark Management S.A., a company owned by Technicolor...

.

A fusion research project was not regarded as immediately profitable. 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

United States Atomic Energy Commission

The United States Atomic Energy Commission was an agency of the United States government established after World War II by Congress to foster and control the peace time development of atomic science and technology. President Harry S...

, 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 the timing was bad; Hirsch himself had recently revealed the great progress being made by the Soviets using the tokamak

Tokamak

A tokamak is a device using a magnetic field to confine a plasma in the shape of a torus . Achieving a stable plasma equilibrium requires magnetic field lines that move around the torus in a helical shape...

. In response to this surprising development, the AEC decided to concentrate funding on large tokamak projects, and reduce backing for alternative concepts.

Work at Brigham Young University

Farnsworth then moved to Brigham Young University

Brigham Young University

Brigham Young University is a private university located in Provo, Utah. It is owned and operated by The Church of Jesus Christ of Latter-day Saints , and is the United States' largest religious university and third-largest private university.Approximately 98% of the university's 34,000 students...

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 spent all of Farnsworth's savings. The IRS

Internal Revenue Service

The Internal Revenue Service is the revenue service of the United States federal government. The agency is a bureau of the Department of the Treasury, and is under the immediate direction of the Commissioner of Internal Revenue...

seized their assets in February 1971, and in March Farnsworth suffered a bout of pneumonia

Pneumonia

Pneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...

which resulted in his death. The fusor effectively died along with him.

Recent developments

In the early 1980s, disappointed by the slow progress on "big machines", a number of physicists took a fresh look at alternative designs. George H. Miley at the University of Illinois

University of Illinois at Urbana-Champaign

The University of Illinois at Urbana–Champaign is a large public research-intensive university in the state of Illinois, United States. It is the flagship campus of the University of Illinois system...

picked up on the fusor and re-introduced it into the field. A low but steady interest in the fusor has remained since then. An important development was the successful commercial introduction of a fusor-based neutron generator

Neutron generator

Neutron generators are neutron source devices which contain compact linear accelerators and that produce neutrons by fusing isotopes of hydrogen together. The fusion reactions take place in these devices by accelerating either deuterium, tritium, or a mixture of these two isotopes into a metal...

. From 2006 until his death in 2007, Robert W. Bussard

Robert W. Bussard

gave talks on a reactor similar in design to the Fusor, now called Polywell

Polywell

A polywell device is a type of fusion reactor that was originated by Robert Bussard under a U.S. Navy research contract. It traps electrons in a magnetic confinement inside its hollow center. The negatively charged electrons then accelerate positively charged ions for the purpose of achieving...

, that he stated would be capable of useful power generation.

Use as a power source

Basic fusion

Nuclear fusion

refers to reactions in which lighter nuclei

Atomic nucleus

The nucleus is the very dense region consisting of protons and neutrons at the center of an atom. It was discovered in 1911, as a result of Ernest Rutherford's interpretation of the famous 1909 Rutherford experiment performed by Hans Geiger and Ernest Marsden, under the direction of Rutherford. The...

are combined to become heavier nuclei. Several such reactions release energy that can, in principle, be harnessed to provide fusion power

Fusion power

. The lowest energy reaction occurs in a mix of deuterium

Deuterium

Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...

and tritium

Tritium

Tritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...

, when the ions have to have a temperature of at least 4 keV (kiloelectronvolts), equivalent to about 45 million kelvin

Kelvin

The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...

s. At such temperatures, the fuel atoms are ionized and constitute a plasma

Plasma (physics)

. In a practical fusion power plant, fusion reactions have to occur fast enough to make up for energy losses. The rate of reaction varies with the temperature and the density of the fuel and the loss rate is characterized by the energy confinement time τ_E. The minimum conditions required are expressed in the Lawson criterion

Lawson criterion

In nuclear fusion research, the Lawson criterion, first derived on fusion reactors by John D. Lawson in 1955 and published in 1957, is an important general measure of a system that defines the conditions needed for a fusion reactor to reach ignition, that is, that the heating of the plasma by the...

. In magnetic confinement fusion

Magnetic confinement fusion

, the necessary conditions are approached by heating a plasma contained by magnetic fields. This has proven to be very difficult in practice. The complexity of the systems applied detracts from the usefulness of the design for a practical generator.

Fusor fusion

In the original fusor design, several small particle accelerator

Particle accelerator

A particle accelerator is a device that uses electromagnetic fields to propel charged particles to high speeds and to contain them in well-defined beams. An ordinary CRT television set is a simple form of accelerator. There are two basic types: electrostatic and oscillating field accelerators.In...

s, essentially TV tubes with the ends removed, inject ions at a relatively low voltage into a vacuum

Vacuum

In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...

chamber. In the Hirsch version of the fusor, the ions are produced by ionizing a dilute gas in the chamber. In either version there are two concentric spherical electrode

Electrode

An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...

s, the inner one being charged negatively with respect to the outer one (to about 80 kV). Once the ions enter the region between the electrodes, they are accelerated towards the center.

In the fusor, the ions are accelerated to several keV by the electrodes, so heating as such is not necessary (as long as the ions fuse before losing their energy by any process). Whereas 45 megakelvins is a very high temperature by any standard, the corresponding voltage is only 4 kV, a level commonly found in such devices as neon lights and television

Television

Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...

s. To the extent that the ions remain at their initial energy, the energy can be tuned to take advantage of the peak of the reaction cross section

Cross section (physics)

A cross section is the effective area which governs the probability of some scattering or absorption event. Together with particle density and path length, it can be used to predict the total scattering probability via the Beer-Lambert law....

or to avoid disadvantageous (for example neutron-producing) reactions that might occur at higher energies.

The ease with which the ion energy can be increased appears to be particularly useful when "high temperature" fusion reactions

Aneutronic fusion

Aneutronic fusion is any form of fusion power where neutrons carry no more than 1% of the total released energy. The most-studied fusion reactions release up to 80% of their energy in neutrons...

are considered, such as proton

Proton

The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....

-boron

Boron

Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...

-11, which has plentiful fuel, requires no radioactive tritium

Tritium

Tritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...

, and produces no neutrons in the primary reaction.

Power density

Because an electrostatic potential well cannot simultaneously trap both ions and electrons, there must be some regions of charge accumulation, which will result in an upper limit on the achievable density. The corresponding upper limit on the power density, even assuming D-T fuel, may be too low for power production.

Thermalization of the ion velocities

When they first fall into the center of the fusor, the ions will all have the same energy, but the velocity distribution will rapidly approach a Maxwell-Boltzmann distribution. This would occur through simple Coulomb collision

Coulomb collision

A Coulomb collision is a binary elastic collision between two charged particles interacting through their own Electric Field. As with any inverse-square law, the resulting trajectories of the colliding particles is a hyperbolic Keplerian orbit...

s in a matter of milliseconds, but beam-beam instabilities will occur orders of magnitude faster still. In comparison, any given ion will require a few minutes before undergoing a fusion reaction, so that the monoenergetic picture of the fusor, at least for power production, is not appropriate. One consequence of the thermalization is that some of the ions will gain enough energy to leave the potential well, taking their energy with them, without having undergone a fusion reaction.

Electrodes

There are a number of unsolved challenges with the electrodes in a fusor power system. To begin with, the electrodes cannot influence the potential within themselves, so it would seem at first glance that the fusion plasma would be in more or less direct contact with the inner electrode, resulting in contamination of the plasma and destruction of the electrode. However, the majority of the fusion tends to occur in microchannels formed in areas of minimum electric potential, seen as visible "rays" penetrating the core. These form because the forces within the region correspond to roughly stable "orbits". Approximately 40% of the high energy ions in a typical grid operating in star mode may be within these microchannels. Nonetheless, grid collisions remain the primary energy loss mechanism for Farnsworth-Hirsch fusors. Complicating issues is the challenge in cooling the central electrode; any fusor producing enough power to run a power plant seems destined to also destroy its inner electrode. As one fundamental limitation, any method which produces a neutron flux that is captured to heat a working fluid will also bombard its electrodes with that flux, heating them as well.

Attempts to resolve these problems include Bussard

Robert W. Bussard

's Polywell

Polywell

system, D. C. Barnes' modified Penning trap

Penning trap

Penning traps are devices for the storage of charged particles using a homogeneous static magnetic field and a spatially inhomogeneous static electric field. This kind of trap is particularly well suited to precision measurements of properties of ions and stable subatomic particles which have...

approach, and the University of Illinois's fusor which retains grids but attempts to more tightly focus the ions into microchannels to attempt to avoid losses. While all three are IEC devices, only the last is actually a "fusor".

Bremsstrahlung

One oft-presented concern is bremsstrahlung

Bremsstrahlung

Bremsstrahlung is electromagnetic radiation produced by the deceleration of a charged particle when deflected by another charged particle, typically an electron by an atomic nucleus. The moving particle loses kinetic energy, which is converted into a photon because energy is conserved. The term is...

. In Fundamental limitations on plasma fusion systems not in thermodynamic equilibrium, Todd Rider shows that a quasineutral isotropic plasma will lose energy due to Bremsstrahlung at a rate prohibitive for any fuel other than D-T (or possibly D-D or D-He3). This paper is not applicable to IEC fusion, as a quasineutral plasma cannot be contained by an electric field, which is a fundamental part of IEC fusion. However, in a further paper, "A general critique of inertial-electrostatic confinement fusion systems", Rider addresses the common IEC devices directly, including the fusor. In the case of the fusor the electrons are generally separated from the mass of the fuel isolated near the electrodes, which limits the loss rate. However, Rider demonstrates that practical fusors operate in a range of modes that either lead to significant electron mixing and losses, or alternately lower power densities. This appears to be a sort of catch-22

Catch-22

Catch-22 is a satirical, historical novel by the American author Joseph Heller. He began writing it in 1953, and the novel was first published in 1961. It is set during World War II in 1943 and is frequently cited as one of the great literary works of the twentieth century...

that limits the output of any fusor-like system.

Use as a neutron source

Production source
Neutron Neutron The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of... s
Energy	2.45 MeV MEV MeV and meV are multiples and submultiples of the electron volt unit referring to 1,000,000 eV and 0.001 eV, respectively.Mev or MEV may refer to:In entertainment:* Musica Elettronica Viva, an Italian musical group...
Mass	940 MeV MEV MeV and meV are multiples and submultiples of the electron volt unit referring to 1,000,000 eV and 0.001 eV, respectively.Mev or MEV may refer to:In entertainment:* Musica Elettronica Viva, an Italian musical group...
Electric charge	0 C
Spin	1/2

Regardless of its possible use as an energy source, the fusor has already been demonstrated as a viable neutron source

Neutron source

A Neutron source is a device that emits neutrons. There is a wide variety of different sources, ranging from hand-held radioactive sources to neutron research facilities operating research reactors and spallation sources...

. Fluxes are not as high as can be obtained from nuclear reactor

Nuclear reactor

A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...

or particle accelerator

Particle accelerator

sources, but are sufficient for many uses. Importantly, the neutron generator

Neutron generator

easily sits on a benchtop, and can be turned off at the flick of a switch. A commercial fusor was developed as a non-core business within DaimlerChrysler Aerospace - Space Infrastructure, Bremen between 1996 and early 2001. After the project was effectively ended, the former project manager established a company which is called NSD-Fusion http://www.nsd-fusion.com.

Patents

Bennett, W. H., , February 1964. (Thermonuclear power)
P.T. Farnsworth, , June 1966 (Electric discharge — Nuclear interaction)
P.T. Farnsworth, . June 1968 (Method and apparatus)
Hirsch, Robert, . September 1970 (Apparatus)
Hirsch, Robert, . September 1970 (Generating apparatus — Hirsch/Meeks)
Hirsch, Robert, . October 1970 (Lithium-Ion source)
Hirsch, Robert, . April 1972 (Reduce plasma leakage)
P.T. Farnsworth, . May 1972 (Electrostatic containment)
R.W. Bussard, "Method and apparatus for controlling charged particles", , May 1989 (Method and apparatus — Magnetic grid fields).
R.W. Bussard, "Method and apparatus for creating and controlling nuclear fusion reactions", , November 1992 (Method and apparatus — Ion acoustic waves).

External links

David, Schneider, "Fusion from Television?". American Scientist
American Scientist
American Scientist is the bimonthly science and technology magazine published since 1913 by Sigma Xi. Each issue includes four to five feature articles written by scientists and engineers. These authors review research in all fields of science...

, July–August
University of Wisconsin-Madison IEC homepage
RTFTechnologies.org IEC Fusion Reactor Detailed IEC reactor construction information
Mr. Fusion — Blog of an experimenter
Neutrons for sale — New Scientist
New Scientist
New Scientist is a weekly non-peer-reviewed English-language international science magazine, which since 1996 has also run a website, covering recent developments in science and technology for a general audience. Founded in 1956, it is published by Reed Business Information Ltd, a subsidiary of...

article
Fusion Experiments Show Nuclear Power's Softer Side — Wired
Wired (magazine)
Wired is a full-color monthly American magazine and on-line periodical, published since January 1993, that reports on how new and developing technology affects culture, the economy, and politics...

article
Various Patents and Articles Related to Fusion, IEC, ICC and Plasma Physics
How a Small Vacuum System and a Bit of Basketweaving Will Get You a Working Inertial-Electrostatic Confinement Neutron Source
Description of Bussard's "aneutronic" boron version
Fusor.net Forum for hobbyist fusor builders
NSD-Fusion
Should Google Go Nuclear? Clean, cheap, nuclear power (no really) Google Video of Dr. Bussard explaining his work

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

History

Design

Robert Hirsch

Work at Farnsworth Television labs

Work at Brigham Young University

Recent developments

Use as a power source

Basic fusion

Fusor fusion

Power density

Thermalization of the ion velocities

Electrodes

Bremsstrahlung

Use as a neutron source

Patents

Further reading

External links